The role of attention in central and peripheral motion integration.

Attention has been shown to modulate visual processing in a wide variety of tasks. We tested the influence of attention on the temporal integration of motion for both central and peripherally viewed targets (6 degrees x 6 degrees ). Consistent with previous results, motion sensitivity for a brief motion signal (70-3500 ms) embedded in noise (10 s) increased as a function of motion duration up to a critical duration of about 1.5 s. Summation times for centrally and peripherally viewed targets were similar. An effect of eccentricity was found, however, in a double-motion task, in which two brief (150 ms) motion signals were presented with varying delays (0-7 s) of random noise between the two signals. Specifically, the maximum delay between the two signals that still supported temporal summation (summation constant) was about three times longer for centrally viewed targets (3.5-4.5 s versus 1.5-2 s). We investigated the role of spatial attention in the double-motion task by adding a concurrent color contrast discrimination task. The addition of the concurrent task dramatically reduced differences in the summation constant for central and peripheral targets, without reducing overall motion sensitivity. Thus, attention appears to specifically modulate temporal summation, suggesting that the long integration times found for motion coherence are mediated by attention.