Temporal integration depends on increased prestimulus beta band power

Temporal integration was examined using a missing element task, in which task performance depends on the ability to integrate brief successive stimulus displays. Previous studies have suggested that temporal integration is under endogenous control and that integration is more likely when stimuli match the observer’s temporal expectancies. Beta oscillations have previously been related to such cognitive (and attentional) control, as well as to audiovisual integration. We thus hypothesized that prestimulus power in the beta frequency band might reflect “integration readiness” and distinguish trials in which stimuli were successfully integrated from unsuccessful ones. The results showed increased upper beta power (21–30 Hz) prior to successful integration over central and parietal electrodes. This finding supported the idea that increased prestimulus beta power might reflect general control processes that can facilitate integration. Descriptors: Temporal integration, EEG, Beta frequency band, Prestimulus activity The ability to perceive events in time allows us to maintain coherency in an ever-changing stream of perceptual input and enables appropriate actions. Event perception relies heavily on temporal integration: When visual stimuli appear in rapid succession within 200 ms, the brain tends to treat them as a single, integrated event (Eriksen & Collins, 1967). Temporal integration has been observed with various types of stimuli, such as letters that form a word (Forget, Buiatti, & Dehaene, 2010), two halves of faces (Cheung, Richler, Phillips, & Gauthier, 2011), and dot matrices (Hogben & Di Lollo, 1974). Temporal integration is not entirely automatic, however. Several factors influence whether integration will occur. Stimulus characteristics such as duration and luminance affect integration frequency (Di Lollo, 1977, 1980; Hogben & Di Lollo, 1974; Long & Beaton, 1982). Endogenous factors that reflect the state of the observer’s cognitive and perceptual system, such as the expected presentation speed (Akyürek, Toffanin, & Hommel, 2008) and the availability of (transient) attention, also affect integration (Visser & Enns, 2001; Yeshurun & Levy, 2003). Electrophysiological studies on temporal integration have shown resultant modulations of the N1, N2, P3, and N2pc components of the event-related potential (ERP), each of which might indeed relate to endogenous factors (Akyürek & Meijerink, 2012; Akyürek, Schubö, & Hommel, 2010). However, ERPs do not allow for examination of prestimulus effects, which could be important if the state of the perceptual system—even before stimulus onset—indeed affects temporal integration. Prestimulus effects on temporal integration may be detected by examining electroencephalogram (EEG) oscillatory power, in particular in the beta frequency band, which has been related to cognitive control as well as audiovisual integration (Engel & Fries, 2010; Keil, Müller, Ihssen, & Weisz, 2012). Both preand poststimulus beta oscillations are also linked to attention (Deiber et al., 2007; Gross et al., 2004; Kranczioch, Debener, Maye, & Engel, 2007; Wróbel, 2000). A common theme in these studies is that beta power (and/or synchrony) and task performance increase when the perceptual system is optimally set up to process the current or the upcoming stimulus, the latter due to successful prediction or because the previous stimuli were similar. Importantly, when controlling temporal integration is concerned, this optimal state could be related closely to the currently preferred duration of event timing. To determine whether prestimulus differences in oscillatory power might affect temporal integration, data presented in Akyürek et al. (2010) were presently reanalyzed. In this experiment, participants performed a missing element task (MET), in which two successive stimulus displays (S1 and S2) were presented with a 10-ms interstimulus interval (ISI). Each display contained 12 out of 25 possible squares in a 5 ¥ 5 matrix. One matrix position remained empty, and participants were instructed to localize that missing element. When the two displays are perceived separately, this is very hard to accomplish in a limited amount of time (here 1800 ms). However, when the two displays are temporally integrated into one percept, the missing element is easy to spot. When S1 was presented for 70 ms and S2 for 10 ms, participants responded correctly in about half of the trials. This allowed a Address correspondence to: Elkan G. Akyürek, Department of Psychology, Experimental Psychology, University of Groningen, Grote Kruisstraat 2/1, 9712 TS Groningen, The Netherlands. E-mail: [email protected] bs _b s_ ba nn er Psychophysiology, 49 (2012), 1464–1467. Wiley Periodicals, Inc. Printed in the USA. Copyright © 2012 Society for Psychophysiological Research DOI: 10.1111/j.1469-8986.2012.01453.x