The grasping side of post-error slowing

“Errare humanum est, sed in errore perseverare diabolicum” is probably one of the most famous quote by Seneca. The central message of this quote is that humans are error-prone by nature, and that immediate steps need to be taken to ensure that the same errors are avoided in the future. Indeed, reacting efficiently to our errors is a fundamental ability to interact with the outside world. For this reason, error reactivity is the focus of a growing body of research in cognitive neuroscience. In this respect, the study of the brain mechanisms underlying error processing has greatly advanced in the last few years. The discovery of specific event-related potentials, such as the error-related negativity (ERN), and of neural networks associated to error commission have contributed to our understanding of the processes taking place after error commission. If, on the one hand, the findings obtained in neuroimaging studies on error processing seem to be robust and consistent, on the other hand how such neural activity translates into a differential movement pattern has yet to be fully understood. So far what is known is that people tend to respond more slowly after making an error, an effect termed post-error slowing (PES; Rabbitt, 1966). PES has been traditionally hypothesized to reflect a strategic increase in response caution, aimed at preventing the occurrence of new errors. This interpretation of PES, however, has been challenged on multiple fronts. Firstly, recent investigations have suggested that errors may produce a decrement in performance accuracy and that PES might occur because error processing has a detrimental effect on subsequent information processing. Secondly, this research has been criticized because of the limited ecological validity of speeded RT tasks. The present work aims to extend previous literature by investigating for the first time the post-error effect in the context of realistic goal-directed actions. For this purpose I examined the effect of errors on both the preparation and the execution of reach-to-grasp movements. The introductory section of this thesis will focus on some of the most important empirical data acquired during the last years of research in experimental psychology and cognitive neuroscience regarding error-reactivity. In Chapter 1, after a detailed introduction to behavioral adjustments following errors (sections 1.1 and 1.2), a set of neuroimaging studies investigating the neural mechanisms underlying error-reactivity will be exposed (section 1.3). Then, I shall review the most important theoretical accounts of error-reactivity (section 1.5). In Chapter 2, I shall introduce the experimental window used to explore PES in the context of goal directed actions, namely the reach to grasp movement. The second part of the present thesis concerns the experimental work I undertook. Chapter 3 provides a description of the general methodology common to the entire experimental work. In the first experiment (Chapter 4) a novel task to study error-reactivity will be described. Participants were asked to reach out and grasp a steel ball positioned upon a wooden support, without knock it over. In addition to RTs, a kinematical analysis was performed in order to asses if error-reactivity extends at the level of movement execution. In a subsequent experiment (Chapter 5), a similar paradigm was adopted, but the task was chiefly concerned with a reaching movement. This experiment was ran with the specific aim to investigate whether error-reactivity has a different impact on the grasping and the reaching components or whether it produces an unspecific slowdown of the whole movement. In Chapter 6, I shall describe an experiment in which kinematical analysis was coupled with transcranial magnetic stimulation (TMS) in order to measure corticospinal excitability after an error and whether behavioral and neural measures do correlate in such circumstances. In a further experiment (Chapter 7) the effect of error observation on the reach-to-grasp movement was examined via kinematical analysis. A general discussion (Chapter 8), contextualizing the results obtained by the studies presented in the present thesis will follow. Overall, these studies will help to understand how error-reactivity influence our behavior and the way errors are interpreted and evaluated by the human mind