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Although there is evidence that the effect of including a concurrent processing demand on the storage of information in working memory is disproportionately larger for older than younger adults, not all studies show this age-related impairment, and the critical factors responsible for any such impairment remain elusive. Here we assess whether domain overlap between storage and processing activities, and access to semantic representations, are important determinants of performance in a sample of younger and older adults (N = 119). We developed four versions of a processing task by manipulating the type of stimuli involved (either verbal or non-verbal) and the decision that participants had to make about the stimuli presented on the screen. Participants either had to perform a spatial judgement, in deciding whether the verbal or non-verbal item was presented above or below the centre of the screen, or a semantic judgement, in deciding whether the stimulus refers to something living or not living. The memory task was serial-ordered recall of visually presented letters. The study revealed a large increase in age-related memory differences when concurrent processing was required. These differences were smaller when storage and processing activities both used verbal materials. Dual-task effects on processing were also disproportionate for older adults. Age differences in processing performance appeared larger for tasks requiring spatial decisions rather than semantic decisions. We discuss these findings in relation to three competing frameworks of working memory and the extant literature on cognitive ageing. [ABSTRACT FROM AUTHOR]

Counting is an important activity because it gives rise to a whole range of arithmetic activities. Counting objects requires subjects to point at each object and to say the corresponding number-word. Furthermore, to determine the correct cardinal of a set, the two activities of pointing and saying must be synchronized. This perfect correspondence between the two activities is achieved by a coordination process. Using Camos et al.'s (2001) paradigm, the present study tested the hypothesis that this coordination process will induce its own cognitive cost and that this cost would decrease with age. Eight-year-old children and adults were asked to say the numberline from 1 to 23, from 61 to 83, and from 111 to 133. They also pointed at objects in arrays that did or did not include distracters. Finally, they counted objects in arrays with or without distracters using the numberline starting at 1, then at 61, and then at l 11. In children, as in adults, the simultaneous increase in the attentional demand of the pointing (due to the distracters) and the saying (for the numberline starting at 61 or 111) affected counting performance. However, it never made coordination more difficult. The coordination process in counting thus has a negligible cost. Moreover, an unexpected facilitation effect was observed. Indeed, when the attentional demand of saying was high, the simultaneous production of pointing increased the performance in saying the numberline. In other words, a verbal activity was facilitated by a concurrent motor activity. The negligible cost of coordination and the facilitation effect were both explained by an early compilation of counting as defined in ACT-R (Anderson, 1983, 1993). [ABSTRACT FROM AUTHOR]