Visual Causality Judgments Correlate with the Phase of Alpha Oscillations

Abstract

The detection of causality is essential for our understanding of whether distinct events relate. A central requirement for the sensation of causality is temporal contiguity: As the interval between events increases, causality ratings decrease; for intervals longer than approximately 100 msec, the events start to appear independent. It has been suggested that this effect might be due to perception relying on discrete processing. According to this view, two events may be judged as sequential or simultaneous depending on their temporal relationship within a discrete neuronal process. To assess if alpha oscillations underlie this discrete neuronal process, we investigated how these oscillations modulate the judgment of causality. We used the classic launching effect with concurrent recording of EEG signal. In each trial, a disk moved horizontally toward a second disk at the center of the screen and stopped when they touched each other. After a delay that varied between 0 and 400 msec after contact, the right disk began to move. Participants were instructed to judge whether or not they had a feeling that the first disk caused the movement of the second disk. We found that frontocentral alpha phase significantly biased causality estimates. Moreover, we found that alpha phase was concentrated around different angles for trials in which participants judged events as causally related versus not causally related. We conclude that alpha phase plays a key role in biasing causality judgments.

Exploring the relationship of phase and peak-frequency EEG alpha-band and beta-band activity to temporal judgments of stimulus duration

“…In the circumstances of this study, however, we did not observe the predicted association between peak-frequency and task performance, and we did not show a relationship between peak-frequency and temporal judgments or sensitivity to the task. The results are consistent with a large amount of evidence demonstrating the functional significance of pre-stimulus phase changes in neuronal oscillations (Busch et al, 2009;Cravo et al, 2015;Mathewson et al, 2009;VanRullen, 2016). On the basis of findings from previous temporal paradigms (Cravo et al, 2015;Milton & Pleydell-Pearce, 2016;Varela et al, 1981) we expected an effect of alpha phase on visually-presented temporal judgments.…”

“…In line with previous findings (Cravo et al, 2015;Mathewson et al, 2009;Milton & Pleydell-Pearce, 2016;Varela et al, 1981), we predicted an effect in the alpha range (7-14 Hz, see Haegens, Cousijn, Wallis, Harrison, & Nobre, 2014 for justification of this definition of the alpha-band frequency range), so analysis focused on a cluster of occipital electrodes (O1, O2, POZ, OZ). An occipital cluster was chosen due to its relevance to the visual nature of the task, and because occipital electrodes have been previously demonstrated to be associated with phase effects on temporal judgments (Milton & Pleydell-Pearce, 2016;Varela et al, 1981), and previous effects of peak alphaband frequency on two-flash discrimination have been reported at occipital electrodes (Coffin & Ganz, 1977;.…”

“…For each participant, the cluster-level (second-order) mean phase angle for each perceptual response was calculated (Zar, 1999). Across-participant differences in the cluster-level mean phase angles for each response were then tested for each frequency and time point using the non-parametric paired test for angular difference described by Zar (Zar, 1999) (see also Cravo et al, 2015) and controlled using non-parametric clusterbased permutation analysis (1000 permutations; entry-threshold <.05; cluster statistic threshold of <.05) (Maris & Oostenveld, 2007). Clusters in the original data could form on the basis of significant phase differences (α < .05) being adjacent in frequency and/or time.…”

“…Pre-stimulus phase Pre-stimulus phase was analysed at the occipital electrode cluster described in the Methods. In the prestimulus window (−600 ms to −2 ms), phase differences between Longer and Shorter temporal judgments were explored for frequencies 5-48 Hz using the nonparametric test of angular differences in paired data (Zar, 1999; see also Cravo et al, 2015), corrected with non-parametric cluster-based permutation analysis. This revealed phase differences between the two subsequent temporal judgments (Monte Carlo p = 0.018).…”

“…Thus when two discrete stimuli occur within the same perceptual frame they are more likely to be experienced as simultaneous rather than as temporally segregated. More recently, a number of findings consistent with this framing hypothesis have demonstrated effects of oscillatory pre-stimulus phase on fine-grained temporal judgments (Baumgarten, Schnitzler, & Lange, 2015;Chakravarthi & Vanrullen, 2012;Cravo, Santos, Reyes, Caetano, & Claessens, 2015;Milton & Pleydell-Pearce, 2016). These studies investigated temporal judgments at or shorter than the hypothesized frame duration, typically thought to involve thẽ 10 Hz (~100 ms) alpha cycle for visual stimuli (Cravo et al, 2015;Milton & Pleydell-Pearce, 2016;Varela et al, 1981).…”