David E. Irwin

Our Eyes do Not Always Go Where we Want Them to Go: Capture of the Eyes by New Objects

Observers make rapid eye movements to examine the world around them. Before an eye movement is made, attention is covertly shifted to the location of the object of interest. The eyes typically will land at the position at which attention is directed. Here we report that a goal-directed eye movement toward a uniquely colored object is disrupted by the appearance of a new but task-irrelevant object, unless subjects have a sufficient amount of time to focus their attention on the location of the target prior to the appearance of the new object. In many instances, the eyes started moving toward the new object before gaze started to shift to the color-singleton target. The eyes often landed for a very short period of time (25–150 ms) near the new object. The results suggest parallel programming of two saccades: one voluntary, goal-directed eye movement toward the color-singleton target and one stimulus-driven eye movement reflexively elicited by the appearance of the new object. Neuroanatomical structures responsible for parallel programming of saccades are discussed.

Information Integration across Saccadic Eye Movements.

The visual world contains more information than can be perceived in a single glance. Consequently, ones perceptual representation of the environment is built up via the integration of information across saccadic eye movements. The properties of transsaccadic integration were investigated in six experiments. Subjects viewed a random-dot pattern in one fixation, then judged whether a second dot pattern viewed in a subsequent fixation was identical to or different from the first. Interpattern interval, pattern complexity, and pattern displacement were varied in order to determined the duration, capacity, and representational format of transsaccadic memory. The experimental results indicated that transsaccadic memory is an undetailed, limited-capacity, long-lasting memory that is not strictly tied to absolute spatial position. In all these respects it is similar to, and perhaps identical with, visual short-term memory. The implication of these results for theories of perceptual stability across saccades are discussed.

Memory for position and identity across eye movements.

A «transsaccadic» partial report procedure was used to measure memory for position and identity information across saccades. Delaying the partial-report cue after the eye movement had little effect on report accuracy. Mask presentation hindered recall only at the shortest delay. Accuracy was much higher when the letter array contained 6 letters than when it contained 10 letters. Intra-array errors were much more frequent than extra-array errors. These results suggest that memory across eye movements decays slowly, has a limited capacity, is maskable for a brief time, and retains identity information better than position information

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.

Eye movements and scene perception: Memory for things observed

In this study, we examined the characteristics of on-line scene representations, using a partial-report procedure. Subjects inspected a simple scene containing seven objects for 1, 3, 5, 9, or 15 fixations; shortly after scene offset, a marker cued one scene location for report. Consistent with previous research, the results indicated that scene representations are relatively sparse; even after 15 fixations on a scene, the subjects remembered the position/identity pairings for only about 78% of the objects in the scene, or the equivalent of about five objects-worth of information. Report of the last three objects that were foveated and of the object about to be foveated was very accurate, however, suggesting that recently attended information in a scene is represented quite well. Information about the scene appeared to accumulate over multiple fixations, but the capacity of the on-line scene representation appeared to be limited to about five items. Implications for recent theories of scene representation are discussed.

Attentional and oculomotor capture by onset, luminance and color singletons

In three experiments we investigated whether attentional and oculomotor capture occur only when object-defining abrupt onsets are used as distractors in a visual search task, or whether other salient stimuli also capture attention and the eyes even when they do not constitute new objects. The results showed that abrupt onsets (new objects) are especially effective in capturing attention and the eyes, but that luminance increments that do not accompany the appearance of new objects capture attention as well. Color singletons do not capture attention unless subjects have experienced the color singleton as a search target in a previous experimental session. Both abrupt onsets and luminance increments elicit reflexive, involuntary saccades whereas transient color changes do not. Implications for theories of attentional capture are discussed.

Syntactic effects of information availability in sentence production

Two experiments investigated sentence production processes underlying the tendency for given information to precede new information in a sentence. The factors hypothesized to contribute to this effect were referential availability and lexical availability. Experiment 1 found that information coreferential with an antecedent referring expression tended to occur earlier in produced sentences than new information. This effect was more pronounced when the information was lexically identical to its antecedent. Experiment 2 found lexical availability effects when referential functions were minimized. These results may be accounted for by assuming that both referential availability and lexical availability contribute to the speed of lexicalization processes in sentence production, and that the order in which constituents become available after lexicalization influences surface syntactic organization processes.

Conversation Disrupts Change Detection in Complex Traffic Scenes

A set of studies examined the effects of cognitive distraction on visual scanning and change detection in natural traffic scenes. Experiment 1 found that a naturalistic hands-free phone conversation could disrupt change detection, thereby degrading the encoding of visual information and increasing the frequency of undetected changes. Data also revealed a tendency for conversation to impair knowledge-driven orienting of attention in older adults. Experiment 2 found that an attentive listening task produced no such effects. Actual or potential applications of this research include the design of displays and interventions to minimize the effects of cognitive distraction on human performance.

Visual masking and visual integration across saccadic eye movements.

The visual world appears unified, stable, and continuous despite rapid changes in eye position. How this is accomplished has puzzled psychologists for over a century. One possibility is that visual information from successive eye fixations is fused in memory according to environmental or spatiotopic coordinates. Evidence supporting this hypothesis was provided by Davidson, Fox, and Dick (1973). They presented a letter array in one fixation and a mask at one letter position in a subsequent fixation and found that the mask inhibited report of the letter that shared its retinal coordinates but appeared to occupy the same position as the letter that shared its spatial coordinates. This suggests the existence of a retinotopic visual persistence at which transsaccadic masking occurs and a spatiotopic visual persistence at which transsaccadic integration, or fusion, occurs. Using a similar procedure, we found retinotopic masking and retinotopic integration: The mask interfered with the letter that shared its retinal coordinates, but also appeared to cover that letter. In another experiment, instead of a mask we presented a bar marker over one letter position, and subjects reported the letter that appeared underneath the bar; subjects usually reported the letter with the same retinal coordinates as the bar, again suggesting retinotopic rather than spatiotopic integration across saccades. In Experiment 3 a bar marker was again presented over one letter position, but in addition a visual landmark was presented after the saccade so that subjects could localize the bars spatial position; subjects still reported that the letter that shared the bars retinal coordinates appeared to be under it, but they were also able to accurately specify the bars spatial position. This ability could have been based on retinal information (the visual landmark) present in the second fixation only, however, rather than spatiotopic visual persistence. Because such a visual landmark was present in the Davidson et al. (1973) experiments, we conclude that their findings can be explained solely in retinotopic terms and provide no convincing evidence for spatiotopic visual persistence. But the exposure parameters that Davidson et al. (1973) and we used were biased in favor of retinotopic, rather than spatiotopic, coding: The stimuli were presented very briefly just before a saccadic eye movement, and subjects are poor at spatially localizing stimuli under these conditions. Thus, in Experiment 4 we presented the letter array about 200 ms before the saccade; then, subjects reported that the letter with the same spatial coordinates as the bar appeared under it.(ABSTRACT TRUNCATED AT 400 WORDS)

Visual memory and the perception of a stable visual environment

The visual world appears stable and continuous despite eye movementa. One hypothesisabout how this perception is achieved is that the contents of succesaivatienn~arefusedinmemory according to environmental coordinates. Two experiments failed to support this hypothesis; they showed that one’s ability to detecta grating presented after a saccade is unaffected by the presentation of a grating with the same spatial frequency in the same spatial location before the saccade. A third experiment tested an alternative explanation of perceptual stability that claims that the contents of successive fixations are compared, rather than fused, across-saccades, allowing one to determine whether the world has remained stable. This hypothesis was supported: Experienced subjects could accurately determine whether two patterns viewed in successive fixationswere identical or different, evenwhenthe two patterns appeared in different spatial positions across the saccade. Taken together, these results suggest that perceptual stability and information integration across saccades rely on memory for the relative positions of objects in the environment, rather than on the spatiotopic fusion of visual information from successive fixations.