Biomedical subjects

J Theeuwes

Publications and source records attributed to J Theeuwes.

6 recordsLinked to original sources

PubMed1992

Perceptual selectivity for color and form.

Three visual-search experiments tested whether the preattentive parallel stage can selectively guide the attentive stage to a particular known-to-be-relevant target feature. Subjects searched multielement displays for a salient green circle that had a unique form when surrounded by green nontarget squares or had a unique color when surrounded by red nontarget circles. In the distractor conditions, a salient item in the other dimension was present as well. As an extension of earlier findings (Theeuwes, 1991), the results showed that complete top-down selectivity toward a particular feature was not possible, not even after extended and consistent practice. The results reveal that selectivity depends on the relative discriminability of the stimulus dimensions: the presence of an irrelevant item with a unique color interferes with parallel search for a unique form, and vice versa.

Adolescent↗

PubMed1991

Categorization and identification of simultaneous targets.

Early and late selection theories of visual attention disagree about whether identification occurs before or after selection. Studies showing the category effect, i.e., the time to detect a letter is hardly affected by the number of digits present in the display, are taken as evidence for late selection theories since these studies suggest parallel identification of all items in the display. As an extension of previous studies, in the present study two categorically different targets were presented simultaneously among a variable number of nontargets. Subjects were shown brief displays of two target letters among either 2, 4 or 6 nontarget digits. Subjects responded 'same' when the two letters were identical and 'different' otherwise. Since the 'same-different' response reflects the combined outcome of the simultaneous targets, late-selection theory predicts that the time to match the target letters is independent of the number of nontarget digits. Alternatively, early-selection theory predicts a linear increase of reaction time with display size since the presence of more than one target disrupts parallel preattentive processing, leading to a serial search through all items in the display. The results provide evidence for the early-selection view since reaction time increased linearly with the number of categorically different nontargets. A control experiment revealed that none of the alternative explanations could account for the display size effect.

Adolescent↗

PubMed1991

Exogenous and endogenous control of attention: the effect of visual onsets and offsets.

Two experiments were carried out to investigate the relation between exogenous and endogenous control of visual attention. Subjects searched for a target letter among three nontarget letters that were positioned on an imaginary circle around a fixation point. At different cue-display intervals, a centrally located arrowhead cue reliably indicated the location of the target letter. At different SOAs, a peripheral line segment near one of the letters was either abruptly switched on (Experiment 1) or abruptly switched off (Experiment 2). Presenting the central arrowhead after display onset prevents attention from being focused in advance on the critical location. In this unfocused attentional state, both onset and offset transients attracted attention. When the central arrowhead was available in advance, the focusing of attention prior to display onset precluded attention attraction to the location of the onset or offset transient. Contrary to an offset transient, an onset transient presented at the attended location disrupted performance, indicating that an onset within the spotlight of attention attracts attention. The results are reconciled by means of the zoom-lens theory of attention, suggesting that outside the focus of attention, abrupt transients are not capable of attracting attention. Since the size of the zoom lens is under voluntary control, it can be argued that transients do not fulfill the intentionality criterion of automaticity.

Adolescent↗

PubMed1991

Cross-dimensional perceptual selectivity.

Three visual search experiments tested whether top-down selectivity toward particular stimulus dimensions is possible during preattentive parallel search. Subjects viewed multielement displays in which two salient items, each unique in a different dimension--that is, color and intensity (Experiment 1) or color and form (Experiments 2 and 3)--were simultaneously present. One of the dimensions defined the target; the other dimension served as distractor. The results indicate that when search is performed in parallel, top-down selectivity is not possible. These findings suggest that preattentive parallel search is strongly automatic, because it satisfies both the load-insensitivity and the unintentionality criteria of automaticity.

Adolescent↗

PubMed1990

Perceptual selectivity is task dependent: evidence from selective search.

Four visual search experiments examined the allocation of attention in a multi-item display with a salient stimulus difference. If, irrespective of its relevance to performance, an item with a unique property attracts attention, it can be said that the unique property automatically captures attention. Alternatively, if capturing attention depends on the relevance of the unique property it would suggest that subjects are capable of engaging in active filtering. In the experiments, subjects searched visually for a horizontal line segment positioned in either one of the 4, 8 or 16 surrounds, arranged in an imaginary circle around the fixation point. In each trial, there was always one surround that differed from the others. The data showed that attention was not automatically attracted to the exceptional form (experiment 1) or exceptional color (experiment 2). The control conditions showed that form and color differences could serve as the basis for active allocation of attention to the unique item. Attention capturing is occasionally observed when the surround changes abruptly in form (experiment 3) but not when it changes abruptly in color (experiment 4). Implications of these findings are discussed in relation to theories of attention that distinguish between a first, parallel stage of perceptual processing followed by a second stage of limited capacity. The results are compatible with the notion that pre-attentive processing is under strategic control and can be stopped by filtering on a spatial basis. The results are related to the specific properties of the transient channels in the visual system.

Adolescent↗

PubMed1989

Effects of location and form cuing on the allocation of attention in the visual field.

Two experiments were conducted which tested the effect of two different types of cues on the allocation of attention in the visual field. Subjects responded to a target appearing either 6.5 degrees to the right or to the left of fixation in a field filled with small randomly positioned line segments. The target form was either a circle or diamond in which a horizontal or vertical line segment was positioned. Subjects made a speeded discrimination response on the basis of the orientation of this line segment. In the first experiment, there was always one target at each trial. In the second experiment, both circle and diamond were presented left or right of fixation simultaneously whereby the line segment only appeared in one of the forms. In different conditions, the most likely target location (left or right) and form (circle or diamond) were cued. Control conditions served as a baseline for determining costs and benefits. Reaction time measures showed that the validity of the location cue resulted in both costs and benefits, whereas the validity of the form cue had no such effects. The results cannot be reconciled with the claim of zoom lens theories that spatial attention can switch between different modes of operations. They are also at odds with theories that claim that attention has no spatial locus. The results are consistent with a simple spotlight theory in which spatial attention involves selecting a particular restricted area of the visual field for which the perceptual efficiency is enhanced.

Attention↗