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Chapter III The space between the body: Interpersonal space

3.4 How many spaces around the body?

The use of space by both animals and humans is inherent in social interactions, which have been most effectively mapped through observing the behaviour of the individual and through measuring proximity and factors that mediate its use. In the social psychology literature, the space around the body has been defined as the ‘area individuals maintain around themselves into which others cannot intrude without arousing discomfort or even withdrawal’ (Hayduk, 1983; Sommer, 1969). Once intruded the person may experience a perception of threat of psychological or biological integrity (Horowitz et al., 1964), which clearly emphasises the important influence that emotional and motivational factors can have on the use of space between people. At this point, this claim should sound familiar. In fact, the idea of body buffer zone and the proposed link between surrounding space and defence of the body come from IPS literature, but it has been recycled in the neurocognitive field as one of the functions assigned to PPS.

Graziano and Cooke were perhaps the first who formalized this hypothesis: “One possibility is that this nearby attentional space is related to the protective personal space described by Hall and others and the defensive flight zone described by Hediger. […] Neurons in cortical areas VIP and PZ are multimodal, responding to tactile, visual, and sometimes auditory stimuli […]. The receptive fields are usually though not always confined to the space near the body. These receptive fields are like bubbles of space anchored to the body surface. […] We speculate that these body-centred receptive fields in VIP and PZ could also form the neural basis for the psychological phenomenon of personal space and the ethological phenomenon of a flight zone” (Graziano and Cooke, 2006, pp.848-9).

Successively, Lloyd (2009) extended this view and claimed that the mechanisms and principles underlying the individual representation of the space surrounding the human body also mediate the space between interacting human partners. The purpose of her review was to bring together evidence from the disparate fields of cognitive neuroscience and neuropsychological studies of PPS, which typically focus on the behavioural and neural factors underlying the spatial coding of a single individual (or single body parts), with more ecologically valid studies of interpersonal behaviour. Aware of the two isolated fields of neurocognitive study of PPS and research on IPS behaviour, through a phenomenological approach Lloyd proposed a framework that aimed at investigating and interpreting the "neural mechanisms of ’social space’" (p. 298).

Hence, scholars from cognitive neuroscience and social psychology have looked w ith ever-growing interest at the possibility that IPS may emerge from lower level sensorimotor processing of PPS. Both representations, indeed, emphasize the importance of the body and are thought to serve a

protective function in response to possible threats approaching the body. Crucially, both are highly flexible and their plasticity depends on the dynamic relationship one is stabling with the surroundings: PPS is modulated to adapt to the constantly changing action requirements of our environment, while IPS is adjusted to maintain a comfortable distance from other individuals. Last, as previously reviewed, social interactions as well as other social and affective cues can also modulate the boundary of PPS (and, by definition, the boundary of IPS).

In this regard, Iachini and Coello (2015) stated that “social interactions require accurate control of interpersonal distances, and this would suggest that the encoding of peripersonal space is crucial, not only for the regulation of interactions with objects, but also for our social life” (p.208).

They offered the thesis that the two spaces share a common motor nature and pushed forward their speculations by going as far as to state that “From a theoretical perspective, […] the motor nature of space perception plays a crucial role in complex social processing, as peripersonal space encodi ng represents a key element in the regulation of distances in social interaction situations.” (Quesque et al., 2017, p.11), defining such motor nature as a “common underlying causal factor” (Quesque et al., 2017, p.2). In a more attenuated and testable form of such hypothesis, one might propose that the two representations are, at least, similarly sensitive to social aspects. In support of this, in a series of experiments the authors jointly assessed PPS and IPS in a virtual environment to investigate whether the two representations refer to a similar or different physical distance. To this aim, Iachini and Coello’s group compared PPS and IPS by means of two standard paradigms: reachability distance and comfort distance judgments towards human (male and female avatars) and nonhuman (cylinder and robot) virtual stimuli while standing still or walking towards stimuli (Iachini et al., 2014). Results showed that comfort distance was larger than reachability distance when participants were passive, being approached by the virtual stimuli. Nevertheless, reachability and comfort distances did not differ when participants could actively move towards the stimuli.

This finding was interpreted as evidence that the same motor processes subtending reachability judgments and the encoding of PPS also contribute to specify comfortable social distances. The other finding that should suggest communality between the two spaces is that both distances are modulated by human versus nonhuman stimuli. Somehow in line with previous data (Teneggi et al., 2013), distances were expanded with virtual objects and reduced with virtual humans. In addition,

there was a contraction of distance with virtual females as compared to males and an expansion with cylinder as compared to robot. In a subsequent examination, the same group replicated these patterns of results showing how distances are affected by the gender of the confederates: distance was smaller for female than male confederates. This effect was actually evident for comfort distance and as long as participants had to remain passive. In the latter case, i.e., when participants were passive and approached, both reachability and comfort distances were larger for the male than the female confederate. On the other hand, when participants could actively approach the confederates, they chose similar reachability distance for both female and male confederates. By examining age effects, it was also demonstrated that the comfort distance was larger when facing a virtual old adult than a young adult or child, in line with previous findings in social psychology (Iachini et al., 2016).

Not only “demographical” variables, but also contingency factors such as moral evaluation and facial expressions have been tested to explore the relationship between PPS and IPS. It was observed an increase of distance when seeing angry rather than happy virtual human, regardless of who was moving (i.e., whether the participant was approaching the virtual human or vice versa). The effect also appeared in reachability distance, but only if participants were passive and approached by the virtual human (Ruggiero et al., 2016). In the case of the manipulation of perceived morality, comfort distance was modulated according the negative (immoral), positive (moral), and neutral description of the virtual human facing participants, with largest comfort distance found in the negative and the smallest comfort distance in the positive condition. In contrast, in reachability only the moral – immoral comparison was significant (Iachini et al., 2015).

Highlighting the similar rather the different modulations, these findings were interpreted as providing support to the view that peripersonal and interpersonal spaces share a common motor nature and are endowed with finely tuned mechanisms for processing social information (Coello and Iachini 2016). Despite the fact that the analogy between such different construals developed within such separate domains is a very interesting approach, I would like to stress here that the lack of difference neither indicates the two construals are actually the same one nor implies they underlie a common psychological entity. Before concluding I wish also highlighting that, although it is an important issue that is currently the object of a very lively debate, it would be premature to draw any conclusions on the outcomes of these first studies. Keeping this in mind, one of the aims of this dissertation is thoroughly testing the possible relationships between PPS and IPS.