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Carrasco, M., Penpeci-Talgar, C. & Eckstein, M. (2000). Spatial attention
increases contrast sensitivity across the CSF: Support for signal enhancement.
Vision Research, 40: 1203-1215.
Abstract
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
target alone was presented in the absence of a local post-mask. We used
a peripheral 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 1Ð4), detection
(Experiments 2 and 3) and localization (Experiment 3) tasks. In all four
experiments the target (a Gabor patch ranging in spatial frequency from
0.5 to 10 cpd) was presented alone in one of eight possible locations
equidistant from fixation. Contrast sensitivity was consistently higher
for peripherally- than for neutrally-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 were presented with vertical and horizontal
Gabor patches an external noise reduction signal detection model accounted
for the cueing benefit in a discrimination task (Experiment 1). However,
such a model could not account for this benefit when location uncertainty
was reduced, either by: (a) Increasing overall performance level (Experiment
2); (b) increasing stimulus contrast 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 variables predicted by the external
noise reduction model, these results support the signal enhancement model
of attention.
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