Age-related differences in the role of explicit encoding instructions on verbal, visual and spatial Hebb learning

Hebb repetition learning - the improved recall performance for repeated sequences compared to non-repeated sequences - is widely used as a laboratory measure of learning. Recent research has demonstrated that awareness of the repeated sequence enhances learning, although there is reason to believe that older adults may not benefit from such foreknowledge in the same way as younger adults. In three experiments, we systematically investigated the role of foreknowledge in younger and older adults, across verbal, visual and spatial Hebb repetition learning. Each experiment employed a serial recall task (of letters, Chinese characters or dot locations), in which a repeated sequence was presented on every third trial. Half of the participants received foreknowledge - they were informed that a repeated sequence would occur and were signalled the presence prior to its presentation. The remaining participants received no foreknowledge and were not explicitly made aware of the repeated sequence. We compared learning rates between younger and older adults, in both foreknowledge and no foreknowledge conditions. Across all experiments, we found comparable Hebb learning between younger and older adults in the no foreknowledge condition. However, the foreknowledge condition revealed that the additional cue provided substantially greater benefit for learning the repeated sequence in younger adults compared to older adults. We suggest this pattern reflects older adults' difficulties in forming associations, in this case, between the foreknowledge cue and the repeated sequence, which limits their ability to use the cue to enhance learning.