Abstract
In four experiments, we studied the time course of interference between detection of an oddball orientation target (OT) in an 8-item circular search display, and identification of a letter target (LT) in a central stream of distractor letters. Dual-task performance for different temporal lags between targets was compared to single-task performance. When the LT preceded the OT, dual-task performance levels were reduced at short inter-target intervals of 0 and 166 ms; when the OT preceded the LT, the dual-task interference was unexpectedly stronger and lasted for up to 500 ms. Resource competition due to temporally overlapping target processing cannot account for this result, because the feature search task is easier than the letter identification task, and therefore would have generated less interference when presented first. Two alternative explanations were explored. First, by manipulating the spatial inter-target distance, we investigated to what degree there is a penalty associated with directing the attentional window from a large object (the search display) to a smaller object (the central letter stream). Second, by varying the duration of the OT and subsequent mask, we studied whether the interference was caused by the difficulty of disengaging attention from the search display. Results support this second explanation and thus indicate that switching attention to the letter stream is hampered by the continuing presence of (masked) search display items. This result shows that attentional effects may play a major role in dual-task execution and can easily obscure interference due to other factors such as resource competition.
Highlights
Everyday experience teaches us that it can be very difficult to perform several tasks at once
In four experiments we examined the time course of dual task interference for a combination of an orientation search task and a letter identification task
We reversed task order, starting out from the hypothesis that when the search task is performed first, processing resources should be promptly available for the second task
Summary
Everyday experience teaches us that it can be very difficult to perform several tasks at once. While supporting the notion that pop-out search is not free from interference with other task, the results of Ettwig and Bronkhorst [12] further demonstrate that the degree and duration of the interference depends strongly on both task difficulty and the specific combination of target features Why is it that the combination of a letter-RSVP with an orientation search display yields such a strong and lasting interference, even exceeding the duration required for a spatial shift of attention [13]? Because the search task is relatively easy, the prediction would be that when it precedes the RSVP-task, overlap in the processing of the two target stimuli should only occur at very short inter target intervals in the dual-task condition We tested this prediction by performing a replication of the dual-task experiment of Joseph, Chun and Nakayama [3], in which the RSVP-target precedes the orientation target, followed by a second experiment in which the task order was reversed. Experiment 1 – Interference between a Search Task and a Preceding Letter-Discrimination Task
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