The role of dorsal and ventral visual pathways on holistic processing of indivudual facial parts

The main purpose of this study is to examine the behavioral and electrophysiological responses that occur in the process of holistic perception of individual facial parts. It has been demonstrated in the literature that humans process faces holistically, and that manipulations at spatial frequencies also affect this processing. In the ERP studies conducted through the inversion and composite face paradigms, it was found that the ERP components that emerge when the face configuration is distorted differ from the processing of normal faces. In addition, it has been shown in the literature that faces in different spatial frequency bands differ in terms of holistic processing. However, in this context, there is no study conducted using the part/whole task. It can be said that the dorsal and ventral visual pathways are the regions where the information reaching the visual system is evaluated at the highest level. Many neuroimaging studies have shown that some regions, especially in the ventral pathway, have an active role in face processing. However, a recent study has shown that the dorsal pathway also plays an active role in the perception of configurational changes in faces. In this study, the part/whole task was applied to the participants in different spatial frequency conditions, and the accuracy of their answers, response times, and also EEG measurements were recorded. These recorded measurements were analyzed to evaluate both the part/whole effect at different spatial frequencies and the spatial frequency effect on the responses given in part and whole conditions. In addition, EEG data were used for the analysis of P100, N170 and N250 event-related potentials (ERP) emerging in the occipital, dorsal and ventral region electrodes. Spatial frequency effect as well as part/whole effect were evaluated in ERPs occurring in all electrode regions. In addition, OIPs occurring in the ventral and dorsal region electrodes were compared. It has been shown that participants can recognize a part of a face better than when they are in a whole face condition in all spatial frequencies. In addition, consistent with the previous literature, it was observed that the part/whole effect was higher in the low spatial frequency condition than in the other conditions in this study. On the other hand, the findings regarding the ERP components were observed to cause P100, N170 and N250 components with higher amplitudes in the ventral region electrodes of both face parts and whole faces at all spatial frequencies compared to the dorsal region electrodes. However, while the N170 and N250 components that emerged in the ventral region differed in all spatial frequencies in part and whole conditions, no part/whole effect on these components was observed at high spatial frequencies in the dorsal region electrodes. It was also found that in most conditions unfiltered and low spatial frequency stimuli caused higher P100 and N170 but lower N250 component amplitudes than those at high spatial frequency.