Carrasco, M, Giordano, AM,
& McElree, B (2003). Can covert attention eliminate temporal disparities
in the visual field? Vision Sciences Society. Sarasota, FL.
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.