Abstract
Recently, a number of authors have advocated the introduction of gross motor tasks into research on sleep-related motor offline learning. Such tasks are often designed to be more complex than traditional key-pressing tasks. However, until now, little effort has been undertaken to scrutinize the role of task complexity in any systematic way. Therefore, the effect of task complexity on the consolidation of gross motor sequence memory was examined by our group in a series of three experiments. Criterion tasks always required participants to produce unrestrained arm movement sequences by successively fitting a small peg into target holes on a pegboard. The sequences always followed a certain spatial pattern in the horizontal plane. The targets were visualized prior to each transport movement on a computer screen. The tasks differed with respect to sequence length and structural complexity. In each experiment, half of the participants initially learned the task in the morning and were retested 12 h later following a wake retention interval. The other half of the subjects underwent practice in the evening and was retested 12 h later following a night of sleep. The dependent variables were the error rate and total sequence execution time (inverse to the sequence execution speed). Performance generally improved during acquisition. The error rate was always low and remained stable during retention. The sequence execution time significantly decreased again following sleep but not after waking when the sequence length was long and structural complexity was high. However, sleep-related offline improvements were absent when the sequence length was short or when subjects performed a highly regular movement pattern. It is assumed that the occurrence of sleep-related offline performance improvements in sequential motor tasks is associated with a sufficient amount of motor task complexity.
Highlights
For two decades, there has been mounting evidence showing that sleep plays a crucial role in learning and memory consolidation (Smith, 1995; Stickgold et al, 2001; Walker, 2005; Genzel et al, 2014)
Sleep has been implicated in the consolidation process of motor skill memory following initial acquisition, with delayed learning being achieved in the absence of further practice
A specific role in memory consolidation has been attributed to sleep-related processes enhancing the respective skill representation during retention in the absence of any further physical practice
Summary
There has been mounting evidence showing that sleep plays a crucial role in learning and memory consolidation (Smith, 1995; Stickgold et al, 2001; Walker, 2005; Genzel et al, 2014). The authors attributed this significant result to the combined demand of memory load (i.e., sequence length) and the extent of movement coordination (i.e., the number of hands and digits required) and concluded that the more ‘‘complex’’ a task is, the larger the degree of sleep-dependent offline learning is Taking these propositions as a starting point to further elucidate the relationship between task complexity and motor memory consolidation, in our present work, we tried to (a) disentangle different complexity components, which are normally intertwined in many motor acts, and we (b) adopted a gross motor skill for a criterion task that incorporated functional requirements typical of numerous activities of daily living. The pegboard consisted of two horizontal wooden bars (41.7 cm long, 16 cm apart), each containing 10 holes that were 22.22 mm in depth, 12.7 mm in diameter, 25.4 mm apart in the left-right and 195 mm apart in the forward-backward dimensions (see Figure 1)
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