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Perseveration in Aphasia
PERSEVERATION IN APHASIA Martin L. Albert and Jennifer Sandson (Department of Neurology, Aphasia Research Center, Boston University Medical School, and Boston Veterans Administration Medical Center; and the Department of Psychology, Cornell University, Ithaca, New York)
Studies of perseveration in aphasia have generally considered perseverative deficits to be orthogonal to linguistic deficits. These studies usually approach perseveration from one of three perspectives, that of task variables (e.g. automatic versus non-automatic); stimulus variables (e.g. modality of input); and subject variables (e.g. location, size, and etiology of lesion). In the present study, we consider the possibility that perseveration has a special, and perhaps integral, link to aphasia, while systematically exploring it from all three perspectives. We have recently proposed a taxonomy of perseverative behavior consisting of three categories: recurrent, continuous, and stuck-in-set perseveration (Sandson and Albert, 1984). Recurrent perseveration is the inappropriate recurrence of a previous response following intervening production or a subsequent stimulus. Continuous perseveration is the inappropriate prolongation or continuation without cessation of a behavior. Stuck-in-Set perseveration is the inappropriate maintenance of a category or framework. While all three categories have been reported in patients with aphasia, recurrent perseveration is by far the most common and is the focus of the current study. Before discussing our experiments, we shall review previous studies of perseveration in aphasia, focusing respectively on task, stimulus, and subject variables.
Task Variables
Perseveration in aphasia has been shown to be more easily elicited by some tasks, both verbal and non-verbal, than by others. Allison and Hurwitz (1967) tested a mixed group of 24 aphasic patients on a series of tasks including: searching for objects; drawings and constructions; exeCortex (1986) 22, 103-115
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cuting gestures and pantomime; carrying out verbal commands; repeating and reversing series; naming seen objects; naming objects from memory; reading; writing; and spontaneous speech. Sixteen subjects perseverated on at least one task and no subject perseverated on all tasks. Per severation was common in response to verbal commands, in naming seen objects, in reversing over-learned series, in writing (although only in association with other dysgraphia), and in spontaneous speech. It was unusual in naming from memory and in reading. Helmick and Berg (1976) examined 30 brain damaged' patients, 18 with aphasia, on a similar battery of tests. They found perseveration, which was significantly more frequent in patients with aphasia, to be more common on reversing series, writing sentences, and drawing designs from memory, and least common on answering short questions, defining words, and describing pictures. Santo-Pietro and Rigrodsky 0982) elicited significantly fewer perseverations on a word reading task than on picture naming or sentence completion tasks utilizing similar stimuli. In all three studies, perseverations usually consisted of inappropriate repetitions of previously produced responses following one or more subsequent stimuli, i.e. recurrent perseveration. Stimulus Variables
In some cases, perseveration is more easily elicited by certain classes of stimuli than by others, even when utilized for the same task. Halpern (1965) presented 33 aphasic subjects of mixed etiology with 72 words for verbalization. Each word was presented in a visual, an auditory, and an auditory-visual modality. Perseveration correlated with stimulus length in all modalities and with abstractness in the visual modality. There was no correlation between perseveration and word frequency or part of speech. Santo-Pietro and Rigrodsky (1982), on the other hand, reported a significant effect of semantic difficulty (determined by word frequency) on perseveration. They also demonstrated a significant decrease in perseveration when inter-trial intervals were increased from one to ten seconds. Subject Variables
Research has also focused on the relation of perseveration to variables such as location, etiology, and size of lesion, time post onset, and aphasia type. Shindler, Caplan and Hier (1984) administered tests of confrontation naming, word association, and vocabulary definition to 20 aphasic patients. Five of the six patients (83%) with Wernicke's aphasia, three of the six patients (50%) with Broca's aphasia, and three of the eight
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patients (38%) with anomic aphasia produced at least one intrusion. Santo-Pietro and Rigrodsky (1982) also reported significantly fewer perseverations in Broca's than in Wernicke's and anomic aphasia. Mateer (1978) found that both aphasic (fluent) and non-aphasic patients with left hemisphere damage perseverated more on a task of imitating oral movements than either right hemisphere patients or controls. Helmick and Berg (1976) and Allison and Hurwitz (1967) noted significantly more perseveration in patients with aphasia of vascular etiology than in patients with tumor or trauma. Both studies also described a decrease in perseveration as a function of time elapsed since onset. Santo-Pietro and Rigrodsky, though, did not find differences between patients more or less than one year post onset. In summary
Studies of perseveration in aphasia to date demonstrate that perseveration, particularly of the recurrent variety, is a common symptom in aphasia. These results suggest that recurrent perseveration may be closely linked to (may even comprise an integral part of) specific language deficits in aphasia. The occurrence of perseveration in aphasia, however, seems to be related to specific task, stimulus, and subject variables, in a manner which has not yet been systematically explored. The goal of the study reported in this paper was a systematic exploration of the effects of selected task variables (especially that of examiner versus subject controlled presentation), stimulus variables (especially .verbal versus non-verbal) and subject variables (such as location of lesion and aphasia type) on perseveration in aphasia. We hypothesized that perseveration on both verbal and non-verbal tasks would be especially linked to fluent aphasia, and would be particularly common following posterior lesions in the left hemisphere. MATERIALS AND METHODS
Subjects
Eighteen aphasic patients with left hemisphere lesion, 13 patients with right hemisphere lesion, and 13 hospitalized controls with no known cerebral lesion were tested for recurrent perseveration. Neurologically impaired subjects were volunteers from the Aphasia/Neurobehavior and Rehabilitation Units at the Boston Veterans Administration Medical Center. Control subjects were volunteers from the Orthopedics Service. Patients with history of progressive cognitive decline or psychiatric illness were excluded. The mean age, education, score on the Mini-Mental State examination (Folstein, Folstein and McHugh, 1975), and time elapsed post-onset for each group are presented in Table I. Group differ-
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TABLE I
Mean Age, Education, Mental Status Score, and Time Post-Onset for the Three Subject Groups Aphasic (N = 18)
Right hemisphere (N = 13)
Age
56.94 (11.5)
Education (in years) Mental status score
13.50 (2.9) 23.82 (4.0)
52.46 (12.4) 11.91 (2.0) 25.64 (2.0)
Time post-onset (in months)
20.15 (27.8)
45.15 (70.1)
Control (N 13)
=
49.08 (13.9) 13.62 (2.1) 27.69 (2.3)
Numbers in brackets are standard deviations.
ences were not significant for any measures except mental status score. This effect was attributable to significantly lower performance by the aphasic group than by the controls (t = 3.017, dJ. = 28, P = .017) due to the large linguistic component of the Mini-Mental State examination. 11.1 % of aphasic and 7.6% of right hemisphere patients were left-handed. Aphasia types spanned the complete range assigned by the Boston Diagnostic Aphasia Examination (GoodgIass and Kaplan, 1983). Ten patients were classified as fluent and eight as non-fluent. Lesion localization was determined by computerized axial tomography. Eight of the 18 aphasics had lesions involving only one lobe, ten had lesions involving two or more lobes. Pathological involvement of frontal lobe was found in 11 aphasic subjects, parietal lobe in 10 subjects, and temporal lobe in 10 subjects. CT scan uncovered clinically unsuspected small right hemisphere lesions in three aphasic sUbjects. Information about volume of lesion was not available at the time of this analysis. Detailed CT scan information is not available for many of our patients with right hemisphere damage. Most of our subjects with right hemisphere damage had been transferred from other hospitals to our Rehabilitation service, which does not routinely obtain CT scans. Diagnosis of right hemisphere damage was thus primarily based on history of illness, clinical examination, and brief radiological reports from other hospitals. No patient in the right hemisphere group had a known lesion in the left hemisphere.
Experimental Test Procedures Four tests of recurrent perseveration were administered in the same order to all subjects. These tests comprised the first section of a larger battery. In the order of administration, they included: (1) a test of confrontation naming; (2) drawing objects to command; (3) a word list generation task; and (4) a design generation task.
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In the confrontation naming task, subjects were asked to name 15 pictures chosen from the Boston Naming Test (Kaplan, Goodglass and Weintraub, 1983) ranging in familiarity from tree to trellis. Several of the pictured items (e.g. harmonica and accordian; faucet, funnel, and nozzle) are related in meaning, and several begin with the same sound (e.g. tree, trelllis). Semantic cues designed to facilitate recognition (e.g. "used for cutting" for scissors) were provided- in response to failures of recognition. Phonological cues consisting of the first phoneme or consonant cluster were provided in response to other naming failures. Responses were recorded by the examiner during testing. The drawing task consisted of drawing six objects from memory: (1) a clock with numbers and the hands set to ten minutes after eleven; (2) a daisy; (3) a Christmas tree with decorations; (4) a sailboat; (5) a tree other than a Christmas tree; and (6) a hurtlau hand. The stimuli were selected so that each object could contain elements in common with the preceding drawing. In the word list generation (FAS) task (Thurstone and Thurstone, 1962), subjects were asked to list as many words as they could think of in one minute starting with each of the letters f, a, and s. Subjects were instructed not to list proper nouns or derivatives of words previously listed. Responses were recorded by the examiner as they were produced. The design generation task (lones-Gotman and Milner, 1977) consisted of having subjects produce as many different designs containing four distinct lines as possible in a four minute period. Subjects were provided with examples of possible designs containing straight and curved lines on the response sheet. Cognitive status was estimated by performance on the Mini-Mental State Examination (Folstein, Folstein and McHugh, 1975). This short standardized test consists of items evaluating orientation, registration, attention and calculation, and language.
Scoring Procedures Protocols from the aphasic group were scored by two independent raters. Inter-rater reliabilities were computed and found to be high (r > .90) for all tests. Differences between the raters were resolved through discussion. There were two ratings of perseveration for each subject on the naming test. Recurrent (lexical) perseveration was defined as the repetition of all or part (e.g. one or more syllables) of a previous response to a subsequent stimulus (e.g. the re-utterance of faucet in response to funnel, or the production of vinor for trellis one stimulus after the presentation of a visor). Total number of perseverations included lexical recurrent perseverations as well as mUltiple repetitions of the same word during one trial (e.g. funnel, funnel, funnel) and inappropriate recurrences of individual sounds or clusters (e.g. paucet for faucet following plug). The percentage of each subject's responses containing perseveration and the percentage of subjects producing one or more perseverations were both computed with the total perseveration score. There were two perseveration scores for each subject on the drawing task. These were a dichotomous score reflecting either the presence or absence of perseveration and the total number of perseverations across drawings. Perseverations included inappropriate recurrences after intervening drawing (Figure I) and inappropriate continuations of a particular segment (Figure 2).
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Fig. 1 - Recurrent perseveration, produced by an aphasic patient, resulting in the production of two lOs on the drawing of a clock.
Both a dichotomous (present/absent) and a total perseveration score were also computed for the word fluency test. The percentage of perseverations per total responses (acceptable and non-acceptable) was computed using the total perseveration score. Only exact repetitions were considered to be perseverations. Because some derivatives are orthographically diverse, consistency in scoring could only be achieved by considering all derivatives (including phonologically similar pairs such as "sanity" following "sane") as incorrect but not perseverative. Words from a previous category, however, were considered perseverations. Design fluency was scored in the same manner as the word fluency test. Only exact reproductions were considered to be perseverations. Figures differing from previous productions in angle or orientation (e.g. a diamond following a square) were considered to be acceptable productions. Figures differing from previous productions only in size were considered perseverations. RESULTS
On the confrontation naming test, aphasic subjects correctly named significantly fewer items than either patients with right hemisphere damage or controls. Significant group effects were also obtained on the confrontation naming test for number of recurrent lexical perseverations, total number of perseverations, percentage of each subject's responses containing perseveration, and percentage of subjects producing one or more perseverations (Table II). These effects are attributable to significantly greater perseveration by the aphasics than by either of the other two groups. Perseveration in the aphasic group was negatively correlated
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TABLE II Perseveration on Confrontation Naming Aphasic
Right hemisphere
Control
Avs. RH A vs. C
Number of items named correctly
7.28 (4.6)
12.23 (2.8)
13.54 (0.9)
t (29)=3.35** t (29)=4.68**
Number of lexical perseverations
1.28 (1.0)
0.15 (0.4)
0.15 (0.5)
t (29)=3.60** t (29)=3.44**
Total number of perseverations
1.78 (1.4)
0.15 (0.4)
0.15 (0.5)
t (29)=4.07** t (29)=3.96**
14.31 (11.7)
1.06 (2.5)
1.02 (3.5)
t (29)=3.88** t (29)=3.83**
72.2
15.4
07.7
Mean ratio of perseveration total responses Percentage of Ss perseverating at least once
chF (1)= 9.8** chF (1)= 12.8**
** p<.Ol. Numbers in brackets are standard deviations.
with number of items correctly named (r = .549, P < .05). Right hemisphere patients did not differ from the controls on any measure. Group effects remained robust when the contribution of time post onset and mental status score were partialled out through analysis of covariance. More than half (52.2%) of all lexical perseverations ·produced by patients in the aphasic group were semantically related to the current target. These included, for example, the recurrence of faucet in "running faucet" in response to nozzle, and the production of "hartical" in response to accordian five stimuli subsequent to the picture of a harmonica. Perseveration on confrontation naming was associated with posterior, rather than anterior, lesions. Three of the five aphasic subjects not producing any perseveration on confrontation naming had lesion restricted to the frontal lobe. One non-perseverator had a primarily frontal lesion extending throughout the perisylvian region and another had a small lesion lateral to the left occipital hom. All but the last were non-fluent; and all correctly named at least ten of the fifteen items. In contrast, only one of eight aphasic subjects producing three or more perseverations (severe perseverators) had lesions restricted to the frontal lobe. Five of the severe perseverators had frontal involvement, five had parietal involvement, and six had temporal lobe involvement. Similarly, only one of the five subjects producing one or two perseverations (moderate perseverators) had a lesion restricted to the frontal lobe. Of the remaining four, one had frontal involvement, three parietal involvement and three temporal involvement. There were no instances of perseveration on the drawing protocols of
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Perseveration on Drawing to Command Aphasic
Right hemisphere
Avs. RH
Percent of subjects perseverating at least once
44.4
23.1
chF (1)= 1.48
Mean number of perseverations per protocol
.889 (1.2)
.231 (0.4)
t (29)= 1.84
Numbers in brackets are standard deviations.
control subjects (Table III). Control subjects were thus excluded from the statistical analyses of perseveration on the. drawing task. Patients with right hemisphere damage did not differ from the aphasic patients with respect to either the percentage of subjects in each group producing perseveration or the number of perseverations per protocol. There was no clear pattern of lesion localization distinguishing the aphasic subjects who perseverated on the drawing task. The nature of the perseverations produced on drawing by the two groups of brain damaged subjects, however, was qualitatively different. Fourteen of the sixteen perseverations produced by the aphasic subjects were recurrent in nature, consisting either of repetition of numbers on the
Fig. 2 - Continuous perseveration, produced by a patient with right hemisphere damage, resulting in the production of six fingers in the drawing of a hand.
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clock or of the inappropriate recurrence of a feature from a previous drawing (Figure 1). Only two of the sixteen instances (12.5%) were continuous, involving the production of an extra finger on the hand. In contrast, the few perseverations produced by the right hemisphere patients were primarily of the continuous variety (Figure 2). The two brain-damaged groups produced fewer acceptable responses than the controls on both the world list and design generation tasks. The patients with right hemisphere damage generated more words on the F AS task than the aphasics, but the two groups did not differ on design generation. There were no significant differences with respect to perseveration on either of these subject-controlled tasks. The number of acceptable responses, number of perseverations, and percentage of responses that were perseverations are presented in Tables IV and V.
TABLE IV
Perseveration on Word List Generation Aphasic
Right hemisphere
Control
A vs. RH Avs. C
Number of acceptable responses produced
11.92 (8.7)
23.38 (9.3)
3S.69 (8.4)
t (24)=3.13* t (24)=6.80**
Number of perseverations
1.00 (1.2)
1.00 (1.1)
Perseverationl Total responses :p < .05.
6.43 (8.8)
3.67 (4.2)
2.1 (2.3) ~ 4.42 (4.3)
t (24)=0.00
t (24)= 1.44
t (24)=0.98
t (24)=0.71
**p < .01. Numbers in brackets are standard deviations.
TABLE V
Perseveration on DeSign Generation Aphasic
Right hemisphere
Control
A vs. RH A vs. C
Number of acceptable designs
10.22 (S.4)
7.77 (6.1)
lS.8S (S.3)
t (28)= 1.23 t (28)=2.61 *
Number of' perseverations
1.44 (1.9)
0.77 (1.0)
0.54 (1.2)
t (28)= 1.60
9.81 (13.3)
6.74 (9.4)
2.S2 (S.1)
t (28)=0.81 t (28)= 1.37
Perseverationl Total responses *p < .05.
Numbers in brackets are standard deviat(ons.
t (28)= 1.26
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DISCUSSION
Left hemispheric aphasia-producing lesions often produce perseveration as welL More aphasic subjects than controls produced perseveration (generally of the recurrent variety) on two examiner controlled tasks, one verbal and one non-verbal, but not on two subject controlled tasks. Patients with right hemisphere damage did not differ from the controls with respect to perseveration on any task. Aphasic patients produced significantly more perseverations than either patients with right hemisphere damage or age-matched controls on a confrontation naming task. Most of these perseverations consisted of the inappropriate recurrence of all or part (at least one syllable) of a previously produced word. The remaining perseverations consisted either of multiple productions of an utterance in response to one stimulus or the inappropriate recurrence of a sound or consonant cluster on a subsequent stimulus. Perseveration on the confrontation naming test was primarily associated with aphasia due to posterior left hemisphere lesions. Perseveration was most frequent in patients with temporal or parietal involvement (9/10 patients with temporal involvement and 8110 with parietal involvement produced at least one perseveration), and least frequent in patients with frontal involvement (7/11). Three of the five aphasic patients with lesions restricted to the left frontal region produced no perseverations. We suggest several possible explanations for these results. The first is that decreased verbal fluency associated with frontal lobe lesions results in decreased output, inhibiting both intended responses and perseverations. This alternative is supported by the presence of frontal lobe lesions in the. three subjects with the highest ratio of perseveration to total responses. However, this explanation cannot be the only one, since the three aphasic non-perseverators with lesions restricted to the left frontal lobe all correctly named at least ten items. A second explanation is that verbal recurrent perseveration has a preferential link with the temporal or parietal lobes, particularly within the zone of language. Our anatomicoclinical correlations support this alternative. A third possibility, that perseveration is simply associated with larger lesions regardless of location, is the focus of current study. The correlation between perseveration and anomia raises questions about the cognitive mechanisms of verbal recurrence within the context of confrontation naming. One possible explanation is that verbal recurrences occur spontaneously, perhaps as the result of an abnormal priming mechanism (e.g. Scarborough, Cortese and Scarborough, 1977) which is independent of the naming process. Another alternative is that verbal recurrences occur only if triggered by a disruption in the naming process,
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perhaps as a result of failure to locate a target in semantic memory or the lexicon. Either alternative is compatible with the finding of increased perseveration in patients with greater word finding difficulty, as the production of a correct response might inhibit the spontaneous recurrences of the first hypothesis. Each of these alternative hypotheses could be tested by manipulating the difficulty of target production and observing changes in perseveration. Another major finding with respect to perseveration on the naming task is the extent to which perseverative responses were semantically related to the actual target. This result raises questions about the nature of the re-accessed mental representations and the cognitive processes involved in verbal recurrent perseveration. It suggests, perhaps, that semantic representations located in long term memory are at least as likely as lexical or articulatory representations (located in a short term memory buffer) to be re-activated. This possibility can be investigated by systematically manipulating the semantic and phonological relatedness of stimuli and evaluating their effects on perseveration. The nature of perseveration on this naming task leads us to speculate about the possible role of perseveration in specific linguistic deficits in aphasia. It seems likely, for example, that perseveration contributes to the production of semantic and literal paraphasias and neologisms, especially in aphasic patients with poor self-monitoring (see Buckingham, 1985). On the other hand, perseverative tendencies, in patients with intact self monitoring abilities, might contribute to blocking and thus to reduced output. Aphasic patients produced considerably more perseveration than normal controls on the drawing task. In addition, qualitative analysis of the perseverations in the drawings of aphasic patients uncovered differences from those produced by patients with right hemisphere damage. Aphasics' perseverations were almost always recurrent in type, consisting either of reproduction following intervening marking within a drawing or of carry-over of a feature from one drawing to a subsequent drawing. In contrast, the few perseverations produced by the right hemisphere subjects were continuous, consisting of inappropriate prolongation, such as the production of a sixth finger on a hand. The nature of the perseveration interfering with drawing in aphasic patients, then, seems to be the same as that interfering with naming, and different from that which occurs in patients with right hemisphere injury. There were no group differences for either word list or design generation. These tasks differ from confrontation naming and drawing to command in that responses are subject-regulated, rather than tied to specific stimuli controlled by the examiner. The subject controlled tasks, unlike the examiner-controlled tasks, require subjects to pay attention to
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Martin L Albert and Jennifer Samison
and remember their previous responses. The subject-regulated tasks, on the other hand, seem to require less specific retrieval than the examinercontrolled tasks. Once subjects have accessed the appropriate region of the lexicon on the F AS task, there are numerous acceptable responses available for retrieval. The presence of alternative responses eliminates the need to continue searching for an unavailable target response. In contrast, there is only one acceptable response for each stimulus on the confrontation naming task. It may be the lack of availability of specific, acceptable responses which leads to perseveration. The results for word list and design generation are equally notable for the absence of much perseveration in aphasia and the consistent presence of a low level of perseveration in controls. The explanation for these results is almost certainly multi-factorial. It seems likely, for example, that increased memory and attentional demands contribute to the increased perseveration in controls (who produce the greatest number of responses) on the subject-controlled tasks. The lower levels of perseveration in aphasic subjects, on the other hand, might be attributable to reduced requirements for specific access and retrieval on the subject-controlled tasks. The possibility that perseveration in aphasia is linked to a failure to access specific information was independently suggested by the negative correlation between perseveration and naming scores and discussed above. In conclusion, perseveration does playa special role in the language deficits of many aphasic subjects. Severity of perseveration in aphasia is influenced by task variables, occurring more often on a task in which responses were constrained by specific stimuli than on an open-ended task, and by stimulus variables, occurring less often on drawing than on naming to command. The nature of perseveration in aphasia is consistently recurrent. Subject variables such as location of lesion, general level of intellectual functioning, and severity and type of aphasia also contribute to the pattern and degree of perseveration in aphasia. The findings of this study have direct applicability to the development of perseveration de.;.blocking programs for use in aphasia therapy.
ABSTRACf
We developed a battery of tests to evaluate the relationship of perseveration to aphasia, and tested 44 subjects (18 with aphasia, 13 with right hemispheric lesions, 13 normal controls). Several major findings emerged: (1) left hemispheric, posteriorly located, aphasia producing lesions also produced abundant perseverations, both verbal and non-verbal, which were primarily recurrent in type; (2) right hemispheric lesions produced few perseverations, and these were pri-
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marily of the continuous type; (3) more than half of the verbal recurrent perseverations of aphasia on a naming task were semantic in nature. We conclude that recurrent perseveration has a special, perhaps integral, link to language disorders of aphasia, particularly fluent aphasia associated with posterior lesions. Acknowledgements. Research reported in this paper was supported in part by funds from the Medical Research Service of the Veterans Administration and by NIH grant number NS06209. We thanks Drs. Martha Farah, Hiram Brownell, and Marlene Berman for . help in the development of this paper.
REFERENCES
ALLISON, R., and HURWITZ, L. On perseveration in aphasics. Brain, 90: 429-448; 1967. BUCKINGHAM, H. Perseveration in aphasia. In S. Newman and R. Epstein (Eds.), Current Perspectives in Dysphasia. Edinburgh: Churchill Livingstone, 1985. FOLSTEIN, M., FOLSTEIN, S., and McHUGH, P. "Mini-Mental State": A practical method for grading the cognitive state of patients for the clinician. Journal of Psychiatric Research, 12: 189-198, 1975. GOODGLASS, H., and KAPLAN, E. The Assessment of Aphasia and Related Disorders. Philadelphia: Lea and Febiger, 1983. HALPERN, H. Effect of stimulus variables on verbal perseveration of dysphasic subjects. Perceptual and Motor Skills, 20: 421-429, 1965. HELMICK, J., and BERG, C. Perseveration in brain-injured adults. Journal of Communication Disorders, 9: 143-156, 1976. JONES-GoTMAN, M., and MILNER, B. Design fluency: The invention of nonsense drawings after focal cortical lesions. Neuropsychologia, 15: 658-674, 1977. KAPLAN, E., GoODGLASS, H., and WEINTRAUB, S. Boston Naming Test, Philadelphia: Lea and Febiger, 1983. MATEER, C. Impairments of nonverbal oral movements after left hemisphere damage: a follow up analysis of errors. Brain and Language, 6: 334-341, 1978. SANDSON, J., and ALBERT, M.L. Varieties of perseveration. N europsychologia, 22: 715-732, 1984. SANTO-PIETRO, M., and RIGRODSKY, S. The effect of temporal and semantic conditions on the occurrence of the error response of perseveration in adult aphasics. Journal of Speech and Hearing Research, 25: 184-192, 1982. SCARBOROUGH, D.L., CORTESE, c., and SCARBOROUGH, H.S. Frequency and repetition effects in lexical memory. Journal of Experimental Psychology: Human Perception and Performance,3: 1-17, 1977. SHINDLER, A., CAPLAN, L., and HIER, D. Intrusions and perseverations. Brain and Language,23: 148-158, 1984. THURSTONE, L., and THURSTONE, T. Primary Mental Abilities. Chicago: Science Research Associates, 1962. Martin L. Albert, Jennifer Sandson, Department of Neurology, Boston, VA Hospital, 150 South Huntington Avenue, Boston, Massachusetts, 12130.
Studies of perseveration in aphasia have generally considered perseverative deficits to be orthogonal to linguistic deficits. These studies usually approach perseveration from one of three perspectives, that of task variables (e.g. automatic versus non-automatic); stimulus variables (e.g. modality of input); and subject variables (e.g. location, size, and etiology of lesion). In the present study, we consider the possibility that perseveration has a special, and perhaps integral, link to aphasia, while systematically exploring it from all three perspectives. We have recently proposed a taxonomy of perseverative behavior consisting of three categories: recurrent, continuous, and stuck-in-set perseveration (Sandson and Albert, 1984). Recurrent perseveration is the inappropriate recurrence of a previous response following intervening production or a subsequent stimulus. Continuous perseveration is the inappropriate prolongation or continuation without cessation of a behavior. Stuck-in-Set perseveration is the inappropriate maintenance of a category or framework. While all three categories have been reported in patients with aphasia, recurrent perseveration is by far the most common and is the focus of the current study. Before discussing our experiments, we shall review previous studies of perseveration in aphasia, focusing respectively on task, stimulus, and subject variables.
Task Variables
Perseveration in aphasia has been shown to be more easily elicited by some tasks, both verbal and non-verbal, than by others. Allison and Hurwitz (1967) tested a mixed group of 24 aphasic patients on a series of tasks including: searching for objects; drawings and constructions; exeCortex (1986) 22, 103-115
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Martin L Albert and Jennifer Sandson
cuting gestures and pantomime; carrying out verbal commands; repeating and reversing series; naming seen objects; naming objects from memory; reading; writing; and spontaneous speech. Sixteen subjects perseverated on at least one task and no subject perseverated on all tasks. Per severation was common in response to verbal commands, in naming seen objects, in reversing over-learned series, in writing (although only in association with other dysgraphia), and in spontaneous speech. It was unusual in naming from memory and in reading. Helmick and Berg (1976) examined 30 brain damaged' patients, 18 with aphasia, on a similar battery of tests. They found perseveration, which was significantly more frequent in patients with aphasia, to be more common on reversing series, writing sentences, and drawing designs from memory, and least common on answering short questions, defining words, and describing pictures. Santo-Pietro and Rigrodsky 0982) elicited significantly fewer perseverations on a word reading task than on picture naming or sentence completion tasks utilizing similar stimuli. In all three studies, perseverations usually consisted of inappropriate repetitions of previously produced responses following one or more subsequent stimuli, i.e. recurrent perseveration. Stimulus Variables
In some cases, perseveration is more easily elicited by certain classes of stimuli than by others, even when utilized for the same task. Halpern (1965) presented 33 aphasic subjects of mixed etiology with 72 words for verbalization. Each word was presented in a visual, an auditory, and an auditory-visual modality. Perseveration correlated with stimulus length in all modalities and with abstractness in the visual modality. There was no correlation between perseveration and word frequency or part of speech. Santo-Pietro and Rigrodsky (1982), on the other hand, reported a significant effect of semantic difficulty (determined by word frequency) on perseveration. They also demonstrated a significant decrease in perseveration when inter-trial intervals were increased from one to ten seconds. Subject Variables
Research has also focused on the relation of perseveration to variables such as location, etiology, and size of lesion, time post onset, and aphasia type. Shindler, Caplan and Hier (1984) administered tests of confrontation naming, word association, and vocabulary definition to 20 aphasic patients. Five of the six patients (83%) with Wernicke's aphasia, three of the six patients (50%) with Broca's aphasia, and three of the eight
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patients (38%) with anomic aphasia produced at least one intrusion. Santo-Pietro and Rigrodsky (1982) also reported significantly fewer perseverations in Broca's than in Wernicke's and anomic aphasia. Mateer (1978) found that both aphasic (fluent) and non-aphasic patients with left hemisphere damage perseverated more on a task of imitating oral movements than either right hemisphere patients or controls. Helmick and Berg (1976) and Allison and Hurwitz (1967) noted significantly more perseveration in patients with aphasia of vascular etiology than in patients with tumor or trauma. Both studies also described a decrease in perseveration as a function of time elapsed since onset. Santo-Pietro and Rigrodsky, though, did not find differences between patients more or less than one year post onset. In summary
Studies of perseveration in aphasia to date demonstrate that perseveration, particularly of the recurrent variety, is a common symptom in aphasia. These results suggest that recurrent perseveration may be closely linked to (may even comprise an integral part of) specific language deficits in aphasia. The occurrence of perseveration in aphasia, however, seems to be related to specific task, stimulus, and subject variables, in a manner which has not yet been systematically explored. The goal of the study reported in this paper was a systematic exploration of the effects of selected task variables (especially that of examiner versus subject controlled presentation), stimulus variables (especially .verbal versus non-verbal) and subject variables (such as location of lesion and aphasia type) on perseveration in aphasia. We hypothesized that perseveration on both verbal and non-verbal tasks would be especially linked to fluent aphasia, and would be particularly common following posterior lesions in the left hemisphere. MATERIALS AND METHODS
Subjects
Eighteen aphasic patients with left hemisphere lesion, 13 patients with right hemisphere lesion, and 13 hospitalized controls with no known cerebral lesion were tested for recurrent perseveration. Neurologically impaired subjects were volunteers from the Aphasia/Neurobehavior and Rehabilitation Units at the Boston Veterans Administration Medical Center. Control subjects were volunteers from the Orthopedics Service. Patients with history of progressive cognitive decline or psychiatric illness were excluded. The mean age, education, score on the Mini-Mental State examination (Folstein, Folstein and McHugh, 1975), and time elapsed post-onset for each group are presented in Table I. Group differ-
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TABLE I
Mean Age, Education, Mental Status Score, and Time Post-Onset for the Three Subject Groups Aphasic (N = 18)
Right hemisphere (N = 13)
Age
56.94 (11.5)
Education (in years) Mental status score
13.50 (2.9) 23.82 (4.0)
52.46 (12.4) 11.91 (2.0) 25.64 (2.0)
Time post-onset (in months)
20.15 (27.8)
45.15 (70.1)
Control (N 13)
=
49.08 (13.9) 13.62 (2.1) 27.69 (2.3)
Numbers in brackets are standard deviations.
ences were not significant for any measures except mental status score. This effect was attributable to significantly lower performance by the aphasic group than by the controls (t = 3.017, dJ. = 28, P = .017) due to the large linguistic component of the Mini-Mental State examination. 11.1 % of aphasic and 7.6% of right hemisphere patients were left-handed. Aphasia types spanned the complete range assigned by the Boston Diagnostic Aphasia Examination (GoodgIass and Kaplan, 1983). Ten patients were classified as fluent and eight as non-fluent. Lesion localization was determined by computerized axial tomography. Eight of the 18 aphasics had lesions involving only one lobe, ten had lesions involving two or more lobes. Pathological involvement of frontal lobe was found in 11 aphasic subjects, parietal lobe in 10 subjects, and temporal lobe in 10 subjects. CT scan uncovered clinically unsuspected small right hemisphere lesions in three aphasic sUbjects. Information about volume of lesion was not available at the time of this analysis. Detailed CT scan information is not available for many of our patients with right hemisphere damage. Most of our subjects with right hemisphere damage had been transferred from other hospitals to our Rehabilitation service, which does not routinely obtain CT scans. Diagnosis of right hemisphere damage was thus primarily based on history of illness, clinical examination, and brief radiological reports from other hospitals. No patient in the right hemisphere group had a known lesion in the left hemisphere.
Experimental Test Procedures Four tests of recurrent perseveration were administered in the same order to all subjects. These tests comprised the first section of a larger battery. In the order of administration, they included: (1) a test of confrontation naming; (2) drawing objects to command; (3) a word list generation task; and (4) a design generation task.
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In the confrontation naming task, subjects were asked to name 15 pictures chosen from the Boston Naming Test (Kaplan, Goodglass and Weintraub, 1983) ranging in familiarity from tree to trellis. Several of the pictured items (e.g. harmonica and accordian; faucet, funnel, and nozzle) are related in meaning, and several begin with the same sound (e.g. tree, trelllis). Semantic cues designed to facilitate recognition (e.g. "used for cutting" for scissors) were provided- in response to failures of recognition. Phonological cues consisting of the first phoneme or consonant cluster were provided in response to other naming failures. Responses were recorded by the examiner during testing. The drawing task consisted of drawing six objects from memory: (1) a clock with numbers and the hands set to ten minutes after eleven; (2) a daisy; (3) a Christmas tree with decorations; (4) a sailboat; (5) a tree other than a Christmas tree; and (6) a hurtlau hand. The stimuli were selected so that each object could contain elements in common with the preceding drawing. In the word list generation (FAS) task (Thurstone and Thurstone, 1962), subjects were asked to list as many words as they could think of in one minute starting with each of the letters f, a, and s. Subjects were instructed not to list proper nouns or derivatives of words previously listed. Responses were recorded by the examiner as they were produced. The design generation task (lones-Gotman and Milner, 1977) consisted of having subjects produce as many different designs containing four distinct lines as possible in a four minute period. Subjects were provided with examples of possible designs containing straight and curved lines on the response sheet. Cognitive status was estimated by performance on the Mini-Mental State Examination (Folstein, Folstein and McHugh, 1975). This short standardized test consists of items evaluating orientation, registration, attention and calculation, and language.
Scoring Procedures Protocols from the aphasic group were scored by two independent raters. Inter-rater reliabilities were computed and found to be high (r > .90) for all tests. Differences between the raters were resolved through discussion. There were two ratings of perseveration for each subject on the naming test. Recurrent (lexical) perseveration was defined as the repetition of all or part (e.g. one or more syllables) of a previous response to a subsequent stimulus (e.g. the re-utterance of faucet in response to funnel, or the production of vinor for trellis one stimulus after the presentation of a visor). Total number of perseverations included lexical recurrent perseverations as well as mUltiple repetitions of the same word during one trial (e.g. funnel, funnel, funnel) and inappropriate recurrences of individual sounds or clusters (e.g. paucet for faucet following plug). The percentage of each subject's responses containing perseveration and the percentage of subjects producing one or more perseverations were both computed with the total perseveration score. There were two perseveration scores for each subject on the drawing task. These were a dichotomous score reflecting either the presence or absence of perseveration and the total number of perseverations across drawings. Perseverations included inappropriate recurrences after intervening drawing (Figure I) and inappropriate continuations of a particular segment (Figure 2).
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Martin L Albert and Jennifer Sane/son
Fig. 1 - Recurrent perseveration, produced by an aphasic patient, resulting in the production of two lOs on the drawing of a clock.
Both a dichotomous (present/absent) and a total perseveration score were also computed for the word fluency test. The percentage of perseverations per total responses (acceptable and non-acceptable) was computed using the total perseveration score. Only exact repetitions were considered to be perseverations. Because some derivatives are orthographically diverse, consistency in scoring could only be achieved by considering all derivatives (including phonologically similar pairs such as "sanity" following "sane") as incorrect but not perseverative. Words from a previous category, however, were considered perseverations. Design fluency was scored in the same manner as the word fluency test. Only exact reproductions were considered to be perseverations. Figures differing from previous productions in angle or orientation (e.g. a diamond following a square) were considered to be acceptable productions. Figures differing from previous productions only in size were considered perseverations. RESULTS
On the confrontation naming test, aphasic subjects correctly named significantly fewer items than either patients with right hemisphere damage or controls. Significant group effects were also obtained on the confrontation naming test for number of recurrent lexical perseverations, total number of perseverations, percentage of each subject's responses containing perseveration, and percentage of subjects producing one or more perseverations (Table II). These effects are attributable to significantly greater perseveration by the aphasics than by either of the other two groups. Perseveration in the aphasic group was negatively correlated
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TABLE II Perseveration on Confrontation Naming Aphasic
Right hemisphere
Control
Avs. RH A vs. C
Number of items named correctly
7.28 (4.6)
12.23 (2.8)
13.54 (0.9)
t (29)=3.35** t (29)=4.68**
Number of lexical perseverations
1.28 (1.0)
0.15 (0.4)
0.15 (0.5)
t (29)=3.60** t (29)=3.44**
Total number of perseverations
1.78 (1.4)
0.15 (0.4)
0.15 (0.5)
t (29)=4.07** t (29)=3.96**
14.31 (11.7)
1.06 (2.5)
1.02 (3.5)
t (29)=3.88** t (29)=3.83**
72.2
15.4
07.7
Mean ratio of perseveration total responses Percentage of Ss perseverating at least once
chF (1)= 9.8** chF (1)= 12.8**
** p<.Ol. Numbers in brackets are standard deviations.
with number of items correctly named (r = .549, P < .05). Right hemisphere patients did not differ from the controls on any measure. Group effects remained robust when the contribution of time post onset and mental status score were partialled out through analysis of covariance. More than half (52.2%) of all lexical perseverations ·produced by patients in the aphasic group were semantically related to the current target. These included, for example, the recurrence of faucet in "running faucet" in response to nozzle, and the production of "hartical" in response to accordian five stimuli subsequent to the picture of a harmonica. Perseveration on confrontation naming was associated with posterior, rather than anterior, lesions. Three of the five aphasic subjects not producing any perseveration on confrontation naming had lesion restricted to the frontal lobe. One non-perseverator had a primarily frontal lesion extending throughout the perisylvian region and another had a small lesion lateral to the left occipital hom. All but the last were non-fluent; and all correctly named at least ten of the fifteen items. In contrast, only one of eight aphasic subjects producing three or more perseverations (severe perseverators) had lesions restricted to the frontal lobe. Five of the severe perseverators had frontal involvement, five had parietal involvement, and six had temporal lobe involvement. Similarly, only one of the five subjects producing one or two perseverations (moderate perseverators) had a lesion restricted to the frontal lobe. Of the remaining four, one had frontal involvement, three parietal involvement and three temporal involvement. There were no instances of perseveration on the drawing protocols of
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Martin L Albert and Jennifer Sandson TABLE III
Perseveration on Drawing to Command Aphasic
Right hemisphere
Avs. RH
Percent of subjects perseverating at least once
44.4
23.1
chF (1)= 1.48
Mean number of perseverations per protocol
.889 (1.2)
.231 (0.4)
t (29)= 1.84
Numbers in brackets are standard deviations.
control subjects (Table III). Control subjects were thus excluded from the statistical analyses of perseveration on the. drawing task. Patients with right hemisphere damage did not differ from the aphasic patients with respect to either the percentage of subjects in each group producing perseveration or the number of perseverations per protocol. There was no clear pattern of lesion localization distinguishing the aphasic subjects who perseverated on the drawing task. The nature of the perseverations produced on drawing by the two groups of brain damaged subjects, however, was qualitatively different. Fourteen of the sixteen perseverations produced by the aphasic subjects were recurrent in nature, consisting either of repetition of numbers on the
Fig. 2 - Continuous perseveration, produced by a patient with right hemisphere damage, resulting in the production of six fingers in the drawing of a hand.
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111
clock or of the inappropriate recurrence of a feature from a previous drawing (Figure 1). Only two of the sixteen instances (12.5%) were continuous, involving the production of an extra finger on the hand. In contrast, the few perseverations produced by the right hemisphere patients were primarily of the continuous variety (Figure 2). The two brain-damaged groups produced fewer acceptable responses than the controls on both the world list and design generation tasks. The patients with right hemisphere damage generated more words on the F AS task than the aphasics, but the two groups did not differ on design generation. There were no significant differences with respect to perseveration on either of these subject-controlled tasks. The number of acceptable responses, number of perseverations, and percentage of responses that were perseverations are presented in Tables IV and V.
TABLE IV
Perseveration on Word List Generation Aphasic
Right hemisphere
Control
A vs. RH Avs. C
Number of acceptable responses produced
11.92 (8.7)
23.38 (9.3)
3S.69 (8.4)
t (24)=3.13* t (24)=6.80**
Number of perseverations
1.00 (1.2)
1.00 (1.1)
Perseverationl Total responses :p < .05.
6.43 (8.8)
3.67 (4.2)
2.1 (2.3) ~ 4.42 (4.3)
t (24)=0.00
t (24)= 1.44
t (24)=0.98
t (24)=0.71
**p < .01. Numbers in brackets are standard deviations.
TABLE V
Perseveration on DeSign Generation Aphasic
Right hemisphere
Control
A vs. RH A vs. C
Number of acceptable designs
10.22 (S.4)
7.77 (6.1)
lS.8S (S.3)
t (28)= 1.23 t (28)=2.61 *
Number of' perseverations
1.44 (1.9)
0.77 (1.0)
0.54 (1.2)
t (28)= 1.60
9.81 (13.3)
6.74 (9.4)
2.S2 (S.1)
t (28)=0.81 t (28)= 1.37
Perseverationl Total responses *p < .05.
Numbers in brackets are standard deviat(ons.
t (28)= 1.26
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Martin L Albert and Jennifer Sandson
DISCUSSION
Left hemispheric aphasia-producing lesions often produce perseveration as welL More aphasic subjects than controls produced perseveration (generally of the recurrent variety) on two examiner controlled tasks, one verbal and one non-verbal, but not on two subject controlled tasks. Patients with right hemisphere damage did not differ from the controls with respect to perseveration on any task. Aphasic patients produced significantly more perseverations than either patients with right hemisphere damage or age-matched controls on a confrontation naming task. Most of these perseverations consisted of the inappropriate recurrence of all or part (at least one syllable) of a previously produced word. The remaining perseverations consisted either of multiple productions of an utterance in response to one stimulus or the inappropriate recurrence of a sound or consonant cluster on a subsequent stimulus. Perseveration on the confrontation naming test was primarily associated with aphasia due to posterior left hemisphere lesions. Perseveration was most frequent in patients with temporal or parietal involvement (9/10 patients with temporal involvement and 8110 with parietal involvement produced at least one perseveration), and least frequent in patients with frontal involvement (7/11). Three of the five aphasic patients with lesions restricted to the left frontal region produced no perseverations. We suggest several possible explanations for these results. The first is that decreased verbal fluency associated with frontal lobe lesions results in decreased output, inhibiting both intended responses and perseverations. This alternative is supported by the presence of frontal lobe lesions in the. three subjects with the highest ratio of perseveration to total responses. However, this explanation cannot be the only one, since the three aphasic non-perseverators with lesions restricted to the left frontal lobe all correctly named at least ten items. A second explanation is that verbal recurrent perseveration has a preferential link with the temporal or parietal lobes, particularly within the zone of language. Our anatomicoclinical correlations support this alternative. A third possibility, that perseveration is simply associated with larger lesions regardless of location, is the focus of current study. The correlation between perseveration and anomia raises questions about the cognitive mechanisms of verbal recurrence within the context of confrontation naming. One possible explanation is that verbal recurrences occur spontaneously, perhaps as the result of an abnormal priming mechanism (e.g. Scarborough, Cortese and Scarborough, 1977) which is independent of the naming process. Another alternative is that verbal recurrences occur only if triggered by a disruption in the naming process,
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perhaps as a result of failure to locate a target in semantic memory or the lexicon. Either alternative is compatible with the finding of increased perseveration in patients with greater word finding difficulty, as the production of a correct response might inhibit the spontaneous recurrences of the first hypothesis. Each of these alternative hypotheses could be tested by manipulating the difficulty of target production and observing changes in perseveration. Another major finding with respect to perseveration on the naming task is the extent to which perseverative responses were semantically related to the actual target. This result raises questions about the nature of the re-accessed mental representations and the cognitive processes involved in verbal recurrent perseveration. It suggests, perhaps, that semantic representations located in long term memory are at least as likely as lexical or articulatory representations (located in a short term memory buffer) to be re-activated. This possibility can be investigated by systematically manipulating the semantic and phonological relatedness of stimuli and evaluating their effects on perseveration. The nature of perseveration on this naming task leads us to speculate about the possible role of perseveration in specific linguistic deficits in aphasia. It seems likely, for example, that perseveration contributes to the production of semantic and literal paraphasias and neologisms, especially in aphasic patients with poor self-monitoring (see Buckingham, 1985). On the other hand, perseverative tendencies, in patients with intact self monitoring abilities, might contribute to blocking and thus to reduced output. Aphasic patients produced considerably more perseveration than normal controls on the drawing task. In addition, qualitative analysis of the perseverations in the drawings of aphasic patients uncovered differences from those produced by patients with right hemisphere damage. Aphasics' perseverations were almost always recurrent in type, consisting either of reproduction following intervening marking within a drawing or of carry-over of a feature from one drawing to a subsequent drawing. In contrast, the few perseverations produced by the right hemisphere subjects were continuous, consisting of inappropriate prolongation, such as the production of a sixth finger on a hand. The nature of the perseveration interfering with drawing in aphasic patients, then, seems to be the same as that interfering with naming, and different from that which occurs in patients with right hemisphere injury. There were no group differences for either word list or design generation. These tasks differ from confrontation naming and drawing to command in that responses are subject-regulated, rather than tied to specific stimuli controlled by the examiner. The subject controlled tasks, unlike the examiner-controlled tasks, require subjects to pay attention to
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Martin L Albert and Jennifer Samison
and remember their previous responses. The subject-regulated tasks, on the other hand, seem to require less specific retrieval than the examinercontrolled tasks. Once subjects have accessed the appropriate region of the lexicon on the F AS task, there are numerous acceptable responses available for retrieval. The presence of alternative responses eliminates the need to continue searching for an unavailable target response. In contrast, there is only one acceptable response for each stimulus on the confrontation naming task. It may be the lack of availability of specific, acceptable responses which leads to perseveration. The results for word list and design generation are equally notable for the absence of much perseveration in aphasia and the consistent presence of a low level of perseveration in controls. The explanation for these results is almost certainly multi-factorial. It seems likely, for example, that increased memory and attentional demands contribute to the increased perseveration in controls (who produce the greatest number of responses) on the subject-controlled tasks. The lower levels of perseveration in aphasic subjects, on the other hand, might be attributable to reduced requirements for specific access and retrieval on the subject-controlled tasks. The possibility that perseveration in aphasia is linked to a failure to access specific information was independently suggested by the negative correlation between perseveration and naming scores and discussed above. In conclusion, perseveration does playa special role in the language deficits of many aphasic subjects. Severity of perseveration in aphasia is influenced by task variables, occurring more often on a task in which responses were constrained by specific stimuli than on an open-ended task, and by stimulus variables, occurring less often on drawing than on naming to command. The nature of perseveration in aphasia is consistently recurrent. Subject variables such as location of lesion, general level of intellectual functioning, and severity and type of aphasia also contribute to the pattern and degree of perseveration in aphasia. The findings of this study have direct applicability to the development of perseveration de.;.blocking programs for use in aphasia therapy.
ABSTRACf
We developed a battery of tests to evaluate the relationship of perseveration to aphasia, and tested 44 subjects (18 with aphasia, 13 with right hemispheric lesions, 13 normal controls). Several major findings emerged: (1) left hemispheric, posteriorly located, aphasia producing lesions also produced abundant perseverations, both verbal and non-verbal, which were primarily recurrent in type; (2) right hemispheric lesions produced few perseverations, and these were pri-
Perseveration in aphasia
115
marily of the continuous type; (3) more than half of the verbal recurrent perseverations of aphasia on a naming task were semantic in nature. We conclude that recurrent perseveration has a special, perhaps integral, link to language disorders of aphasia, particularly fluent aphasia associated with posterior lesions. Acknowledgements. Research reported in this paper was supported in part by funds from the Medical Research Service of the Veterans Administration and by NIH grant number NS06209. We thanks Drs. Martha Farah, Hiram Brownell, and Marlene Berman for . help in the development of this paper.
REFERENCES
ALLISON, R., and HURWITZ, L. On perseveration in aphasics. Brain, 90: 429-448; 1967. BUCKINGHAM, H. Perseveration in aphasia. In S. Newman and R. Epstein (Eds.), Current Perspectives in Dysphasia. Edinburgh: Churchill Livingstone, 1985. FOLSTEIN, M., FOLSTEIN, S., and McHUGH, P. "Mini-Mental State": A practical method for grading the cognitive state of patients for the clinician. Journal of Psychiatric Research, 12: 189-198, 1975. GOODGLASS, H., and KAPLAN, E. The Assessment of Aphasia and Related Disorders. Philadelphia: Lea and Febiger, 1983. HALPERN, H. Effect of stimulus variables on verbal perseveration of dysphasic subjects. Perceptual and Motor Skills, 20: 421-429, 1965. HELMICK, J., and BERG, C. Perseveration in brain-injured adults. Journal of Communication Disorders, 9: 143-156, 1976. JONES-GoTMAN, M., and MILNER, B. Design fluency: The invention of nonsense drawings after focal cortical lesions. Neuropsychologia, 15: 658-674, 1977. KAPLAN, E., GoODGLASS, H., and WEINTRAUB, S. Boston Naming Test, Philadelphia: Lea and Febiger, 1983. MATEER, C. Impairments of nonverbal oral movements after left hemisphere damage: a follow up analysis of errors. Brain and Language, 6: 334-341, 1978. SANDSON, J., and ALBERT, M.L. Varieties of perseveration. N europsychologia, 22: 715-732, 1984. SANTO-PIETRO, M., and RIGRODSKY, S. The effect of temporal and semantic conditions on the occurrence of the error response of perseveration in adult aphasics. Journal of Speech and Hearing Research, 25: 184-192, 1982. SCARBOROUGH, D.L., CORTESE, c., and SCARBOROUGH, H.S. Frequency and repetition effects in lexical memory. Journal of Experimental Psychology: Human Perception and Performance,3: 1-17, 1977. SHINDLER, A., CAPLAN, L., and HIER, D. Intrusions and perseverations. Brain and Language,23: 148-158, 1984. THURSTONE, L., and THURSTONE, T. Primary Mental Abilities. Chicago: Science Research Associates, 1962. Martin L. Albert, Jennifer Sandson, Department of Neurology, Boston, VA Hospital, 150 South Huntington Avenue, Boston, Massachusetts, 12130.