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Peter Squire, Pamela Greenwood, Raja Parasuraman; Involuntary but not voluntary orienting modulates the splitting of attention. Journal of Vision 2009;9(8):133. doi: 10.1167/9.8.133.
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Background: The focus of attention need not be unitary but can be split between noncontiguous locations. However, in the absence of a suppressive mechanism triggered by external noise (e.g. distractors) attention appears to be scaled rather than split (Awh & Pashler, 2000). This need for a suppressive mechanism to induce splitting suggests that involuntary but not voluntary orienting of attention may modulate the splitting of attention. Involuntary orienting may have both suppressive and excitatory effects, whereas voluntary orienting may have only suppressive effects (Lu & Dosher, 2000). Based on these findings, we predicted that when orienting was voluntary, attention would be split via a suppressive mechanism but when orienting was involuntary, attention would split or scaled depending on task demands for suppression or enhancement. The hypothesis was tested in two experiments that manipulated the orienting and distribution (the scale of the attentional focus) of attention and the level of external noise. Method: A cued search task precued location of a target digit in a search array of distractor letters. Conditions were: orienting type (involuntary and voluntary); distribution type (constricted, scaled, or split); external noise (high and low). External noise was manipulated by the distance between stimuli (i.e. near and far) in Experiment 1 and the similarity between stimuli (i.e. low and high) in Experiment 2. All cues were valid in predicting target location. Following array offset, participants made unspeeded responses about the presence of the target digit. Accuracy of target response was used as the dependent measure. Results and Conclusions: The ability to split the focus of attention was modulated with involuntary but not voluntary orienting. These results indicate that involuntary orienting of attention uses both suppressive and excitatory mechanisms, while voluntary orienting of attention uses only a suppressive mechanism.
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