Emotion Effects on Timing Figure 1. The sequence and duration of stimuli during a trial in Experiment 1 are shown. doi:10.1371/journal.pone.0021829.g001 levels) as repeated measures factors. There were significant main 2 effects of S2 Duration (F(3, 39) = 73.24, p,.001, g partial = .849) 2 and Emotion (F(1, 13) = 9.67, p,.01, g partial = .426). Participants were more likely to respond ‘‘shorter’’ with decreasing S2 duration and when S2 was preceded by a negative as compared to a neutral picture (Fig. 2). The absence of an interaction between S2 Duration and Emotion (p..1) indicated that the two main effects were independent. Discussion In contrast to previous studies, we found that participants underestimated stimulus duration during emotional as compared to neutral trials. Specifically, participants in the present experi- ment were more likely to indicate that S2 duration was shorter than that of S1 when S2 was preceded by a negative as compared to neutral picture. Given the nature of the present paradigm, one may speculate that attention, rather than pacemaker rate, accounts for the observed effects. Emotional modulation of attention may have caused participants to accumulate fewer pacemaker pulses such that perceived S2 duration was reduced. However, before such a conclusion can be drawn, alternative accounts require consideration. Specifically, it is possible that the relatively short interval between the picture and S2 accounts for the observed effects. Perhaps the negative picture engaged perceptual mechanisms that led to a transient distraction causing the participant to miss S2 onset. Evidence for this possibility comes from research employing the ‘‘attentional blink’’ paradigm. In this paradigm, participants are presented with a stream of distracters and one or two targets. Participants are likely to miss a second target if it closely follows the first target [41–42]. Based on this evidence researchers argued that attention capturing stimuli elicit an attentional blink, which may last up to 500 ms and which compromises the perception of subsequent information. Although the present study used picture durations of 800 ms, which exceeds the typical stimulus duration of an attentional blink paradigm (,100 ms), the interval between picture offset and S2 onset was only 500 ms. Thus, one may ask whether emotional pictures, due to their capacity for attention capture [43], elicited an extended attentional blink that accounts Figure 2. The group mean probability of responding ‘‘shorter’’ and standard error of the mean are plotted for each S2 duration in Experiment 1. doi:10.1371/journal.pone.0021829.g002 PLoS ONE | www.plosone.org 3 July 2011 | Volume 6 | Issue 7 | e21829