Pauline Welby
email: pauline.welby@lpl-aix.fr

Máire Ní Chiosáin
email: maire.nichiosain@ucd.ie

Brian Ó Raghallaigh
email: brian.oraghallaigh@dcu.ie

Total eclipse of the heart? The production of eclipsis in two speaking styles of Irish

We examined the production of the Irish initial mutation eclipsis in two speaking styles. In initial mutation phenomena, a word appears with a different initial sound depending on the lexical or morphosyntactic environment (e.g., croí [kɾ ɣ i] '(a) heart' (radical form), (a) chroí [xɾ ɣ i] '(his) heart/darling' (séimhiú-lenition form), and (a) gcroí [ɡɾ ɣ i] 'their heart/darling' (eclipsis form)). The goals of the study were: 1. To examine whether there are acoustic differences between the initial consonants of radical word forms (e.g., [ɡ] of gruig '(a) frown/scowl') and the corresponding consonants of eclipsis forms (e.g., [ɡ] of gcroí), as has been found for similar phenomena in other languages. 2. To examine variability in the patterns of initial mutation in the speech of present-day speakers of Irish. Our analyses offer limited evidence that there may be phonetic differences between radical and corresponding eclipsis consonants, but the current data do not allow us to rule out alternative explanations.

The realization of initial mutations in semi-spontaneous speech differed dramatically both from that of read speech and from the expectations of the traditional grammar. The results suggest that the realization of eclipsis and other initial mutations may be style-or registerdependent. We also found some evidence that it may vary by consonant type, in part due to phonological frequency patterns of the language.

Place of articulation

Labial Velar

Introduction

Irish initial mutation processes

Irish, like all the Celtic languages, has a system of initial mutations, in which the initial sound of a word alternates depending on the context in which it appears. For example, the Irish word croí [kɾ ɣ i] 'heart' has three forms in the singular, each of which appears in specific lexical or morphosyntactic environments: croí [kɾ ɣ i], chroí [xɾ ɣ i], and gcroí [ɡɾ ɣ i].

These initial mutations are pervasive, in both the written and the spoken language, affecting about 1 out of 6 words. i They appear in dozens of environments, affecting not only nouns, but also verbs and adjectives, and involve almost all initial consonants, as well as all initial vowels. The most common of the initial mutation types are séimhiú-lenition ii and urúeclipsis (eclipsis).

Historically, the initial mutations were sandhi processes conditioned by the preceding phonetic context. Séimhiú-lenition was triggered by vowel-final proclitics and eclipsis by proclitics ending in a nasal [START_REF] Thurneysen | A Grammar of Old Irish. Baile Átha Cliath: Institiúid Árd-Léinn Bhaile Átha Cliath. Translation Section, the Houses of the Oireachtas[END_REF]. At some point during the Primitive Irish period (5th and 6th centuries), the initial mutations became part of the morphosyntax and began to constitute grammatically significant phonemic alternations [START_REF] Mccone | Towards a relative chronology of ancient and mediaeval Celtic sound change[END_REF]. In the modern Celtic languages, the initial mutations are clearly no longer phonetically or phonologically conditioned, as we will see shortly.

To date there have been very few experimental studies examining initial mutations, and we therefore know very little about the phonetic properties of mutation consonants. For example, is the [ɡ] of a gcroí [ɡɾ ɣ i] 'their heart', an eclipsis form, acoustically different from the initial [ɡ] of gruig [ɡɾ ɣ ɪɟ] '(a) frown, scowl', a radical form? Does the [ɡ] of the eclipsis form gcroí 'heart' reflect any of the properties of the [k] of the radical form croí? In other words, is there a complete or incomplete neutralization -a total or a partial eclipse? To our knowledge, these questions have not yet been addressed. Our first goal in this study was to examine whether there are measurable acoustic differences between the "same" consonant in radical contexts and in eclipsis contexts. Our second goal was to examine the variability of patterns of initial mutation in the speech of present-day speakers of Irish, a topic that has received little attention outside of the prescriptivist literature.

The paper is structured as follows: in the Introduction, we give necessary background on the initial mutations ( § 1.1) and discuss reported incomplete neutralization processes in other languages ( § 1.2). In the Methods, we describe the variety of Irish under investigation and the sociolinguistic context ( § 2.1), give information on the experiment participants ( § 2.2), and detail the materials ( § 2.3), the data collection procedures ( § 2.4), and the data analysis ( §2.5).

We then report the results ( § 3) and offer a discussion of the implications and directions for future research ( § 4).

The environments of the mutations

We start with a brief overview, first of the environments or contexts in which the radical and mutation forms appear, then of the nature of the sound alternations involved. The examples in

(1) illustrate radical (base or citation) forms and the corresponding séimhiú-lenition and eclipsis forms for words beginning with a small sample of sounds in a few different environments.

( 'their magic' a n-aintín [n̪ ɣ aṉ j ṯ j in j ] 'their aunt'

The form of the word that appears depends on the context or environment, which can be either lexical or morphosyntactic. The examples in (1) illustrate lexical contexts: the homophonous possessive adjectives a 'his' and a 'their' (both [!]) are followed by the séimhiúlenition form (1b) and the eclipsis form (1c), respectively. Examples of morphosyntactic contexts are given in (2).

(2) a. cat masc bán [b ɣ ɔn̪ ɣ ] 'white cat' bó fém bhán [wɔn̪ ɣ ] 'white cow' b.

Cuir [k ɣ ɪɹ j ] iii ort do chóta. 'Put your coat on.'

Chuir [x ɣ ɪɹ j ] mé orm mo chóta. 'I put my coat on.'

Irish attributive adjectives appear in the radical form if they modify a masculine noun and in the séimhiú-lenition form if they modify a feminine noun, as illustrated in (2a). Past tense verbs appear in the séimhiú-lenition form, as illustrated in (2b).

Note that in Irish, and indeed in all the modern Celtic languages, initial mutations are clearly not phonologically conditioned, as a comparison between the forms in (1b) and (1c)

shows: the phonological context preceding the initial phoneme is identical ([ə]), but the mutation differs depending on the lexical context. In (2b), both verb forms Cuir and Chuir are in sentence-initial position.

As [START_REF] Green | The independence of phonology and morphology: The Celtic mutations[END_REF][START_REF] Green | The independence of phonology and morphology: The Celtic mutations[END_REF] notes, "[t]he environments for the mutations are extremely varied, arbitrary, and unpredictable, and are often subject to dialectal variation " (2006: p. 1951). To take the example of just one mutation type, historically and according to traditional grammars, eclipsis is found in seven specific contexts (Translation Section 1958[START_REF] Congáil | Irish grammar book. Indreabhán: Cló Iar Chonnachta[END_REF]. In Connemara Irish (the dialect under consideration here), nouns appear in their eclipsis forms in the contexts given in (3).

(

deich [ḏ j ɛ(ç)] 'ten' deich [ḏ j ɛ(ç)] n-uaire [n̪ ɣ uəɾ j ə] 'ten times'
Verbs appear in eclipsis form in the contexts listed in (4).

(4) a.

after certain particles and conjunctions: go

[gə] 'that', cá [kɔ] 'where', an [ən̪ ɣ ]
or [əṉ j ] (interrogative particle), etc.

An nglacann [ŋl̪ ɣ ɑk ɣ ən̪ ɣ ] tú siúcra? 'Do you take sugar?' b. after the indirect relative particle a [ə]

an fear a dtáinig [d̪ ɣ ɔṉ j ɪɟ] mé leis 'the man who I came with'

The sound alternations of the initial mutations <Table 1 about here>

We turn now to the nature of the sound alternations involved in the initial mutations. Table 1 shows the initial mutation alternations of Connemara Irish and their orthographic representations. Each main column contains a pair of phonemically contrastive consonants, one that is often (but not always) produced with a velar secondary articulation and one that is often (but not always) produced with a palatal secondary articulation. Note that we do not indicate secondary palatalization or velarization for consonants with the same primary and secondary articulations (palatals and velars). Example minimal pairs illustrating lexical and grammatical contrasts include those given in (5).

(5) a. i. naoi /n ɣ iː/ [n̪ ɣ i] 'nine'

ii. ní /n j iː/ [ṉ j i] (negative particle) b. i. leabhar /l j a͡ ur ɣ / [ḻ j a͡ uɹ ɣ ] book (nom. sg., gen. pl.)

ii. leabhair /l j a͡ ur j / [ḻ j a͡ uɹ j ] iv book (nom. pl., gen. sg.)

Irish initial mutations are always marked in the orthography: séimhiú-lenition by adding an <h> after the first letter (see examples in (1b) and ( 2b)), eclipsis by adding before the first letter the letter (or two letters in the case of /f/) corresponding to the eclipsis consonant (see examples in (2c)). Note for some consonants, the eclipsis form and/or the séimhiú-lenition form is identical to the radical form (the shaded cells in Table 1).

As the name suggests, in séimhiú-lenition, the initial consonant is weakened. The sound alterations of séimhiú-lenition are given in ( 6). The sound alternations of eclipsis are given in ( 7).

(7) The sound alterations of eclipsis a. i. Voiceless stops and the labial fricatives As Table 1 shows, there is often not a one-to-one relationship between a séimhiú-lenition or eclipsis consonant and the corresponding radical consonant.

[f ɣ ] and [f j ] become voiced cat [kʌt̪ ɣ ] '(a) cat', seacht [ʃaxt̪ ɣ ] gcat [ɡʌt̪ ɣ ] 'seven cats' faoileán [f ɣ iḻ ʲ ɔn̪ ɣ ] '(a)

Accounts of the initial mutations

The sound alternations described above clearly show a certain "phonetic unity" (see Ewen [1982: 78] on the "phonetic unity" of the Welsh initial consonant mutations). For example, in séimhiú-lenition, there is a weakening, and place of articulation/active articulator is almost always preserved, i.e., labial remains labial, dorsal remains dorsal, etc. For consonants, this is always the case in eclipsis and often the case in séimhiú-lenition (e.g., for all labial oral stops and nasals). This synchronic phonetic unity, together with the history of the mutations as phonetically triggered sandhi processes, has motivated many researchers to seek an explanation for the mutations in the phonology. There are, however, many complications to this apparent phonetic unity that require additional explanation (change in place of articulation for [d̪ ɣ ], deletion of labial fricatives, prefixation of of [n̪ ɣ ] or [ṉ j ] to vowels, etc.).

Many phonological (or partially phonological) accounts of the initial mutations of Irish and the other Celtic languages have been proposed, grounded in a number of theoretical frameworks and spanning several decades, including [START_REF] Hamp | Morphophonemes of the Keltic mutations[END_REF], [START_REF] Rogers | The initial mutations in Modern Scots Gaelic[END_REF][START_REF] Lieber | New developments in autosegmental morphology: consonant mutation[END_REF][START_REF] Chiosáin | Topics in the phonology of Irish[END_REF], [START_REF] Swingle | The Irish and other mutations[END_REF], [START_REF] Grijzenhout | Irish consonant mutation and phonological theory[END_REF], [START_REF] Pyatt | An Integrated model of the syntax and phonology of Celtic mutation[END_REF][START_REF] Wolf | For an autosegmental theory of mutation[END_REF]. Another longstanding and growing body of scholarship argues that the initial mutations belong, at least in part, to the morphology or the lexicon, including [START_REF] Hamp | Morphophonemes of the Keltic mutations[END_REF], [START_REF] Oftedal | A morphemic evaluation of the Celtic initial mutations[END_REF], [START_REF] Green | The independence of phonology and morphology: The Celtic mutations[END_REF][START_REF] Green | The independence of phonology and morphology: The Celtic mutations[END_REF][START_REF] Green | Phonology Limited[END_REF], [START_REF] Stewart | Mutation as morphology: bases, stems, and shapes in Scottish Gaelic[END_REF], [START_REF] Mittendorf | A Treatment of Welsh initial mutation[END_REF], [START_REF] Iosad | All that glistens is not gold: against autosegmental approaches to initial consonant mutations[END_REF][START_REF] Iosad | Right at the left edge: initial consonant mutations in the world's languages[END_REF][START_REF] Iosad | The phonology and morphosyntax of Breton mutation[END_REF], [START_REF] Hannahs | Celtic initial mutation: Pattern extraction and subcategorisation[END_REF]. For details of these models, the reader is referred to the original sources, as well as to the summaries and discussions in [START_REF] Stewart | Mutation as morphology: bases, stems, and shapes in Scottish Gaelic[END_REF] and [START_REF] Hannahs | Celtic Mutations[END_REF]. Our current data do not allow us to draw conclusions about the linguistic nature of the initial mutations, so we do not address that question here.

Stability and variability in the initial mutations

The second main goal of the study was to examine variability in the patterns of initial mutation in the speech of present-day speakers of Irish. To do so, we use data from a novel card game task developed for the study, as well as from a reading task.

According to prescriptive grammars of Irish and pedagogical materials, all initial mutations, including eclipsis and séimhiú-lenition, are obligatory in both the spoken language and the written language. Any variability in the realization of the initial mutations is generally discussed in the context of language decline or language death [START_REF] Dillon | Vestiges of the Irish dialect of East Mayo[END_REF][START_REF] Stockman | Linguistic trends in the terminal stage of Q-Celtic dialects[END_REF], McGahan 2009, inter alia). Ó Broin (2014) compares the Irish of urban (Dublin and Belfast)

and Gaeltacht (official Irish-speaking district) radio broadcasters, including their realization of the initial mutations, although these figures are not reported separately. He reports low vs.

high "error" (non-realization) rates in Gaeltacht and urban broadcasters, respectively.

The traditional dialect descriptions follow a template that generally does not include a description of the reflexes and conditioning environments of the initial mutations. Exceptions to this generalization include de [START_REF] De Bhaldraithe | Gaeilge Chois Fhairrge : An deilbhíocht[END_REF] and Mhac an Fhailligh (1968). More recently, Ó [START_REF] Curnáin | The Irish of Iorras Aithneach, County Galway. Baile Átha Cliath: Institiúid Árd-Léinn Bhaile Átha Cliath[END_REF] includes a detailed description of application and variation of initial mutations in one Connemara dialect (Iorras Aithneach, Co. Galway). Only a few authors mention factors that might condition variability in the realization of the initial mutations. For example, [START_REF] Thurneysen | A Grammar of Old Irish. Baile Átha Cliath: Institiúid Árd-Léinn Bhaile Átha Cliath. Translation Section, the Houses of the Oireachtas[END_REF] writes "The initial mutations occur most consistently within a word-group the members of which, closely connected in speech, form a notional unit. The looser the connexion, the less frequently and regularly do the mutations appear" (p. 140). Ó [START_REF] Siadhail | Modern Irish: Grammatical structure and dialectal variation[END_REF] observes variability after certain mutation "triggers"; he writes that the preposition as "lenites sporadically" (p. 115) and that the verbal form ba "also sometimes lenites" (p. 116). Ó [START_REF] Sé | Gaeilge Chorca Dhuibhne. Baile Átha Cliath: Institiúid Teangeolaíochta Éireann[END_REF] writes of the optional nature of séimhiú-lenition in the past tense passive and the conditional.

The extent to which speaking style or register affects the realization of Irish initial mutations has rarely been addressed in the literature. The literature on Irish, including the accounts discussed above, typically distinguishes only between the obligatory presence and the obligatory absence of a mutation; optional or variable mutation is rarely described. To our knowledge, there has been almost no discussion of the possible influence of style or register.

As [START_REF] Hamp | Morphophonemes of the Keltic mutations[END_REF] notes for Breton, "Most of the standard grammatical works are based on the 'written' language. No wonder the phonological facts of Breton have remained so obscure" (p. 244). The same could be said for Irish -almost all accounts assume the all-or-nothing mutation prescribed by the official standard (An Caighdeán Oifigiúil, Translation Section, 1958): they do not take into account or even note the variability in mutation in the spoken language. The assumption that speakers who depart from this official standard, which predicts 100% realization of mutations in licensed environments, are not good speakers is particularly common in academic circles.

Incomplete neutralization processes in other languages

Research on apparent neutralization processes in other languages have uncovered subtle but systematic differences between different types of consonants. These studies include phonetic and psycholinguistic studies on production and perception, as well as corpus studies.

There is a large body of research on the acoustic characteristics of French resyllabification processes (liaison, as well as enchaînement and elision) and their effects on perception. A number of studies have shown systematic differences or incomplete neutralization between these "resyllabified" consonants and corresponding base consonants (e.g. between the [t] of petit tamis 'little sieve' [pəti.tami] and the [t] of petit ami 'boyfriend'

[pəti.tami]) (see for example, [START_REF] Fougeron | Looking for acoustic cues of resyllabification in French[END_REF][START_REF] Spinelli | Processing resyllabified words in French[END_REF][START_REF] Fougeron | Word boundaries and contrast neutralization in the case of enchaînement in French[END_REF], Spinelli, Welby & Schaegis 2007, inter alia), although these differences may not be present in all contexts [START_REF] Gaskell | Perception of resyllabification in French[END_REF], Nguyen et al. 2007, inter alia).

Similarly, many studies of the apparent neutralization of the voicing contrast in word-or syllable-final obstruents in German, Dutch, and other languages have shown subtle phonetic differences between the final stops of apparently homophonous words like Rad 'wheel ' [ʁaːt] and Rat 'council' [ʁaːt] [START_REF] Dinnsen | The three degrees of vowel duration in German[END_REF][START_REF] Charles-Luce | Word-final devoicing in German: Effects of phonetic and sentential contexts[END_REF][START_REF] Port | Incomplete neutralization and pragmatics in German[END_REF], and many others. See [START_REF] Roettger | Assessing incomplete neutralization of final devoicing in German[END_REF] and references therein for an exhaustive list and discussion), while a few other studies have failed to find differences (Fourakis & Iverson 1984, inter alia).

Closer to home, in the literature on the Celtic languages, we rarely find mention of differences between mutation consonants and their corresponding radical consonants. One exception is [START_REF] Falc'hun | Le système consonantique du breton avec une étude comparative de phonétique expérimentale[END_REF], who recorded and examined Breton minimal pairs such as (8).

( Falc'hun reports that voiced stops with voiceless radicals (3a) are longer and have stronger release bursts than their corresponding radical voiced stops (3b). He states that this pronunciation distinction between "strong" (fort) and "weak" (doux) consonants is only possible before vowels and "plays only a negligible role in the language" [our translation] (p. 65), but specifies that the distinction is clearly perceptible to native speakers.

For (Scottish) Gaelic, a sister language of Irish, Ó [START_REF] Maolalaigh | The development of eclipsis in Gaelic[END_REF][START_REF] Maolalaigh | The development of eclipsis in Gaelic[END_REF] reports that "[t]he non-radical nasals in [the] Type C [initial mutation] apparently differ phonetically from radical nasals in that the former are denasalized towards the end of their articulation: a short oral stop is frequently audible at the end of such nasals" (p. 160), referring to the work of [START_REF] Borgstrøm | A linguistic survey of the Gaelic dialects of Scotland. The dialects of the Outer Hebrides[END_REF] and [START_REF] Oftedal | The Gaelic of Leurbost Isle of Lewis[END_REF]. According to Ó Maolalaigh, mutation "involves the nasalisation (or partial nasalisation) of all stops without resultant neutralization between both sets of stops as the post-aspirated stops retain their aspiration" (p. 159). Borgstrom (1940) writes "The non-radical nasals […] may occasionally give the same acoustic impression as the radical ones, but in principle they are different: at the end of the nasal one usually hears a very short and soft occlusive. What actually happens must probably be that the velum is raised to close the nasal passage a little earlier than the clusion of the lips (for m) or of the tongue against its place of articulation (for N, N', ŋ, ŋ') is loosened, so that the end of the nasal is denasalized; this is in any case what I think I must do to imitate the pronunciation" (p. 22).

Given this cross-linguistic evidence of incomplete neutralization, we expected that we might find similar kinds of differences in Irish between radical and mutated consonants. To address this issue, we compare the initial stop consonants of radical and eclipsis forms, examining measures relevant to the phonological voiced/voiceless contrast.

Methods

Connemara Gaeltacht

<Figure 1 about here>

We focused on the Irish spoken in Connemara, County Galway in the west of Ireland, in the province of Connaught. As Ní Chiosáin, Welby & Espesser (2012) describe, "Irish is a minority language spoken today as a community language in a number of mostly rural areas predominantly along the west coast. The Connemara Gaeltacht is one of the stronger official Irish-speaking districts, but like all Gaeltachtaí the language is under increasing pressure from English (see e.g., [START_REF] Giollagáin | Comprehensive linguistic study of the use of Irish in the Gaeltacht: Principal findings and recommendations[END_REF]. All present-day Irish speakers also speak English 5 although the reverse is not true, even in the Gaeltachtaí. Footnote 5 [of Ní [START_REF] Chiosáin | Is the syllabification of Irish a typological exception? An experimental study[END_REF]: The one exception is some children growing up in Irish-speaking households, who are monolingual in early childhood.": 70-71).

Participants

Seven native speakers of Connemara Irish participated in the experiment, three women (Participants 1, 2, 3) and four men (Participants 4, 5, 6, 7). Six of the participants ranged in age from the late teens to mid-20s, with an average age of 20.2. The last participant (Participant 2) was 43 years old. All participants were raised in the Connemara Gaeltacht (official Irish-speaking district), grew up speaking Irish at home with at least one parent, completed their primary and secondary education in Irish-medium schools and at the time of the recordings were students at Acadamh na hOllscolaíochta Gaeilge, an Irish-medium university campus in the Connemara Gaeltacht. Most (6 of 7) were currently living in the Gaeltacht community where they were recorded. One (Speaker 1) was living in Galway city.

Most (5 of 7) had lived in the community their entire lives and had never lived outside the 16 16

Gaeltacht. One student (Participant 2, the oldest participant) had lived in England for many years before returning to the Gaeltacht. All participants also have native-language competence in English. Speakers received €15 for their participation, which lasted about one hour.

Materials

We constructed sets of word triplets: 7 sets for each of 2 consonant types (the labial stops and voiceless unaspirated stops (short-lag VOT). The pattern is similar to that of English and German.

For clarity, the target nouns are underlined in the examples in (9); there was no underlining in the sentences presented to participants. 'Put the hammer next to the apple.'

The experimental sentences formed the "moves" of the card game described in §2.4.1.

All three contexts were designed to place the target nouns in prosodic phrase-final position where they were likely to be pronounced with a pitch accent, since these factors have been

shown to affect production in many languages [START_REF] Fougeron | Articulatory strengthening at edges of prosodic domains[END_REF], Turk & Shattuck-Hufnagel 2007, inter alia).

We chose not to use minimal sets (of the type ar an gcasúr [ɡɑs ɣ uɹ ɣ ] 'on the hammer'/gasúr [ɡɑs ɣ uɹ ɣ ] 'child'), which might induce unnatural disambiguation strategies ("hyperarticulation due to minimal pair awareness" discussed by [START_REF] Roettger | Assessing incomplete neutralization of final devoicing in German[END_REF]. Rather, target nouns had the structure C 1 V 1 C 2 *, where within a set: words were matched in number of syllables (1, 2 or 3), with the initial consonant C 1 differing only in voicing, and the same following vowel V 1 . To control for coarticulation, the following consonant C 2 was matched in terms of primary articulator and the broad/slender phonemic distinction characteristic of Irish consonants (see §1.1.2). Note that the C 1 is in medial position of a prosodic word (for example, an gadaí 'the robber'). The Kleene star represents optional additional material after the first three segments.

There were a total of 42 critical items (7 sets × 2 consonant types × 3 conditions) and an additional 14 filler items, which were included to introduce more variety in the potential initial mutations present (e.g., t-prefixation: seamróg [ʃam ɣ ɾ ɣ oɡ] '(a) shamrock', an tseamróg [ṯ j am ɣ ɾ ɣ oɡ] 'the shamrock').

Procedures

Participants completed two tasks, a card game task and a reading task. Each task was performed twice. All participants first completed two "rounds" of the card game, then moved on to the reading task.

Card game task

We developed a novel card game for the study. The game was designed to induce speech that was unprepared and spontaneous but constrained along a number of dimensions, and contained multiple tokens of the targets in the experimental conditions (in the tradition of the tasks developed by [START_REF] Anderson | The HCRC map task corpus[END_REF][START_REF] Schafer | Intonational disambiguation in sentence production and comprehension[END_REF][START_REF] Ito | Using interactive tasks to elicit natural dialogue[END_REF], inter alia).

In the game, two players sit near each other at a table. One player, the Director (the participant) sees card moves displayed on a computer screen (via a Microsoft PowerPoint presentation with timed transitions to create animation). The Director then describes out loud the move he or she sees, guiding the Mover (a confederate, author BÓR), in placing cardboard game cards to match the move displayed on the screen.

<Figure 2 about here>

The game moves exploit the fact that, in the traditional grammar, eclipsis of a wordinitial consonant is expected after the definite article in the dative singular when preceded by one of a closed class of 11 common prepositions (ar 'on', le(is) 'with', etc.). There were five possible moves, given in (10), where X and Y stand for the names of pictures displayed on the game cards. Target nouns in the eclipsis condition always appeared in the context ar an target noun (move 10a). Example screen displays are given in Figure 2. The game proceeded at a self-selected, untimed pace. A second experimenter (author PW) confirmed the successful completion of each move by the Mover (Sin é 'That's it.' Go maith 'good', etc.), before continuing on to the next move.

Reading task

After "playing" two rounds of the card game, participants read a list of sentences corresponding to the canonical form of the instructions from the card game (that is, with either radical or mutation forms, as called for by the traditional grammar). As discussed in §1.1.2, Irish initial mutations are always reflected in the orthography; the eclipsis of the target nouns in the eclipsis context was therefore always orthographically marked. The sentences were presented one-by-one on a computer screen, and each participant read the list two times, at a self-selected, untimed pace. headworn microphone and a Marantz PMD 660 digital recorder at a sampling rate of 48 kHz.

Data analysis

Each sentence was saved as an individual sound file, using a Praat [START_REF] Boersma | Praat: Doing phonetics by computer[END_REF] script to semi-automate the task. For each task (card game, reading), there were two repetitions of 42 critical items (7 sets × 2 consonant types × 3 conditions), for a total of 84 critical tokens for each of the 7 participants (588 in total). All labeling and acoustic analyses were performed in Praat, with label positions determined by hand and scripts used to semiautomate the process.

Reading task <Figure 3 about here>

An example label file is given in Figure 3. For the critical items in the reading task, the following segment boundaries of the target noun were labeled, using standard segmentation criteria [START_REF] Peterson | Duration of syllable nuclei in English[END_REF]: beginning of the target noun (beginning of the stop closure), end of the target noun, end of the first consonant (C 1 , always a stop), beginning and end of the first vowel (V 1 ), stop release burst (b), and onset of voicing (v). The beginning of the closure was marked by an abrupt cessation of formant structure and the end of the stop at the onset of a release burst. Onset of voicing was defined, as in Cho & Ladefoged (1999: 215) as the "first complete vibration of the vocal folds" (see discussion in Di Paolo & Yaeger-Dror 2011). The release burst was usually clearly visible as a transient in the waveform. In cases where there was more than one release burst (particularly common for the velars, as has been often observed in the literature), we labeled both the first and the last burst.

The boundary between vowel and a following [ɹ ɣ ] was difficult to determine. We therefore decided to systematically place the boundary after the voiced portion of the [ɹ ɣ ].

This was an acceptable decision, since vowel duration was only used in the calculation of relative intensity of the stop burst. Another segmentation difficulty was posed by the boundary between two vowels (e.g., in Cuir an cárta [kɔɹ ɣ t̪ ɣ ə] os [ʌs ɣ ] cionn an tseangáin.

'Put the card over the ant.'). In these cases, we relied on formant transitions; when this was not possible, we took the end of the first vowel to be the midpoint of the vocalic region.

A total of 106 tokens were excluded from the phonetic analyses, leaving a total of 482 tokens. There were several types of exclusions: tokens with dysfluencies or hesitations in the target region (20 items), one token in which a speaker mispronounced the article in the target region, tokens in which C 1 was produced not as a stop, but with another manner of articulation (fricative, glide, nasal) (a further 61 items). Note that the vast majority of exclusions of this type (41 of the 61) were due to an oversight in the design of the experimental materials. The target noun in these cases was feminine and the initial consonant of feminine nouns appears in séimhiú-lenition form after the nominative definite article. For these items, séimhiú-lenition was therefore indicated in the orthography (e.g. an charraig

[xɑɾ ɣ əɟ] 'the rock') and a fricative was produced. Tokens where there was no clear release burst visible, either in the waveform or the spectrogram, were also excluded from the analyses (a further 23 cases), as was 1 token in which there was no clear distinction between the closure for the coda nasal of the article and the following oral plosive closure. These last two types of tokens were excluded not because they would not be judged as acceptable productions of the target consonants, but because of the difficulty (or impossibility) of taking the relevant measurements for the phonetic analyses (e.g., intensity of the stop burst or VOT).

We further address the distribution of tokens without a clear release burst in the discussion section.

We measured: duration of the initial consonant of the target noun (C 1 ), duration of the C 1 closure, C 1 voice onset time (VOT), and relative intensity of the C 1 stop burst. These measures are all relevant to the phonological voiced/voiceless contrast and are among the measures for which differences have been found in cases of incomplete neutralization in other languages (see §1.2). All target nouns were preceded by the definite article an. We coded whether or not the [n̪ ɣ ] of this definite article was elided (i.e., whether the definite article was pronounced with a coda [n̪ ɣ ] or as [ə]). The presence or absence of this coda [n̪ ɣ ] was clear, both auditorily and visually (on the spectrogram: see Figure 3). For more details about this coding, see §3.1.3.

Game task

Most participants produced relatively few (or no) eclipsis consonants in the mutation (eclipsis) contexts. It was evident from the first experimental sessions that we would not have enough tokens for the type of acoustic analyses performed for the reading task.

Unsurprisingly, the semi-spontaneous speech collected in this task was more variable in many respects than the more controlled read speech.

We therefore adopted different labeling conventions for the game task data. We performed three types of binary coding. We coded each target consonant according to whether it was produced as 1. an eclipsis consonant or 2. a séimhiú-lenition consonant, v and 3. we coded the elision of the [n̪ ɣ ] of the definite article an. Note that given that our target consonants were stops ([p ɣ ] and [k]), the first two coding decisions could be reduced to: Is the target consonant voiced? Is the target consonant phonetically realized as a fricative? In the game task, participants sometimes used a term other than expected target noun (e.g., caitín or cat rather than puisín 'kitten'). We excluded these items from the analyses (14 total exclusions), except in cases where the unexpected and expected terms had the same initial consonant (e.g., puiscín rather than puisín 'kitten', gairdín for garraí 'garden') (38 total exclusions). In addition, in the game task, the mutation context was occasionally not preserved. For example, rather than the expected Cuir an gaineamh faoin nathair 'Put the sand under the snake' (where the target gaineamh is in a non-mutation (radical) context), one participant said Cuir an nathair os coinn an ngaineamh 'Put the snake over the sand'. Of course, the two moves achieve the same goal in the context of the game, but the version produced by the participant puts the target noun in an unexpected eclipsis context. In addition, on a few occasions, participants chose to "pass" or skip an item or move.

Statistical procedures

For the reading task, voice onset time (VOT), duration, and relative stop burst intensity results

were analyzed in R (R Core Team 2013) using linear mixed effects models (LMEMs) with the package lme4 [START_REF] Bates | lme4: Linear mixed-effects models using S4 classes. R package version 0[END_REF]. For all models, the two fixed effects were: Place of Articulation (2-level factor: Labial, Velar) and Mutation (3-level factor: Radical, Eclipsis, Control). In order to test whether the two fixed effects were significant we first built the LMEM with the maximal random structure. Since this model never converged, we simplified it step-by-step, following the [START_REF] Barr | Random effects structure for confirmatory hypothesis testing: Keep it maximal[END_REF] guidelines as closely as possible. We first removed correlation parameters for the random effects, then the random intercepts for our two fixed effects (which were both within-subject effects). If necessary we then removed another term (an interaction term). Following Barr et al., we always retained random slopes for the fixed effects. For all the LMEMs, we used the default settings of the lmer() function.

Results

Reading task

Durations

In the reading task, items were almost always read as expected. That is, target consonants were produced as stops (over 95% of the time) and words orthographically marked for an initial mutation (eclipsis and other mutations (for some non-target nouns)) were produced as spelled, with the expected mutation.

VOT <Figure 4 about here>

Fifty tokens in which the stop closure was partially or fully voiced were removed from the VOT analyses, since we cannot average positive and negative VOT values. These tokens are discussed further at the end of the current section. After the exclusion of items with voicing in the closure, there were 432 observations for the VOT analysis (482-50 = 432).

The pattern of results for VOT is illustrated in Figure 4. As described in § 2.5. In order to test whether there was an interaction between the two fixed factors, we performed a likelihood ratio test (LRT) between the models with and without the interaction Place of Articulation × Mutation. The results showed that the interaction was not significant (χ = 2.0946, df = 2, p = 0.3509).

To test whether the fixed factor Mutation had a main effect, we performed an LRT between models with and without the factor Mutation. There was a significant effect of this factor (χ 2 = 530.69, df = 2, p < 0.001). An examination of the model (Table 2) showed that the contrast between Labial Eclipsis and Labial Control consonants was highly significant (t = 7.763), vii but that the contrast between Labial Eclipsis and Labial Radical consonants was not significant (t = -0.673). Given that the interaction between the two fixed factors is not significant (PlaceArtVelar × MutationControl: t = -0.857, PlaceArtVelar × MutationRadical: t = -0.772), we obtain the same patterns of results for the contrasts between Velar Eclipsis and Velar Control consonants and between Velar Eclipsis and Velar Radical consonants.

Recall that Control consonants are voiceless and aspirated, while Radical and Eclipsis consonants are phonetically voiceless and unaspirated, as reflected by these VOT patterns.

The aspiration of the initial consonant of the Radical form (e.g., the [k] of casúr) is not present in the initial consonant of the Eclipsis form (e.g., the [ɡ] of (ar an) gcasúr).

The effect of the fixed factor Place of Articulation is only marginally significant (1.936), although in the direction predicted, given the results in the literature for other languages, where velars have been found to have longer VOTs than labials (see [START_REF] Cho | Variation and universals in VOT: Evidence from 18 languages[END_REF].

Voicing in the target stop closure

We examined the data to see whether the voicing in the closure of the target stop produced in 50 tokens was related to speaker, mutation condition or production of the coda [n̪ ɣ ] of the preceding definite article. It was not possible to draw firm conclusions from so few tokens, so we report the general patterns observed. There is some evidence of inter-speaker variability:

four participants (Speakers 3, 4, 5, and 6) accounted for 92% of tokens with voicing in the stop closure. Unsurprisingly, very few (2) cases of voicing were found in the Control conditions, since these stops are voiceless and aspirated. no voicing in the closure) to be exploited, prevoicing is not generally employed by speakers to distinguish Eclipsis consonants from their Radical counterparts.

C 1 duration <Figure 5 about here>

Figure 5 shows the pattern of results for the duration of the initial consonant (C 1 ). A second analysis using LMEMs examined C 1 duration. There were 482 observations. We first built the LMEM with the maximal random structure, then simplified the model step-by-step as described in § 2.5.3. The model retained is given in Table 3.

<Table 3 about here>

In order to test whether there was an interaction between the two fixed factors, we performed a likelihood ratio test (LRT) between the models with and without the interaction (Place of Articulation × Mutation). This interaction was not significant (χ 2 = 1.2137, df = 2, p = 0.5451).

To test for a main effect of the fixed factor Mutation, we performed an LRT between models with and without this factor. There was a significant effect of Mutation (χ 2 = 252.56, df = 2, p < 0.001). This effect was due to the contrast between Labial Eclipsis and Labial Control consonants, which was highly significant (t = 5.039) (Table 3). The contrast between Labial Eclipsis and Labial Radical consonants, however, was not significant (t = -1.322).

Given that the interaction between the two fixed factors is not significant, we obtain the same patterns of results for the contrast between Velar Eclipsis and Velar Control consonants which was significant (PlaceArtVelar × MutationControl: t = -0.798) and between Velar Eclipsis and Velar Radical consonants which was not significant (PlaceArtVelar × MutationRadical: t = 0.292). Finally, the effect of Place of Articulation was not significant (t = -1.350).

C 1 closure duration

Figure 6 shows the pattern of results for duration of closure of the initial consonant (C 1 ).

<Figure 6 about here>

As with the earlier analyses, we used LMEMs to examine C 1 closure duration. There were 482 observations. We first built the LMEM with the maximal random structure, then simplified the model step-by-step as described in § 2.5.3. The model retained is given in Table 4.

<Table 4 about here>

In order to test whether there was an interaction between the two fixed factors, we performed a likelihood ratio test (LRT) between the models with and without the interaction (Place of Articulation × Mutation). The results showed that the Place of Articulation ×

Mutation was not significant. The difference between the two models is so small that R returns the statistics χ 2 = 0, df = 2, p = 1, presumably due to rounding.

Neither the contrast between Labial Eclipsis and Labial Control consonants (t = -1.323)

nor the contrast between Labial Eclipsis and Labial Radical was significant (t = -1.192) (Table 4). Given that the interaction between the two fixed factors was not significant, we obtain the same pattern of results for the contrast between Velar Eclipsis and Velar Control consonants and between Velar Eclipsis and Velar Radical consonants (neither of which was significant: PlaceArtVelar × MutationControl, t = 0.063, PlaceArtVelar × MutationRadical t = -0.166).

There was a significant effect of Place of Articulation (t = -3.881). The difference in Labial and Velar closure duration (m = 58, m = 43 ms, respectively) was in the direction found in the literature across languages, with longer closures for labials (see [START_REF] Maddieson | Phonetic universals[END_REF].

Relative intensity of the C 1 stop burst <Figure 7 about here>

The pattern of results for relative intensity of the C 1 stop burst is illustrated in Figure 7.

Cross-linguistically, voiceless stops have been reported to have more intense bursts than their voiced counterparts [START_REF] Lisker | A cross-language study of voicing in initial stops: Acoustical measurements[END_REF], Sils & Cohen 1969, inter alia). If eclipsis consonants reflect characteristics of the corresponding voiceless consonants, for relative intensity of the stop burst, we would expect the pattern Control (voiceless) ≥ Eclipsis (voiced) > Radical (voiced).

We measured the intensity of the stop burst with respect to that of the following vowel.

We calculated the intensity of the burst (dB) over a 10 ms window centered on the burst release. In cases of multiple bursts, we used the first burst. For cases in which there was prevoicing throughout the closure we applied a 200 Hz high pass filter (Hann window). We then subtracted the intensity of the burst from the maximum intensity of the vowel (dB) [START_REF] Stoel-Gammon | Cross-language differences in phonological acquisition: Swedish and American /t[END_REF]. A larger relative intensity value therefore indicates a larger difference with respect to the vowel and a less intense burst.

Relative intensity of the burst was analyzed using linear mixed effects models (LMEMs).

There were 482 observations. We first built the LMEM with the maximal random structure, then simplified the model step-by-step as described in § 2.5.3. The model retained is given in Table 5.

<Table 5 about here>

In order to test whether there was an interaction between the two fixed factors, we performed a likelihood ratio test (LRT) between the models with and without the Place of Articulation × Mutation interaction. The results showed that this interaction was not significant (χ 2 = 0.6498, df = 2, p = 0.7226).

To test whether the fixed factor Mutation had a main effect, we performed an LRT between models with and without the factor Mutation. An LRT between models with and without the factor Mutation showed a significant effect of this factor (χ 2 = 23.357, df = 2, p < 0.001).

The contrast between Labial Eclipsis and Labial Radical consonants was significant (t = 2.226, Table 5), with Labial Eclipsis consonants having stronger bursts, but the contrast between Labial Eclipsis and Labial Control consonants was not significant (t = -0.380).

Given that the interaction between the two fixed factors is not significant, we obtain the same pattern of results for the contrast between Velar Eclipsis and Velar Radical consonants, which was significant (PlaceArtVelar × MutationRadical, t = -0.666) and between Velar Eclipsis and Velar Control consonant (PlaceArtVelar × MutationControl, t = 0.034). This pattern (Control (voiceless) ≥ Eclipsis (voiced) > Radical (voiced)) is the predicted pattern of results:

the relative burst intensity of Eclipsis consonants resembles that of Control consonants.

There was no main effect of Place of Articulation (t = -1.671), although the results were in the direction expected given observations in the literature for other languages (Repp 1984, inter alia), where labial bursts have been found to be softer than velar bursts (and so to have lower relative intensity), due to the absence of a front cavity.

To summarize the main results thus far: for C 1 closure duration, we found a main effect of Place of Articulation, with longer closures for Labials than for Velars, in line with reports in the literature for other languages. For VOT, the effect of Place of Articulation, also in the expected direction, was only marginally significant. For C 1 duration and relative intensity of C 1 burst, there were no main effects of Place of Articulation. It is the main effect of Mutation that is crucial to testing our hypothesis that Eclipsis consonants differ from Radical consonants and reflect characteristics of Control (voiceless) consonants. For VOT and C 1 duration, there were main effects of Mutation; these effects, however, were due to differences between the Control condition and the other two conditions. We did not find the critical duration differences expected between Eclipsis and Radical consonants; in particular, we did not find longer C 1 duration, C 1 closure duration or VOT for Eclipsis consonants than for Radical consonants. For the relative intensity of C 1 burst, we did find the expected pattern of results: the relative burst intensity of Eclipsis consonants was greater than that of Radical consonants and comparable to that of Control consonants. Surprisingly, there was no main effect of Place of Articulation for relative burst intensity.

Elision of the [n̪ ɣ ] of the definite article an preceding the target noun (reading task)

<Table 6 about here> Although the targets were inserted in segmentally and prosodically controlled carrier contexts, we observed that for most speakers the coda nasal of the definite article preceding the noun (e.g., an [ən̪ ɣ ] pota 'the pot') was sometimes elided, with the rate of elision depending on the Mutation condition. While the elision itself was not unexpected, the variation across conditions was unanticipated. It is important, however, to take into account this difference across conditions in the realization of the definite article, because it often creates different phonetic environments across conditions.

Table 6 presents the rate of elision of this [n̪ ɣ ] in the three Mutation conditions for each speaker for the 482 tokens included in the phonetic analyses. One speaker (Speaker 5) never elided the [n̪ ɣ ] for any item in any of the three conditions. The other participants systematically elided the [n̪ ɣ ] more often in the Eclipsis condition (31.6-100% of cases) than in the Radical and Control conditions (0-44.4 % of cases). It is unlikely, however, that this difference is directly linked to eclipsis itself, since we also observe it in filler items with the same structure (prep E + definite article + C), where there is no eclipsis since the initial consonant is identical in Radical and Eclipsis environments (e.g., the [m ɣ ] in ar an madra [m ɣ ɑd̪ ɣ ə] 'on the dog', see Table 1).

Therefore, in the reading task, the target nouns in the Radical and Control conditions are often directly preceded by a nasal consonant (because the definite article is pronounced [ən̪ ɣ ],

e.g. an pota [ən̪ ɣ p ɣ ʌt̪ ɣ ə] 'the pot'), while the target nouns in the Eclipsis condition are often preceded by a vowel (because the definite article is pronounced [ə], e.g. ar an bpota [ɛɾ j əb ɣ ʌt̪ ɣ ə] 'on the pot').

To control for this unexpected variability, we attempted to perform the analyses excluding items produced with elision of the [n̪ ɣ ] of the definite article. This, however, proved impracticable. While only 8.9% of items in the Control condition and 12.6% of items in the Radical condition are realized with elision of the coda nasal of the preceding article, this is the case for 63.0% of Eclipsis items. Elision in the Control and Radical conditions is not the typical realization. In addition, most 86.0% (49 of 57 cases) of the elision realizations in the Eclipsis condition are due to only three speakers (Speakers 1, 5, and 7). We come back to this point in the discussion.

Card game task

Production of mutations <Figure 8 about here>

In the card game task, we observed a great deal of variability in the realization of the initial mutations (Figure 8). Only one speaker, Speaker 1 produced a pattern approaching that predicted by the traditional grammar, i.e., 100% mutation in the Eclipsis condition, with no difference according to place of articulation. This speaker produced 88% of items in the Eclipsis condition with eclipsis. In this same condition, three speakers (2, 3, and 4) produced eclipsis in about 40-50% of items. Speaker 7 produced eclipsis in about 25% of eclipsis contexts, while two speakers (5 and 6) almost never produced eclipsis. For Speaker 7, eclipsis was markedly more frequent in the second round (block) of the card game (43% of items) than in the first round (7%). We discuss this pattern further in the discussion section. Two speakers (Speakers 2 and 5) also produced eclipsis in the Radical or Control conditions, although there was no environment triggering eclipsis.

In most cases where speakers did not produce eclipsis in the Eclipsis condition, they produced a Radical consonant (producing, for example, ar an casúr 'on the hammer' with no mutation). Speakers 1-6 all very occasionally produced séimhiú-lenition in the Radical and/or Eclipsis Conditions (1-3 items total for each speaker), although there was no eclipsis environment. Speaker 7 produced séimhiú-lenition in these unexpected contexts in 30% of his productions for these conditions (12 times total), with more in the second round than in the first (8 vs. 4 items).

A number of speakers produced eclipsis in the Eclipsis condition more often for velar stops than for labial stops (compare the white and black bars of Figure 7). This difference is particularly striking for Speakers 1, 2, and 3. We examined whether this difference in the realization of eclipsis across consonant types could be due to an effect of lexical frequency.

The seven /k ɣ /-initial words and the seven /p ɣ /-initial target nouns do not differ in lexical frequency, no matter what measure of frequency we use (for lemma frequency: t = 1.836, df = 12, p = 0.091, for token frequency of the eclipsed form: t = 1.129, df = 12, p = 0.281, for eclipsis realizations/lemma realizations: t = 0.498, df = 12, p = 0. 627). However, in the Irish lexicon, there is a marked difference in the frequency of words beginning with these consonants. In the Foclóir Póca dictionary (Ó Baoill 1986), there are 6.8 times more words beginning with /k ɣ / than with /p ɣ /. The pattern also holds more generally, independent of the phonemic distinction between so-called broad and slender consonants (see §1.1.3): there are 5.9 times more words beginning with velar stops (/k ɣ / and /k j /) than with labial stops (/p ɣ / and /p j /). This imbalance is due to the history of the Celtic languages: Proto-Indo-European *p was lost in the proto-Celtic period and re-entered the consonant inventories much later (McCone 1994).

Elision of the [n̪ ɣ

] of the definite article an preceding the target noun (card game task)

<Table 7 about here>

As for the reading task, for the card game task, we coded the presence or absence of the definite article preceding the target noun. Since we did not perform acoustic analyses for the card game task (see § 2.5.2), this coding is not directly related to the primary goals of the present paper. It is, however, related to the broader question of differences between the speaking styles, so we briefly report the results here. To enable a comparison between speaking conditions, we first coded the presence or absence of a hesitation or pause in the critical region (between the definite article and the noun). As expected for this speaking style, hesitations were quite common: across speakers and across Mutation conditions, 30% of items were produced with hesitations in the critical region, with considerable variation across speakers (from only 7.6% of items for Speaker 3 to 74.3% of items for Speaker 1).

Elision of the [n̪ ɣ ] of the definite article after an immediately preceding hesitation was extremely rare, accounting for only 0.7% of items. Two speakers (Speaker 2 and Speaker 6) accounted for all of these occurrences. Prosodic factors likely account for part of the variation in the elision of this [n̪ ɣ ].

Table 7 presents the rate of elision of [n̪ ɣ ], considering only items where there was no pause or hesitation in the critical region. We do not consistently find the same pattern of elision for the same speaker between the two tasks, as a comparison of Tables 6 and7 shows.

Discussion

Phonetic characteristics of eclipsis consonants

One of the two main goals of our study was to provide evidence about the phonetic characteristics of eclipsis consonants. We examined whether eclipsis consonants (like the Our analyses offer limited evidence that there may indeed be phonetic differences between Radical and corresponding eclipsis consonants, in the direction predicted by the hypothesis. The analysis of the relative intensity of the stop burst showed that eclipsis stops have stronger bursts than corresponding radical stops, and also the bursts of eclipsis stops and those of control stops do not differ, in line with an incomplete neutralization hypothesis that eclipsis stops will share some characteristics of their corresponding voiceless control stops.

These results are incompatible with models that predict no difference between "underlying"

[ɡ] and [ɡ] arising from eclipsis.

It is possible that this observed difference in the relative intensity of the stop burst reflects a real difference between eclipsis and radical consonants. There are, however, a number of alternative explanations that need be considered. For example, frequent words are known to be phonetically reduced and less frequent words to be more carefully articulated (see, for example, Bybee 2001, 2007 andreferences therein), and frequency measures show that the /b ɣ /and /ɡ ɣ /initial radical forms used in the current study are more frequent than their eclipsis counterparts. At least in some environments, initial mutations may be part of a speaking style that is more formal and less familiar (at least in production). The observed differences in relative intensity of the stop burst may be due to hyperarticulated pronunciation of the radical consonants in our dataset. Two patterns in the data make this explanation less plausible: careful pronunciations are likely to have longer segmental durations and to be produced with release bursts. Yet we do not observe longer C 1 and C 1 closure durations in the eclipsis condition, and there are more tokens released without a clear release burst in the eclipsis condition than in the other two mutation conditions. (Recall that tokens without clear release bursts were excluded from the analyses; see § 2.5.1.) In addition, as we caution above, since the [n̪ ɣ ] of the definite article is often elided in the eclipsis context used in our study, the preceding phonetic context varied somewhat across conditions. Another possibility is that the observed differences in relative intensity of the stop burst are due to an effect of orthography, since Irish mutations are represented with a digraph (e.g., <gc> ~ [ɡ] in a gcroí [ɡɾ ɣ i] and radical consonants by a single letter (e.g., <g> ~ [ɡ] in gruig [ɡɾ ɣ ɪɟ]). In their study of Dutch, for example, [START_REF] Warner | Orthographic vs. morphological incomplete neutralization effects. Letter to the editor[END_REF] report an influence of orthography on the production of homophones. Given the growing evidence on interactions between orthographic and phonological knowledge, we expect such an effect to be present even in a non-reading task.

We predict that this influence of orthography should be weaker in non-reading tasks, in line with [START_REF] Winter | The nature of incomplete neutralization in German[END_REF] who predict that effects of incomplete neutralization in German should be stronger in tasks in which "participants are thinking actively about the formal written language (e.g. when dictating a text)" (p. 67) than in "regular" incomplete neutralization (where there is no reading and attention is not drawn to the written language).

The VOT and segmental duration analyses revealed no differences in the critical comparisons. Voiceless consonants are known to be typically longer than their corresponding voiced consonants, and we had hypothesized that if eclipsis consonants reflect characteristics of the corresponding radical consonants, this difference might be present. In this case, the [ɡ]

of a gcroí would be more /k ɣ /-like. While certain duration results are in the predicted direction (for example, the C 1 duration in the eclipsis condition lies between that of the control and radical conditions), these critical duration comparisons are not significant. For VOT, C 1 duration and C 1 closure duration, eclipsis consonants did not differ from radical consonants.

In particular, it was not the case that eclipsis consonants had values intermediate between control and radical consonants, as would be expected if eclipsis consonants reflect properties of the corresponding voiceless consonants.

The very little experimental work that has been done on the question of incomplete neutralization of distinctions in Irish initial mutation has been done with small samples of speakers (seven in this study, four in an earlier pilot study [START_REF] Welby | A phonetic investigation of Irish eclipsis: Preliminary results and challenges[END_REF])), with somewhat conflicting results. [START_REF] Roettger | Assessing incomplete neutralization of final devoicing in German[END_REF] raise concerns about the small sample sizes used in many studies of incomplete neutralization in German word-final devoicing, concerns that are also relevant here. For example, one participant in the pilot study showed a clear difference in duration with longer C 1 duration for eclipsis than Radical consonants, and longer C 1 closure duration. In our analyses in [START_REF] Welby | La production des consonnes éclipsées chez de jeunes locuteurs de l'irlandais[END_REF] of a subset of the data presented here, we also found significant differences in the direction predicted by the hypothesis for VOT and C 1 duration. In that study, however, we used linear mixed-effects models with random intercepts only, which have since been criticized by [START_REF] Barr | Random effects structure for confirmatory hypothesis testing: Keep it maximal[END_REF] as being prone to type II errors (incorrect rejection of the null hypothesis). We now use more conservative statistical tests (LMEMs with random slopes).

Our current results do not allow us to decide whether we are dealing with a partial or total eclipse. Additional production studies designed to correct the issues identified above (number of speakers, lexical frequency, etc.) might shed light on this question.

Variability of initial mutation patterns in present-day Irish

Our second main goal was to examine variability in patterns of initial mutation. The realization of these mutations appears to be style-or register-dependent, similar in some ways to that of French liaison. It was clear from our pre-and post-experiment discussions with our participants that some initial mutations are present in their spontaneous speech. In addition, although most participants do not produce mutations consistently in the semi-spontaneous speech of the card game task, they were fully comfortable reading sentences containing initial mutations, consistently producing the mutations specified by the orthography, even when they were immediately preceded by a pause or a hesitation. Participants also did not have any difficulty in understanding the speech of the experimenters BÓR and PW, who have more conservative patterns of initial mutations.

The realization of initial mutations in semi-spontaneous speech differed dramatically from the expectations of the traditional grammar. The following observation of [START_REF] Ball | Mutation in Welsh[END_REF] for Welsh holds also for Irish: "Teachers lay great stress on 'correct' (i.e. standard) mutation usage; however…first-language speakers consistently replace certain mutation contexts by non-mutation…" (p. 221). The only participant who produced eclipsis in most (88%) of the eclipsis contexts in the game task (Speaker 1) was working as an Irish-English interpreter, in addition to studying for a master's degree. To obtain certification as an interpreter, one needs to demonstrate mastery of the prescriptive grammar, including the system of initial mutations. Another participant (Speaker 7) was clearly influenced by the prescriptive grammar. As discussed in § 3.2.1, his pattern of mutations changed mid-way through the game task. He produced more eclipsed consonants in expected contexts, but he also produced séimhiú-lenition consonants in unexpected contexts. In the post-recording discussion, this participant volunteered without prompting that his non-native speaker classmates from Dublin had better Irish than he and his native speaker friends from his Gaeltacht community, explicitly referring to knowledge of the official standard grammar (An Caighdeán Oifigiúil, Translation Office 1958). That said, explicit corrections in the game task were exceedingly rare; there were only two cases in which participants "corrected" themselves to produce the eclipsed form called for by the prescriptive grammar.

In the card game task, we found some evidence that eclipsis may vary by consonant type.

A number of speakers produced more eclipsis forms for labials than for velars, a pattern that may be in part due to the much greater frequency of /k ɣ /and /k j /-initial words in the language. We are not aware of any mention in the literature of a tendency to produce more eclipsis forms for labial-initial than for velar-initial words, although there is some discussion about the reluctance of Irish speakers to séimhiú-lenite /f ɣ / and /f j / (which are deleted in séimhiú-lenition, see [START_REF] Stenson | Patterns of mutation in Irish loanwords[END_REF][START_REF] Frenda | Gender in Irish between continuity and change[END_REF] and references therein). In the literature on other Celtic languages and other contexts, there is some discussion of the effect of lexical frequency. For example, working on the then moribund East Sutherland dialect of Scottish Gaelic, [START_REF] Dorian | Grammatical change in a dying dialect[END_REF] notes that since most irregular verbs are very frequent and begin with mutatable consonants, there is "inordinately heavy reinforcement of its mutational phenomena" (pp. 417-418). She makes a similar argument about the stability of mutation in "obligatory-lenition adjuncts", commenting that it is "difficult to understand why the variability is not further advanced…unless the sheer statistical frequency of these morphemes has a braking effect on the process of change" (p. 418).

Spontaneous speech corpora will be essential to advancing our understanding of the variability in the realization of initial mutations. For example, we will be able to look beyond the limits of the experimental materials of the current study, which included only one eclipsis context. We therefore do not have the data to examine variation potentially due to factors such as linguistic structure, functional load, and prosodic phrasing. For example, in most contexts, eclipsis and the other initial mutations have very little functional load: they rarely convey semantic or syntactic information. One exception is the third person pronouns, which are segmentally identical (a masc. sg. , a fem. sg. , a pl. : all [ə], but distinguished by the initial mutations that follow them (e.g., a dheirfiúr [jɾ j ɪf j uɹ ɣ ] 'his sister' (séimhiú-lenition), a deirfiúr [ḏ j ɾ j ɪf j uɹ ɣ ] 'her sister' (no mutation), a ndeirfiúr [ṉ j ɾ j ɪf j uɹ ɣ ] 'their sister' (eclipsis)) (see [START_REF] Frenda | Gender in Irish between continuity and change[END_REF], also

Thomas & Gathercole 2007 on the acquisition of the comparable pronominal/mutation system in Welsh). Corpus studies will also allow us to examine whether the imbalance in eclipsis Kevin Scannell for the written corpus statistics, participants of the Celtic Linguistics 6

(Dublin) and PhonLex (Toulouse) conferences for their helpful feedback, and Amandine

Michelas for her advice on the LMEMs. We also thank three anonymous reviewers and JIPA editor Amalia Arvaniti for their critical reading of previous versions of the manuscript and their constructive comments. All remaining errors are, of course, our own. This work was funded under the Ulysses France-Ireland research scheme. Partial results of this study were presented in [START_REF] Welby | La production des consonnes éclipsées chez de jeunes locuteurs de l'irlandais[END_REF]. 'foot' *Note that in Irish the acute accent marks a phonemically long vowel (not stress). Lexical stress is on the first syllable for these (and virtually all) monomorphemic nouns.

Appendix: Items

Control

Table 1 The initial mutation alternations of Connemara Irish. The three main columns represent the radical consonants and corresponding séimhiú-lenition and eclipsis consonants. Each main column contains a pair of phonemically contrastive consonants, followed in angled brackets by the grapheme used to orthographically represent these consonants. We use phonemic representation here in order to represent the opposition of the secondary articulations in Irish. Consonants in parentheses appear word-initially only in mutation contexts (with very few exceptions, such as loan words, e.g., hata 'hat').

  article in the dative singular leis [ḻ j ɛʃ] an [ən̪ ɣ ] gcasúr [ɡɑs ɣ uɹ ɣ ] 'with the hammer' (nouns beginning with [d ɣ ], [t ɣ ], [ḏ j ], and [ṯ j ] appear in their radical form in this context) b. in the genitive plural praghas [p ɣ ɾ ɣ a͡ is ɣ ] na [n̪ ɣ ə] gcapall [ɡɑp ɣ əl̪ ɣ ] 'the price of the horses' c. after the prepositions i [ɪ] 'in' and sa 'in the' i bPáras [b ɣ ɔɾ ɣ əs ɣ ] 'in Paris' sa [s ɣ ə] mbosca [m ɣ ʌs ɣ k ɣ ə] 'in the box' d. in a few fixed expressions ar [ɛɹ j ] gcúl [ɡul̪ ɣ ] 'behind' e. after the possessive adjectives ár [ɔɹ ɣ ] 'our', bhur [wuɹ ɣ ] 'your (pl)', a [ə] 'their' a n-athair [n̪ ɣ ɑhɪɹ j ] 'their father' f. after the numbers seacht [ʃaxt̪ ɣ ] 'seven', ocht [ʌxt̪ ɣ ] 'eight', naoi [n̪ ɣ i] 'nine', and

( 6 )

 6 The sound alterations of séimhiú-lenition a. i. Oral stops and the bilabial nasal stops [m ɣ ] and [m j ] become fricatives or glides. bó [b ɣ o] '(a) cow', an [ən̪ ɣ ] bhó [wo] 'the cow' muc [m ɣ ʊk] '(a) pig', an mhuc [wʊk] 'the pig' ii. The voiced coronal stop [d̪ ɣ ] also changes in place of articulation. dobharchú [d̪ ɣ a͡ uɹ ɣ xu] 'otter', dhá [ɣɔ] dhobharchú [ɣa͡ uɹ ɣ xu] 'two otters' iii. The voiceless coronal stops [t̪ ɣ ] and [ṯ j ] are debuccalized. turtar [t̪ ɣ ʌɹ ɣ t̪ ɣ əɹ ɣ ] 'turtle', dhá thurtar [hʌɹ ɣ t̪ ɣ əɹ ɣ ] 'two turtles' b. The sibilant fricatives [s ɣ ] and [ʃ] are debuccalized. Sadhbh [s ɣ a͡ iv ɣ ] (girl's first name), a [ə] Shadhbh! [ha͡ iv ɣ ] (vocative particle + first name) c. The labial fricatives [f ɣ ] and [f j ] are deleted. fia [f j iə]'(a) deer', ar [ɛɹ j ] fhia [iə] 'on a deer'

  seagull', seacht bhfaoileán [wiḻ ʲ ɔn̪ ] 'seven seagulls' ii. The labial fricative [f ɣ ] also often changes in manner: [w]. b. Voiced stops become nasals. bó [b ɣ o] '(a) cow', seacht mbó [m ɣ o] seven cows' c. The nasal [n̪ ɣ ] or [ṉ j ] is prefixed to vowels. oisín [ʌʃiṉ j ] '(a) fawn', seacht n-oisín [n̪ ɣ ʌʃiṉ j ] 'seven fawns'

  [p ɣ ], [b ɣ ] and the velar stops [k], [ɡ]). To build the materials we conducted pattern searches on an electronic version of the Irish dictionary Foclóir Póca (Ó Baoill 1986), to select common, picturable nouns meeting the required characteristics. These target nouns were inserted into three types of contexts, as shown in (1): a. a no-mutation context consistent with the radical form of the initial (phonologically) voiced stop ([b ɣ ], [ɡ]), b. a context consistent with eclipsis of an initial (phonologically) voiceless stop ([p ɣ ], [k]), and c. a control context with an initial (phonologically) voiceless stop ([p ɣ ], [k]) in the radical form. This control condition allowed us to measure acoustic characteristics of voiceless stops and see whether any of these characteristics were present in the eclipsed consonants. Note that Irish has a two-way phonological voicing contrast between voiceless aspirated (long-lag VOT (voice-onset time))

  : Cuir an gadaí [ɡɑd̪ ɣ i] ar an oifig. 'Put the robber on the office.' b. Eclipsis: Cuir an oifig ar an gcasúr [ɡɑs ɣ uɹ ɣ ]. 'Put the office on the hammer.' c. Control (radical): Cuir an casúr [kɑs ɣ uɹ ɣ ] in aice leis an úll.

  an X ar an Y. 'Put the X on the Y.' b. Cuir an X os cionn an Y. 'Put the X above the Y' c. Cuir an X in aice leis an Y. 'Put the X next to the Y.' d. Cuir an X faoin Y. 'Put the X under the Y.' e. Cuir an X agus an Y le chéile. 'Put the X and the Y together.' Each participant completed two training session. In the first session, pairs of cards were presented on the screen and one of the cards was named by a recorded voice (a female native speaker of Connemara Irish).Participants were asked to point to the named card. In the second session, 10 practice instructions (moves) were presented visually via PowerPoint presentation, with accompanying oral instructions given by the same recorded voice. These practice sessions familiarized participants with the names of the cards and the moves and allowed them to practice playing the game.

  Each participant was recorded individually in September 2010 in a quiet classroom on the campus of Acadamh na hOllscolaíochta Gaeilge, a university campus in Connemara where the language of instruction is Irish. The one exception was the reading task of Participant 1, which took place in June 2013 in Dublin. Recordings were done using a Shure SM10A

  [ɡ] of a gcroí 'their heart') differ from the corresponding radical consonants (like the [ɡ] in gruig '(a) frown, scowl'), in particular whether these eclipsis consonants reflect characteristics of their voiceless counterparts (like the [k] of croí '(a) heart'). Eclipsis, radical, and control (voiceless) consonants were compared in terms of VOT, C 1 duration, C 1 closure duration, and relative intensity of the C 1 burst.

  observed in the current study is due to the consonant type (velar vs. labial) or to the experimental items themselves. A similar phenomenon, French liaison, is known to be in part item-dependent. Corpora available for future investigations include the GaLa/Comhrá corpus of spoken Irish (Uí Dhonnchadha, Frenda & Vaughan 2012) and the GaelChaint corpus of conversations between pairs of native speakers of Connemara Irish (Ó Raghallaigh, Ní Chiosáin & Welby 2014).

Figure 2

 2 Figure 2Screens corresponding to the move Cuir an folcadán ar an bpota

Figure 3

 3 Figure 3Praat TextGrid file with example labels. Zoom on ar an gcasúr from the

Figure 4 Figure 6 Figure 7

 467 Figure 4Voice onset time (VOT) by Mutation and Place of Articulation (reading

Table 3

 3 The LMEM retained for C 1 duration (reading task)

	Fixed effects:
		Estimate	Std. Error	t value
	(Intercept)	84.215	8.106	10.389
	PlaceArtVelar	-6.772	5.016	-1.350
	MutationRadical	-10.594	8.014	-1.322
	MutationControl	35.726	7.090	5.039
	PlaceArtVelar:MutationRadical	1.689	5.774	0.292
	PlaceArtVelar:MutationControl	-4.163	5.217	-0.798

Table 4

 4 The LMEM retained for C 1 closure duration (reading task)

	Fixed effects
		Estimate	Std. Error	t value
	(Intercept)	62.8515	7.2307	8.692
	PlaceArtVelar	-15.3406	3.9528	-3.881
	MutationRadical	-7.1156	5.9676	-1.192
	MutationControl	-6.7826	5.1285	-1.323
	PlaceArtVelar:MutationRadical	0.6667	4.0205	0.166
	PlaceArtVelar:MutationControl	-0.2666	4.2334	-0.063

Table 5

 5 The LMEM retained for relative intensity of the C 1 stop burst (reading task)

	Fixed effects
		Estimate	Std. Error	t value
	(Intercept)	14.36470	1.43098	10.038
	PlaceArtVelar	-2.11060	1.26271	-1.671
	MutationRadical	2.19291	0.98525	2.226
	MutationControl	-0.27960	0.73614	-0.380
	PlaceArtVelar:MutationRadical	-0.82189	1.23402	-0.666
	PlaceArtVelar:MutationControl	0.03361	0.99748	0.034

Table 6

 6 Rate of elision (%) of the [n̪ ɣ ] in the definite article preceding the target noun according to

	Mutation condition (Reading task)
		Radical	Control	Eclipsis
	Speaker
	1	44.4	31.8	64.3
	2	0	0	100
	3	3.7	4.5	75
	4	20	5.9	90
	5	0	0	0
	6	17.9	18.2	96.3
	7	0	0	31.6

Table 7

 7 Rate of elision (%) of the [n̪ ɣ ] in the definite article an preceding the target noun according to Mutation condition for items with no hesitation or pause in the critical region (Game task) Map of Ireland with the official Irish-speaking regions (Gaeltachtaí) shaded

		Radical	Control	Eclipsis
	Speaker
	1	0	16.7	41.7
	2	9.5	26.1	81.3
	3	0	3.7	3.8
	4	0	8.7	0
	5	0	4.5	0
	6	92.9	85.2	61.9
	7	0	8.7	0

Acknowledgments

We are grateful to the staff of Acadamh na hOllscolaíochta Gaeilge, An Cheathrú Rua, Connemara for hosting the recordings and to our speakers for their participation. We thank

iii Note that in present-day Irish, /r j / is not consistently palatalized, particularly among younger speakers. Traditional speakers of the dialect in question generally realize non-initial /r j / as an apico-postalveolar fricative. See Ní [START_REF] Chasaide | Irish[END_REF] on Gaoth Dobhair Irish. iv In the Celticist tradition, these consonants are referred to as "broad" and "slender", respectively. By convention, broad consonants are left unmarked in the phonemic transcription and slender consonants are marked with a prime (e.g., naoi /niː/ 'nine', ní /nʹiː/ (negative particle)). This phonemic contrast is not relevant to the aims of this study. For more details, see Ní [START_REF] Chiosáin | Topics in the phonology of Irish[END_REF], Ní [START_REF] Chasaide | Irish[END_REF], and [START_REF] Bennett | An ultrasound study of Connemara Irish palatalization and velarization[END_REF]. For transcription conventions for Connemara Irish, see Ó Raghallaigh (2014).

v We decided to code the initial mutation process of séimhiú-lenition, because some speakers produced séimhiú-lenition forms even when there was no context licensing this mutation. vi In the interest of replicability, we give the R syntax for the maximal model for the VOT analysis. In the interest of brevity, we do not give the maximal models for the other analyses. Note however that for these models only the dependent variable changes (vot, etc.).

vii The significance threshold is standardly assumed to be t > |2|. It is currently not possible to obtain pMCMC values for recent versions of lme4 for models with random correlation parameters. Mutation condition Relative intensity of C1 burst (dB)


E Sorokin
email: e.sorokin@tuwien.ac.at

I T Sorokina
email: sorokina@ntnu.no

J Mandon

G Guelachvili

N Picqué

Sensitive multiplex spectroscopy in the molecular fingerprint 2.4 µm region with a Cr 2+ :ZnSe femtosecond laser

Keywords: 300.6390 Spectroscopy, molecular, 320.0320 Ultrafast optics

An ultrashort-pulse Cr 2+ :ZnSe laser is a novel broadband source for sensitive high resolution molecular spectroscopy. A 130-fs pulse allows covering of up to 380 cm -1 spectral domain around 2.4 µm which is analyzed simultaneously with a 0.12 cm -1 (3.6 GHz) resolution by a Fouriertransform spectrometer. Recorded in 13 s, from 70-cm length absorption around 4150 cm -1 , acetylene and ammonia spectra exhibit a 3800 signal-tonoise ratio and a 2.4•10 -7 cm -1 •Hz -1/2 noise equivalent absorption coefficient at one second averaging per spectral element, suggesting a 0.2 ppbv detection level for HF molecule. With the widely practiced classical tungsten lamp source instead of the laser, identical spectra would have taken more than one hour.

Introduction

Mode-locked lasers and femtosecond frequency combs actively enter [START_REF] Mandon | Femtosecond laser Fourier transform absorption spectroscopy[END_REF][START_REF] Thorpe | Cavity-ringdown molecular spectroscopy based on an optical frequency comb at 1.45-1.65 µm[END_REF][START_REF] Diddams | Molecular fingerprinting with the resolved modes of a femtosecond laser frequency comb[END_REF][START_REF] Thorpe | Broadband Cavity Ringdown Spectroscopy for Sensitive and Rapid Molecular Detection[END_REF][START_REF] Schliesser | Frequency-comb infrared spectrometer for rapid, remote chemical sensing[END_REF][START_REF] Mandon | Picqué are preparing a manuscript to be called "Doppler-limited multiplex frequency comb spectrometry[END_REF] the field of broadband spectrometry. In particular, their high brightness allows improving the signal to noise ratio (SNR) of the traditional absorption spectroscopy [START_REF] Mandon | Femtosecond laser Fourier transform absorption spectroscopy[END_REF]. For spectroscopic applications, the mid-infrared spectral region is of special interest, as most of molecules have intense vibration-rotation transitions lying in this domain. Developing sensitive techniques in this region results therefore in improved detection levels. High resolution is also advantageous because the Doppler profiles of the infrared lines are narrow and their resolved observation increases the sensitivity. The accuracy of the absolute frequency reading is required for unambiguous identification of the lines and species. Additionally, the broadband simultaneous detection is often necessary, for instance, for multi-species trace gas sensing or for accurate renewed molecular theoretical approaches. Most of the traditional spectrometric approaches encounter severe limitations if these four features are to be met simultaneously. For example, the multichannel grating spectrometers have poor efficiency both from the point of view of spectral resolution and broadband coverage; and wavelength agile laser techniques [START_REF] Hult | High bandwidth absorption spectroscopy with a dispersed supercontinuum source[END_REF] have limited accuracy. In addition, the mid-infrared region has been suffering from a lack of convenient broadband laser sources, while the spectral radiance of incoherent sources is insufficient for sensitive measurements. A broadband mid-infrared approach to high resolution sensitive spectroscopy is therefore highly desirable. A solution to this challenging problem may be found in the multiplex high resolution spectral analysis using the newly developed femtosecond mode-locked lasers and frequency comb sources.

In this paper, we report the implementation of a new spectrometric method based on a femtosecond laser taking the full benefit of the direct access to the mid-infrared wavelength range. We apply the first femtosecond solid-state mode-locked laser source in the molecular fingerprint region above 2 µm to high resolution spectroscopy. The radiation of a Cr 2+ :ZnSe mode-locked laser is absorbed by the gas sample and analyzed by a commercial Fourier transform (FT) spectrometer. Examples of acetylene and ammonia spectra covering up to 380 cm -1 in the 4150 cm -1 region are shown. The first sub-ps mode-locked operation of Cr 2+ :ZnSe lasers has been reported recently [START_REF] Sorokina | Femtosecond Pulse Generation from a SESAM Mode-Locked Cr:ZnSe Laser[END_REF], with pulse duration down to 80 fs at 80 mW of output power [START_REF] Sorokina | Chirped-Mirror Dispersion Controlled Femtosecond Cr:ZnSe Laser[END_REF][START_REF] Sorokina | Broadband mid-infrared solid-state lasers[END_REF]. In the present experiment, we have set up a prismless femtosecond laser following the design of Ref. [START_REF] Sorokina | Chirped-Mirror Dispersion Controlled Femtosecond Cr:ZnSe Laser[END_REF], optimized for a long-term hands-free stable operation. The laser is based on a 4 mm thick Brewster-cut Cr 2+ :ZnSe crystal (Fig. 1). The crystal temperature is maintained at 20.5 °C by a recirculating water chiller system. The astigmatically compensated X-fold cavity consists of 75-mm and 100-mm radius-of-curvature dichroic mirrors, a 50-mm radius of curvature chirped mirror focusing the light onto an InAs/GaSb semiconductor saturable absorber mirror (SESAM), and an output coupler with transmission of 2 % at 4100 cm -1 . Optical pumping is achieved with a 1607 nm Er-doped fiber laser, focused onto the crystal by an uncoated lens of 40 mm focal length. The self-starting mode-locking results from the use of the SESAM, which has several hundreds of picoseconds relaxation time. Dispersion compensation is provided by a combination of a 6.5 mm thick uncoated YAG plate and the spherical chirped mirror. This provides about -1500 fs 2 round-trip group delay dispersion (GDD), which is almost flat over 500 cm -1 . The cavity length is about 75 cm, corresponding to 200 MHz pulse repetition rate.

Experiment

In order to get rid of the strong absorption lines of water vapor, which are present in the vicinity of 2.4 µm, the oscillator is placed inside a sealed enclosure. The enclosure is equipped with windows made of BK7 on the Er:fiber laser side and of CaF 2 on the Cr 2+ :ZnSe laser output side. The enclosure is first evacuated under primary vacuum conditions and then filled with dry nitrogen. Under these conditions, with 1.9 W of pumping power, stable mode-locked operation is obtained during hours with ~50 mW average output power. The main stability limitation has been identified as arising from temperature increase of the SESAM heatsink, which was not attached to the cooling circuit, and resulted in slow decrease of the output power (and pulse broadening) during the laser operation. Fig. 2 provides a low resolution (30 GHz -1 cm -1 ) spectrum and an interferometric autocorrelation trace of the laser pulses. The full width at half maximum (FWHM) of the autocorrelation trace is 250 fs, which leads to a pulse width of the order of 130 fs, consistent with the 76 cm -1 measured FWHM of the corresponding spectrum, which has almost perfect sech 2 profile, as shown on Fig. 2. The pulse duration could be decreased by dispersion optimization [START_REF] Sorokina | Chirped-Mirror Dispersion Controlled Femtosecond Cr:ZnSe Laser[END_REF], but we opted to improve the operation stability by providing some additional negative GDD. The laser emission is centered at 4157 cm -1 . As compared to the open-air operation, the emission peak is not shifted towards longer wavelengths. This is different from our previous observation of the non-stationary continuous-wave operation of the Cr 2+ :ZnSe laser under secondary vacuum [START_REF] Picqué | Time-resolved Fourier transform intracavity spectroscopy with a Cr 2+ :ZnSe laser[END_REF], where the decrease of the water absorption (growing towards smaller wavenumbers) after air removal resulted in a shift of the laser wavelength by ~75 cm -1 to the infrared. More surprisingly, the pulse spectral width also doesn't increase when the air humidity absorption disappears. Our explanation is that the high losses of the mode-locked setup (12% unsaturated absorption in the SESAM alone) significantly exceed the integrated absorption in the narrowband water vapor lines, thus making the setup almost insensitive to the air humidity.

After the exit window, the laser pulses pass through a 70 cm-long single-pass absorption cell, filled with the gas of interest, and ~5 m of open-air propagation before finally reaching the spectrometer. The laser radiation is analyzed by a commercial FT spectrometer (max. resolution 0.12 cm -1 ) equipped with a fluorine beam-splitter and a thermoelectrically cooled InAs detector. The laser beam has to be attenuated in order not to saturate the detector.

As a first demonstration of the capabilities of the source for broadband absorption spectroscopy, the rovibrational spectra of acetylene and ammonia have been recorded around 4150 cm -1 . Figure 3 gives an illustration of the C 2 H 2 spectrum, in the region of the ν 1 +ν 5 1 band [START_REF] Cunha | Analysis of the high-resolution spectrum of acetylene in the 2.4 µm region[END_REF]. The full width at half maximum of the spectrum is 75 cm -1 . Resolution is limited by the spectrometer to 3.6 GHz (0.12 cm -1 ). With the total recording time T=13 s we benefit from an uppermost SNR better than 3800. With spectral boundaries defined by a SNR relatively degraded by a factor 1000, the spectral range extends over 380 cm -1 , from 3980 cm -1 to 4360 cm -1 . This corresponds to a number of spectral elements M equal to 3167. The cell is filled with acetylene at 23 hPa (17 Torr) pressure. The absorption lines shown on Fig. 3 are due to the acetylene bands and the water vapor lines [13] from the open-air propagation. Figure 4 displays a portion of a NH 3 recorded absorption spectrum, with a NH 3 pressure equal to 261 hPa (196 Torr). The spectral lines of ammonia belong to the ν 1 + ν 2 and ν 2 + ν 3 rovibrational combination bands [14]. As the spectrum is complex and crowded, high resolution is essential to discriminate against the various lines. The recording conditions are the same as for the acetylene spectrum. Figure 3: Part of a C 2 H 2 spectrum at 0.12 cm -1 resolution in the 2.4 µm region. The baseline modulation is not noise-related but due to a channel spectrum from an unwedged window. The strongest spectral features are the P, Q and R branches of the ν 1 +ν 5

1 band [START_REF] Cunha | Analysis of the high-resolution spectrum of acetylene in the 2.4 µm region[END_REF] of 12 C 2 H 2 , centered at 4090 cm -1 . The intensity alternation is obvious in the R-branch. The upper left inset is a zoom showing acetylene and residual water vapor lines coming from a 5 meters air path between the cell and the interferometer. The H 2 O lineshapes reveal an atmospheric-pressure broadening. The rotational assignment for the H 2 O lines [13] gives (J,K a ,K c ).

Results and discussion

In these spectra, the noise equivalent absorption coefficient (NEA) reaches 3.7×10 -6 cm -1 . NEA at one second averaging per spectral element (L × SNR) -1 × (T/M) 1/2 = 2.4 ×10 -7 cm -1 . Hz -1/2 , where L is the absorption path length. In the present spectral region, this level of sensitivity allows for the high resolution detection of 22 parts per billion by volume (ppbv) of C 2 H 2 , and 160 ppbv of NH 3 at 1 s of integration time per spectral element. These detection limit values are still relatively high because the combination bands of C 2 H 2 and NH 3 in this region are weak: their intensity, of the order of 10 -21 cm•molecule -1 , is not higher than in the 1.5 µm region. For hydrogen fluoride HF (1-0 band, with intensity of the R(2) line at 4075 cm - 1 equal to 2.3•10 -18 cm•molecule -1 [13]), the corresponding detection level is 200 parts per trillion by volume (pptv) in the 2.4 µm spectral region. For a fair comparison, we recorded a spectrum using a traditional tungsten lamp, which is the most widely used broadband source in the near-and mid-infrared absorption FTS. Under identical experimental conditions, the SNR was degraded by about 17. The recording time would have then been 300 times longer to get identical results. This is not surprising as this 50 mW femtosecond laser source has a spectral radiance which is about 2.8•10 5 times stronger than a 3000 K blackbody source. Actually, a signal-to-noise ratio enhancement of about 500 should be achieved. This could not be demonstrated in the present experiment: as the 50 mW power of the laser saturates the detector, we had to attenuate the beam by more than two orders of magnitude before entering in the interferometer. To make a proper use of the abundant power, one should e.g. employ a classical multipass cell. In this case increase of the absorption path by more than two orders of magnitude would then improve the sensitivity by the same factor, without lowering the SNR.

It is also interesting to compare our experimental results with a recent near-infrared comb-based experiment [START_REF] Thorpe | Cavity-ringdown molecular spectroscopy based on an optical frequency comb at 1.45-1.65 µm[END_REF]. By coupling a 1550 nm Er-fiber based frequency comb to a cavity with a finesse higher than 3100, Ref. [START_REF] Thorpe | Cavity-ringdown molecular spectroscopy based on an optical frequency comb at 1.45-1.65 µm[END_REF] obtains a NEA at one second averaging equal to 2•10 -8 cm -1 .Hz -1/2 , with an equivalent absorption path length higher than 3000 m. This absorption path length is about 4300 times higher than ours whereas the resulting sensitivity is only one order of magnitude better. Moreover, the resolution of the grating spectrometer is limited to 25 GHz. The acquisition of a broad spectral domain is a sequential, long and inaccurate process, whereas in the present experiment, 13 seconds are enough to measure simultaneously 3167 individual spectral elements spanning 380 cm -1 , that are only limited by the laser emission, at 3.6 GHz resolution. Actually, during these 13 seconds, the FT spectrometer samples a 15800 cm -1 broad spectral domain by 131650 independent spectral elements. A more detailed discussion of the advantages of using a FT spectrometer for this kind of experiments may be found in [START_REF] Mandon | Femtosecond laser Fourier transform absorption spectroscopy[END_REF].

Further improvements of the present experiment can be made in several directions. The resolution can easily be improved up to the Doppler width of the lines by using a higher resolution interferometer. It is also possible to significantly increase the measured spectral domain. The enormous bandwidth of the Cr 2+ :ZnSe laser allows indeed coverage of a much broader spectral region, either by tuning, or more interestingly by construction of a few-cycle laser source to observe hundreds of nm simultaneously. Alternatively generation of a midinfrared supercontinuum in highly nonlinear fibers looks promising, as we demonstrated it recently in the near infrared spectral region [15]. Using of a broadband source is especially attractive for FT spectroscopy, where measurement time is independent of the spectral domain width. As discussed above, sensitivity improvement can benefit from absorption path length enhancement either by use of a classical multipass cell or by injection of a fs frequency comb in a high finesse cavity. Use of a comb can bring additional sensitivity gain by performing high frequency synchronous detection, which also leads to the advantage of allowing simultaneous measurement of the absorption and dispersion associated with the spectral features, as experimentally established in [START_REF] Mandon | Picqué are preparing a manuscript to be called "Doppler-limited multiplex frequency comb spectrometry[END_REF].

Conclusion

Summarizing, we have demonstrated the first spectroscopic application of a mid-infrared femtosecond mode-locked laser used as a broadband infrared source with a high resolution FT spectrometer. This simple experimental setup already exhibits high sensitivity and resolution over a broad spectral domain. Sub-ppb detection levels should be easily obtained for a large panel of molecules thanks to absorption path length enhancement and high frequency detection. Further improvements in resolution and acquisition time are also in progress. This will include taking advantage of the comb structure of a stabilized mode-locked Cr 2+ :ZnSe laser by combination of the complementary methods developed in [START_REF] Thorpe | Broadband Cavity Ringdown Spectroscopy for Sensitive and Rapid Molecular Detection[END_REF] and in [START_REF] Mandon | Picqué are preparing a manuscript to be called "Doppler-limited multiplex frequency comb spectrometry[END_REF].

Figure 1 :

 1 Figure 1: Experimental set-up. CM: chirped mirror. OC: output coupler. Atten: attenuator.

Figure 2 :

 2 Figure 2: (a) Spectrum (FWHM: 76 cm -1 ) and (b) interferometric autocorrelation (FWHM: 250 fs) of a 130-fs pulse of the Cr 2+ :ZnSe mode-locked laser. Pump power: 1.9 W, output power: 50 mW, repetition rate 200 MHz.

Figure 4 :

 4 Figure 4: Spectrum of NH 3 in the 2.4 µm region illustrating the spectral bandwidth and SNR capabilities of the spectrometric technique. The ν 1 + ν 2 and ν 2 + ν 3 combination bands are observed. The upper part of the figure shows the whole spectral domain covered in a singe recording while the lower part shows a portion expanded in wavenumber and intensity scales.

Acknowledgments

P. Jacquet (Laboratoire de Photophysique Moléculaire, Orsay) is warmly thanked for his participation to the experiments. I. T. Sorokina acknowledges Université Paris-Sud for a position of invited professor. This work is accomplished in the framework of the Programme Pluri-Formation de l'Université Paris-Sud "Détection de traces de gaz" 2006-2009 and the Austrian Fonds zur Förderung der wissenschaftlichen Forschung project P17973.