Effects of Task Requirements . . . continued
Thirty male and 20 female undergraduate
psychology students aged between 17 and 30 years (M = 19.49, SD
2.41 years) participated. Each subject was allocated at random to either
Group Number or Group Longer.
Apparatus and Procedure:
Subjects were told that a series of
two shapes would be presented as well as a tone. They were instructed to
perform two tasks concurrently8:
Subjects in both groups received the same
stimulus arrangements. Shape presentations were arranged into four blocks
of 24. Each block consisted of 12 presentations of a circle and 12 presentations
of an ellipse (see Figure 2). Seventy-five percent of the presentations
of each shape lasted for 5 s, whereas the remaining presentations lasted
for 7 s (i.e., longer-than-usual). Shape presentations were separated by
intertrial intervals that varied among 9, 12, and 15 s with a mean of 12
The counting task. Group Number
were instructed to count the number of presentations of one shape (circle/ellipse)
and to ignore presentations of the other shape (ellipse/circle). Group
Longer were instructed to count the number of longer-than-usual presentations
of one shape (circle/ellipse) and to ignore presentations of the other
shape (ellipse/circle). The shape to be counted is designated as task-relevant,
whereas the shape to be ignored is designated as task-irrelevant irrespective
of its duration.
The RT task. Subjects were asked to press a button on
a microswitch a quickly as possible whenever a tone was presented, including if it was presented
during shape presentations or between shape presentations.
The RT probe was a tone presented for
500 ms at a frequency of 1000 Hz. Forty-eight of the RT probes were
presented during the intertrial intervals (12 in each block). The remaining
48 probes were presented during the shapes. Within each block, six probes
were presented during the circle and six during the ellipse. For each shape,
two of the probes were presented each at 50, 150, and 250 ms following
The dependent measures consisted of:
Number of shapes counted as per the instructions
for each group.
The presence of a button press during
shapes that did not contain a RT probe stimulus (referred to here as "false
Secondary RT to probes presented during
the shapes at the three probe positions of 50, 150, and 250 ms.