The practice of different tasks in a random order induces better retention than practising them in a blocked order, a phenomenon known as the contextual interference (CI) effect . This phenomenon, though counterintuitive in the first look, has been reported to be useful in a number of studies that involved teaching a new set of skills to people of old age and people with some neurodegenerative disorders. Though the higher levels of contextual interference lead to poorer performance during the practice sessions, the eventual retention and transfer performance are always better than in the training that involves a blocked session.
In a study where the researchers compared the effects of such random practising versus a categorized practice among both young and older adults, they found that older adults retained sequences better when trained in a random condition than in a blocked condition, although the random condition incurs greater task-switching costs in older adults during practice . In another similar research involving aged subjects with Parkinson's disease, the findings showed that employing a cognitively demanding practice environment improved motor skill learning .
The neural basis for these clinically promising observations has been analysed. During the random mode of the practice session, the frequent switching of tasks requires more attention to be deployed to the external features (such as visual) of the task at hand for detailed processing of the stimulus, as well as the movement-generated visual feedback. The learner integrates this visual information highly attentively with his/her somatosensory processing, coupling this with an appropriate motor program for each subtask. A random practice context is hence expected to provoke higher involvement of externally driven movements, bypassing the network encompassing the impaired (or aged) brain region. Another finding worth mentioning from the same study is that with practice, the activity in the Default Mode Network (DMN) regions in the brain decreases significantly in the random group as compared to the blocked group. As it is known that DMN regions are particularly vulnerable to ageing effects, decreased activity in the region might help explain why the training-induced ability to suppress this core region is beneficial for skill retrieval.
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