Academic journal article Perception and Psychophysics

What Influences Visual Search Efficiency? Disentangling Contributions of Preattentive and Postattentive Processes

Academic journal article Perception and Psychophysics

What Influences Visual Search Efficiency? Disentangling Contributions of Preattentive and Postattentive Processes

Article excerpt

The present experiments introduce a new search technique for disentangling contributions of preattentive guidance and postattentive template matching to search efficiency. Participants performed searches (for negative or positive faces in Experiment 1; pop-out search in Experiment 2; conjunction search in Experiment 3) under either standard viewing conditions or a new restricted viewing condition in which items were occluded by black placeholders and revealed only when a participant moved the mouse pointer over the black square. Under full viewing conditions, search performance can be aided by both preattentive and postattentive mechanisms, whereas the mouse-contingent search relies solely on postattentive template-matching processes. Results demonstrate the utility of this new methodology for distinguishing contributions of preattentive guidance and postattentive template-matching processes in ambiguous search situations. Furthermore, application of the new restricting viewing method to search for emotionally expressive faces suggested that emotional information is processed preattentively and influences the allocation of focal attention.

Visual search is a common, everyday activity. Indeed, the act of searching only becomes salient to us when search is difficult thus requiring effort and time for us to find the object of our search. Other times, we do not even notice that we have searched, because the object we are looking for just "pops out" of its surroundings. Understanding the basic mechanisms that underlie visual search has been a focus of considerable research (e.g., Duncan & Humphreys, 1989; Treisman & Gelade, 1980; Wolfe, 1994). Perhaps the most dominant view that has emerged from laboratory studies is that the efficiency of visual search depends on two distinct yet interrelated processes-namely, (1) preattentive processing, which is the processing of objects prior to attentional selection (i.e., unattended objects), and (2) postattentive processing, which is the processing of objects within the focus of attention (i.e., attended objects). Search performance is typically thought to be determined by some combination of these two processes and, as such, in many search situations, it has proven difficult to isolate the distinct contributions of the two processes.

In the present article, we develop a new methodology designed to separate the contribution of preattentive and postattentive processes during search. This procedure extends die moving-window technique developed in studies of reading (McConkie & Rayner, 1975; Rayner, 1995, 1998) and visual search (Gilchrist North, & Hood, 2001; Thomas et al., 2006; van Diepen & d' Ydewalle, 2003). Specifically, we compared performance in a standard visual search task in which target and distractors were presented simultaneously in full view, with performance in a modified visual-search task, in which die search items were occluded by black squares and participants had to move the mouse pointer over the black square to reveal the object underneath. To illustrate the utility of tins metiiodology, we applied the procedure in a context in which the relative contributions of preattentive guidance and postattentive processing have been contentious-namely, search for faces expressing positive and negative emotions. To further explore the boundary conditions of the novel methodology, we also applied it to a simple feature search, as well as an inefficient conjunction search.

Measuring the Mechanisms Underlying Visual Search

In the laboratory, the mechanisms underlying visual search have been examined using a variety of different search tasks. In a typical search task, participants are shown displays consisting of a target item embedded among a varying number of distractor items. Their task is to find the target as fast and as accurately as possible. By varying the number of distractors in the display (i.e., set size), it is possible to plot a search function relating the time to detect a target to the number of items in the display. …

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