Effects of Visual Imagery on Visual Sensitivity and Pupil Diameter

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Abstract
Sensitivity to a visual stimulus can be reduced by instructions to S to maintain a visual image (Segal, 1971). Imagery in turn may produce an increase in pupil diameter (Simpson & Paivio, 1966). It is possible that changes in pupil diameter might change sensitivity in the experimental conditions used by Segal, so that the decline in sensitivity produced by imagery might be a result of pupillary dilation in response to imagery. This possible explanation of the decline in sensitivity was tested in this experiment and rejected. Other possible peripheral explanations of the effect require further research, including possible changes in accommodation that might be induced by visual imagery.