Effects of Clock Monitoring on Electroencephalographic Activity

Abstract

Electroencephalographic (EEG) activity was recorded while participants waited to make spontaneous key-press movements (Experiment 1) or waited for tones in a pitch judgment task (Experiment 2). In one condition of each experiment, participants also had to report the position of a spot traveling on a clock at the crucial time point (i.e., when they decided to move or when the tone was presented), mimicking a procedure used to assess the time of conscious awareness of an event of interest. In a second condition, there was no clock or temporal judgment. Average EEG activity preceding key presses was substantially different when participants had to monitor the clock than when they did not. Smaller clock-related differences in average EEG activity were also present preceding tone onsets. The effects of clock monitoring on EEG activity could be responsible for previous reports that movement-related brain activity begins before participants have consciously decided to move (e.g., Libet, Gleason, Wright, & Pearl, 1983).

The What, the When, and the Whether of Intentional Action in the Brain: A Meta-Analytical Review

“…For example, Lau et al (2004a) associated the judgment of the onset of the intention to move with activation of the pre-SMA (Lau et al, 2004a). Libet' s paradigm has a number of limitations (see for example Trevena and Miller, 2002; Lau H. et al, 2006; Miller et al, 2011), first and foremost, of being meta-cognitive in nature and perhaps not terribly well-suited to fMRI given the temporal resolution of the technique and the time scale of the neurophysiological events seen with EEG during the paradigm.…”

Nowhere and Everywhere: The Causal Origin of Voluntary Action

“…We refer to this view of action initiation, where a decision-to-move (conscious or not) precedes the RP which in turn leads to an action, as the 'early decision' account. Libet's (1983) experiment has been replicated numerous times (Haggard and Eimer 1999;Keller and Heckhausen 1990;Miller et al 2011;Schurger et al 2012;Miller 2002, 2010), including a recent replication using single-neuron recordings in humans that confirms a gradual increase in firing rate of individual neurons in advance of reported conscious-decision time (Fried et al 2011).…”

Time to lay the Libet experiment to rest: Commentary on Papanicolaou (2017).

“…For all the various arguments over measurement error, Libet's critics missed an important feature of his experiment: Subjects must keep track of a timer while they're deciding to move. Miller and his colleagues (Miller, Shepherdson, & Trevena, 2011) replicated Libet's procedure, and observed a clear PNS. But they also ran a control condition in which subjects made spontaneous movements, but did not watch the clock.…”