Impairment in facial expression perception but normal biological motion perception in a patient with a lesion to right posterior STS

Abstract

Humans often perceive body and facial expression cues simultaneously, but it is unclear whether these perceptual processes rely on joint or separate neural mechanisms. Support for joint mechanisms comes from recent studies showing that brain regions in the pSTS processing facial dynamics adjoin or somewhat overlap those processing human biological motion. On the other hand, support for disjoint mechanisms comes from LG, a developmental visual agnosic individual with normal biological motion perception but impaired perception of dynamic face expressions. To gain further insights about these mechanisms, here we investigated Faith, a 55-year-old woman with acquired prosopagnosia. Faith reports problems deciphering facial expressions but not body language. We tested her ability to perceive facial expressions from dynamic subtle or intense cues, and her biological motion perceptual thresholds from point light displays. In line with Faith’s subjective reports, we first found that her biological motion perceptual thresholds and her reaction times were in the normal range compared to age and gender-matched neurotypical controls (n=17) or to other control groups (n=13, n=18, n=18). Second, we found that her perception of subtle dynamic facial expressions was significantly impaired. We also delineated Faith’s lesion (extending into her right temporal and ventral cortex), and compared it to the expected locations of pSTS regions sensitive to facial expressions and to biological motion. While brain lesions do not often follow regional borders, Faith’s dissociation provides further evidence that the perception of dynamic body cues and the perception of dynamic facial cues depend on different processing routes.

Acknowledgement: This research was supported by the Israel Science Foundation (grant No. 4115841) to SGD, by the NSF Graduate Research Fellowship to SBH, and by the NSF grant 1634098 to BD.