Talgar C & Carrasco M (2002,
May). Covert transient attention increases the gain of spatial frequency
channels. Vision ScienceS Society, Sarasota, FL. 194-B2.59.
Directing transient covert attention to the target location enhances contrast
sensitivity across the contrast sensitivity function (Carrasco, Penpeci-Talgar
& Eckstein, 2001). Using critical band masking to characterize letter
identification, Solomon and Pelli (1994) reported that although observers
have access to many different bands of spatial frequencies to perform
the task, a single spatial frequency channel mediates letter identification.
In the present study, we used critical band masking to investigate whether
covert attention affects the gain and/or the spatial frequency tuning
of the channel mediating letter identification. We manipulated attention
using either a peripheral (cue at target location), a neutral-central
(cue at fixation) or neutral-distributed (one cue at each of 8 possible
locations) cue. All three cues indicated the time of target onset but
only the peripheral cue was informative about target location. The target
letter (N, Z, or X; presented for 40 ms in low or high-pass noise with
different cutoff frequencies) followed the cue at one of the 8 locations.
Distracter letters (V's) occupied the remaining locations. We measured
the energy threshold elevation (using the modified Quest staircase procedure;
Watson & Pelli, 1983; King-Smith et al. 1994) at each of the low and high-pass
cutoff noise frequencies. To derive frequency-dependent power gain of
the inferred filter, we took the derivative of the threshold energy with
respect to the cutoff frequency. We found that directing covert transient
attention to the target location using a peripheral cue resulted in an
enhanced gain of the channel mediating the task compared to when the two
different neutral cues were used. Having established that attention enhances
contrast sensitivity (Carrasco, Penpeci-Talgar & Eckstein, 2001), the
present results indicate that this enhancement is a result of a change
in the gain of the spatial frequency channel mediating the task.