The effects of implicit motor imagery in aging using the hand laterality judgment task
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Cognitive states like motor imagery (MI; simulating actions without overtly executing them) share a close correspondence with action execution, and hence, activate the motor system in a similar way. However, as people age, reduction in specific cognitive abilities like motor action simulation and action planning/prediction are commonly experienced. Previous research has shown that with age, the ability to implicitly simulate upper-limb movements declines. At present, most research on implicit motor imagery has focused largely on young healthy adults. Using the hand laterality judgement task, the present study examined sex differences, which have not previously been reported for older adults. In addition, this study examined the influence of aging on implicit simulation processes for both simple and difficult upper-limb movements. Forty right-handed young adults (20 male, 20 female; M = 22, SD = 5.05) and forty right-handed old adults (16 male, 24 female; M = 76.5, SD = 7.33) with normal or corrected-to-normal were recruited. Response times and accuracy were recorded as participants indicated the laterality of right-and-left hand images from two different views and four different orientations. We expected older adults to be less accurate and have slower reaction times than younger adults in their left-right hand judgments when presented with hand stimuli in both simple and difficult orientations from different viewpoints. Several main findings emerged: (1) Older adults were slower to respond to both canonical (0° and 90°M) and difficult (90°L and 180°) orientations from different viewpoints than younger adults, suggesting an age-related decline in implicit simulation processes; (2) For older adults, a medial-over-lateral advantage was found for both back and palm views, whereas for younger adults, this effect was only evident for palm views; (3) Older adults had higher proportion of errors at both viewpoints compared to younger adults, but performed equally well on both canonical and difficult orientations suggesting that although older adults take longer to respond to simple and difficult orientations they are just as accurate as younger adults; (4) Males of all ages made more errors for palms than back views, but for females, this difference was only apparent in older females, suggesting a decline in implicit motor imagery among certain sexes and age groups. This study reports new findings about sex differences in individuals' use of strategies (visual vs. motor imagery) to solve the hand laterality judgement task. Furthermore, these findings complement the literature showing age-related declines in motor simulation processes.