Integration Times Reveal Mechanisms Responding to Isoluminant Chromatic Gratings: A Two-Centre Visual Evoked Potential Study

© Oxford University Press, 2014. Visual evoked potentials (VEPs) provide an objective technique for monitoring the integrity of visual pathways and have been used to monitor the activity of post-receptoral chromatic mechanisms. The temporal properties of visual processing may now be characterized in terms of VEP integration time, defined as the stimulus duration during which response components are summed to give the highest amplitude VEP. The onset of a luminance-modulated pattern of moderate spatial frequency elicits the largest VEP when the grating appearance is brief, i.e. about 40-60 ms, consistent with predominant activation of transient mechanisms. Likewise, the greatest amplitude chromatic VEPs are obtained with isoluminant coarse L/M gratings when the offset period exceeds the onset duration. This chapter compares L/M tritan integration times by obtaining VEP responses to the onset of two cycles per deg gratings of varying onset durations, in order to characterize the temporal response mechanisms contributing to the two chromatic processing streams.