Selective attention can be studied in visual and spatial tasks. In visual
task, one method is to ask participants to ignore some stimulus dimensions
(e.g., identity, location) and respond based on a target dimension
(e.g., color). In this study, we asked the subjects to attend to color and
ignore the shape of stimuli.
The stimuli were some familiar colored shapes. Each stimulus had
one of four colors (red, yellow, green, and white), and had one of four
shapes (triangle, quadrangle, hexagon and round). The two stimuli in
a pair were sequentially presented. The first stimulus and the second
stimulus were presented on a monitor screen for 300 ms each with an
inter-stimulus interval of 500 ms. Another trial began after 5 s ITI
(inter-trial interval) (see Fig. 1). The stimuli were presented at the
screen center of a computer-controlled monitor to each participant
with a black background. The stimulus pairs were randomly presented
50 times in sequence and had equal probability. Subjects were seated
at 1 m distance from the screen. They were instructed to sit quietly
and to look at the cross in the center of the screen. The averaged visual
angle of S1 and S2 was adjusted to 2.1°. In this task, participants were
asked to discriminate whether the color of S2 was identical to that of
S1 and ignored the shape of the stimulus. When the color of S2 was
the same as that of S1, they were asked to press the left button of a
push pad; when the color of S2 differed from S1, they pressed the
right button. In statistic analysis, we divided the stimuli into two types
(color match and color mismatch).