Visual information processing on symmetric and asymmetric objects in human brain—an evoked potential study

Electrophysiological studies on brain evoked potential (BEP) have shown that the discrimination between object categories starts in the occipito-temporal cortex, while the relatively simple characteristics of objects are differentiated in the visual cortex. However, where and when the discrimination of symmetrical level in the visual general object starts are questions whose answers are largely unclear. This study is aimed at investigating the BEP patterns in humans when perceiving symmetry-variated complex object images. Using 12S-channel EEG scalp electrodes, the BEP responses from seven healthy subjects to the gray-scaled images of five different objects with different levels of horizontal and vertical symmetry were recorded. The results showed that the BEPs recorded from visual cortex and centro-parietal sites at around 100 ms and 300 ms, respectively, after stimulus onset were not significantly affected. The correlation between BEP and symmetry level seemed to be revealed by the latency differences at occipito-temporal sites around 170 ms after stimulus onset.