Episodic memory

The Rey Auditory Verbal Learning Test (RAVLT)

The RAVLT assessed verbal episodic memory and was classified as a test of verbal learning and recall. Table 7.11 shows the raw RAVLT scores for the present study using only the control group (n=32) compared to healthy subjects from Australian published norms (n=62; Geffen et al., 1990). Subjects in the published norms were physically healthy and free of neurological symptoms by self-report. They had an average education of 11.2 (2.2) years, with a range of 7-22 years. Their average estimated IQ (derived from error scores on the NART) was 116 (7.3), with a range of 94-127.

Table 7.11 Comparison of performance on the Rey Auditory Verbal Learning Test (RAVLT) between the present study control values with Australian published norms by age (mean, SD)

Present study (norms) by age Published norms by age

RAVLT items 50-59 Source: Geffen, Moar, O’Hanlon et al., 1990: Data for healthy Australian adults stratified by age group

As shown in Table 7.11 the scores of individual subtests on the RAVLT in the present study were comparable to the Australian published norms of Geffen et al. (1990). In both studies there was a trend for a steady decline in performance with increasing age on the total amount of words recalled after an interference list. This declining trend was also observed for the 20-minute delayed recall component. In the present study, subjects aged 60-69 years had slightly higher scores. However, the data remained comparable because the means for this age group fell within the SD of the published norms. Both data sets highlight that increasing age is accompanied by a decline in performance on episodic memory tasks, especially those which tax the memory system.

As previously discussed, since recall of Trial 1 is considered a measure of short-term memory, and approximates Digit Span (WAIS-R) to within one or two points (Hodges, 1994), the control values in the present study will therefore approximate published norms on Digit Span. This is supported by the similar performance on RAVLT between the control values in the present study with published Australian norms.

Rey-Osterrieth Complex Figure Test (ROCFT)

The ROCFT test assessed visual episodic memory and was classified as a test of visual recall and visuo-spatial ability. Table 7.12 shows the raw ROCFT scores for the present study using only the control group (n=32) compared to published control values (n=698; Strauss et al., 2006).

Subjects in the published norms were well educated (mean=14 years), physically healthy and free of neurological symptoms.

Table 7.12 Comparison of performance on the Rey-Osterrieth Complex Figure Test (ROCFT) between the present study control values with published norms by age (mean, SD)

Present study (norms) by age Published norms by age

ROCFT 50-59

Table 7.12 shows the copy scores on the ROCFT in the present study were slightly higher than the published norms for different age categories (Strauss et al., 2006). The recall scores in both data sets were comparable (means are within 1 SD of each other) and showed the classical discrepancy in performance between copy and recall, which is greater for the 70+ age group than for the younger age groups.

7.7.3 Semantic Memory Word Fluency

Word fluency assessed semantic memory and was classified as a test of verbal ability. Table 7.13 shows the word fluency scores for the present study using only the control group (n=32) compared to healthy subjects recruited from Canadian published norms (n=698; Tombaugh et al., 1999).

The Canadian subjects were healthy volunteers recruited from different sources within the community (e.g., shopping centres). They were free of psychiatric and neurological illness and spoke English as a first language.

Table 7.13 Comparison of performance on word fluency between the present study control values with published norms by age (mean, SD)

Present study (norms) by age Published norms by age Word Source for word fluency: Tombaugh et al., 1999: Data for the FAS and animal naming for a sample of healthy adults stratified by demographic groups.

As shown in Table 7.13, performance on word fluency for animals and letters was similar in both studies for subjects aged 50-59 and 60-69.

This is shown by the similar means and SDs. In the present study, animal fluency scores were slightly higher (20) than in the published norms (16) for subjects aged 70-79. However, the data remained comparable because the SDs overlapped each other. Both data sets further show a decline in performance on category fluency and verbal fluency with increasing age.

The Boston Naming Test (BNT)

The BNT assessed semantic memory and was also classified as a test of verbal ability. Table 7.14 shows the raw BNT scores for the present study using only the control group (n=32) compared to healthy subjects from Australian published norms (n=136; Worrall et al., 1995). Subjects in

the published norms consisted of independently living older persons, recruited through advertisements. All subjects were free of neurological disease and spoke English as a first language. The mean age for the sample was 70.4 (SD=7.8) years.

Table 7.14 Comparison of performance on the Boston Naming Test (BNT) between the present study control values with Australian published norms by age (mean, SD)

As shown in Table 7.14 comparison of the raw naming scores for the controls in the present study with the Australian published norms of Worrall et al. (1995) shows a similar pattern of performance for both studies across the age categories. This is supported by the SDs within the present study which overlapped with published data.

7.7.4 Visuomotor speed and executive functioning Trail-Making A and B

The Trail-Making test A and B assessed visuo-motor speed and executive functioning, respectively (see Methods). Table 7.15 shows the raw Trail-Making test scores for the present study using only the control group (n=32) compared to healthy subjects from Canadian published norms

recruited from the community (e.g., shopping centres) and were free of neurological, psychiatric and medical symptoms by self-report. Their mean age and years of education were 58 (21.7) and 12.6 (2.6), respectively. All subjects had MMSE scores >23.

Table 7.15 shows there was generally good agreement between the Trail Making A and B scores with the healthy control data in the present study and published norms (Tombaugh, 2004). Both studies showed a trend for increased task time with increased task complexity, especially in subjects aged 70-79 years with lower levels of education. The differences in the standard deviations in the present study reflect low subject numbers for some of the data cells.

Table 7.15 Comparison of performance on the Trail-Making Test between the controls in the present study with published norms (mean seconds, SD)

Present study (norms) by age Published norms by age Education

Means and SDs are expressed in seconds. Lower scores indicate better performance. The time limit for Trail B is 300 seconds. A score of 300 is recorded if the task is not completed within this period.

Source: Tombaugh, 2004. Data for a sample of healthy Canadian adults stratified by Age and Education

In summary, the controls in the present study were comparable to healthy aged-matched norms on all the neuropsychological tests reviewed.

The mean scores were found to be either very close or within 1 SD of published norms. Thus, the controls in the present study were considered to represent a group of subjects with normal cognitive functioning between the age of 50 and 79.

The z-scores derived from the control group data were therefore used to compare the performance of subjects using a neuropsychological test battery. The z-scores were calculated for each of the cognitive tests and then aggregated, if necessary, for each of the cognitive domains. The next section provides a discussion on z-scores.