Psycholinguistics: Visual Processing

Low-Level Vision

Over four decades of research with deaf individuals have been conducted using various visual tasks that ask observers to make simple responses indicating discrimination or detection of low-level features such as a target’s brightness or color, where a target appears, or which way it moves. From this work, it is clear that the quality or efficiency of low-level perceptual sensations is not enhanced in deaf people. For example, the ability to report motion direction or speed, temporal order judgment, shape identification, numerosity judgment, visual tracking of multiple moving objects, visual digit span, and line orientation judgment are not altered in deaf individuals. Despite these reports of no changes in perceptual sensitivity, one finding that has consistently emerged is that deaf individuals are generally faster at detecting abrupt visual onsets in the visual periphery.

Visual Attention

It has become clear that differences between deaf and hearing participants usually emerge with tasks that engage spatial attention to targets appearing in the peripheral visual field. For example, while performing a shape identification task, distractors that appear within central vision are more distracting for hearing than for deaf individuals, while distractors that appear outside of this central vision region are more distracting for deaf than for hearing individuals. These results are often interpreted to mean that deaf individuals place their greatest concentration of attention in the periphery, while hearing individuals place it in the central visual field.

Other, similar evidence comes from studies using a pre-cue paradigm to manipulate where subjects covertly place their “spotlight” of attention (while fixating straight ahead) during a task in which subjects have to quickly report the location of a target that appears briefly within random peripheral locations. The target could be preceded by one of three cue types: a valid cue that tells the subjects where the target will appear, a neutral pre-cue that provides no information, or an invalid pre-cue that provides the wrong information. As expected, all subjects do well when the valid pre-cue informs them where the stimulus will appear, and they perform more poorly when the target is in a different place than where the neutral or invalid pre-cue appeared. Most interestingly, the deaf participants are less impaired than hearing controls when responding to targets at the uncued or invalid locations. This finding is usually interpreted as evidence that deaf people are more efficient at redirecting attention from one part of the visual field to another.

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