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Biomedical subjects

J Theeuwes

Publications and source records attributed to J Theeuwes.

At least 19 recordsLinked to original sources
PubMed2001

Spatial attention in early vision.

The present study addressed whether the allocation of attention to a particular region in space can prevent processing of distractor information from non-attended regions. A cue indicated the area in visual space where the target singleton would be presented. Observers were required to detect this target singleton and ignore a distractor singleton presented within a non-attended region. The results indicate that the allocation of attention to a region in space cannot prevent the processing of unwanted information from elsewhere in the visual field. It is concluded that the function of the allocation of attention is not to enhance the processing capacity within the attended region but rather to attenuate interference from distractors in unattended regions.

Adult↗
PubMed2001

Visual marking beside the mark: prioritizing selection by abrupt onsets.

In a standard visual marking experiment, observers are presented with a display containing one set of elements (old elements) followed after a certain time interval by a second set of elements (new elements). The task of observers is to search for a target among the new elements. Typically, the time to find the target depends only on the number of new elements in the display and not on the number of old elements, showing that observers search only among the new elements. This effect of prioritizing new elements over old elements is explained in terms of top-down inhibition of old objects-that is, visual marking (Watson & Humphreys, 1997). The present study addressed whether this prioritizing is in fact mediated by top-down inhibition of old objects, as suggested by Watson and Humphreys (1997), or whether it is mediated by the abrupt onsets of the newly presented elements (Yantis & Jonides, 1984). In three experiments, the presentations of the old and new elements were or were not accompanied by a luminance change. The results showed that if new elements were equiluminant with the background, no visual marking occurred, suggesting that new elements must have a luminance onset in order to be prioritized over old elements. Implications for current theories on visual selection are discussed.

Adult↗
PubMed2000

Age differences in the control of looking behavior: do you know where your eyes have been?

Previous research has shown that during visual search young and old adults' eye movements are equivalently influenced by the appearance of task-irrelevant abrupt onsets. The finding of age-equivalent oculomotor capture is quite surprising in light of the abundant research suggesting that older adults exhibit poorer inhibitory control than young adults on a variety of different tasks. In the present study, we examined the hypothesis that oculomotor capture is age invariant when subjects' awareness of the appearance of task-irrelevant onsets is low, but that older adults will have more difficulty than young adults in inhibiting reflexive eye movements to task-irrelevant onsets when awareness of these objects is high. Our results were consistent with the level-of-awareness hypothesis. Young and old adults showed equivalent patterns of oculomotor capture with equiluminant onsets, but older adults misdirected their eyes to bright onsets more often than young adults did.

Adolescent↗
PubMed1999

Attentional effects on preattentive vision: spatial precues affect the detection of simple features.

Most accounts of visual perception hold that the detection of primitive features occurs preattentively, in parallel across the visual field. Evidence that preattentive vision operates without attentional limitations comes from visual search tasks in which the detection of the presence of absence of a primitive feature is independent of the number of stimuli in a display. If the detection of primitive features occurs preattentively, in parallel and without capacity limitations, then it should not matter where attention is located in the visual field. The present study shows that even though the detection of a red element in an array of gray elements occurred in parallel without capacity limitations, the allocation of attention did have a large effect on search performance. If attention was directed to a particular region of the display and the target feature was presented elsewhere, response latencies increased. Results indicate that the classic view of preattentive vision requires revision.

Adolescent↗
PubMed1999

Influence of attentional capture on oculomotor control.

Previous research has shown that when searching for a color singleton, top-down control cannot prevent attentional capture by an abrupt visual onset. The present research addressed whether a task-irrelevant abrupt onset would affect eye movement behavior when searching for a color singleton. Results show that in many instances the eye moved in the direction of the task-irrelevant abrupt onset. There was evidence that top-down control could neither entirely prevent attentional capture by visual onsets nor prevent the eye from starting to move in the direction of the onset. Results suggest parallel programming of 2 saccades: 1 voluntary goal-directed eye movement toward the color singleton target and 1 stimulus-driven eye movement reflexively elicited by the abrupt onset. A neurophysiologically plausible model that can account for the current findings is discussed.

Adolescent↗
PubMed1999

Attentional capture and aging: implications for visual search performance and oculomotor control.

Two studies examined potential age-related differences in attentional capture. Subjects were instructed to move their eyes as quickly as possible to a color singleton target and to identify a small letter located inside it. On half the trials, a new stimulus (i.e., a sudden onset) appeared simultaneously with the presentation of the color singleton target. The onset was always a task-irrelevant distractor. Response times were lengthened, for both young and old adults, whenever an onset distractor appeared, despite the fact that subjects reported being unaware of the appearance of the abrupt onset. Eye scan strategies were also disrupted by the appearance of the onset distractors. On about 40% of the trials on which an onset appeared, subjects made an eye movement to the task-irrelevant onset before moving their eyes to the target. Fixations close to the onset were brief, suggesting parallel programming of a reflexive eye movement to the onset and goal-directed eye movement to the target. Results are discussed in terms of age-related sparing of the attentional and oculomotor processes that underlie attentional capture.

Adult↗
PubMed1998

Attentional control during visual search: the effect of irrelevant singletons.

Four experiments investigated whether a highly salient color singleton can be ignored during serial search. Observers searched for a target letter among nontarget letters and were instructed to ignore an irrelevant, highly salient color singleton that was either compatible or incompatible with the response to the target letter. The results indicate that it was possible to prevent attentional capture by the irrelevant singleton only when both the target and the distractor color were known. When either the color of the target or the color of the to-be-ignored singleton were varied over trials, the irrelevant singleton captured attention. The ability to selectively filter singleton distractors during serial search depends on the presence of an attentional set for a specific feature value of both target and distractor. In the absence of a consistently predictable feature value of both target and distractor, top-down control is not possible.

Adolescent↗
PubMed1998

Attentional control within 3-D space.

Four experiments investigated whether directing attention to a particular plane in depth enables observers to filter out information from another depth plane. Observers viewed stereoscopic displays and searched for a red line segment among green line segments. The results showed that directing attention to a particular depth plane cannot prevent attentional capture from another depth plane when the colors of the target and distractor are identical. However, it can prevent attentional capture by a singleton from another depth plane when the colors of the target and distractor are different. These results indicate that only when both color and depth information are selective in guiding attention to the target singleton can attentional capture by irrelevant singletons be prevented. The results also suggest that retinal disparity does not have the same special status as location information in two dimensions and should be considered as just another feature along which selection may occur.

Adolescent↗
PubMed1997

The effectiveness of side marker lamps: an experimental study.

The present experiment investigated the effect of small amber lamps mounted near the front and rear on each side of a passenger car-so called side marker lamps-on visual detection and recognition of passenger cars in complex nighttime environments. It was determined whether cars equipped with side marker lamps are detected and recognized earlier and more accurately than cars without side marker lamps. Subjects were presented with slides of natural nighttime scenes in which a car, either with or without side marker lamps, viewed from its side, approaching from a side street, was either present or not. Subjects determined as fast as possible whether a car was present or not. Reaction time measures (speed and accuracy) indicated that both under clear and fog visibility conditions, a car equipped with side marker lamps was detected and recognized earlier and more accurately than a car without side marker lamps. The results indicate that side marker lamps increase both lateral conspicuity and recognizability suggesting that side marker lamps may be effective in reducing the number of nighttime angle collisions.

Accidents, Traffic↗
PubMed1995

Daytime running lights as a vehicle collision countermeasure: the Swedish evidence reconsidered.

In Sweden the use of daytime running lights (DRL) was made mandatory on 1 October 1977 for all motor vehicles at once, during all seasons and for all areas. According to a study conducted by Andersson and Nilsson (1981) [Andersson and Nilsson. VTI Swedish Road and Transport Research Institute, Report No. 208A; 1981] the introduction of DRL resulted in a reduction of 11% of multiple accidents during daytime. In many discussions on the effectiveness of DRL, these findings have been considered as the strongest evidence that the use of DRL is an effective vehicle collision countermeasure. The present study reexamines this evidence and shows that the reported 11% effect of DRL in the Swedish study is spurious. The effect is mainly the result of the application of a model that shows selective effects of DRL through modelling of unexplained changes in the number of single accidents. It is concluded that the Swedish data fail to show a clear effect of DRL.

Accidents, Traffic↗
PubMed1995

Abrupt luminance change pops out; abrupt color change does not.

The present studies investigated whether an isoluminant color change pops out, indicating that it can be detected preattentively in parallel. The results of Experiment 1 show that an abrupt color change presented on an equiluminant background does not pop out. However, when the color change is accompanied by a small luminance change, it does pop out. The results of Experiment 2 show that the pop-out is fully due to the luminance change and not to the color change. The results of Experiments 3 and 4 show that the failure to find a pop-out at equiluminance cannot be attributed to the limited temporal resolution for chromatic stimuli. The results of Experiment 5 show that particular search strategies cannot be responsible for the obtained results. The results are in agreement with physiological findings regarding the parvo and magno systems.

Attention↗
PubMed1994

The effects of location cuing on redundant-target processing.

The present study is concerned with the redundany gain: the observation that subjects respond faster to simultaneously presented redundant targets than to single targets. This finding is usually interpreted as evidence for parallel, self-terminating, unlimited-capacity processing. Alternatively, it has been claimed that the reaction-time advantage with redundant targets is simply due to spatial uncertainty under single-target conditions. The present study tested this hypothesis. In Experiment 1, subjects responded when one, two, or three letters E were presented, and refrained from responding when one, two, or three letters F were presented. In half of the trials, location uncertainty was eliminated by presentation of a line segment at one the locations of the subsequently appearing target letters. The results reject the alternative spatial-uncertainty explanation: even when the location of the impending target is cued in advance, there is no attenuation of the redundancy gain. Experiment 2 served as a control experiment and showed a clear redundancy gain, even in conditions in which it was ensured that, before display onset, attention was directed to a location of one of the impending targets.

Adolescent↗
PubMed1994

Parallel search for a conjunction of contrast polarity and shape.

When a target object embedded in an array of other objects can be distinguished along a single feature dimension (e.g. color or shape), it can be detected in parallel. When a target object is defined by a conjunction of stimulus features, at least some serial search is required, indicating that the visual system is less efficient in conducting a parallel search over two stimulus dimensions simultaneously. Some exceptions to this finding have been reported. The present results suggest another exception: search for a conjunction of contrast polarity and shape can be conducted in parallel while the same conjunction consisting of color and shape requires some serial search. The neurophysiological implications are discussed.

Color Perception↗
PubMed1994

Stimulus-driven capture and attentional set: selective search for color and visual abrupt onsets.

Recent evidence suggests that attentional capture is contingent on the attentional control setting induced by the task demands (C. L. Folk, R. Remington, & J. C. Johnston, 1992). Because the experiments on which these conclusions are based can be criticized for several reasons, the contingent capture hypothesis was tested using 2 visual search tasks in which subjects searched multielement displays in which a color singleton and onset singleton were simultaneously present. Both experiments show that the contingent capture hypothesis does not hold: Irrespective of attentional set, attention was captured by the most salient singleton. The findings suggest a stimulus-driven model of performance in which selection is basically determined by the properties of the featural singletons present in the visual field.

Adolescent↗
PubMed1994

Endogenous and exogenous control of visual selection.

Among the most fundamental issues of visual attention research is the extent to which visual selection is controlled by properties of the stimulus or by the intentions, goals, and beliefs of the observer. Before selective attention operates, preattentive processes perform some basic analyses segmenting the visual field into functional perceptual units. The crucial question is whether the allocation of attention to these perceptual units is under the endogenous control of the observer (intentions, goals, beliefs) or under the exogenous control of attention in tasks in which subjects search for a particular 'basic' feature (eg search for a unique colour, shape, or brightness). In the present review it is suggested that selectivity in these types of search tasks is dependent on the relative saliency of the stimulus attributes. It is concluded that the visual system automatically calculates differences in basic features (eg difference in shape, colour, or brightness) and that visual information occupying the position of the highest saliency across stimulus dimensions is exogenously passed on to the 'central presentation' that is responsible for further stimulus analysis. Alternative explanations of the present findings and tentative speculations resulting from the present approach are discussed.

Attention↗
PubMed1993

Visual selective attention: a theoretical analysis.

The present paper outlines a framework which allows a consistent interpretation of data regarding visual selection in visual search tasks. It organizes and reviews visual search tasks in which the target is defined by primitive features, by conjunctions of features and when the target is categorically different from non-targets. The special role of spatial attention is reviewed and different theoretical accounts are discussed. Because visual selection depends principally on the outcome of the early parallel preattentive stage of processing, the main focus will be on this stage. It is concluded that visual selection is to a large extent determined by the physical characteristics of the stimuli present in the visual field. The early preattentive parallel process computes how different each object is from each of the other objects within a particular stimulus dimension. Attention is automatically drawn to the location having the highest activation, implying that the object at that location is automatically selected irrespective of the intentions of the subject. The model also assumes some top-down control. It is well known that attention can be voluntarily directed to nonfixated locations in visual space, varying from a uniform distribution over the visual field to a highly focused concentration. The model assumes that the endogenous direction of attention to an area in the visual field is the only top-down manner of affecting visual selection. Within the area of directed attention, no top-down control is possible: selection is completely determined by the physical properties of the stimuli.

Attention↗