Academic journal article Attention, Perception and Psychophysics

Target Grouping in Visual Search for Multiple Digits

Academic journal article Attention, Perception and Psychophysics

Target Grouping in Visual Search for Multiple Digits

Article excerpt

Published online: 26 August 2014

© The Psychonomic Society, Inc. 2014

Abstract In four experiments in which participants searched for multiple target digits we hypothesized that search should be fastest when the targets are arranged closely together on the number line without any intervening distractor digits, i.e., the targets form a contiguous and coherent group. In Experiment 1 search performance was better for targets defined by numerical magnitude than parity (i.e., evenness); this result supports our hypothesis but could also be due to the linear separability of targets from distractors or the numerical distance between them. Experiment 2 controlled for target-distractor linear separability and numerical distance, yielding faster search when targets were surrounded by distractors on the number line than when they surrounded distractors. This result is consistent with target contiguity and coherence but also with grouping by similarity of target shapes. Experiment 3 controlled for all three alternative explanations (linear separability, numerical distance, and shape similarity) and search performance was better for contiguous targets than separated targets. In Experiment 4 search performance was better for a coherent target group than one with intervening distractors. Of the possibilities we considered, only the hypothesis based on the contiguity and coherence of the target group on the number line can account for the results from all four experiments.

Keywords Visual search . Workingmemory . Text comprehension

According to the classical perception-cognition divide, visual processing proceeds without interference from higher-level cognition, or in other words perception can be considered to be cognitively impenetrable (Pylyshyn, 1999). The notion that visual perception is cognitively impenetrable enjoys widespread support from the vast and ever-increasing collection of visual illusions for which the illusory appearance persists in spite of knowledge that is inconsistent with the visual experience (Firestone & Scholl, 2014). For example, even if the observer knows that the two lines in the Müller-Lyer illusion (1889) are equally long, the Y-terminated line appears to be longer than the arrow-terminated line. Nevertheless, a growing body of evidence has found that language can influence visual perception. Presenting a verbal label can enhance the ability to detect an object that is rendered invisible by continuous flash suppression (Lupyan &Ward, 2013), to identify the motion direction of dots at motion coherence threshold (Meteyard, Bahrami, & Vigliocco, 2007), and to distinguish between intact and distorted versions of high-level stimuli such as faces (Puri & Wojciulik, 2008). Here we investigate the interaction between perception and cognition in visual search for digits that are semantically associated with the numerical quantities they represent.

Historically, attempts to uncover a role for the semantic associations of letters and numbers in visual search experiments have been hindered by the fact that manipulating the semantic associations of alphanumeric characters typically entails also manipulating the characters' perceptual features (i.e., among single-digit numbers 2 is numerically small and 9 is numerically large but the two characters also have different shapes). As a result, it is difficult to disentangle conceptual and perceptual effects on search (Krueger, 1984), to such an extent that Wolfe and Horowitz (2004) expressed doubt that alphanumeric concepts could guide search. As Wolfe (1998) notes, while many visual search tasks have used alphanumeric characters as targets and distractors, such tasks might in fact be perceptual feature searches in the guise of alphanumeric searches.

Nevertheless, by carefully controlling the shape of the items used in visual search, Lupyan (2008) showed that the semantic heterogeneity of distractors can influence search efficiency. …

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