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Performance in simple visual search at threshold contrasts

J Laarni1, R Näsänen, J Rovamo

  • 1Department of Psychology, University of Helsinki, Finland.

Investigative Ophthalmology & Visual Science
|July 1, 1996
PubMed
Summary
This summary is machine-generated.

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Even with a large orientation difference, visual search for a target among distractors showed a set-size effect. This means performance decreased as more locations were possible, likely due to positional uncertainty.

Area of Science:

  • Visual perception
  • Cognitive psychology
  • Human factors

Background:

  • Visual search efficiency is often assumed to be independent of the number of items (set size) when targets and distractors differ significantly.
  • This has led to theories of parallel, unlimited-capacity visual processing.

Purpose of the Study:

  • To investigate if a maximal orientation difference (90 degrees) between target and distractor gratings creates a set-size effect at contrast threshold.
  • To determine if positional uncertainty can account for any observed set-size effect in this visual search task.

Main Methods:

  • Participants performed a two-interval, forced-choice task searching for a horizontal Gabor target among vertical distractor Gabors.
  • The number of possible target locations varied (1 to 8), and contrast thresholds were measured under search and single-element conditions.

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Main Results:

  • Contrast thresholds significantly increased (nearly doubled) as the number of possible target locations rose from 1 to 8.
  • This set-size effect was observed even with the maximal orientation difference between target and distractors.

Conclusions:

  • A set-size effect exists in visual search even when target-distractor orientation differences are maximal.
  • Positional uncertainty appears to be the primary factor driving this observed set-size effect.