Visuo-attention has been studied experimentally for about 150 years. The journey took us from general laws of perception and behavior, through association strength, object recognition, visual search, visual-spatial attention, level-dependent attention, and measuring interference within the (differing) stimulus (proportions), to measuring attentional weighting using a visual search task as a probe task. Across three published studies, this thesis explored crucial processes in adaptation to stimulus demands utilizing this probe task, demonstrating preparation and persistence of attentional weighting across spatial locations or hierarchical levels of a stimulus, disentangling (a)symmetry effects and aesthetic-dependent processing of symmetrical and asymmetrical Eriksen stimuli. Conclusively, the validated probe task method was applied to demonstrate instruction-dependent adjustment of visuospatial attention in a protocol in which the compound stimulus demands the same response for both instructions (thus, no errors occur from omitting the instructions). However, the intermixed probe task, sensitive to attentional distribution, was capable of detecting instruction-dependent shifts in attentional weighting. The concept of facultative attention is introduced later in the thesis to describe this specific experimental situation, and its potential relevance for broader questions of cognitive control is briefly discussed. This monograph required minor adjustments to the original publications in order to ensure a consistent presentation of e.g., sections, tables, and figures, and to correct minor errors (mostly in formatting and numbering). Abstract of Study 1. Attention can be directed to the global or local level of a visual stimulus (i.e., Navon figure). Previous studies yielded reliable trial-to-trial level switch costs (i.e., worse performance when responding to the other level than on a previous trial), even though level cueing effects indicated anticipatory deployment of attention to the upcoming target level. To investigate the interplay of attentional preparation and persistence, we applied a probe trial method assumed to ensure a high degree of preparation for the upcoming target level and minimizing stimulus-specific proactive interference. Mirroring previous findings obtained in the domain of spatial attention, we found evidence for anticipatory attentional focusing on global/local target levels but not for persistence of the attentional set adopted on the previous trial. In a second experiment, we prevented preparation for upcoming attentional demands (in both global-local and spatial attention tasks). This resulted in the modulation of performance (in critical probe trials) by the attentional demands of the predecessor trial. Together, our findings demonstrate sensitivity of the probe trial method for attentional persistence and raise the possibility that such persistence can be completely eliminated by sufficiently strong preparation for the attentional demands of the following trial. Abstract of Study 2. Visual attention can be adjusted to task requirements. We asked participants to switch between judging the symmetry of vertically presented three-letter strings and identifying the central stimulus (i.e., Eriksen task) to investigate anticipatory adjustment of attention. Our experiments provide evidence for anticipatory adjustment of visual attention, depending on the cued task (i.e., focusing and defocusing of attention after the Eriksen task cue and after the symmetry task cue, respectively). Although symmetry judgments were, overall, considerably slower than the identification of the central letter, the effects of response congruency between tasks were comparable in the two tasks, which suggested strong response priming from concurrent symmetry judgment in Eriksen task trials. Symmetry judgment performance was best for homogeneous letter strings (e.g., HHH), worst for strings that were symmetrical and inhomogeneous (e.g., XHX), and intermediate for asymmetrical strings (e.g., HHX). The difficulty of categorizing symmetrical-inhomogeneous items markedly deviated from the aesthetic ratings of the stimuli, displaying a pronounced preference for symmetrical strings, but only little difference among the symmetrical items, and might be accounted by conflict with response priming based on inhomogeneity detection. Although our study provides little evidence for an effect of aesthetic appreciation in simple symmetry judgments, it demonstrates the strong role of contextual dependencies. Abstract of Study 3. 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.
Svantje Tabea Kähler (Wed,) studied this question.