@article {4552, title = {The speed of human social interaction perception}, journal = {NeuroImage}, year = {2020}, month = {Jan-04-2020}, pages = {116844}, abstract = {

The ability to perceive others{\textquoteright} social interactions, here defined as the directed contingent actions between two or more people, is a fundamental part of human experience that develops early in infancy and is shared with other primates. However, the neural computations underlying this ability remain largely unknown. Is social interaction recognition a rapid feedforward process or a slower post-perceptual inference? Here we used magnetoencephalography (MEG) decoding to address this question. Subjects in the MEG viewed snapshots of visually matched real-world scenes containing a pair of people who were either engaged in a social interaction or acting independently. The presence versus absence of a social interaction could be read out from subjects{\textquoteright} MEG data spontaneously, even while subjects performed an orthogonal task. This readout generalized across different people and scenes, revealing abstract representations of social interactions in the human brain. These representations, however, did not come online until quite late, at 300 ms after image onset, well after feedforward visual processes. In a second experiment, we found that social interaction readout still occurred at this same late latency even when subjects performed an explicit task detecting social interactions. We further showed that MEG responses distinguished between different types of social interactions (mutual gaze vs joint attention) even later, around 500 ms after image onset. Taken together, these results suggest that the human brain spontaneously extracts information about others{\textquoteright} social interactions, but does so slowly, likely relying on iterative top-down computations.

}, issn = {10538119}, doi = {10.1016/j.neuroimage.2020.116844}, url = {https://www.ncbi.nlm.nih.gov/pubmed/32302763}, author = {Leyla Isik and Mynick, Anna and Pantazis, Dimitrios and Nancy Kanwisher} } @article {4296, title = {Brain Signals Localization by Alternating Projections}, year = {2019}, month = {08/2019}, abstract = {

We present a novel solution to the problem of localization of brain signals. The solution is sequential and iterative, and is based on minimizing the least-squares (LS) criterion by the alternating projection (AP) algorithm, well known in the context of array signal processing. Unlike existing solutions belonging to the linearly constrained minimum variance (LCMV) and to the multiple-signal classification (MUSIC) families, the algorithm is applicable even in the case of a single sample and in the case of synchronous sources. The performance of the solution is demonstrated via simulations.

}, author = {Amir Adler and Mati Wax and Pantazis, Dimitrios} } @article {4180, title = {How face perception unfolds over time}, journal = {Nature Communications}, volume = {10}, year = {2019}, month = {01/2019}, abstract = {

Within a fraction of a second of viewing a face, we have already determined its gender, age and identity. A full understanding of this remarkable feat will require a characterization of the computational steps it entails, along with the representations extracted at each. Here, we used magnetoencephalography (MEG) to measure the time course of neural responses to faces, thereby addressing two fundamental questions about how face processing unfolds over time. First, using representational similarity analysis, we found that facial gender and age information emerged before identity information, suggesting a coarse-to-fine processing of face dimensions. Second, identity and gender representations of familiar faces were enhanced very early on, suggesting that the behavioral benefit for familiar faces results from tuning of early feed-forward processing mechanisms. These findings start to reveal the time course of face processing in humans, and provide powerful new constraints on computational theories of face perception.

}, doi = {10.1038/s41467-019-09239-1}, url = {http://www.nature.com/articles/s41467-019-09239-1}, author = {Dobs, Katharina and Leyla Isik and Pantazis, Dimitrios and Nancy Kanwisher} }