Working memory span assesses the maximum number of items that can be remembered in the face of concurrent processing. Models of working memory differ on several dimensions, yet many rely exclusively on this span procedure for their evidence. Three experiments consider an alternative paradigm that attempts to capture the endurance limits for remembering a fixed number of items during concurrent processing. Eight-year-old children performed two versions of this working memory period measure--operation period and reading period. Period scores show healthy test-retest reliability and external validity for scholastic attainment, comparing well with span scores in these respects. In addition, period is highly correlated with span and shows similar effects of varying the order in which stimuli are presented. We conclude that the durability of representations is an important factor in both span and period.

In two studies, children between 5 and 10 years of age were asked to reach to grasp an object without sight of the hand during the movement. The oldest children and adults were faster when they could see the hand and increased maximum grip aperture when they could not see the hand. The 10-year-olds were less able to integrate grasp and lift than adults when they could see their hands. Children aged 5 and 6 showed no increase in movement time when they could not see the hand and did not adapt maximum grip aperture to lack of sight. These effects remained when children were encouraged to reach for and lift the target as quickly as possible. The results indicate that younger children did not give preference to vision in the control of prehension, while older children used visual feedback to improve efficiency. Dependence on sight of the hand for the control of prehension does not simply decrease with age, but it may be integrated into an anticipatory control strategy where it contributes to the efficiency of control.

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The authors investigated whether 5- to 10-year-old children (N = 75) differ from adults (N = 12) in the developmental course of distance scaling and the adaptations to the inability to see the hand during prehension movements. The children reached under a surface and grasped and lifted an object suspended through it. All children scaled velocity appropriately for movement distance, both with and without sight of the hand. However, 5- to 6-year-old children did not increase grip aperture with increased distance, whereas older children and adults did. The older children and adults spent longer after peak deceleration when they could not see the hand, and maximum grip aperture (MGA) was larger, providing an increased safety margin. Children aged 5 to 6 spent the same amount of time between peak deceleration and grasp, whether or not they could see the hand, and they failed to increase MGA when they could not see the hand. Prehension in the younger children differed from that of older children in two ways: The younger children did not integrate reach and grasp over different distances and did not use visual information about hand position to optimize accuracy.

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