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PhD Defence Jonathan Barnhoorn

motor sequence learning in older adults 

Jonathan Barnhoorn is a PhD student in the research group Cognitive Psychology and Ergonomic. His supervisor is prof.dr.ing. W.B. Verwey from the faculty of Behavioural, Management and Social Sciences (BMS).  

 The aging society calls for increased understanding of age-related cognitive and neural changes in motor learning. Why do healthy older adults have difficulties learning new motor skills, and how can we support them in their learning? The aim of this dissertation was to zoom in on the age-related differences in the cognitive processes underlying sequential motor skill, and explore avenues for enhancing motor learning in older adults.

The experiments were all centered on motor sequence learning. Motor sequences are the building blocks of complex motor actions, this paradigm is often used to study the cognitive underpinnings of learning motor sequences. Three types of motor tasks were used. In the sequence-tapping task, the goal is to perform a sequence (e.g., “3 - 5 - 2 - 4 - 2”) that is continuously displayed on the screen as often as possible. The flexion-extension (FE) task requires participants to move a cursor on the screen as quickly and smoothly as possible to succeeding targets using elbow flexion-extension movements. Finally, in the discrete sequence production (DSP) task, participants perform a sequence by responding to series of succeeding cues as quick as possible.

Chapter 2 examined whether older adults are able to develop and use the so-called effector-independent, visuospatial sequence representation that young adults have been shown to develop during the early stages of learning a motor sequence. This type of representation is thought to facilitate the flexible application of learned motor skills in new contexts. Therefore, it is relevant to know whether this mechanism is affected by advanced age. In the experiment, the older participants indeed displayed the ability to use sequence knowledge that was developed using FE movements in a test phase where the same sequence was to be performed using key-presses. However, when the practice phase consisted of key-presses and the ensuing test phase of FE movements, the older adults showed no benefit from practice while young participants did show slight transfer. We concluded that, although high age seems to affect the amount of transfer, the ability to apply sequence knowledge in a flexible manner seems to be largely preserved in older adults.

Chapter 3 scrutinized older adults’ ability to develop motor chunking behavior. Being able to develop and use motor chunks is important because it is associated with reduced attentional demands and thus frees capacity to focus on things besides controlling movement, like watching the road while shifting gears in a car. Chapter 3 complements Chapter 2 because this type of sequence representation is developed after the visuospatial representation. The results confirmed that the older participants are indeed able to develop chunking behavior, but just need more practice than their younger counterparts.

Chapter 4 tested the hypothesis that the careful, error-averse way in which older adults perform motor tasks stimulates their reliance on external guidance and prevents them from developing more efficient, chunking based representations. The participant sample was divided into a speed group that received the instruction to perform the DSP task as fast as possible, and an accuracy group instructed to make as few errors as possible. The intervention sorted the expected effect with fast responses and relatively many errors in the speed group, and the opposite pattern in the accuracy group. However, our measure of chunking showed no group difference at any moment of practice. Furthermore, in the test phase, the speed group was not more successful in performing the sequences by heart than the accuracy group. Based on these results we concluded that speedy, error-rich performance during practice does not have a beneficial effect on the development of motor chunks in older adults.

Chapter 5 explored the potential of transcranial direct current stimulation (tDCS) as a technique to enhance motor learning in older adults. While previous research suggested that tDCS indeed offers beneficial effects, the literature also calls for replications and incremental steps to add much-needed robustness to the existing results. We therefore tried to reproduce the results of a particular sequence learning study. In line with the results of that study, the replication condition in our study showed that tDCS indeed accelerates skill development in a simple but elegant sequence-tapping task. Importantly, we also showed for the first time that tDCS affected the development of sequence-specific skill, and not the general ability to perform such sequencing tasks.

In general, the findings suggest that the cognitive processes underlying skill acquisition are largely the same for the age groups investigated. Older adults proved to be able to develop the visuospatial representation necessary for the flexible application of motor skill, and also showed the ability to develop motor chunks, albeit after extensive practice. Our attempt to speed up the development of motor chunks by motivating participants to practice sequences as fast as possible was not successful. On the contrary, non-invasive brain stimulation did improve motor learning, confirming the promise this technique brings for enhancing skill development in older adults.