Statistical stability and set size exert distinct influences on visual search

Corbett, Jennifer E.; Munneke, Jaap · 2020 · Crossref

DOI: 10.3758/s13414-019-01905-2

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Summary

This study investigates how statistical stability in the visual environment and attentional demands (indexed by set size) independently influence visual search performance. The research addresses a fundamental question in visual perception: how the visual system maintains a stable impression of the world despite continuous retinal changes while simultaneously detecting salient objects. Previous work suggested that repeating the average size of background items across trials facilitates search, but it remained unclear whether this facilitation interacts with attentional mechanisms typically affected by the number of items in a display. To disentangle these factors, the authors conducted two experiments using a conjunction search task. Participants searched for a target Gabor patch defined by a unique combination of orientation and spatial frequency within displays of distractor Gabors. The key manipulation involved the "statistical stability" of the background: in stable sequences, the mean size of the distractors remained constant across successive trials, whereas in unstable sequences, the mean size changed on every trial. Experiment 1 manipulated set size (10, 20, or 30 items) across sequences while holding it constant within each sequence. Experiment 2 provided a stronger test by varying set size (10, 20, 30, or 40 items) on every non-baseline trial, ensuring that set size was unstable even when mean size was stable. This design allowed the researchers to determine if the benefits of statistical stability persist when attentional load fluctuates trial-by-trial. The results from both experiments demonstrated distinct, additive effects of statistical stability and set size on reaction times. In Experiment 1, participants responded faster in stable conditions compared to unstable ones, and slower as set size increased, with no significant interaction between the two factors. Bayesian analysis confirmed that a model including only main effects fit the data better than one including an interaction. Experiment 2 replicated these findings: statistical stability facilitated search performance independently of the varying set sizes. Even when the number of items changed unpredictably from trial to trial, maintaining a stable mean size of the background elements continued to speed up search. There was no evidence that statistical stability attenuated or eliminated the typical linear increase in search time associated with larger set sizes. These findings conclude that statistical stability and attentional processing demands exert independent influences on visual search. The visual system utilizes inherent statistical redundancies in the environment to stabilize perception and facilitate detection, a process that operates separately from the limited-capacity attentional mechanisms responsible for handling increasing numbers of items. This supports the proposal that our stable perception of the world and our ability to attend to salient events are governed by distinct mechanisms: one relying on efficient, parallel statistical representations of the background context, and the other subject to the serial, capacity-limited constraints of focused attention.

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Topics

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• visual search
• inattentional change blindness