Claus Bundesen

A theory of visual attention

A unified theory of visual recognition and attentional selection is developed by integrating the biased-choice model for single-stimulus recognition (Luce, 1963; Shepard, 1957) with a choice model for selection from multielement displays (Bundesen, Pedersen, & Larsen, 1984) in a race model framework. Mathematically, the theory is tractable, and it specifies the computations necessary for selection. The theory is applied to extant findings from a broad range of experimental paradigms. The findings include effects of object integrality in selective report, number and spatial position of targets in divided-attention paradigms, selection criterion and number of distracters in focused-attention paradigms, delay of selection cue in partial report, and consistent practice in search. On the whole, the quantitative fits are encouraging.

A Neural Theory of Visual Attention: Bridging Cognition and Neurophysiology

A neural theory of visual attention (NTVA) is presented. NTVA is a neural interpretation of C. Bundesens (1990) theory of visual attention (TVA). In NTVA, visual processing capacity is distributed across stimuli by dynamic remapping of receptive fields of cortical cells such that more processing resources (cells) are devoted to behaviorally important objects than to less important ones. By use of the same basic equations used in TVA, NTVA accounts for a wide range of known attentional effects in human performance (reaction times and error rates) and a wide range of effects observed in firing rates of single cells in the primate visual system. NTVA provides a mathematical framework to unify the 2 fields of research--formulas bridging cognition and neurophysiology.

Clever homunculus: is there an endogenous act of control in the explicit task-cuing procedure?

Does the explicit task-cuing procedure require an endogenous a act of control? In 5 experiments, cues indicating which task to perform preceded targets by several stimulus onset asynchronies (SOAs). Two models were developed to account for changes in reaction time (RT) with SOA. Model 1 assumed an endogenous act of task switching for cue alterations but not for cue repetitions. Model 2 assumed no such act. In Experiments 1 and 2, the cue was masked or not masked. Masking interacted underadditively with repetition and alternation, consistent with Model 2 but not Model 1. In Experiments 3 and 4, 2 cues were used for each task. RT was slower for task repetition than for cue repetition and about the same as RT for task alternation, consistent with Model 2 but not Model 1. The results suggest that the explicit task-cuing procedure does not require an endogenous act of control.

Systematic analysis of deficits in visual attention.

A variety of impairments in visual attention can follow damage to the brain. The authors develop systematic methods for analyzing such impairments in terms of C. Bundesens (1990) Theory of Visual Attention and apply these in a group of 9 patients with parietal lobe lesions and variable spatial neglect. In whole report, patients report letters from brief, vertical arrays in left or right visual field. The results show substantial, largely bilateral impairments in processing capacity, implying a major nonlateralized aspect to neglect. In partial report, arrays contain 1 or 2 letters in red and/or green. The task is to report only those letters in a specified target color. In addition to the expected bias against left-sided letters, patients show striking, bilateral preservation of top-down control, or attentional priority for targets. The results show how differentiation of attentional impairments can be informed by a theory of normal function.

Visual Transformation of Size.

To investigate human visual identification of different-sized objects as identically shaped, matching reaction times were measured for pairs of simultaneously presented random figures. In three experiments, reaction time for correct reactions to test pairs of figures of the same shape and orientation consistently increased approximately linearly as a function of the linear size ratio of the figures. In the second experiment, where this ratio was defined for control pairs as well as for test pairs, reaction time for correct reactions to control pairs showed a similar increase as a function of size ratio. The results suggest that the task was performed by a gradual process of mental size transformation of one of the members of each pair of figures to the format of the other one.

Size scaling in visual pattern recognition.

Human visual recognition on the basis of shape but regardless of size was investigated by reaction time methods. For successive matching of random figures, reaction time increased linearly with the linear size ratio of stimulus pairs. For single-character classification, reaction time increased with divergence between cued size format and stimulus format such that for character nonrepetitions, the increment in latency was approximately proportional to the logarithm of the linear size ratio of the two formats. However, when reactions to character repetitions were faster than those to nonrepetitions, the repetition reaction time function was similar to that for successive matching of random figures. The results suggested two processes of size scaling: mental-image transformation and perceptual-scale transformation. Image transformation accounted for matching performance based on visual short-term memory, whereas scale transformation accounted for size invariance in recognition based on comparison against visual representations in long-term memory.

Color segregation and selective attention in a nonsearch task

Relations between selective attention and perceptual segregation by color were investigated in binary-choice reaction time experiments based on the non search paradigm of Eriksen and Eriksen (1974). In focused attention conditions (Experiment 1), noise letters flanking a central target letter caused less interference when they differed from the target in color, although color carried no information as to whether or not a letter was the target. When blocking of trials favored a strategy of dividing attention between target and noise letters (Experiment 2), no benefit accrued from difference between target color and noise color. The results supported an attentional interpretation of the effect of color demonstrated in Experiment 1, implying that perceptual segregation by color improved the efficiency of focusing attention on the target.

Color segregation and visual search

Visual search of color-coded alphanumeric displays was investigated by reaction time methods. The task was to indicate the alphanumeric class of a target item, singled out by appearing in a designated color which varied across trials. Mean reaction time increased with both the number of colors and the number of items in the displays. When same-colored noise items appeared in spatial proximity (organized displays), mean reaction time was a linear function of the number of colors for each level of number of items, and effects of the two factors were additive. For displays constructed by random assignment of colors to individual noise items (scrambled displays), temporal effects of the same factors showed strong interaction. Search times for scrambled displays were predictable from search times for organized displays by use of subjective estimates of the number of phenomenally separate groups of displayed items. The results suggest that visual search for items in the target color consisted in sequentially examining groups of same-colored items, unitized in accordance with Gestalt principles of proximity and similarity, until a unit in the target color was found.

Principles of Visual Attention: Linking Mind and Brain

1. Introduction PART I - THE PSYCHOLOGY OF VISUAL ATTENTION 2. Psychological research on visual attention 3. A psychological theory of visual attention (TVA) 4. Explaining divided attention by TVA 5. Explaining focused attention by TVA PART II - THE NEUROPHYSIOLOGY OF VISUAL ATTENTION 6. Effects of visual attention in single neurons 7. A neural theory of visual attention (NTVA) 8. Explaining attentional effects in single neurons by NTVA PART III - THE ANATOMY OF VISUAL ATTENTION 9. Brain imaging of visual attention 10. Disturbances of visual attention 11. TVA-based assessment CONCLUSION 12. A unified theory of visual attention

Very clever homunculus: Compound stimulus strategies for the explicit task-cuing procedure

In two experiments, subjects were given arbitrary letter cues or meaningful word cues that specified the task to be performed on a subsequent target stimulus. Letter and word cues were presented in separate blocks. There were two cues of each type for each task. Three kinds of transitions separated tasks:cue repetitions, in which both the cue and the task repeated;task repetitions, in which the cue changed but the task repeated; andtask alternations, in which both the cue and the task changed. Responses were faster for cue than for task repetitions for both cue types. With word cues, task repetitions were not reliably faster than task alternations. With letter cues, task repetitions were reliably faster than task alternations in the first block but not in the second block. The results suggest that subjects responded to the compound of the cue and the target rather than switching task set between trials.