Effects of spatial attention on detection and identification of oriented lines

In this paper, we study the effects of spatial attention on detection and identification of oriented lines presented at near-threshold luminance. In the first experiment, we found that the cuing effect was greater when observers had to discriminate between two close orientations than when they had to discriminate between two far-apart orientations. In the second experiment, we examined the effects of peripheral cues on summation of low-contrast oriented lines. We found that the range of orientations within which summation occurred was greater when the cues were invalid than when they were valid. Our results suggest that attention to a specific location in the visual field modulates the neural channels which code orientation in at least two different ways: (a) spatial attention increases the responsivity of these channels to stimuli presented at this location, and (b) it reduces the bandwidths or ranges of orientations to which these channels are sensitive. These results suggest that the properties of the orientation-tuned channels, including those that seem to exert their effects at early stages of orientation processing (e.g., tuning function), may not be fixed, but rather vary according to the attention being paid to the spatial region within which the target stimulus is presented. (C) 2002 Elsevier Science B.V. All rights reserved.