The effects of normal ageing and processing style on explicit and implicit memory

Explicit memory (e.g. recognition) declines with age, but there is disagreement about whether implicit memory (e.g. priming) declines or remains intact with age. Processing style is one primary factor that may explain this discrepancy: there is evidence that ageing does not affect conceptual (meaning-based) and perceptual (feature-based) processing equally, yet processing demands have varied in prior studies. The aim of this thesis is to understand how the type of cognitive processing affects the magnitude of age effects on implicit memory. Five experiments were conducted (four online and one lab-based) to compare the performance of young (18-30 years) and older (+65 years) adults on a range of implicit tests while varying conceptual /perceptual processing at encoding (Experiments 1A, 1B and 2), and both encoding and test (Experiments 3-4). In Experiments 1A and 1B a perceptual implicit memory task (Continuous Identification Task with Recognition; CID-R) was used, while in Experiment 2 a conceptual implicit task (Category Exemplar Generation; CEG) was used, and a recognition task was also included to assess explicit memory. In Experiment 3 both conceptual and perceptual tasks were used in a within-subjects design, and the conceptual implicit task was changed to Category Verification with Recognition (CV-R). Experiment 4 replicated Experiment 3 but was performed in person after COVID-19 restrictions ended.

The results showed an age-related decline in explicit memory in all experiments except Experiment 3, and the key finding in relation to implicit memory is that age differences were affected by the type of processing. In most cases, priming was reduced by age when items were encoded conceptually and the test phase involved perceptual processing. These new findings challenge the widely held view that implicit memory remains stable with age and suggest that age differences in implicit memory are mediated by the type of processing at encoding and test.