Effects of Task Requirements . . . continued
The instruction to count the number
of longer-than-usual task-relevant shapes resulted in a more difficult
task than counting the number of task-relevant shapes. Fifteen participants
in Group Number reported the correct number (i.e., 48), whereas only three
participants in Group Longer gave the correct number (i.e., 12).
The frequency of false alarms committed
in each block, collapsed across groups, is shown in Figure 3. As can be
seen, more false alarms occurred during task-relevant shapes than during
task-irrelevant shapes in each trial block.
When group RT was compared, the results
did not replicate those found by Siddle et al. (1996). Thus, there was
no interaction between the group, probe position, and stimulus type factors.
Figure 4 shows secondary RT to probes presented during task-relevant and
task-irrelevant shapes in Group Number (top panel) and Group Longer (lower
panel). As can be seen, secondary RT was slower during task-irrelevant
shapes than during task-relevant shapes at all three probe positions
in both groups. This difference represents the pattern in secondary RT
that is characteristic of the dissociation effect.
Two additional results are shown in
Figure 4. First, the difference between shapes tended to be the
same across the three probe positions. Second, there was a downward trend
in secondary RT across probe positions (i.e., secondary RT at the 50 ms
probe positions was slower than at the 150 and 250 ms probe positions and
RT at the 150 ms probe position was slower than at the 250 ms probe position).
Thus, the data showed a downward parallel trend in secondary RT
for the task-relevant and task-irrelevant shapes.
Groups differed only in overall secondary
RT across the experiment. Secondary RT was slower in Group Longer
than in Group Number in the first trial block. In all subsequent trial
blocks, however, this pattern was reversed.