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Positive stimuli
Positive stimuli also trigger spatial orientation of attention (Brosch, Sander, Pourtois, & Scherer, 2008; Pool, Brosch, Delplanque, & Sander, 2015). Due to their rewarding and hedonic nature, they elicit approach behaviors, hence, they also should modify PPS representation. To test this, Coello et al. (2018) asked participants to select tokens on a 40-inch touch screen table. The token selected could lead to a reward of 1 point or 0 point, the goal being to obtain the highest final score. Depending on the group (control, near, far), the proportion of rewarding tokens in the near half portion of the table could be of 50%, 75% or 25% respectively (thus respectively 50%, 25% and 75% chance of reward in the far space). Prior and after the token selection task, PPS boundaries of participants were established with a reachability judgment task. First, results revealed that participants of the near group implicitly reduced progressively their token selection to the near space whereas the opposite was observed for the far group. No specific strategy was observed for the control group. Second, PPS boundaries changed accordingly in posttest in comparison to pretest. PPS representation decreased for the near group and increased for the far group. Implicitly modifying the motor exploration of participants by changing the valence of the space led to changes in PPS representation. Similar effects have also been observed in patients with spatial neglect but on the sagittal plane, leading to motor exploration of the left neglected space (Lucas et al., 2013). Thus, PPS representation is dependent on the intention to interact with our environment which is suggested by the valence of the elements that composes it, even when the emotional allocation of that space is not consciously perceived.
Taken together, these data revealed that the perceived valence of the stimuli contributes to the specification of PPS. PPS is sensitive to the valence of the elements of our environment because our actions, and by extension our survival, depend on this valence. Although PPS represents a space for action but also a space for protection, the representation format of the defensive space is not fully understood yet. This suggests however that PPS representation should be influenced by the social context as distance plays a crucial role in social interactions.
Social dependency of PPS
As a social animal, the representation we have of others’ action-space is particularly important and this can be observed at the cerebral level. Just as one’s own actions and those of others seems to be coded in a similar way in the monkey brain (di Pellegrino, Fadiga, Fogassi, Gallese, & Rizzolatti, 1992; Rizzolatti, Fadiga, Gallese, & Fogassi, 1996), similar brain areas respond to the presence of stimuli close to one ‘s own body and others’ body (Ishida, Nakajima, Inase, & Murata, 2010). Indeed, monkeys’ visuo-tactile neurons in the parietal cortex fire when visual or tactile stimuli are presented near their body as well as near others’ body.
Furthermore, when PPS of two individuals overlap, it results in the modulation of PPS representation. For instance, animal study revealed that if two monkeys share a portion of their PPS in which there is some food, but one of them is a dominant male, the parietal activity of the submissive monkey is dramatically reduced and this later barely tries to get the food (Fujii, Hihara, & Iriki, 2007). This indicates that PPS for the submissive monkey was reshaped. In this situation, the prefrontal activity of the dominant monkey increases whereas that of the submissive one decreases in comparison to when there is no spatial competition for food (Fujii, Hihara, Nagasaka, & Iriki, 2009). Thus, spatial representation relies on the social context and one’s PPS is related to the PPS of others.
Similar observations are reported in human studies. Indeed, using a multisensory integration task, Teneggi et al. (2013) revealed that PPS of participants shrank if another individual faced them compared to a mannequin as if they were leaving some space for the other individual. However, authors also reported that, after playing cooperatively with the other person, participant’s PPS merged with the one of the other. Likewise, using a multisensory integration task, Pellencin et al. (2017) found an increase in PPS representation when encountering moral individual in comparison to amoral ones. Coello et al. (2018) found similar effects of those observed by Teneggi et al. (2013) during a cooperative task of token selection (as described in section I.2.3). While the amplitude of movement of the two individuals facing each other decreased when selecting tokens, as if they were splitting the work; their PPS representation increased. Interestingly, using the same cooperative task but changing the spatial probability of being rewarded (e.g., 75% chances of getting a reward when selecting a token in the proximal space of one participant, thus 25% in the proximal space of the other), the authors revealed that both the amplitude of movement and the PPS representation increased, but only if the greater chance of success was in the distal space of participants (Gigliotti, Coelho, Coutinho, & Coello, 2019). Taken together, the results suggest that PPS representation is sensitive to social context.
Relation between IPD and PPS
IPD is at the core of social interaction. Thus, it seems fundamental to understand how it is built. A growing body of evidence suggests that IPD is built on sensorimotor representations. According to Hall (1966), beyond IPD’s sensitivity to the degree of intimacy of the individual with the interlocutor, IPD or “personal distance” allows the clear visibility of the others’ face and trunk and favors an efficient verbal interaction. At this distance, we can clearly be heard by the other without the need of forcing our voice. Hence, this distance seems particularly suitable for fostering social interactions relatively to sensorial input.
Furthermore, IPD seems to be built on motor representations. IPD is about one arm length and is related to the size of individuals (Hall, 1966; Hartnett, Bailey, & Hartley, 1974; Hayduk, 1983; Pazhoohi et al., 2019). This suggests that this space between individuals is also particularly conducive to potential physical interaction. Moreover, IPD seems to be intrinsically linked to PPS. Indeed, an increasing body of evidence suggests that IPD is built on PPS, although it depends on specific factors (Iachini, Coello, Frassinetti, & Ruggiero, 2014; Iachini, Pagliaro, & Ruggiero, 2015; Quesque et al., 2017; Vieira, Pierzchajlo, & Mitchell, 2019, described in the following section). For instance, Iachini et al. (2014) revealed that IPD decreases in the presence of virtual human-like characters in comparison to non-human-like characters, just as the PPS representation (Teneggi et al., 2013). This suggests that proper social interaction requires a distance between individuals that is sufficiently short (around PPS boundaries) to engage private interaction while ensuring PPS integrity.
Supporting this view, a behavioral study revealed that IPD is sensitive to motor representations (Quesque et al., 2017). In this study, Quesque et al. (2017) asked participants to perform an IPD judgment task with a point-light walker (PLW) that crossed them at different inter-shoulder distances (varying from collision to large inter-shoulder distance) in a virtual environment. The PLW could start from the left or the right side of the participants or right in front of them. Therefore, PLW either crossed participants’ midsagittal plane or not (when starting in front of them). Following this session, participants performed a second task during which they had to reach and retrieve tokens displayed at different distances from them with a rake with a short or a long handle. Finally, they performed an ultimate IPD judgment task. First, authors revealed that IPD were larger when the PLW crossed participant’s midsagittal plane than when it did not. This could be related to the need for keeping PPS preserved during social interactions. Second, they observed an increase in IPD following the use of the tool with a long handle only. This supports the hypothesis that IPD and PPS share common motor mechanisms and that IPD seems to be built on PPS representation. This hypothesis has also been corroborated by a brain imagery study revealing that the frontoparietal areas known to be involved in PPS representation were also activated by approaching social stimuli (Vieira et al., 2019).
Table of contents :
Acknowledgements
Abstract
Publications
Communications
Contents
Figures
Tables
Abbreviations
INTRODUCTION
I. The space around us
I.1. An action space
How to test PPS representation
I.1.1. Peripersonal space in the (human and primate) brain
I.1.2. PPS representation depends on action
I.2. A space depending on the value of objects
I.2.1. The valence of the stimulus modifies behavioral tendency
I.2.2. Negative stimuli
I.2.3. Positive stimuli
I.3. Social dependency of PPS
I.4. A social space
How to test IPD
I.4.1. Relation between IPD and PPS
I.4.2. IPD depends on individuals’ characteristics
I.4.3. What PPS and IPD are to each other?
II. The Processing of Emotional information
II.1. Facial expression: a relevant emotional information from others
II.1.1. Facial expression, a biologically relevant stimulus
II.1.2. Behavioral response from the body
II.2. Context-dependency on judgment
II.2.1. Assimilation effects
II.2.2. Contrast effect
II.2.3. Contrast or assimilation?
II.2.4. Emotional context on space perception
III. FE perception: what happens in the body?
III.1. Central nervous system
III.2. Autonomic nervous system
III.3. Threat perception
Rationale of the Thesis
General method
Virtual reality and human-like stimuli
Material
Stimuli
Physiological recording: Electrodermal activity
Experimental task: interpersonal distance judgment
Method of constant stimuli
Statistical estimation of IPD
Study 1
Foreword
Physiological Response to Facial Expressions in Peripersonal Space Determines Interpersonal Distance in a Social Interaction Context
Abstract
Introduction
Materials and Methods
Results
Discussion
Conclusion
Study 2
Foreword
The influence of facial expression at perceptual threshold on electrodermal activity and social comfort distance
Abstract
Introduction
Method
Results
Discussion
Appendix
Study 3
Foreword
Contrast effect of emotional context on interpersonal distance with neutral social stimuli
Abstract
Introduction
Method
Results
Discussion
Study 4
Foreword
Wearing a face mask against COVID-19 results in a reduction of social distancing
Abstract
Introduction
Method
Discussion
GENERAL DISCUSSION
I. Overall summary
II. Binding of PPS and valence information in IPD specification
III. Towards a new theoretical approach of IPD adjustment
IV. A Framework for new research avenues
IV.1. Valence intensity
IV.2. The nature of the relationship between PPS, emotion valence and IPD
IV.3. Investigating rapid motor responses
IV.4. A new framework for psychopathological investigations?
IV.5. Interoception as a crucial component of physiological responses
V. Concluding remarks
REFERENCES
