Abstract
The spatial distribution and the temporal dynamics of attention have been studied countless times. Although these two factors are well understood in isolation, their interaction remains much less clear. How does the shape of the attentional focus evolve across time? To answer this question we measured a quantitative space-time map of both endogenous and exogenous attention in humans. To sample attention effects in the space-time domain we tested the visibility of a low contrast target presented at different distances and delays from a cue in a noisy background. For exogenous attention we used a non-informative high-contrast peripheral cue at a random location 5° from fixation. In the endogenous condition we used a central informative arrow cue pointing left or right. We sampled the spatial domain as the Euclidean cue-target distance, locating the target randomly on the screen in the exogenous condition, and randomly along the horizontal midline in the endogenous condition. As an indirect measure of attention, we determined, for each distance and delay from the cue, the background contrast compensation required to keep performance at 75% (adjusted with a staircase procedure). After more than 94,000 trials in 13 subjects, the space-time mapping of exogenous attention revealed a progressive enhancement from 50 to 275 ms, extending up to 8° from the cue. Endogenous attention maps (over 40,000 trials in 8 subjects) showed an early (100 ms) enhancing effect centered on the cue, with a later deployment at the cued side peaking between 8 and 10° at 400 ms after cue onset. Finally, we measured the interdependency between the spatial pattern of visual attention and its temporal dynamics: most of the data could be explained by a constant spotlight shape, independent of time. Our results represent the first detailed space-time maps of both endogenous and exogenous visual attention.
CONICYT, EURYI and ANR 06JCJC-0154.