Probing instructed but unnecessary switches of attentional strategy.

It is widely assumed that attentional strategies can be intentionally shifted. Experimental evidence of such adjustment stems almost exclusively from situations associated with changes concerning perceptual stimulus features, stimulus-related contingencies, or response demands, however. In a series of experiments, we investigated intention- (i.e., instruction-) based shifts of attentional strategy in the absence of additional changes in the task/stimulus environment compared with conditions associated with maintenance of the attentional strategy (i.e., keeping task stimuli, responses, stimulus-response assignments, and presentation contingencies constant for conditions of shift and maintenance). Our method involved a probe task procedure diagnostic of the attentional strategy applied (i.e., strong or weak focusing of visual attention on the centrally presented stimulus element). In Experiment 1, participants were instructed to change the strategy after the first half of the trials. Probe task results provided evidence for adherence to instruction. In Experiments 2 and 3, which involved presenting instructional cues on a trial-by-trial basis, adjustment of attentional strategy appeared confined to a high degree of motivation. Experiment 4 suggests the carryover of instructed attentional strategies to a following (probe task) trial when no novel instruction was presented. Our study demonstrates instruction-based shifts in attentional strategy that are discernably unnecessary for solving the current task and occur without support from a change in the task/stimulus environment.