Age differences in verbal short-term memory and the process of redintegration

There are long-standing but ongoing debates in the literature about the composition of memory and the causes of short-term forgetting. Some researchers believe human memory is a dual system that comprises separate stores for verbal short-term memory (STM) and long-term memory (LTM), best exemplified by Baddeley and Hitch’s (1974) Working Memory Model. Dual memory researchers also believe that information stored in verbal STM decays over time if it is not refreshed through engaging in some form of covert rehearsal. However, other researchers believe verbal STM and LTM are intrinsically related, with short-term forgetting resulting from some level of interference that disrupts encoding the newly acquired information into verbal STM. The literature has indicated that the Working Memory Model could explain some but not all of the effects in verbal STM. In addition, while information degrades from verbal STM, it is not entirely lost and individuals use their LTM to assist with short-term recall. Moreover, researchers have found that decay does not explain all short-term forgetting and that interference does cause short-term forgetting. This thesis examined the unitary view of human memory by investigating the redintegration explanation for short-term recall, whereby individuals access long-term knowledge to aid in the reconstruction of degraded phonological memory traces for later recall. Redintegration emphasises that verbal STM and LTM work in unison to help individuals retrieve information for later recall. The three studies comprising this thesis examined the predictions of redintegration in relation to short-term recall and age differences by varying the difficulty level of the memory task. All studies operationalised task difficulty by manipulating the combination of recall intervals (immediate vs. delayed), study conditions (silence vs. irrelevant speech), and presentation rates (one second vs. two seconds). Twenty young and 20 older adults were instructed to remember short lists of words across eight different memory conditions. In Study one, redintegration was measured using the word length effect (Baddeley, Thompson, & Buchanan, 1975) and findings showed that as task difficulty increased, recall was higher for short words because they had fewer segments to reassemble from LTM compared with long words. In Study two, redintegration was measured using associate word pairs and findings showed that as task difficulty increased, recall was higher for words in the associate pairs because participants used the semantic relationships in LTM as additional retrieval cues to reconstruct the short-term phonological traces that rapidly dissipated during encoding. In Study three, redintegration was measured using the false memory effect (Roediger III & McDermott, 1995) and findings showed that as task difficulty increased, recall was higher for words related to a non-presented critical lure words because participants used the relatedness among the words along with the critical lure as additional retrieval cues to search LTM and reconstruct the degraded short-term phonological traces. For all studies, there were no significant age differences in redintegration, suggesting that young and older adults engage in the same process by using long-term information to rebuild the rapidly dissipating phonological memory traces for short-term recall and use additional retrieval cues to enhance the redintegration process. Collectively, these findings provide support for the redintegration process that emphasises the intrinsic relationship between verbal STM and LTM. When short- term recall became difficult, young and older adults effectively cued the search for long-term information to facilitate the redintegration process and aid short-term recall. This thesis also substantiated the interference view on short-term forgetting, where increasing task difficulty increased the reliance on redintegration to improve verbal STM performance.