Ling, S, & Carrasco, M
(2003). Sustained and Transient Covert Attention: A Test for Signal Enhancement.
Vision Sciences Society. Sarasota, FL.
We know that the former is conceptually-driven and voluntary, whereas
the latter is stimulus-driven and automatic. However, we do not know whether
both types of attention are mediated by similar mechanisms. It has been
shown that the Signal Enhancement Model can account for the effect of
transient attention (Carrasco, Penpeci-Talgar, Eckstein, 2000). In this
study, by using either an endogenous or exogenous precue, we investigated
whether the same mechanism could mediate both sustained and transient
by comparing their effects on contrast sensitivity across a range of spatial
frequencies. Either an endogenous (a 150ms central pointer indicating
target location followed by a 150ms ISI) or exogenous (a small circle
peripherally flashed for 40ms adjacent to the target location followed
by a 60ms ISI) precue was used to indicate the location of the target
- a Gabor patch ranging in spatial frequency from 1-8 cpd. Five observers
performed a 2AFC orientation discrimination task on a supra-threshold
target tilted 4° to the right or left. The target appeared for 100ms at
one of 8 possible locations at 4° eccentricity. To eliminate all variables
that could be accounted for by an External Noise Reduction model, the
target was supra-threshold and presented alone, without any distracters
or masks. Contrast thresholds were obtained via an adaptive staircase
procedure (QUEST). We compared the magnitude of contrast sensitivity enhancement
brought about by both types of attention. According to External Noise
Reduction, in the absence of any added external noise there should be
no attentional effect on contrast sensitivity. However, given these conditions,
we found that sustained covert attention enhanced contrast sensitivity.
Moreover, the magnitude of the effect was similar to that of transient
attention. These results provide evidence in support of the existence
of Signal Enhancement for both types of covert attention.