The Attentional Blink is Modulated by First Target Contrast: Implications of an Attention Capture Hypothesis

The Attentional Blink is Modulated by First Target Contrast: Implications of an Attention Capture Hypothesis Simon Nielsen * (sini@imm.dtu.dk) Tobias S. Andersen (ta@imm.dtu.dk) Cognitive Systems Section, Institute for Informatics and Mathematical Modeling Richard Petersens Plads, Building 321 Technical University of Denmark 2800 Lyngby, Denmark Corresponding author Abstract When two targets (T1 & T2) are presented in rapid succession, observers often fail to report T2 if they attend to T1. The bottleneck theory proposes that this attentional blink (AB) is due to T1 occupying a slow processing stage when T2 is presented. Accordingly, if increasing T1 difficulty increases T1 processing time, this should cause a greater AB. The attention capture hypothesis suggests that T1 captures attention, which cannot be reallocated to T2 in time. Accordingly, if increasing T1 difficulty decreases T1 saliency, this should cause a smaller AB. In two experiments we find support for an attention capture hypothesis. In Experiment 1 we find that AB magnitude increases with T1 contrast – but only when T1 is unmasked. In Experiment 2 we add Gaussian noise to targets and vary T1 contrast but keep T1‘s SNR constant. Again we find that AB magnitude increases with T1 contrast. Keywords: Attentional Blink; Attention Capture; Dual Target Interference; Temporal Attention; Exogenous Attention; Spatial Attention; Human Vision. Introduction The attentional blink (AB) paradigm is widely used to study temporal attention and refers to the finding that observers often fail to report the second of two targets (T1 & T2) presented in rapid succession. Raymond, Shapiro and Arnell (1992) reported that accuracy of T2 report is a u-shaped function of the lag between T1 and T2 onset. They systematically varied the time between a white letter target (T1) and a black probe (T2, an ‘X’) embedded in a rapid serial visual presentation (RSVP) stream of black letter distractors. When T2 was presented within 500 ms of T1 observers rarely detected the probe. The AB has predominantly been examined in the RSVP paradigm where stimuli are presented central at fixation. However, Duncan and colleagues (Duncan, Ward & Shapiro, 1994; Ward, Duncan & Shapiro, 1996) used the two-target paradigm where two masked targets are presented consecutively in different locations. They observed a phenomenon similar to the AB, which they referred to as the attentional dwell time. Later Ward, Duncan and Shapiro (1997) argued that the dwell time effect may be the consequence of the location switch and not comparable to the AB. To examine this they introduced the skeletal paradigm where two consecutive masked targets are presented in the same location. The authors found a dwell time similar to what they observed with the two-target paradigm, and suggested that all three paradigms (RSVP, two-target, skeletal) tap a common attentional limitation - an assumption that is adopted in this study. One theory offered to explain the AB is the bottleneck theory (Chun & Potter, 1995; Jolicoeur, 1998). This theory assumes two processing stages and suggests that the AB occurs due to slow second stage processing causing a perceptual bottleneck. The first processing stage is rapid, analyzing target features such as color and form. However, the first stage representation is volatile and susceptible to both decay and interference from other objects. In the second stage objects are consolidated and transferred to more durable memories necessary for conscious report. This stage is slow and capacity limited. According to the bottleneck theory the AB occurs when T2 requires second stage processing while T1 occupies the second stage. The bottleneck theory predicts that making T1 identification more difficult prolongs second stage processing and consequently increases the AB (Chun & Potter, 1995). This prediction has led to several studies examining how T1 difficulty influences the AB. Target difficulty can be approached in either a data limited or resource limited fashion (Norman & Bobrow, 1975). Data limited methods vary T1 difficulty by varying stimulus attributes whereas resource limited methods do it by varying the task or introducing distractors to occupy attentional resources. Here we limit analysis to studies using a data limited approach. McLaughlin, Shore and Klein (2001) varied T1 exposure duration in three conditions mixed within blocks in the skeletal paradigm and observed no effect on the AB between conditions. They suggested that data limited manipulations does not affect the AB unless observers can prepare for a given difficult level in advance and allocate resources appropriately. Shore, McLaughlin and Klein (2001) later replicated this study only this time they varied T1 exposure between blocks and found that increasing T1 exposure decreased AB magnitude, which is in accordance to the bottleneck theory. A study by Christmann and Leuthold (2004) reported similar results. They varied T1 contrast in three conditions between blocks in an RSVP stream and found that increasing T1 contrast decreases AB magnitude. That the effect of T1