Spatial and symbolic implicit sequence learning in young and older adults.

In three experiments, we examined the effects of age and spatial processing on implicit sequence learning. In experiment 1, 48 older adults (OA) and 48 young adults (YA) performed the alternating serial reaction time task (ASRT) under one of four conditions in which spatial processing demands were either present or absent from stimulus presentation (spatial vs. symbolic cueing) and/or response execution (spatial manual vs. vocal responses). Surprisingly, OA exhibited more learning than YA in the two vocal response conditions. In two follow-up experiments, we increased the response selection demands of the sequence learning task by asking new groups of YA and OA participants to make word categorization responses with 1:1 stimulus-response mapping (experiment 2) and 2:1 mapping (experiment 3) rather than letter reading (vocal response condition of experiment 1). The results showed that YA had increased learning under the more challenging response selection conditions (experiments 2 and 3) while OA did not. We propose that (1) manipulating the spatial aspects of implicit sequence learning does not necessarily impact the amount of learning for OA, (2) implicit sequence learning depends on both the structure of response execution and relative task difficulty, and (3) these factors affect implicit sequence learning for both YA and OA.