M. Carrasco et al., Spatial covert attention increases contrast sensitivity across the CSF: support for signal enhancement, VISION RES, 40(10-12), 2000, pp. 1203-1215
This study is the first to report the benefits of spatial covert attention
on contrast sensitivity in a wide range of spatial frequencies when a targe
t alone was presented in the absence of a local post-mask. We used a periph
eral precue (a small circle indicating the target location) to explore the
effects of covert spatial attention on contrast sensitivity as assessed by
orientation discrimination (Experiments 1-4), detection (Experiments 2 and
3) and localization (Experiment 3) tasks. In all four experiments the targe
t (a Gabor patch ranging in spatial frequency from 0.5 to 10 cpd) was prese
nted alone in one of eight possible locations equidistant from fixation. Co
ntrast sensitivity was consistently higher for peripherally- than for neutr
ally-cued trials, even though we eliminated variables (distracters, global
masks, local masks, and location uncertainty) that are known to contribute
to an external noise reduction explanation of attention. When observers wer
e presented with vertical and horizontal Gabor patches an external noise re
duction signal detection model accounted for the cueing benefit in a discri
mination task (Experiment 1). However, such a model could not account for t
his benefit when location uncertainty was reduced, either by: (a) Increasin
g overall performance level (Experiment 2); (b) increasing stimulus contras
t to enable fine discriminations of slightly tilted suprathreshold stimuli
(Experiment 3); and (c) presenting a local post-mask (Experiment 4). Given
that attentional benefits occurred under conditions that exclude all variab
les predicted by the external noise reduction model, these results support
the signal enhancement model of attention. (C) 2000 Elsevier Science Ltd. A
ll rights reserved.