Academic journal article Attention, Perception and Psychophysics

Driving Forces in Free Visual Search: An Ethology

Academic journal article Attention, Perception and Psychophysics

Driving Forces in Free Visual Search: An Ethology

Article excerpt

Published online: 3 January 2014

© Psychonomic Society, Inc. 2014

Abstract Visual search typically involves sequences of eye movements under the constraints of a specific scene and specific goals. Visual search has been used as an experimental paradigm to study the interplay of scene salience and top-down goals, as well as various aspects of vision, attention, and memory, usually by introducing a secondary task or by controlling and manipulating the search environment. An ethology is a study of an animal in its natural environment, and here we examine the fixation patterns of the human animal searching a series of challenging illustrated scenes that are well-known in popular culture. The search was free of secondary tasks, probes, and other distractions. Our goal was to describe saccadic behavior, including patterns of fixation duration, saccade amplitude, and angular direction. In particular, we employed both new and established techniques for identifying top-down strategies, any influences of bottom-up image salience, and the midlevel attentional effects of saccadic momentum and inhibition of return. The visual search dynamics that we observed and quantified demonstrate that saccades are not independently generated and incorporate distinct influences from strategy, salience, and attention. Sequential dependencies consistent with inhibition of return also emerged from our analyses.

Keywords Visual search . Ethology . Free search . Inhibition of return . Saccadic momentum

Visual search entails a complex interplay between scene salience and search strategy. Although we are capable of looking at any scene feature as often as we wish, it is usually in our best interest to be guided in our search by scene elements that closely resemble the object of our search, or to focus on locations that we believe will provide the most information. But search can also be influenced by bottom-up saliency; that is, it can be driven by attention-grabbing features in the search array, such as motion, sudden onsets, high contrast, or unique color or size (see Wolfe & Horowitz, 2004,fora review). A further source of influence is midlevel mech- anisms (Hooge, Over, van Wezel, & Frens, 2005;Klein & MacInnes, 1999; MacInnes & Klein, 2003; Smith & Henderson, 2009, 2011a) that drive the saccadic system toward novel regions, as has been suggested by models of human search performance (Itti & Koch, 2001)and neurophysiological investigations in rhesus monkeys (Dorris, Klein, Everling, & Munoz 2002; Fecteau & Munoz, 2006). Two such midlevel effects that could drive the saccadic system toward novel locations are inhibition of return, which is a bias away from previous fixations, and saccadic momentum, which is a bias to repeat the most recent saccadic vector.

We move our eyes roughly three times every second to bring new parts of the environment to the central, high- resolution part of the retina. Patterns of these saccades can provide information on underlying visual processes and have been used to produce and test many models of sac- cadic behavior in visual search (Foulsham & Kingstone, 2012; Itti & Koch, 2001; Wolf, 2007). Saccade patterns are dependent on instructions (Yarbus, 1967), scene salience (Henderson, 2003), the entropy of the search array (Gilchrist & Harvey, 2006), and the previous state of the oculomotor system (Zelinsky, 1996). Although the impor- tance of a low-level salience map (e.g., Itti & Koch, 2001) for the control of overt orienting has been challenged (Einhäuser & König, 2003; Tatler, Baddeley, & Gilchrist, 2005; Tatler, Hayhoe, Land, & Ballard, 2011), these chal- lenges are aimed at narrow definitions of a salience map. Some have sought to overcome the challenges by redefining salience to include deviation or "surprise" (Itti & Baldi, 2006), a retinotopic priority map (Wischnewski, Belardinelli, & Schneider, 2010), or object-level salience (Einhäuser, Spain, & Perona, 2008). …

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