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Saccade target selection during visual search
1Department of Psychology, University of Durham, U.K. J.M.Findlay@durham.ac.uk
Abstract:
Five experiments are reported in which eye movements were recorded while subjects carried out a visual search task. The aim was to investigate whether an accurate initial target directed saccade could be programmed. In experiments 1-2, subjects moved their eyes to targets defined by colour, which were presented with seven non-targets in a circular array. Accurate saccades with short latencies were common but errors sometimes occurred and search for an "oddity" target, defined exclusively by difference in colour from a homogeneous set of distractors, was particularly error prone. In Experiment 3, occasional trials contained double targets. First saccades sometimes landed at an intermediate position between the targets. In Experiments 4 and 5, targets were presented with 15 distractors in two concentric rings of 8. Targets specified by shape could be located accurately with a single saccade. Search for a colour-shape conjunction was more difficult but targets in the inner ring were located frequently with a single saccade. The results suggest that the control of the initial eye movement during both simple and conjunction searches is through a spatially parallel process.
Insights
This study on visual search found that while accurate eye movements (saccades) are common, errors occur, especially when searching for unique color targets. The findings suggest a parallel processing system guides initial eye movements in visual search tasks.
Area of Science:
- Cognitive Psychology
- Neuroscience
- Visual Perception
Background:
- Understanding the mechanisms of visual search is crucial for explaining how humans efficiently process complex visual scenes.
- Eye movements, specifically saccades, play a critical role in directing attention and gathering information during visual search.
Purpose of the Study:
- To investigate the accuracy and programming of the initial target-directed saccade during visual search tasks.
- To determine if visual search relies on a spatially parallel process for initial eye movement control.
Main Methods:
- Eye movements were recorded from subjects performing visual search tasks with varying target definitions (color, shape, conjunctions) and distractor configurations.
- Experiments involved targets presented in circular arrays and concentric rings, with varying numbers of distractors.
Main Results:
- Accurate, short-latency saccades were frequent for simple targets (e.g., color, shape).
- Search for 'oddity' targets (unique color) and conjunction targets (color-shape) was more error-prone.
- In some cases with double targets, initial saccades landed between targets.
- Targets in the inner ring of a two-ring display were located more frequently with a single saccade.
Conclusions:
- The control of initial eye movements in visual search, including simple and conjunction searches, appears to be mediated by a spatially parallel process.
- While efficient, the visual search system is susceptible to errors, particularly with complex target definitions or specific spatial arrangements.