Academic journal article Attention, Perception and Psychophysics

Mechanisms of Priming of Pop-Out: Stored Representations or Feature-Gain Modulations?

Academic journal article Attention, Perception and Psychophysics

Mechanisms of Priming of Pop-Out: Stored Representations or Feature-Gain Modulations?

Article excerpt

Previous research has shown that repetition of a task-relevant attention-capturing feature facilitates pop-out search. This priming of pop-out effect is due to some residual memory from recent trials. We explore two possible mechanisms of priming of pop-out: a top-down attentional benefit from a memory of the previous target representation that is stored in visual short-term memory (VSTM) and a bottom-up change of attentional gains from perceptual features of the previously attended target. We manipulated participants' ability to form a memory trace in VSTM by occupying it with a distractor task and found that occupying VSTM did not interfere with priming of pop-out. We next manipulated attentional gains associated with feature values by inserting an irrelevant task between pop-out searches. We found that the color of the target from the intervening perceptual task influenced pop-out search: The current pop-out search was facilitated when the intervening task's target matched the target color of the pop-out search. These results suggest that priming of pop-out might not be due to a memory trace of the previous targets in VSTM but, rather, might be due to changes in attentional control based on priming from relatively low-level feature representations of previously attended objects.

Because of its limited computational capacity, the human brain does not fully process all of the information in a visual scene. Selective attention compensates for limitations on information processing capacity by filtering the spatiotemporal stream of information. Many accounts of attentional selection propose both bottom-up and topdown mechanisms for directing attention to objects in a visual scene. In addition to the often-discussed bottom-up and top-down attentional control processes, attention is also directed by past experience. Past experience affects our current performance across a variety of domains and experimental paradigms (see Fecteau & Munoz, 2003; Mozer, Kinoshita, & Shettel, 2007; Mozer, Shettel, & Vecera, 2006), and a prior deployment of attention influences how attention will subsequently be directed.

Several experimental results have demonstrated that past experience affects visual attention in the context of visual search, in which observers search for a known target among distractors. In a series of studies, Maljkovic and Nakayama (1994, 1996, 2000; also see Hillstrom, 2000; Huang, Holcombe, & Pashler, 2004; and Olivers & Humphreys, 2003) investigated the influence of past experience in a simple feature search task. Observers saw three diamond-shaped items with a chip off either the left or right side. Two of the objects were the same color, and the third was a unique color. The target was the uniquely colored object in the display, and observers reported the side of the chip on this singleton target. The goal of the studies was to compare performance when the singleton target remained the same from trial to trial (e.g., a red target followed by a red target) with that when it changed (e.g., a red target followed by a green target). The results showed a clear benefit of the repetition of the singleton feature: Reaction times (RTs) fell significantly when the singleton feature had appeared on an earlier trial, and this benefit extended to five or six previous trials. That is, a same-colored target that appeared five trials earlier (trial n-5) could produce faster RTs on the current trial (trial n). Maljkovic and Nakayama (1994, 1996, 2000) called this phenomenon priming of pop-out (PoP).

PoP does not passively encode all items appearing in the visual field. In order to create a persistent memory trace, the object in the visual field must be attended (Goolsby & Suzuki, 2001), although there is also memory for the distractors' identities. Distractor repetition also decreases RTs, although not as much as does target repetition (Maljkovic & Nakayama, 1994). The memory trace formed by the previously attended object, however, does not seem to be under voluntary control. …

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