Response characteristics of the normal retino-cortical pathways as determined with simultaneous recordings of pattern visual evoked potentials and simple motor reaction times

Purpose: In an attempt to explain the existing discrepancies regarding the relationship between electrophysiological and psychophysical measurements o f visual transmission time we compared, in humans, the response characteris tics of the normal retino-cortical pathways with simultaneously obtained pa ttern visual evoked potentials (PVEP) and simple motor reaction times (RT). Methods: PVEPs and manual RTs were recorded simultaneously using a reversi ng checkerboard with different spatial frequency and contrast combinations chosen to elicit responses favoring the magnocellular or parvocellular path ways. The amplitude and peak time of the P1 wave of the PVEP were compared to the mean RT. Other parameters of the RT, such as mode and standard devia tion were also considered. Results: The RT is not modified in the same fash ion as the peak time of the P1 wave of the PVEP, the peak time of the PVEP demonstrating a spatial frequency selectivity, while the RT does not. Furth er comparative analysis of the PVEP and RT shows that the RT is faster for stimuli of lower contrast and spatial frequency, while the PVEP amplitude i s larger and its peak time shorter for higher contrast and spatial frequenc y stimuli. Conclusions: Our findings suggest that PVEP and RT measures recr uit distinct physiological characteristics and appear to be differently mod ulated while travelling along the retino-cortical pathway. Our results also show the importance of obtaining electrophysiological and psychophysical m easures concomitantly to insure elimination of combined inter-stimulus and inter-session variability. (C) 2001 Elsevier Science Ltd. All rights reserv ed.