Inverted versus straight handwriting posture: a family study.
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Practice on a novel sequence of movements can lead to two expressions of procedural memory consolidation: delayed performance gains evolving hours after training, and a decrease in the susceptibility of the training-related gains to interference by subsequent experience. It has been assumed that behavioral interference occurs only if a critical overlap between the representations of the two tasks exists, and that such overlap is more likely when the two tasks are novel, competing for general resources for their execution. We investigated whether the delayed gains in the simple finger-opposition sequence (FOS) learning task are more prone to interference by well practiced than by less practiced complex hand movements. Participants were trained on the FOS task in a baseline (no interference) and an interference training condition. In the Interference condition, after FOS practice, participants wrote Hebrew common words in Hebrew (native script) or a Latin script (Heblatin). Native script writing but not the less practiced Heblatin, interfered with FOS learning, with significantly reduced delayed gains. Our results show that interference can occur even when two tasks share little or no kinematic or dynamic features and indicate that the representation of complex but well-practiced movement sequences may overlap with the representation of simpler ones. This result is in line with the notion that well-practiced complex movement sequences come to be represented as simpler ones in long-term motor memory.
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Claims that time has a special role in the control of writing and the specific claim that writing time is absolutely invariant across changes in writing size are evaluated in two experiments. The first examined writing time for 24 undergraduate subjects who produced the string eyleyl with the dominant hand or arm in blocked repetitions having different vertical size targets. These variations produced small but systematic changes in writing time. The second experiment explored whether the small range of writing-time variation observed in experiment 1 was due to structural or strategic limitations. This experiment showed, for four undergraduate subjects, that writing time can be varied precisely across a wide range (0.6 to 1.66 of 'normal') while maintaining shape and vertical size constant. Taken together, these experiments suggest that, although relative stroke timing is approximately maintained, absolute timing is not critical to writing. The limited range of writing times typically observed should, rather, be ascribed to a strategic gradient that, along with other influences, broadly defines preferred writing times. This paper also describes a new application of Generalized Procrustes Analysis of shape, and this procedure is applied to the trajectories generated in both experiments. Although several small failures are noted, these analyses generally confirmed previous claims that shape is invariant across changes in writing time, size, and writing with the hand versus the arm. This result is a necessary buttress to the conclusions just described. Shape variability was also assessed in these analyses. This variability soared as writing time was reduced from normal, but showed only a small, insignificant increase as writing time was increased from normal. There were also small, predictable changes in spatial variability across changes in size and effector.
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We report the unusual case of AZO, who professionally used handwritten shorthand writing, and became dysgraphic after a stroke. AZO suffered from a complex cognitive impairment, and part of her spelling errors resulted from damage to auditory input processing, to phonology-orthography conversion procedures and to the ortographic output lexicon. However, analysis of her writing performance showed that the same variables affected response accuracy in alphabetic and shorthand writing; and, that the same error types, including transpositions, were observed in all tasks in the two types of writing. These observations are consistent with damage to the graphemic buffer. They suggest that, in multiple-code writing systems (e.g., stenography, Japanese, or in the case of multilingual speakers of languages that use different spelling codes), the graphemic buffer is shared by all codes.
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