INT'L. J. AGING AND HUMAN DEVELOPMENT, VOI. 9(3), 1978-79
COGNITIVE RIGIDITY IN THE AGED AND THE MENTALLY RETARDED
N. H. KIRBY T. NETTELBECK S. GOODENOUGH Department of Psychology University of Adelaide
ABSTRACT
Three groups, one of elderly, one of young mentally retarded, and one of nonretarded young persons were compared on a visual recognition task which involved changing from one category of identification to another. The mentally retarded participants had greater difficulty in changing categories than did the non-retarded participants. Results for the elderly were similar but may have been partly due to the choice of stimulus material. In a second task, the same elderly and nonretarded young participants named as many objects as possible in one minute. The elderly group produced fewer responses on average than the young group and fewer categories of such responses. Results suggested that older persons find it more difficult to change between different categories of identification.
Welford has reported an unpublished study by O'Doherty which 111, following Korchin and Basowitz compared old and young individuals on a task requiring change from one category of identification to another [Z]. Participants were shown series of pictures on cards in which one familiar object gradually changed into another. O'Doherty found that when the pictures on the first and last cards were of objects belonging to closely similar categories (e.g., jugteapot), there was little difference in the point at which young and old persons recognized the new object. However, when the pictures were of objects belonging to different categories (e.g., mousecar), the older 263
0 1979, Baywood Publishing Co.,Inc.
doi: 10.2190/RN5F-VP7P-FPTY-GPU7 http://baywood.com
264 I N. H. KIRBY, T. NETTELBECK AND S. GOODENOUGH
participants identified the new object much later in the series than did the younger. Although both groups abandoned their initial classification at about the same point, the young were quicker than the older to recognize the new picture: the older participants tended to persevere with identification for several cards within the same category as the first card. Welford recognized that this tendency of elderly persons to persevere within the same category of response and to repeat previous responses might be due to “the task of identification (being) more laborious than older subjects are willing to undertake” [ l , p. 1811, but considered it more reasonable to attribute the tendency to slower searching among the possible categories of identification. One way of testing between these two alternative explanations might be to time the two tasks. If perseveration on the part of older persons was due to slower searching through possible categories then they should require more time to complete the task. If, however, older persons simply repeated previous responses or responded within the same category because they considered the task to be “too laborious,” they should take the same or less time overall. One aim of the present experiment was to replicate O’Doherty’s study but with the additional measure of time taken to complete the task. Further evidence cited by Welford in support of the hypothesis that older individuals find the search process more difficult included an unpublished study by Speakman who asked his participants to name as many “things” or nouns as they could within a period of one minute. He found that the number of things mentioned declined with age. There was also some suggestion that fewer categories of object were mentioned by the older participants, although it was not possible to test this statistically. A second aim of the present experiment was therefore to replicate Speakman’s study with an additional analysis of the numbers of categories mentioned. The suggestion that older people may find it difficult to shift from one category of response to another is similar to the often reported observation that retarded persons tend to perseverate in giving previous responses even when they are no longer appropriate [3-61. Indeed, evidence of this sort led Kounin to hypothesize that such rigidity increased with both age and feeblemindedness [3]. However, Kounin’s work has been criticized, for example by Werner [5, 61, who showed that among the mentally retarded rigidity was not a unitary trait. An implication of Kounin’s hypothesis is that the performances of mentally retarded and older individuals should be very similar in tasks such as that of O’Doherty, although Werner’s studies would suggest that there may well be qualitative differences in the kinds of rigidity displayed by the two groups. Accordingly, a group of mentally retarded persons was also included in the present experiment to allow detailed comparisons of their performance with that of an older group. Both groups were compared with a group of young persons of average intelligence.
COGNITIVE RIGIDITY / 265
METHOD Participants The group of thirteen elderly participants was made up of four males and nine females. None of these was in an institution and all had adequate vision. Their ages ranged from sixty to seventy-nine years (mean = 70 years) and their IQ scores, as measured by the Raven Standard F’rogressive Matrices, ranged from sixty-five to ninetyeight (mean = 78). The younger group consisted of eighteen high school students, nine males and nine females. Ages ranged from fifteen to eighteen years (mean = 15 years 6 months) and IQ scores from ninety-four to 141 (mean = 115). Although IQ scores in the older group appeared to be lower overall than those for the younger, they were in fact slightly greater than average when compared with the scores found for older subjects by Foulds and Raven [7]. It would therefore appear reasonable to treat the non-retarded younger and older groups as approximately equivalent in this regard. The mentally retarded group consisted of seventeen students from a special school for the retarded, ten males and ten females. In no case was retardation thought to be due to brain injury. Reading ages as measured by the Schonell Reading test ranged from zero to eleven years one month (mean = 7 years 6 months). Their ages ranged from fourteen to nineteen years (mean = 16 years 8 months).
Apparatus A tape recorder was used to record each participant’s responses to each of the tests. This enabled an accurate analysis of replies to be made following the
experimental session. As there was no record of the cards used by O’Doherty, sets were constructed portraying the two series reported by Welford; i.e., jug and teapot, mouse and car [I]. The degree of change between cards was specified by a computer programme which operated on the original picture (a matrix of dots) and formed each successive card by randomizing about 10 per cent of the dots making up the previous picture. The final card after eleven such steps was a random array of dots. Series were combined to form the two sets of twenty-four cards shown in Figure 1. Pictures were photographed to produce copies of a convenient size (10 X 13 cm). In the original series used by O’Doherty, each picture gradually changed into another without first passing through complete randomness. The method used in the present experiment should have the advantage of helping to separate the point at which participants abandon their first identification from the point at which they make their new identification.
266 / N. H. KIRBY, T. NETTELBECK A N D S. GOODENOUGH
Figure 1. The two sets of twenty-four stimulus cards used in the replication of O’Doherty’s task.
Procedure The older participants were tested in their own homes. The others were tested in school settings. Participants were first given O’Doherty’s test. They were told that it was not an intelligence test and that there was no time limit. They were asked to identify what they saw as the cards were presented one by one, and were told that acceptable answers included “nothing.” About half the persons in each group completed the jug-teapot set first followed by the mouse-car. The rest completed the two sets in the reverse
COGNITIVE RIGIDITY / 267
order. Speakman's test was then given to all but the retarded participants for whom it was considered to be too difficult. Participants were asked to close their eyes and name as many different things as they could in one minute. If they seemed in doubt as to what was required, examples were given.
RESULTS AND DISCUSSION Two kinds of comparison were made in order to test the hypothesis that older and retarded persons have greater difficulty in changing between different categories of identification. Firstly, following O'Doherty, the three groups were compared on each set of cards. Examination of the data showed that there were large differences between some of the standard deviations found in the three groups. Non-parametric Kruskal-Wallace one way analyses of variance were therefore used. Secondly, performance within each group was examined separately on each of the two sets using the Wilcoxon matchedpairs signed-ranks test. All differences reported as significant had a probability value of less than .01 except where stated otherwise.
O'Doherty's Test The only significant effects due to the order of presentation in O'Doherty's test consisted of a tendency for the younger groups, both the non-retarded and the retarded, to change to the car classification earlier than they changed to the mouse classification. It seems possible that the car was of greater interest than the mouse to the younger participants. Table 1 shows the numbers of individuals in each group changing at each card within both sets of cards. It can be seen that there was little difference between the three groups in the point at which they abandoned their initial classification. None of the differences was significant, although several members of the mentally retarded group did not change until well into the second half of each series. When making the new identification the only significant difference between the three groups was found for the mouse-car set. Non-retarded younger participants made their identification significantly earlier than did either the older or the mentally retarded participants. Comparing results for the two series within each of the groups separately, the only significant result was that older participants made their new identification later when the pictures were from different categories than when similar categories were involved. Thus, the outcome of comparisons both within and between groups supported the hypothesis of greater difficulty when changing between different categories for the older group. For the retarded group, only the
.
Pi Categories very similar: (jug-teapot) Point at which old identification is abandoned: Older Younger Mentally Retarded Point at which new identification is achieved: Older Younger Mentally Retarded
.Categories very different: (mousecar) Point at which old identification is abandoned: Older Younger Mentally Retarded Point at which new identification is achieved: Older Younger Mentally Retarded
Group
~~
1
2
1
1
1
2
1 2
4
1
2 1 2
1
2 1
6 6 6
1 1
3
1 6 2
1 1
1 1
5 1 4
1
2 2 1
5 4 4
1
1
10 1 1 12 13 14 15 16 17 18 19 20 21 22 23 24
3 2 2 1 1 1 3 4 5 2 1 1 1 1 1 3 1 1 3
2
2 1 2 2 1 1 2 1 2 4 4 1 2 5 1 1 2 3 2 3 1
1 2 3 4 5 6 7 8 9
Card in series of 24 at which change occurred
Table 1. The Numbers of Older, Younger, and Mentally Retarded Participants Making Changes in Category of Identification as a Function of Degree of Change Required in the Replication of O’Doherty’s Task
1 1 5
6
1
No Change By 24th Card
COGNITIVE RIGIDITY I 269
comparisons between groups supported this hypothesis. Approximately onethird of the retarded participants failed to identify the last card in both sets. Since every member of the retarded group was able to name the first and last cards of each set correctly when they were subsequently placed side by side, their failure suggests that many of them had difficulty in switching between objects from the same category as well as between objects from different categories. The fact that both retarded and non-retarded younger participants identified the car earlier than the mouse raises the possibility that at least part of the difference between the older and the non-retarded young participants was due to the greater interest of the car for the young. Separate analyses for identification of the mouse and of the car were therefore carried out. It was found that the mentally retarded identified both the mouse and the car significantly later than did the non-retarded young group, even though both groups identified the car significantly earlier than the mouse. The older participants, on the other hand, identified only the car significantly later than did the non-retarded young participants: there was no significant difference between these two groups in the point at which they identified the mouse. Thus, while there seemed to be a genuine tendency for the retarded participants to have greater difficulty than the non-retarded younger participants in changing to the new identification when the objects were from different categories, the difference between the older and the younger nonretarded groups could have been due to the greater interest of the car for the younger participants. If so, it provides an alternative to the hypothesis that older persons find greater difficulty in changing between different categories. Responses were further divided into four classes: repetitions of the first response; identifications as objects in the same category as the initial response; identifications as objects of a different category; and “don’t know.” These are shown in Table 2. It can be seen that for both sets of cards there was little difference between the three groups in the number of “don’t know” responses. Retarded participants made more repetition responses, and hence less same category and other category responses than participants in the other groups. However, in each set only the differences between retarded and nonretarded younger participants were statistically significant (p < .05). Table 3 shows the mean times taken by each group for each of the sets. It can be seen that, on average, the older group took considerably longer on both sets than either the retarded or non-retarded younger groups. This fact suggests that the present results, and by implication those of O’Doherty, were not due to the tasks being “more laborious” than the older persons were willing t o undertake. It indicates that the older participants found greater difficulty, and hgnce took longer, to switch both between categories and also within the same category. It is clear that while the results have indicated some similarity between the
270 I N. H. KIRBY, T. NETTELBECK AND S. GOODENOUGH
Table 2. The Mean and Standard Deviation (in Parentheses) for the Numbers of Responses, Classified in Terms of the Initial Response, Given by the Three Groups in the Replication of O'Doherty's Task Type of response
Group
Categories very different: (mouse-car) Older Younger Mentally Retarded Categories very similar: (jug-teapot) Older Younger Mentally Retarded
Repetition
Same Category
Different Category
"Don't Know"
7.3 (4.8) 5.5 (2.4) 9.4 (6.3)
1.0 (2.0) 0.8 (1.8) 0.1 (0.5)
6.1 (3.8) 7.0 (4.0) 4.9 (3.3)
9.7 (5.1) 10.7 (4.1) 9.9 (5.6)
8.2 (4.9) 7.8 (4.0) 12.1 (6.4)
5.9 (2.5) 5.5 (2.1) 3.7 (2.7)
1.4 (1.4) 2.9 (4.2) 1.1 (2.3)
8.6 (3.9) 7.7 (4.5) 7.3 (4.0)
performance of q e older and the mentally retarded participants, they have also indicated a number of important differences. The older participants took longer to complete the task, appeared to make fewer repetition responses and did not respond differently to the mouse and the car. These differences suggest that it was correct to assume that the older participants in this experiment were not mentally retarded even though they did have lower IQ scores than the young non-retarded participants. It was assumed that the older and non-retarded participants were approximately equivalent regarding IQ because scores among the former group were slightly higher than the average found for older persons by Foulds and Raven [7]. An older group of retarded persons could not be obtained for this experiment but the use of such a group would perhaps have helped to determine the combined as well as the separate effects of age and mental retardation. If these effects were assumed to be additive to some extent, then the present results would suggest that older retarded persons might have greater difficulty in changing between categories than either young mentally retarded or older non-retarded persons. In addition, because of their age, older retarded persons would be expected to take longer to complete the task than younger persons, and not to respond differently to the car and the mouse. Because of their mental retardation, they would also bs expected to make more repetition responses than non-retarded persons.
COGNITIVE RIGIDITY / 271
Table 3. Mean and Standard Deviation (in Parentheses) for the Time Taken in Seconds by the Three Groups for Each Set of Cards in the Replication of O'Doherty's Task Categories very different: (mouse-car)
Categories very similar: (jug-teapot)
Older
263 (108)
257 (141)
Younger
109 (53)
127 (46)
Mentally Retarded
110 (55)
105 (68)
Group
Speakman's Task The mean numbers of words and of different categories of words named in one minute are shown in Table 4. It can be seen that the older participants produced significantly fewer words than the younger, in agreement with Speakman's finding. The older participants also produced significantly fewer categories of words. They also tended to produce longer runs of words in the same category: in both groups, most runs were one or two in length, but the older participants tended to make proportionally more runs of four, five and six in length. However, there were insufficient data to test this statistically. There were no significant correlations in either group between IQ and the number of either words or categories produced. The average number of objects named was less for both age groups than for the corresponding groups in Speakman's study, perhaps because participants in our experiment were instructed to close their eyes during the task. Nevertheless, the results support Speakman's original finding that older persons name fewer objects in a given time, and have confirmed his tentative suggestion that they also name fewer categories of object than do younger persons. Taken together, the results of both the present experiments generally Table 4. Mean and Standard Deviation (in Parentheses) for the Numbers of Words Named and Categories of Words Named in One Minute by the Older and Non-Retarded Younger Groups in the Replication of Speakman's Task Group ~
Words named ~
Categories of woro's named
~
Older
25.2 (9.1)
6.1 (1.8)
Younger
32.6 (7.4)
9.2 (2.1)
272 / N . H . K I R B Y , T . N E T T E L B E C K AND S. GOODENOUGH
support the hypothesis that older persons find greater difficulty in switching between different categories of identification. However, while the replication of Speakman’s experiment is certainly consistent with this hypothesis, the evidence from the replication of O’Doherty’s task is less conclusive, and suggests that ease or difficulty of switching from one category of identification to another may be, at least in part, a result of interest or lack of it in particular categories of object. Be this as it may, the results of the two experiments with regard to both age and retardation raise the possibility that if such factors as the relative interest of the stimulus material were first equated, these tasks might provide the basis of a useful clinical technique. The material is sufficiently simple to be readily understood, and is quickly and easily administered. REFERENCES
1 . A. T. Welford, Ageing and Human Skill, Oxford University Press, London, 1958. 2. S. J . Korchin and H. Basowitz, The Judgment of Ambiguous Stimuli as an Index of Cognitive Functioning in Aging, Journal of Personality, 25, pp. 8195, 1956. 3. J. S. Kounin, Experimental Studies of Rigidity, Character and Personality, 9, pp. 251-282, 1941. 4. K. Goldstein, Concerning Rigidity, Character and Personality, 1 1 , pp. 209226, 1943. 5. H. Werner, Abnormal and Subnormal Rigidity, Journal of Abnormal and Social Psychology, 41, pp. 15-24, 1946. 6 . H. Werner, The Concept of Rigidity: A Critical Evaluation, Psychological Review, 53, pp. 42-53, 1946. 7 . G. A. Foulds and J. C. Raven, Normal Changes in the Mental Abilities of Adults as Age Advances, Journal of Mental Science, 94, pp. 133-142, 1948. ACKNOWLEDGEMENT
We are grateful for the helpful cooperation of the staff and students of both Kensington Special School and Marden High School. We are also grateful to Professor A. T. Welford for helpful comments on an earlier draft of this paper. The work was supported by a grant from the Australian Research Grants Committee to A. T. Welford, T. Nettelbeck and N. H. Kirby. Direct reprint requests to:
Dr. N. H. Kirby Department of Psychology University of Adelaide Box 498, G.P.O., Adelaide South Australia 5001
COGNITIVE RIGIDITY IN THE AGED AND THE MENTALLY RETARDED
N. H. KIRBY T. NETTELBECK S. GOODENOUGH Department of Psychology University of Adelaide
ABSTRACT
Three groups, one of elderly, one of young mentally retarded, and one of nonretarded young persons were compared on a visual recognition task which involved changing from one category of identification to another. The mentally retarded participants had greater difficulty in changing categories than did the non-retarded participants. Results for the elderly were similar but may have been partly due to the choice of stimulus material. In a second task, the same elderly and nonretarded young participants named as many objects as possible in one minute. The elderly group produced fewer responses on average than the young group and fewer categories of such responses. Results suggested that older persons find it more difficult to change between different categories of identification.
Welford has reported an unpublished study by O'Doherty which 111, following Korchin and Basowitz compared old and young individuals on a task requiring change from one category of identification to another [Z]. Participants were shown series of pictures on cards in which one familiar object gradually changed into another. O'Doherty found that when the pictures on the first and last cards were of objects belonging to closely similar categories (e.g., jugteapot), there was little difference in the point at which young and old persons recognized the new object. However, when the pictures were of objects belonging to different categories (e.g., mousecar), the older 263
0 1979, Baywood Publishing Co.,Inc.
doi: 10.2190/RN5F-VP7P-FPTY-GPU7 http://baywood.com
264 I N. H. KIRBY, T. NETTELBECK AND S. GOODENOUGH
participants identified the new object much later in the series than did the younger. Although both groups abandoned their initial classification at about the same point, the young were quicker than the older to recognize the new picture: the older participants tended to persevere with identification for several cards within the same category as the first card. Welford recognized that this tendency of elderly persons to persevere within the same category of response and to repeat previous responses might be due to “the task of identification (being) more laborious than older subjects are willing to undertake” [ l , p. 1811, but considered it more reasonable to attribute the tendency to slower searching among the possible categories of identification. One way of testing between these two alternative explanations might be to time the two tasks. If perseveration on the part of older persons was due to slower searching through possible categories then they should require more time to complete the task. If, however, older persons simply repeated previous responses or responded within the same category because they considered the task to be “too laborious,” they should take the same or less time overall. One aim of the present experiment was to replicate O’Doherty’s study but with the additional measure of time taken to complete the task. Further evidence cited by Welford in support of the hypothesis that older individuals find the search process more difficult included an unpublished study by Speakman who asked his participants to name as many “things” or nouns as they could within a period of one minute. He found that the number of things mentioned declined with age. There was also some suggestion that fewer categories of object were mentioned by the older participants, although it was not possible to test this statistically. A second aim of the present experiment was therefore to replicate Speakman’s study with an additional analysis of the numbers of categories mentioned. The suggestion that older people may find it difficult to shift from one category of response to another is similar to the often reported observation that retarded persons tend to perseverate in giving previous responses even when they are no longer appropriate [3-61. Indeed, evidence of this sort led Kounin to hypothesize that such rigidity increased with both age and feeblemindedness [3]. However, Kounin’s work has been criticized, for example by Werner [5, 61, who showed that among the mentally retarded rigidity was not a unitary trait. An implication of Kounin’s hypothesis is that the performances of mentally retarded and older individuals should be very similar in tasks such as that of O’Doherty, although Werner’s studies would suggest that there may well be qualitative differences in the kinds of rigidity displayed by the two groups. Accordingly, a group of mentally retarded persons was also included in the present experiment to allow detailed comparisons of their performance with that of an older group. Both groups were compared with a group of young persons of average intelligence.
COGNITIVE RIGIDITY / 265
METHOD Participants The group of thirteen elderly participants was made up of four males and nine females. None of these was in an institution and all had adequate vision. Their ages ranged from sixty to seventy-nine years (mean = 70 years) and their IQ scores, as measured by the Raven Standard F’rogressive Matrices, ranged from sixty-five to ninetyeight (mean = 78). The younger group consisted of eighteen high school students, nine males and nine females. Ages ranged from fifteen to eighteen years (mean = 15 years 6 months) and IQ scores from ninety-four to 141 (mean = 115). Although IQ scores in the older group appeared to be lower overall than those for the younger, they were in fact slightly greater than average when compared with the scores found for older subjects by Foulds and Raven [7]. It would therefore appear reasonable to treat the non-retarded younger and older groups as approximately equivalent in this regard. The mentally retarded group consisted of seventeen students from a special school for the retarded, ten males and ten females. In no case was retardation thought to be due to brain injury. Reading ages as measured by the Schonell Reading test ranged from zero to eleven years one month (mean = 7 years 6 months). Their ages ranged from fourteen to nineteen years (mean = 16 years 8 months).
Apparatus A tape recorder was used to record each participant’s responses to each of the tests. This enabled an accurate analysis of replies to be made following the
experimental session. As there was no record of the cards used by O’Doherty, sets were constructed portraying the two series reported by Welford; i.e., jug and teapot, mouse and car [I]. The degree of change between cards was specified by a computer programme which operated on the original picture (a matrix of dots) and formed each successive card by randomizing about 10 per cent of the dots making up the previous picture. The final card after eleven such steps was a random array of dots. Series were combined to form the two sets of twenty-four cards shown in Figure 1. Pictures were photographed to produce copies of a convenient size (10 X 13 cm). In the original series used by O’Doherty, each picture gradually changed into another without first passing through complete randomness. The method used in the present experiment should have the advantage of helping to separate the point at which participants abandon their first identification from the point at which they make their new identification.
266 / N. H. KIRBY, T. NETTELBECK A N D S. GOODENOUGH
Figure 1. The two sets of twenty-four stimulus cards used in the replication of O’Doherty’s task.
Procedure The older participants were tested in their own homes. The others were tested in school settings. Participants were first given O’Doherty’s test. They were told that it was not an intelligence test and that there was no time limit. They were asked to identify what they saw as the cards were presented one by one, and were told that acceptable answers included “nothing.” About half the persons in each group completed the jug-teapot set first followed by the mouse-car. The rest completed the two sets in the reverse
COGNITIVE RIGIDITY / 267
order. Speakman's test was then given to all but the retarded participants for whom it was considered to be too difficult. Participants were asked to close their eyes and name as many different things as they could in one minute. If they seemed in doubt as to what was required, examples were given.
RESULTS AND DISCUSSION Two kinds of comparison were made in order to test the hypothesis that older and retarded persons have greater difficulty in changing between different categories of identification. Firstly, following O'Doherty, the three groups were compared on each set of cards. Examination of the data showed that there were large differences between some of the standard deviations found in the three groups. Non-parametric Kruskal-Wallace one way analyses of variance were therefore used. Secondly, performance within each group was examined separately on each of the two sets using the Wilcoxon matchedpairs signed-ranks test. All differences reported as significant had a probability value of less than .01 except where stated otherwise.
O'Doherty's Test The only significant effects due to the order of presentation in O'Doherty's test consisted of a tendency for the younger groups, both the non-retarded and the retarded, to change to the car classification earlier than they changed to the mouse classification. It seems possible that the car was of greater interest than the mouse to the younger participants. Table 1 shows the numbers of individuals in each group changing at each card within both sets of cards. It can be seen that there was little difference between the three groups in the point at which they abandoned their initial classification. None of the differences was significant, although several members of the mentally retarded group did not change until well into the second half of each series. When making the new identification the only significant difference between the three groups was found for the mouse-car set. Non-retarded younger participants made their identification significantly earlier than did either the older or the mentally retarded participants. Comparing results for the two series within each of the groups separately, the only significant result was that older participants made their new identification later when the pictures were from different categories than when similar categories were involved. Thus, the outcome of comparisons both within and between groups supported the hypothesis of greater difficulty when changing between different categories for the older group. For the retarded group, only the
.
Pi Categories very similar: (jug-teapot) Point at which old identification is abandoned: Older Younger Mentally Retarded Point at which new identification is achieved: Older Younger Mentally Retarded
.Categories very different: (mousecar) Point at which old identification is abandoned: Older Younger Mentally Retarded Point at which new identification is achieved: Older Younger Mentally Retarded
Group
~~
1
2
1
1
1
2
1 2
4
1
2 1 2
1
2 1
6 6 6
1 1
3
1 6 2
1 1
1 1
5 1 4
1
2 2 1
5 4 4
1
1
10 1 1 12 13 14 15 16 17 18 19 20 21 22 23 24
3 2 2 1 1 1 3 4 5 2 1 1 1 1 1 3 1 1 3
2
2 1 2 2 1 1 2 1 2 4 4 1 2 5 1 1 2 3 2 3 1
1 2 3 4 5 6 7 8 9
Card in series of 24 at which change occurred
Table 1. The Numbers of Older, Younger, and Mentally Retarded Participants Making Changes in Category of Identification as a Function of Degree of Change Required in the Replication of O’Doherty’s Task
1 1 5
6
1
No Change By 24th Card
COGNITIVE RIGIDITY I 269
comparisons between groups supported this hypothesis. Approximately onethird of the retarded participants failed to identify the last card in both sets. Since every member of the retarded group was able to name the first and last cards of each set correctly when they were subsequently placed side by side, their failure suggests that many of them had difficulty in switching between objects from the same category as well as between objects from different categories. The fact that both retarded and non-retarded younger participants identified the car earlier than the mouse raises the possibility that at least part of the difference between the older and the non-retarded young participants was due to the greater interest of the car for the young. Separate analyses for identification of the mouse and of the car were therefore carried out. It was found that the mentally retarded identified both the mouse and the car significantly later than did the non-retarded young group, even though both groups identified the car significantly earlier than the mouse. The older participants, on the other hand, identified only the car significantly later than did the non-retarded young participants: there was no significant difference between these two groups in the point at which they identified the mouse. Thus, while there seemed to be a genuine tendency for the retarded participants to have greater difficulty than the non-retarded younger participants in changing to the new identification when the objects were from different categories, the difference between the older and the younger nonretarded groups could have been due to the greater interest of the car for the younger participants. If so, it provides an alternative to the hypothesis that older persons find greater difficulty in changing between different categories. Responses were further divided into four classes: repetitions of the first response; identifications as objects in the same category as the initial response; identifications as objects of a different category; and “don’t know.” These are shown in Table 2. It can be seen that for both sets of cards there was little difference between the three groups in the number of “don’t know” responses. Retarded participants made more repetition responses, and hence less same category and other category responses than participants in the other groups. However, in each set only the differences between retarded and nonretarded younger participants were statistically significant (p < .05). Table 3 shows the mean times taken by each group for each of the sets. It can be seen that, on average, the older group took considerably longer on both sets than either the retarded or non-retarded younger groups. This fact suggests that the present results, and by implication those of O’Doherty, were not due to the tasks being “more laborious” than the older persons were willing t o undertake. It indicates that the older participants found greater difficulty, and hgnce took longer, to switch both between categories and also within the same category. It is clear that while the results have indicated some similarity between the
270 I N. H. KIRBY, T. NETTELBECK AND S. GOODENOUGH
Table 2. The Mean and Standard Deviation (in Parentheses) for the Numbers of Responses, Classified in Terms of the Initial Response, Given by the Three Groups in the Replication of O'Doherty's Task Type of response
Group
Categories very different: (mouse-car) Older Younger Mentally Retarded Categories very similar: (jug-teapot) Older Younger Mentally Retarded
Repetition
Same Category
Different Category
"Don't Know"
7.3 (4.8) 5.5 (2.4) 9.4 (6.3)
1.0 (2.0) 0.8 (1.8) 0.1 (0.5)
6.1 (3.8) 7.0 (4.0) 4.9 (3.3)
9.7 (5.1) 10.7 (4.1) 9.9 (5.6)
8.2 (4.9) 7.8 (4.0) 12.1 (6.4)
5.9 (2.5) 5.5 (2.1) 3.7 (2.7)
1.4 (1.4) 2.9 (4.2) 1.1 (2.3)
8.6 (3.9) 7.7 (4.5) 7.3 (4.0)
performance of q e older and the mentally retarded participants, they have also indicated a number of important differences. The older participants took longer to complete the task, appeared to make fewer repetition responses and did not respond differently to the mouse and the car. These differences suggest that it was correct to assume that the older participants in this experiment were not mentally retarded even though they did have lower IQ scores than the young non-retarded participants. It was assumed that the older and non-retarded participants were approximately equivalent regarding IQ because scores among the former group were slightly higher than the average found for older persons by Foulds and Raven [7]. An older group of retarded persons could not be obtained for this experiment but the use of such a group would perhaps have helped to determine the combined as well as the separate effects of age and mental retardation. If these effects were assumed to be additive to some extent, then the present results would suggest that older retarded persons might have greater difficulty in changing between categories than either young mentally retarded or older non-retarded persons. In addition, because of their age, older retarded persons would be expected to take longer to complete the task than younger persons, and not to respond differently to the car and the mouse. Because of their mental retardation, they would also bs expected to make more repetition responses than non-retarded persons.
COGNITIVE RIGIDITY / 271
Table 3. Mean and Standard Deviation (in Parentheses) for the Time Taken in Seconds by the Three Groups for Each Set of Cards in the Replication of O'Doherty's Task Categories very different: (mouse-car)
Categories very similar: (jug-teapot)
Older
263 (108)
257 (141)
Younger
109 (53)
127 (46)
Mentally Retarded
110 (55)
105 (68)
Group
Speakman's Task The mean numbers of words and of different categories of words named in one minute are shown in Table 4. It can be seen that the older participants produced significantly fewer words than the younger, in agreement with Speakman's finding. The older participants also produced significantly fewer categories of words. They also tended to produce longer runs of words in the same category: in both groups, most runs were one or two in length, but the older participants tended to make proportionally more runs of four, five and six in length. However, there were insufficient data to test this statistically. There were no significant correlations in either group between IQ and the number of either words or categories produced. The average number of objects named was less for both age groups than for the corresponding groups in Speakman's study, perhaps because participants in our experiment were instructed to close their eyes during the task. Nevertheless, the results support Speakman's original finding that older persons name fewer objects in a given time, and have confirmed his tentative suggestion that they also name fewer categories of object than do younger persons. Taken together, the results of both the present experiments generally Table 4. Mean and Standard Deviation (in Parentheses) for the Numbers of Words Named and Categories of Words Named in One Minute by the Older and Non-Retarded Younger Groups in the Replication of Speakman's Task Group ~
Words named ~
Categories of woro's named
~
Older
25.2 (9.1)
6.1 (1.8)
Younger
32.6 (7.4)
9.2 (2.1)
272 / N . H . K I R B Y , T . N E T T E L B E C K AND S. GOODENOUGH
support the hypothesis that older persons find greater difficulty in switching between different categories of identification. However, while the replication of Speakman’s experiment is certainly consistent with this hypothesis, the evidence from the replication of O’Doherty’s task is less conclusive, and suggests that ease or difficulty of switching from one category of identification to another may be, at least in part, a result of interest or lack of it in particular categories of object. Be this as it may, the results of the two experiments with regard to both age and retardation raise the possibility that if such factors as the relative interest of the stimulus material were first equated, these tasks might provide the basis of a useful clinical technique. The material is sufficiently simple to be readily understood, and is quickly and easily administered. REFERENCES
1 . A. T. Welford, Ageing and Human Skill, Oxford University Press, London, 1958. 2. S. J . Korchin and H. Basowitz, The Judgment of Ambiguous Stimuli as an Index of Cognitive Functioning in Aging, Journal of Personality, 25, pp. 8195, 1956. 3. J. S. Kounin, Experimental Studies of Rigidity, Character and Personality, 9, pp. 251-282, 1941. 4. K. Goldstein, Concerning Rigidity, Character and Personality, 1 1 , pp. 209226, 1943. 5. H. Werner, Abnormal and Subnormal Rigidity, Journal of Abnormal and Social Psychology, 41, pp. 15-24, 1946. 6 . H. Werner, The Concept of Rigidity: A Critical Evaluation, Psychological Review, 53, pp. 42-53, 1946. 7 . G. A. Foulds and J. C. Raven, Normal Changes in the Mental Abilities of Adults as Age Advances, Journal of Mental Science, 94, pp. 133-142, 1948. ACKNOWLEDGEMENT
We are grateful for the helpful cooperation of the staff and students of both Kensington Special School and Marden High School. We are also grateful to Professor A. T. Welford for helpful comments on an earlier draft of this paper. The work was supported by a grant from the Australian Research Grants Committee to A. T. Welford, T. Nettelbeck and N. H. Kirby. Direct reprint requests to:
Dr. N. H. Kirby Department of Psychology University of Adelaide Box 498, G.P.O., Adelaide South Australia 5001
