Galiñanes Plaza

J Delarue
email: julien.delarue@agroparistech.fr

L Saulais

The pursuit of ecological validity through contextual methodologies

Introduction and background

It is vastly recognized that context impacts consumers' liking and choice of food, with direct implications regarding the validity of measures of the latter obtained in a given context. This issue is key for the food industry, whose strategic choices require reliable models of consumers' liking and behavior in order to predict the commercial success of a product. Yet, the everyday practice of consumer tests appears very heterogeneous regarding the inclusion of context variables, which may contribute to the low reliability of hedonic data used in the industry.

Since [START_REF] Meiselman | Obstacles to studying real people eating real meals in real situations[END_REF] proposed to study real foods in real contexts [START_REF] Meiselman | Obstacles to studying real people eating real meals in real situations[END_REF], several studies have been conducted in natural consumption settings in an effort to improve the ecological validity of consumer data used in sensory science [START_REF] Bell | Time to eat: The relationship between the number of people eating and meal duration in three lunch settings[END_REF][START_REF] De Castro | Family and friends produce greater social facilitation of food intake than other companions[END_REF][START_REF] Hetherington | Situational effects on meal intake: A comparison of eating alone and eating with others[END_REF][START_REF] Marshall | Meal construction: exploring the relationship between eating occasion and location[END_REF]. However, the gain in realism of studies in natural contexts is obtained to the detriment of control over context variables, questioning the reproducibility and transferability of the results.

In the past decades, several approaches have been developed in order to fill the gap between laboratory and natural contexts. They encompass evoked context studies, immersive technologies or the use of virtual reality. These approaches are intended to provide richer contextual realism to standard laboratory approaches by playing on contextual variables such as the physical or social contexts, or by using advanced technology in the case of the virtual reality. However, there are no standardized criteria to determine the type of variable that should or should not be added, and how and when they should be. Therefore, the question of validity and transferability of the data obtained in such conditions remains.

Based on a narrative review, this article discusses the added value of contextual approaches to increase the validity of consumer and sensory data. We argue that the addition of contextual cues in experimental approaches should be based on sufficient experimental evidence gathered within a clear theoretical framework. This review examines the notion of validity and ecological validity through the prism of different experimental disciplines (and particularly consumer psychology and behavioral economics) and draws some implications for sensory and consumer science. We review the recent research on context studies and the effect of context on consumers' liking, choice and intake. We also discuss the use of contextual variables in laboratory settings and the emerging use of new methodologies.

This article sets out to (1) define an analytical framework for assessing the relevance of moving towards more ecological validity; (2) assess evidence on how contextual effects should be taken into account in sensory and consumer science studies; and (3) identify the conditions and potential critical points for the design of experiments that take into account context to ensure ecological validity.

The concept of validity in sensory and consumer studies

Evaluating the validity of an experiment: internal, external and ecological validity

The experimental approach is used in various scientific fields concerned with individual behaviors. In particular, consumer psychology and economics use experiments to investigate consumer behaviors and preferences. In these fields, the role of theory in the experimental approach is significant, although not systematic (for a discussion on the role of theory in experimental economics, the reader is directed to [START_REF] Card | The Role of Theory in Field Experiments[END_REF]. For instance, experiments in economics aim to either (i) test theoretical assumptions, (ii) generate data on a little known phenomenon or (iii) evaluate the potential impact of policy scenarios or private sector innovations [START_REF] Rozin | Whispering in the ears of… companies ? Experimental Economics as a Tool for decision in the private sector [Murmurer à l'oreille[END_REF].

In consumer psychology, experiments use conceptual models and psychology theories [START_REF] Kempen | Expectancy-value theory contributes to understanding consumer attitudes towards cow's milk alternatives and variants[END_REF][START_REF] Köster | Diversity in the determinants of food choice: A psychological perspective[END_REF] such as the Theory of Planned Behavior or the Expectancy-value theory [START_REF] Ajzen | Effects of a breakfast spread out over time on the food intake at lunch and the hormonal responses in obese men[END_REF]. While studies in sensory science share this overall goal of better understanding consumer behavior, they often focus on operational objectives, such as to support product development through consumer tests.

In the various scientific fields relating to consumer science, experiments range from controlled, standardized laboratory experiments (standard approach) to natural experiments (experiments run in natural contexts), including different types of field experiments or field data (for more detailed information on field experiments, the reader is directed to the seminal papers by [START_REF] Carpenter | Field Experiments in Economics: an Introduction[END_REF][START_REF] Harrisson | Field Experiments[END_REF]List, 2004; and to the Fréchette & Schotter, 2015 (Part IV: The Lab and the Field) for a more recent view).

In general, the validity of experimental data is assessed from two complementary perspectives: internal and external validity. While internal validity refers to the ability of experimental data to provide understanding and to explain the causal relations within an experiment, external validity refers to the ability of the results of a given experiment to be generalized to other situations [START_REF] Guala | Experimentation in Economics[END_REF][START_REF] Roe | Internal and external validity in economics research: Tradeoffs between experiments, field experiments, natural experiments, and field data[END_REF]. Therefore, moving from controlled to natural experiments implies a tradeoff between these two perspectives.

Ecological validity refers to the representation of the studied stimuli in an environment. This concept was introduced by Egon Brunswik in the area of the psychology of perception [START_REF] Brunswik | Organismic achievement and environmental probability[END_REF][START_REF] Brunswik | Representative design and probabilistic theory in a functional psychology[END_REF]. "Representative design" addresses the ecological validity issue by considering a stimuli representative of the organism-environment relation. Brunswik therefore proposes to move from the study of people to the study of situations, replacing proper sampling of participants with representative sampling of a situation or task; and moving from "artificial" to "natural" contexts [START_REF] Diehl | Ecological Validity as a Key Feature of External Validity in Research on Human Development[END_REF]. On the other hand, [START_REF] Brofenbrenner | Toward an Experimental Ecology of Human Development[END_REF] also includes the role of the researcher in the definition of ecological validity. The degree of ecological validity may be determined by the researchers who should ensure that the environment experienced by the subjects has similar properties to the context of interest.

The ecological validity of a study thus depends on whether the task performed in an experimental context is relevant in the context of interest. If a researcher runs an experiment in the context of interest without modifying the ecology of that particular context, the internal validity as well as the ecological validity of that context can be ensured. However, if the researcher runs an experiment in a context that highly differs from the context of interest or has to modify it to establish internal validity, the inferences for ecological validity may not be guaranteed. This definition of ecological validity generates an ambiguity between the notions of external and ecological validity making it difficult to understand the real purpose of adding ecological value to consumer and sensory studies. Nevertheless, we can assume that a greater ecological validity leads to a greater external validity of the results. Some of the main features of laboratory experiments is the required control over the studied stimuli and the control of the environment in which the experimental study takes place. Laboratory or central location experiments may also allow better control of participants' characteristics (e.g. weigh, hunger state, fasting period…). These factors ensure the ability to explain causal relationships between the stimuli and response. Natural experiments may lack of control over those factors, however they ensure greater ecological validity as natural relationships between the participants and the stimuli occur without restrictions or control of the environment. As an intermediate approach, field experiments attempt to reinforce both internal validity, obtained through strict control over the experimental task, and external validity through the use of a natural physical context, following the rationale that if causality is determined by internal validity, the probability that this relationship (stimuli-response) will be relevant in another ecologically valid setting may increase [START_REF] Roe | Internal and external validity in economics research: Tradeoffs between experiments, field experiments, natural experiments, and field data[END_REF].

These concepts, defined below (Table 1) highlight the importance of three features of an experiment when considering whether it is ecologically valid: the nature of the environment, the nature of the stimuli (in this paper we will refer to the nature of the product) and, the nature of the task. Following the works of experimental economists, we propose to consider an additional criterion: the participants -and more precisely, the nature of the pool of participants and the experience they can bring to the task [START_REF] Carpenter | Field Experiments in Economics: an Introduction[END_REF].

Table 1 Definitions and quotes

The different types of experiments

Laboratory or controlled experiments:

"allows underlying causal relations to become manifest at the level of empirical regularities. In Notions commonly used to evaluate experimental data Validity: "the best available approximation to the truth of a given proposition, inference, or a competently performed experiment, single causal connections can be "read off" directly from statistical associations." (Guala, 2012, p.613) Field experiments: "define what might be better called an ideal experiment, in the sense that one is able to observe a subject in a controlled setting but where the subject does not perceive any of the controls as being unnatural and there is no deception being practiced." [START_REF] Harrisson | Field Experiments[END_REF], p.1010) Natural experiments: "researcher cannot manipulate the stimulus or influence the data generation process. Rather, the researcher takes advantage of a change in context or setting that occurs for some subjects due to natural causes or social changes beyond the researcher's and subjects' influence" [START_REF] Roe | Internal and external validity in economics research: Tradeoffs between experiments, field experiments, natural experiments, and field data[END_REF], p.1267) conclusion." [START_REF] Trochim | Introduction to Validity[END_REF] Robustness: "measure of the method's capability to remain unaffected by small, but deliberate variations in method parameters (environment, protocol, laboratory, equipment, staff, ...)." (Boutrolle, Arranz, Rogeaux, & Delarue, 2005, p.707) Reliability: "the degree to which the result of a measurement, calculation, or specification can be depended on to be accurate." (Oxford Online Dictionary, « Reliability », https://en.oxforddictionaries.com/ viewed online July 2 nd , 2018) Replicability: "the ability of a scientific experiment or trial to be repeated to obtain a consistent result." (Oxford Online Dictionary, « Replicability », https://en.oxforddictionaries.com/ viewed online July 2 nd , 2018)

Critical points in sensory and consumer studies

In sensory and consumer sciences, laboratories and central location test (CLT) have long been considered the "gold" standard for the study of consumers' liking and behavior. Those scenarios have offered great reliability and robustness of results due to the control of experimental variables through the application of standards (e.g. the AFNOR V09-500 in France) which establishes a methodological framework to explain causal relations. However, in the last decades, the high rate of market failures of new food products that had been selected on the sole basis of CLT, has prompted researchers and industrials to question the ability of these methodological approaches to provide reliable data [START_REF] Garber | Measuring consumer response to food products[END_REF][START_REF] Jaeger | Future directions in sensory and consumer science: Four perspectives and audience voting[END_REF][START_REF] Köster | Flops analysis: A useful tool for future innovations (Part 2: The reduction of future flop risks)[END_REF].

Using the perspective of the four criteria listed above, we try to identify the main critical points that should be considered when assessing the validity of experimental data in sensory and consumer science.

Experimental environment

Context was defined by [START_REF] Meiselman | The role of context in food choice, food acceptance and food consumption[END_REF] as the specific physical, social and situational conditions in which food and beverages are consumed. Several studies have shown that the context in which food is evaluated impacts consumers' liking scores and food choices [START_REF] Edwards | The influence of eating location on the acceptability of identically prepared foods[END_REF][START_REF] King | The effect of meal situation, social interaction, physical environment and choice on food acceptability[END_REF][START_REF] Meiselman | Demonstrations of the influence of the eating environment on food acceptance[END_REF][START_REF] Stroebele | Effect of ambience on food intake and food choice[END_REF]. These effects can be seen as a result of the role of context as a whole, or more specifically as a result of the presence or absence of some specific contextual variables in a given setting. These aspects will be more specifically addressed in the next section of the article (section 3) 2.2.2. Nature of the product In this review, focus is placed on studies related to food products, although most considerations would also apply to other product categories. In laboratory settings, food products are usually evaluated as single items (bite or dish) and not as part of a meal; even the portion's size is usually smaller than in more natural settings. However, several studies have shown that products evaluated as part of a meal are higher appreciated than individual items [START_REF] King | The effects of contextual variables on food acceptability: A confirmatory study[END_REF][START_REF] King | The effect of meal situation, social interaction, physical environment and choice on food acceptability[END_REF]. [START_REF] Rozin | Whispering in the ears of… companies ? Experimental Economics as a Tool for decision in the private sector [Murmurer à l'oreille[END_REF] have described the concept of "eating reference unit" as the size of the tested food (bite, dish, meal, diet pattern) over time. Each reference unit has a different level of complexity, temporal and spatial importance, and research application. For example, a bite is a unit of reference eaten in a short period of time, in a single space and it is used by sensory and product developers; however, a meal is a unit of reference more complex that includes smaller reference unit as bites and that would be used by food service and institutional researchers [START_REF] Meiselman | The role of context in food choice, food acceptance and food consumption[END_REF].

However, in studies taking meals into account rather than isolated products, the definition of "meal" is not standardized, as it depends on the researchers' culture and orientations [START_REF] Meiselman | The role of context in food choice, food acceptance and food consumption[END_REF][START_REF] Pliner | Workshop summary : What to eat : A multi-discipline view of meals[END_REF].

Another critical aspect regarding the ecological validity of the product is its method of preparation.

Sensory tests usually employ optimized, standardized cooking methods and minimize variations between batches of products. However, the method of food preparation is involved in the formulation of the hedonic judgement, therefore questioning the ecological validity of the standardized approach [START_REF] Delarue | The effects of context on liking : implications for hedonic measurements in new product development[END_REF]. Several studies have reported a direct effect of preparation methods on liking and discrimination when consumers have the freedom to taste products according to their own habits as they do in natural conditions [START_REF] Matuszewska | Comparison of three procedures for consumer assessment of fat spreads : Short report[END_REF][START_REF] Posri | Improving the predictability of consumer liking from central location test in tea[END_REF]. Variations in preparation methods occur in real life situations, where optimized conditions are rarely met. Yet the standardized tests rarely account for the possible impacts of these variations in the data obtained.

Selection of participants

The mindset of participants when performing a study is a key element in the pursuit of ecological validity. Initial beliefs, attitudes, intentions, knowledge and exposure can all have a significant impact on perceptions and decisions, yet they are rarely taken into account in the interpretation of sensory tests [START_REF] Bernard | Are beliefs stronger than taste? A field experiment on organic and local apples[END_REF][START_REF] Boutrolle | Use of a test of perceived authenticity to trigger affective responses when testing food[END_REF][START_REF] Cardello | Attitudes of consumers toward military and other institutional foods[END_REF][START_REF] Edwards | Institutional meals[END_REF][START_REF] Kempen | Expectancy-value theory contributes to understanding consumer attitudes towards cow's milk alternatives and variants[END_REF][START_REF] Mahon | The role of attitudes, subjective norm, perceived control and habit in the consumption of ready meals and takeaways in Great Britain[END_REF][START_REF] Tuorila | School meal acceptance depends on the dish, student, and context[END_REF].

In addition to this, the way participants are involved in the test seems to impact consumers' evaluation.

Recent studies have pointed out the motivation and involvement of participants as a critical factor when analyzing and comparing different type of experiments [START_REF] Bangcuyo | The use of immersive technologies to improve consumer testing: The role of ecological validity, context and engagement in evaluating coffee[END_REF][START_REF] Hathaway | The impact of multiple immersion levels on data quality and panelist engagement for the evaluation of cookies under a preparation-based scenario[END_REF].

The way the participants are selected and recruited may also constitute an issue. One of the main criticisms made to inferences drawn in sensory and consumer studies has been the use of nonrepresentative populations. This concern is primarily directed to studies conducted for academic purposes, which frequently use student populations. However, this factor only needs to be considered if the mechanisms or tasks involved in a particular behavior depend on the population type. Depending on the research question, specific populations may be required and in this case, the recruitment of the wrong population may compromise the generalization of the results to a more diverse population [START_REF] Harrisson | Field Experiments[END_REF]).

Evaluation task

The features of the experimental task (experimental procedure or instrumental measure) may also have a significant impact on the respondents' behavior -and therefore on the validity of data. The importance of the nature of the evaluation task performed, as well as the psychological processes involved in the task, have been the focus of several studies in the fields of experimental economics and experimental psychology [START_REF] Carpenter | Field Experiments in Economics: an Introduction[END_REF]. In sensory and consumers' studies, participants generally answer a questionnaire after tasting a product. The framing of a task, the number and the way of asking the questions have been found to have an impact on consumers' responses [START_REF] Cardello | Hedonic scaling: assumptions, contexts and frames of reference[END_REF][START_REF] Kwak | Correlation of liking and disliking measurements in consumer acceptance tests[END_REF][START_REF] Kwak | Presentation methods for unidirectional scales to measure consumers' liking and disliking percepts[END_REF][START_REF] Lim | Hedonic scaling: A review of methods and theory[END_REF][START_REF] Prescott | Analytic approaches to evaluation modify hedonic responses[END_REF]. Furthermore, some factors such as attention or time perception are known to play a significant role in judgement and decision-making and may directly affect the outcome of a hedonic test or a choice experiment [START_REF] Dijksterhuis | The Unconscious Consumer: Effects of Environment on Consumer Behavior[END_REF][START_REF] Köster | The psychology of food choice: some often encountered fallacies[END_REF].

Another critical point related to the task is the incentive to reply. The presence of incentives directly associated to an experimental task has been shown to have an impact on the way participants report their willingness to pay for a product. In the absence of an incentive (and even in the presence of a remuneration for their participation), responses tend to exhibit a hypothetical bias, which often manifests in the form of an over-evaluation of the product compared with a consequential task [START_REF] Carson | Incentive and informational properties of preference questions[END_REF][START_REF] Shogren | Chapter 19 Experimental Methods and Valuation[END_REF]. However, despite its possible implications for new product development, this question has not, to our knowledge, been investigated in the field of hedonic evaluation yet.

Increasing ecological validity: what do context studies say?

3.1. From laboratory to natural settings As a way of addressing the concerns identified in the previous section regarding the validity of such data, it has been suggested to move from controlled settings towards more natural environments -that is to say, to use more contextualized approaches.

Indeed, as an alternative to the laboratory, consumers can be studied in non-standardized, natural consumption environments. The advantage of this field approach is that it reinforces the ecological validity of the experimental setting (environment), allowing researchers to study the interactions between the multiple contextual variables and the consumer's behavior. Regarding the product, while a food product in a laboratory is tested alone and punctually (such as a food product tested as a single dish and presented in a small quantity), the same stimulus in a natural environment (such as a restaurant) may occur in a different, more ecological manner (such as a food product consumed within a meal, in a large quantity). Regarding the task, participants can be unaware of the existence and of the purpose of the study (pure observation of choices or food intake) or be made aware only of some aspects, at the end of the consumption (questionnaires that can be delivered once participants have finished eating or have selected their food) [START_REF] Lin | Restaurant Servicescape, Service Encounter, and Perceived Congruency on Customers' Emotions and Satisfaction[END_REF].

While adding contextual elements may reinforce ecological validity by nature, we are still not sure about the transferability of the data obtained in natural environments in other contexts -not only because of the environment, but also because the stimulus or product itself and, the features of the task performed are different. In the following subsections, we examine more closely the question of ecological validity of context studies.

Do context parameters play a role in the validity of data?

The way to see ecological validity and its potential effects on consumer judgment has direct methodological implications. In the field of sensory and consumer science, studies looking at the validity of contextualized experiments fall into two categories: those that approach the issue of ecological validity as a whole (the experimental context consist of a combination of the environment and the task performed and, attempts to keep most of them as close to natural as possible) and those that focus on specific factors that are found to have an impact on the measures and, try to make these more ecologically valid.

The studies following a global approach compare scores on food liking and choices in different natural environments (restaurants, canteens, prisons) with those obtained on laboratory or central location settings showing differences on hedonic scores [START_REF] Edwards | The influence of eating location on the acceptability of identically prepared foods[END_REF][START_REF] King | The effect of meal situation, social interaction, physical environment and choice on food acceptability[END_REF][START_REF] Meiselman | Demonstrations of the influence of the eating environment on food acceptance[END_REF]. Those differences are usually related to the degree of discrimination among products -consumers being more discriminant in natural settings than in laboratory settings -or to the higher scores on natural settings versus laboratory settings. The studies focusing on context variables compare how the addition of contextual variables in controlled experiments affect food liking and choice [START_REF] King | The effect of meal situation, social interaction, physical environment and choice on food acceptability[END_REF][START_REF] Stroebele | Effect of ambience on food intake and food choice[END_REF]Weber, King, & Meiselman, 2004). We may first notice that several classifications of contextual variables have been proposed: [START_REF] Rozin | Whispering in the ears of… companies ? Experimental Economics as a Tool for decision in the private sector [Murmurer à l'oreille[END_REF] divide contextual variables into either product and non-product variables and subdivide them in simultaneous and temporal contextual factors; [START_REF] Meiselman | The contextual basis for food acceptance, food choice and food intake: the food, the situation and the individual[END_REF], proposes to distinguish between three categories of variables (the situation, the individual and the product); whereas [START_REF] Stroebele | Effect of ambience on food intake and food choice[END_REF], divide the contextual variables into social context variables, physical surroundings, time related characteristics and distraction and/or television viewing. From these studies, it is difficult to fully disentangle the various factors and isolate a specific context effect. The relevance of those contextual variables thus remains unclear. To date, the lack of knowledge of the combined effects of these contextual variables on consumers' responses compromises the ability to identify causal relationships through experimental approaches. In practice, a consequence of this is that participants to a test may not perceive the study context the way the researcher assumes they would. This questions the ecological validity as defined by Brofenbrenner.

The issue seen as a whole would naturally lead to global changes in the test design, while dividing context into separate variables would bring targeted improvements of the experimental setup, keeping the rest of the task and environment potentially non ecological. For this literature review, a search on Google Scholar and Science Direct was conducted using the following keywords: 'context'; 'consumption context'; 'social facilitation'; 'food liking'; 'food choice'; 'food intake'. These keywords were used in combination to identify studies on the effect of the contextual factors (context, consumption context, social facilitation) on consumers' evaluation and behaviors (food liking, food choice, food intake). The reference lists and citations of eligible publications were also reviewed to identify pertinent literature.

A criterion for inclusion in the review was that the study had an experimental design in which either food liking, choice or intake was manipulated by a contextual variable (physical, social or food related). Table 2 shows a complete list of all the studies related to context effects following a a) global, b) separated variable and/or c) global and separated variable approach. We analyzed how those studies try to answer to the question of ecological validity by considering the four factors (participant, stimuli as food product, environment and task) previously presented. Twenty articles were identified that met these selection criteria. Of these, the majority (13) measured food acceptability as the dependent variable of interest, whereas nine articles investigated consumers' choice and intake as regards of meal duration and social facilitation.

On the other hand, in the interpretation of the table we also discuss studies that did not meet our inclusion criteria, but which provided additional insight as regards the use of context and ecological validity. As can be seen from Table 2, some studies show that context effects on food acceptability differ depending on product categories. Social facilitation shows to increase meal duration as well as food intake whereas food choice seems to increase food acceptability.

Similarities and differences are found when comparing the results from studies following a global approach with those following a separated variable approach. The studies following a global approach study consumer behavior through observation (there is no control over the contexts, products, participants and task) or task modulation. When only observation is used, ecological validity is ensured as consumers behave in their regular basis. In this type of studies, food choice, meal duration and intake can be analyzed, however food perception or liking cannot. When the task is modulated (questionnaire filling, food diary), social facilitation increases food intake and differences in hedonic scores are observed across studies. However, these results are controversial as in some situations no differences were observed [START_REF] Kozlowska | Hedonic tests in different locations as predictors of apple juice consumption at home in elderly and young subjects[END_REF]. These studies ensured ecological validity as the contexts, products and participants are not altered, however the transferability of the results into another context should be questioned.

The studies following a separated variable approach modify not just one contextual factor but several factors at a time (for example the nature of the product or the evaluation task) decreasing the internal validity of the results as well as the ecological validity. In this type of studies, the effect of context on product category should be highlighted as differences between snacks and meals ratings are observed, as well as the effect of the use of congruent elements on consumers' liking. This type of studies has also shown controversial results, being significant in some cases and irrelevant in others [START_REF] Hersleth | Consumer acceptance of cheese, influence of different testing conditions[END_REF][START_REF] Petit | Testing consumer preferences for iced-coffee: Does the drinking environment have any influence?[END_REF].

The following parts discuss the outcomes of the literature review regarding the four factors from the previously proposed framework to analyze ecological validity.

Experimental environment

Context has shown to have a certain impact on consumers' liking [START_REF] Boutrolle | Central location test vs. home use test: Contrasting results depending on product type[END_REF][START_REF] De Graaf | A comparison between liking ratings obtained under laboratory and field conditions: The role of choice[END_REF][START_REF] Edwards | The influence of eating location on the acceptability of identically prepared foods[END_REF][START_REF] García-Segovia | Influences of table setting and eating location on food acceptance and intake[END_REF]. The experimental environment is the most studied factor in the literature on context. However, the comparison of completely different contexts or the addition of contextual variables have led to controversial results as we have previously indicated. The ecological validity of the results can be compromised due to the use of different participant pool in the case of the global approach (different age, social status, etc.) or to the use of incongruent elements in the case of the separated variable approach [START_REF] García-Segovia | Influences of table setting and eating location on food acceptance and intake[END_REF][START_REF] Petit | Testing consumer preferences for iced-coffee: Does the drinking environment have any influence?[END_REF]. As shown in Table 2, participants and contexts are confounding elements (i.e.

we cannot dissociate both variables) because comparative studies are usually conducted according to a between-group design.

Besides, consumers' expectations and beliefs towards specific food consumption contexts play a key role on consumers' judgement [START_REF] Bernard | Are beliefs stronger than taste? A field experiment on organic and local apples[END_REF][START_REF] Köster | The psychology of food choice: some often encountered fallacies[END_REF]. Hence, it must be stressed that comparing laboratory settings to natural consumption contexts may lead to results as different as comparing hedonic scores from two natural contexts (e.g. school canteen and restaurant). Not only the products may differ in both situations, but also consumers' expectations. Unfortunately, participants' expectations are never really taken into account in studies on context even if they could help to explain differences in consumer behavior and hedonic scores.

Nature of the product

Concerning the nature of the product, when the served food sample in a laboratory setting is not representative of the regular amount, preparation and presentation of the same food in a natural setting, it may be hazardous to compare studies because the product/meal combination may not be representative of participants' previous experiences and may convey dissonance and related biases [START_REF] Rozin | Whispering in the ears of… companies ? Experimental Economics as a Tool for decision in the private sector [Murmurer à l'oreille[END_REF]. In fact, we can observe how some products like snacks are able to "pass across contexts" without significant differences on the hedonic scores whereas meals do not [START_REF] De Graaf | A comparison between liking ratings obtained under laboratory and field conditions: The role of choice[END_REF][START_REF] Edwards | The influence of eating location on the acceptability of identically prepared foods[END_REF]. This aspect linked to the product category is important to ensure the ecological validity of the results in both global and separated variable approach.

As regards the effect of food combination and sequence of food items during a meal, it is interesting to notice that most of the research on human eating behavior has been focused on food items instead of food combinations. In the last decades, researchers have shown that suitable food combinations result in more pleasant recipes and this is translated in higher overall hedonic scores (Di [START_REF] Monaco | Effect of social interaction and meal accompaniments on acceptability of sourdough prepared croissants: An exploratory study[END_REF][START_REF] Elzerman | Consumer acceptance and appropriateness of meat substitutes in a meal context[END_REF][START_REF] Hersleth | Effect of contextual factors on liking for wine-use of robust design methodology[END_REF][START_REF] Pagliarini | Consumer testing with children on food combinations for school lunch[END_REF]. While others have also studied how much of each meal component contributes to that [START_REF] Jimenez | Seeing a meal is not eating it : Hedonic context effects differ for visually presented and actually eaten foods[END_REF][START_REF] Meiselman | The role of context in food choice, food acceptance and food consumption[END_REF]. In addition to this, the sequence and appropriateness of mealtimes when evaluating products has produced different results [START_REF] Boutrolle | Central location test vs. home use test: Contrasting results depending on product type[END_REF][START_REF] Cardello | Predictors of food acceptance, consumption and satisfaction in specific eating situations[END_REF][START_REF] King | The effect of meal situation, social interaction, physical environment and choice on food acceptability[END_REF][START_REF] Meiselman | The role of context in food choice, food acceptance and food consumption[END_REF]. Therefore, the study of products as food items instead of part of a meal may contribute to misleading results that cannot be generalized from one context to another.

Another important aspect that has been already mentioned is that consumers and locations are most often confounded variables. They cannot be studied independently as they are intimately related to consumers' expectations and mindset. Even if a food is exactly the same in two different contexts, consumers may not bring to those contexts the same experience, beliefs and/or expectations. As a consequence, even if they like a given food in one context, consumers may prefer another one that fits better another context. Besides, when comparing consumption settings and particularly meals, the preparation method is a key element in the variability of the sensory properties of the product and may be the source of beliefs, that could, in turn, affect hedonic responses [START_REF] De Graaf | A comparison between liking ratings obtained under laboratory and field conditions: The role of choice[END_REF][START_REF] Edwards | Institutional meals[END_REF].

Selection of participants

In Table 2, we highlighted the following participant-related aspects found in the literature on context: remuneration, group size and relations and, consumers' familiarity. Most of the participants in laboratory settings are recruited on-purpose and compensated whereas participants to natural context studies are not. This aspect can have a strong impact on consumers' implication and therefore, on obtained data. However, remuneration of participants has not been really explored in the literature on context. On the other hand, some of the studies have compared hedonic scores among different contexts were the studied population was too small to generalize their findings [START_REF] Edwards | The influence of eating location on the acceptability of identically prepared foods[END_REF][START_REF] Zeinstra | The influence of preparation method on children's liking for vegetables[END_REF]. Moreover, the degree of relation between participants have shown to have different impact on consumers' behavior. When participants know each other they behave in their regular basis whereas when it is not the case, negative correlation with the hedonic scores is obtained (Di [START_REF] Monaco | Effect of social interaction and meal accompaniments on acceptability of sourdough prepared croissants: An exploratory study[END_REF]. As regards consumers' familiarity toward the tested products, it must be noted that most of the studies have recruited regular consumers of the tested product. This is an important factor when comparing contexts because some studies have shown that products familiarity may reduce contexts' effects whereas unfamiliar products may be more context-dependent [START_REF] Giacalone | Situational appropriateness of beer is influenced by product familiarity[END_REF][START_REF] Hersleth | Consumer acceptance of cheese, influence of different testing conditions[END_REF][START_REF] Kim | Familiarity and liking playing a role on the perception of trained panelists: A cross-cultural study on teas[END_REF]. However, we should be very cautious with this notion because in the case of main dishes, familiarity may also be related to particular consumption contexts. [START_REF] Kozlowska | Hedonic tests in different locations as predictors of apple juice consumption at home in elderly and young subjects[END_REF][START_REF] Meiselman | Demonstrations of the influence of the eating environment on food acceptance[END_REF].

Evaluation task

Besides, we may observe that, even when the task is the same, hedonic scales and questionnaires frequently differ from one experiment to another as well as from one study to another. We also notice important differences in experimental procedures when comparing one context to another. For example, questionnaires are distributed or displayed differently in different contexts (e.g. paper and pencil vs. digital screen). The same goes with the way to ask participants to test the products, etc. It should also be added that tests in laboratory or in central location do not usually account for the fact in natural situations consumers may have the possibility to choose the food they want to eat. This may have important consequences in consumers' mindset, not to mention the product experience itself.

All in all, the lack of standardization of protocols in the reviewed literature may (at least partly) explain the lack of consistent results as regards the effects of context on consumers' evaluation and behavior.

We argue that ecological validity cannot be seen as independent of internal validity but complementary, and that the focus should be shifted from a search for realism to the definition of clear criteria for transferability from one context to another. Moreover, the focus should be placed on how to isolate the causal effect rather than on the realism from one context to another in order to explain differences among contexts. The pursuit of ecological validity may be seen as a good opportunity to implement the methodologies currently used in the laboratory and try to find a satisfying compromise between the laboratory results and natural setting data.

4. New methodological approaches: towards increased transferability? [START_REF] Rolls | Both naturalistic and laboratory-based studies contribute to the understanding of human eating behavior[END_REF] already anticipated the need to bring together the best features of laboratories and natural consumption contexts in order to study the interactions between contextual variables, but in a controlled way. We identify five approaches designed to address the question of ecological validity. The first one, the classical approach, is the use of natural context that we already described in section 3. The four other approaches are more recent: Living Labs, evoked contexts, immersive contexts and virtual reality. Some of these methods have been described in previous reviews, in particular by [START_REF] Jaeger | Consumption context in consumer research: methodological perspectives[END_REF].

We will first define each type of approach, and then characterize the different studies according to this typology.

(a) Living labs -Even if a no clear definition for Living labs is found in the literature, the authors have decided to use the definition given by Dell'Era & Landoni (2014) (p.139) where Living Lab is defined as "a design research methodology aimed at co-creating innovation through the involvement of aware users in a real-life setting". In Living labs, the researcher can control and record a selected number of contextual variables and the interaction between them, within a natural consumption situation. Living lab experiments can be seen as an attempt to compromise with the limitations and advantages of laboratory and field experiments, as the control of contextual variables increases the internal validity of the study, while the situation is kept as ecological as possible. Examples of Living labs dedicated to food studies are "The Restaurant of the Future" Wageningen, Netherlands [START_REF] Hinton | Using photography in 'The Restaur ant of the Future'. A useful way to assess portion selection and plate cleaning[END_REF][START_REF] Zeinstra | The influence of preparation method on children's liking for vegetables[END_REF], "The Grill Room" in Bournemouth, United Kingdom [START_REF] Bell | Effects of adding an Italian theme to a restaurant on perceived ethnicity, acceptability, and selection of foods[END_REF][START_REF] Meiselman | Demonstrations of the influence of the eating environment on food acceptance[END_REF] and "The Living Lab" at the Research Centre of the Institute Paul Bocuse in Ecully, France (Allirot et al., 2014;[START_REF] Iborra-Bernad | Sensory analysis and observational study in an experimental restaurant: Pilot study[END_REF].

(b) Evoked contexts -In the evoked contexts approach, the researcher places the consumer in a typical laboratory evaluation task, but uses either text, audio recordings, and/or pictures that evoke what would be a natural consumption situation of the product [START_REF] Jaeger | Consumption context in consumer research: methodological perspectives[END_REF]. In this case, consumers have to imagine themselves in a particular situation and evaluate a product or a set of products. This approach is well established in other disciplines such as marketing studies [START_REF] Bitner | Evaluating Service Encounters: The Effects of Physical Surroundings and Employee Responses[END_REF][START_REF] Daunt | Unpacking the perceived opportunity to misbehave: The influence of spatio-temporal and social dimensions on consumer misbehavior[END_REF][START_REF] Esmark | I'll Be Watching You: Shoppers' Reactions to Perceptions of Being Watched by Employees[END_REF].

(c) Immersive contexts -To define immersive contexts, we should first define what immersion means. Immersion is defined by [START_REF] Witmer | Measuring Presence in Virtual Environments -A Presence Questionaire[END_REF] as "a psychological state characterized by perceiving oneself to be enveloped by, included in, and interacting with an environment that provides a continuous stream of stimuli and experiences". The main difference between immersive and evoked context approaches is that consumers do not have to imagine themselves in a particular consumption situation, but they experience it instead.

Three main features describe the characteristics of immersive contexts: lack of awareness of time, loss of awareness of the real world, involvement and a sense of being in the task environment [START_REF] Jennett | Measuring and defining the experience of immersion in games[END_REF]. These approaches usually imply a wealth of means (videos displayed on large screens, multisensory stimulation, including temperature, background sounds, odours, etc.). Within this category, we can also include the recreated environments.

Recreated environments are a form of immersive approach where the setting reproduces the physical natural environment where the food consumption would be done, and consumers actually experience a similar situation as in a natural context.

(d) Virtual reality -Finally, the virtual reality approach is defined by the "use of virtual environments to present digitally recreated real world activities to participants via immersive (head-mounted displays) and non-immersive (2D computer screens) mediums" (Parson, 2015). We argue that including non-immersive mediums such as the 2D computer screen in the virtual reality definition may create certain confusion with the evoked and immersive contexts categories, where such tools can be also used. For this reason, we have considered only virtual reality studies where head-mounted displays are used.

Following these definitions, Table 3 provides an analysis of these four new methodological approaches through the prism of the four criteria of experimental validity that were previously discussed. Before analyzing each approach, as a general comment, we would like to highlight that the results obtained from each approach may differ depending on the nature of the product (product category) and the familiarity with the product. Certain products may be more affected by situation-specific cues than others. Therefore, special attention should be given to these aspects when analyzing and comparing products evaluations from one context to another.

As it can be seen in the Living Lab studies (Table 3, section a) the characteristics of the participants, the nature of the product and the environment are kept as realistic as possible, whereas the evaluation task through the inclusion of questionnaires may compromise the external validity of the results in a certain way. Consumers experience a natural consumption situation, therefore the transferability of the data to another setting that follows similar patterns can be achieved. However, the use of this type of settings may be costlier and require additional logistics compared to the use of other contextual methodologies.

Concerning the evoked context studies, this approach is easy to apply and inexpensive because not physical elements are added. However, the degree to which participants project themselves to the evoked context is not controlled, despite attempts to measure vividness of evocations, making generalization of results to other contexts difficult [START_REF] Köster | The psychology of food choice: some often encountered fallacies[END_REF]. Therefore, the gain in ecological validity due to evocation of a consumption situation is difficult to assess, and may very well be outweighed by the loss due to artificiality of the projective task implied by such a procedure.

Immersive approaches have been hypothesized to improve consumers' involvement as well as product discrimination as participants may experience similar psychological processes that in natural contexts [START_REF] Andersen | Desires for beverages and liking of skin care product odors in imaginative and immersive virtual reality beach contexts[END_REF]. As it was previously discussed, consumers' experiences and prior beliefs about particular contexts are key elements when conducting sensory evaluations in contexts studies [START_REF] Köster | The psychology of food choice: some often encountered fallacies[END_REF]. The fact that consumers experience a natural consumption situation even if it is under controlled conditions may ensure the ecological validity of the results and improve the external validity. However, as it can be seen in Table 3 -section c, there is a lack of standardization of the contextual variables in the immersive studies that have been conducted so far,different degrees of immersion can be shown -therefore there is limited knowledge about the relevance of each contextual variable and their contribution to the outcome of experimental studies.

Moreover, the higher costs that these methodologies involve have been highlighted as main drawbacks in their use.

To our knowledge, so far only one published study has attempted to compare immersive and natural settings methodologies. In a study of the impact of context on food evaluation of airplane meals, Holthuysen, Vrijhof, de Wijk, & Kremer, (2017) compared overall liking and just-about-right ratings in laboratory, recreated airplane and an actual plane. Recreated and actual plane settings showed similar results, contrary to laboratory settings. However, in this case it should be highlighted that the actual immersive context was a recreated environment. A flight was recreated through the use of a physical environment (cabin creation), use of boarding passes and hand luggage, flight instructions, regular time of flight, etc. Unlike most immersive tests, recreated environments do not place participants in a location where screens, sounds or smells are combined. Further work is therefore needed in the definition and categorization of immersive experiments and on the comparison of external validity between this approach and natural settings.

Finally, an increasingly popular methodological approach to improve the ecological validity is the use of virtual reality. Until now, most of these studies have focused on consumers' purchasing behavior in food stores. This methodological approach has offered controversial results as regards product discrimination and consumer behavior [START_REF] Dreyfuss | Incontext consumer research: Benefits and opportunities for immersive techniques[END_REF]. Whereas in some studies similar results have been obtained in virtual and natural environments, in other situations an over effect has been reported. The virtual reality allows participants to place themselves in particular contexts (telepresence) and improve products usability increasing the engagement in the task. However, in some situations, depending on the type of used technology, the use of electronic devices may compromise the "natural" experience and biases the obtained results even if consumers are used to this type of technology. Moreover, the nature of the environment remains non-ecological when 2D computer screens are used as well as the product evaluation task, especially when the research question is related to product acceptability. For further discussion about virtual reality studies, the reader is directed to [START_REF] Stelick | Thinking outside the booth -the eating environment , context and ecological validity in sensory and consumer research[END_REF].

Contribution

Research

Our analysis of context studies in sensory and consumer science considers four critical points when evaluating the need for a given contextual parameter: the experimental environment, the nature of the product, the selection of participants, and the evaluation task. This review adds evidence to the lack of standardized methodologies and analytical framework highlighted by several previous reviews, as well as the problems of robustness and reliability of the results that it induces. We suggest that the use of contextual variables needs to be assessed according to their contribution to ecological, but also internal validity.

There has been a lot of research on the effects of context on consumers' hedonic response, food choice or intake, however the overall inconsistency of findings renders difficult their integration into clear guidelines to improve the ecological validity of a study. In particular, to date, the results are too context-specific, product category specific or task specific to enunciate more general principles that could be used to develop such a framework. This has led to the emergence of new methodological approaches, with limited effort to determine how, and whether, each of these methods may complement or outrank the other. This review also highlights that contexts and consumers are confounded variables that make the generalization of the results even more hazardous, as hedonic responses are deeply related to consumers' expectations, which are themselves related to each context. Therefore, we propose to pursue the ecological validity in sensory and consumer studies from a complementary perspective, in which laboratory and new methodological approaches work together in complementarity. When and how we should consider ecological validity as a goal in research on context should be the most important question. Living labs and immersive studies may be able to reinforce ecological validity when looking at consumers' choice or purchase intention. However, no study has yet examined the external validity of data acquired in such conditions. It is advisable for researchers to plan studies to compare similar methodological approaches (internal comparisons of living labs and immersive studies) across different contexts and different product categories in order to gain better knowledge and understanding of the reliability of the applied methodologies.

In line with the theories of behavioral economics, in particular Prospect Theory [START_REF] Tversky | Loss Aversion in Riskless Choice : A Reference-Dependent Model Author ( s ): Amos Tversky and Daniel Kahneman Published by[END_REF], we also propose to give more attention to context-induced reference points when evaluating products. Beliefs (prior experiences) associated to a particular context may indeed play a role by predisposing consumers to a different framework of evaluation. Reference points have been shown to greatly modulate judgement and decision making. Even if very few studies have focused on the effects of context and beliefs on food evaluation, the reference framework of evaluation is likely to be an important factor explaining context effects [START_REF] Bernard | Are beliefs stronger than taste? A field experiment on organic and local apples[END_REF][START_REF] Kempen | Expectancy-value theory contributes to understanding consumer attitudes towards cow's milk alternatives and variants[END_REF].

Practical implications

This review has several practical implications. Firstly, we observe that, even though contextual variables have been found to modulate consumer behavior, we cannot establish clear operational recommendations because of the heterogeneity of results found in the literature.

However, this review provides a framework and criteria to assess ecological validity, which could contribute to increase methodological thoroughness in the fields of sensory and consumers' studies, providing workable outcomes to the private sector, notably for product development.

Among all the attempts to improve context, based on our review of the (limited number of) works using recent methodologies, it seems that consumers are more engaged in the task and able to experience a natural context in living lab and immersive approaches. A possible explanation could be that unlike in evoked settings and virtual reality, participants do not have to put too much effort in imagining a consumption situation or use electronic devices which could make the task more ecologically valid. However, this type of experiments can be expensive and difficult to logistically handle, and this conclusion needs to be strengthened by more comparative data.

As regards the nature of the food, it is important to consider, especially in the context of new product development, the type of product that the test aims to evaluate, at which stage of development process the data is needed, and in which settings the final product will be consumed. It has been shown that the impact of context depends on the product category and units of evaluation (e.g. product vs dish).

Moreover, familiarity towards the tested product seems to modulate the contexts effects: while a product familiar to consumers can be eaten in several contexts, unfamiliar products can be related to particular occasions and consumption contexts. In the early stages of product development, when specific sensory product characteristics should be defined, laboratory settings should be considered as the best solution. However, when it comes to the choice or purchase intention, more naturalistic environments may be needed to ensure product success.

Although survey institutes and stakeholders in the industry are well aware of the necessity to recruit consumer samples that are representative of a target population, other participant-related factors (the way the participants are recruited and the incentives they receive to take part in the studies) are less considered and yet may also be relevant concerning the validity of hedonic results. Besides, some studies have shown that is important to consider participants' prior experiences, expectations and beliefs when testing a food, as those factors can tell us more about the consumer and the way he/she will behave in a specific context. These aspects are particularly important when evaluating full dishes.

In particular, when comparing natural contexts (institutional meals, restaurants, etc.), food preparation has been shown to have a direct impact on the sensory properties of a product and to indirectly influence consumers' evaluation due to the associations made between context and served food.

Finally, as regards the evaluation task, we should consider several aspects. First of all, when comparing contexts, we should ensure that the task and the experimental procedure are the same in order to be able to compare the results. Moreover, it is important to keep in mind, consumers will be more focused on the task performance, therefore on the product itself, in laboratory settings than in the natural consumption settings where the hedonic score can include other aspects such as the actual experience, environment, etc. Therefore, further research is needed to improve the understanding of the effect of experimental procedures and instrumental measures used when comparing settings on the participants' evaluation processes.

Limitations

The lack of homogeneity in the definition and the lack of consistency and standardization in the use of contextual variables and associated tools to measure consumers' behavior may have limited the conclusions that could be drawn from this review.

Another important point is that, although the literature has shown different ways of classifying contextual variables, the relative weight and significance of those variables on consumer behavior need further assessment, especially through replicated studies. Moreover, as it has been shown, several experimental procedures are used through the different studies, thus making it difficult to compare their findings. We suggest that further research should dedicate more attention to the understanding of the nature of the task.

Conclusion & Perspectives

Increasing the number of consumer studies in natural settings was pointed as one of the most important challenges for research during the 11 th Pangborn Sensory Science Symposium [START_REF] Jaeger | Future directions in sensory and consumer science: Four perspectives and audience voting[END_REF]. In the past decades, sensory and consumer scientists have tried to move from laboratory experiments to natural experiments and different alternative approaches, such as evoked or immersive contexts or virtual reality, have emerged with the purpose of ensuring better ecological validity.

Ecological validity is achieved if participants perceive the experimental environment, the food they taste and the task they perform to be representative of a natural consumption situation.

On the other hand, as [START_REF] Guala | Experimentation in Economics[END_REF] proposes, internal validity should be firstly addressed to tackle the problem of external validity. By knowing under which circumstances the results can be extrapolated may allow us to find the specific reasons to explain why results may not be generalized. The problem of external validity might be related to the lack of important factors or the presence of artificial conditions in the experimental design that are far from the natural situations. However, is it important to determine the extent to which those factors can be transferred and reproduced in the laboratory, whether this is always possible, and what is the degree of ecological validity and realism that the researcher should assume and seek depending on the purpose and finality of the study.

3. 3 .

 3 Key determinants of ecological validity: a literature review 3.3.1. Methodology

Table 2 .

 2 Summary of 20 context studies (using a) global approach, b) separated variable approach and c) global and separated variable approach).

	333
	a) Global approach
	Study	Studied response	Studied factor	Selection of participants	Nature of the product	Experimental environment	Evaluation task	Results	Comments
	de Castro,	Food intake	Social	515 participants	Regular meals Natural	Food diary for 7	Meals eaten with	Ecological validity and
	(1994)		facilitation	Participants were pre-recruited and remunerated		consumption contexts	consecutive days: what was eaten or drunk, time, amount,	other people were larger and longer compared to meals eaten alone. Meals	external validity may have been ensured because no changes were done in the contexts and the regular
				Between-group design			preparation method, type and	eaten with spouse and family were larger and	task (eat) was not affected No food type comparison
							gender of people	eaten faster, while
							eating with.	meals eaten with
							Hunger, degree of	friends were larger
							elation and anxiety	and of longer duration
							ratings
	Meiselman et al., (2000)	Food acceptance	Eating location	Cross-cultural study: 74 and 125 participants (UK data) Participants were recruited for all locations except sensory laboratory	• Menu based on canned food • Menu main dish Chicken fettuccine Alfredo	• Training restaurant vs Student cafeteria (UK); • Training rest. vs Food lab vs cafeteria (USA)	Food acceptance on a 9-point hedonic scale (UK) Food attributes (flavor, texture, color, overall rating) on a 7-point hedonic scale (USA)	Hedonic scores were 1 point higher in the restaurant > cafeteria. Regarding hedonic attributes (texture, flavor, color), ratings were higher in the restaurant > cafeteria ones	The tested canned food may be unfamiliar to the UK tested population. The nature of the task (questionnaire distribution and number of questions) differed between and within contexts. Participants in the lab condition were in a very
				Between-group					specific context and mood
				design					state (students in
									attendance to take a final
									exam)

) Global and separated variable approach

	3.3.2. Main results	Participants were pre-recruited design Between-group	commercial, savory of snacks (sweet commercial,	• Laboratory + choice	products and of the tested that included some soldiers chose three meals for the	of foods were offered a choice laboratory subjects Correlations improved when	The nature of the task the iced coffee (a product situations. impacted the evaluation of regular meal consumption 28°C) may have also lab data as small bites cannot be compared to room temperature in the different studies (22°C vs
				sweet		evaluated them		(questionnaire filling) typically consumed in
				military,		Participants chose		differs within the field summer)
				savory		three menus in a		and between the lab The evaluation task also
				military),		short period of		experiment. There is no differs among contexts:
				• 3 entire meal menus		time. participants tested Laboratory:		control over the sequential presentation foods were tested and conditions under which versus simultaneous
						small bites of the		evaluated (by soldiers)
						stimuli		which may compromise
						Choice simulation:		the comparison of the
						participants		data.
						chose three		Scope for choice may
						products from a		increase ecological
						range of stimuli +		validity as the task is
						tasted and		closer to natural
						evaluated in the		consumption situations
						laboratory
	Study De Graaf et al., (2005) Petit & Siefferman, (2007)	Studied response Liking ratings Eating Studied factor location Choice Liking and consumption Product preparation Eating location	Selection of participants Participants and soldiers: • T1: 199 • T2: 36 • T3: 36 Participants: • T1: 96 • T2: 96 • T3: 52 • T4: 55 Participants were recruited for the laboratory study Between-group design	Nature of the product • Main dishes (unfamiliar and familiar) • 4 groupings Iced coffee: water and milk based	Experimental environment 3contexts: • Field study (military camp) • Laboratory 4 contexts: • T1: Laboratory • T2: Laboratory + contextual elements (curtains, pictures, etc.) • T3: meeting room • T4: cafeteria	Evaluation task Liking ratings on a 9-point hedonic scale Field environment: before breakfast, • Overall liking and ranging on a 21-point scale + short questionnaire (demographic + consumption habits)	Results High correlation between field and laboratory scores for snacks but not for main dishes. No significant differences between T1 and T2 Significant product differences in T3 Differences between laboratory and natural settings	Comments Nature of the product differs between contexts (entire meal vs small bites); this compromises The nature of the product differs in each context as the preparation method differs. The experimental environment in the T2 may has not been perceived as representative of real life because of external elements that were incongruent (ex: curtains, candles, etc…). the ecological validity of Differences regarding the
						23

Table 2

 2

	reveals that different tasks have been applied across studies: comparison of overall impression
	of served food by 9-point hedonic scale, comparison of overall liking by visual analogue scale (VAS),
	comparison of food attributes, comparison of consumers' willingness to pay, etc. (De Graaf et al.,
	2005; García-Segovia, Harrington, & Seo, 2015;

Table 3

 3 Summary of new methodological approach studies (a) Living Labs, b) Evoked contexts, c) Immersive contexts, d) Virtual reality) 509

	a) Living Labs
	Study	Studied response	Studied Factor	Selection of participants	Nature of the product	Experimental environment	Evaluation task	Results	Comments
	Bell et al., (1994)	Food acceptability and selection	Decoration	Participants: regular consumers • Test 1: 63 • Test 2: 75 Participants were neither recruited nor remunerate	A full restaurant menu	2 contexts: • T1: regular decoration and British food names • T2: Italian decoration and Italian	Perceived ethnicity rating and hedonic scores of each component of the meal on a 9-point hedonic scale	Food acceptability was not affected by decoration but food selection	Consumers on Italian decoration will may perceived the context as a particular day that may nudges their choices. Scope for choice increase ecological validity of both studies
				Between-group		food names
				design
	Allirot et al., (2014)	Food intake	Food choice	17 participants Participants were recruited and remunerated	A breakfast consumed in one eating episode (F1) and another	2 contexts: • Experimental restaurant • Laboratory	Appetite rating in a VAS* + blood sampling	In F4, participants consumed less food in grams and less energy from low energy dense foods at	Combination of laboratory and field experiments to ensure the ecological validity of the experiment.
				Within-group design	one consumed in 4 eating episodes (F4).			the buffet, but total energy intakes were not different between	No comparison with natural context Scope for choice increase
					Buffet meal			conditions	ecological validity of both
					versus				studies
					standardized
					meal

Acknowledgements

The authors acknowledge Herb Meiselman for his kind comments and suggestions on this paper first draft. This review is part of a PhD project funded by the Food Hygiene Scientific Society (SSHA).