Spatial covert attention increases contrast sensitivity across the CSF: support for signal enhancement

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 1-4), 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.

Voluntary and involuntary attention affect face discrimination differently

“…There are cases in the literature where nonpredictive cues or short SOAs do affect accuracy (e.g., Cameron et al, 2002;Carrasco et al, 2000;Horstmann, 2002;Shiu & Pashler, 1994). One critical difference between those that show an accuracy effect and those that do not is what determines the limits on performance.…”

“…The more practice that observers had, the shorter the critical SOA for voluntary attention, as short as 50 ms. Thus the results of Carrasco et al (2000Carrasco et al ( , 2002 may have reflected voluntary attention.…”

Age-related increase in top-down activation of visual features

“…The agerelated increase in top-down attention may represent a compensatory response to age-related decline in the efficiency of bottom-up visual processing (Madden, 2006). As a result, the level of signal is increased, and accompanying noise is decreased (Carrasco, Penpeci-Talgar, & Eckstein, 2000;Kastner, 2004), facilitating the discrimination of target identity. Reaction time as a function of task condition, display size, and age group.…”

Visual attention and stability

“…without making an eye movement) to a stimulus, we perceive that stimulus more clearly than we would if attention were unfocused or directed elsewhere. This increased perceptual ability can be measured as an increased sensitivity to faint stimuli [3], enhancement of perceived contrast [4] and decreased reaction times to attended stimuli [5]. In addition, visual attention is characterized by an inhibitory surround: processing of stimuli outside of but near the focus of attention is suppressed (e.g.…”