Even though the experiment of Kim and Colleagues (2004) very elegantly revealed a direct influence of social context on the encoding of the same otherwise neutral (or at least ambiguous – see Chapter V) facial display, there is, to our knowledge, no other study that used the same approach to further elaborate on context effects in social perception (but see our own experiment [152] mentioned later on).

However, there are other studies employing different approaches to investigate the role of context on social perception. These include intentionality in economic games (Chapter IV.3.1), the presence / absence of an audience during economic games or imagined moral transgressions (Chapter IV.3.2.), or a more basic social versus non-social stimulus content distinction (Chapter IV.3.3.). Interestingly, all such studies only investigated context effects on stimulus encoding and memory retrieval, but not regulation (i.e. re-appraisal or suppression), although this is also a crucial component of social perception (see Chapter I.3.2.).

IV.3.1. Intentionality

Besides direct social context comparison (see Chapter IV.2.1.), one set of experiments on social context effects in relation to social perception used the comparison of fair versus unfair offers during economic games. The social context effect was generated by either receiving offers from intentional or unintentional partners (see Chapter 3.1.2.) or a computer (see Chapter 3.1.1.).

In this sense, the offer received during the economic game constitutes a constant stimulus – like

the surprised face in Kim and colleagues’ studies –, whereas the fact whether the offer came from

a computer, an unintentional human player, or an intentional human player, represents the social context – like the positive or negative sentences in Kim and colleagues’ experiments.

3.1.1. Human Player versus Computer

In a first study of this kind [153], the subjects participated in 30 subsequent ultimatum games


, of which 10 were played with 10 people subjects met beforehand, 10 with a computer, and 10 presented as control trials (roulette wheel). Every trial started with the presentation of the interaction partner (human, computer, or roulette wheel), followed by the monetary offer from the partner, which the subject then could either accept or reject (in this study, the participant was therefore always the second player).

The fMRI results revealed that unfair offers from human partners (as compared to similar offers by the computer or during the control trials) elicited highest activity in bilateral anterior insula, ACC, and DLPFC, representing negative emotion processing, cognitive conflict, and executive control, respectively (see Chapter III for more details on the functional anatomy of the these brain regions).

Such higher activations to intentional human players making unfair offers suggest that the anterior insula, ACC, and DLPFC did not only represent the amount of money offered during unfair trials, but also the social context – namely the degree of unfairness – that was associated with any unfair offer.

3.1.2. Intentional versus unintentional Human Player

A similar experiment made use of the sequential prisoner’s dilemma game


to establish a moral status for previously unknown faces [154]. The game partners either acted freely and thus intentionally, or were told how to behave, and were thus acting unintentionally. Subsequent to the game, the participants saw the faces of the game partners again, intermingled with new faces, and had to perform a gender decision task while undergoing fMRI scanning. Finally, after scanning, the subjects participated in a memory task and provided likeability ratings for each face.

4 During the ultimatum game, two players interact by making decisions upon the division of a given amount of money. The first player proposes how to divide the sum between the two players, and the second player can either accept or reject this proposal. If the second player rejects, neither player receives anything. If the second player accepts, the money is split according to the proposal. The game is played only once so that reciprocation is not an issue.

5 During the sequential prisoner’s dilemma game, a first player can trust a second player by sending his/her starting points (transferred to money at the end of the game) to the other player, knowing that each point sent will be tripled. The second player then has the opportunity to reciprocate (by sending money back, which is also tripled), resulting in equal payoffs for both players. The second player, however, can decide to keep the money and maximize his own earnings at the expense of the first player.

The results showed an increased activity in a number of brain areas important for social perception (including amygdala, ventral striatum, and pSTS) in response to the co-operators versus defectors, and that the latter effects were stronger for intentional versus unintentional agents. The study could demonstrate that reward-related activity during reciprocal trials was not only representing the positive experience of monetary gain per se, but was also related to the intrinsic social (intentional) value of cooperation.

IV.3.2. Presence / Absence of Audience

Besides the use of economic games where the game partners can either act in- or unintentionally, two other studies used the imagined (Chapter 3.2.1.) or real presence / absence (Chapter 3.2.2.) of an audience during different social scenarios.

3.2.1. Imagined Presence / Absence of an Audience

In one experiment [155], subjects were shown a set of written social stories and told to imagine them from a first-person perspective while they underwent fMRI scanning. Importantly, all stories had three different endings, which could either be neutral, or include a moral or a social transgression. Finally, these three scenarios could either be experienced alone (i.e. “… no one else is around to watch you …”), or with the presence of an audience (i.e. “… people across the street watch you …”). Along these lines, the constant stimulus was the imagined social scenario, and the presence or absence of an audience represented the difference in social context.

The results revealed that a single brain region, namely the left amygdala, was more activated for stories with the presence of an audience regardless of the story ending condition (neutral, or moral or social transgression). Such an activation pattern was interpreted by the fact that the description of the presence of an audience was always linked with the notion of “… staring at the participant

…”, and that the amygdala has previously been shown to be implicated in gaze processing and anticipation of direct gaze [155].

3.2.2. Real Presence or Absence of an Audience

Another experiment used a simple monetary betting task where participants had to bet on

the color of a card, which could either be red or green with a probability of 50%, so that they could

win or lose the amount betted on each trial [156]. The difference in social context was created by the fact that some trials were played by the subject in the fMRI scanner alone, whereas other trials were played by the subject plus another person sitting in the control room. Brain activity during the time window between the color choice and the feedback presentation was investigated.

The experimental data revealed that two brain areas, namely bilateral amygdala and right DLPFC, were more activated during the feedback expectation for social versus non-social trials. Whereas the DLPFC effect was difficult to interpret, amygdala activation was linked with heightened vigilance, reflecting a warning signal associated with the detection of an unknown “social other”, promoting avoidance behavior. Moreover, an inverse effect was detected in the ventral striatum, which was more activated for non-social versus social trials. This was also interpreted in terms of a warning signal by the presence of a “social other” mitigating approach behavior, which is normally encoded by the ventral striatum during reward experience promoting the approach of a positive stimulus [156].

IV.3.3. Basic Social versus Non-Social Stimulus Content Distinction

Finally, instead of manipulating intentionality (Chapter IV.3.1.), by involving subjects into one- versus two-player economic games (Chapter IV.3.2.1.) or instructing them to mentally imagine social scenarios with or without the presence of an audience (Chapter IV.3.2.2.), one can simply modulate the nature of stimuli themselves by exposing the subjects to social versus non-social images in the fMRI scanner. This could represent a basic human animate versus inanimate distinction, but also entail a more complex separation of processes related to the computation of complex social interaction scenarios involving social semantic meaning and intentionality as opposed to the mental representation of more basic biological drives, such as appetite/food, desire and disgust [157, 158].

Despite the fact that a social versus non-social distinction is rather straight-forward, not many

experiments have employed it up to date. However, what is evident from the studies available in

the literature is the fact that the amygdala was consistently found to show greater response for

social as compared to non-social images, besides an emotional (negative versus positive) versus

neutral effect [157-160]. Thereby, especially the superficial amygdala has been linked with the

selective extraction of the social value of incoming stimuli [160]. Other regions preferentially

computing social versus non-social information have been identified in the STS (theory of mind

through perceived action), hippocampus (autobiographic memory), posterior cingulate (evaluation

of current and past experience), dorsal ACC (only activated for social sadness / rejection and thus

related to conflict / pain), FFA (face perception), and MPFC and DMPFC (mentalizing in general and action monitoring more specifically). In contrary, non-social images were found to induce increased BOLD signal change in the insula (interoception) and in visual cortex (attention). For more details on the functional neuro-anatomy of the abovementioned brain areas, please see Chapter III).

One possible caveat of such a basic social versus non-social distinction by means of image content is the fact that there are important discrepancies in stimulus properties. Firstly, social images normally entail a higher complexity and thus require more cognitive computation capacities.

Second, social versus non-social images tend to differ on the arousal / intensity dimension, especially if social images include displays of mutilated bodies (negative) or erotic couples (positive). Finally, inanimate pictures are normally associated with greater emotional control than their animate counterparts [161]. However, when controlling for social complexity, arousal, and emotional control, as well as for other basic visual image properties such as luminance and/or spatial frequency, manipulating the social versus non-social stimulus content can be an effective approach (see following Chapters).

In the experimental work of the present thesis, social context was manipulated either directly by pairing different facial emotional expressions (i.e. smiling/happy and angry faces) with verbal information (comparable to Kim and colleagues [2003, 2004] studies) or by using the distinction between basic social versus non-social stimulus properties (see Chapter V). The information provided above about these two methods of context manipulation should thus be particularly kept in mind for the reading of the remaining parts of the present thesis.

Because intentional stimuli were always found to produce larger effects than their non-intentional

counterparts (see above), no difference between intentional and non-intentional agents was

employed for the experimental work within the present thesis. Likewise, the concept of audience

was not applied in the experiments, because previous studies using audience manipulation only

found effects related to vigilance or eye gaze (see above), which are not very specific in terms of

their impact on social and emotion perception.

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