Background: 1) In addition to improving discriminability, covert attention accelerates the rate of visual information processing (Carrasco & McElree, 2001). 2) Contrast sensitivity is better along the horizontal than vertical meridian and better at the South than North location. These asymmetries are more pronounced as eccentricity increases. Covert attention improves discriminability at all locations to a similar degree (Carrasco et al., 2001, 2002). 3) Recently we have found that information accrual is faster: (a) at far than near eccentricities, (b) at the horizontal than vertical meridian, and within the vertical meridian at the S than N location. Goal: We investigated whether covert attention affects the rate of visual information processing as a function of: (a) eccentricity (4 or 9), (b) location at a given eccentricity (cardinal and intercardinal points at 4 or 9). Methods: We collected time-course functions for orientation discrimination with the response-signal speed-accuracy trade-off (SAT) procedure. Each trial began with a cue (67 ms), which was either informative (dot indicating the target location) or neutral (a dot at fixation). After a 53 ms ISI, Gabor patches with 0 or 7 distracters appeared for 40 ms. The target and distracters were presented at 8 equidistant locations from fixation at 4 or 9 eccentricity. A tone sounded at 1 of 7 SOAs, ranging from 40 to 2000 ms, prompting observers to respond. Results: Covert attention accelerated information accrual: (a) similarly for far and near eccentricities, (b) more on the vertical than the horizontal meridian and more at the N than S location. Conclusion: Covert attention improves visual temporal dynamics to the same degree at different eccentricities, but it speeds up information accrual more at the least privileged locations, i.e. along the vertical meridian, thus eliminating temporal asymmetries at a given eccentricity.
ASJC Scopus subject areas
- Sensory Systems