Eye-movement control in visual search: How direct is visual span control?

Jacobs, Arthur M. · 1986 · OpenAlex-citations

DOI: 10.3758/bf03207583

archive: archived pipeline: cataloged verified

Get this paper ↗ (DOI — opens at the source; we link to it, we don't host it)

Summary

This study investigates the extent to which eye-movement control in visual search is directly governed by low-level sensory constraints, specifically the limits of spatial visibility or "visual span." The research aims to distinguish between the effects of early visual mechanisms and higher-level cognitive factors on oculomotor behavior. The authors test the "visual span control hypothesis," which posits that in tasks with minimal cognitive load, saccade sizes and fixation durations are determined directly by the spatial limits of what can be recognized around the fixation point. Previous studies using reading or complex search tasks failed to show this direct dependence, suggesting higher-level factors dominated. To isolate sensory effects, this study employs a simple letter detection task where cognitive load is reduced to a binary discrimination decision. The experimental design consisted of two phases using the same subjects, stimuli, and conditions. First, a psychophysical experiment measured visual span using an adaptive procedure. Visual span was manipulated by varying viewing distance (60 cm vs. 120 cm), interletter spacing (normal vs. double), and target-background similarity (four levels of graphic similarity between the target letter and the background 'x's). Results confirmed that visual span decreased systematically as similarity, distance, or spacing increased. Second, a visual search experiment measured eye movements while subjects scanned lines of letters for a target. Eye movements were recorded using a photoelectric scleral reflection technique. The analysis focused on lines containing no targets to assess scanning behavior independent of target detection events. The results provided strong support for the visual span control hypothesis regarding spatial parameters. Approximately 80% of the variance in mean saccade sizes was accounted for by changes in visual span, with a significant linear relationship observed between the two variables. Specifically, as target-background similarity increased and visual span narrowed, saccade sizes decreased significantly. However, the hypothesis was less supported for temporal parameters; less than 50% of the variance in fixation durations was determined by visual span changes. Additionally, while distance and spacing significantly affected visual span, they did not show significant effects on mean saccade sizes, likely due to the high variability in eye-movement data compared to the precise psychophysical thresholds. The study concludes that in simple visual search tasks with minimal cognitive load, saccade sizes are primarily controlled by low-level sensory constraints limiting peripheral visibility. This confirms that oculomotor control can be directly driven by spatial visibility limits when higher-level processing demands are minimized. However, the weaker correlation for fixation durations suggests that higher-level factors, possibly related to decisional processes or the computation of saccade parameters, still play a significant role in the temporal aspects of scanning behavior. These findings support models of eye-movement control involving largely independent subsystems functioning in parallel, where spatial adjustments are tightly coupled to sensory input, while temporal adjustments involve more complex processing.

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed.

Summary generated by qwen3.6-27b-prismaquant on 2026-06-25; verification: verified.

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• visual search
• eye movements scanning
• useful field of view