Temporal response of the human visual system to suprathreshold luminance and opponent colour contrast gratings

The goal of the present study was to characterize the temporal processing of both suprathreshold luminance and opponent-colour defined contrast in the human visual system. We used a detection task in five experiments; following a 900 Hz, 2-cycle tone, observers were presented with a sinusoidal grating stimulus. The interval separating the waming tone and the presentation of the grating was manipulated to determine the influences of attentional dwell time in a cross-modal task. This theory states that the first of two successive events will interfere with the processing of the second event. In all four luminance experiments the gratings were presented with contrast levels of 8, 16 and 64 percent contrast. In the first experiment the contrast gratings were presented following interstimulus intervals (lSls) ranging from 100 to 1000 ms in 100 ms intervals. In Experiment 2 the lSls were 1000 ms and 1500 ms. In the third experiment gratings were presented following lSls ranging from 500 to 2000 ms in 500 ms intervals. In Experiment 4 gratings were presented following lSls ranging from 250 to 1000 ms in 250 ms intervals. In the opponent-colour experiment the gratings were presented with colour contrasts of red-green (R6), blue-yellow (BY) or red-blue (RB) following lSls of 100, 250, 500, and 750 ms. In all experiments the mean luminance of the gratings and the grey background was 10 cd/m2. Reaction times (RTs) were used to measure the latency difference in processing these gratings. The findings demonstrated that increases in suprathreshold contrast resulted in a significant decrease in response latency. In addition, we found decreased RTs for RG as opposed to BY and RB gratings. Finally, we were able to demonstrate an attentional dwell time in a cross-modal task. The implications of the above findings were discussed in conjunction with the relevant literature