Academic journal article Perception and Psychophysics

Dividing Attention between Two Different Categories and Locations in Rapid Serial Visual Presentations

Academic journal article Perception and Psychophysics

Dividing Attention between Two Different Categories and Locations in Rapid Serial Visual Presentations

Article excerpt

When two targets are embedded in a rapid serial visual presentation (RSVP) stream of abstractors, perception of the second target is impaired if the intertarget lag is relatively short (less than 500 msec). This phenomenon, called attentional blink, has been attributed to a temporal inability of attentional resources. Nevertheless, a recent study found that observers could monitor two RSVP streams concurrently for up to four items presented in close succession, suggesting a much larger visual capacity limit. However, such high-capacity performance could be obtained by a rapid shift of attention, rather than concurrent monitoring of multiple locations. Therefore, the present study examined these alternatives. Results from six experiments indicate that observers can concurrently monitor two noncontiguous locations, even when targets and distractors are from different categories, such as digits, English alphabet letters, Japanese characters, and pseudocharacters. These results can be explained in terms of a modified input-filtering model in which a multidimensional attentional set can be flexibly configured at different spatial locations.

As shown by the fact that using a cell phone while driving can have serious consequences (Strayer, Drews, & Johnston, 2003), there is a cost to distributing attention to more than one task. Even in simplified tasks, when observers are engaging in a primary undertaking, they frequently fail to notice the occurrence of a salient but incidentally presented object (the inattentional blindness phenomenon; Mack & Rock, 1998; Most, Scholl, Clifford, & Simons, 2005). The same is true with experimentally controlled but natural environments (Simons & Chabris, 1999). These findings suggest that the ability of the human visual system is clearly limited. However, recent studies have also shown that our visual system has a strong capability to process natural scenes (e.g., Kirchner & Thorpe, 2006). Moreover, Li, VanRullen, Koch, and Perona (2002) found that observers can categorize briefly presented natural scenes even when they are simultaneously conducting a foveal task that is known to be attentionally demanding, suggesting that some types of objects can be recognized without attentional requirements.

Researchers have tackled the question of whether attention is required to perceive objects (Broadbent & Broadbent, 1987; Evans & Treisman, 2005; Joseph, Chun, & Nakayama, 1997; Sagi & Julesz, 1985) by asking how many objects we can process at a time. The attentional blink (AB; Shapiro, Arnell, & Raymond, 1997) procedure is a subtype of dual-task paradigm that is one major way to examine this issue. In this procedure, observers find two targets (e.g., letters) embedded in a rapid serial visual presentation (RSVP) of distractors (e.g., digits). When the intertarget interval is less than 500 msec, observers frequently miss the second target, although they correctly identify the first target. The AB deficit is not limited in the perception of RSVP stream; a similar pattern of results has been found when two targets and their masks are presented (Ward, Duncan, & Shapiro, 1996). Because varieties of stimuli and procedure can produce this dual target deficit (Pashler, 1997; Shapiro, 2001), the deficit has been ascribed to temporal unavailability of attention and has been used as a tool to control temporal aspects of attention and awareness (e.g., Kawahara, 2002; Kunar, Shapiro, & Humphreys, 2006).

It has been generally agreed that this AB deficit indicates that the visual system can process only one item at a time. For example, Shapiro et al. (1997) claimed that this deficit occurs because the attentional resource is depleted by processing the first target, resulting in resource scarcity for processing the second target when me temporal lag between the targets is short. The deficit recovers at longer lags because the resource is released after completion of first target processing. …

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