Cameron, EL, Tai, JC, & Carrasco, M (2001, May). Effects of transient
covert attention on the psychometric function. Vision ScienceS Society,
Sarasota, FL. 78-B11.
Purpose. Directing attention to a particular location is known to improve
accuracy and decrease reaction time for stimuli that appear at that location.
In this study we assessed how transient covert attention affects the psychometric
function by measuring performance on an orientation discrimination task
as a function of target contrast while directly manipulating transient
Methods. Observers performed a 2-AFC orientation discrimination task on
targets (Gabor patches between 2 and 12 cpd) that appeared at 4.5 degrees
eccentricity at one of 8 equally spaced locations around a canonical circle.
The timing between pre-cue onset and target offset was brief enough to
preclude saccadic eye movements. We used the method of constant stimuli
and measured performance (percent correct) as a function of stimulus contrast
in neutral and peripheral pre-cue conditions. Both pre-cues signaled target
onset, but only the peripheral pre-cue indicated target location.
Results. Performance increased as a function of stimulus contrast for
both neutral and peripheral pre-cue conditions. Overall, performance was
higher in the peripheral pre-cue condition, and the largest improvement
was in the threshold region (60-90% correct). In the peripheral pre-cue
condition, the psychometric function shifted towards lower contrasts and
had a shallower slope. In addition, we replicated a horizontal meridian
advantage and an impairment for targets that appear directly above fixation
(Carrasco, Penpeci-Talgar & Cameron, Spatial Vision, in press). Moreover,
performance fields showed a similar pattern at all but the highest contrast,
where performance was at asymptote. The slope of the psychometric function
was steeper for targets on the horizontal than on the vertical meridian.
Conclusion. Overall, performance is higher in peripheral than in neutral
pre-cue conditions. Attention decreases the slope and shifts the psychometric
to lower contrasts at all target locations.