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Why are there eccentricity effects in visual search? Visual and attentional hypotheses
J M Wolfe1, P O'Neill, S C Bennett
1Harvard Medical School, Brigham & Women's Hospital, Department of Ophthalmology, Boston, MA 02115, USA. wolfe@search.bwh.harvard.edu
Perception & Psychophysics
|March 21, 1998
Summary
Visual search is more efficient for central targets due to an attentional bias favoring fixation. This "eccentricity effect" is not explained by visual factors but by how attention is allocated during search.
Area of Science:
- Cognitive Psychology
- Neuroscience
- Visual Perception
Background:
- Standard visual search tasks assume random target locations.
- Previous research indicates targets near fixation are found more efficiently.
- This phenomenon is known as the eccentricity effect.
Purpose of the Study:
- To investigate the primary cause of the eccentricity effect in visual search.
- To determine if attentional bias or visual factors underlie the eccentricity effect.
- To test an attention allocation model for visual search.
Main Methods:
- Conducted six experiments manipulating target eccentricity and set size.
- Ruled out peripheral visual sensitivity, crowding, and cortical magnification as explanations.
- Tested an attention allocation model and analyzed reaction time (RT) by set size interactions.
Main Results:
- The eccentricity effect cannot be explained by peripheral visual reductions.
- An attentional bias favoring central items is proposed as the main cause.
- Reaction time by set size effects can be independent of eccentricity.
- Effective set size in search depends on target eccentricity, with search proceeding outward from fixation.
Conclusions:
- The eccentricity effect in visual search is primarily driven by attentional bias.
- Attention is preferentially allocated to central visual field items.
- Search strategy involves scanning outward from the point of fixation.