How do we process multiple-person scenario?
(Project THEMPO – ERC StG)
Trani, Puglia. Photo by Giovanni Albore
The ability to quickly recognize conspecifics among other entities and to understand rapidly what they are doing, is a fundamental requirement for a social species such as the human. In the past decades, cognitive neuroscientists have gained important knowledge on these abilities, by studying how the human mind/brain recognizes a face or a body, and infers the goal and intention behind the current body pose or activity. However, in real life, a person is most often seen among other persons. For instance, when there is one person who is speaking, it is very likely that she is nearby one or more individuals who are listening. The readiness with which an observer understands that people in the scene are communicating, makes it unlikely that this understanding is achieved through a sequential, one-by-one processing of each person’s face, body posture, motor activity, goal, intention, emotion, and so on. Our work starts from the hypothesis that the human brain must be equipped with specialized mechanisms to parse the environment, select the portion in which a social interaction is happening, and process that portion of the environment as a whole. Our main objective is to explain how this is done, in terms of cognitive stages and neural operations. In this effort, we take advantage of cognitive manipulations, neurostimulation methodology (TMS) and advanced analytical approaches to decode information latent in neural patterns recorded with functional neuroimaging (fMRI).
Over the past decades, cognitive neuroscientists have gathered evidence showing that a human face or a human body is special to our mind/brain, that is, it is processed with the highest priority and more efficiently than other objects in the environment. But how does the system behave when, instead on one person, we see two (or more) people?
We have set up a behavioral paradigm, based on backward masking, to measure the potency of stimuli in gaining access to awareness. In this paradigm, stimuli are presented at perceptual threshold so that sometimes the visual system fails to process them. The rationale is that, under conditions of low-visibility, stimuli that are privileged by the human visual system are more likely to pass the threshold to be recognized correctly, than other stimuli. In this way, we have shown that two bodies facing one another were more likely to be recognized than the same two bodies facing away away from each other (Papeo et al., 2017). Moreover, we have measured the inversion effect (IE), the cost on recognition, of seeing bodies upside-down as opposed to upright, as an index of visual sensitivity: the greater the visual sensitivity, the greater the IE. IE was increased for facing (vs. nonfacing) dyads, whether the head/face direction was visible or not, which implies that visual sensitivity concerns two bodies, not just two faces/heads. Moreover, the difference in IE for facing vs. nonfacing dyads disappeared when one body was replaced by another object. This implies selective sensitivity to a body facing another body, as opposed to a body facing anything. Finally, the IE was reduced when reciprocity was eliminated (one body faced another but the latter faced away) (Papeo & Abassi, 2019). Thus, the visual system is sensitive selectively to dyadic configurations that approximate a prototypical social exchange with two bodies spatially close and mutually accessible to one another.
This research adds to a body of results, showing that the human perceptual system is tuned to entities with social value, and go beyond this showing that visual perception is sensitive not only to socially-relavant entities but also to socially-relevant relations between those entities.
Papeo L., Stein T., Soto-Faraco S. (2017). The two-body inversion effect. Psychological Science, 28(3), 369-379 » PDF
Papeo L., Abassi E. (2019). Seeing social events: The visual specialization for dyadic human-human interactions. the Journal of Experimental Psychology: Human Perception and Performance, XX(X), XX-XX » PDF
Neural selectivity to a two-body shape
fMRI results coming soon 🙂
Abassi E. & Papeo L. (in prep). Neural sensitivity to a two-body shape Submitted for publication, XX(X), XXX » PDF