Biomedical subjects

Jude F Mitchell

Publications and source records attributed to Jude F Mitchell.

4 recordsLinked to original sources

PubMed2005

Interacting competitive selection in attention and binocular rivalry.

Visuomotor processing is selective - only a small subset of stimuli that impinge on the retinae reach perceptual awareness and/or elicit behavioral responses. Both binocular rivalry and attention involve visual selection, but affect perception quite differently. During rivalry, awareness alternates between different stimuli presented to the two eyes. In contrast, attending to one of the two stimuli impairs discrimination of the ignored stimulus, but without causing it to perceptually disappear. We review experiments demonstrating that, despite their phenomenological differences, attention and rivalry depend upon shared competitive selection mechanisms. These experiments, moreover, reveal stimulus selection that is surface-based and requires coordination between the different neuronal populations that respond as a surface changes its attributes (type of motion) over time. This surface-based selection, in turn biases interocular competition, favoring the eye whose image is consistent with the selected surface. The review ends with speculation about the role of the thalamus in mediating this dynamic coordination, as well as thoughts about what underlies the differences in the phenomenology of selective attention and rivalry.

Animals↗

PubMed2004

Object-based attention determines dominance in binocular rivalry.

A question of long-standing interest to philosophers, psychologists and neuroscientists is how the brain selects which signals enter consciousness. Binocular rivalry and attention both involve selection of visual stimuli, but affect perception quite differently. During binocular rivalry, awareness alternates between two different stimuli presented to the two eyes. In contrast, attending to one of two different stimuli impairs discrimination of the ignored stimulus, but without causing it to disappear from consciousness. Here we show that despite this difference, attention and rivalry rely on shared object-based selection mechanisms. We cued attention to one of two superimposed transparent surfaces and then deleted the image of one surface from each eye, resulting in rivalry. Observers usually reported seeing only the cued surface. They were also less accurate in judging unpredictable changes in the features of the uncued surface. Our design ensured that selection of the cued surface could not have resulted from spatial, ocular or feature-based mechanisms. Rather, attention was drawn to one surface, and this caused the other surface to be perceptually suppressed during rivalry. These results raise the question of how object representations compete during these two forms of perceptual selection, even as the features of those objects change unpredictably over time.

Attention↗

PubMed2003

Attentional selection of superimposed surfaces cannot be explained by modulation of the gain of color channels.

When two differently colored, superimposed patterns of dots rotate in opposite directions, this yields the percept of two superimposed transparent surfaces. If observers are cued to attend to one set of dots, they are impaired in making judgments about the other set. Since the two sets of dots are overlapping, the cueing effect cannot be explained by spatial attention. This has led to the interpretation that the impairment reflects surface-based attentional selection. However, recent single-unit recording studies in monkeys have found that attention can modulate the gain of neurons tuned for features such as color. Thus, rather than reflecting the selection of a surface, the behavioral effects might simply reflect a reduction in the gain of color channels selective for the color of the uncued set of dots (feature-based attention), as if viewing the surfaces through a colored filter. If so, then the impairment should be eliminated when the two surfaces are made the same color. Instead, we find that the impairment persists with no reduction in strength. Our findings thus rule out the color gain explanation.

Adult↗

PubMed2003

Sequential memory-guided saccades and target selection: a neural model of the frontal eye fields.

We present a neural model of the frontal eye fields. It consists of several retinotopic arrays of neuron-like units that are recurrently connected. The network is trained to make memory-guided saccades to sequentially flashed targets that appear at arbitrary locations. This task is interesting because the large number of possible sequences does not permit a pre-learned response. Instead locations and their priority must be maintained in active working memory. The network learns to perform the task. Surprisingly, after training it can also select targets in visual search tasks. When targets are shown in parallel it chooses them according to their salience. Its search behavior is comparable to that of humans. It exhibits saccadic averaging, increased reaction times with more distractors, latency vs accuracy trade-offs, and inhibition of return. Analysis of the network shows that it operates like a queue, storing the potential targets in sequence for later execution. A small number of unit types are sufficient to encode this information, but the manner of coding is non-obvious. Units respond to multiple targets similar to quasi-visual cells recently studied [Exp. Brain Res. 130 (2000) 433]. Predictions are made that can be experimentally tested.

Fixation, Ocular↗