Chapter Five presents the aspects of memory which will be utilised in the present study: verbal free recall, nonverbal free recall, short-term memory, working memory, face recognition, and prospective memory. The methodological issue of cross-sectional versus longitudinal designs is then discussed. Finally, the predictions for the present study are stated.
Verbal Recall
Arguably, the most common verbal recall tasks are those requiring participants to study and then recall a list of words, which may be unrelated to one another or, alternatively, able to be categorised. A robust finding in memory research is that of a significant decline of self-initiated recall from episodic memory with aging (Kausler, 1994;
Wingfield & Kahana, 2002). This deficit can be observed in significant age differences in word list recall, reflecting a common complaint among older adults of increasing difficulty with memory for learned names and recently experienced events (Gilweski & Zelinski, 1986). Unlike recognition memory and cued recall, free recall requires participants to initiate retrieval cues that may aid access to the desired information, making it a likely reason that recall is one of the most age-sensitive of cognitive tasks (Craik & Jennings, 1992). Thus, recall tests offer a useful paradigm for researching verbal memory processes (Brand & Jolles, 1985; Engle, Clarke, & Cathcart, 1980). Zacks, Hasher, and Li (2000) suggest that, in addition to creating retrieval cues, success in recall depends on the effective inhibition of related, but non-required
memories. Failure to inhibit such irrelevant information may result in false memories, a problem which increases with advancing age (Norman & Schacter, 1997).
The number of words normal participants recall immediately after study remains
relatively stable through the early and middle adult years (Lezak, 1995). When five age groups (20s, 30s, 40s, 50s, and 60s) of men were tested with familiar one-syllable words, participants did not differ on lists of up to seven words (Talland, 1965).
lists, and the three oldest groups did less well when lists were extended to 13 words. Delbecq-Derouesné and Beauvois (1989) found participants from 55 - 65 years retrieved significantly fewer words than three younger age groups when tested on recall from 12 lists of 15 words.
In an early study of word recall, Schonfield (1965) found a clear pattern of consistent decline in word recall on a list of 24 words which were presented singly on a screen at intervals of 4 seconds. For 20 - 29, 30 - 39, 40 - 49, 50 - 59, and 60+ year age ranges, participants recalled 13.8, 12.3, 10.0, 9.6, and 7.5 words, respectively (SDs were not reported). A similar word list used as a recognition test showed no decline across the age groups, which Schonfield interpreted as suggesting that age-related impairment of long-term memory may be confined to situations which involve the retrieval of acquired material from storage.
A similar decline in middle age was evident in a 16-year longitudinal study of changes in memory and cognition in older adults (Zelinski & Burnight, 1997). This study
incorporated free recall of a list of 20 nouns with immediate recall. List recall was scored as the proportion of the 20 words remembered. Over the five age groups of 30 - 36, 55 - 59, 60 - 63, 64 - 69, and 70 - 81 years, Zelinski and Burnight found a change (reported as z-scores) over 16 years of -0.113, -0.434, -0.579, -1.224, and -0.476, respectively. Recall significantly declined over time, with the greatest decline observed between 64 and 69 years of age, similar to the ‘watershed’ between 65 and 74 years suggested by Giambra, Arenberg, Zonderman, Kawas, and Costa (1995). The oldest- old were not represented in this study.
A similar problem of the exclusion of the oldest-old arises in the investigation by Hultsch et al. (1992) who measured word and text recall in young-old and old groups over a 3-year period. The old cohort showed a slight deterioration which did not reach a statistically reliable level compared to the young-old cohort which showed stability over the tasks. However, as the groups of adults consisted of adults from 55 - 70 years and 71 - 86 years, the research could not show whether the deterioration in the old group reflected the beginning of an accelerating deterioration with advancing age – arguably the question of greatest interest when investigating memory in very elderly adults.
Salthouse (1996a) did include some oldest-old in a study which included a free recall task presenting 10-word lists at each of three stimulus presentation rates: 0.5, 1, or 2
seconds per word. Immediate word recall declined significantly across the age groups (18 - 39, 40 - 59, and 60 - 93), but as the oldest age group ranged over more than 30 years, the pattern of decrement for the very oldest participants is not evident.
In a recent review of cognitive aging (Salthouse, 2004), data from 997 adults
aggregated across several recent studies (Salthouse, 2001a; 2001b; Salthouse et al., 2003; Salthouse & Ferrer-Caja, 2003; Salthouse, Hambrick, & McGuthry, 1998; Salthouse et al., 2000) were reported for a memory test involving three auditory
presentations of the same list of unrelated words, with the participants required to recall as many words as possible after each presentation. The age-related effects on recall memory were relatively large, with the performance for adults in their early 20s being near the 75th percentile in the population, whereas the average for adults in their early 70s was near the 20th percentile (Salthouse, 2004).
Schaie and Willis (1993), presenting cross-sectional data from the fifth (1984) wave of the Seattle Longitudinal Study (SLS), reported significant differences with increasing age, with the greatest declines between 67 and 74, and between 81 and 88 years of age. When a delay between study and recall of 1 hour was imposed, the rate of decline increased from the age of 67 years. For example, reporting on delayed recall Schaie and Willis found 29-year-olds to demonstrate a total score of 57.68 (SD = 8.16), whereas for 67, 74, 81, and 88-year-olds the scores were 48.61 (9.11), 44.52 (7.61), 41.10 (8.41), and 38.59 (7.92), respectively. Seven years later, in the 1991 wave of testing in the SLS (Kennet, McGuire, Willis, & Schaie, 2000), participants studied a list of 20 concrete nouns for 3.5 minutes and then engaged in immediate and delayed (1 hour) recall tasks. The main effect of age group indicated that mean word recall proportions were significantly lower for each successive age group over middle age. Furthermore, a significant Age x Occasion interaction was obtained, indicating a decline in the oldest cohort (M = 74.42, SD = 2.89) over seven years. It is to be noted that the oldest participant in this report was 86 years of age – the oldest-old were not included.
Of particular interest for the current study, the Leiden 85-Plus Study, a population- based study investigated 599 (87% of the 1912 to 1914 cohort) inhabitants of Leiden in the Netherlands. Van Exel et al. (2001) utilised word lists to test immediate and
delayed (25-minute) recall. This oldest-old sample demonstrated a large difference between immediate and delayed scores with females recalling 21 to 29 words (M = 26),
and males recalling 20 to 27 words (M = 23) (possible number not reported). After a 25- minute delay interval, however, both males and females recalled an average of only 9 words (range 7 to 11). Education (higher education ≥ 6 years) did not make a
difference in verbal recall scores, although the Stroop test and the letter-digit test showed a strong education effect in the same study.
A comprehensive review of post-1975 studies of memory and aging was carried out by Verhaeghen, Marcoen, and Goossens (1993). Regarding word-list recall, the authors reported several types of moderators to account for results in this ability. Firstly, increasing the categorisability of words leads to a decrease in age differences, suggesting the process or strategy of spontaneously organising information is age- sensitive. Klatzky (1980) suggested attempts to organise or categorise words into clusters are, in general, correlated positively with recall. Burke and Light (1981) argue that if older adults do not spontaneously engage in organisational strategies, their recall performance should be poorer than that of young people. Indeed, decreases in
spontaneous organisation have been found in free recall of unrelated words, with poorer performance for older adults (e.g., Hultsch, 1974). However, overall, Burke and Light suggest that whilst older adults engage in less spontaneous organisation during recall, there is little evidence that this is because they do not organise at all. When they are able to use organisational cues supplied by the experimenter at recall, age
differences in performance remain. Secondly, self-pacing during encoding does not yield smaller age differences. Similarly, slower pacing in experimenter-paced
conditions does not reduce age differences. In the reviewed studies, pace ranged from 1- to 20-seconds per word, with a median split of 5 seconds per word. At encoding, no significant differences were found for either learning instructions (intentional versus incidental). Nor was there a reliable difference in effect sizes for semantic versus nonsemantic orienting tasks within incidental learning studies. For intentional learning, findings indicate that the elderly benefit as much as younger adults from manipulations aimed at directing attention to the material to be remembered.
Verhaeghen et al. (1993) suggest that the age difference in list recall performance is situated at the encoding or storage stage of processing rather than at the retrieval
stage. Overall, the authors found that providing both young and older adults with retrieval cues does not reduce age differences. The finding that age differences in recall are attributable to differences in encoding activity has been well established (e.g.,
Craik, 1977; Craik & Rabinowitz, 1984; Hasher & Zacks, 1979; Light & Singh,
1987).The Verhaeghen et al. (1993) review found no age differences as a function of recall delay. In contrast, Hassing et al. (1998), in a study of nonagenarians (M = 92.03, SD = 2.24), found that in a free recall of a 12-word list, participants remembered 4.91 (SD = 1.76) on immediate recall, and 1.73 (SD = 1.88) after a 20-minute delay. In summary, a robust finding in memory research is that self-initiated recall from episodic memory declines significantly with advancing adult age. Because free recall requires individuals to initiate retrieval cues, it is likely that free recall is one of the most age-sensitive of cognitive tasks. Free recall of verbal material seems to be relatively stable until the mid-50s or early 60s, followed by a relatively linear decline from then until approximately 80 years of age. It is not yet clear whether the linear decline continues in the same manner into the late ninth and tenth decades of life, or whether there is acceleration or slowing of the decline. Few studies have included oldest-old participants, or have included the oldest-old as part of an age band which may span as many as 30 years.
Nonverbal Recall
Many studies have demonstrated that pictorial material is more memorable to both younger and older adults than verbal material – the pictorial superiority effect (e.g., Park & Puglisi, 1985; Park, Puglisi, & Smith, 1986; Park, Puglisi, & Sovacool, 1983). The effectiveness of memory depends on how readily and completely information can be retrieved – the process of memory recall (Lezak, 1995). Pavio (1971) suggests that nonverbal material is typically remembered better than words because it is more likely to be stored in both verbal and imaginal codes. In contrast, Feenan and Snodgrass (1990) argue that as verbal items are more polysemous than pictorial items which have only one semantic representation, pictures are less likely to be confused than words which may have many semantic representations. Nonverbal memory is more difficult to assess than verbal memory. Finding stimuli that cannot easily be encoded verbally is problematical (Butters & Delis, 1995).
As visual patterns frequently involve highly distinctive stimuli, memory for them could be expected to be insulated from the influences of aging (Giambra et al., 1995). This does not, however, appear to be so. The visual reproduction (VR) sub-test of the
Wechsler Memory Scale - Revised (Wechsler, 1987) requires participants to reproduce geometric line drawings immediately after studying the stimuli (one at a time for 10 seconds) to assess short-term storage for geometric designs. In a delay condition, the task is attempted following 30 minutes of unrelated testing to assess longer-term storage. It has been reported that the VR sub-test has the steepest age gradient of all the Wechsler memory tests (Margolis & Scialfa, 1984; McCarty et al., 1982). Ivnik, Malec, and Smith (1992) found average performance in the 30 - 35 point range at ages 56 - 66 years dropping to a 20 - 28 point range for those aged 77 - 87 years.
Futhermore, Lezak (1995) reports that 80 - 92 year old adults exhibit VR recall 2.6 SDs below that of 20 - 29 year olds. A sharp decline was also found by Haaland, Linn, Hunt, and Goodwin (1983) in a study where participants over 80 years of age demonstrated VR recall 1.3 standard deviations below the mean of 65 - 69 year olds. Other cross- sectional studies of WMS subtests (e.g., Bak & Greene, 1980; Fastenau et al., 1996; McCarty, Logue, Power, Ziesat, & Rosentiel, 1980) indicate that such decreases in VR memory performance may begin around, or even before, the age of 50 years.
The cross-sectional findings hold true for longitudinal studies. For example, McCarty et al. (1982), using two cohorts from the Duke Longitudinal Study (those aged 70 or less and those aged 71 or more at Wave 2 testing) found significant longitudinal declines on the VR test after 4, 10, and 16 years for individuals initially 60 - 80 years old. McCarty et al. (1982) comment that whilst the longitudinal curves “no doubt provided an overestimate of memory scores and an underestimate of expected declines” (p. 174), the findings support previous reports of the relative vulnerability of nonverbal compared with verbal memory test performance.
The Benton Visual Retention Test (BVRT) (Benton, 1974) also requires immediate reproduction of geometric designs after a 10-second study period. In an extensive investigation of BVRT performance Arenberg (1982), in the Baltimore Longitudinal Study of Aging (BLSA) (Shock et al., 1984), reported that the mean number of recall errors of adults 80 - 89 years of age was 3.7 SDs above the mean number of errors for 20 - 29 year olds. The performance measure was the total number of errors in
reproducing the 18 original designs. In addition, longitudinal change was consistent
with the cross-sectional findings: for adults 20 - 39 years of age at baseline there was little or no change, whereas for adults initially in their 40s, 50s, 60s, and 70s there were increasingly larger changes (Giambra et al., 1995). In the BLSA study, Giambra et al.
reported that immediate visual memory began to show decrement by late middle age, and the decrement accelerated thereafter when measured cross-sectionally.
Longitudinally, the intraindividual change was not significant until after 64 years. It was noted that the 65 - 70 year age period is particularly important because from this period the older a participant is at later testing, the greater the magnitude of the decrement, providing evidence of a positively accelerating age decline. This concurs with Schaie (1994) who asserted that, consistent with the results of 30 years of longitudinal study of primary mental abilities in the Seattle Longitudinal Study, “reliable average decrement is indeed found for all abilities by age 67” (p. 308).
The Memory-For-Designs Test (MFD) (Graham & Kendall, 1946, 1960) is, according to Dustman and Beck (1980), one of the most widely used of any single psychological test for the diagnosis of perceptual, motor, and memory deficits related to brain dysfunction. In a study of 80 adult males divided into 21 - 30, 41 - 50, 61 - 70, and 71 - 90 years groups, the 15 geometric designs which comprise the MFD were presented, one at a time, for 0.5 seconds, differing from other studies which utilise a 5-second exposure. Participants were required to draw as much as they remembered immediately after each exposure. Results showed that although there was no difference between the two youngest groups or between the two oldest groups, collapsing the two youngest and two oldest groups resulted in a significant difference between younger and older adults. Kendall (1962) added thirty 61 - 70 year-olds, and six 71 - 88 year-olds to the original sample reported in the MFD Manual (Graham & Kendall, 1960). While only a gradual decline in ability with age occurred in earlier years, after the age of 60 there was a marked and disproportionate decline in performance. Riege, Kelly, and Klane (1981) found age reliably predicted performance on the MFD for 120 normal, healthy adults from 20 to 84 years of age, divided equally into decade age bands. Riege et al. found that adults over 60 years of age demonstrated omission and distortion errors at three to four times the rate of those less than 40 years of age.
A possible source of an age-related decline in immediate visual memory is slower reproduction time. It has been found that the memory span for verbal items appears to be limited to material that can be spoken in 2 seconds (Schweickert, 1993). It may be that items in immediate verbal memory decay irretrievably in about two seconds in the absence of rehearsal. In other words, the longer it takes to produce items from
immediate memory, the fewer items will be recalled. Giambra et al. (1995) note that the BVRT requires each geometric design be reproduced on paper. It has been
established that older adults are slower figure tracers and hand-writers than younger people (Dixon, Kurzman, & Friesen, 1993; Welford, 1977), so it may well be that slower reproduction has an effect on the number and accuracy of geometric figures recalled.
Short-Term Memory
In the present study, short-term memory will be measured by the digit span subtest from the WAIS-III (Wechsler, 1997a). The digit span test depends both on auditory attention and short-term storage capacity (Shum, McFarland, & Bain, 1990). Many studies, such as that of Ryan, Lopez, and Paolo (1996), have utilised digit span as a measure of attention-concentration, working memory, and/or short-term memory. In an examination of digit span performance of persons 75 to 96 years of age, Ryan et al. report that individuals ≥75 years should repeat at least 4 or 5 digits forward. Years of education were found to affect scores, and indicated normal expectations for elderly participants are 4 digits forward span with ≤11 years of education, and 5 digits forward span with ≥12 years of education. Similarly, when Orsini et al. (1986) investigated the effects of age, education, and sex on the digit span task in adults from 20 to 99 years of age, the oldest-old (80 - 99 years) (n = 125) demonstrated increasing scores with increasing years of education. Those with 0 - 5, 6 - 12, or 12 years of education, attained scores of 4.34 (SD = .72), 5.12 (SD = 1.07), and 5.68 (SD = 1.0) digits remembered, respectively.
In a study of healthy, very old adults, Wahlin et al. (1993) administered the digit span test to 228 adults divided into four age groups: 75 - 79, 80 - 84, 85 - 89, and 90 - 96 years. Digits remembered for each of the four groups averaged 5.53 (SD = 1.14), 5.63 (SD = 1.12), 5.35 (SD = .88), and 5.88 (SD = .91), respectively. Similarly, in the Ryan et al. (1996) study, young-old participants (75 - 79 years) demonstrated an average score of 5.80 digits remembered (SD = 5.80), and the old-old (≥ 80 years) achieved 5.79 (SD = 1.27) digits remembered. In a study of 17 young-old (65 - 74 years) and 34 oldest-old (84 - 100 years), Howieson et al. (1993), the young-old participants obtained an average score of 6.1 digits remembered (range = 4 - 9), whilst the oldest-old
participants remembered 5.7 (range = 4 - 8).
Whilst Ryan et al. (1996) found that age and gender did not impact on digit span performance, both education and past occupation was meaningfully associated with the task. It is suggested that information on these variables is important with reporting
test results of elderly people, as many senior citizens have achieved occupational success without the benefit of long years of education.
Beside the studies cited, a large body of research has found a lack of significant change in digit span scores with advancing age (e.g., Aronson & Vroonland, 1993; Craik, 1986; Dobbs & Rule, 1989; Hickman et al., 2000; Perlmutter & Nyquist, 1990; Salthouse & Babcock, 1991; Small, Fratiglioni, von Strauss, & Bäckman, 2003).
Working Memory
A decline of working memory is clearly implicated in age-related declines in memory as a whole. In recent years, considerable attention has been focused on determining the