engleski

Neurodynamics of very early face processing

Our analysis of the entire transient evoked MEG response to faces indicated a distributed cortical network involved in face processing whose complexity was task dependent. In this talk, we will present our results on very early face processing. Firstly, we wanted to determine the earliest dissociation of MEG responses to faces and objects avoiding the differences in the low-level physical features of the stimuli, which are known to modulate early brain responses. A novel set of stimuli was created so that their combinations did not have any differences in the visual-field location, spatial frequency or luminance contrast. Differing responses to face and object (flower) stimuli were found about 100 ms after stimulus onset in the occipital cortex. In further study, we explored the earliest neuromagnetic responses to a change in face stimulus. Upright and inverted faces were presented in an oddball paradigm in which standards and deviants differed in emotion or identity. MEG responses and dynamics of estimated sources revealed larger and earlier responses to deviant compared to standard faces around 100 ms only in upright position, implying that face-related processing takes place at these early latencies. To explore how quickly we can recognize a face as a face, and how long it takes to recognize face identity and emotional expression, we used the onset of eye blink as a behavioral response. The subjects were more correct and faster to distinguish between faces and houses than when responding to particular face emotion and identity. However, our data indicated that we can recognize face identity and emotion very quickly, sometimes only 150 ms after stimulus onset. This corroborates our previous results from MEG studies on the face-sensitive response around 100 ms after stimulus onset. References (1) Susac A, Ilmoniemi RJ, Pihko E, Nurminen J, Supek S: Early dissociation of face and object processing: a magnetoencephalographic study. Hum Brain Mapp, 30, 917-927, 2009 (2) Susac A, Ilmoniemi RJ, Pihko E, Ranken D, Supek S: Early cortical responses are sensitive to changes in face stimuli. Brain Res, 1346, 155-164, 2010 (3) Susac A, Ilmoniemi RJ, Ranken D, Supek S: Face activated neurodynamic cortical networks. Med Biol Eng Comput, 49, 531-543, 2011 (4) Usakli AB, Susac A, Gurkan S: Fast face recognition: eye blink as a reliable behavioral response. Neurosci Lett, 504, 49-52, 2011

magnetoencephalography (MEG); face processing; object recognition; human visual system; nonlinearity

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