Analysis of Visually Psychological Phenomena Using Electroencephalograph

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Apparent motion is a perceptual phenomenon of motion that occurs when at least two spatially separated visual stimuli are presented under appropriate temporal conditions. After the presentation of alternating apparent motion stimuli, motion perception is replaced by the cessation of motion, breakdown. This study investigates the neural activities of the brain using steady-state visual evoked potentials (SS-VEPs) during continuous perception of visual motion. Psychophysical measurements were taken to analyze the stimulus conditions that induce coherent apparent motion. Time till breakdown (TTB) was used as a measurement of motion strength in alternate motion.The results showed that the optimal stimulus condition for inducing coherent motion was (a) between 2 Hz and 3 Hz temporal frequency and (b) less than 2 degrees of stimulus separation. SS-VEPs in response to continuously alternating apparent motion stimuli with 2 Hz of temporal frequency and with 2 degree of spatial separation were measured (apparent motion perception). For the control condition, SS-VEPs, in response to two point simultaneous presented stimuli were also measured. A prominent positive peak around the same latencies, particularly over the right occipital and temporal regions, was observed for SS-VEPs responses to apparent motion stimulation.To investigate the localization of the neural sources, brain evoked magnetic fields in response to apparent motion stimuli were measured using a whole-head magnetometer. Peak magnetic fields were observed in the latency range of at around 180 msec after the stimulus onset. The neural sources in this epoch were estimated to lie in the border between occipital and temporal areas in the contra-lateral hemisphere, which corresponds to the extrastriate visual cortex, including the middle temporal area.These results suggest that the larger positive potentials elicited over the right occipital to temporal region continuously perceive apparent motion.