Perceptual SpanPerceptual Span

Fourteen college students read passages displayed on a cathode-ray tube as their eye movements were monitored in a study that examined (1) whether letters that lie in the center of vision are used earlier in the fixation than letters further to the right, (2) how soon after a stimulus event that event can affect eye movement control, and (3) how soon in a fixation the presence of an orthographically inappropriate letter string can be shown to influence eye movement decisions. During occasional fixations, all letters to the left of the directly fixated letter yr all letters more than four to the right of the fixated letter were replaced by other letters. This replacement occurred either for only the first ms. of the fixation or only after the first 100 ms. of the fixation. The eye movement data indicated that the eyes can respond to change in the visual stimulus within less than 100 ms., and to orthographic irregularity in the text within less than 160 ms. No evidence was found for a left-to-right attentional scan during a fixation. The findings suggest that the response time of the eyes is shorter than usually proposed in theories of visual processing, and that eye movement decisions are made later in the fixation than has often been assumed. In addition, they show that much of the processing takes place too late to affect the immediately following saccade and hence is revealed only later in the eye movement pattern. Thirty-six references are listed. (Author/FL)

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