J. C O M M U N . DISORD.
23 (1990), 151-161
SPEECH RATE AND SYNTACTIC COMPLEXITY EFFECTS ON THE AUDITORY COMPREHENSION OF ALZHEIMER PATIENTS C H E R Y L K. T O M O E D A , K A T H R Y N A. B A Y L E S , D A N I E L R. B O O N E Department of Speech and Hearing Sciences, University of Arizona
A L F R E D W. K A S Z N I A K Department of Psychology, University of Arizona
T H O M A S J. S L A U S O N Restorative Services, Tucson Medical Center
The purpose of this investigation was to examine the effects of speech rate and syntactic complexity on the auditory language comprehension of individuals with presumptive Alzheimer's disease, compared to healthy elderly controls. Three presentation rates and command statements of increasing syntactic complexity were used. Although rate of presentation did not significantly affect comprehension in either group, both groups demonstrated increased difficulty with stimuli of greater syntactic complexity, with Alzheimer's patients performing significantly poorer at all levels.
INTRODUCTION Although a literature now exists documenting the deleterious effects of Alzheimer's disease (AD) on communicative function (Bayles, 1982; Bayles and Kaszniak, 1987; Bayles and Tomoeda, 1983; Cummings, Benson, Hill, and Read, 1985; Martin and Fedio, 1983; Obler, 1983; Schwartz, Matin, and Saffran, 1979), few investigations of the effect of therapeutic intervention on communicative ability have been published. Such investigations seem reasonable because of the evidence from longitudinal studies that many patients remain in the various stages of dementia for months and even years (Bayles and Kaszniak, 1987; Reisberg et al., 1986; Storandt, Botwinick, and Danziger, 1984). During these plateau periods, linAddress correspondence to Cheryl K. Tomoeda, Department of Speech and Hearing Sciences, University of Arizona, Tucson, AZ 85721. © 1990 by Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010
151 0021-9924/90/$3.50
152
C.K. TOMOEDA et al.
guistic and other cognitive functions remain stable and patients may be responsive to palliative interventions designed to help them perform optimally. Bayles and Kaszniak (1987) have suggested that the systematic manipulation of certain communication variables, such as rate and syntactic complexity, may assist patients in functioning maximally. A rationale for the supposition that speech rate may affect linguistic comprehension comes from aphasiologists who report improved comprehension in aphasia patients when speech rate is slower than normal (Gordon, 1970; Lasky, Weidner, and Johnson, 1976; Pasheck and Brookshire, 1982; Weidner and Lasky, 1976). This finding has been interpreted as evidence that a temporal processing deficit underlies the auditory comprehension impairment in aphasia. The effect of speech rate on language comprehension in Alzheimer's patients has not been established, and predicting rate effects is complicated by the nature of patients' memory deficits. AD patients experience deficits in working memory and secondary memory with particular impairment in the semantic and episodic memory subsystems of secondary memory (Bayles and Kaszniak, 1987). In patients with these memory deficits, slowing speech rate may exacerbate their inability to remember the stimuli. Syntactic complexity, like speech rate, is known to affect linguistic comprehension of aphasia patients (DeRenzi and Vignolo, 1962; Kreindler, Gheorghita, and Voinescu, 1971). That is, simplifying syntax facilitates linguistic comprehension. It might be expected that the same would hold true for AD patients, in whom auditory comprehension problems are well documented (Appell, Kertesz, and Fisman, 1982; Bayles and Kaszniak, 1987; Cummings, Benson, Hill, and Read, 1985; Kaszniak, Wilson, Fox, and Stebbins, 1986). Yet several investigators have reported that syntactic knowledge is generally intact until the late stages of the disease (Bayles, 1982; Bayles and Kaszniak, 1987; Hier, Hagenlocker, and Shindler, 1985; Schwartz, Marin, and Saffran, 1979). As yet, empirical support of facilitating effects, on auditory comprehension of AD patients, from slowing speech rate and decreasing syntactic complexity is lacking. Therefore, this study was designed to explore in AD patients the effects of speech rate and syntactic complexity on auditory language comprehension as measured by performance on items selected from the R e v i s e d Token Test (McNeil and Prescott, 1978).
METHODS Subjects Thirteen individuals with presumptive AD and 17 healthy elderly controls participated in the study. All participants passed a pure-tone audiometric screening test by demonstrating hearing levels at less than 40 dB averaged
RATE AND SYNTACTIC COMPLEXITY
153
Table 1. Demographic Characteristics of Subjects Sex Groups Elderly controls Alzheimer's patients
N
X Age
M
F
X Estimated 1.Q.
X GDS" stage
17
70.7
5
12
115
1.0
13
76.4
2
11
111
4.8
a GDS, Gt)bal Deterioration Scale.
across four speech frequencies (500, 1000, 2000, and 4000 hertz) for each ear. In addition, each subject met the following selection criteria: (1) native speaker of English; (2) right-handed; (3) adequate visual acuity to distinguish colors and shapes; (4) nonalcoholic; and (5) normal premorbid intelligence as determined by a validated regression equation that uses demographic information to estimate intelligence (Wilson, Rosenbaum, and Brown, 1979). Elderly control subjects were community-residing individuals, who were either spouses of AD subjects or members of local volunteer organizations. No previous or current neurological or psychiatric illnesses were known to exist in these subjects. All AD patients met the diagnostic criteria for probable AD, as specified by the NINCDS-ADRDA Task Force on Alzheimer's Disease (McKhann et al., 1985). Severity of dementia was determined using the Global Deterioration Scale (Reisberg, Ferris, and Crook, 1982), a seven-point rating scale that describes stages of dementia with well-specified observational criteria. A GDS rating of 1 represents normal behavior, and stage 7 represents severe dementia. Demographic characteristics of the subject groups are presented in Table 1. A borderline statistically significant difference was obtained (t = -2.04, p = .051) between the two groups in relation to their mean age. This mean difference was of a magnitude less than six years. Such a difference is quite unlikely to affect results, as age effects in normal individuals (in the range of 29-76 years) have not been found with the type of task employed in the present study (DeRenzi, 1979; Noll and Randolph, 1978). No difference in estimated premorbid intelligence was observed (t = 1.38, p = .177).
Task Subjects were asked to manipulate tokens in the form of colored wooden circles and squares, in response to audiorecorded command statements. Three speech presentation rates and command statements of increasing
154
C . K . TOMOEDA et al.
syntactic complexity were used. The commands consisted of four sets of ten stimulus sentences from the Revised Token Test (RTT) (McNeil and Prescott, 1978). In this test, examinees demonstrate auditory comprehension of spoken directions by manipulating large and small circles and squares of four different colors. The syntactic complexity of the commands increases with succeeding subtests in the RTT, but the difficulty level of vocabulary remains constant. Thus, stimuli from the Token Test (DeRenzi and Vignolo, 1962) frequently have been used to measure the effect of syntactic complexity on auditory comprehension. In this study, each of the four sets of stimulus commands (one practice set and three scored sets) contained one command from each of the ten R T T subtests. The following is an example of a set constructed for this study: Example of item from: Subtest 1 - - T o u c h the blue square. Subtest 2 - - T o u c h the big green circle. Subtest 3 - - T o u c h the red circle and the white circle. Subtest 4 - - T o u c h the big blue circle and the little green square. Subtest 5 - - P u t the black square by the red circle. Subtest 6 - - P u t the little red circle beside the big blue circle. Subtest 7 ~ P u t the red square to the left of the white circle. Subtest 8 ~ P u t the big black square to the right of the little red circle. Subtest 9 - - T o u c h the blue circle instead of the green square. Subtest 10--1nstead of the big red square touch the big white circle. The order of presentation of command statements was partially randomized. Within each set, the five commands requiring the use of only large tokens (commands from odd-numbered subtests) were presented first, followed by the commands that required both large and small tokens. This was done so the examiner did not have to place or remove the small tokens after each command. Rather, the small tokens only needed to be added once, after the fifth command of each set. The order of command presentations within each subset was randomized. Stimulus commands were recorded on audiotape using three speech rates: a slow rate of 120 words per minute (wpm), a normal rate of 160 wpm, and a fast rate of 200 wpm. Fairbanks (1960) identified the average rate of speech as ranging from 160 to 170 wpm. The slow and fast rates used in this study represent a 25% decrease and increase, respectively, from the normal rate of 160 wpm. A male speaker (DRB, an expert in voice and articulation) was trained to present the stimulus sentences at the different speaking rates. The rate of presentation of each stimulus
RATE AND SYNTACTIC COMPLEXITY
155
sentence was checked by dividing the number of words in the sentence by the time taken to say the sentence. All sentences were within plus-orminus 2 wpm from the target speech rate. In an attempt to control for a possible order effect for presentation rate, two audiorecordings were made. In both recordings, the practice set and the first scored set of ten commands were presented at the normal rate, followed by the two other scored rate conditions. In one recording, the slow rate preceded the fast rate, and in the other recording, the order was reversed. Presentation of the audiorecordings was randomized across subjects. Tokens were placed on a table in front of subjects following the procedures described in the R T T manual. The examiner explained the nature of the task and played the audiotape. After each command was presented, subjects were expected to perform the required task within a 12-second pause that occurred between each stimulus command. This length of time was selected after pilot testing the task with four AD subjects. According to pilot test data, AD subjects performed all the required manipulations of tokens within I0 seconds of the command presentation. In the present study, a point was awarded for each correct, complete response to each command. RESULTS The data were subjected to a mixed factorial analysis of variance (repeated measures) with two within-subjects factors of rate and syntactic complexity and one between-subjects factor for groups. Computation was performed within the S P S S / P C + M A N O V A (Norusis, 1986) statistical analysis software routine. A univariate test of between-subjects effects revealed a significant main effect for group [F(1,28) = 62.12, p < .001]. AD subjects performed significantly more poorly than normals in terms of the number of correct responses across the three rate conditions and ten levels of syntactic complexity. Multivariate tests of significance (Wilk's lambda) were used to assess possible within-subjects effects (see Hertzog and Rovine, 1985, for review of the M A N O V A approach to univariate measures analysis). This procedure was used because Mauchly's test of sphericity (Mauchly, 1940) indicated the inappropriateness of assuming equal variances and covarlances equal to zero for either of the within-subjects effects (p < .05). Mean scores o f the two subject groups for each of the three rate conditions collapsed across the R T T subtest (complexity) levels are shown in Table 2. A significant main effect was not found for rate of stimulus presentation [Wilks lambda = .93, approximate F(2,27) = 1.02, p = .374],
156
C. K. TOMOEDA Table 2. Mean Scores of Healthy Subjects for Each Rate Condition Subtest Levels
Elderly and Alzheimer Collapsed Across the RTT
Healthy elderly Rate
et al.
Alzheimer subjects
x
SD
x
Slow
9.65
0.70
3.85
3.08
Normal
9.12
1.41
3.38
3.04
Fast
8.71
1.49
3.38
2.66
SD
nor was a group by rate interaction obtained [Wilks lambda = .93, approximate F(2,27) = .94, p = .401]. Table 3 contains group means for each of the 10 RTT subtest (complexity) levels, collapsed across rate conditions. A significant main effect for level of syntactic complexity [Wilks lambda = .40, approximate F(9,20) = 3.32, p = .012] was found, although a significant group by complexity interaction was not obtained [Wilks lambda = 0.64, approximate F(9,20) = 1.23, p = 0.3301. Level of syntactic complexity is confounded with sentence length in this study as in everyday communication. In Table 4 are the mean number of subjects who correctly responded to each length of command (number of words per sentence). A clear effect for sentence length is not present, although AD patients responded less well on sentences with eight words or more. Borderline significant interaction effects were found for rate by complexity [Wilks lambda = .21, approximate F(18,ll) = 2.33, p = .077] Table 3.
Mean Scores of Healthy Elderly and Alzheimer Subjects for Each RTT Subtest Level, Collapsed across Rate Conditions Alzheimer RTT subtest levels 1 2 3 4 5 6 7 8 9 10
Healthy
elderly
subjects
x
SD
x
SD
3.00 3.00 2.71 2.88 2.71 2.59 2.76 2.71 2.65 2.47
0.00 0.00 0.47 0.33 0.59 0.62 0.56 0.59 0.61 0.87
2.00 1.69 0.92 0.38 1.08 1.00 1.00 0.69 1.00 0.92
1.32 1.18 1.12 0.65 1.12 1.00 1.15 0.95 0.91 1.04
RATE AND SYNTACTIC COMPLEXITY
157
Table 4. Mean Number of Subjects Correctly Responding to RTT Commands of Increasing Length N u m b e r of words per sentence
Healthy elderly ( N = 17)
Alzheimer's disease (N = 13)
4 6 8 9 10 11 12 13
17.0 17.0 15.3 15.5 15.1 15.0 15.0 15.3
8.0 7.3 4.3 4.0 3.3 4.4 3.0 3.0
and for group by rate by complexity [Wilks lambda = . 19, approximate F(18,11) = 2.57, p = .057]. It should be noted that the less conservative univariate tests (not used for hypotheses-testing here because of violation of sphericity assumptions) o f the rate by complexity and the group by rate by complexity interaction terms were both highly significant (p < .001 and p = .005, respectively). Percentage of correct responses for each group on each of the R T T subtests (complexity) levels for the three rate conditions are displayed graphically in Figure 1.
DISCUSSION The question considered in this study was whether, in AD and healthy elderly control subjects, rate of speech and level of syntactic complexity affect auditory language comprehension as measured by performance on items from the RTT. Level of syntactic complexity, but not speech rate, was found to significantly affect linguistic comprehension in AD patients and elderly controls. Both groups performed best on stimuli from the first two R T T subtests, in which command statements are simple imperatives (e.g., Touch the white square). AD subjects had the most difficulty with subtests 4 and 10. In subtest 4, the stimulus construction is: verb + determiner + 2 modifiers + noun + conjunction + determiner + 2 modifiers + noun (e.g., Touch the big blue circle and the little green square). In subtest 10, there is a main clause and a dependent clause (e.g., Touch the little blue square, if there is a big black circle). With syntactically more complex commands, sentence length increases and the individual must attend to, store, and encode larger amounts of information. Since m e m o r y impairment is a hallmark characteristic of individuals with AD, it is not surprising that the performance of AD patients suffered as syntactic complexity and length increased.
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C.K. TOMOEDA et al.
1.0 0.9 0.8 0.7
'--I---'~-".,.
. J " . . . . . . . . . "-,
..,,V
0.6 0,5 0.4 0.3 0.2
0.1 0.0 o
REVISED TOKEN TEST SUBTESTS Figure 1. Percentage of correct responses for healthy elderly and Alzheimer's disease subjects on each complexity level for each rate.
Although the normal elderly controls and AD patients achieved their highest performance scores in the slow (120 wpm) rate condition, rate of stimulus presentation did not significantly affect the ability of either group to comprehend the stimulus sentences. Our findings appear to support the conclusions of investigators who have found that speech rate alone does not facilitate auditory language comprehension in certain brain-damaged populations (Blumstein, Katz, Goodglass, Shrier, and Dworetsky, 1985; Brookshire and Nicholas, 1984). However, the modest size of the samples in this study make replication of this finding important. Finally, when the within subject effect of syntactic complexity by rate was examined, an interaction effect approached significance (p =- .077) between the ten syntactic complexity levels and the three rate conditions, indicating a trend towards subjects having difficulty with more syntactically complex statements at faster rates. A three-way interaction effect
RATE AND SYNTACTIC COMPLEXITY
159
of borderline significance (p = .057) was obtained for group by complexity by rate. The elderly controls tended to have the most difficulty when more complex sentences were presented at the faster rate. However, with the AD patients, once the stimuli were no longer simple imperatives, rate did not significantly influence sentence comprehension. This is likely due to " f l o o r effects" in patients' performance for the more complex sentences. In summary, AD patients performed significantly worse than the healthy elderly in each rate condition and at each level of syntactic complexity, thereby documenting the profound auditory comprehension deficit experienced by AD patients. While it is acknowledged that the R T T does not measure the entire domain of auditory language comprehension, it does systematically sample one pattern of auditory linguistic processing. With this cautionary note, it is possible to draw some general clinical implications from the study results. The findings of this study indicate that individuals communicating with AD patients can improve patients' ability to comprehend by speaking in short and syntactically simple sentences. Although rate alone did not appear to significantly affect comprehension, the near significant interaction of rate and syntactic complexity suggests that comprehension is reduced when faster, more complex statements are used.
REFERENCES Appell, J., Kertesz, A., and Fisman, M. (1982). A study of language functioning in Alzheimer patients. Brain Lang. 17:73-91. Bayles, K. A. (1982). Language function in senile dementia. Brain Lang. 16:265280. Bayles, K. A., and Kaszniak, A. W. (1987). CommuniCation and Cognition in Normal Aging and Dementia. Boston: College-Hill Pr6s~/Little, Brown & Co. Bayles, K. A., and Tomoeda, C. K. (1983). Confrontation ri~ih~jr/~impairment in dementia. Brain Lang. 19:98-114. Biumstein, S. E., Katz, B., Goodglass, H., Shrier, R., and Dworetsky, B. (1985). The effects of slowed speech on auditory comprehension in aphasia. Brain Lang. 24:246-265. Brookshire, R. H., and Nicholas, L. E. (1984). Consistency of effects of slow rate and pauses on aphasic listener's comprehension of spoken sentences. J. Speech Hear. Res. 27:323-328. Cummings, J. L., Benson, D. F., Hill, M., and Read, S. (1985). Aphasia in dementia of the Alzheimer's type. Neurology 34:394-397. DeRenzi, E. (1979). A shortened version of the Token Test. In F. Boiler and M. Dennis (eds.), Auditory Comprehension: Clinical and Experimental Studies with the Token Test. (pp. 33-34). New York: Academic Press.
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DeRenzi, E., and Vignolo, L. (1962). The Token Test: A sensitive test to detect receptive disturbances in aphasics. Cortex 85:655-678. Fairbanks, G. (1960). Voice and Articulation Drillbook. New York: Harper & Row. Gordon, M. C. (1970). Some effects of stimulus presentation rate and complexity on perception and retention in brain-damaged patients. Cortex 6:273-286. Hertzog, C., and Rovine, M. (1985). Repeated-measures analysis of variance in developmental research: Selected issues. Child Dev. 56:787-809. Hier, D. B., Hagenlocker, K., and Shindler, A. G. (1985). Language disintegration in dementia: Effects of etiology and severity. Brain Lang. 25:117-133. Kaszniak, A. W., Wilson, R. S., Fox, J. H., and Stebbins, G. T. (1986). Cognitive assessment in Alzheimer's disease: Cross-sectional and longitudinal perspectives. Can. J. Neurol. Sci. 13:420-423. Kreindler, A., Gheorghita, N., and Voinescu, I. (1971). Analysis of verbal reception of a complex order with three elements in aphasics. Brain 94:375-386. Lasky, E. Z., Weidner, W. E., and Johnson, J. P. (1986). Influence of linguistic complexity, rate of presentation, and interphrase pause time on auditory-verbal comprehension of adult aphasic patients. Brain Lang. 3:386-395. Martin, A., and Fedio, P. (1983). Word production and comprehension in Alzheimer's disease: The breakdown of semantic knowledge. Brain Lang. 19:124141. Mauchly, J. W. (1940). Significance test for sphericity of a normal n-variate distribution. Ann. Math. Stat. 1] :204-209. McKhann, G., Drachman, D., Folstein, M., Katzman, R., Price, D., and Stadlan, E. M. (1984). Clinical diagnosis of Alzheimer's disease: Report of the NINCDS° ADRDA work group under the auspices of Department of Health and Human Services Task Force on Alzheimer's disease. Neurology 34:939-944. McNeil, M. R., and Prescott, T. E. (1978). Revised Token Test. Baltimore: University Park Press. Noll, J. D., and Randolph, S. R. (1978). Auditory semantic, syntactic, and retention errors made by aphasic subjects to the Token Test. J. Commun. Disord. I 1:543-553. Norusis, M. J. (1986). Advances in Statistics: SPSS/PC + for the I B M PC/XT/ AT. Chicago, IL: SPSS. Obler, L. K. (1983). Language and brain dysfunction in dementia. In S. Segalowitz (ed.), Language Functions and Brain Organization (pp. 267-282). New York: Academic Press. Pashek, G. V., and Brookshire, R. H. (1982). Effects of rate of speech and linguistic stress on auditory paragraph comprehension. J. Speech Hear. Res. 25:377-382. Reisberg, B., Ferris, S. H., and Crook, T. (1982). Signs, symptoms, and course of age-associated cognitive decline. In S. Corkin, K. L. Davis, J. H. Growdon, E. Usdin, and R. L. Wurtman (eds.), Aging: Vol. 19, Alzheimer's Disease: A Report o f Progress (pp. 177-181). New York: Raven Press.
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Reisberg, B., Ferris, S. H., Shulman, E., Steinberg, G., Buttinger, C., Sinaiko, E., Borenstein, J., de Leon, M. J., and Cohen, J. (1986). Longitudinal course of normal aging and progressive dementia of the Alzheimer's type: A prospective study of 106 subjects over a 3.6 year mean interval. Prog. NeuroPsychopharmacol. Biol. Psychiatry 10:571-578. Schwartz, M. F., Marin, O. S. M., and Saffran, E. M. (1979). Dissociations of language function in dementia: A case study. Brain Lang. 7:277-306. Storandt, M., Botwinick, J., and Danziger, W. (1986). Longitudinal changes in patients with mild SDAT and matched healthy controls. In L. W. Poon, T. Crook, B. Gurland, A. W. Kaszniak, L. W. Thompson, K. L. Davis, and C. Eisdorfer (Eds.), Handbook for Clinical Memory Assessment of Older Adults (pp. 277-284). Washington, DC: American Psychological Association. Weidner, W. E., and Lasky, E. Z. (1976). The interaction of rate and complexity of stimulus on the performance of adult aphasic subjects. Brain Lang. 3:3440. Wilson, R. S., Rosenbaum, G., and Brown, G. (1979). The problem of premorbid intelligence in neuropsychological assessment. J. Clin. Neuropsychol. 1:49-53.
23 (1990), 151-161
SPEECH RATE AND SYNTACTIC COMPLEXITY EFFECTS ON THE AUDITORY COMPREHENSION OF ALZHEIMER PATIENTS C H E R Y L K. T O M O E D A , K A T H R Y N A. B A Y L E S , D A N I E L R. B O O N E Department of Speech and Hearing Sciences, University of Arizona
A L F R E D W. K A S Z N I A K Department of Psychology, University of Arizona
T H O M A S J. S L A U S O N Restorative Services, Tucson Medical Center
The purpose of this investigation was to examine the effects of speech rate and syntactic complexity on the auditory language comprehension of individuals with presumptive Alzheimer's disease, compared to healthy elderly controls. Three presentation rates and command statements of increasing syntactic complexity were used. Although rate of presentation did not significantly affect comprehension in either group, both groups demonstrated increased difficulty with stimuli of greater syntactic complexity, with Alzheimer's patients performing significantly poorer at all levels.
INTRODUCTION Although a literature now exists documenting the deleterious effects of Alzheimer's disease (AD) on communicative function (Bayles, 1982; Bayles and Kaszniak, 1987; Bayles and Tomoeda, 1983; Cummings, Benson, Hill, and Read, 1985; Martin and Fedio, 1983; Obler, 1983; Schwartz, Matin, and Saffran, 1979), few investigations of the effect of therapeutic intervention on communicative ability have been published. Such investigations seem reasonable because of the evidence from longitudinal studies that many patients remain in the various stages of dementia for months and even years (Bayles and Kaszniak, 1987; Reisberg et al., 1986; Storandt, Botwinick, and Danziger, 1984). During these plateau periods, linAddress correspondence to Cheryl K. Tomoeda, Department of Speech and Hearing Sciences, University of Arizona, Tucson, AZ 85721. © 1990 by Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010
151 0021-9924/90/$3.50
152
C.K. TOMOEDA et al.
guistic and other cognitive functions remain stable and patients may be responsive to palliative interventions designed to help them perform optimally. Bayles and Kaszniak (1987) have suggested that the systematic manipulation of certain communication variables, such as rate and syntactic complexity, may assist patients in functioning maximally. A rationale for the supposition that speech rate may affect linguistic comprehension comes from aphasiologists who report improved comprehension in aphasia patients when speech rate is slower than normal (Gordon, 1970; Lasky, Weidner, and Johnson, 1976; Pasheck and Brookshire, 1982; Weidner and Lasky, 1976). This finding has been interpreted as evidence that a temporal processing deficit underlies the auditory comprehension impairment in aphasia. The effect of speech rate on language comprehension in Alzheimer's patients has not been established, and predicting rate effects is complicated by the nature of patients' memory deficits. AD patients experience deficits in working memory and secondary memory with particular impairment in the semantic and episodic memory subsystems of secondary memory (Bayles and Kaszniak, 1987). In patients with these memory deficits, slowing speech rate may exacerbate their inability to remember the stimuli. Syntactic complexity, like speech rate, is known to affect linguistic comprehension of aphasia patients (DeRenzi and Vignolo, 1962; Kreindler, Gheorghita, and Voinescu, 1971). That is, simplifying syntax facilitates linguistic comprehension. It might be expected that the same would hold true for AD patients, in whom auditory comprehension problems are well documented (Appell, Kertesz, and Fisman, 1982; Bayles and Kaszniak, 1987; Cummings, Benson, Hill, and Read, 1985; Kaszniak, Wilson, Fox, and Stebbins, 1986). Yet several investigators have reported that syntactic knowledge is generally intact until the late stages of the disease (Bayles, 1982; Bayles and Kaszniak, 1987; Hier, Hagenlocker, and Shindler, 1985; Schwartz, Marin, and Saffran, 1979). As yet, empirical support of facilitating effects, on auditory comprehension of AD patients, from slowing speech rate and decreasing syntactic complexity is lacking. Therefore, this study was designed to explore in AD patients the effects of speech rate and syntactic complexity on auditory language comprehension as measured by performance on items selected from the R e v i s e d Token Test (McNeil and Prescott, 1978).
METHODS Subjects Thirteen individuals with presumptive AD and 17 healthy elderly controls participated in the study. All participants passed a pure-tone audiometric screening test by demonstrating hearing levels at less than 40 dB averaged
RATE AND SYNTACTIC COMPLEXITY
153
Table 1. Demographic Characteristics of Subjects Sex Groups Elderly controls Alzheimer's patients
N
X Age
M
F
X Estimated 1.Q.
X GDS" stage
17
70.7
5
12
115
1.0
13
76.4
2
11
111
4.8
a GDS, Gt)bal Deterioration Scale.
across four speech frequencies (500, 1000, 2000, and 4000 hertz) for each ear. In addition, each subject met the following selection criteria: (1) native speaker of English; (2) right-handed; (3) adequate visual acuity to distinguish colors and shapes; (4) nonalcoholic; and (5) normal premorbid intelligence as determined by a validated regression equation that uses demographic information to estimate intelligence (Wilson, Rosenbaum, and Brown, 1979). Elderly control subjects were community-residing individuals, who were either spouses of AD subjects or members of local volunteer organizations. No previous or current neurological or psychiatric illnesses were known to exist in these subjects. All AD patients met the diagnostic criteria for probable AD, as specified by the NINCDS-ADRDA Task Force on Alzheimer's Disease (McKhann et al., 1985). Severity of dementia was determined using the Global Deterioration Scale (Reisberg, Ferris, and Crook, 1982), a seven-point rating scale that describes stages of dementia with well-specified observational criteria. A GDS rating of 1 represents normal behavior, and stage 7 represents severe dementia. Demographic characteristics of the subject groups are presented in Table 1. A borderline statistically significant difference was obtained (t = -2.04, p = .051) between the two groups in relation to their mean age. This mean difference was of a magnitude less than six years. Such a difference is quite unlikely to affect results, as age effects in normal individuals (in the range of 29-76 years) have not been found with the type of task employed in the present study (DeRenzi, 1979; Noll and Randolph, 1978). No difference in estimated premorbid intelligence was observed (t = 1.38, p = .177).
Task Subjects were asked to manipulate tokens in the form of colored wooden circles and squares, in response to audiorecorded command statements. Three speech presentation rates and command statements of increasing
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C . K . TOMOEDA et al.
syntactic complexity were used. The commands consisted of four sets of ten stimulus sentences from the Revised Token Test (RTT) (McNeil and Prescott, 1978). In this test, examinees demonstrate auditory comprehension of spoken directions by manipulating large and small circles and squares of four different colors. The syntactic complexity of the commands increases with succeeding subtests in the RTT, but the difficulty level of vocabulary remains constant. Thus, stimuli from the Token Test (DeRenzi and Vignolo, 1962) frequently have been used to measure the effect of syntactic complexity on auditory comprehension. In this study, each of the four sets of stimulus commands (one practice set and three scored sets) contained one command from each of the ten R T T subtests. The following is an example of a set constructed for this study: Example of item from: Subtest 1 - - T o u c h the blue square. Subtest 2 - - T o u c h the big green circle. Subtest 3 - - T o u c h the red circle and the white circle. Subtest 4 - - T o u c h the big blue circle and the little green square. Subtest 5 - - P u t the black square by the red circle. Subtest 6 - - P u t the little red circle beside the big blue circle. Subtest 7 ~ P u t the red square to the left of the white circle. Subtest 8 ~ P u t the big black square to the right of the little red circle. Subtest 9 - - T o u c h the blue circle instead of the green square. Subtest 10--1nstead of the big red square touch the big white circle. The order of presentation of command statements was partially randomized. Within each set, the five commands requiring the use of only large tokens (commands from odd-numbered subtests) were presented first, followed by the commands that required both large and small tokens. This was done so the examiner did not have to place or remove the small tokens after each command. Rather, the small tokens only needed to be added once, after the fifth command of each set. The order of command presentations within each subset was randomized. Stimulus commands were recorded on audiotape using three speech rates: a slow rate of 120 words per minute (wpm), a normal rate of 160 wpm, and a fast rate of 200 wpm. Fairbanks (1960) identified the average rate of speech as ranging from 160 to 170 wpm. The slow and fast rates used in this study represent a 25% decrease and increase, respectively, from the normal rate of 160 wpm. A male speaker (DRB, an expert in voice and articulation) was trained to present the stimulus sentences at the different speaking rates. The rate of presentation of each stimulus
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sentence was checked by dividing the number of words in the sentence by the time taken to say the sentence. All sentences were within plus-orminus 2 wpm from the target speech rate. In an attempt to control for a possible order effect for presentation rate, two audiorecordings were made. In both recordings, the practice set and the first scored set of ten commands were presented at the normal rate, followed by the two other scored rate conditions. In one recording, the slow rate preceded the fast rate, and in the other recording, the order was reversed. Presentation of the audiorecordings was randomized across subjects. Tokens were placed on a table in front of subjects following the procedures described in the R T T manual. The examiner explained the nature of the task and played the audiotape. After each command was presented, subjects were expected to perform the required task within a 12-second pause that occurred between each stimulus command. This length of time was selected after pilot testing the task with four AD subjects. According to pilot test data, AD subjects performed all the required manipulations of tokens within I0 seconds of the command presentation. In the present study, a point was awarded for each correct, complete response to each command. RESULTS The data were subjected to a mixed factorial analysis of variance (repeated measures) with two within-subjects factors of rate and syntactic complexity and one between-subjects factor for groups. Computation was performed within the S P S S / P C + M A N O V A (Norusis, 1986) statistical analysis software routine. A univariate test of between-subjects effects revealed a significant main effect for group [F(1,28) = 62.12, p < .001]. AD subjects performed significantly more poorly than normals in terms of the number of correct responses across the three rate conditions and ten levels of syntactic complexity. Multivariate tests of significance (Wilk's lambda) were used to assess possible within-subjects effects (see Hertzog and Rovine, 1985, for review of the M A N O V A approach to univariate measures analysis). This procedure was used because Mauchly's test of sphericity (Mauchly, 1940) indicated the inappropriateness of assuming equal variances and covarlances equal to zero for either of the within-subjects effects (p < .05). Mean scores o f the two subject groups for each of the three rate conditions collapsed across the R T T subtest (complexity) levels are shown in Table 2. A significant main effect was not found for rate of stimulus presentation [Wilks lambda = .93, approximate F(2,27) = 1.02, p = .374],
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C. K. TOMOEDA Table 2. Mean Scores of Healthy Subjects for Each Rate Condition Subtest Levels
Elderly and Alzheimer Collapsed Across the RTT
Healthy elderly Rate
et al.
Alzheimer subjects
x
SD
x
Slow
9.65
0.70
3.85
3.08
Normal
9.12
1.41
3.38
3.04
Fast
8.71
1.49
3.38
2.66
SD
nor was a group by rate interaction obtained [Wilks lambda = .93, approximate F(2,27) = .94, p = .401]. Table 3 contains group means for each of the 10 RTT subtest (complexity) levels, collapsed across rate conditions. A significant main effect for level of syntactic complexity [Wilks lambda = .40, approximate F(9,20) = 3.32, p = .012] was found, although a significant group by complexity interaction was not obtained [Wilks lambda = 0.64, approximate F(9,20) = 1.23, p = 0.3301. Level of syntactic complexity is confounded with sentence length in this study as in everyday communication. In Table 4 are the mean number of subjects who correctly responded to each length of command (number of words per sentence). A clear effect for sentence length is not present, although AD patients responded less well on sentences with eight words or more. Borderline significant interaction effects were found for rate by complexity [Wilks lambda = .21, approximate F(18,ll) = 2.33, p = .077] Table 3.
Mean Scores of Healthy Elderly and Alzheimer Subjects for Each RTT Subtest Level, Collapsed across Rate Conditions Alzheimer RTT subtest levels 1 2 3 4 5 6 7 8 9 10
Healthy
elderly
subjects
x
SD
x
SD
3.00 3.00 2.71 2.88 2.71 2.59 2.76 2.71 2.65 2.47
0.00 0.00 0.47 0.33 0.59 0.62 0.56 0.59 0.61 0.87
2.00 1.69 0.92 0.38 1.08 1.00 1.00 0.69 1.00 0.92
1.32 1.18 1.12 0.65 1.12 1.00 1.15 0.95 0.91 1.04
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Table 4. Mean Number of Subjects Correctly Responding to RTT Commands of Increasing Length N u m b e r of words per sentence
Healthy elderly ( N = 17)
Alzheimer's disease (N = 13)
4 6 8 9 10 11 12 13
17.0 17.0 15.3 15.5 15.1 15.0 15.0 15.3
8.0 7.3 4.3 4.0 3.3 4.4 3.0 3.0
and for group by rate by complexity [Wilks lambda = . 19, approximate F(18,11) = 2.57, p = .057]. It should be noted that the less conservative univariate tests (not used for hypotheses-testing here because of violation of sphericity assumptions) o f the rate by complexity and the group by rate by complexity interaction terms were both highly significant (p < .001 and p = .005, respectively). Percentage of correct responses for each group on each of the R T T subtests (complexity) levels for the three rate conditions are displayed graphically in Figure 1.
DISCUSSION The question considered in this study was whether, in AD and healthy elderly control subjects, rate of speech and level of syntactic complexity affect auditory language comprehension as measured by performance on items from the RTT. Level of syntactic complexity, but not speech rate, was found to significantly affect linguistic comprehension in AD patients and elderly controls. Both groups performed best on stimuli from the first two R T T subtests, in which command statements are simple imperatives (e.g., Touch the white square). AD subjects had the most difficulty with subtests 4 and 10. In subtest 4, the stimulus construction is: verb + determiner + 2 modifiers + noun + conjunction + determiner + 2 modifiers + noun (e.g., Touch the big blue circle and the little green square). In subtest 10, there is a main clause and a dependent clause (e.g., Touch the little blue square, if there is a big black circle). With syntactically more complex commands, sentence length increases and the individual must attend to, store, and encode larger amounts of information. Since m e m o r y impairment is a hallmark characteristic of individuals with AD, it is not surprising that the performance of AD patients suffered as syntactic complexity and length increased.
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C.K. TOMOEDA et al.
1.0 0.9 0.8 0.7
'--I---'~-".,.
. J " . . . . . . . . . "-,
..,,V
0.6 0,5 0.4 0.3 0.2
0.1 0.0 o
REVISED TOKEN TEST SUBTESTS Figure 1. Percentage of correct responses for healthy elderly and Alzheimer's disease subjects on each complexity level for each rate.
Although the normal elderly controls and AD patients achieved their highest performance scores in the slow (120 wpm) rate condition, rate of stimulus presentation did not significantly affect the ability of either group to comprehend the stimulus sentences. Our findings appear to support the conclusions of investigators who have found that speech rate alone does not facilitate auditory language comprehension in certain brain-damaged populations (Blumstein, Katz, Goodglass, Shrier, and Dworetsky, 1985; Brookshire and Nicholas, 1984). However, the modest size of the samples in this study make replication of this finding important. Finally, when the within subject effect of syntactic complexity by rate was examined, an interaction effect approached significance (p =- .077) between the ten syntactic complexity levels and the three rate conditions, indicating a trend towards subjects having difficulty with more syntactically complex statements at faster rates. A three-way interaction effect
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159
of borderline significance (p = .057) was obtained for group by complexity by rate. The elderly controls tended to have the most difficulty when more complex sentences were presented at the faster rate. However, with the AD patients, once the stimuli were no longer simple imperatives, rate did not significantly influence sentence comprehension. This is likely due to " f l o o r effects" in patients' performance for the more complex sentences. In summary, AD patients performed significantly worse than the healthy elderly in each rate condition and at each level of syntactic complexity, thereby documenting the profound auditory comprehension deficit experienced by AD patients. While it is acknowledged that the R T T does not measure the entire domain of auditory language comprehension, it does systematically sample one pattern of auditory linguistic processing. With this cautionary note, it is possible to draw some general clinical implications from the study results. The findings of this study indicate that individuals communicating with AD patients can improve patients' ability to comprehend by speaking in short and syntactically simple sentences. Although rate alone did not appear to significantly affect comprehension, the near significant interaction of rate and syntactic complexity suggests that comprehension is reduced when faster, more complex statements are used.
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