the cue was large (509 ms; 4.7% errors). We conclude that participants were not able to process a large cue any faster than a small cue, suggesting that differences in processing speed between the letters of different sizes cannot account for our findings. Whereas Belopolsky et al. [14] demonstrated a Cue size 6 Set size interaction, the present study revealed a clear effect of cue size, but this effect was independent of the number of elements in the display. An important difference is that Belopolsky et al. used color singletons, which were always present, and therefore constantly salient. In contrast, capture by audiovisual events, as investigated here, has a discrete, ‘‘all or nothing’’ nature, because the visual target only becomes temporarily salient, at the moment of the color change, when accompanied by an auditory signal. If participants miss this temporally salient visual event (e.g. due to the size of the attentional window), they may wait for the second opportunity (the subsequent audiovisual event; on average 900 ms later) to detect the pop out, resulting in additive cue size and set size effects. One might argue that there was no need for the participants to wait for the second opportunity since the target was always present, also before any sound or color change occurred. However, given its serial nature, such a purely visual search would not result in an additive effect of the cue with set size. It appears that observers often preferred to wait for the next sound rather than engage in an effortful search. Further support for an effect of attentional window size on audiovisual attentional capture comes from an analysis of eccentricity effects. Eccentricity effects are expected to be reduced when attention is more diffuse (as induced by a large cue), whereas if attention is focused at central fixation (as induced by a small Figure 3. Proportion of correct responses faster than 1,200 ms after the first audiovisual event, as a function of cue size and eccentricity (distance between fixation and target location). doi:10.1371/journal.pone.0039137.g003 Attentional Window Affects Audiovisual Capture cue), especially targets at eccentricity should suffer [23]. We limited this analysis to only those responses that were made to the very first audiovisual target event (i.e. within 1200 ms post onset; note that target events occurred every 900 ms, but we assume that no reasonable response could occur within 300 ms). Because our cue was only brief (150 ms), we expected the attentional window manipulation to be only temporarily effective, but at the very least affect the first synchronized event. After this event, participants may have been able to return to their ‘default’ attentional window. Figure 3 presents the results (collapsed over set size). Proportion of responses were subjected to an ANOVA with cue size (small vs. large), and eccentricity (3.0u, 4.6u vs. 6.2u) as within-subjects variables. Consistent with Carrasco et al. (1995), there was a reliable eccentricity effect as the proportion responses decreased with increasing eccentricity, F(2, 18) = 95.8, p,.001. The main effect of cue size was not significant, F(1, 9) = 3.3, p = .104. More importantly however, the interaction between cue size and eccentricity was reliable, F(2, 18) = 5.4, p = .01, confirming the notion that the size of the cue affected the attentional window (cue size) adopted by the participants. As is clear from Figure 3, the size of the attentional window affects capture by audiovisual synchro- ny, but only for targets presented far from fixation. One potential caveat in the present experiment is that the result we obtained has nothing to do with the occurrence of the synchronized audio-visual event (the pip and pop effect) but would also occur in conditions in which no auditory signal is present. In other words, it is feasible that in conditions in which the target has to be detected by effortful serial search the window manipulation would generate a benefit for the diffuse relative to the focused condition. Experiment 2 was designed to rule out this possibility. Experiment 2 The present experiment was identical to the previous experi- ment, except that no tone was present. We expect slower search times and steeper search slopes relative to those obtained in Experiment 1, because the absence of the sound would require serial effortful search [6,7]. If the attentional window manipulation is tied to the occurrence of the synchronized audio-visual event we expect that in this experiment in which no sound is presented, this manipulation should have no effect. Results and Discussion The RT results are presented in Figure 4. RT data. RTs increased with increasing set size, F(1, 9) = 37.7, p,.001. Contrary to Experiment 1, responses were slower when the cue was large (3,612 ms) than when the cue was small (3,318 ms). More importantly, the effect of cue size was not reliable, F(1, 9) = 2.4, p = .158. The interaction between cue size and set size was also not reliable (F,1). Error data. Overall mean error rate was 4.8%. The ANOVA on Errors revealed no reliable main effect of set size, and cue size, F(1, 9) = 2.3, p = .163, and F(1, 9) = 1.4, p = .260, respectively. Neither was the interaction reliable (F,1). As is clear from the RT and Error data, the cue size effect in Experiment 1 cannot be explained in terms of a purely visual mechanism of the attentional window on target detection, as there was no cue size effect in the present experiment (if anything the effect was in the opposite direction). Alternatively, one might argue that in Experiment 1 performance was better in the large cue condition because eyes tend to move when attention is distributed. In this case, RTs were faster in the diffuse attentional window condition since overt attention facilitated target detection. PLoS ONE | www.plosone.org 4 July 2012 | Volume 7 | Issue 7 | e39137