In Papiamento-Dutch bilingual speech, the nominal construction is a potential ‘conflict site’ if there is an adjective from one language and a noun from the other. Adjective position is pre-nominal in Dutch (cf. rode wijn ‘red wine’) but post-nominal in Papiamento (cf. biña kòrá ‘wine red’). We test predictions concerning the mechanisms underpinning word order in noun-adjective switches derived from three accounts: (i) the adjective determines word order (Cantone & MacSwan, 2009), (ii) the matrix language determines word order (Myers-Scotton, 1993, 2002), and (iii) either order is possible (Di Sciullo, 2014). An analysis of spontaneous Papiamento-Dutch code-switching production (Parafita Couto & Gullberg, 2017) could not distinguish between these predictions. We used event-related brain potentials (ERPs) to measure online comprehension of code-switched utterances. We discuss how our results inform the three theoretical accounts and we relate them to syntactic coactivation and the production-comprehension link.

Any repeatedly performed action is characterized by endogenous variability, affecting both speed and accuracy—for a large part presumably caused by fluctuations in underlying brain and body states. The current research questions concerned (a) whether such states are accessible to us and (b) whether we can act upon this information to reduce variability. For example, when playing a game of darts, there is an implicit assumption that people can wait to throw until they are in the right perceptual-attentional state. If this is true, taking away the ability to self-pace the game should worsen performance. We first tested precisely this assumption asking participants to play darts in a self-paced and a fixed-paced condition. There was no benefit of self-pacing, showing that participants were unable to use such control to improve their performance and reduce their variability. Next, we replicated these findings in 2 computer-based tasks, in which participants performed a rapid action-selection and a visual detection task in 1 self-paced and 3 forced-paced conditions. Over 4 different empirical tests, we show that the self-paced condition did not lead to improved performance or reduced variability, nor to reduced temporal dependencies in the reaction time (RT) series. Overall, it seems that, if people have any access to their fluctuating performance-relevant inner states, this access is limited and not relevant for upcoming performance.

Human performance shows substantial endogenous variability over time, and this variability is a robust marker of individual differences. Of growing interest to psychologists is the realisation that variability is not fully random, but often exhibits temporal dependencies. However, their measurement and interpretation come with several controversies. Furthermore, their potential benefit for studying individual differences in healthy and clinical populations remains unclear. Here, we gather new and archival datasets featuring 11 sensorimotor and cognitive tasks across 526 participants, to examine individual differences in temporal structures. We first investigate intra-individual repeatability of the most common measures of temporal structures — to test their potential for capturing stable individual differences. 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. Thus, some measures of serial dependencies may be stable individual traits, but their usefulness in capturing individual differences in other constructs typically associated with variability in performance seems limited. We conclude with comprehensive recommendations for researchers.

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.