Interhemispheric difference for upright and inverted face perception in humans: an event-related potential study

We recorded event-related potentials (ERPs) to investigate the interhemispheric difference of the N170 component for upright and inverted face perception in detail in fifteen healthy subjects. This is the first ERP study focusing on interhemispheric differences for face perception by showing faces in the hemifield. The face inversion effect, the prolonged latency and enhanced amplitude were found in both hemispheres. We found that the peak latency of the N170 following both upright and inverted face stimulation showed no significant difference between each hemisphere, though the N170 latency for the inverted face in the left hemisphere was shorter than that in the right hemisphere. The N170 recorded from the hemisphere ipsilateral to the stimulated hemifield showed unique findings. The interhemispheric time difference of the N170 between the right and the left hemispheres when the inverted face was presented in the left hemifield was significantly shorter than in the other three conditions. This unique finding may indicate that the conduction time from the right to the left for inverted face perception is faster than the other conditions, or that the left hemisphere specifically processed the inverted face very rapidly after receiving signals from the right hemisphere. If the N170 was generated by some, at least two, temporally overlapping activities, the different style of a summation of these activities may cause the unique findings found in this study. In conclusion, by presenting face stimuli in the hemifields, we could identify several new findings regarding the N170 component related to the face inversion effect.