The role of eye fixations in concentration and amplification effects during multiple object tracking

Doran, Matthew M.; Hoffman, James E.; Scholl, Brian J. · 2008 · Visual Cognition

DOI: 10.1080/13506280802117010

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Summary

This study investigates whether "attentional concentration" and "attentional amplification" effects observed in multiple object tracking (MOT) are driven by covert attentional mechanisms or by overt eye movements. Previous research indicated that when tracking spatially extended objects, attention is preferentially directed toward object centers (concentration) and this bias intensifies as object length increases (amplification). However, it remained unclear if these effects resulted from the strategic allocation of attention or from participants naturally fixating on the centers of objects, thereby benefiting from foveal acuity. The authors aimed to disentangle these factors by employing a dual-task paradigm combining MOT with probe detection while monitoring eye movements. The researchers conducted two experiments using a MOT task where participants tracked moving lines while detecting probes appearing at either the center or the ends of the objects. In Experiment 1, participants engaged in free viewing while eye-tracking data recorded fixation locations. The analysis compared probe detection rates for probes that were equidistant from the point of fixation, effectively controlling for the visual advantage of foveal processing. In Experiment 2, participants were required to maintain strict central fixation throughout the task, eliminating eye movements entirely. This design allowed the authors to test whether concentration and amplification effects persisted when differences in fixation location were neutralized or when eye movements were prohibited. The results confirmed the presence of both concentration and amplification effects: probes at object centers were detected more accurately than those at the ends, and this disparity grew with object length. Crucially, these effects remained significant even when probes were equated for distance from fixation in Experiment 1, indicating that differential fixation alone did not account for the performance gap. Furthermore, Experiment 2 demonstrated that concentration and amplification effects persisted under conditions of strict central fixation, where no eye movements occurred. These findings indicate that the prioritization of object centers is not a byproduct of saccadic targeting or foveal acuity advantages. The study concludes that attentional concentration and amplification reflect genuine mechanisms of covert attention, specifically the prioritization of spatial regions within extended objects independent of eye movements. This distinction clarifies the nature of object-based attention, demonstrating that attention is not uniformly distributed across an object’s extent but is instead concentrated at its center, with this concentration scaling with object size. The results support the view that MOT involves complex interactions between spatial and object-based attentional processes, where covert attention plays a primary role in segregating and prioritizing information within tracked objects.

Key finding

Attentional concentration and amplification effects during multiple object tracking persist under conditions of strict central fixation and when controlling for distance from fixation, indicating they are driven by covert attention rather than eye movements.

Methodology

lab_experiment

Sample size: 20

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• eye movements scanning