Investigating the (ir)reducibility and within- and between-subject correlates of intra-individual variability

Intra-individual variability is a prominent characteristic of our behaviour. A large part of this variability is endogenous – arising from fluctuations in our own inner states. In the Introduction, I identify two distinct literatures: 1) the intuitive perspective, which describes variability as a consequence of meta-cognitive fluctuations, and 2) the intrinsic perspective, which describes variability as a necessary feature of our nervous system. In this thesis, I compare these two literatures across four chapters. In Chapter 1, I examined variability in the oculomotor system during rest, and found that variability is repeatable within. In Chapter 2, I found similar intra-individual reliability in variability on a rhythmic manual task, and in the temporal properties of variability. Furthermore, temporal structures correlated positively with variability, but did not correlate with subjective attentional state. In both chapters, variability did not correlate with ADHD, mind wandering, and impulsivity questionnaires. In Chapter 3, I examined the relationships between variability, metacognition, and underlying neural activity. Results showed that participants were more variable on the task prior to off-task compared to on-task reports. Furthermore, neural states underlying attentional state reports showed overlap with those underlying behavioural variability. However, effect sizes were weak – implying that variability and meta-cognition are poor markers of each other. In Chapter 4, I tested a common intuition that people have some access to their fluctuating inner states which they can use to improve their performance. I found evidence against this assumption in both an ecological (darts) and two psychophysical tasks. All in all, while the intuitive framework typically assumes a strong and possibly direct link between meta-cognition and behavioural variability, my current findings indicate that this link is clearly weak

Temporal structure in sensorimotor variability: a stable trait, but what for?

Perquin M, Bompas A. Temporal structure in sensorimotor variability: a stable trait, but what for? bioRxiv. 2019.Human performance shows substantial endogenous variability over time, and this variability is a robust marker of individual differences. Variability is not fully random, but often exhibits temporal dependencies. However, their measurement and interpretation come with several controversies, and their potential benefit for studying individual differences remains unclear. Two recent studies have linked individual differences in temporal structures to task performance on the same data, but with contrasting results. Here we use the metronome task, requiring participants to press a button in synchrony with a tone, widely used to study sensorimotor variability. We first investigate the intra-individual repeatability of the most common measures of temporal structures. Secondly, we examine inter-individual correlates of these measures with: 1) task performance assessed from the same data series, 2) meta-cognitive ratings of on-taskness from thought probes occasionally presented throughout the task, and 3) self-assessed traits commonly assumed to relate to attention or sensorimotor control (ADHD tendencies, mind wandering, and impulsivity). Autocorrelation at lag 1 and Power Spectra Density slope showed high repeatability and good correlations with task performance. Detrended Fluctuation Analysis slope showed the same pattern, but less reliably. The long-term component (d) of the ARFIMA(1,d,1) model shows poor repeatability and no correlation to performance. None of these measures showed external validity when correlated to either mean subjective attentional state or self-assessed traits between participants. In sum, some measures of serial dependencies may be stable individual traits, but their usefulness to study individual differences in other constructs typically associated with variability in performance remains elusive

Reliability and correlates of intra-individual variability in the oculomotor system

Perquin M, Bompas A. Reliability and correlates of intra-individual variability in the oculomotor system. Journal of Eye Movement Research. 2019;12(6).Even if all external circumstances are kept equal, the oculomotor system shows intra-individual variability over time, affecting measures such as microsaccade rate, blink rate, pupil size, and gaze position. Recently, some of these measures have been associated with ADHD on a between-subject level. However, it remains unclear to what extent these measures constitute stable individual traits. In the current study, we investigate the intra-individual reliability of these oculomotor features. Combining results over three experiments (>100 healthy participants), we found evidence for intra-individual reliability over different time points (repeatability) as well as over different conditions (generalization). Furthermore, we correlated oculomotor variability with self-assessed ADHD tendencies, mind wandering, and impulsivity, and found evidence against such correlations. As such, the oculomotor system shows reliable intra-individual reliability, but its use for distinguishing self-assessed individual differences in healthy subjects remains unclear. With our results, we highlight the importance of reliability and statistical power when studying between-subject differences

Variance (un)explained: Experimental conditions and temporal dependencies explain similarly small proportions of reaction time variability in perceptual and cognitive tasks

Perquin M, Heed T, Kayser C. Variance (un)explained: Experimental conditions and temporal dependencies explain similarly small proportions of reaction time variability in perceptual and cognitive tasks. bioRxiv. 2023.Any series of sensorimotor actions shows fluctuations in speed and accuracy from repetition to repetition, even when the sensory input and the motor output requirements remain identical over time. Such fluctuations are particularly prominent in reaction time (RT) series from laboratory neurocognitive tasks. Despite their omnipresent nature, trial-to-trial fluctuations remain poorly understood. Here, we systematically analysed RT series from various neurocognitive tasks, quantifying how much of the total trial-to-trial RT variance can be explained by three sources of variability that are frequently investigated in behavioural and neuroscientific research: 1) the experimental conditions, which are commonly employed to induce systematic patterns in variability, 2) short-term temporal dependencies such as the autocorrelation between subsequent trials, and 3) long-term temporal trends over entire experimental blocks and sessions. Furthermore, we examined to what extent the explained variances by these sources are shared or unique. In total we analysed 1913 unique RT series from 30 different cognitive control and perception-based tasks. On average, the three sources together explained only about 8-17% of the total variance. The experimental conditions explained on average about 2.5-3.5%, but did not share explained variance with temporal dependencies. Thus, the largest part of the trial-to-trial fluctuations in RT remained unexplained by the three variability sources that are typically analysed here. These may be attributable to observable endogenous factors, such as ongoing fluctuations in brain activity and bodily states, though some extent of randomness may be a feature of behaviour rather than just nuisance

Directional biases in whole hand motion perception revealed by mid-air tactile stimulation

Perquin M, Taylor M, Lorusso J, Kolasinski J. Directional biases in whole hand motion perception revealed by mid-air tactile stimulation. Cortex. 2021;142:221-236.Many emerging technologies are attempting to leverage the tactile domain to convey complex spatiotemporal information translated directly from the visual domain, such as shape and motion. Despite the intuitive appeal of touch for communication, we do not know to what extent the hand can substitute for the retina in this way. Here we ask whether the tactile system can be used to perceive complex whole hand motion stimuli, and whether it exhibits the same kind of established perceptual biases as reported in the visual domain. Using ultrasound stimulation, we were able to project complex moving dot percepts onto the palm in mid-air, over 30cm above an emitter device. We generated dot kinetogram stimuli involving motion in three different directional axes ('Horizontal', 'Vertical', and 'Oblique') on the ventral surface of the hand. Using Bayesian statistics, we found clear evidence that participants were able to discriminate tactile motion direction. Furthermore, there was a marked directional bias in motion perception: participants were both better and more confident at discriminating motion in the vertical and horizontal axes of the hand, compared to those stimuli moving obliquely. This pattern directly mirrors the perceptional biases that have been robustly reported in the visual field, termed the 'Oblique Effect'. These data demonstrate the existence of biases in motion perception that transcend sensory modality. Furthermore, we extend the Oblique Effect to a whole hand scale, using motion stimuli presented on the broad and relatively low acuity surface of the palm, away from the densely innervated and much studied fingertips. These findings highlight targeted ultrasound stimulation as a versatile method to convey potentially complex spatial and temporal information without the need for a user to wear or touch a device. Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved