- Email: [email protected]
The “social” facilitation of eating without the presence of others: Self-reflection on eating makes food taste better and people eat more
Physiology & Behavior 179 (2017) 23–29
Contents lists available at ScienceDirect
Physiology & Behavior journal homepage: www.elsevier.com/locate/physbeh
The “social” facilitation of eating without the presence of others: Selfreflection on eating makes food taste better and people eat more
MARK
Ryuzaburo Nakata, Nobuyuki Kawai⁎ Graduate School of Information Science, Nagoya University, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Social facilitation Mirror Eating with others Eating alone Elderly adults
Food tastes better and people eat more of it when eaten with company than alone. Although several explanations have been proposed for this social facilitation of eating, they share the basic assumption that this phenomenon is achieved by the existence of co-eating others. Here, we demonstrate a similar “social” facilitation of eating in the absence of other individuals. Elderly participants tasted a piece of popcorn alone while in front of a mirror (which reflects the participant themselves eating popcorn) or in front of a wall-reflecting monitor, and were found to eat more popcorn and rate it better tasting in the self-reflecting condition than in the monitor condition. Similar results were found for younger adults. The results suggest that the social facilitation of eating does not necessarily require the presence of another individual. Furthermore, we observed a similar “social” facilitation of eating even when participants ate a piece of popcorn in front of a static picture of themselves eating, suggesting that static visual information of “someone” eating food is sufficient to produce the “social” facilitation of eating.
1. Introduction Human behaviors are influenced by the presence of others. For instance, people rate food as tasting better [1] and eat much more of it [2] when another individual is present than when eating alone. This facilitation effect has been well documented in a wide variety of situations [3–6] and is referred to as the “social facilitation of eating”. Several explanations have been proposed for this phenomenon [2]. One line of thinking concerns positive mood—when people eat together in company, they typically communicate with each other and experience social bonding [7], which helps them feel comfortable and relax [8,9]; these positive changes in mood or atmosphere, in turn, lead to the social facilitation of eating [8,10,11]. The quality of the social relationships with others is also considered an important factor for such facilitation. When the other individuals present during meals are friends or family members, people tend to consume more food than when these others are strangers [5,8,12]. Recently, attempts have been made to show results that are contrary to what previous studies have propounded on social facilitation. For example, chocolate was judged as more likeable and flavorful when two unfamiliar participants tasted it together even though they did not have any communication with each other [13]. Mood changes also did not seem to contribute to this facilitation effect. Therefore, social communication among people and mood changes in the situation do not appear to be necessary for the occurrence of social facilitation of eating. This
⁎
drives us to the question what is the minimum requirement for this effect to occur. One possibility is that the physical presence of another individual is sufficient for the occurrence of social facilitation of eating. Another is that information suggesting presence of other individuals may be enough to induce the social facilitation effect. However, no studies have ever questioned whether the presence of another individual is in fact necessary for producing the “social” facilitation of eating. This may be because presence of other individuals is usually treated as a basic premise for producing the social facilitation of eating, primarily because this facilitation has only been observed when an individual eats together with other individuals [2]. The aim of this study was to analyze and answer this question. We hypothesized that the social facilitation of eating would occur without the actual presence of other individuals. Eating with others is ubiquitous for many people. It has been found to strengthen the social bonds between individuals [14,15] and thereby enhance team performance [16]. However, at present, numerous elderly adults eat alone in Japan [17]. Research has shown that the quality of life of elderly adults is associated with food enjoyment [18] and a high frequency of eating alone in elderly adults is associated with depression [19] and loss of appetite [20]. If elderly adults exhibit a social facilitation of eating when eating in front of a mirror, this setting could be used to promote their quality of life. From this point of view, we recruited elderly individuals in both Experiment 1 and Experiment 2.
Corresponding author at: Graduate School of Information Science, Nagoya University, Furocho, Chikusaku, Nagoya 464-8601, Japan. E-mail address: [email protected] (N. Kawai).
http://dx.doi.org/10.1016/j.physbeh.2017.05.022 Received 28 February 2017; Received in revised form 27 April 2017; Accepted 17 May 2017 Available online 19 May 2017 0031-9384/ © 2017 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai
2. Experiment 1
and, after an alarm call signaled the beginning of the tasting period, began to taste the popcorn while alone in the booth. The tasting period lasted for 90 s. After another alarm call signaling the end of the tasting period, they completed a short questionnaire indicating their subjective evaluations of the popcorn. The participants then began a new condition with new popcorn. The short questionnaire contained a number of questions in Japanese assessed on a 6-point scale (from “not at all” to “extremely”) that reflected participants' subjective evaluations of the popcorn: “How good is this popcorn?” “How do you feel about the quality of the popcorn?” “How much do you like this popcorn?” “How filling is the popcorn?” “How salty is this popcorn?” “How sweet is this popcorn?” and “How bitter is this popcorn?” We also calculated the consumption ratio of each bowl of popcorn by subtracting the ratio of the quantity of the remaining popcorn from its initial quantity ratio (i.e., 100%).
To test the prediction, we set up an experiment (Experiment 1) wherein individuals ate alone in front of a mirror. In this situation, the mirror would reflect the individuals themselves eating food, thus giving them the objective visual information of an eating behavior when the individual is in fact eating alone. 2.1. Material and methods 2.1.1. Participants Sixteen elderly adults (5 females and 11 males; aged 65–74 years with a mean of 68.4; all Japanese) recruited by a job placement agency for elderly adults participated in exchange for a cash incentive. We verified that all participants had normal cognitive status before the experiment by using the Revised Hasegawa's Dementia Scale (HDS-R) [21]. None of the participants met the criteria for dementia (i.e., a score of 20 or less as suggestive of dementia; mean for this sample = 28.56). We also confirmed that all participants were naïve to the purpose of the experiment and had them complete a demographic questionnaire assessing their suitability for the study—namely, that they had good health, no food allergies, no history of eating disorders, and no special dietary restrictions.
2.1.3. Ethics statement The protocols of all of the experiments in this study accorded with the Declaration of Helsinki and were approved by the Ethics Committee of the Graduate School of Information Science at Nagoya University. Written informed consent was obtained before participation. 2.2. Results 2.2.1. Subjective evaluations of the food Participants' ratings of the popcorn and consumption ratio in each condition were analyzed using a two-way analysis of variance (ANOVA) with the factors of the presence of a mirror (mirror vs. monitor) and test food (salt flavored vs. caramel flavored). The results indicated that the goodness (F1,15 = 32.43, P < 0.01), quality (F1,15 = 5.21, P < 0.05), and liking (F1,15 = 10.00, P < 0.01) of the popcorn were all significantly higher in the mirror condition than in the monitor condition. The mean consumption ratio in the mirror condition was also significantly greater than that in the monitor condition (F1,15 = 15.40, P < 0.01; Fig. 1). The sweetness of the caramel flavored popcorn (F1,15 = 154.29, P < 0.01) was significantly higher than that of the salt flavored popcorn. Furthermore, the saltiness of the caramel flavored popcorn (F1,15 = 34.01, P < 0.01) was significantly lower than that of the salt flavored popcorn. These comparisons were conducted as to verify that participants' sense of taste was valid.
2.1.2. Procedure The experiment comprised 3 consecutive phases: pre-tasting survey, tasting, and post-tasting survey. 2.1.2.1. Pre-tasting and post-tasting surveys. The pre-tasting and posttasting surveys were presented before and after the tasting period, respectively. The Japanese version [22] of UWIST (University of Wales Institute of Science and Technology) Mood Adjective Checklist (UMACL) [23] was used to assess participants' mood states. It comprises 20 items that participants must rate in terms of their applicability to participants' present mood on a 4-point scale (from 1 = “definitely not” to 4 = “definitely”). In this checklist, two independent factors were provided. The scores of the specific 10 items (e.g., active) composed energetic arousal (EA) and those of the other 10 items (e.g., nervous) composed tense arousal (TA). Each score ranged from 10 to 40. The combination of these two factors structured mood dimension. For example, higher energetic arousal and lower tense arousal indicated the increase of pleasant mood (positive mood) [22–24].
2.2.2. Mood Participants rated their mood state before and after tasting in terms of the two independent scores (EA and TA). Our special interest here was to assess whether there were any changes in their mood state when tasting food in front of a mirror. Therefore, the ratings of arousal scales from the pre-tasting and post-tasting surveys were analyzed using twotailed paired t-tests. There were no significant differences between the ratings of EA in pre-tasting and post-tasting period (pre-tasting: M = 22.25, SD = 3.53, post-tasting: M = 23.38, SD = 3.07, t(15) = 0.93). There were also no significant differences between the ratings of TA in pre-tasting and post-tasting period (pre-tasting: M = 21.38, SD = 3.36, post-tasting: M = 21.06, SD = 2.38, t(15) = 0.27).
2.1.2.2. Tasting. Before the tasting, participants were told that they would be evaluating the taste of different types of popcorn, and that they could eat as much of the popcorn as they liked. To examine the influence of the presence of a mirror, a rectangular mirror (42 cm × 60 cm) was placed on a desk in the small booth (120 cm × 175 cm) in which the participants sat, at a distance of approximately 40 cm from the participant; the mirror reflected the upper half of the participant's body when he/she sat in front of it (the mirror condition). A 24-in. vertical LED monitor (38 cm × 57 cm) was placed at the same distance as the mirror on the desk in another booth. An image of the wall behind the booth was taken in advance and displayed on the monitor (the wall-reflecting monitor condition). Two types of popcorn were placed in paper bowls on the desk of each booth. They differed in terms of flavor and color: one was salt flavored (Kikuya Co. Ltd., 6 g per bowl, 582 kcal per 100 g) and the other was caramel flavored (Tominaga Boueki Kaisha Ltd., 20 g per bowl, 468 kcal per 100 g). Participants tasted one type of popcorn at a time. Taken together, we introduced four (2 × 2) different conditions into the tasting period in a randomized order. The experimental procedure was as follows: participants went into one of the booths in the experimental room, picked up a white paper bowl that was half-full of popcorn (prepared just before the tasting),
2.3. Discussion Our main finding in Experiment 1 was that the popcorn tasted better and was consumed more when the participants tasted popcorn alone in front of a mirror than in front of a wall-reflecting monitor. This is the first experimental demonstration that eating alone in front of a mirror significantly enhanced the perceived taste of the food as well as the amount of food consumed. Although there has as yet been no study that investigated the effect of a mirror in the literature on social facilitation, several attempts have been made to investigate the behavioral influences of eating in front of 24
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai
Fig. 1. Results from Experiment 1: mean ratings of the goodness of the popcorn and mean consumption ratio. The vertical bars represent the standard errors.
the participants considered popcorn as relatively desirable, even though it was unclear whether popcorn was perceived as healthy food. Present results appear to be similar to those found in studies on the social facilitation of eating with other individuals, which is often attributed to the highlighted mood with others. However, the scores of EA and TA did not deviate from the center of each score range (from 10 to 40 scores), there was no significant increase in mood between before and after the tasting in the present study when participants were eating in front of a mirror, which suggests that the facilitation effect observed herein could not be attributed to the influence of mood. More noteworthy is that this facilitation of eating without the presence of other individuals occurred only when there was dynamic visual information of “someone” eating. Our results suggest that the facilitation of eating in social situations does not necessarily require the presence of another individual, but it does seem to require visual information of “someone” including a mirror-reflected image.
a mirror [25–28]. These studies mainly intended to assess whether a mirror could serve to reduce the consumption of food by showing the participants their own eating behaviors in the mirror [26]. Therefore, studies used undesirable food in terms of health (e.g., fatty food) or anti-obesity and assessed to what extent the food was favorable as well as the consumption of unhealthy food. As expected, eating in front of a mirror suppressed the amount of food consumed in the case of undesirable food [26–28]. For instance, consumption of unhealthy food, such as full-fat cream cheese and margarine, was suppressed in front of a mirror, while consumption of other foods (i.e., reduced-fat and fat-free cream cheese and margarine) was not [26]. The suppression effect was also obtained with obese and non-obese participants by their observing themselves eating chicken soup, which generally seems not to be unhealthy food [25]. However, participants rated the chicken soup as tasting better in front of a mirror [25]. In contrast, previous studies on social facilitation effect of eating did not pay attention to the characteristics of the food, such as its nutrient value and desirability. Therefore, ubiquitous foods, such as popcorn [4], pasta [29], bread [9,30], and cheese [5] were employed. These studies focused on the increment of food consumption in the presence of the other individuals. Although the present study investigated food consumption in front of a mirror, similar to what other studies on food suppression in front a mirror had studied; however, the present study used neither unhealthy food nor unhealthy participants (e.g., obese individual). It focused on the “social influence” by “the other” individual rather than on the desirability of food itself. Interestingly, if the food was desirable or preferable one (i.e., sweet chocolate), the presence of another individual made the food tasty, whereas if the food was unpleasant (i.e., bitter chocolate), the presence of another individual suppressed the likability of the bitter chocolate than when tasting alone [13]. Thus, we hypothesize that eating in front of a mirror may have a twofold effect: If a food is undesirable, eating in front of a mirror would suppress the desire to consume it. On the other hand, if it is a preferable food, the suppression effect would be weak, and eating in front of a mirror would make the food taste better, thus enhancing the consumption of food due to the “social facilitation” effect. In our study, we used popcorn as a food that is “not” undesirable to eat for the purpose of investigating the facilitation effect when participants tasted the food alone in front of a mirror. Actually, the participants' likability ratings for the popcorn while they were seated in front of a mirror were relatively high (overall average was 3.91, with a maximum rating of 6). These ratings were not low even in the monitor condition (overall average was 3.41). Therefore, it may be assumed that
3. Experiment 2 Experiment 1 was not able to determine which aspects of the visual information of eating influence the facilitation effect. The dynamic visual information of the self-image reflected from the mirror may have contributed to the social facilitation effect observed in Experiment 1. To test this, in Experiment 2, we examined whether the social facilitation effect of eating without the presence of others still occurred when a static self-image of the participant is present. 3.1. Material and methods 3.1.1. Participants Twelve elderly adults participated in this study (7 females and 5 males; ages 66–74 years with a mean of 68.9 years; all Japanese). None of the participants met the criteria for dementia (mean = 28.83). All of the participants were naïve to the purpose of the experiment and completed a demographic questionnaire, as in Experiment 1. 3.1.2. Procedure The procedure of Experiment 2 was identical to that of Experiment 1 except for the following: (1) instead of using a mirror, a static image of the participant tasting food (soybeans), taken in advance, was displayed on a 24-in. vertical LED monitor, and (2) the participants tasted only one type of popcorn (caramel flavor). Therefore, there were only two conditions: the static image of the participant tasting food (static self25
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai
Fig. 2. Results from Experiment 2: mean ratings of the goodness of the popcorn and mean consumption ratio. The vertical bars represent the standard errors.
image condition) and the static image of the wall of the booth (wallimage condition, which was identical to the monitor condition in Experiment 1). These were presented in a randomized order to all participants. A bowl of soybean was placed in front of the participants and they could eat soybean as much as they liked.
eating in front of a self-reflection. However, the facilitation effect of eating with a self-reflection might be generalized to other age groups. In this experiment, we validated whether a younger age population would demonstrate a similar effect when eating alone in front of a mirror as shown by elderly adults in Experiment 1.
3.2. Results
4.1. Material and methods
3.2.1. Subjective evaluations of the food We conducted two-tailed paired t-tests to compare participants' ratings and the mean consumption ratios between the static self-image and wall-image conditions. Participants reported that the goodness of the popcorn was significantly higher in the static self-image condition (M = 5.08, SD = 0.90) than in the wall-image condition (M = 4.75, SD = 0.97), t(11) = 2.35, P < 0.05. Furthermore, the mean consumption ratio of the popcorn was significantly higher in the static self-image condition (M = 48.18, SD = 15.02) than in the wall-image condition (M = 40.31, SD = 17.97), t(11) = 3.76, P < 0.05 (Fig. 2). The responses to the other items did not differ across conditions.
4.1.1. Participants Sixteen young adults (5 females and 11 males; ages 20–23 years with an average of 21.5 years; all Japanese) from a local university participated in exchange for partial fulfillment of their course credit. All participants completed a demographic questionnaire assessing their suitability for the study (i.e., good health, no food allergies, no history of eating disorders, and no special dietary restrictions). 4.1.2. Procedure The procedure was identical to that of Experiment 1. 4.2. Results and discussion
3.2.2. Mood The ratings of arousal scales (EA and TA) from the pre-tasting and post-tasting surveys were analyzed using two-tailed paired t-tests. There were no significant differences between the ratings of EA in pre-tasting and post-tasting period (pre-tasting: M = 23.0, SD = 5.08, post-tasting: M = 24.33, SD = 3.96, t(11) = 1.37) and the same is true of TA in pretasting and post-tasting period (pre-tasting: M = 22.08, SD = 5.76, post-tasting: M = 22.25, SD = 4.65, t(11) = 0.18).
4.2.1. Subjective evaluations of food in young adults A two-way ANOVA with the factors of presence of a mirror (mirror vs. monitor) and test food (salt flavored vs. caramel flavored) was used for the analysis. The goodness (F1,15 = 6.04, P < 0.05), quality (F1,15 = 4.47, P < 0.05), and liking (F1,15 = 4.60, P < 0.05) of both types of popcorn in the mirror condition were all significantly higher than in the monitor condition. Furthermore, the quality of the caramel flavored popcorn (F1,15 = 10.04, P < 0.05) was significantly higher than that of the salt flavored popcorn. The mean consumption ratio in the mirror condition was significantly higher than that in the monitor condition (F1,15 = 8.86, P < 0.01). Additionally, the sweetness of the caramel flavored popcorn (F1,15 = 135.12, P < 0.01) was significantly greater than that of the salt flavored popcorn, while the saltiness of the salt flavored popcorn (F1,15 = 23.81, P < 0.01) was significantly higher than that of the caramel flavored one. There were no significant interactions between these factors.
3.3. Discussion Our results indicated that the popcorn tasted better and was eaten more often when participants tasted the popcorn in front of a static selfimage than when in front of a static image of the wall. Here, the static image reflected a participant's past eating behavior rather than the dynamic visual information of eating. These results suggest that the dynamic visual information of eating is not always required for the social facilitation of eating.
4.2.2. Mood in young adults The ratings of arousal scales (EA and TA) before and after the tasting were analyzed using two-tailed paired t-tests. There were no significant differences between the ratings of EA in pre-tasting and posttasting period (pre-tasting: M = 23.81, SD = 1.84, post-tasting: M = 23.31, SD = 2.7, t(15) = 1.04. There were also no significant
4. Experiment 3 Only elderly adults were included as participants in Experiments 1 and 2, which beg the question of whether the findings are specific to the elderly. As noted above, elderly adults may receive a greater benefit of 26
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai
of goodness and saltiness among younger participants may merely reflect their familiarity to this food. More importantly, the mirror led to a facilitation effect of eating in both age groups, indicating that the influence of a self-reflecting mirror is not limited to elderly adults. This suggests that the cognitive abilities required for the social facilitation of eating function independently of those abilities that show age-related declines [32,33]. The fact that this facilitating effect of self-reflection was observed in a broader age range means that the method may be beneficial to many more people, given that eating food is a major source of pleasure in human life [34]. It has been reported that eating together with family members is important for the psychological well-being and avoidance of risk behavior among adolescents [35,36]. Although the effects from Experiment 2 were not replicated by the young adults in this study, we expect that they will show similar results in a static self-image situation. Experiment 2 was conducted to determine the critical factor to produce “social facilitation effect.” For the daily-use purpose, however, the mirror is easier to set up in a room than a large size self-image. Thus, we did not pursue the results of Experiment 2 with the young adults. However, further examination of the mirror effect on adolescents might be performed.
differences between the ratings of TA in pre-tasting and post-tasting period (pre-tasting: M = 21.0, SD = 1.98, post-tasting: M = 21.19, SD = 1.48, t(15) = 0.35). These results of Experiment 3 indicated that the popcorn tasted better and was eaten more when young individuals ate it in front of a mirror than when they ate it in front of a wall-reflecting monitor. These findings confirm that the “social” facilitation effect of eating without others being present occurs among younger adults as well. The next step would be to compare these results with those of the elderly adults from Experiment 1. 4.2.3. Direct comparison between young and elderly adults. To compare the results of the elderly adults (Experiment 1) with those of the young adults (Experiment 3), we combined the data of these two experiments and analyzed them by using a three-way mixed ANOVA with the factors of presence of a mirror (mirror vs. monitor), test food (salt flavored vs. caramel flavored), and age of participants (young vs. elderly). Our results indicated that most ratings of the mirror condition were significantly higher than were those of the monitor condition (goodness: F1,30 = 23.88, P < 0.01; quality: F1,30 = 9.88, P < 0.01; liking: F1,30 = 11.89, P < 0.05; fillingness: F1,30 = 4.62, P < 0.05; mean consumption ratio: F1,30 = 20.24, P < 0.01). Interestingly, we observed no significant interactions between the age groups and presence of the mirror for any of the variables (Fig. 3). The main effect of age was confirmed for the goodness (F1,60 = 10.84, P < 0.01), quality (F1,60 = 5.64, P < 0.05), liking (F1,60 = 6.51, P < 0.05), and saltiness of the popcorn (F1,60 = 6.63, P < 0.05), with the young adults having significantly higher ratings than the elderly adults (Table 1). The sweetness of the caramel flavored popcorn (F1,30 = 285.25, P < 0.01) was significantly higher than that of the salt flavored popcorn. Moreover, there were significant three-way interactions between these factors for the sweetness (F1,30 = 4.64, P < 0.05). The simple main effect of test food was confirmed for all combinations between the factors of presence of a mirror and age of participants. The saltiness of the caramel flavored popcorn (F1,30 = 55.23, P < 0.01) was significantly lower than that of the salt flavored popcorn. These comparisons were conducted as to verify that participants' sense of taste was valid. The results of this comparison indicated only slight differences between the age groups. The young participants rated the popcorn as tasting better and ate more of it than did the elderly participants. It is possible that the different amounts of exposure between young and elderly adults to popcorn might have caused the difference between two age groups, as hardly elderly adults in Japan eat popcorn in their daily life. A previous study indicated that repeated exposure to one food leads to more positive evaluations of that food [31]. Thus, the higher ratings
5. General discussion The most important finding of our study was that the social facilitation of eating was observed when individuals ate alone in front of a mirror or a static image of themselves eating. These findings suggest that the facilitation of eating does not require the presence of another individual. Rather, static visual information of “someone” eating food is sufficient to produce the “social” facilitation of eating. The present findings do not exclude the potential contribution of other social factors in real-life situations because a number of psychological processes could contribute to the occurrence of an eating facilitation effect [9]. Although the existence of the mirror or the static photograph of themselves eating did not affect the subjective saltiness and sweetness of the popcorn in this study, It is possible that the basic taste perception might be influenced more by information present in social relationships or interpersonal communications. Future research would be necessary to extend the current results into more externally valid situations, and it will also be important to consider how other social factors relate to the perceived goodness of the food. The relationship between the facilitation effect observed herein and other non-social environmental factors that influence food evaluations and food consumption [37] must also be investigated. Interestingly, most studies focusing on the social facilitation of eating have given little attention to subjective changes in food taste as opposed to the consumption of the food; a prominent aspect of the social facilitation of eating is that eating with others leads people to eat more [2]. In contrast, the results of our study—particularly those concerning effect
Fig. 3. Mean ratings for goodness of the popcorn and mean consumption ratio among elderly adults (Experiment 1) and young adults (Experiment 3). The vertical bars represent the standard errors.
27
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai
Table 1 Summary of mean ratings of the popcorn and mean consumption ratio in Experiments 1–3. Experiment 1
Experiment 2
Experiment 3
Elderly
Elderly
Young
Caramel
Salt
Salt
Goodness Quality Liking Fillingness Saltiness Sweetness Bitterness Consumptions
Caramel
Caramel
Mirror
Monitor
Mirror
Monitor
Mirror
Monitor
Mirror
Monitor
Mirror
Monitor
3.94 (0.32) 3.13 (0.34) 3.50 (0.38) 3.56 (0.24) 3.63 (0.31) 2.19 (0.25) 1.63 (0.13) 39.80 (5.98)
3.25 (0.36) 2.94 (0.31) 3.12 (0.34) 3.38 (0.33) 3.44 (0.41) 1.75 (0.23) 1.56 (0.16) 34.89 (4.78)
4.38 (0.29) 3.88 (0.20) 4.32 (0.34) 3.89 (0.29) 1.88 (0.30) 4.82 (0.32) 1.31 (0.19) 35.47 (3.83)
3.88 (0.32) 3.25 (0.30) 3.69 (0.34) 3.81 (0.31) 1.88 (0.29) 5.13 (0.18) 1.56 (0.22) 26.16 (2.54)
5.08 (0.26) 4.08 (0.38) 4.75 (0.28) 4.00 (0.28) 1.42 (0.19) 4.92 (0.19) 1.25 (0.13) 48.18 (4.38)
4.75 (0.28) 4.25 (0.28) 4.41 (0.34) 4.25 (0.22) 1.50 (0.19) 4.92 (0.26) 1.58 (0.26) 40.32 (5.19)
4.94 (0.19) 3.75 (0.19) 4.50 (0.26) 3.88 (0.26) 4.63 (0.18) 1.88 (0.22) 1.31 (0.15) 43.23 (6.71)
4.38 (0.20) 3.50 (0.22) 4.25 (0.28) 3.31 (0.27) 4.31 (0.24) 2.06 (0.27) 1.44 (0.20) 30.42 (3.76)
5.06 (0.17) 4.44 (0.20) 4.81 (0.19) 4.25 (0.25) 2.63 (0.40) 5.31 (0.25) 1.56 (0.18) 40.13 (3.57)
4.69 (0.20) 4.06 (0.19) 4.25 (0.27) 4.06 (0.32) 2.75 (0.37) 5.31 (0.15) 1.69 (0.25) 33.31 (3.08)
Values are presented in means (SE).
cantly greater differences in the popcorn goodness ratings between eating in front of the mirror and eating in front of the wall-reflecting monitor (salt flavor popcorn: elderly adults showing a tendency to eat alone: M = 0.75, SD = 0.89, and elderly adults not showing this tendency, M = 0.63, SD = 0.52), t(14) = 0.34, n.s.; caramel flavor popcorn: elderly adults showing a tendency to eat alone M = 0.38, SD = 0.74, and elderly adults not showing this tendency M = 0.63, SD = 0.74, t(14) = 0.67, n.s). Thus, the facilitation of eating without the presence of others may occur regardless of individuals' experiences of eating alone in daily life. Further studies focused on the frequencies of daily social eating will be needed to confirm this. The significant changes in mood are often observed when people eat together in company [8,10,11]. However, throughout the experiments, eating with the presence of self-image did not significantly affect the mood. The social facilitation of eating would not be always attributed to the elevation of the mood. The present findings provided us the opportunity to understand an important aspect of the social facilitation of eating. Similar results might be observed for other social facilitation phenomena involving coaction effects (e.g., size perception [42], motor performance [43], and attention [44]). Given that these facilitations might also occur without the actual existence of others, our findings might be helpful in understanding the true nature of social facilitation and co-action effects beyond those related to eating.
of the self-reflection on goodness and consumption ratio of the popcorn—suggested that both subjective evaluations and actual consumption of food can be simultaneously facilitated. It is likely that subjective evaluations of food are an important aspect of the social facilitation of eating, and must be examined to tell us the nature of the facilitation effect. Further studies are needed to understand the underlying mechanisms for each facilitation (e.g., whether these facilitation effects occur independently or are in some way correlated [2]). It should be noted that only self-images were used in this study. Thus, we cannot rule out the possibility that our use of a static image of the participants themselves may have had some influence on the facilitation effect (e.g., familiarity). In a future study, one must examine whether the facilitation of eating with static images is replicated by using static images of another person as well. It is essential to control various social factors, which may influence eating behavior when eating with other individuals, such as social modeling and the social norms of eating [38]. In this study, all the self-images reflected eating behaviors. It is unclear whether “eating” images are crucial to produce the “social” facilitation effect of eating. A future investigation would be determining whether the mere presence of themselves lead to a facilitation effect of eating, even when they does not eat anything (i.e., audience effect [39]), There is good evidence indicating that eating in the presence of a non-eating observer can make the food taste worse [13] and suppress individuals' actual consumption [40]. Therefore, a presentation of static image of another individual's non-eating action may produce the opposite pattern of the results in Experiment 2. The social facilitation of eating in situations of eating together has been often referred to as an example of so-called “co-action effects,” which arise when individuals simultaneously engage in an activity with others [39]. Interestingly, previous studies have shown that thinking about events related to food (e.g., imagining that someone prepared your food kindly) has been found to improve that food's taste [41]. It may be that individuals' mental representations of co-eating are more important for the facilitation effect of eating than are perceptual cues of that co-eating. Therefore, one possibility is to assume that the visual information of “eating” food is an important aspect of the social facilitation of eating. We must also examine the contribution of the familiarity of the situation of eating alone to the observed facilitation effect. We asked elderly adults who participated in Experiment 1 whether they had a tendency to eat alone for their daily meals. About half of the elderly individuals (i.e. 8 out of the 16 participants) answered that they more often ate alone than with others for everyday meals. Furthermore, more elderly individuals answered that they had a tendency to eat alone compared to the young adults in Experiment 3 (where only 4 out of the 16 participants had such a tendency). On the other hand, a tendency to eat alone among elderly individuals was not associated with signifi-
Conflict of interest All authors declare that there is no conflict of interest. Funding This study was supported by JSPS KAKENHI Grant Number JP15k16230 and JP17k12918. Acknowledgements We thank Shota Watanabe for his support in data acquisition and Dr. Namiko Kubo-Kawai for her critical reading of the manuscript. References [1] F. Bellisle, A.M. Dalix, Cognitive restraint can be offset by distraction, leading to increased meal intake in women, Am. J. Clin. Nutr. 74 (2001) 197–200 (PMID: 11470720). [2] C.P. Herman, The social facilitation of eating. A review, Appetite 86 (2015) 61–73, http://dx.doi.org/10.1016/j.appet.2014.09.016 (PMID: 25265153). [3] J.M. de Castro, E.S. de Castro, Spontaneous meal patterns of humans: influence of the presence of other people, Am. J. Clin. Nutr. 50 (1989) 237–247, http://dx.doi. org/10.1016/0031-9384(86)90128-9 (PMID: 2756911).
28
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai [4] B. Wansink, S.B. Park, At the movies. How external cues and perceived taste impact consumption volume, Food Qual. Prefer. 12 (2001) 69–74, http://dx.doi.org/10. 1016/S0950-3293(00)00031-8. [5] V.I. Clendenen, C.P. Herman, J. Polivy, Social facilitation of eating among friends and strangers, Appetite 23 (1994) 1–13, http://dx.doi.org/10.1006/appe.1994. 1030 (PMID: 7826053). [6] S.C. King, H.L. Meiselman, A.W. Hottenstein, T.M. Work, V. Cronk, The effect of contextual variables on food acceptability: a confirmatory study, Food Qual. Prefer. 18 (2007) 58–65, http://dx.doi.org/10.1016/j.foodqual.2005.07.014. [7] R.F. Baumeister, M.R. Leary, The need to belong: desire for interpersonal attachments as a fundamental human motivation, Psychol. Bull. 117 (1995) 497–529, http://dx.doi.org/10.1037/0033-2909.117.3.497 (PMID: 7777651). [8] M.M. Hetherington, Cues to overeat: psychological factors influencing overconsumption, Proc. Nutr. Soc. 66 (2007) 113–123, http://dx.doi.org/10.1017/ S0029665107005344 (PMID: 17343777). [9] M.M. Hetherington, A.S. Anderson, G.N.M. Norton, L. Newson, Situational effects on meal intake: a comparison of eating alone and eating with others, Physiol. Behav. 88 (2006) 498–505, http://dx.doi.org/10.1016/j.physbeh.2006.04.025 (PMID: 16757007). [10] K.A. Patel, D.G. Schlundt, Impact of moods and social context on eating behavior, Appetite 36 (2001) 111–118, http://dx.doi.org/10.1006/appe.2000.0385 (PMID: 11237346). [11] W. Sommer, B. Stürmer, O. Shmuilovich, M. Martin-Loeches, A. Schacht, How about lunch? Consequences of the meal context on cogntion and emotion, PLOS ONE 8 (2013) e70314, http://dx.doi.org/10.1371/journal.pone.0070314 (PMID: 23936184). [12] S.J. Salvy, M. Howard, M. Read, E. Mele, The presence of friends increases food intake in youth, Am. J. Clin. Nutr. 90 (2009) 282–287, http://dx.doi.org/10.3945/ ajcn.2009.27658 (PMID: 19535431). [13] E.J. Boothby, M.S. Clark, J.A. Bargh, Shared experiences are amplified, Psycol. Sci. 25 (2015) 2209–2216, http://dx.doi.org/10.1177/0956797614551162 (PMID: 25274583). [14] L. Miller, P. Rozin, P.F. Alan, Food sharing and feeding another person suggest intimacy; two studies of American college students, Eur. J. Soc. Psychol. 28 (1998) 423–436, http://dx.doi.org/10.1002/(SICI)1099-0992(199805/06) 28:3<423::AID-EJSP874>3.0.CO;2-V. [15] K.M. Kniffin, B. Wansink, It's not just lunch: extra-pair commensality can trigger sexual jealousy, PLOS ONE 7 (2012) e40445, http://dx.doi.org/10.1371/journal. pone.0040445 (PMID: 22792327). [16] K.M. Kniffin, B. Wansink, C.M. Devine, J. Sobal, Eating together at the firehouse: how workplace commensality relates to the performance of firefighters, Hum Perform. 28 (2015) 281–306, http://dx.doi.org/10.1080/08959285.2015.1021049 (PMID: 27226698). [17] N. Sakai, The psychology of eating from the point of view of experimental, social, and applied psychology, Psychol. Russia 7 (2014) 14–22, http://dx.doi.org/10. 11621/pir.2014.0102. [18] L.I. Vailas, S.A. Nitzke, M. Becker, J. Gast, Risk indicators for malnutrition are associated inversely with quality of life for participants in meal programs for older adults, J. Am. Diet. Assoc. 98 (1998) 548–553, http://dx.doi.org/10.1016/S00028223(98)00123-0 (PMID: 9597027). [19] Y. Tani, Y. Sasaki, M. Haseda, K. Kondo, N. Kondo, Eating alone and depression in older men and women by cohabituation status: the JAGES longitudinal survey, Age Ageing 44 (2015) 1019–1026, http://dx.doi.org/10.1093/ageing/afv145 (PMID: 26504120). [20] L.M. Donini, C. Savina, C. Cannella, Eating habits and appetite control in the elderly: the anorexia of aging, Int. Psychogeriatr. 15 (2003) 73–87, http://dx.doi. org/10.1017/S1041610203008779 PMID: 12834202). [21] Y. Imai, K. Hasegawa, The revised Hasegawa's dementia scale (HDS-R) –evaluation of its usefulness as a screening test for dementia, J. Hong Kong Coll. Psychiatr. 4 (1994) 22–24. [22] S. Shirasawa, T. Ishida, Y. Hakoda, M. Haraguchi, The effects of energetic arousal on memory search, Jpn. J. Psychon. Sci. 17 (1999) 93–99 (in Japanese). [23] G. Matthews, D.M. Jones, A.G. Chamberlain, Refining the measurement of mood:
[24] [25] [26]
[27] [28] [29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39] [40]
[41]
[42]
[43]
[44]
29
the UWIST mood adjective checklist, Br. J. Psychol. 81 (1990) 17–42, http://dx.doi. org/10.1111/j.2044-8295.1990.tb02343.x. R.E. Thayer, Toward a psychological theory of multidimensional activation (arousal), Motiv. Emot. 2 (1978) 1–34, http://dx.doi.org/10.1007/BF00992729. P. Pliner, G. Iuppa, Effects of increasing awareness on food consumption in obese and normal weight subjects, Addict. Behav. 3 (1978) 19–24. S.M. Sentyrz, B.J. Bushman, Mirror, mirror on the wall, who's the thinnest one of all? Effect of self-awareness on consumption of full-fat, reduced-fat, and no-fat products, J. Appl. Psychol. 83 (1998) 944–949. A. Alawad, Y. Mahgoub, F. Yousef, The mirror, as a self-awareness enhancing tool, which can modify food consumption behaviors, J. Nat. Sci. Res. 5 (2015) 90–95. A. Jami, Healthy reflections: the influence of mirror induced self-awareness on taste perceptions, J. Assoc. Consum. Res. 1 (2016) 57–70. J. Koh, P. Pliner, The effects of degree of acquaintance, plate size, and sharing on food intake, Appetite 52 (2009) 595–602, http://dx.doi.org/10.1016/j.appet.2009. 02.004 (PMID: 19501755). J.Y. Kim, H.R. Kissileff, The effect of social setting on response to a preloading manipulation in non-obese women and men, Appetite 27 (1996) 25–40, http://dx. doi.org/10.1016/appe.1996.0031 (PMID: 8879417). P. Pliner, The effects of mere exposure on liking for edible substances, Appetite 3 (1982) 283–290, http://dx.doi.org/10.1016/S0195-6663(82)80026-3 (PMID: 7159080). E.A. Kensinger, A.H. Gutchess, Cognitive aging in a social and affective context: advances over the past 50 years, J. Gerontol. B Psychol. Sci. Soc. Sci. (2016), http:// dx.doi.org/10.1093/geronb/gbw056 (PMID: 27233290). C.T. Salthouse, Selective review of cognitive aging, J. Int. Neuropsychol. Soc. 16 (2010) 754–760, http://dx.doi.org/10.1017/S1355617710000706 (PMID: 20673381). P. Rozin, Towards a psychology of food and eating: from motivation to module to model to marker, morality, meaning, and metaphor, Curr. Dir. Psychol. Sci. 5 (1996) 18–24, http://dx.doi.org/10.1111/1467-8721.ep10772690. M.E. Eisenberg, R.E. Olson, D. Neumark-Sztainer, M. Story, L.H. Bearinger, Correlations between family meals and psychosocial well-being among adolescents, Arch. Pediatr. Adolesc. Med. 158 (2004) 792–796, http://dx.doi.org/10.1001/ archpedi.158.8.792 (PMID: 15289253). D.L. Franko, D. Thompson, S.G. Affenito, B.A. Barton, R.H. Striegel-Moore, What mediates the relationship between family meals and adolescent health issues? Health Psychol. 27 (2008) S109–S117, http://dx.doi.org/10.1037/0278-6133.27. 2(suppl.)S109 (PMID: 18377152). C. Space, V. Harrar, B. Piqueras-Fiszman, Assessing the impact of the tableware and other contextual variables on multisensory flavour perception, Flavour 1 (2012) 7, http://dx.doi.org/10.1186/2044-7248-1-7. T. Cruwys, K.E. Bevelander, R.C.J. Hermans, Social modeling of eating: a review of when and why social influence affects food intake ad choice, Appetite 86 (2015) 3–18, http://dx.doi.org/10.1016/j.appet.2014.08.035 (PMID: 25174571). R.B. Zajonc, Social facilitation, Science 149 (1965) 269–274, http://dx.doi.org/10. 1126/science.149.3681.269 (PMID: 14300526). D.A. Roth, C.P. Herman, J. Polivy, P. Pliner, Self-presentational conflict in social eating situations: a normative perspective, Appetite 36 (2001) 165–171, http://dx. doi.org/10.1006/appe.2000.0338 (PMID: 11237352). K. Gray, The power of good intentions: perceived benevolence soothes pain, increases pleasure, and improve taste, Soc. Psychol. Pers. Sci. 3 (2012) 639–645, http://dx.doi.org/10.1177/1948550611433470. T. Garcia-Marques, A. Fernandes, M. Prada, R. Fonseca, S. Haga, Seeing the big: size perception is more context sensitive in the presence of others, PLOS ONE 10 (2015) e0141992, http://dx.doi.org/10.1371/journal.pone.0141992 (PMID: 26562518). C. Anderson-Hanley, A.L. Snyder, J.P. Nimon, P.J. Arciero, Social facilitation in virtual reality-enhanced exercise: competitiveness moderates exercise effort of older adults, Clin. Interv. Aging 6 (2011) 275–280, http://dx.doi.org/10.2147/CIA. S25337 (PMID: 22087067). D. Muller, F. Butera, The focusing effect of self-evaluation threat in coaction and social comparison, J. Pers. Soc. Psychol. 93 (2007) 194–211, http://dx.doi.org/10. 1037/0022-3514.93.2.194 (PMID: 17645395).
Contents lists available at ScienceDirect
Physiology & Behavior journal homepage: www.elsevier.com/locate/physbeh
The “social” facilitation of eating without the presence of others: Selfreflection on eating makes food taste better and people eat more
MARK
Ryuzaburo Nakata, Nobuyuki Kawai⁎ Graduate School of Information Science, Nagoya University, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Social facilitation Mirror Eating with others Eating alone Elderly adults
Food tastes better and people eat more of it when eaten with company than alone. Although several explanations have been proposed for this social facilitation of eating, they share the basic assumption that this phenomenon is achieved by the existence of co-eating others. Here, we demonstrate a similar “social” facilitation of eating in the absence of other individuals. Elderly participants tasted a piece of popcorn alone while in front of a mirror (which reflects the participant themselves eating popcorn) or in front of a wall-reflecting monitor, and were found to eat more popcorn and rate it better tasting in the self-reflecting condition than in the monitor condition. Similar results were found for younger adults. The results suggest that the social facilitation of eating does not necessarily require the presence of another individual. Furthermore, we observed a similar “social” facilitation of eating even when participants ate a piece of popcorn in front of a static picture of themselves eating, suggesting that static visual information of “someone” eating food is sufficient to produce the “social” facilitation of eating.
1. Introduction Human behaviors are influenced by the presence of others. For instance, people rate food as tasting better [1] and eat much more of it [2] when another individual is present than when eating alone. This facilitation effect has been well documented in a wide variety of situations [3–6] and is referred to as the “social facilitation of eating”. Several explanations have been proposed for this phenomenon [2]. One line of thinking concerns positive mood—when people eat together in company, they typically communicate with each other and experience social bonding [7], which helps them feel comfortable and relax [8,9]; these positive changes in mood or atmosphere, in turn, lead to the social facilitation of eating [8,10,11]. The quality of the social relationships with others is also considered an important factor for such facilitation. When the other individuals present during meals are friends or family members, people tend to consume more food than when these others are strangers [5,8,12]. Recently, attempts have been made to show results that are contrary to what previous studies have propounded on social facilitation. For example, chocolate was judged as more likeable and flavorful when two unfamiliar participants tasted it together even though they did not have any communication with each other [13]. Mood changes also did not seem to contribute to this facilitation effect. Therefore, social communication among people and mood changes in the situation do not appear to be necessary for the occurrence of social facilitation of eating. This
⁎
drives us to the question what is the minimum requirement for this effect to occur. One possibility is that the physical presence of another individual is sufficient for the occurrence of social facilitation of eating. Another is that information suggesting presence of other individuals may be enough to induce the social facilitation effect. However, no studies have ever questioned whether the presence of another individual is in fact necessary for producing the “social” facilitation of eating. This may be because presence of other individuals is usually treated as a basic premise for producing the social facilitation of eating, primarily because this facilitation has only been observed when an individual eats together with other individuals [2]. The aim of this study was to analyze and answer this question. We hypothesized that the social facilitation of eating would occur without the actual presence of other individuals. Eating with others is ubiquitous for many people. It has been found to strengthen the social bonds between individuals [14,15] and thereby enhance team performance [16]. However, at present, numerous elderly adults eat alone in Japan [17]. Research has shown that the quality of life of elderly adults is associated with food enjoyment [18] and a high frequency of eating alone in elderly adults is associated with depression [19] and loss of appetite [20]. If elderly adults exhibit a social facilitation of eating when eating in front of a mirror, this setting could be used to promote their quality of life. From this point of view, we recruited elderly individuals in both Experiment 1 and Experiment 2.
Corresponding author at: Graduate School of Information Science, Nagoya University, Furocho, Chikusaku, Nagoya 464-8601, Japan. E-mail address: [email protected] (N. Kawai).
http://dx.doi.org/10.1016/j.physbeh.2017.05.022 Received 28 February 2017; Received in revised form 27 April 2017; Accepted 17 May 2017 Available online 19 May 2017 0031-9384/ © 2017 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai
2. Experiment 1
and, after an alarm call signaled the beginning of the tasting period, began to taste the popcorn while alone in the booth. The tasting period lasted for 90 s. After another alarm call signaling the end of the tasting period, they completed a short questionnaire indicating their subjective evaluations of the popcorn. The participants then began a new condition with new popcorn. The short questionnaire contained a number of questions in Japanese assessed on a 6-point scale (from “not at all” to “extremely”) that reflected participants' subjective evaluations of the popcorn: “How good is this popcorn?” “How do you feel about the quality of the popcorn?” “How much do you like this popcorn?” “How filling is the popcorn?” “How salty is this popcorn?” “How sweet is this popcorn?” and “How bitter is this popcorn?” We also calculated the consumption ratio of each bowl of popcorn by subtracting the ratio of the quantity of the remaining popcorn from its initial quantity ratio (i.e., 100%).
To test the prediction, we set up an experiment (Experiment 1) wherein individuals ate alone in front of a mirror. In this situation, the mirror would reflect the individuals themselves eating food, thus giving them the objective visual information of an eating behavior when the individual is in fact eating alone. 2.1. Material and methods 2.1.1. Participants Sixteen elderly adults (5 females and 11 males; aged 65–74 years with a mean of 68.4; all Japanese) recruited by a job placement agency for elderly adults participated in exchange for a cash incentive. We verified that all participants had normal cognitive status before the experiment by using the Revised Hasegawa's Dementia Scale (HDS-R) [21]. None of the participants met the criteria for dementia (i.e., a score of 20 or less as suggestive of dementia; mean for this sample = 28.56). We also confirmed that all participants were naïve to the purpose of the experiment and had them complete a demographic questionnaire assessing their suitability for the study—namely, that they had good health, no food allergies, no history of eating disorders, and no special dietary restrictions.
2.1.3. Ethics statement The protocols of all of the experiments in this study accorded with the Declaration of Helsinki and were approved by the Ethics Committee of the Graduate School of Information Science at Nagoya University. Written informed consent was obtained before participation. 2.2. Results 2.2.1. Subjective evaluations of the food Participants' ratings of the popcorn and consumption ratio in each condition were analyzed using a two-way analysis of variance (ANOVA) with the factors of the presence of a mirror (mirror vs. monitor) and test food (salt flavored vs. caramel flavored). The results indicated that the goodness (F1,15 = 32.43, P < 0.01), quality (F1,15 = 5.21, P < 0.05), and liking (F1,15 = 10.00, P < 0.01) of the popcorn were all significantly higher in the mirror condition than in the monitor condition. The mean consumption ratio in the mirror condition was also significantly greater than that in the monitor condition (F1,15 = 15.40, P < 0.01; Fig. 1). The sweetness of the caramel flavored popcorn (F1,15 = 154.29, P < 0.01) was significantly higher than that of the salt flavored popcorn. Furthermore, the saltiness of the caramel flavored popcorn (F1,15 = 34.01, P < 0.01) was significantly lower than that of the salt flavored popcorn. These comparisons were conducted as to verify that participants' sense of taste was valid.
2.1.2. Procedure The experiment comprised 3 consecutive phases: pre-tasting survey, tasting, and post-tasting survey. 2.1.2.1. Pre-tasting and post-tasting surveys. The pre-tasting and posttasting surveys were presented before and after the tasting period, respectively. The Japanese version [22] of UWIST (University of Wales Institute of Science and Technology) Mood Adjective Checklist (UMACL) [23] was used to assess participants' mood states. It comprises 20 items that participants must rate in terms of their applicability to participants' present mood on a 4-point scale (from 1 = “definitely not” to 4 = “definitely”). In this checklist, two independent factors were provided. The scores of the specific 10 items (e.g., active) composed energetic arousal (EA) and those of the other 10 items (e.g., nervous) composed tense arousal (TA). Each score ranged from 10 to 40. The combination of these two factors structured mood dimension. For example, higher energetic arousal and lower tense arousal indicated the increase of pleasant mood (positive mood) [22–24].
2.2.2. Mood Participants rated their mood state before and after tasting in terms of the two independent scores (EA and TA). Our special interest here was to assess whether there were any changes in their mood state when tasting food in front of a mirror. Therefore, the ratings of arousal scales from the pre-tasting and post-tasting surveys were analyzed using twotailed paired t-tests. There were no significant differences between the ratings of EA in pre-tasting and post-tasting period (pre-tasting: M = 22.25, SD = 3.53, post-tasting: M = 23.38, SD = 3.07, t(15) = 0.93). There were also no significant differences between the ratings of TA in pre-tasting and post-tasting period (pre-tasting: M = 21.38, SD = 3.36, post-tasting: M = 21.06, SD = 2.38, t(15) = 0.27).
2.1.2.2. Tasting. Before the tasting, participants were told that they would be evaluating the taste of different types of popcorn, and that they could eat as much of the popcorn as they liked. To examine the influence of the presence of a mirror, a rectangular mirror (42 cm × 60 cm) was placed on a desk in the small booth (120 cm × 175 cm) in which the participants sat, at a distance of approximately 40 cm from the participant; the mirror reflected the upper half of the participant's body when he/she sat in front of it (the mirror condition). A 24-in. vertical LED monitor (38 cm × 57 cm) was placed at the same distance as the mirror on the desk in another booth. An image of the wall behind the booth was taken in advance and displayed on the monitor (the wall-reflecting monitor condition). Two types of popcorn were placed in paper bowls on the desk of each booth. They differed in terms of flavor and color: one was salt flavored (Kikuya Co. Ltd., 6 g per bowl, 582 kcal per 100 g) and the other was caramel flavored (Tominaga Boueki Kaisha Ltd., 20 g per bowl, 468 kcal per 100 g). Participants tasted one type of popcorn at a time. Taken together, we introduced four (2 × 2) different conditions into the tasting period in a randomized order. The experimental procedure was as follows: participants went into one of the booths in the experimental room, picked up a white paper bowl that was half-full of popcorn (prepared just before the tasting),
2.3. Discussion Our main finding in Experiment 1 was that the popcorn tasted better and was consumed more when the participants tasted popcorn alone in front of a mirror than in front of a wall-reflecting monitor. This is the first experimental demonstration that eating alone in front of a mirror significantly enhanced the perceived taste of the food as well as the amount of food consumed. Although there has as yet been no study that investigated the effect of a mirror in the literature on social facilitation, several attempts have been made to investigate the behavioral influences of eating in front of 24
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai
Fig. 1. Results from Experiment 1: mean ratings of the goodness of the popcorn and mean consumption ratio. The vertical bars represent the standard errors.
the participants considered popcorn as relatively desirable, even though it was unclear whether popcorn was perceived as healthy food. Present results appear to be similar to those found in studies on the social facilitation of eating with other individuals, which is often attributed to the highlighted mood with others. However, the scores of EA and TA did not deviate from the center of each score range (from 10 to 40 scores), there was no significant increase in mood between before and after the tasting in the present study when participants were eating in front of a mirror, which suggests that the facilitation effect observed herein could not be attributed to the influence of mood. More noteworthy is that this facilitation of eating without the presence of other individuals occurred only when there was dynamic visual information of “someone” eating. Our results suggest that the facilitation of eating in social situations does not necessarily require the presence of another individual, but it does seem to require visual information of “someone” including a mirror-reflected image.
a mirror [25–28]. These studies mainly intended to assess whether a mirror could serve to reduce the consumption of food by showing the participants their own eating behaviors in the mirror [26]. Therefore, studies used undesirable food in terms of health (e.g., fatty food) or anti-obesity and assessed to what extent the food was favorable as well as the consumption of unhealthy food. As expected, eating in front of a mirror suppressed the amount of food consumed in the case of undesirable food [26–28]. For instance, consumption of unhealthy food, such as full-fat cream cheese and margarine, was suppressed in front of a mirror, while consumption of other foods (i.e., reduced-fat and fat-free cream cheese and margarine) was not [26]. The suppression effect was also obtained with obese and non-obese participants by their observing themselves eating chicken soup, which generally seems not to be unhealthy food [25]. However, participants rated the chicken soup as tasting better in front of a mirror [25]. In contrast, previous studies on social facilitation effect of eating did not pay attention to the characteristics of the food, such as its nutrient value and desirability. Therefore, ubiquitous foods, such as popcorn [4], pasta [29], bread [9,30], and cheese [5] were employed. These studies focused on the increment of food consumption in the presence of the other individuals. Although the present study investigated food consumption in front of a mirror, similar to what other studies on food suppression in front a mirror had studied; however, the present study used neither unhealthy food nor unhealthy participants (e.g., obese individual). It focused on the “social influence” by “the other” individual rather than on the desirability of food itself. Interestingly, if the food was desirable or preferable one (i.e., sweet chocolate), the presence of another individual made the food tasty, whereas if the food was unpleasant (i.e., bitter chocolate), the presence of another individual suppressed the likability of the bitter chocolate than when tasting alone [13]. Thus, we hypothesize that eating in front of a mirror may have a twofold effect: If a food is undesirable, eating in front of a mirror would suppress the desire to consume it. On the other hand, if it is a preferable food, the suppression effect would be weak, and eating in front of a mirror would make the food taste better, thus enhancing the consumption of food due to the “social facilitation” effect. In our study, we used popcorn as a food that is “not” undesirable to eat for the purpose of investigating the facilitation effect when participants tasted the food alone in front of a mirror. Actually, the participants' likability ratings for the popcorn while they were seated in front of a mirror were relatively high (overall average was 3.91, with a maximum rating of 6). These ratings were not low even in the monitor condition (overall average was 3.41). Therefore, it may be assumed that
3. Experiment 2 Experiment 1 was not able to determine which aspects of the visual information of eating influence the facilitation effect. The dynamic visual information of the self-image reflected from the mirror may have contributed to the social facilitation effect observed in Experiment 1. To test this, in Experiment 2, we examined whether the social facilitation effect of eating without the presence of others still occurred when a static self-image of the participant is present. 3.1. Material and methods 3.1.1. Participants Twelve elderly adults participated in this study (7 females and 5 males; ages 66–74 years with a mean of 68.9 years; all Japanese). None of the participants met the criteria for dementia (mean = 28.83). All of the participants were naïve to the purpose of the experiment and completed a demographic questionnaire, as in Experiment 1. 3.1.2. Procedure The procedure of Experiment 2 was identical to that of Experiment 1 except for the following: (1) instead of using a mirror, a static image of the participant tasting food (soybeans), taken in advance, was displayed on a 24-in. vertical LED monitor, and (2) the participants tasted only one type of popcorn (caramel flavor). Therefore, there were only two conditions: the static image of the participant tasting food (static self25
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai
Fig. 2. Results from Experiment 2: mean ratings of the goodness of the popcorn and mean consumption ratio. The vertical bars represent the standard errors.
image condition) and the static image of the wall of the booth (wallimage condition, which was identical to the monitor condition in Experiment 1). These were presented in a randomized order to all participants. A bowl of soybean was placed in front of the participants and they could eat soybean as much as they liked.
eating in front of a self-reflection. However, the facilitation effect of eating with a self-reflection might be generalized to other age groups. In this experiment, we validated whether a younger age population would demonstrate a similar effect when eating alone in front of a mirror as shown by elderly adults in Experiment 1.
3.2. Results
4.1. Material and methods
3.2.1. Subjective evaluations of the food We conducted two-tailed paired t-tests to compare participants' ratings and the mean consumption ratios between the static self-image and wall-image conditions. Participants reported that the goodness of the popcorn was significantly higher in the static self-image condition (M = 5.08, SD = 0.90) than in the wall-image condition (M = 4.75, SD = 0.97), t(11) = 2.35, P < 0.05. Furthermore, the mean consumption ratio of the popcorn was significantly higher in the static self-image condition (M = 48.18, SD = 15.02) than in the wall-image condition (M = 40.31, SD = 17.97), t(11) = 3.76, P < 0.05 (Fig. 2). The responses to the other items did not differ across conditions.
4.1.1. Participants Sixteen young adults (5 females and 11 males; ages 20–23 years with an average of 21.5 years; all Japanese) from a local university participated in exchange for partial fulfillment of their course credit. All participants completed a demographic questionnaire assessing their suitability for the study (i.e., good health, no food allergies, no history of eating disorders, and no special dietary restrictions). 4.1.2. Procedure The procedure was identical to that of Experiment 1. 4.2. Results and discussion
3.2.2. Mood The ratings of arousal scales (EA and TA) from the pre-tasting and post-tasting surveys were analyzed using two-tailed paired t-tests. There were no significant differences between the ratings of EA in pre-tasting and post-tasting period (pre-tasting: M = 23.0, SD = 5.08, post-tasting: M = 24.33, SD = 3.96, t(11) = 1.37) and the same is true of TA in pretasting and post-tasting period (pre-tasting: M = 22.08, SD = 5.76, post-tasting: M = 22.25, SD = 4.65, t(11) = 0.18).
4.2.1. Subjective evaluations of food in young adults A two-way ANOVA with the factors of presence of a mirror (mirror vs. monitor) and test food (salt flavored vs. caramel flavored) was used for the analysis. The goodness (F1,15 = 6.04, P < 0.05), quality (F1,15 = 4.47, P < 0.05), and liking (F1,15 = 4.60, P < 0.05) of both types of popcorn in the mirror condition were all significantly higher than in the monitor condition. Furthermore, the quality of the caramel flavored popcorn (F1,15 = 10.04, P < 0.05) was significantly higher than that of the salt flavored popcorn. The mean consumption ratio in the mirror condition was significantly higher than that in the monitor condition (F1,15 = 8.86, P < 0.01). Additionally, the sweetness of the caramel flavored popcorn (F1,15 = 135.12, P < 0.01) was significantly greater than that of the salt flavored popcorn, while the saltiness of the salt flavored popcorn (F1,15 = 23.81, P < 0.01) was significantly higher than that of the caramel flavored one. There were no significant interactions between these factors.
3.3. Discussion Our results indicated that the popcorn tasted better and was eaten more often when participants tasted the popcorn in front of a static selfimage than when in front of a static image of the wall. Here, the static image reflected a participant's past eating behavior rather than the dynamic visual information of eating. These results suggest that the dynamic visual information of eating is not always required for the social facilitation of eating.
4.2.2. Mood in young adults The ratings of arousal scales (EA and TA) before and after the tasting were analyzed using two-tailed paired t-tests. There were no significant differences between the ratings of EA in pre-tasting and posttasting period (pre-tasting: M = 23.81, SD = 1.84, post-tasting: M = 23.31, SD = 2.7, t(15) = 1.04. There were also no significant
4. Experiment 3 Only elderly adults were included as participants in Experiments 1 and 2, which beg the question of whether the findings are specific to the elderly. As noted above, elderly adults may receive a greater benefit of 26
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai
of goodness and saltiness among younger participants may merely reflect their familiarity to this food. More importantly, the mirror led to a facilitation effect of eating in both age groups, indicating that the influence of a self-reflecting mirror is not limited to elderly adults. This suggests that the cognitive abilities required for the social facilitation of eating function independently of those abilities that show age-related declines [32,33]. The fact that this facilitating effect of self-reflection was observed in a broader age range means that the method may be beneficial to many more people, given that eating food is a major source of pleasure in human life [34]. It has been reported that eating together with family members is important for the psychological well-being and avoidance of risk behavior among adolescents [35,36]. Although the effects from Experiment 2 were not replicated by the young adults in this study, we expect that they will show similar results in a static self-image situation. Experiment 2 was conducted to determine the critical factor to produce “social facilitation effect.” For the daily-use purpose, however, the mirror is easier to set up in a room than a large size self-image. Thus, we did not pursue the results of Experiment 2 with the young adults. However, further examination of the mirror effect on adolescents might be performed.
differences between the ratings of TA in pre-tasting and post-tasting period (pre-tasting: M = 21.0, SD = 1.98, post-tasting: M = 21.19, SD = 1.48, t(15) = 0.35). These results of Experiment 3 indicated that the popcorn tasted better and was eaten more when young individuals ate it in front of a mirror than when they ate it in front of a wall-reflecting monitor. These findings confirm that the “social” facilitation effect of eating without others being present occurs among younger adults as well. The next step would be to compare these results with those of the elderly adults from Experiment 1. 4.2.3. Direct comparison between young and elderly adults. To compare the results of the elderly adults (Experiment 1) with those of the young adults (Experiment 3), we combined the data of these two experiments and analyzed them by using a three-way mixed ANOVA with the factors of presence of a mirror (mirror vs. monitor), test food (salt flavored vs. caramel flavored), and age of participants (young vs. elderly). Our results indicated that most ratings of the mirror condition were significantly higher than were those of the monitor condition (goodness: F1,30 = 23.88, P < 0.01; quality: F1,30 = 9.88, P < 0.01; liking: F1,30 = 11.89, P < 0.05; fillingness: F1,30 = 4.62, P < 0.05; mean consumption ratio: F1,30 = 20.24, P < 0.01). Interestingly, we observed no significant interactions between the age groups and presence of the mirror for any of the variables (Fig. 3). The main effect of age was confirmed for the goodness (F1,60 = 10.84, P < 0.01), quality (F1,60 = 5.64, P < 0.05), liking (F1,60 = 6.51, P < 0.05), and saltiness of the popcorn (F1,60 = 6.63, P < 0.05), with the young adults having significantly higher ratings than the elderly adults (Table 1). The sweetness of the caramel flavored popcorn (F1,30 = 285.25, P < 0.01) was significantly higher than that of the salt flavored popcorn. Moreover, there were significant three-way interactions between these factors for the sweetness (F1,30 = 4.64, P < 0.05). The simple main effect of test food was confirmed for all combinations between the factors of presence of a mirror and age of participants. The saltiness of the caramel flavored popcorn (F1,30 = 55.23, P < 0.01) was significantly lower than that of the salt flavored popcorn. These comparisons were conducted as to verify that participants' sense of taste was valid. The results of this comparison indicated only slight differences between the age groups. The young participants rated the popcorn as tasting better and ate more of it than did the elderly participants. It is possible that the different amounts of exposure between young and elderly adults to popcorn might have caused the difference between two age groups, as hardly elderly adults in Japan eat popcorn in their daily life. A previous study indicated that repeated exposure to one food leads to more positive evaluations of that food [31]. Thus, the higher ratings
5. General discussion The most important finding of our study was that the social facilitation of eating was observed when individuals ate alone in front of a mirror or a static image of themselves eating. These findings suggest that the facilitation of eating does not require the presence of another individual. Rather, static visual information of “someone” eating food is sufficient to produce the “social” facilitation of eating. The present findings do not exclude the potential contribution of other social factors in real-life situations because a number of psychological processes could contribute to the occurrence of an eating facilitation effect [9]. Although the existence of the mirror or the static photograph of themselves eating did not affect the subjective saltiness and sweetness of the popcorn in this study, It is possible that the basic taste perception might be influenced more by information present in social relationships or interpersonal communications. Future research would be necessary to extend the current results into more externally valid situations, and it will also be important to consider how other social factors relate to the perceived goodness of the food. The relationship between the facilitation effect observed herein and other non-social environmental factors that influence food evaluations and food consumption [37] must also be investigated. Interestingly, most studies focusing on the social facilitation of eating have given little attention to subjective changes in food taste as opposed to the consumption of the food; a prominent aspect of the social facilitation of eating is that eating with others leads people to eat more [2]. In contrast, the results of our study—particularly those concerning effect
Fig. 3. Mean ratings for goodness of the popcorn and mean consumption ratio among elderly adults (Experiment 1) and young adults (Experiment 3). The vertical bars represent the standard errors.
27
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai
Table 1 Summary of mean ratings of the popcorn and mean consumption ratio in Experiments 1–3. Experiment 1
Experiment 2
Experiment 3
Elderly
Elderly
Young
Caramel
Salt
Salt
Goodness Quality Liking Fillingness Saltiness Sweetness Bitterness Consumptions
Caramel
Caramel
Mirror
Monitor
Mirror
Monitor
Mirror
Monitor
Mirror
Monitor
Mirror
Monitor
3.94 (0.32) 3.13 (0.34) 3.50 (0.38) 3.56 (0.24) 3.63 (0.31) 2.19 (0.25) 1.63 (0.13) 39.80 (5.98)
3.25 (0.36) 2.94 (0.31) 3.12 (0.34) 3.38 (0.33) 3.44 (0.41) 1.75 (0.23) 1.56 (0.16) 34.89 (4.78)
4.38 (0.29) 3.88 (0.20) 4.32 (0.34) 3.89 (0.29) 1.88 (0.30) 4.82 (0.32) 1.31 (0.19) 35.47 (3.83)
3.88 (0.32) 3.25 (0.30) 3.69 (0.34) 3.81 (0.31) 1.88 (0.29) 5.13 (0.18) 1.56 (0.22) 26.16 (2.54)
5.08 (0.26) 4.08 (0.38) 4.75 (0.28) 4.00 (0.28) 1.42 (0.19) 4.92 (0.19) 1.25 (0.13) 48.18 (4.38)
4.75 (0.28) 4.25 (0.28) 4.41 (0.34) 4.25 (0.22) 1.50 (0.19) 4.92 (0.26) 1.58 (0.26) 40.32 (5.19)
4.94 (0.19) 3.75 (0.19) 4.50 (0.26) 3.88 (0.26) 4.63 (0.18) 1.88 (0.22) 1.31 (0.15) 43.23 (6.71)
4.38 (0.20) 3.50 (0.22) 4.25 (0.28) 3.31 (0.27) 4.31 (0.24) 2.06 (0.27) 1.44 (0.20) 30.42 (3.76)
5.06 (0.17) 4.44 (0.20) 4.81 (0.19) 4.25 (0.25) 2.63 (0.40) 5.31 (0.25) 1.56 (0.18) 40.13 (3.57)
4.69 (0.20) 4.06 (0.19) 4.25 (0.27) 4.06 (0.32) 2.75 (0.37) 5.31 (0.15) 1.69 (0.25) 33.31 (3.08)
Values are presented in means (SE).
cantly greater differences in the popcorn goodness ratings between eating in front of the mirror and eating in front of the wall-reflecting monitor (salt flavor popcorn: elderly adults showing a tendency to eat alone: M = 0.75, SD = 0.89, and elderly adults not showing this tendency, M = 0.63, SD = 0.52), t(14) = 0.34, n.s.; caramel flavor popcorn: elderly adults showing a tendency to eat alone M = 0.38, SD = 0.74, and elderly adults not showing this tendency M = 0.63, SD = 0.74, t(14) = 0.67, n.s). Thus, the facilitation of eating without the presence of others may occur regardless of individuals' experiences of eating alone in daily life. Further studies focused on the frequencies of daily social eating will be needed to confirm this. The significant changes in mood are often observed when people eat together in company [8,10,11]. However, throughout the experiments, eating with the presence of self-image did not significantly affect the mood. The social facilitation of eating would not be always attributed to the elevation of the mood. The present findings provided us the opportunity to understand an important aspect of the social facilitation of eating. Similar results might be observed for other social facilitation phenomena involving coaction effects (e.g., size perception [42], motor performance [43], and attention [44]). Given that these facilitations might also occur without the actual existence of others, our findings might be helpful in understanding the true nature of social facilitation and co-action effects beyond those related to eating.
of the self-reflection on goodness and consumption ratio of the popcorn—suggested that both subjective evaluations and actual consumption of food can be simultaneously facilitated. It is likely that subjective evaluations of food are an important aspect of the social facilitation of eating, and must be examined to tell us the nature of the facilitation effect. Further studies are needed to understand the underlying mechanisms for each facilitation (e.g., whether these facilitation effects occur independently or are in some way correlated [2]). It should be noted that only self-images were used in this study. Thus, we cannot rule out the possibility that our use of a static image of the participants themselves may have had some influence on the facilitation effect (e.g., familiarity). In a future study, one must examine whether the facilitation of eating with static images is replicated by using static images of another person as well. It is essential to control various social factors, which may influence eating behavior when eating with other individuals, such as social modeling and the social norms of eating [38]. In this study, all the self-images reflected eating behaviors. It is unclear whether “eating” images are crucial to produce the “social” facilitation effect of eating. A future investigation would be determining whether the mere presence of themselves lead to a facilitation effect of eating, even when they does not eat anything (i.e., audience effect [39]), There is good evidence indicating that eating in the presence of a non-eating observer can make the food taste worse [13] and suppress individuals' actual consumption [40]. Therefore, a presentation of static image of another individual's non-eating action may produce the opposite pattern of the results in Experiment 2. The social facilitation of eating in situations of eating together has been often referred to as an example of so-called “co-action effects,” which arise when individuals simultaneously engage in an activity with others [39]. Interestingly, previous studies have shown that thinking about events related to food (e.g., imagining that someone prepared your food kindly) has been found to improve that food's taste [41]. It may be that individuals' mental representations of co-eating are more important for the facilitation effect of eating than are perceptual cues of that co-eating. Therefore, one possibility is to assume that the visual information of “eating” food is an important aspect of the social facilitation of eating. We must also examine the contribution of the familiarity of the situation of eating alone to the observed facilitation effect. We asked elderly adults who participated in Experiment 1 whether they had a tendency to eat alone for their daily meals. About half of the elderly individuals (i.e. 8 out of the 16 participants) answered that they more often ate alone than with others for everyday meals. Furthermore, more elderly individuals answered that they had a tendency to eat alone compared to the young adults in Experiment 3 (where only 4 out of the 16 participants had such a tendency). On the other hand, a tendency to eat alone among elderly individuals was not associated with signifi-
Conflict of interest All authors declare that there is no conflict of interest. Funding This study was supported by JSPS KAKENHI Grant Number JP15k16230 and JP17k12918. Acknowledgements We thank Shota Watanabe for his support in data acquisition and Dr. Namiko Kubo-Kawai for her critical reading of the manuscript. References [1] F. Bellisle, A.M. Dalix, Cognitive restraint can be offset by distraction, leading to increased meal intake in women, Am. J. Clin. Nutr. 74 (2001) 197–200 (PMID: 11470720). [2] C.P. Herman, The social facilitation of eating. A review, Appetite 86 (2015) 61–73, http://dx.doi.org/10.1016/j.appet.2014.09.016 (PMID: 25265153). [3] J.M. de Castro, E.S. de Castro, Spontaneous meal patterns of humans: influence of the presence of other people, Am. J. Clin. Nutr. 50 (1989) 237–247, http://dx.doi. org/10.1016/0031-9384(86)90128-9 (PMID: 2756911).
28
Physiology & Behavior 179 (2017) 23–29
R. Nakata, N. Kawai [4] B. Wansink, S.B. Park, At the movies. How external cues and perceived taste impact consumption volume, Food Qual. Prefer. 12 (2001) 69–74, http://dx.doi.org/10. 1016/S0950-3293(00)00031-8. [5] V.I. Clendenen, C.P. Herman, J. Polivy, Social facilitation of eating among friends and strangers, Appetite 23 (1994) 1–13, http://dx.doi.org/10.1006/appe.1994. 1030 (PMID: 7826053). [6] S.C. King, H.L. Meiselman, A.W. Hottenstein, T.M. Work, V. Cronk, The effect of contextual variables on food acceptability: a confirmatory study, Food Qual. Prefer. 18 (2007) 58–65, http://dx.doi.org/10.1016/j.foodqual.2005.07.014. [7] R.F. Baumeister, M.R. Leary, The need to belong: desire for interpersonal attachments as a fundamental human motivation, Psychol. Bull. 117 (1995) 497–529, http://dx.doi.org/10.1037/0033-2909.117.3.497 (PMID: 7777651). [8] M.M. Hetherington, Cues to overeat: psychological factors influencing overconsumption, Proc. Nutr. Soc. 66 (2007) 113–123, http://dx.doi.org/10.1017/ S0029665107005344 (PMID: 17343777). [9] M.M. Hetherington, A.S. Anderson, G.N.M. Norton, L. Newson, Situational effects on meal intake: a comparison of eating alone and eating with others, Physiol. Behav. 88 (2006) 498–505, http://dx.doi.org/10.1016/j.physbeh.2006.04.025 (PMID: 16757007). [10] K.A. Patel, D.G. Schlundt, Impact of moods and social context on eating behavior, Appetite 36 (2001) 111–118, http://dx.doi.org/10.1006/appe.2000.0385 (PMID: 11237346). [11] W. Sommer, B. Stürmer, O. Shmuilovich, M. Martin-Loeches, A. Schacht, How about lunch? Consequences of the meal context on cogntion and emotion, PLOS ONE 8 (2013) e70314, http://dx.doi.org/10.1371/journal.pone.0070314 (PMID: 23936184). [12] S.J. Salvy, M. Howard, M. Read, E. Mele, The presence of friends increases food intake in youth, Am. J. Clin. Nutr. 90 (2009) 282–287, http://dx.doi.org/10.3945/ ajcn.2009.27658 (PMID: 19535431). [13] E.J. Boothby, M.S. Clark, J.A. Bargh, Shared experiences are amplified, Psycol. Sci. 25 (2015) 2209–2216, http://dx.doi.org/10.1177/0956797614551162 (PMID: 25274583). [14] L. Miller, P. Rozin, P.F. Alan, Food sharing and feeding another person suggest intimacy; two studies of American college students, Eur. J. Soc. Psychol. 28 (1998) 423–436, http://dx.doi.org/10.1002/(SICI)1099-0992(199805/06) 28:3<423::AID-EJSP874>3.0.CO;2-V. [15] K.M. Kniffin, B. Wansink, It's not just lunch: extra-pair commensality can trigger sexual jealousy, PLOS ONE 7 (2012) e40445, http://dx.doi.org/10.1371/journal. pone.0040445 (PMID: 22792327). [16] K.M. Kniffin, B. Wansink, C.M. Devine, J. Sobal, Eating together at the firehouse: how workplace commensality relates to the performance of firefighters, Hum Perform. 28 (2015) 281–306, http://dx.doi.org/10.1080/08959285.2015.1021049 (PMID: 27226698). [17] N. Sakai, The psychology of eating from the point of view of experimental, social, and applied psychology, Psychol. Russia 7 (2014) 14–22, http://dx.doi.org/10. 11621/pir.2014.0102. [18] L.I. Vailas, S.A. Nitzke, M. Becker, J. Gast, Risk indicators for malnutrition are associated inversely with quality of life for participants in meal programs for older adults, J. Am. Diet. Assoc. 98 (1998) 548–553, http://dx.doi.org/10.1016/S00028223(98)00123-0 (PMID: 9597027). [19] Y. Tani, Y. Sasaki, M. Haseda, K. Kondo, N. Kondo, Eating alone and depression in older men and women by cohabituation status: the JAGES longitudinal survey, Age Ageing 44 (2015) 1019–1026, http://dx.doi.org/10.1093/ageing/afv145 (PMID: 26504120). [20] L.M. Donini, C. Savina, C. Cannella, Eating habits and appetite control in the elderly: the anorexia of aging, Int. Psychogeriatr. 15 (2003) 73–87, http://dx.doi. org/10.1017/S1041610203008779 PMID: 12834202). [21] Y. Imai, K. Hasegawa, The revised Hasegawa's dementia scale (HDS-R) –evaluation of its usefulness as a screening test for dementia, J. Hong Kong Coll. Psychiatr. 4 (1994) 22–24. [22] S. Shirasawa, T. Ishida, Y. Hakoda, M. Haraguchi, The effects of energetic arousal on memory search, Jpn. J. Psychon. Sci. 17 (1999) 93–99 (in Japanese). [23] G. Matthews, D.M. Jones, A.G. Chamberlain, Refining the measurement of mood:
[24] [25] [26]
[27] [28] [29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39] [40]
[41]
[42]
[43]
[44]
29
the UWIST mood adjective checklist, Br. J. Psychol. 81 (1990) 17–42, http://dx.doi. org/10.1111/j.2044-8295.1990.tb02343.x. R.E. Thayer, Toward a psychological theory of multidimensional activation (arousal), Motiv. Emot. 2 (1978) 1–34, http://dx.doi.org/10.1007/BF00992729. P. Pliner, G. Iuppa, Effects of increasing awareness on food consumption in obese and normal weight subjects, Addict. Behav. 3 (1978) 19–24. S.M. Sentyrz, B.J. Bushman, Mirror, mirror on the wall, who's the thinnest one of all? Effect of self-awareness on consumption of full-fat, reduced-fat, and no-fat products, J. Appl. Psychol. 83 (1998) 944–949. A. Alawad, Y. Mahgoub, F. Yousef, The mirror, as a self-awareness enhancing tool, which can modify food consumption behaviors, J. Nat. Sci. Res. 5 (2015) 90–95. A. Jami, Healthy reflections: the influence of mirror induced self-awareness on taste perceptions, J. Assoc. Consum. Res. 1 (2016) 57–70. J. Koh, P. Pliner, The effects of degree of acquaintance, plate size, and sharing on food intake, Appetite 52 (2009) 595–602, http://dx.doi.org/10.1016/j.appet.2009. 02.004 (PMID: 19501755). J.Y. Kim, H.R. Kissileff, The effect of social setting on response to a preloading manipulation in non-obese women and men, Appetite 27 (1996) 25–40, http://dx. doi.org/10.1016/appe.1996.0031 (PMID: 8879417). P. Pliner, The effects of mere exposure on liking for edible substances, Appetite 3 (1982) 283–290, http://dx.doi.org/10.1016/S0195-6663(82)80026-3 (PMID: 7159080). E.A. Kensinger, A.H. Gutchess, Cognitive aging in a social and affective context: advances over the past 50 years, J. Gerontol. B Psychol. Sci. Soc. Sci. (2016), http:// dx.doi.org/10.1093/geronb/gbw056 (PMID: 27233290). C.T. Salthouse, Selective review of cognitive aging, J. Int. Neuropsychol. Soc. 16 (2010) 754–760, http://dx.doi.org/10.1017/S1355617710000706 (PMID: 20673381). P. Rozin, Towards a psychology of food and eating: from motivation to module to model to marker, morality, meaning, and metaphor, Curr. Dir. Psychol. Sci. 5 (1996) 18–24, http://dx.doi.org/10.1111/1467-8721.ep10772690. M.E. Eisenberg, R.E. Olson, D. Neumark-Sztainer, M. Story, L.H. Bearinger, Correlations between family meals and psychosocial well-being among adolescents, Arch. Pediatr. Adolesc. Med. 158 (2004) 792–796, http://dx.doi.org/10.1001/ archpedi.158.8.792 (PMID: 15289253). D.L. Franko, D. Thompson, S.G. Affenito, B.A. Barton, R.H. Striegel-Moore, What mediates the relationship between family meals and adolescent health issues? Health Psychol. 27 (2008) S109–S117, http://dx.doi.org/10.1037/0278-6133.27. 2(suppl.)S109 (PMID: 18377152). C. Space, V. Harrar, B. Piqueras-Fiszman, Assessing the impact of the tableware and other contextual variables on multisensory flavour perception, Flavour 1 (2012) 7, http://dx.doi.org/10.1186/2044-7248-1-7. T. Cruwys, K.E. Bevelander, R.C.J. Hermans, Social modeling of eating: a review of when and why social influence affects food intake ad choice, Appetite 86 (2015) 3–18, http://dx.doi.org/10.1016/j.appet.2014.08.035 (PMID: 25174571). R.B. Zajonc, Social facilitation, Science 149 (1965) 269–274, http://dx.doi.org/10. 1126/science.149.3681.269 (PMID: 14300526). D.A. Roth, C.P. Herman, J. Polivy, P. Pliner, Self-presentational conflict in social eating situations: a normative perspective, Appetite 36 (2001) 165–171, http://dx. doi.org/10.1006/appe.2000.0338 (PMID: 11237352). K. Gray, The power of good intentions: perceived benevolence soothes pain, increases pleasure, and improve taste, Soc. Psychol. Pers. Sci. 3 (2012) 639–645, http://dx.doi.org/10.1177/1948550611433470. T. Garcia-Marques, A. Fernandes, M. Prada, R. Fonseca, S. Haga, Seeing the big: size perception is more context sensitive in the presence of others, PLOS ONE 10 (2015) e0141992, http://dx.doi.org/10.1371/journal.pone.0141992 (PMID: 26562518). C. Anderson-Hanley, A.L. Snyder, J.P. Nimon, P.J. Arciero, Social facilitation in virtual reality-enhanced exercise: competitiveness moderates exercise effort of older adults, Clin. Interv. Aging 6 (2011) 275–280, http://dx.doi.org/10.2147/CIA. S25337 (PMID: 22087067). D. Muller, F. Butera, The focusing effect of self-evaluation threat in coaction and social comparison, J. Pers. Soc. Psychol. 93 (2007) 194–211, http://dx.doi.org/10. 1037/0022-3514.93.2.194 (PMID: 17645395).