Gordon C. Baylis

Visual attention and objects: Evidence for hierarchical coding of location.

In 5 experiments, it was found that judging the relative location of 2 contours was more difficult when they belonged to 2 objects rather than 1. This was observed even when the 1- and 2-object displays were physically identical, with perceptual set determining how many objects they were seen to contain. Such a 2-object cost is consistent with object-based views of attention and with a hierarchical scheme for position coding, whereby object parts are located relative to the position of their parent object. In further experiments, it was shown that in accord with this hierarchical scheme, the relative location of objects could disrupt judgments of the relative location of object parts, but the reverse did not occur. This was found even when the relative position of the parts could be judged more quickly than that of the objects.

Selective reaching: evidence for action-centered attention

Most studies of selective attention briefly present static 2-dimensional stimuli and require arbitrary responses such as verbal naming or a keypress. Many of our perceptual-motor interactions with the environment, however, require reaching directly toward an object while ignoring other objects in the scene. A series of experiments examines selective attention in the latter reaching situation. Effects previously observed in the traditional experimental procedures were obtained, suggesting that the models developed (which propose inhibitory mechanisms, e.g.) apply to ecologically valid situations. Attention accesses action-centered internal representations during such tasks.

Visual parsing and response competition: The effect of grouping factors.

When the task is to categorize a target letter at a known location, subjects shaw more interference from incongruent distractors that are relatively close (B. A. Eriksen & C. W. Eriksen, 1974) or that share common motion with the target (Driver & Baylis, 1989). In eight experiments, we examined whether static factors other than proximity can afreet the amount of interference. When distractors and the target letter were in the same color, the distractors interfered more than they did when they were in a different color, even when the latter were closer to the target. Good continuation between the target and distractors also led to more interference. These results suggest that the efficiency of selection is determined by several aspects of the relation between targets and distractors in addition to their proximity, and thus that visual attention is not directed on the basis of position information alone.

Contrast polarity and face recognition in the human fusiform gyrus

Functional imaging has revealed face-responsive visual areas in the human fusiform gyrus, but their role in recognizing familiar individuals remains controversial. Face recognition is particularly impaired by reversing contrast polarity of the image, even though this preserves all edges and spatial frequencies. Here, combined influences of familiarity and priming on face processing were examined as contrast polarity was manipulated. Our fMRI results show that bilateral posterior areas in fusiform gyrus responded more strongly for faces with positive than with negative contrast polarity. An anterior, right-lateralized fusiform region is activated when a given face stimulus becomes recognizable as a well-known individual.

Visual extinction and stimulus repetition

Five patients with visual extinction following unilateral brain injury were briefly presented with colored letters in either or both visual fields, and required to report and locate the colors or the shapes. On double simultaneous stimulation, they tended to miss the event contralateral to their lesion. This extinction was increased when the two stimuli were the same on the reported dimension, Similarity on the irrelevant dimension had no effect. These data suggest that extinguished colors and shapes may be correctly extracted by the visual system (when task-relaant) even though they are unavailable for verbal report. An analogy is made with the phenomena of repetition blindness in normal observers, and it is proposed that extinction may reflect failure in a token-individuation process for correctly extracted visual types.

Edge-Assignment and Figure-Ground Segmentation in Short-Term Visual Matching.

Eight experiments examined the role of edge-assignment in a contour matching task. Subjects judged whether the jagged vertical edge of a probe shape matched the jagged edge that divided two adjoining shapes in an immediately preceding figure-ground display. Segmentation factors biased assignment of this dividing edge toward a figural shape on just one of its sides. Subjects were faster and more accurate at matching when the probe edge had a corresponding assignment. The rapid emergence of this effect provides an on-line analog of the long-term memory advantage for figures over grounds which Rubin (1915/1958) reported. The present on-line advantage was found when figures were defined by relative contrast and size, or by symmetry, and could not be explained solely by the automatic drawing of attention toward the location of the figural region. However, deliberate attention to one region of an otherwise ambiguous figure-ground display did produce the advantage. We propose that one-sided assignment of dividing edges may be obligatory in vision.

Effects of increased response dominance and contextual disintegration on the Stroop interference effect in older adults

In the study we considered the ability of the relative speed of processing-automaticity (RSOP-A) and contextual disintegration (CD) models of the Stroop interference effect to account for the age-related increase in Stroop interference typically observed in older adults. Findings from the first experiment were partially consistent with predictions of the RSOP-A model because response dominance was greater for older adults than for younger adults. However, the age-related increase in interference was independent of this increase in response dominance, suggesting that factors other than those postulated in the RSOP-A model contributed to the greater interference observed in older adults. Results of the second experiment were consistent with the CD model, which suggests that older adults had difficulty maintaining a color-naming strategy to guide task performance.

Individual differences in working memory capacity and enumeration

Two experiments are reported in which subjects performed working memory and enumeration tasks. In the first experiment, subjects scoring low on the working memory task also performed poorly on the attention-demanding “counting” portion of the enumeration task. Yet no span differences were found for the non-attention-demanding “subitizing” portion. In Experiment 2, conjunctive and disjunctive distractors were added to the enumeration task. Although both high and low working memory span subjects were adversely affected by the addition of conjunctive distractors, the effect was much greater for the low-span subjects. Implications from these findings are that differences in working memory capacity correspond to differences in capability for controlled attention.

Shape-coding in IT cells generalizes over contrast and mirror reversal, but not figure-ground reversal

We assessed how the visual shape preferences of neurons in the inferior temporal cortex of awake, behaving monkeys generalized across three different stimulus transformations. Stimulus-preferences of particular cells among different polygon displays were correlated across reversed contrast polarity or mirror reversal, but not across figure–ground reversal. This corresponds with psychological findings on human shape judgments. Our results imply that neurons in inferior temporal cortex respond to components of visual shape derived only after figure–ground assignment of contours, not to the contours themselves.

Procedural learning. I, Locus of practice effects in speeded choice tasks

When subjects perform 750 trials of a speeded choice task mapping different categories of symbols (e.g., letters, digits) onto different responses, excellent transfer is observed to new items in the trained categories (Experiment 1). However, when arbitrary sets of stimuli are mapped onto each response, introducing new stimuli substantially retards performance (Experiment 2), even when the size of the potential stimulus set remains constant (Experiment 3). Surprisingly, responses to already trained items are as slow as responses to new items in these transfer tests. When the mapping is categorical, shuffling the assignment of stimuli to responses drastically slows responses (Experiment 4). However, changing to a spatially homologous mapping with responses on the other hand produces excellent transfer (Experiment 5). Together, these results indicate that practice in speeded choice tasks affects primarily the response selection stage, rather than perceptual processing or motor responses. These data suggest that practice primarily strengthens links between category representations and spatially defined responses. Furthermore, when an arbitrary collection of symbols is mapped onto a given response, practice produces an ad hoc category representation and strengthens links between individual items and the category, as well as links between the category and the response.