Encoding of biologically significant information in the human brain: face and biological motion perception.

Abstract

Inherently social, humans communicate identity, emotion, and intention mainly via visual signals ― faces and body motions. We are highly efficient in processing and recognizing such biologically salient cues, so much so that it seems effortless. This dissertation presents four studies which employ both psychophysical and brain imaging techniques to probe the neural encoding of faces and biological motion. Study 1 behaviorally demonstrates that a substantial amount of information, including face orientation, can be processed in the absence of observers’ conscious awareness. Study 2 and Study 3 further examine the cortical and sub-cortical processing of facial information that take place at the subconscious level. By rendering face images invisible through interocular suppression, distinct patterns of responses are revealed in FFA, STS, and the amygdala, with STS and the amygdala being selectively sensitive to facial-expression information. Study 4 focuses on the processing of local biological motion signals. A series of experiments show that such signals are processed automatically in the visual system independent of global form and global pattern of motion, and that dorsal occipito-parietal areas are the prime neural candidate for the "life motion detector". Together, these studies indicate that the human visual system is sensitive to biologically significant information, which can be processed without awareness. The findings add to our understandings of the brain mechanisms underlying humans' superb processing of face and biological motion information.