Cabrera Laurianne
email: laurianne.cabrera@gmail.com

Lorenzi Christian

Bertoncini Josiane

Infants discriminate voicing and place of articulation with reduced spectral and temporal modulation cues

Keywords: Speech perception, Amplitude modulation, Frequency modulation, Infants

Infants discriminate voicing and place of articulation with reduced spectral and temporal modulation cues

Laurianne Cabrera, Christian Lorenzi, Bertoncini

I. INTRODUCTION

A large number of studies have investigated separately auditory and speech perception in infants (for a review see [START_REF] Kuhl | Early language acquisition: cracking the speech code[END_REF][START_REF] Saffran | The infant's auditory world: Hearing, speech, and the beginnings of language[END_REF][START_REF] Saffran | The infant's auditory world: Hearing, speech, and the beginnings of language[END_REF], but knowledge about the auditory capacities involved in the typical early development of speech processing is still lacking. A better characterization of these early auditory capacities is important because accurate sensory coding of acoustic cues is required for robust speech perception in real-life listening conditions (e.g., [START_REF] Moore | Cochlear Hearing Loss: Physiological, Psychological and Technical Issues[END_REF]. The development of the basic auditory capacities involved in the extraction of these acoustic cues has been assessed extensively with non-linguistic sounds such as pure tones, complex tones or noises. These capacities appear to be "adultlike" by 6 months of age (e.g., [START_REF] Levi | Amplitude modulation detection in infancy: Update on 3-month-olds[END_REF][START_REF] Spetner | Auditory frequency resolution in human infancy[END_REF][START_REF] Werner | Human Auditory Brainstem Response to Temporal Gaps in Noise[END_REF], although some continue to develop until late into childhood (see, [START_REF] Burnham | Auditory development[END_REF][START_REF] Saffran | The infant's auditory world: Hearing, speech, and the beginnings of language[END_REF]. Recently, the low-level spectro-temporal auditory abilities involved in the perception of speech signals have been investigated for adults using speech-processing algorithms called vocoders (see [START_REF] Shamma | On the balance of envelope and temporal fine structure in the encoding of speech in the early auditory system[END_REF] for a review). The present study extended this investigation to the discrimination of phonetic contrasts for infants.

Speech signals are commonly assumed to be decomposed by the cochlea into a series of narrowband signals (usually described as 32 independent frequency bands) each with a passband equal to one "equivalent-rectangular bandwidth" (ERB N which is an approximation of the auditory filter bandwidth given by the equation: ERB = 24.7(4.37F + l) with F in kHz corresponding to the center frequency of the filter) [START_REF] Glasberg | Derivation of auditory filter shapes from notchednoise data[END_REF][START_REF] Moore | Speech processing for the hearing-impaired: successes, failures, and implications for speech mechanisms[END_REF].

Each 1-ERB N wide band may be viewed as a sinusoidal carrier with superimposed amplitude modulation (AM, or relatively slow modulations in amplitude over time) and frequency modulation (FM or relatively fast fluctuations in instantaneous frequency over time; e.g., [START_REF] Drullman | Temporal envelope and fine structure cues for speech intelligibility[END_REF][START_REF] Shamma | On the balance of envelope and temporal fine structure in the encoding of speech in the early auditory system[END_REF][START_REF] Shannon | Speech recognition with primarily temporal cues[END_REF][START_REF] Sheft | Speech identification based on temporal fine structure cues[END_REF][START_REF] Smith | Chimaeric sounds reveal dichotomies in auditory perception[END_REF][START_REF] Zeng | Speech recognition with amplitude and frequency modulations[END_REF]. In a seminal review, [START_REF] Rosen | Temporal information in speech: acoustic, auditory and linguistic aspects[END_REF] systematically described how AM (temporal envelope) and FM (temporal fine structure) cues signal phonetic contrasts. The slowest AM cues (i.e., <16 Hz) are mostly related to speech rhythm and syllabicity and the fastest AM cues and FM cues are mostly related to formant transitions (i.e., ~30 Hz) and voice-pitch information (i.e., periodicity cues, between 50-500Hz).

Vocoders are signal-processing algorithms that extract (i.e., compute) the AM and FM cues of speech signals from different analysis frequency bands [START_REF] Dudley | Remaking speech[END_REF]. Using vocoders, one can therefore manipulate the relative strength of the AM and FM components and the fine spectral cues 1 conveying the phonetic information of the vocoded speech. Over the last decades, vocoder studies have repeatedly demonstrated the importance of AM and FM cues in speech perception for adults (e.g., [START_REF] Sheft | Speech identification based on temporal fine structure cues[END_REF][START_REF] Smith | Chimaeric sounds reveal dichotomies in auditory perception[END_REF][START_REF] Zeng | Speech recognition with amplitude and frequency modulations[END_REF]. Normal-hearing adults showed accurate speech recognition in quiet when listeners are presented with syllables or sentences vocoded to preserve only the slowest AM cues (< 16 Hz) extracted (i.e., computed) from four broad frequency bands (e.g., [START_REF] Shannon | Speech recognition with primarily temporal cues[END_REF].

Additional work suggested that faster and fine spectro-temporal modulations (that is, FM cues and fine spectral cues) are required for robust speech recognition in adverse listening conditions such as when speech is interrupted or masked by noise (e.g., [START_REF] Eaves | Benefit of temporal fine structure to speech perception in noise measured with controlled temporal envelopes[END_REF][START_REF] Gnansia | Effects of spectral smearing and temporal fine structure degradation on speech masking release[END_REF][START_REF] Nelson | Factors affecting speech understanding in gated interference: cochlear implant users and normal-hearing listeners[END_REF][START_REF] Qin | Effects of simulated cochlear-implant processing on speech reception in fluctuating maskers[END_REF]. Recent studies suggest that the high recognition performance demonstrated by adults when listening to vocoded speech retaining AM cues only may be due to their phonological and lexical skills (e.g., [START_REF] Hervais-Adelman | Perceptual learning of noise vocoded words: Effects of feedback and lexicality[END_REF][START_REF] Sohoglu | Predictive top-down integration of prior knowledge during speech perception[END_REF].

The present study explored the extent to which 6-month-old infants, whose perception of segmental cues is not yet tuned to their native language (e.g., [START_REF] Kuhl | Early language acquisition: cracking the speech code[END_REF] are able to use the AM, FM and fine spectral cues of speech when discriminating phonetic contrasts.

To the best of our knowledge, only a few studies have assessed the ability of infants and children to use these spectro-temporal modulation cues in discrimination and identification tasks using noise or tone-excited vocoded stimuli. As for children, [START_REF] Newman | Toddlers' recognition of noise-vocoded speech[END_REF] showed that English-learning 2-year-old toddlers accurately identify vocoded words when AM cues are extracted and preserved from 8 frequency bands. For older children, [START_REF] Eisenberg | Speech recognition with reduced spectral cues as a function of age[END_REF] found that English-learning 5-to 7-year-old children require a greater number of frequency bands than adults to identify vocoded words and sentences. More recently, [START_REF] Bertoncini | Discrimination of speech sounds based upon temporal envelope versus fine structure cues in 5-to 7-year-old children[END_REF] showed that French-learning 5-year-old children discriminate nonsense bisyllables as well as older children and adults when only the relatively slow (< 64 Hz) AM cues are preserved within 16 frequency bands.

Identification and discrimination task do not involve the same auditory and linguistic processes. For instance, sentence identification tasks require speech segmentation and lexical access. These studies suggest that, for tasks requiring elaborate or higher-level (cognitive/linguistic) processing such as tasks requiring to identify words and sentences, younger children may require greater redundancy in the speech signal (that is, a greater number of frequency bands, and therefore fine spectral cues) than older ones or adults. When the task is less demanding, as in the case of discrimination of isolated phonemes or syllables, younger children may be able to make accurate responses based on limited sensory cues, and this is why performance is similar across age groups.

Less information is available regarding infants. [START_REF] Bertoncini | Six-month-old infants discriminate voicing on the basis of temporal envelope cues[END_REF] studied the ability of French-learning 6-month-olds to discriminate a /apa/-/aba/ voicing contrast when the relatively slow (< 64 Hz) AM cues were preserved within 16 frequency bands using a tone-excited vocoder. Such a tone-excited vocoder degrades the fine spectro-temporal modulations by reducing the spectral resolution (i.e., only 16 frequency bands are used) and by replacing the FM cues by pure tones in each frequency band. As in [START_REF] Bertoncini | Discrimination of speech sounds based upon temporal envelope versus fine structure cues in 5-to 7-year-old children[END_REF], the speech AM cues were low-pass filtered at 64 Hz, attenuating the fast periodic AM cues related to formant transitions, bursts and periodic fluctuations produced by the vocal folds at the fundamental frequency (F0) rate (see [START_REF] Rosen | Temporal information in speech: acoustic, auditory and linguistic aspects[END_REF]. A head-turn preference procedure was used to assess preference for sequences composed of alternated versus repeated /apa/ and /aba/ stimuli. The head-turn preference procedure consists in the presentation of sound sequences while infants look at a blinking light on their right or left side. The results showed that infants listened longer to the alternating vocoded stimuli, providing evidence that fast AM cues (>64 Hz) and fine spectro-temporal modulations (FM cues and fine spectral cues) are not required to discriminate voicing by the age of 6 months.

Recently, [START_REF] Cabrera | Perception of Speech Modulation Cues by 6-Month-Old Infants[END_REF] showed that infants are able to discriminate the voicing contrast even when speech signals contain only the slowest (< 16 Hz) AM cues in 32 frequency bands and when AM cues are preserved within 4 broad frequency bands. Thus, fast AM cues, FM cues and fine spectral cues are not required for voicing discrimination at this early age. Interestingly, the results suggested that the vocoded-speech conditions required extra processing effort compared to the condition where speech was unprocessed. Indeed, the head-turn procedure used in this study included a familiarization phase of one or two minutes to a given phonetic category processed using a specific vocoder. Then, the infants' looking time for the blinking lights was recorded during 8 trials: 4 trials presenting a "novel" phonetic category, and 4 trials presenting the familiar one processed with the same vocoder as used in the familiarization phase. Results showed that familiarization time had to be increased by a factor 2 for infants to discriminate the vocoded-speech contrast (1 versus 2 min). In addition, in the different vocoder conditions, discrimination (at the group level) was revealed either by a classical preference for novelty (when AM and FM cues were intact), or by a preference for the familiar stimuli (when FM and AM cues were both reduced).

The present study aimed to investigate further the importance of spectro-temporal modulation cues in phonetic discrimination at 6 months and the impact of exposure time to the impoverished speech sounds. Previous work on infants was restricted to the perception of voicing, which is known to be robust for normal-hearing adults in the sense that it is resistant to the effect of filtering and masking noise (e.g., [START_REF] Miller | An analysis of perceptual confusions among some English consonants[END_REF]. The present study attempted to extend this investigation to another phonetic feature, that is, place of articulation, a feature known to be more susceptible to signal distortions such as those produced by filtering, noise or vocoding (e.g., [START_REF] Gilbert | The ability of listeners to use recovered envelope cues from speech fine structure[END_REF][START_REF] Gnansia | Effect of masker modulation depth on speech masking release[END_REF][START_REF] Gnansia | Effects of spectral smearing and temporal fine structure degradation on speech masking release[END_REF][START_REF] Miller | An analysis of perceptual confusions among some English consonants[END_REF][START_REF] Shannon | Speech recognition with primarily temporal cues[END_REF]. In his seminal review, [START_REF] Rosen | Temporal information in speech: acoustic, auditory and linguistic aspects[END_REF] suggested that the perception of voicing is conveyed by both temporal-envelope, periodicity and temporal fine structure cues (that is, slow AM, fast AM and FM features, respectively), whereas the perception of place is more dependent on fine spectro-temporal cues (that is, fine spectral and FM features). The present study therefore tested whether infants show this pattern of dependency on AM, FM and fine spectral cues when discriminating voicing and place.

To address this issue, four tone-excited vocoders 2 were designed to evaluate the respective role of FM cues, fast AM cues and spectral resolution (that is, fine spectral cues) in voicing and place discrimination. Thus, a total of eight independent groups of 6-month-old infants were tested in the four vocoder conditions and with the two phonetic contrasts. It was expected that discrimination of place would be more affected than discrimination of voicing in French-learning infants when target syllables were vocoded to selectively degrade fine spectral and FM cues. Instead of using the head-turn preference procedure and a preset amount of familiarization to the vocoded-speech sounds as in [START_REF] Cabrera | Perception of Speech Modulation Cues by 6-Month-Old Infants[END_REF], the current study introduced an infant-controlled habituation phase using the visual habituation procedure (see [START_REF] Colombo | Infant visual habituation[END_REF][START_REF] Werker | Three methods for testing infant speech perception[END_REF]. This procedure has mostly been used to assess speech contrast discrimination in infants. This procedure consisted in the presentation of a visual display on a screen together with sequences of repeated sounds. In each vocoder condition, several sequences of the same sound category were played during the habituation phase. When the infant's looking time for the visual display decreased and reached a criterion preset by the experimenter, the test phase started. The habituation criterion corresponded to the most commonly used one in the literature: it was equal to a looking-time decrement of 50 % averaging on 3 consecutive trials and compared to the 3 highest trials. In the test trials, sequences of familiar versus novel sounds were presented to measure the infants' discrimination abilities (i.e., longer looking times for a given sound category). In the present study, the absence of longer looking times for novel sound sequences in the test phase was used to reveal that 6-month-old infants have difficulty in discriminating the vocoded speech stimuli. Moreover, the amount of habituation time required by infants to switch to the test phase was also used to evaluate processing difficulty. [START_REF] Hunter | A multifactor model of infant preferences for novel and familiar stimuli[END_REF] suggested that habituation times required to lead to a novelty preference in infants reflect the interaction between several factors such as stimuli complexity and processing difficulty. Vocoded-speech signals are reduced (that is, less complex) versions of the original speech signals. For this reason, it could be expected that infants would require a shorter habituation time for the most impoverished speech sounds. This is the case: i) when both FM and fast AM cues are reduced (the "32-band AM<16Hz" condition described below), and ii) when both FM and fine spectral cues are reduced (the "8-band AM" condition described below). However, if infants take longer to reach the habituation criterion for one among the two conditions mentioned above, this would reveal that fast AM cues and fine spectral cues do not have equivalent effects on speech processing, and that one among these two spectro-temporal modulation components of the speech signal has greater importance for efficient processing of phonetic cues.

II. METHOD

A. Participants

Six-month-old infants were recruited from the university database of birth announcements in Paris, France. All families were informed about the goals of the current study and provided a written consent before their participation in accordance with the current French ethical requirements. Data from 160 infants from French-speaking families (20 infants x 2 phonetic contrasts x 4 vocoder conditions) were analyzed in this experiment (87 girls; age range: 5 months 27 days -7 months 17 days; mean = 6 months and 12 days; standard deviation (SD) = 10 days). All infants had normal hearing (based on parental report of newborn hearing screening results). The data from 155 additional infants were not included for the following reasons: fussing and crying (n=116), looking time shorter than 1000 ms for one trial (in habituation and test phase, n=12), failure to reach the habituation criteria (n=27, see section D). In the conditions corresponding to the most degraded speech sounds (i.e, when degrading FM cues, fast AM cues and fine spectral cues, see section B), the attrition rate was higher (~50%) compared to conditions corresponding to the "intact" speech sounds (32-band AM+FM; ~40% attrition rate). Although high attrition rates (~40%) are usually observed with the habituation criterion used in the present study (see [START_REF] Narayan | The interaction between acoustic salience and language experience in developmental speech perception: Evidence from nasal place discrimination[END_REF], the high attrition rate found here may be mostly related to fussiness and inherent to the vocodedspeech signals as such (i.e., unfamiliar and distorted speech sounds).

B. Stimuli

Eight exemplars of each category /aba/, /apa/ and /ada/ were selected from a set of vowelconsonant-vowel (VCV) nonsense bisyllables produced by a French female speaker who was asked to speak clearly. The F0 was estimated at 242 Hz using the YIN algorithm (de [START_REF] De Cheveigné | YIN, a fundamental frequency estimator for speech and music[END_REF]. The stimuli were recorded in a soundproof room, and digitized via a 16-bit analog-to-digital converter at a 44.1-kHz sampling rate. The stimuli were not significantly different in duration (mean=634 ms, SD=68.8 ms) for /aba/, mean=632 ms, SD=47.5 ms for /apa/, and mean=622 ms, SD=68.4 ms for /ada/). For each phonetic category, four different sequences were created. Each sequence was composed of four tokens of the same phonetic category, repeated four times in a different random order. Two sequences were used for the habituation phase and two sequences were used for the test phase. The tokens used in the test phase for each category were different from the ones used in the habituation phase. The inter-stimulus interval varied randomly in the 16-item sequences, between 600 and 1300 ms. This variation was introduced to make small variations in duration between items irrelevant within and between categories. All the sequences had the same duration (26 s).

The stimuli were processed by vocoders to alter their spectro-temporal modulations.

Four different vocoder conditions were designed. In the first condition (called "32-band AM+FM speech" or "intact" condition), the original speech signal was passed through a bank of 32 2 nd -order gammatone filters [START_REF] Gnansia | Effects of spectral smearing and temporal fine structure degradation on speech masking release[END_REF][START_REF] Patterson | A pulse ribbon model of monaural phase perception[END_REF], each 1-ERB wide with center frequencies (CFs) uniformly spaced along an ERB scale ranging from 80 to 8,020 Hz. The Hilbert transform was then applied to each bandpass filtered speech signal to compute the AM component and FM carrier. The AM component was low-pass filtered using a zero-phase Butterworth filter (36 dB/octave rolloff) with a cutoff frequency set to ERB N /2. The final narrow-band speech signal was obtained by multiplying each sample of the FM carrier by the filtered AM function. The narrow-band speech signals were finally added up and the level of the wideband speech signal was adjusted to have the same root-mean-square value as the input signal. Thus, the vocoded speech signals retained the original AM and FM speech cues within each of the 32 analysis frequency bands.

In the second condition (called "32-band AM speech"), the same signal processing scheme was used, except that the FM carrier was replaced by a sine wave carrier with frequency at the CF of the gammatone filter, and with random starting phase in each analysis frequency band. Thus, the resulting vocoded speech signal retained AM speech cues within 32 bands, but discarded the original (within-channel) FM speech cues.

In the third condition (called "32-band AM<16Hz speech"), the same signal processing scheme was used as in the "32-band AM speech" condition, except that the AM component was low-pass filtered with a cutoff frequency of 16 Hz for each of the 32 bands in order to remove the fast AM cues. Thus, the resulting vocoded speech signal retained mainly the slowest (< 16 Hz) AM speech cues within 32 bands, and discarded the original FM speech cues.

In the last condition (called "8-band AM speech"), the same signal processing scheme was used as in the "32-band AM speech" condition, except that AM cues were extracted and preserved from only 8 broad (4-ERB N wide) frequency bands. Thus, the original FM speech cues were discarded, and AM cues were distorted substantially compared to the original AM speech cues. It is important to note that this kind of vocoder reducing both the original FM cues (i.e., by replacing them by a noise or tone carrier) and spectral auditory resolution simulates the sound processing achieved by current cochlear implant (CI) sound processors (e.g., [START_REF] Friesen | Speech recognition in noise as a function of the number of spectral channels: comparison of acoustic hearing and cochlear implants[END_REF][START_REF] Shannon | Speech recognition with primarily temporal cues[END_REF][START_REF] Fu | Noise susceptibility of cochlear implant users: the role of spectral resolution and smearing[END_REF].

Figure 1 shows the spectrograms of one exemplar of /aba/ stimuli in each experimental condition.

-Figure 1 about here-

C. Material and Apparatus

Infants were seated on their caregiver's lap in a sound-attenuated room. The caregiver was instructed not to speak and not to point at the screen and wore headphones delivering masking music. Infants faced a 61-cm LCD television screen positioned approximately 1.5 m from the infant. The audio stimuli were presented through two Fostex loudspeakers located on each side of the screen playing the auditory stimuli at a level of approximately 70 dB SPL. A black and white checkerboard was presented on the screen during habituation and test trials.

At the beginning of each trial, a silent flashing ball video was played to attract the infants'attention to the screen. The infant's looking time was monitored online via a video camera positioned 30 cm below the screen and linked to the observer's monitor in the adjacent room. The observer, blind to the audio file presented, recorded the duration of the infant's looking time by a key press and controlled stimuli presentation using Habit X.10 [START_REF] Cohen | Habit 2000: A new program for testing infant perception and cognition[END_REF].

D. Procedure

A visual habituation method was used [START_REF] Mattock | The developmental course of lexical tone perception in the first year of life[END_REF][START_REF] Werker | Three methods for testing infant speech perception[END_REF] in which sound sequences were presented contingently with the infants' look at the black and white checkerboard displayed on a screen.

Auditory and visual presentations continued until the infant looked away for 2 s (automatically calculated by the computer based on the experimenter's key press) or at the end of the sound sequence (maximum 26 s). At the end of the sequence, the checkerboard disappeared and a more attractive display appeared in order to draw the infant's attention to the TV monitor. Once the infant looked at the screen, the experimenter initiated the next sequence. In each vocoder condition, the experiment began with a habituation phase, during which infants heard several sequences of the same sound category. The habituation phase ended when the mean looking time on three consecutive sequences decreased by 50% compared to the longest three consecutive trials from a sliding window. Infants were excluded a posteriori in the analysis only if they habituated with less 50s-cumulated looking time and showed extreme cumulated looking times (more than the group mean cumulated looking time + 2 SD in each condition). The test phase followed immediately. During the test phase infants heard 4 novel (N) and 4 familiar (F) sequences in alternation with order counterbalanced across subjects. Infants who did not reach the end of the test phase because of fussiness were excluded from the analyses.

Four independent groups (n=20) were tested for the voicing contrast (one group per vocoder condition): half of the subjects were habituated with /aba/ stimuli, and the other half with /apa/. Four independent groups (n=20) were tested for the place of articulation contrast (one group per vocoder condition): half of the subjects were habituated with /aba/ stimuli, and the other half with /ada/.

The total looking time to reach habituation criterion and the mean looking times in the test phase for the 4 novel and the 4 familiar test trials were recorded and analyzed in each condition.

III. RESULTS

Discrimination data

Figure 2 shows the mean looking time in the 8 groups of infants (2 phonetic contrasts x 4 vocoder conditions) for both novel and familiar sequences. In all groups, infants showed longer looking times for the novel sequences during the test phase. The discrimination was assessed by comparing the looking times for novel and familiar sequences in the test phase and the effect of Vocoder condition and Phonetic contrast. A 4 (Vocoder conditions: "32-band AM+FM", "32-band AM; "32-band AM<16Hz"; "8-band AM") x 2 (Phonetic contrasts: place versus voicing) X 2 (Sequence type: familiar versus novel) repeated-measure analysis of variance (ANOVA) of looking time was run, with Sequence type as a within-subject factor. This analysis revealed a main effect of Sequence type [mean novel=7.5 s, SD=0.81 s versus mean familiar=6.1 s, SD=0.91 s; F(1,152)=40.11, p<.001, η 2 = 0.21]. There was no effect of Vocoder condition [F(1,152)=2.01, p=.12] or Contrast [F(1,152)=1.67, p=.20], and no significant interaction between factors. The same results have been observed when the analyses were restricted to the first novel and familiar trials or the first 2 novel and familiar trials. Thus, 6-month-olds discriminated voicing and place contrasts regardless of the vocoder condition.

-Figure 2 about here-

Habituation data

Figure 3 shows the mean looking times for the first five habituation trials in each condition collapsed across speech stimuli. The number of habituation trials needed to reach criterion (Figure 4A) and the mean looking times across habituation (Figure 4B) were calculated for each condition collapsed across speech stimuli. Infants required a higher number of habituation trials in the "32-band AM<16Hz speech" condition compared to the other conditions. Moreover, the habituation time was longer in this "32-band AM<16Hz speech" condition [mean=133.9 s; SD=57.4 s] compared to the "8-band AM speech" [mean=108.3 s; SD=47 s] and the "32-band AM speech" [mean=101.6 s; SD=41.8 s] conditions. The habituation time in the "32-band AM+FM speech" condition [mean=96.1 s; SD=44 s] was shorter than that in the other three conditions.

-Figure 3 The same results were observed on the mean cumulated habituation times. A 4 (Vocoder conditions) x 3 (Stimuli:/aba/, /apa/ or /ada/) factorial ANOVA on the mean cumulated habituation times revealed only a main effect of Vocoder condition [F(3,148) = 4.2, p=.007; η 2 = .08]. Post-hoc Tukey tests indicated that habituation times were significantly longer in the "32-band AM<16Hz speech" condition compared to the "32-band AM+FM speech" and "32-band AM speech" conditions. The remaining comparisons were not statistically significant. The analysis also showed no significant effect of Stimuli [F(2;148)=2.46, p=.09] and no significant interaction between Vocoder condition and Stimuli [F(6,148)=1.54, p=.17].

Thus, the analyses of the habituation data reveal that infants require more habituation trials and a higher habituation time to the stimuli (/aba/, /ada/ and /apa) in the "32-band AM<16Hz speech" condition.

IV. DISCUSSION

The present study assessed the ability of French-learning 6-month-old normal-hearing infants to discriminate spectro-temporally degraded speech signals. This study replicated and extended previous results obtained by [START_REF] Bertoncini | Six-month-old infants discriminate voicing on the basis of temporal envelope cues[END_REF] and [START_REF] Cabrera | Perception of Speech Modulation Cues by 6-Month-Old Infants[END_REF] for 6month-old infants learning French.

Discrimination data

The present results showed that 6-month-old infants discriminated the degraded speech signals in all processing conditions. This was manifested by a clear-cut novelty preference. Infants did not require FM, fast (> 16 Hz) AM, or fine spectral speech cues to perceive variations in voicing and place of articulation. Altogether, these results indicate that as early as 6-months, the slowest AM cues extracted from a limited number of broad frequency bands are sufficient to discriminate these two phonetic contrasts. In adults, voicing perception is robust to such degradations (e.g., [START_REF] Gilbert | The ability of listeners to use recovered envelope cues from speech fine structure[END_REF][START_REF] Gnansia | Effect of masker modulation depth on speech masking release[END_REF]2009;[START_REF] Miller | An analysis of perceptual confusions among some English consonants[END_REF][START_REF] Shannon | Speech recognition with primarily temporal cues[END_REF] however, for place of articulation, the spectral details and FM cues [START_REF] Başkent | Speech recognition in normal hearing and sensorineural hearing loss as a function of the number of spectral channels[END_REF][START_REF] Shannon | Speech recognition with primarily temporal cues[END_REF] were found to influence identification responses. Our results indicate that the discrimination of place of articulation-at least the difference between French plosives /b/-/d/-remains possible even with reduced FM cues at 6 months of age. However, it is important note that adults were tested using an identification task, whereas infants were tested using a discrimination task. It is possible that robust speech identification requires greater redundancy (and thus, finer spectral and temporal details) than discrimination. Furthermore, it is possible that the visual habituation procedure used here is not sensitive enough to reveal a difference in the discrimination abilities of infants for voicing and place.

Habituation data

Still, differences appeared in the number of habituation trials and habituation-time data across vocoder conditions. It was initially expected that infants would require a shorter habituation time to the most impoverished (that is, less complex) speech stimuli. In the present experimental design, the most impoverished conditions corresponded to the two following forms of speech processing: i) the "32-band AM<16Hz" condition where FM and fast AM cues were degraded, and ii) the "8-band AM" condition where the FM and fine spectral cues were degraded. Results showed that infants took longer to reach the habituation criterion for the "32-band AM<16Hz" speech condition compared to the "32-band AM+FM" and "32-band AM" speech conditions. The longer habituation time observed for this speech condition not only shows that infants are sensitive to the fast AM cues ordinarily present in speech signals; it also reveals a specific difficulty when processing temporally-smearedspeech sounds, and indicates that fine temporal resolution (fast AM cues) has greater importance than fine spectral resolution (fine spectral details) for efficient processing of phonetic cues in infants. This is consistent with the study of [START_REF] Cabrera | Perception of Speech Modulation Cues by 6-Month-Old Infants[END_REF] showing that with two minutes of familiarization, 6-month-olds exhibited a longer looking time for familiar sounds rather than novel sounds when the speech signals contained only the slowest AM cues.

According to the conceptual framework proposed by [START_REF] Hunter | A multifactor model of infant preferences for novel and familiar stimuli[END_REF][START_REF] Hunter | A multifactor model of infant preferences for novel and familiar stimuli[END_REF][START_REF] Holt | Enhancing Speech Discrimination Through Stimulus Repetition[END_REF], these results suggest that the attenuation of fast AM speech cues increases the processing time required to adequately represent phonetic cues. Thus, the longer habituation required for temporally-smeared speech signals indicates that the fast AM cues corresponding to bursts, formant transitions and periodic F0-related fluctuations may indeed play some role in the accurate/efficient phonetic processing.

The reasons for a greater role of fine temporal cues-that is fast AM cues-in phonetic discrimination for infants are unclear. However, this result is consistent with previous studies emphasizing the role of prosodic cues related to voice-pitch (F0) in infants' speech perception and language learning (e.g., [START_REF] Kemler Nelson | How the prosodic cues in motherese might assist language learning[END_REF][START_REF] Mehler | A precursor of language acquisition in young infants[END_REF]. Previous investigations of auditory development indicate that auditory temporal resolution is mature by 6 months of age (e.g., [START_REF] Levi | Amplitude modulation detection in infancy: Update on 3-month-olds[END_REF]. It is thus unlikely that the greater role of fast AM cues reflects a specific limitation in the sensory encoding of the slow or fast AM components of speech sounds for infants. It is conceivable that greater experience with the native language-and thus, with the acoustic cues related to syllabic ratemay gradually improve the ability to make efficient use of the slow AM speech cues in phonetic perception and/or speech segmentation. Consistent with this idea, psychoacoustic studies indicate that auditory sensitivity to AM improves significantly with training for adults (e.g., [START_REF] Füllgrabe | A perceptual-learning investigation of auditory amplitude-modulation detection: Testing the existence of frequency-selective mechanisms in the temporal-envelope domain[END_REF]. This may explain why the slow AM cues are found to play the most important role in phoneme and sentence identification for adults (e.g., [START_REF] Drullman | Effect of reducing slow temporal modulations on speech reception[END_REF][START_REF] Shannon | Speech recognition with primarily temporal cues[END_REF][START_REF] Stone | Benefit of high-rate envelope cues in vocoder processing: Effect of number of channels and spectral region[END_REF]. This raises the possibility that the processing difficulty and perceptual weight of slow and fast AM speech cues may change during development. Nevertheless, it is still unclear whether fast AM rates play a role in phonetic discrimination in quiet for adults. For instance, previous work focused on identification tasks, and did not report any measure of listening effort (e.g., reaction times) in these tasks. Future studies may investigate this point further by comparing infants (of different ages) and adults' abilities to use the fast versus slow AM cues in phoneme discrimination tasks assessing both accuracy and listening effort.

Further work is required to investigate directly the mutual dependence between spectro-temporal auditory processes on one hand and speech processes on the other hand at an early age of development. The progressive maturation of the auditory system should affect the development of speech perception knowing that, at least for adults, resolving fine spectral and temporal details in speech sounds is indispensable to speech perception (especially, in adverse listening conditions). Despite this, infants demonstrate exquisite abilities to perceive speech sounds and learn the properties of their native language by exposure and social interactions during their first six to twelve months of life [START_REF] Kuhl | Early language acquisition: cracking the speech code[END_REF]. Fine manipulations of the speech signal are now possible using psychoacoustic tools and will participate to reveal the contribution of low-level auditory mechanisms to speech perception during early development.

Clinical implications

In the present experiment, the vocoder extracting AM cues from a small number of frequency bands (8 broad bands) simulates speech processing in CI devices [START_REF] Friesen | Speech recognition in noise as a function of the number of spectral channels: comparison of acoustic hearing and cochlear implants[END_REF][START_REF] Fu | Noise susceptibility of cochlear implant users: the role of spectral resolution and smearing[END_REF]; see also [START_REF] Strydom | The performance of different synthesis signals in acoustic models of cochlear implants[END_REF]. Our results indicated that at 6 months, normal-hearing infants are able to use the highly impoverished speech information transmitted by CI processors to discriminate phonetic contrasts such as voicing or place when the language is syllable-timed (e.g., French). The present results therefore suggest that CI devices deliver sufficient information to the (typical) central auditory system in development for phonetic discrimination in quiet. Consistent with these results, relatively good syllable identification capacities are reported in French children wearing CIs (e.g., [START_REF] Bouton | Reading and reading-related skills in children using cochlear implants: prospects for the influence of cued speech[END_REF][START_REF] Bouton | Perception of speech features by French-speaking children with cochlear implants[END_REF]. However, these studies showed that place of articulation was more difficult to identify than voicing, in contrast with the present study showing no difference between voicing or place discrimination responses in the vocoder condition simulating CI processing. This discrepancy may point to an important limitation in the use of vocoders to simulate CI hearing. Alternatively, the behavioral method used in the present study may fail to demonstrate graded discrimination responses between voicing and place features. Nevertheless, vocoder studies simulating speech perception under CI conditions in normal-hearing infants should help to improve some aspects of early rehabilitation in deaf infants and may help to identify major difficulties in speech discrimination with the current CI processors.

V. CONCLUSION

The current study investigated the role of speech modulation cues in phonetic discrimination for young normal-hearing infants. The results showed that the discrimination of voicing and place of articulation is possible in the absence of FM and fast (> 16 Hz) AM cues when the spectral detail in speech signals is preserved and when spectral information is severely reduced to 8 broad frequency bands.

These results demonstrate that the slowest AM cues are sufficient for phonetic discrimination in infants. However, when the fast AM cues were attenuated, infants required a longer time to habituate to the degraded stimuli, suggesting that fast AM cues may contribute to efficient phonetic processing in infants.

Christian Lorenzi was supported by grants from investissements d'avenir / ANR: ANR-10-LABX-0087 IEC and ANR-10-IDEX-0001-02 PSL*. Josiane Bertoncini was supported by ANR-12-ISH2-0001-01. The authors would like to thank the parents and their kids for their participation. The authors also thank Lynne Werner for detailed comments on this article.

FOOTNOTES

1. "Fine spectral cues" refer to the spectral cues conveyed by stimuli processed by a vocoder using a high spectral resolution (32 analysis bands, that is a spectral resolution mimicking that of the normal human ear; e.g., [START_REF] Glasberg | Derivation of auditory filter shapes from notchednoise data[END_REF]1990). Consequently, a vocoder using a much poorer spectral resolution (e.g., a 8-band vocoder) reduces the fine spectral cues.

2. In the present study, tone-excited vocoders were used instead of noise-excited vocoders [START_REF] Cabrera | Perception of Speech Modulation Cues by 6-Month-Old Infants[END_REF][START_REF] Eisenberg | Speech recognition with reduced spectral cues as a function of age[END_REF][START_REF] Newman | Toddlers' recognition of noise-vocoded speech[END_REF][START_REF] Shannon | Speech recognition with primarily temporal cues[END_REF] because they were found to distort speech AM cues less. [START_REF] Kates | Spectro-temporal envelope changes caused by temporal fine structure modification[END_REF] compared the effect of five different procedures used to preserve AM cues and replace the original FM cues.

This study showed that for each processing scheme (e.g., tone-and noise-excited vocoders), the original AM cues are substantially distorted; however, the most accurate (i.e., less distortive) processing is performed by the tone vocoder. This is due to the fact that noise carrier convey intrinsic random fluctuations in amplitude, that interfere with the auditory processing of the target speech AM cues (see also [START_REF] Dau | Modeling auditory processing of amplitude modulation. II. Spectral and temporal integration[END_REF][START_REF] Stone | Notionally steady background noise acts primarily as a modulation masker of speech[END_REF].

  about here--Figure4about here-A 4 (Vocoder conditions) x 3 (Stimuli:/aba/, /apa/ or /ada/) factorial ANOVA was conducted on the number of habituation trials. A main effect of Vocoder condition was observed [F(3;148) = 3.86; p=0.012; η 2 = .07]. Post-hoc Tukey tests revealed that the "32band AM<16Hz speech" condition led to a higher number of habituation trials compared to the "32-band AM+FM speech" and "32-band AM speech" conditions. No significant effect of Stimuli [F(2;148) = 1.46; p=.24] or interaction [F(6,148) = 0.71; p=.64] were observed.

FiguresFigure

  Figures

  Figure 1. Spectrograms of /aba/ stimuli in each speech-processing condition. Upper left

Figure 2 .

 2 Figure 2. Mean looking times (s) for familiar and novel stimuli during the test phase, for

Figure 3 .

 3 Figure 3. Mean looking time (s) in the four vocoder conditions collapsed across contrast

ACKNOWLEDGMENTS


Laurianne Cabrera
email: laurianne.cabrera@parisdescartes.fr

Ranka Bijeljac-Babic

Josiane Bertoncini

The development of consonant and lexical-tone discrimination between 3 and 6 years: effect of language exposure

Keywords: lexical tones, consonants, childhood, bilinguals, discrimination

Aims and Objectives. The present study explored children's discrimination capacities for lexical tones and consonants between 3 and 6 years of age and the effect of native language on this ability. Recent studies in infants have shown a perceptual rebound for non-native listeners during the second year of life, but only for lexical tones. However, the later stages of development, and particularly when children start preschool, are yet not clear.

Design. Discrimination abilities of 134 children were measured in three age groups between 3 and 6 years using a behavioral task where children detected a change in lexical tones or consonants. Children were either French monolinguals, French bilinguals exposed to an Asian tone language, or French bilinguals exposed to a second non-tone language at home. Data and Analysis. Overall, results indicated that higher detection scores for consonants were observed from 4-5 years, while for lexical tones the highest scores were observed only at 5-6 years. Moreover, bilingual children exposed to an Asian tone language had higher scores for tones compared to monolingual French children. Interestingly, both bilingual groups, whether exposed to an Asian tone language or to a non-tone language, had better scores for tones than for French consonants, while monolinguals performed equally with both.

Conclusions. Language exposure from an early age influences phonological development and bilingualism seems to enhance the perception of prosodic information.

Originality. This study is the first to show a different developmental trajectory for consonant and lexical-tone discrimination between 3 and 6 years according to the native language.

Significance. Similar detection scores for tones and consonants for monolingual French children, and better detection for tones than for consonants for both groups of bilinguals suggest that the perception of lexical tone is determined by both language-specific influences and non-linguistic/auditory processing during childhood.

INTRODUCTION

Understanding the influence of language exposure on phonological development is of fundamental importance in comprehending the mechanisms involved in speech perception and language acquisition. In our multilingual world, more than 50% of children are exposed to several languages [START_REF] Grosjean | Bilingual: Life and reality[END_REF]. These children must, among other things, learn several different phonological repertoires. We know that with exposure to a language, children become better at discriminating the speech contrasts of this language, but they do not show the same improvement for non-native speech contrasts. However, bilingual children exposed to both a tone and a non-tone language must learn that pitch contrasts play different functions in each of their languages. The purpose of the current study was to investigate how phonological development is influenced by exposure to one, or several languages, focusing particularly on tone language. Lexical tone is both a segmental feature, in its linguistic function, and a suprasegmental, or prosodic, feature, by nature (see [START_REF] Burnham | The perception of tones and phones[END_REF]. The two primary acoustic cues differentiating tones are variations in the fundamental frequency level (F0; high, middle, low), and F0 contour variations (steady, rising, falling; e.g., [START_REF] Gandour | Perceptual dimensions of tone: Evidence from Cantonese[END_REF][START_REF] Gandour | Crosslanguage differences in tone perception: A multidimensional scaling investigation[END_REF][START_REF] Khouw | Perceptual correlates of Cantonese tones[END_REF][START_REF] Vance | An experimental investigation of tone and intonation in Cantonese[END_REF]. Being both a segmental and a suprasegmental feature, the status of lexical tone in speech perception, and its functional similarity with consonants, is still an open question (see [START_REF] Burnham | The perception of tones and phones[END_REF]. The current experiment aimed to compare the perceptual development of tones and consonants between 3 and 6 years of age to help to understand the influence of the native language or languages, on phonological development.

The perception of consonants and lexical tones in infancy has been extensively explored. During the first year of life, infants begin to tune in to the speech contrasts present in their native language. The perception of consonants in a native-like fashion has been demonstrated after 8 months of age (e.g., [START_REF] Kuhl | Linguistic experience alters phonetic perception in infants by 6 months of age[END_REF][START_REF] Kuhl | Infants show a facilitation effect for native language phonetic perception between 6 and 12 months[END_REF][START_REF] Polka | Developmental changes in perception of nonnative vowel contrasts[END_REF][START_REF] Werker | Cross-language speech perception: Evidence for perceptual reorganization during the first year of life[END_REF]. For lexical tones, the same pattern has been observed at around the same age. Infants from a non-tone language background show a perceptual decline for non-native tones between 6 and 9 months, while infants from a tone language background do not show any decline for the same tone contrasts at the same age [START_REF] Cabrera | The perception of speech modulation cues in lexical tones is guided by early languagespecific experience[END_REF][START_REF] Mattock | Chinese and English infants' tone perception: Evidence for perceptual reorganization[END_REF][START_REF] Mattock | The developmental course of lexical tone perception in the first year of life[END_REF][START_REF] Yeung | When does native language input affect phonetic perception? The precocious case of lexical tone[END_REF]. However, a perceptual rebound for lexical-tone perception has recently been observed in the second year of life for non-native infants [START_REF] Liu | Perception of tones by infants learning a non-tone language[END_REF]. Dutch infants of 17-18 months have been shown to be able to discriminate a non-native lexical-tone contrast, suggesting that lexical-tone perception is plastic and probably driven by non-speech processing of pitch information. Such a rebound effect has not been observed for consonants (e.g., [START_REF] Werker | Developmental changes across childhood in the perception of non-native speech sounds[END_REF]). Thus, it appears that the perception of consonants and lexical tones may not follow the same developmental trajectory during early development.

Few studies have compared performance of native and non-native children in discriminating consonants and lexical tones during later stages of development. However, the preschool period, between 3 and 6 years, is critical for speech development. At this age, children have received a considerable exposure to their native language, have developed a lexicon, and start to learn to read and write, which probably also affects phonological processing [START_REF] Bertelson | Metaphonological abilities of adult illiterates: New evidence of heterogeneity[END_REF]. Little is known about this developmental period and previous studies have shown that 4-yearold English children seem to be less sensitive to non-native lexical tone variations than Thai children [START_REF] Burnham | The role of linguistic experience in the perception of Thai tones[END_REF]. At the neural level, the mechanisms involved in consonant and lexical tone detection seem to be different in preschool Mandarin children. The morphology and latency of the neural responses to a change in Mandarin consonants and lexical tones are different, probably due to the specific acoustic characteristics of these features. Moreover, these mechanisms are still developing in preschool and school-aged children [START_REF] Liu | Developmental changes in mismatch responses to Mandarin consonants and lexical tones from early to middle childhood[END_REF] . Indeed, for lexical processing in children, [START_REF] Burnham | Are tones phones?[END_REF] showed that phonological awareness develops earlier than tonological awareness. In this study, children aged 4 to 11 years and adults were asked to detect an odd word among three, in which the word either differed in vowel or tone. Results showed that performance was better for changes on the vowel than tone, suggesting that tones are not taken into account during the early stages of auditory lexical access. Moreover, tonological awareness was superior in listeners exposed to a tone language than those using a non-tone language. Thus, the perception of consonants and lexical tones may also not follow the same trajectory in later stages of speech development. It is important to note though, that adult speakers using non-tone languages are also able to discriminate lexical tones, but do not rely on the same acoustic information compared to tone-language adult speakers (e.g., [START_REF] Bent | The influence of linguistic experience on the cognitive processing of pitch in speech and nonspeech sounds[END_REF][START_REF] Cabrera | The role of spectro-temporal fine structure cues in lexical-tone discrimination for French and Mandarin listeners[END_REF][START_REF] Hallé | Identification and discrimination of Mandarin Chinese tones by Mandarin Chinese vs. French listeners[END_REF]. The difference in perception of lexical tones and consonants during development may therefore be related to the nature of the perceptual mechanisms involved, as the perception of lexical tones seems to be determined by both language-specific influences and non-linguistic processing of pitch information.

The present study further explored the ability of children aged between 3 and 6 years to discriminate lexical tones and consonants, as the effect of age and language exposure on phonological development is not yet fully understood. It is also worth noting that at this age children entering pre-school, starting at 3 years in France, who are not exposed to French at home, may start a more formal learning of this language.

This study also aimed to investigate the effect of exposure to one, or more languages, including exposure to a tone language, on the perception of consonants and lexical tones. Previous studies with infants have shown that bilingual infants not previously exposed to a tone language exhibit perceptual rebound for lexical tones earlier than their monolingual peers, at 11-12 months [START_REF] Liu | Perception of tones by bilingual infants learning non-tone languages[END_REF]. Thus, being exposed to various languages, even ones which do not use lexical tone, seems to improve the perception of tones. Similar results have also been observed in a word learning task for bilingual English-Mandarin children at 17 months who were more sensitive to a Thai non-native lexical tone contrast than their monolingual Mandarin peers [START_REF] Burnham | Constraints on Tone Sensitivity in Novel Word Learning by Monolingual and Bilingual Infants: Tone properties are more influential than tone familiarity[END_REF]. In other studies comparing the effect of consonant, vowel and lexical-tone mispronunciation on word learning abilities, language-specific processing of lexical tone was observed only at 2 years of age [START_REF] Singh | Spoken word recognition in early childhood: comparative effects of vowel, consonant and lexical tone variation[END_REF][START_REF] Singh | Influences of vowel and tone variation on emergent word knowledge: a cross-linguistic investigation[END_REF]. At 18 months, English monolinguals, Mandarin-English bilinguals, and bilinguals exposed to English and another non-tone language were able to detect a mispronunciation on lexical tone and vowel in a word learning task. However, at 24 months, only the Mandarin-English bilinguals were able to do so for the lexical-tone mispronunciation. Similar differences in performance between monolinguals and bilinguals have also been observed for other suprasegmental features; Bilingualism in infants has been related not only to a better ability to distinguish between segmental phonemic contrasts of both languages but also between lexical-stress (e.g., [START_REF] Bijeljac-Babic | Effect of bilingualism on lexical stress pattern discrimination in French-learning infants[END_REF][START_REF] Burns | The development of phonetic representation in bilingual and monolingual infants[END_REF][START_REF] Sundara | Development of coronal stop perception: Bilingual infants keep pace with their monolingual peers[END_REF]. For instance, infants exposed to both French that does not use lexical stress pattern, and to another language using stress at the lexical level, showed better stress discrimination abilities than French monolinguals at 10 months. This difference between bilinguals and monolinguals has been observed in the context of high segmental variability, where different words show the same prosodic pattern [START_REF] Abboub | On the importance of being bilingual: Word stress processing in a context of segmental variability[END_REF]. It has been proposed that exposure to numerous languages enhances sensitivity to prosodic cues at an abstract, phonological level [START_REF] Bijeljac-Babic | Effect of bilingualism on lexical stress pattern discrimination in French-learning infants[END_REF], but see also [START_REF] Skoruppa | Language-specific stress perception by 9-month-old French and Spanish infants[END_REF]. Comparing lexical-tone and consonant perception in bilinguals and monolinguals is one way to explore how the perceptual mechanisms for segmental and suprasegmental features are shaped by language exposure. The present study assessed the perception of Thai lexical tones and French consonants in monolingual French children, bilingual children exposed to a tone language at home, and children exposed to a non-tone second language at home by using two behavioral phonetic discrimination tasks. The aim of the present study was two-fold: i) to compare how children perceive lexical tones and consonants between 3 and 6 years of age, ii) to assess the effect of exposure to a tone language on the ability to perceive these two types of phonological contrasts.

Given previous studies on phonetic discrimination in infants and word learning in toddlers, it was expected that consonant and tone discrimination would not follow the same developmental trajectory between 3 and 6 years for all children. Specifically, lexical tone changes are expected to be easier to perceive than consonantal differences as they incorporate both segmental and suprasegmental variation (e.g., [START_REF] Liu | Perception of tones by bilingual infants learning non-tone languages[END_REF]. Moreover, the children's native language background was also expected to influence the perception of consonants and lexical tones (even when bilingual children had been exposed to a different tone language). One possibility is that children exposed to a tone language at home will be better at perceiving lexical tones than French consonants in the present task. Another possibility is that children exposed to a second non-tone language will also show better perception of lexical tones compared to monolinguals as their perception of prosodic cues may be enhanced by exposure to numerous languages.

METHOD

Participants

Data from 134 children were collected from three different kindergarten schools in Paris. Three age groups, corresponding to the three classes, were tested: 3-4 years (N=35, 18 girls), 4-5 years (N=50, 21 girls), 5-6 years (N=49, 22 girls). Data from 14 additional children were excluded because they could not perform the tasks (12 children from the 3-4 year section, 1 child from the 4-5 year section, and 1 from the 5-6 year section). The study was approved by the local university ethics committee and written consent forms were obtained from the parents before the experiment.

The languages spoken by the children were evaluated through a parent questionnaire. This questionnaire aimed to identify the main languages used in the child's everyday life. Parents indicated the main two languages spoken in six situations: by each parent individually (parent 1, parent 2), by the parents when speaking to each other, by the parents when speaking to the child and siblings, by the children themselves, and overall in the house with friends and family. Based on this data, a measure of the proportion of exposure to French, an Asian tone-language (such as Mandarin, Cantonese, Vietnamese or Thai), and any other languages was then computed for each child. This questionnaire revealed that 55 children out of 134 were French monolinguals, that is, only exposed to French at home, 14 were only exposed to an Asian tone language, and 2 children were only exposed to a language that was not French or Asian tone. Among the bilingual children, 31 were exposed to an Asian tone language at home and 35 to a nontone language (3 children were exposed to both an Asian tone and another non-tone language). Figure 1 displays the proportion of these 3 language types for the 3 groups of children.

Stimuli

The stimuli were recorded in a soundproof room, and digitized via a 16-bit analog-to-digital converter at a 44.1-kHz sampling rate. Intensity of each stimulus was equalized.

Two French contrasts were used: a voicing (/aba/-/apa/) and a place of articulation (/aba/-/ada/) contrast. French voicing contrasts involve voiceless consonants, with a ~0 ms voice onset time (VOT), and pre-voiced consonants, with negative VOT values indicative of glottal action preceding the stop burst (i.e., [START_REF] Ryalls | Acoustic integrity of speech production in children with moderate and severe hearing impairment[END_REF][START_REF] Caramazza | Voice onset time in two French dialects[END_REF][START_REF] Serniclaes | Etude expérimentale de la perception du trait de voisement des occlusives du français[END_REF] . In French, stop consonants are non-aspirated, that is, there is no air burst after consonantal release prior to vocal cord vibration (e.g., [START_REF] Cho | Variation and universals in VOT: Evidence from 18 languages[END_REF]. Such phonological characteristics could be unfamiliar for children mainly exposed to Mandarin Chinese or Cantonese that use aspirated voiceless versus non-aspirated voiceless contrasts [START_REF] Zhang | Voicing and Devoicing Rules in East and Southeast Asian Languages[END_REF].

Eight exemplars of /aba/, and four exemplars of /apa/ and /ada/ were selected from a set of vowel-consonant-vowel (VCV) nonsense bisyllables produced by a French female speaker (mean F0 = 254 Hz, F0 range = 212-294 Hz) who was asked to speak clearly. The stimuli were not significantly different in duration (p > .05 for the background category versus each target category). Table 1 summarizes the VOT characteristics (time between the consonant release and voicing), duration, and pitch range of the French VCVs.

Two Thai lexical tone contrasts were also used: a contour-contour (rising tonefalling tone) and a contour-level (rising tone-low tone) contrast. Three lexical tones were recorded from a Thai female speaker (see [START_REF] Cabrera | The role of spectro-temporal fine structure cues in lexical-tone discrimination for French and Mandarin listeners[END_REF][START_REF] Mattock | Chinese and English infants' tone perception: Evidence for perceptual reorganization[END_REF]. A rising tone was contrasted in contour with a falling tone, and was also contrasted in level with a low tone (showing similar F0 trajectories until the mid-point of the tone). Even though these Thai tones are non-native for non-Thai listeners from another Asian tone language background (e.g., Mandarin or Cantonese), non-Thai infants and adult listeners are still able to discriminate them (see [START_REF] Cabrera | The perception of speech modulation cues in lexical tones is guided by early languagespecific experience[END_REF][START_REF] Mattock | Chinese and English infants' tone perception: Evidence for perceptual reorganization[END_REF].

Eight exemplars of /ba/ with a rising tone (i.e., rising F0 trajectory), four exemplars of /ba/ with a falling tone (i.e., falling F0 trajectory), and four exemplars of /ba/ with a low tone (i.e., steady F0 trajectories) were selected from a set of CV nonsense syllables produced by a female native speaker of Thai language (mean F0=207 Hz, F0 range = 100-350 Hz). The duration of the tone stimuli did not differ significantly between the 3 categories (p > .05).

Procedure

Children's ability to discriminate lexical-tone and consonant contrasts was measured using a discrimination task adapted from the Visual Reinforcement Assessment of the Perception of Speech Pattern Contrasts (VRASPAC, e.g., [START_REF] Eisenberg | Perception of phonetic contrasts in infants: Development of the VRASPAC[END_REF] procedure. This procedure combines different behavioral procedures generally used with infants (repeated auditory background) and older children (Change/No-Change procedure) to measure speech and auditory perception abilities in toddlers (e.g., [START_REF] Eisenberg | Perception of phonetic contrasts in infants: Development of the VRASPAC[END_REF][START_REF] Holt | Assessing toddlers' speech-sound discrimination[END_REF][START_REF] Martinez | Assessing speec pattern contrast perception in infants: Early results on VRASPAC[END_REF] and children before 6 years [START_REF] Bertoncini | Discrimination of speech sounds based upon temporal envelope versus fine structure cues in 5-to 7-year-old children[END_REF].

Children were tested individually in a quiet room at school. Each child sat in front of a screen displaying a colorful background picture while listening to a repeated background stimulus presented through two loudspeakers located on each side of the screen and playing sounds at around 70 dB SPL. Children were asked to press a response button as accurately and as fast as they could when (and only when) a change occurred within the continuously repeated sequence of speech stimuli. They were instructed to get ready with their hands above the response button. Each trial was launched by the experimenter, seated next to the child, when the child was judged to be ready-that is, when she/he was looking at the background picture. The experimenter was unaware of the nature of the upcoming trial, but did not wear any headphones in order not to distract the child. Each trial was composed of four exemplars of either the same category as the background stimulus ("no change" trials), or four exemplars of a different category ("change" trials). Ten change trials (5 trials for each contrasting stimuli) and the 5 no-change trials were presented in a random order within each condition (Consonant and Lexical tones). No-change trials were used to assess response bias of the listeners. The silent inter-stimulus interval varied randomly in duration between 450 and 1200 ms during the presentation of the background stimulus as well as during the presentation of both change and no change trials. Thus, no change in stimulus duration or in silent interval duration could be used to detect a change in the repeated stimuli during change trials. The child had to react to the occurrence of the contrasting stimulus within the duration of the "change" trial (that included the four exemplars of one change syllable, from the onset of the first exemplar and the offset of the last exemplar). Each trial ended either when the child made a correct response even before the end of the four exemplars or when the child did not respond within the duration of the four exemplars. Correct responses were reinforced by the presentation of one picture of a colorful character (award figure) on the screen; misses (no response given by the end of the change trial) and false alarms (responses during a no change trial) were followed by a "negative" emoticon. At the end of a trial, the repeated stimulus was restarted. Any response given under 100 ms following the onset of the change was not counted as a hit.

After a short training phase in which children had to discriminate between 2 syllables varying in phonemes and contours /ko/ and /mi/, each child completed a single test session with two conditions (Consonant and Lexical tones) that lasted around 10 mins. The order of the two conditions was counterbalanced between participants. The background stimulus in the consonant condition was the syllable /aba/, and in the lexical tone condition the syllable /ba/ with a rising tone. The change syllables in the consonant condition were either /ada/ or /apa/, and in the lexical-tone condition either /ba/ falling or /ba/ low. Response accuracy was recorded for both the change trials and the no-change trials for each contrast type (Consonants versus Tones).

RESULTS

First, an analysis of children's response accuracy for change trials and no-change trials was conducted. Children were split into 3 groups based on their repeated language exposure: i) only to French (N = 55), ii) to an Asian tone language at home (that is, any proportion of exposure above 0%; N = 45), iii) to any other non-tone language (that is, absence of exposure to any Asian tone language, N = 34). In the group of 3-4-year-old children, this gave 14 French monolinguals, 11 bilinguals and 10 who were exposed to an Asian tone language. In the group of 4-5-year-olds, 25 were French monolinguals, 12 were bilinguals and 10 had been exposed to an Asian tone language. Finally, in the group of 5-6-year-olds, 16 were French monolinguals, 11 were bilinguals and 22 were exposed to an Asian tone language.

A repeated-measures analysis of variance (ANOVA) was conducted to assess whether response accuracy varied according to the within-factor Contrast Type (Consonants versus Tones) and Trial Type (Change versus No Change), and to the between-factor Age Group (3 school year groups) and Language Group (Exposure to a Tone Language versus Exposure to a second Non-Tone Language versus Exposure to French only). This analysis revealed a main effect of Contrast Type [F(1,125) = 17.28, p < .001, η 2 = .12] indicating that overall higher accuracy was observed for tones (mean = 0.90, standard error (SE) = 0.10) than consonants (mean = 0.84, SE = 0.13). The analysis of the interactions revealed a significant interaction between Contrast Type and Language group [F(2,125) = 3.11, p = .048, η 2 = .05], Trial Type and Age group [F(2,126) = 8.45, p < .001, η 2 = .12], and a three-way interaction between Age group, Contrast Type, and Trial Type [F(2,126) = 6.66, p = .002, η 2 = .10].

Figure 2 represents the response accuracy for the Consonant and Tone conditions according to language group illustrating the interaction between Contrast Type and Language group. Post-hoc tests for this interaction indicate that children exposed to an Asian tone language show significantly higher accuracy for tones (mean = 0.92, SE = 0.18) compared to monolingual French children (mean = 0.87, SE = 0.16, p = .031). Moreover, when comparing Contrast Types, children exposed to an Asian tone language and bilingual children not exposed to any tone language, but not French monolinguals, show significantly higher accuracy for tones than for consonants (mean difference = 0.11, 0.06, 0.02, respectively, and p < .001, p = .033 and p = .40). Figure 3 displays the proportion of correct responses for Change trials and No-Change trials for Consonant and Tones according to Age group, illustrating the threeway interaction between Age group, Contrast Type, and Trial Type. Post-hoc tests showed that for Change trials (see Figure 3 left panel) in the Consonant condition, the youngest group (3-4 years) exhibited the lowest scores (mean = 0.75, SE = 0.28) compared to the other two groups (for 4-5 years: mean =0.87, SE = 0.24, p = .001; for 5-6 years: mean = 0.91, SE = 0.24, p < .001), that themselves did not differ from each other (p = .18). For Tones, the oldest group showed nearly perfect detection and had the highest scores (mean = 0.97, SE = 0.16) compared to the other two groups (for 3-4 years: mean = 0.89, SE = 0.18, p = .001; for 4-5 years: mean = 0.90, SE = 0.16, p = .002), that themselves did not differ from each other (p = 0.55). Interestingly, the youngest and oldest groups showed significantly higher scores for Tones than for Consonants (mean difference = 0.14 and 0.06, p < .001 and p = .03, respectively). Regarding No-Change trials (see Figure 3 right panel), children of 4-5 years showed significantly more false alarms (i.e., detecting the No-Change trials as Change trials and thus, showing poorer accuracy on No-Change trials) in the Consonant condition than the Tones (mean difference = 0.09, p = .018, and mean difference = 0.07, p = .055 for 5-6 years), suggesting that tones lead to fewer mistakes and thus, are somewhat easier to discriminate than consonants. Surprisingly, the youngest group (3-4 years) showed an equivalent level of false alarms for consonants and tones (p = .68).

When correcting for response bias, i.e., by subtracting the proportion of false alarms on No-Change trials from the proportion of correct detection on Change trials, a repeated-measures ANOVA showed a main effect of Contrast and a significant Contrast Type X Language group interaction leading to the same results regarding the effect of language exposure on consonant and tone detection.

This first analysis suggests that the detection of a consonant change improves between 3-4 years and 4-5 years, but continues to improve for lexical-tones until 5-6 years. Interestingly, the language spoken at home seems to influence the overall accuracy for lexical-tone detection. Children exposed to an additional language other than French are better able to discriminate lexical-tone than consonant contrasts.

A second series of analyses was then run to assess further the effect of increasing exposure to each language category and the effect of age (as a continuous factor) on the accuracy scores. Here, continuous proportions of Exposure to French, to an Asian tone language and to another non-tone language, estimated from the parent questionnaire, were used to predict accuracy in the tasks. For instance, participant #34 was age 55.57 months and exposed to 42% of French, 0% of another non-tone language, and 58% of an Asian tone language, whereas participant #104 was 42.07 months and exposed to 92% of French, 8% of another Non-Tone Language, and 0% of an Asian tone language (see Figure 1). Thus, instead of group analyses, this approach takes into account the individual characteristics of each participant to assess whether Age and/or Language exposure (estimated with 3 different proportions) could predict individual performance. Regression analyses were used to model how these four continuous factors contribute to the score variability for consonants on the one hand, and tones on the other.

When predicting the accuracy for Change trials in the Consonant condition, a stepwise regression analysis revealed that Age predicted 13.4% of the variance (p < .001). For Change trials in the Tone condition, a stepwise regression analysis revealed that Age also contributed to the model and explained 9% of the variance (p < .001). Finally, when predicting the accuracy for No-Change trials, or when correcting the scores for response bias, none of the factors selected for the stepwise regression analysis significantly contributed to the model for Consonants or Tones.

These analyses indicate that the discrimination ability of consonant and tone contrasts improves with age and did not show a linear effect of language exposure to a tone language on this ability.

DISCUSSION

This study first aimed to examine the perception of both lexical tones and consonants within the same children between 3 and 6 years of age. The results demonstrated that discrimination performance on change trials improves with age for both consonants and tones over the groups of children. As expected, different patterns of development for these two types of contrasts were revealed. Consonant change detection continues to improve until 4-5 years in the present task. This result could simply indicate that children get better at the VRASPAC detection task until 5 years. However, the pattern of improvement is slightly different for the lexical-tone contrasts, suggesting that the present results are not only related to a better understanding of the behavioral procedure with age, but also to the development of phonological processing. Indeed, overall performance continues to improve until 5-6 years of age for lexical-tone discrimination. This slower pattern of development for the detection of lexical-tone contrasts compared to consonants could be related to the slower development for tonological awareness observed in previous studies [START_REF] Burnham | Are tones phones?[END_REF], suggesting different developmental trajectories for consonants and lexical tones. Such differences have also been observed during the second year of life [START_REF] Liu | Perception of tones by infants learning a non-tone language[END_REF] further suggesting different processing for consonants and lexical tones (see [START_REF] Nazzi | The Developmental Origins of the Consonant Bias in Lexical Processing[END_REF], for a review on the pattern of development for vowels versus consonants).

When considering both the responses on Change and No-Change trials over age, even though the picture is slightly different, variations in tones seem overall easier to detect than in consonants. The youngest age group (3-4 years) showed better detection of a change in tone than in consonant and did not show any difference in their false alarm rate. One interpretation is that children's responses to lexical tone changes are mainly driven by pitch variations at the acoustic/phonetic level, while their responses to consonant changes are driven more by linguistic/phonological representations that are still developing. Moreover, in this group the number of children exposed to the different languages was fairly well balanced with 10 children exposed to an Asian tone language, 14 to French only and 11 to another second non-tone language. Thus, any difference could not have been to do with sampling. Therefore, the results suggest that tones are easier to process than consonants at 3 years of age. This pattern of response continues to develop with age. Children aged 5-6 years also show higher accuracy when detecting tone versus consonant changes. In parallel, with age, false alarm rates begin to increase for consonants, such that children make more errors with consonants than tones. This could be an indication of an increasing attentional demand for consonants and could be interpreted as indicating that lexical tones are more discriminable than consonants, requiring less specific attention.

The present study also aimed to assess whether and how the language spoken at home could influence children's discrimination of lexical tones and consonants. Previous studies suggest that according to the linguistic categories present in the child's native language, tones start to be processed on a more phonological basis with age [START_REF] Burnham | Are tones phones?[END_REF][START_REF] Burnham | The role of linguistic experience in the perception of Thai tones[END_REF]. Not surprisingly, the current results show that children exposed to a tone language at home exhibit better detection of lexical-tone contrasts than consonants. This indicates that children exposed to a tone language are better at detecting pitch variations at the syllable level, when they are similar to their native tonological repertoire, compared to French consonant contrasts that may not belong to their native repertoire. Perhaps more surprisingly, children not exposed to a tone language at home but exposed to several languages (such as Cambodian, Arabic, Wolof, English, Romanian, German or Portuguese) show the same effect. The regression analyses also suggest that the detection of lexical tones does not improve proportionally with exposure to a lexical-tone language, consistent with the fact that bilingual children not exposed to any tone language are also better at detecting lexical tones. This is in line with previous studies suggesting that exposure to various languages enhances sensitivity to prosodic cues (e.g., [START_REF] Bijeljac-Babic | Effect of bilingualism on lexical stress pattern discrimination in French-learning infants[END_REF]. Conversely, children who are exposed only to French do not show any difference in the detection of non-native lexical-tone contrasts and French consonants. This group of monolingual children also shows poorer detection of tones than children exposed to an Asian tone language. These results are in line with previous studies showing that non-native listeners are able to detect pitch variations within syllables in simple discrimination tasks (e.g., [START_REF] Cabrera | The role of spectro-temporal fine structure cues in lexical-tone discrimination for French and Mandarin listeners[END_REF] but may perform more poorly than native listeners [START_REF] Burnham | The role of linguistic experience in the perception of Thai tones[END_REF]. This could also reflect the rather particular status of tones in speech perception. Pitch variations, even though not lexically relevant, are present in all non-tone languages, as they can convey syntactic units such as propositions or utterances (e.g., in French, at least for questions), attract attention or give emotional information etc. (e.g., [START_REF] Collier | The role of intonation in speech perception[END_REF][START_REF] Nooteboom | The prosody of speech: melody and rhythm[END_REF]. However, the different pattern of results between French monolinguals and bilinguals, bilingual in either a tone/non-tone language, also suggests that not only does specific exposure to a tone language affect the responsiveness to pitch variations but also exposure to any type of language using prosodic variations at the lexical level to a greater extent than French. How a language uses acoustic information to signal lexical contrast, will likely influence the function attributed to pitch variations and influence phonological development.

Finally, the fact that monolingual French children do not improve with age at detecting a contrast type belonging to their phonological repertoire is rather surprising. Even though monolingual French children show similar detection scores for tones and consonants in the present study, they may not process these contrasts at the same level of processing (acoustic/phonetic versus linguistic/phonological). Previous studies have observed that French adults' perception of tones is mainly driven by the acoustics (physical properties) of the tones, in contrast to Mandarin listeners who are instead biased by the phonological value of tone contours [START_REF] Hallé | Identification and discrimination of Mandarin Chinese tones by Mandarin Chinese vs. French listeners[END_REF]). Thus, it is possible that in the present task, tones were easy to discriminate at a general acoustic/phonetic basis, reaching comparable levels of detection as consonants, which were themselves processed in a more phonological fashion. It remains for future research to determine whether French children improve in their detection of native consonant contrasts with age, but not with non-native lexical tone contrasts by using perceptual tasks that are better able to disentangle the role of acoustic versus phonological processing.

The present behavioral procedure also limits the conclusions that can be made regarding the discrimination of the different phonetic contrasts used in the task. Indeed, the low number of trials used for each pair of speech stimuli prevents comparison between different contrasts, such as place of articulation versus voicing, or pitch height versus pitch contour. Previous studies have shown that discrimination abilities vary according to the speech contrast used in the task (e.g., [START_REF] Cabrera | The role of spectro-temporal fine structure cues in lexical-tone discrimination for French and Mandarin listeners[END_REF][START_REF] Hallé | Identification and discrimination of Mandarin Chinese tones by Mandarin Chinese vs. French listeners[END_REF][START_REF] Narayan | The interaction between acoustic salience and language experience in developmental speech perception: Evidence from nasal place discrimination[END_REF]. The present study used the pitch contrast between falling and rising tones which is usually easier for non-tone language listeners as these pitch variations also convey communicative cues in non-tone languages. Future studies should compare performance between several contrasts to better understand how listeners organize the speech signal to develop a phonological system. Finally, even though the present results reveal an influence of exposure to a lexical-tone language or more generally to a second language, on the processing of lexical tones versus consonants, future studies should recruit more narrowly defined bilingual populations (e.g., children exposed to Mandarin or Cantonese) and consider using native lexical-tone stimuli.

To conclude, the present study provides new evidence that the perception of lexical tones and consonants follows a different developmental trajectory between 3 and 6 years. Specifically, the results suggest that overall 3 and 6 years of age, lexical tones are perceived more accurately than consonants. Instead, the perception of lexical tones seems to be determined by both language-specific influences and nonlinguistic/auditory processing during childhood. However, the results also suggest that as a result of exposure to a tone-language, pitch variations at the syllable level acquire a more specific status, such that they may be processed phonologically. Moreover, exposure to numerous languages seems to enhance the processing of prosodic cues for speech.

Figure 1 .

 1 Figure 1. Proportion of language exposure (filled circle for French, open triangle for any Asian tone language, open circle for any other non-tone language) for each child.

Figure 2 .

 2 Figure 2. Box plots of response accuracy in the Consonant (dark grey bars) and Tone (light grey bars) conditions according to the three groups of languages (Asian Tone, French and Other non-tone language). The three horizontal lines represent the 25th, 50th, and 75th percentiles, respectively, and approximately 95% of the data are expected to lie between the vertical bars. The size of the dots is proportional to the number of overlapping observations: N = 1, 5, 10 to 15.

Figure 3 .

 3 Figure 3. Box plots of response accuracy for Change trials (left panel) and for No-Change trials (right panel) in the Consonant (dark grey bars) and Tone (light grey bars) conditions according to the three age groups. The size of the dots is proportional to the number of overlapping observations: N = 1, 5, 10 to 15.

Table 1 .

 1 Table2summarizes the VOT characteristics, duration and pitch range of the Thai CVs. Characteristics of the French Vowel-Consonant-Vowel (VCV) syllables recorded from a female speaker: Voice Onset Time (VOT, in ms), Total duration (in ms) and Pitch range (in Hz). For the background category, 8 exemplars were selected and only 4 for the change category. The average fundamental frequency is 254 Hz, the first vowel is always higher in pitch than the second one.

	French VCVs	VOT (ms)	Total duration (ms)	Pitch range (Hz)
		1. -210	1. 593	1. 215.7 -292.1
		2. -253	2. 685	2. 212.6 -293
		3. -252	3. 691	3. 212.8 -286.6
	/aba/	4. -236	4. 692	4. 216.7 -291.8
	background	5. -188	5. 659	5. 221.2 -284.9
		6. -207	6. 646	6. 216.2 -288.9
		7. -191	7. 624	7. 216.8 -278
		8. -174	8. 624	8. 250 -283.1
		1. +10	1. 619	1. 234.7 -288.2
	/apa/	2. +8 3. +8	2. 690 3. 571	2. 245 -281.9 3. 235.5 -269.6
		4. +13	4. 656	4. 235.3 -278.7
		1. -212	1. 610	1. 219.6 -285.9
	/ada/	2. -210 3. -347	2. 612 3. 693	2. 220 -286 3. 213.9 -294.3
		4. -395	4. 664	4. 214.4 -292.4
	Thai CVs	VOT (ms)	Total duration (ms)	Pitch range (Hz)
		1. -13	1.	656	1. 138.3 -322
		2. -15	2.	660	2. 134.8 -340.5
		3. -17	3.	664	3. 137.7 -328.4
	/ba/ rising	4. -12	4.	642	4. 137.7 -332.9
	background	5. -17	5.	733	5. 140.9 -349.1
		6. -12	6.	636	6. 140.5 -326.6
		7. -12	7.	630	7. 144.8 -314.8
		8. -12	8.	672	8. 142.8 -321.9
		1. -14	1. 626	1. 105.4 -155.7
	/ba/ low	2. -14	2. 605	2. 98.55 -145.2
		3. -14	3. 610	3. 110 -167.9
		4. -15	4. 620	4. 105.9 -146.3
		1. -14	1. 575	1. 197.37 -280.4
	/ba/ falling	2. -7 3. -11	2. 478 3. 557	2. 223.3 -285.2 3. 100 -277.3
		4. -10	4. 496	4. 197.5 -274.8

Table 2 .

 2 Characteristics of the Thai Consonant-Vowel (CV) syllables recorded from a

female speaker: Voice Onset Time (VOT, in ms), Total duration (in ms) and Pitch range (in Hz). For the background category, 8 exemplars were selected and only 4 for the change category. The average fundamental frequency is 207 Hz.

ACKNOWLEDGMENTS

The authors wish to thank the schools in the XIIIe arr of Paris and all the children who participated in the study, as well as Bronwen Evans for help in manuscript preparation.

FUNDING

JB was supported by the Agence Nationale de la Recherche (ANR-12-ISH2-0001-01).


est destinée au dépôt

An observational study of benzodiazepine prescription during inpatient alcohol detoxification for patients with versus without chronic pretreatment with high dosage baclofen

Nicolas Simon

To cite this version:

Nicolas Simon. An observational study of benzodiazepine prescription during inpatient alcohol detoxification for patients with versus without chronic pretreatment with high dosage baclofen. Fundamental & Clinical Pharmacology, 2018, 32 (2), pp.198-199. 10.1111/fcp.12354. inserm-01968955 Alcohol reduction is currently suggested to most patients with alcohol use disorder (AUD); those who do not require acute detoxification. The treatment strategy to help patients decrease their alcohol consumption varies from country to country. In France, a wide use of baclofen is observed in this indication since the publications of Addolorato's article [1] and Ameisen's book [2]. The benefit of this approach is still a matter of debate among addiction specialists. A drug approval is under evaluation at the French national drug agency (ANSM).

E D I T O R I A L
In the meantime, there are still plenty of patients, among whom some are improved and can be considered as positive responders, but others are not. An open-study evaluating the relationship between baclofen dose, exposure and craving during the first 3 months of treatmentshowed a significant decrease in craving in 38% of patients [3]. Other studies with a randomized and double-blind design described conflicting results [4]. Meanwhile, high doses of baclofen aiming to help patients decrease their consumption are commonly and fairly successfully used and cannot be ignored.

For some patients, the story is somewhat more complicated and despite intensive baclofen use, alcohol detoxification could be required. Such clinical situations will probably arise more and more frequently, and they deserve special attention. Considering that baclofen and benzodiazepine share some side effects, a synergy cannot be ruled out. Furthermore, due to the baclofen mechanism of action, it could be hypothesized that high dosage will lead to a loss of receptor specificity and a stimulation of GABA-A receptor. In an observational clinical study, Martinez et al. [5] addressed this question and interestingly, they did not observe any significant difference between the doses of benzodiazepine required for their patients during detoxification. Despite certain limitations, such as the open and retrospective design as well as the small number of patients included, their results are of interest and worth discussing. However, there is a remaining question about the rational of maintaining baclofen if the patient does not respond. This question raises another one: if alcohol detoxification is required in a patient with insufficient response to baclofen, what should be stopped first, baclofen or alcohol? We also need to define 'failure of baclofen' by deciding to what extent an escalation should be explored? Indeed, in the world of pharmacology, there is no example of a drug active on 100% of patients. It must be admitted that some patients may not respond appropriately or exhibit adverse effects leading to baclofen reduction or withdrawal.

The article by Martinez et al.

[5] provides some information on the management of patients with AUD under baclofen treatment and requiring alcohol detoxification, but a lot remains to be known.

R E F E R E N C E S

  Imbert B., Alvarez J.C., Simon N. Anticraving effect of baclofen in alcohol-dependent patients. Alcohol. Clin. Exp. Res. (2015) 39 1602-1608. 4 Palpacuer C., Duprez R., Huneau A. et al. Pharmacologically controlled drinking in the treatment of alcohol dependence or alcohol use disorders: a systematic review with direct and network meta-analyses on nalmefene, naltrexone, acamprosate, baclofen and topiramate. Addiction (2018) 113 220-237. 5 Martinez L., Vorspan F., Decleves X. et al. An observational study of benzodiazepine prescription during inpatient alcohol detoxification for patients with versus without chronic pretreatment with high dosage baclofen. Fundam. Clin. Pharmacol. (2018) 32 200-205. https://doi.org/10.1111/fcp. 12339.

	1 Addolorato G., Caputo F., Capristo E. et al. Baclofen efficacy in
	reducing alcohol craving and intake: a preliminary double-
	blind randomized controlled study. Alcohol Alcohol. (2002) 37
	504-508.
	2 Ameisen O.. The end of my addiction, 1st edn, Farrar Straus
	Giroux, New York, NY, 2008.

ª 2018 Soci et e Franc ßaise de Pharmacologie et de Th erapeutique 198 Fundamental & Clinical Pharmacology 32 (2018) 198-199 doi: 10.1111/fcp.12354 3 ª 2018 Soci et e Franc ßaise de Pharmacologie et de Th erapeutique Fundamental & Clinical Pharmacology 32 (2018) 198-199

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