Temporal structure in sensorimotor variability is a reliable trait, but is unrelated to attentional state measures
Behavioural performance shows substantial endogenous variability over time, regardless of the task at hand. This intra-individual variability is a reliable marker of individual differences. Of growing interest to psychologists is the realisation that variability is not fully random, but typically exhibits short- and longer-range temporal structures. However, the measurement of temporal structures come with several controversies, and their potential benefit for studying individual differences in healthy and clinical populations remains unclear. The interpretation of these structures is also controversial. Behavioural variability is often implicitly associated with fluctuations in attentional focus, which also fluctuates over time between on- and off-task (e.g., “I was performing poorly because my mind was wandering elsewhere”). However, empirical evidence for this intuition is lacking. In the current research, we analyse the temporal structures in reaction (RT) series from new and archival datasets, using 11 different sensorimotor and cognitive tasks across 526 participants. We first investigate the intra-individual repeatability of the most common measures of temporal structures. Secondly, we examine inter-individual differences in these measures using: 1) task performance assessed from the same data, 2) meta-cognitive ratings of on-taskness from thought probes occasionally presented throughout the task, and 3) self-assessed attention-deficit related traits. Across all datasets, autocorrelation at lag 1 and Power Spectra Density slope showed high intra-individual repeatability across sessions and correlated with task performance. The Detrended Fluctuation Analysis slope showed the same pattern, but less reliably. The long-term component (d) of the ARFIMA(1,d,1) model showed poor repeatability and no correlation to performance. Overall, these measures failed to show external validity when correlated with either mean subjective attentional state or self-assessed traits between participants. Overall, temporal structures may be stable within individuals over time, but their relationship with subjective state and trait measures of attentional state remains elusive.