Healthy ageing effects on implicit auditory memory: from encoding to 6-month retention

Abstract

Any listening task, from sound recognition to sound-based communication, rests on auditory sensory memory which is known to decline in healthy ageing. However, whether this decline maps on to multiple components and stages of auditory memory remains poorly characterised. We tested ageing effects on implicit auditory memory for rapid tone-patterns in an online unsupervised longitudinal study (day 1, day 8 and 6-month sessions) including younger (aged 20-30) and older adults (aged 60-70). The test required participants to quickly respond to rapid regularly repeating patterns (REG) emerging from random sequences. Patterns were novel in most trials (REGn), but unbeknownst to the participants, a few distinct patterns reoccurred identically throughout the sessions (REGr). After correcting for processing speed, reaction times (RTs) to REGn were taken as a measure of the amount of information held in echoic and short-term memory before detecting the pattern; an RT advantage (RTA) to REGr vs REGn was expected to grow with exposure reflecting implicit long-term memory formation and retention. The results showed that older participants were slower than younger adults in detecting REGn and exhibited a smaller RTA to REGr. Computational simulations using a model of auditory sequence memory indicated that these effects reflect age-related limitations both in early and long-term memory stages. In contrast to ageing-related accelerated forgetting of verbal material, the older adults in the present experiment maintained stable memory traces (RTA) for REGr patterns up to 6 months after the first exposure. The results demonstrate that ageing is associated with reduced short-term memory and long-term memory formation for tone-patterns, but not with forgetting, even over surprisingly long timescales.