Visual attention can increase spatial resolution even when it leads to a decrease in performance. Whether this effect is mediated by reduction of external noise or by signal enhancement is an unsettled question. Although we previously demonstrated that attention can improve speed and accuracy in an acuity task, those experiments made use of a local postmask, which could be considered a source of external noise. In this work, a peripheral cue improved observers' abilities to indicate which side of a Landolt-square target had a gap whether or not a local postmask was used and with both central- and spread-neutral cues. In addition, we documented the presence of visual field inhomogeneities in a resolution task. Given that these experiments presented the target alone with no external noise added (i.e., without distracters or masks), our results indicate that transient attention enhanced the quality of the stimulus representation. Furthermore, because performance in the Landolt-square task indexes resolution, this attentional benefit indicates that transient attention can produce signal enhancement through finer spatial resolution.
Transient covert attention affects basic visual dimensions such as contrast sensitivity, spatial resolution, and temporal resolution. Two recent studies provide evidence of corresponding phenomenological changes: The increase in contrast sensitivity and spatial resolution at the attended location is associated with increased apparent contrast (M. Carrasco, S. Ling, & S. Read, 2004) and apparent spatial frequency (J. Gobell & M. Carrasco, 2005). Here, we assessed a phenomenological correlate of attention for temporal vision, asking whether and how transient attention affects perceived flicker rate. We employed a psychophysical method developed to assess changes in appearance by manipulating transient attention via uninformative spatial cues. In each trial, two suprathreshold Gabor stimuli, appearing briefly to the left and right of fixation, were counterphase modulated at either the same or different temporal frequencies. To assess appearance, we asked observers to perform an orientation discrimination task contingent on perceived flicker rate: "What was the orientation of the Gabor that flickered faster?" Results indicated that perceived flicker rate increased at the cued location. A control experiment, in which observers reported the orientation of the Gabor that flickered slower, ruled out a cue bias explanation. We conclude that transient attention increases perceived flicker rate.
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