The effect of target salience and size in visual search within naturalistic scenes under degraded vision

Authors

Antje Nuthmann; Adam C. Clayden; Robert B. Fisher

The effect of target salience and size in visual search within naturalistic scenes under degraded vision

publication date

April 2021

Abstract/Introduction

We address two questions concerning eye guidance during visual search in naturalistic scenes. First, search has been described as a task in which visual salience is unimportant. Here, we revisit this question by using a letter-in-scene search task that minimizes any confounding effects that may arise from scene guidance. Second, we investigate how important the different regions of the visual field are for different subprocesses of search (target localization, verification). In Experiment 1, we manipulated both the salience (low vs. high) and the size (small vs. large) of the target letter (a “T”), and we implemented a foveal scotoma (radius: 1°) in half of the trials. In Experiment 2, observers searched for high- and low-salience targets either with full vision or with a central or peripheral scotoma (radius: 2.5°). In both experiments, we found main effects of salience with better performance for high-salience targets. In Experiment 1, search was faster for large than for small targets, and high-salience helped more for small targets. When searching with a foveal scotoma, performance was relatively unimpaired regardless of the target's salience and size. In Experiment 2, both visual-field manipulations led to search time costs, but the peripheral scotoma was much more detrimental than the central scotoma. Peripheral vision proved to be important for target localization, and central vision for target verification. Salience affected eye movement guidance to the target in both central and peripheral vision. Collectively, the results lend support for search models that incorporate salience for predicting eye-movement behavior.

Conclusion/Results

Methodologically, reliably disentangling stimulus-driven and task-driven influences on human behavior requires researchers to exert experimental control over relevant stimulus dimensions, which is challenging when working with images of naturalistic scenes. Here, we placed context-free targets within scenes using the T.E.A. (Clayden et al., 2020), which allowed us to manipulate their salience and size parametrically. When using these stimuli for a target acquisition task in two experiments, clear effects of target salience on search performance and eye-movement parameters were found. Moreover, the results obtained in different simulated scotoma conditions lend further support to the central-peripheral dichotomy (Zhaoping, 2019).

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