The effects of age and awareness on prism adaptation
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Neglect patients show a lack of awareness of both the prismatic displacement induced during prism adaptation and of the negative aftereffect they display afterwards. They also show significantly larger aftereffects than healthy controls. This study aims to investigate possible factors in this differential level of adaptation by replicating Michel et al.’s (2007) study of the effects of awareness on the magnitude of the prismatic aftereffect, and extending it to examine the effects of age on prism adaptation. 58 participants were recruited (32 young adults, 26 older adults) and assigned to either a single-step or multiple-step condition. In the single-step condition participants were adapted to 10° prisms in one step, in the multiple-step condition they were adapted to 10° prisms in 2° steps. Participants completed a postexperimental awareness questionnaire. A two-way between subjects ANOVA demonstrated that single-step participants were more aware than multiple-step participants, and young adults were more aware than older adults, yet mixed design ANOVAs revealed that single-step participants showed a significantly larger aftereffect than multiple-step participants, thus failing to replicate Michel et al.’s results, and that young adults displayed a significantly larger aftereffect than older adults. Older adults, particularly in the single-step condition showed far less pointing error in the first block of exposure trials than would be expected given a large prismatic displacement has just been introduced. Implications for the relationship between awareness and strategic recalibration and the relationship between awareness and quantity of prism exposure are discussed. The results of this study are considered in relation to neglect. It is suggested that the larger after effect found in neglect patients cannot simply be attributed to a lack of awareness or increased age and that something specific to the brain damage must be responsible for the increased levels of adaptation shown by neglect patients.