Academic journal article Attention, Perception and Psychophysics

The "Beam of Darkness": Spreading of the Attentional Blink within and between Objects

Academic journal article Attention, Perception and Psychophysics

The "Beam of Darkness": Spreading of the Attentional Blink within and between Objects

Article excerpt

When two targets (T1 and T2) are inserted into a rapid serial visual presentation (RSVP) stream of nontargets, observers are impaired at identifying T2 when it is presented within half a second after T1. This transient drop in performance, or attentional blink (AB), has been attributed to a temporary unavailability of task-critical processing resources. In the present study, we investigated how object-based attention modulates the AB, by presenting four synchronized RSVP streams in the corners of two rectangular bars (e.g., one above and one below fixation). The results from four experiments revealed that the AB increased within short temporal lags (of up to ~400 msec) when T2 was presented on the same, rather than a different, bar as T1 (with T1-T2 spatial distance controlled for). Thus, the AB is seen to spread across entire object groupings, suggesting that the spatiotemporal resolution of attention is modulated by global-object information.

Complex, natural environments challenge the visual system in the processing of multiple pieces of information arriving simultaneously from different ambient sources. However, often, even salient events go unnoticed, because of limitations in how much information the visual system can process at a given point in time. Thus, for example, awareness of a given (target) stimulus may be substantially impaired if attention is distracted by a competing stimulus or engaged elsewhere (see, e.g., Kim & Blake, 2005, for a review).

The attentional blink (AB) phenomenon provides a prominent example of such a bottleneck in the processing of multiple stimuli (e.g., Chun & Potter, 1995; Raymond, Shapiro, & Arnell, 1992). In a typical AB experiment, observers are presented with two targets (T1 and T2) embedded within a rapid serial visual presentation (RSVP) stream of nontargets. When the temporal interval between the two targets is less than ~500 msec, observers frequently fail to identify T2, whereas they show good performance in identifying T1. In general, this pattern of performance shows that at least some aspects of visual processing are confined to only one object at a time (but see below). The reduction of T2 identification at relatively short temporal lags occurs because limited attentional resources are still engaged in processing and consolidating T1. At longer lags, the ability to process T2 recovers because resources are released when T1 processing has terminated (for reviews, see Hommel et al., 2006, and Shapiro, Raymond, & Arnell, 1997).

Despite monotonic increases in T2 identification with longer T1-T2 lags, many studies have reported the AB effect to be characterized by a U-shaped function, with relatively unimpaired performance if T2 is presented directly after T1 and a transitory drop in accuracy only thereafter (e.g., Chun & Potter, 1995; Raymond et al., 1992). This effect of lag 1 sparing has been interpreted in terms of the visual system's being able to process the two targets together (in a batch) as long as they appear in direct temporal succession. However, in a meta-analysis of AB experiments, lag 1 sparing has been revealed to occur only in cases in which no attentional switch (between locations or categories) was required between targets (Visser, Bischof, & Di Lollo, 1999; see also Juola, Botella, & Palacios, 2004).

Studies of the AB have primarily investigated the temporal modulation of the attentional engagement, with a stream of stimuli presented at a single spatial location. However, in some studies, attempts have also been made to determine the spatiotemporal characteristics of the AB. Presenting observers with two noncontiguous RSVP streams, Kawahara and Yamada (2006; Yamada & Kawahara, 2007) found, with two T1 and T2 targets that appeared simultaneously at two adjacent spatial positions, that the visual system can monitor multiple concurrent streams. However, if targets switch unpredictably from one to the other of two spatially segregated streams, shifts of attention lead to an increase in the AB at short T1-T2 lags (Juola et al. …

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