that the cue had only a temporary effect. This was statistically confirmed by two-tailed t-tests for each target change interval. The t-tests yielded a reliable cue size effect for the first interval (t(9) = 2.3, p,.05), but not for the remaining intervals (all ts,1.6, ps ..1). In contrast, in the tone absent condition, there was no cue effect (all ts,1.9, ps ..09). General Discussion The present study replicated the pip and pop effect [6,8,10,25,26]. Search times as well as search slopes were markedly reduced when the target color change was accompanied by an auditory signal (Experiment 1) relative to a condition in which no such signal was present (Experiment 2). Important for the present question is that in the tone present condition, responses toward audiovisual events were overall faster when attention was distributed than when attention was focused (as induced by cue size). This effect cannot be explained in terms of a purely visual mechanism, as there was no effect of cue size in the tone absent condition (if anything it was in the opposite direction). Moreover, we found evidence that our attentional window manipulation was effective, since we observed a reliable effect of eccentricity that depended on the size of the attentional window. In other words, participants were better to find the synchronized target in the periphery when they adopted a large attentional window than when they adopted a small attentional window. Whereas the size of an attentional window affected overall search times for synchronized audiovisual events, search slopes remained unaffected, and never reached values typically assumed for parallel search (for instance ,10 ms/item [27]). Thus, even when participants distributed their attention, capture by audio- visual events was not perfect. This was also found by Belopolsky et al. [14], and explanations range from the inability to maintain a wide attentional distribution to a reluctance to adopt one in the first place. Note that without the tone, search is effortful and serial. In other words, the default setting to find the target is presumably a focused attention setting because without the sound Figure 6. The effect of the size of the cue as a function of time (the interval in which the target changed), for the tone present and absent conditions. Cue size effect is the probability of correct response in the large cue condition – probability of correct response in the small cue condition. The data were pooled over set size. doi:10.1371/journal.pone.0039137.g006 Attentional Window Affects Audiovisual Capture increasing the salience of the target, the target is very hard to find. In the more classic singleton capture paradigm [12,20], the target is always the unique pop-out element in the display, allowing participants to consistently adopt a diffuse attention window setting. In this classic task, one will obtain a completely flat search function. Also, in our previous study we have shown that the pip and pop effect is susceptible to whether participants made eye-movements, explaining the presence of some residual slopes as well ([6] Experiment 4). Regardless of the presence of residual search slopes, the present study clearly shows that the size of the attentional window modulates capture by audiovisual synchronization. The present findings are consistent with the visual search literature. For instance, visual attention is readily drawn to visual objects that stand out from the background, such as a unique red object in a field of green objects, or an abrupt onset (e.g. [12,13]). Even though many studies have shown that such salient features capture attention in an automatic, exogenous manner, recent evidence suggests that the size of the attentional window may modulate the extent to which salient events capture attention [14,20,21]. For instance, Theeuwes [20] showed that abrupt onsets do not capture attention when participants focus their attention on valid target location before display onset. Theeuwes suggested that when attention is in an unfocused, distributed state, attention covers the entire visual field. In contrast, an endogenous cue enables attention to ‘‘zoom in’’ on a particular area, which explains why abrupt onsets do not necessarily capture attention when such onsets are located outside the attentional area. Consistent with Theeuwes, we suggest that audiovisual events captures attention in an automatic manner, however, this capture depends on whether the visual event occurs within the attended area. This also explains why we observed an eccentricity effect of the pip and pop phenomenon, because on some trials the attentional window is not wide enough to enable capture by audiovisual synchrony. Whereas many studies reported that multisensory integration occurs automatically [11,28–30], and that multisensory integration can even guide attention [7,10,31], other studies have claimed quit the opposite, that some attention is beneficial (and sometimes even necessary) to establish binding from different modalities [32–38]. In a recent review, Talsma, Senkowski, Soto-Faraco and Woldorff [39] discussed the role of attention in multisensory processing. With regard to the pip and pop effect, they proposed that (p. 400): ‘‘Stimulus-driven, bottom-up mechanisms induced by crossmodal interactions can automatically capture attention towards multisensory events, particularly when competition to focus elsewhere is relatively low.’’ Consistent with this notion, we observed an effect of automatically driven capture as indexed by the pip and pop effect, and that this is stronger when participants adopt a large (i.e. less focussed) attentional window than when they are forced to focus to the small cue prior the first audiovisual event. All in all then, the present study should temper our previous claims that the pip and pop effect occurs automatically indepen- dent of any top-down control [6,9,10]. The current findings suggest that the pip and pop effect occurs in an automatic fashion as long as spatial attention is divided across the visual field. The extent to which attention is divided across the visual field is under top-down control (Theeuwes, 1994, 2010). Our claims are consistent with the results of a study by Ngo and Spence [8] who replicated the pip and pop effect, and reported additional top- down cueing effects depending on the location of the synchronized auditory signal. So, in other words, search was even more improved when the location of the tone predicted the target location correctly than when the location of the tone predicted the PLoS ONE | www.plosone.org 6 July 2012 | Volume 7 | Issue 7 | e39137