Age-related declines in context maintenance and semantic short-term memory

Abstract

This study reports age-related declines in context maintenance (Braver et al., 2001) and semantic short-term memory (STM) and evidence for a relation between the two. A group of younger and older adults completed a context maintenance task (AX-CPT), a semantically oriented STM task (conceptual span), a phonologically oriented STM task (digit span), and a meaning integration task (semantic anomaly judgement). In the AX-CPT task, a target response is required to the probe letter “X” but only when it is preceded by the letter “A” (the context). Either three (short interference) or six distractor letters (long interference) were presented between the cue and the probe. Results indicated an age-related deficit in context maintenance. Age-related declines were also observed for conceptual span and semantic anomaly judgement but not for digit span. Context maintenance was correlated with conceptual span and semantic anomaly judgement but not with digit span. These correlations were largely mediated by age differences, which also explained variance that was unique to (and not shared among) context maintenance, conceptual span, and semantic anomaly judgement.

Notes

EJD was supported by the Economic and Social Research Council (T0262701312).

This is suggested by the absence of word length effects in semantic category cued recall (Haarmann et al., 2003).

The relative percentage change in error rate was calculated as (long − short)/((long + short)/2), where short and long designate error rates in the short and long delay conditions, respectively.

The d′ context provides a focused and unbiased measure of context sensitivity, which is based on AX hits and BX false alarms and corrects for perfect hit rates (1.0) and false alarms (0.0) with a correction factor (i.e., hits = 2^−(1/N) and false alarms = 1 − 2^−(1/N), where N equals the number of target and nontarget trials, respectively; Braver et al., 2001).

The test for the significance of the difference between independent correlations (i.e., comparing correlations obtained from two samples) was computed with the indepcor.exe program, accompanying an article by Crawford, Mychalkiw, Johnson, and Moore (1996). This program implements Howell's (1997) procedures for such a test, following which both correlations are first converted to Fisher's z9, and the difference between them is divided by the standard error of the difference to yield a normal curve deviate (z).

Most of the subjects reported using a covert rehearsal strategy in the digit span test and only a very small minority of subjects (< 5%) reported using a visual strategy.