Research. 42: 949-967.
Cameron, E. L., Tai, J. C., & Carrasco, M. (2002). Covert attention
affects the psychometric function of contrast sensitivity.
We examined the effect of transient covert attention on the psychometric
function for contrast sensitivity in an orientation discrimination
task when the target was presented alone in the absence of distractors
and visual masks. Transient covert attention decreased both the
threshold (consistent with a contrast gain mechanism) and, less
consistently, the slope of the psychometric function. We assessed
performance at 8 equidistant locations (4.5 deg eccentricity)
and found that threshold and slope depended on target location--both
were higher on the vertical than on the horizontal meridian, particularly
directly above fixation. All effects were robust across a range
of spatial frequencies, and the visual field asymmetries increased
with spatial frequency. Notwithstanding the dependence of psychometric
function on target location, attention improved performance to
a similar extent across the visual field. Given that, in this
study, we excluded all sources of external noise, and that we
showed experimentally that spatial uncertainty cannot explain
the present results, we conclude that the observed attentional
benefit is consistent with signal enhancement.