Sentence Comprehension in Alzheimer's Disease

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Psychology and Aging 1997. Vol. 12, No. 1, 3 - 1 1

Sentence Comprehension in Alzheimer's Disease: Effects of Grammatical Complexity, Speech Rate, and Repetition Jeff A. Small and Susan Kemper University of Kansas

Kelly Lyons University of Kansas Medical Center

Caregivers of patients diagnosed with Alzheimer's disease (AD) are often advised to modify their speech to facilitate the patients' sentence comprehension. Three common recommendations are to

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(a) speak in simple sentences, (b) speak slowly, and (c) repeat one's utterance, using the same words. These three speech modifications were experimentally manipulated in order to investigate their individual and combined effects on sentence comprehension in AD. Fifteen patients with mild to moderate AD and 20 healthy older persons were tested on a sentence comprehension task with sentences varying in terms of (a) degree of grammatical complexity, (b) rate of presentation (normal vs. slow), and (c) form of repetition (verbatim vs. paraphrase). The results indicated a significant decline in sentence comprehension for the AD group. Sentence comprehension improved, however, after the sentence was repeated in either verbatim or paraphrased form. However, the patients' comprehension did not improve for sentences presented at the slow speech rate. This pattern of results is explained vis-a-vis the patients' working memory loss. The findings challenge the appropriateness of several clinical recommendations.

Alzheimer's disease (AD) is a progressive neurodegenerative condition that gradually destroys the abilities to remember, reason, and engage in meaningful social interaction. Caregivers of AD patients are often described as the hidden victims of AD because they must deal with the ever-increasing burden of caring for an often physically able but cognitively impaired individual. Memory loss is the primary symptom of AD, but also appearing early in the disease are language and communication impairments (Bayles & Tomoeda, 1991; Cummings, Benson, Hill, & Read, 1985; Kempler, 1991). In fact, AD Caregivers report that much of their stress comes from unsuccessful attempts to communicate with the patients (Orange, 1991; Orange, Lubinski, & Ryan, 1994). In an effort to improve the communicative interaction between caregiver and patient, many clinicians advise caregivers to modify their speech when talking to the patient (Alzheimer's Disease and Related Disorders Association [ADRDA], 1990; Dippel & Hutton, 1988; Gwyther, 1985; Heifer, 1991; Legler, 1993; Ostuni & Santo-Pietro, 1991). Common recommendations include (a) using simple sentences, (b) speaking slowly, and (c) repeating utterances word for word. These recommendations are

Jeff A. Small, Gerontology Center, University of Kansas; Susan Kemper, Department of Psychology, University of Kansas; Kelly Lyons, Department of Neurology, University of Kansas Medical Center. This research was supported by Grant T32 AG00226 from the National Institute on Aging. We thank the Alzheimer's Disease Center at the University of Kansas Medical Center for referring Alzheimer's patients for this research. Correspondence concerning this article should be addressed to Jeff A. Small, who is now at the Gerontology Research Centre, Simon Fraser University at Harbour Centre, #2800-515 West Hastings Street, Vancouver, British Columbia, Canada V6B 5K3. Electronic mail may be sent via Internet to [email protected].

intended to compensate for AD patients' deficits in working memory, information-processing speed, and primary memory, respectively. Simple sentences place minimal demands on (he patients' diminished working memory capacity and should therefore be easy to understand. In a similar manner, slow speech is thought to provide patients with the additional time needed for comprehension as a result of their slower processing speed. Also, repeating an utterance verbatim should reinforce previous memory traces, enabling the patient to recover what was forgotten from the original utterance. The effectiveness of these three speech modifications appears to be based largely on clinical impressions and stereotypes rather than on controlled empirical research. As a result, it is unclear whether these modifications actually improve AD patients' comprehension. Only recently have researchers begun to examine speech addressed to dementia patients and its effects on the patients' understanding. Kemper (1994) examined the speech of caregivers and service providers addressed to young and older demented and nondemented adults. She found that speech addressed to older adults in general was marked by simpler sentence structure, slower rate, more repetitions, and longer pauses. Speech directed to the demented elderly was syntactically simpler and contained longer pauses and more diminutives than was speech addressed to the nondemented elderly. Although these findings verify the use of modified speech with demented individuals, the efficacy of these speech modifications was not assessed. In another study, Kemper, Anagnopoulos, Lyons, and Heberlein (1994) investigated whether caregivers would adopt a specialized speech style when describing pictures to their demented spouses and, if so, what effects it would have on the demented spouse's ability to identify one among several pictures. The results indicated that caregivers used simpler semantic and syntactic content when describing a picture to their de-

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SMALL, KEMPER, AND LYONS

merited spouses than when describing it to the interviewer. Moreover, the demented spouses were more likely to choose the correct picture when caregivers used this simplified speech style. Experimental studies confirm the improvement in dementia patients' comprehension of simplified sentences. Rochon, Waters, and Caplan (1994) and Small, Kempler, and Andersen (1991) tested AD patients' comprehension of simple versus complex sentences, using a sentence-picture matching task. In both studies, patients showed better comprehension for simple and short sentences than for complex and long sentences. In Small et al.'s study, performance on the sentence comprehension task was significantly correlated with the patients' working memory capacities so that as working memory declined, so did ability to understand more complex sentences. The effectiveness of other recommended speech modifications on AD patients' language comprehension is largely unknown. The roles of slow speech and repetition are of particular interest because the cognitive deficits that motivate these speech accommodations (cognitive slowing and decline in primary memory) are prominent symptoms in AD. Cognitive slowing in AD is manifested in the patients' slowerthan-normal response times on a wide variety of cognitive tasks, including reading words, completing sentences, and making decisions about category membership (Nebes & Brady, 1992). It has been hypothesized that because of this slowing, older individuals might benefit from additional time given to processing information (Dancer, 1985; Han & Geha-Mitzel, 1979; Park, 1992). Although clinical observations appear to confirm this hypothesis (Gwyther, 1985; Heifer, 1991; Legler, 1993; Ostuni & Santo-Pietro, 1991), experimental research has not. In only one published study have researchers investigated the influence of a slow speech rate on AD patients' sentence comprehension. Tomoeda, Bayles, Boone, Kaszniak, and Slauson (1990) employed the Revised Token Test as a measure of AD patients' sentence comprehension. In this test, participants must listen to a sentence and manipulate objects of different sizes, colors, and shapes in accordance with the meaning of the sentence. Tomoeda et al. presented the sentence stimuli at three speech rates: normal (160 words per minute [WPM]), slow (120 WPM), and fast (200 WPM). Their results indicated that although AD patients showed better comprehension for simple than for complex sentences, they did not show any effects of speech rate on sentence comprehension. The authors attributed the latter finding to the patients' floor performance on more complex sentences. Declines in AD patients' primary memory are revealed on tasks that require recall of information after a brief delay or distraction period (Morris & Baddeley, 1988). This forgetfulness is one of the earliest symptoms reported by caregivers of AD patients, and it necessitates frequent reminders or repetitions by the caregiver. The use of repetitions, particularly verbatim repetitions, is often recommended in literature for caregivers (e.g., ADRDA, 1990; Dippel & Mutton, 1988). A rationale for repeating an utterance word for word is rarely given, although it is occasionally suggested that repeating an utterance with different words will confuse the patient. There has not been, to the authors' knowledge, any published experimental research addressing either the efficacy of repetitions on AD patients'

sentence comprehension or the putative advantage of verbatim versus other types of repetition. We attempted to extend our understanding of the effects of speech modifications to AD patients in several ways. First, we provided controlled experimental evidence regarding previously assumed benefits of slow speech and verbatim repetition on AD patients' sentence comprehension. Second, we examined the relative importance of the latter two speech modifications visa-vis complexity of sentence structure. Third, we demonstrated the importance of considering the involvement of multiple cognitive deficits when assessing the effectiveness of speech accommodations to AD patients. Following are specific hypotheses that emerge from considering how the three speech modifications might be affected by the multiple cognitive deficits in AD: 1. We predicted that AD patients would show better sentence comprehension for simple than for complex sentences. This prediction was based on previous research showing pronounced working memory deficits in AD (Morris & Baddeley, 1988) and a strong correlation between people's working memory capacity and their ability to understand complex sentences (Carpenter, Miyake, & Just, 1994; King & Just, 1991). It is possible, however, that providing AD patients with more time to process complex sentences (i.e., by slowing the speech rate) will facilitate their comprehension. This hypothesis is supported by research indicating that speed of information activation may be a source of working memory limitations (Salthouse, 1996). 2. We expected the effect of slow speech on sentence comprehension to vary in accordance with the patients' working memory capacity. AD patients with mild working memory loss may benefit from slow speech because it provides more time to process an utterance. Patients with more severe working memory loss, however, may forget early parts of a sentence by the time the end is heard. In the latter case, slow speech may worsen rather than facilitate the patients' comprehension as a result of the increased duration over which parts of the sentence must be retained. 3. We hypothesized that repeating an utterance to AD patients would result in improved comprehension. However, contrary to recommendations in the caregiver literature, we predicted that both verbatim and paraphrased repetitions would be effective, although for different reasons. If the patient has difficulty understanding some aspect of the utterance initially, changing the content or structure of the utterance (i.e., paraphrasing) should facilitate comprehension. On the other hand, if the original sentence is understood but quickly forgotten, a verbatim repetition should facilitate comprehension by reinforcing the memory trace of the original utterance. The outcomes of these predictions would have important theoretical and clinical implications. In the theoretical domain, the results would provide a better understanding of the relative importance of working memory and cognitive processing speed in sentence comprehension. Clinically, the results would indicate the effectiveness of different speech modifications and, therefore, should be valuable in developing more informed clinical recommendations. The limited clinical perspective on which interventions are currently based may be leading caregivers to

SENTENCE COMPREHENSION IN ALZHEIMER'S DISEASE (0-9) stages. Only patients who scored in the mild-to-moderate range were included in this study. Normal control participants who scored below 26 were excluded.

Table 1

Background Characteristics for the Alzheimer's (N = 15) and Normal Control (N = 20) Participants

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Alzheimer's Measure

M

Age Education Mini-Mental State (30 possible) Boston Naming Test (60 possible) Digits forward ( 1 2 possible) Digits backward (12 possible) Days of the week backward Months of the year backward Sentence repetition (30 possible)

72.0

SD 6.9 3.0 5.4

13.8 21.8 35.9

17.0

7.0 4.3 5.9 8.4

2.3 2.2 2.0 3.9

12.9

11.0

Normal control

Naming

M

SD

P

75.2 15.5 28.8 53.7

4.8 3.6 1.3 5.7 1.9 2.3 0.0 0.2 4.7

.13 .14

8.6 7.4 7.0 12.0 25.2

.000 .002

.03

Participants' ability to name objects was measured with the Boston Naming lest (2nd ed.); Kaplan, Goodglass, & Weintraub, 1983). This 60-item test was selected because of its wide use in assessing a range of vocabulary and its past use in measuring degree of anemia in dementia (e.g., Bayles, Tbmoeda, & Trosset, 1992; Nicholas, Obler, Albert, & Helm-Estabrooks, 1985). Participants' scores represent the total number of spontaneously given correct responses.

.000

.04 .003 .001

engage in potentially unnecessary or even detrimental speech accommodations.

Method Participants Fifteen patients with AD were recruited from the Alzheimer's Disease Center at the University of Kansas Medical Center and from local AD caregiver support groups. Twenty normal older adults, matched for age and education with the AD group, were recruited from the local community. Neither the AD patients nor the normal control participants had a history of stroke, ischemia, focal neurological deficit or lesions, depression, psychosis, alcoholism, or drug abuse. The AD group met National Institute of Neurological and Communicative Disorders and StrokeAlzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria for "probable" AD (McKhann et ah, 1984). Participants (or their caregivers) reported normal or corrected-to-normal hearing and vision. Although participants' hearing and vision were not clinically assessed, each participant demonstrated adequate hearing and vision on the word comprehension test (see Procedure section). In order to control for differences in hearing ability, volume levels in the sentence comprehension experiment were adjusted during practice trials to each participant's preferred listening level. Because linguistic variables were manipulated in this investigation, only native speakers of Standard American English were included. Table 1 contains background information on the two participant groups.

Measures All participants were tested on four types of measures: (a) general cognitive functioning, (b) naming pictured objects, (c) working memory, and (d) sentence comprehension.

General Cognitive Functioning The Mini-Mental State Exam (MMSE; Fblstein, Folstein, & McHugh, 1975) was used for assessing each participant's cognitive status. The MMSE is a standard neuropsychological instrument used routinely in the diagnosis of AD. The test taps four domains of cognitive functioning: (a) orientation in time and space, (b) memory and attention, (c) language, and (d) praxis. It is a brief test, usually administered in 20 min. A total of 30 points is possible, with somewhat arbitrary cutoffs for normal (26 and above) and mild (20-25), moderate (10-19), and severe

Working Memory The participants' working memory capacities were measured in order to test the hypothesis that working memory capacity modulates the effects of sentence complexity and slow speech on sentence comprehension. Three kinds of working memory tasks were used: (a) digits span (forward and backward), (b) saying the days of the week and months of the year backward, and (c) sentence repetition. Digit span. The digits span forward and backward subtests were taken from the Wechsler Memory Scale—Revised (Wechsler, 1987). In the digit span task, participants are given a series of numbers to repeat in either forward or backward order. In the forward version, participants are asked to repeat three numbers at Level 1, and they continue repeating longer series of numbers (maximum of eight at Level 6) until neither of two trials at a level are repeated correctly. Participants are given 1 point for each correctly repeated trial. The procedure is the same for digits span backward except that there are two (rather than three) numbers at Level 1 and the maximum is seven numbers at Level 6. Days of week/months of year. On this measure, participants were asked to say the days of the week and the months of the year in backwards order, starting with Saturday and December, respectively Their scores equaled the number of days and months repeated in the correct backward sequence. Sentence repetition. Participants were asked to repeat 30 sentences, one at a time, after the examiner. There were five sentences for each of the six grammatical structures used in the sentence comprehension task (see following section). Past research has shown that older adults' ability to imitate and produce sentences is related to their working memory capacity (Kemper, 1986; Kemper, Kynette, & Norman, 1992; Kemper, Kynetle, Rash, Sprott, & O'Brien, 1989). Participants were given credit for a sentence only if it was repeated in its entirety.

Sentence Comprehension The participants' sentence comprehension was tested with a sentencepicture matching task. In this task, participants listened to a sentence and pointed to one of four pictures depicting the meaning of the sentence. The sentences varied along three dimensions: (a) grammatical complexity, (b) speech rate, and (c) repetition type. Grammatical complexity. Six types of grammatical constructions were used as shown in Table 2. On the basis of findings from previous research (e.g., Bever, 1970; Caplan & Hildebrandt, 1988; Kemper, 1992), the complexity of the sentences was determined by (a) the presence of an embedded clause, (b) the branching direction (left or right) of the embedded clause, and (c) canonical mapping of the thematic roles Agent-Action-Theme onto Nounl-Verb-Noun2 sequences. Sentences were considered to be more complex if they contained an embedded clause, a left-branching embedded clause, and noncanonical mapping of thematic roles onto word order. According to these three criteria, active sentences were considered to be the simplest sentence

SMALL, KEMPER, AND LYONS Table 2 Examples of the Six Sentence Types and Their Paraphrased Versions Sentence type Active Passive Object-subject relative Object-object relative

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Subject-subject relative Subject-object relative

Example The woman beside the boy shouted at the girl. Paraphrase: The woman shouted at the girl. The girl was shouted at by the woman. Paraphrase: The woman shouted at the girl. The woman followed the girl who shouted at the boy. Paraphrase: The woman followed the girl and the girl shouted at the The woman followed the girl who the boy shouted at. Paraphrase: The woman followed the girl and the boy shouted at the The woman who followed the girl shouted at the boy. Paraphrase: The woman followed the girl and the woman shouted at The woman who the girl followed shouted at the boy. Paraphrase: The girl followed the woman and the woman shouted at

type, followed by passive sentences, which have noncanonical mapping of thematic roles (i.e., Nounl = Theme, Noun2 = Agent). Both the object-subject and object-object sentence types have embedded rightbranching clauses, but the object-object type also has noncanonical mapping (i.e., a Noun-Noun-Verb sequence (girl-boy-shouted at), where boy is agent and girl is theme). The subject-subject and subjectobject sentence types are more complex because of the presence of leftbranching embedded clauses. The subject-object type has the additional complexity of noncanonical thematic role assignment. For each sentence, one target picture and three foils (or distracter pictures) were drawn and presented in quadrants (see Figure 1). The

boy. girl. the boy. the boy.

accuracy of the pictures for each sentence was validated by 20 young adults. The three foils were constructed so that the selection of each would indicate the use of a particular strategy (cf., Caplan & Hildebrandt, 1988). Sentence types with embedded clauses (object-subject, object-object, subject—subject, subject-object) had two foils depicting only part of the sentence. Foil 1 depicted only the initial clause of the sentence, and foil 2, only the final clause of the sentence. Selection of one of these two foils would indicate that the participant was processing or retaining only part of the sentence. The third foil was different for each type of embedded sentence. For the object-subject type, the third foil depicted a conjoined interpretation of the sentence (e.g., "the

Foill

Target

Foil 2

Foil 3 The woman who followed the girl shouted at the boy.

Figure 1. Example sentence and pictures from the sentence-picture matching comprehension task. Foil 1 depicts an initial-clause-only interpretation of the sentence; Foil 2 depicts a final-clause-only interpretation; and Foil 3 depicts a minimal distance interpretation.

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SENTENCE COMPREHENSION IN ALZHEIMER'S DISEASE woman followed the girl and the woman shouted at the boy"). Far the object-object type, a linear order interpretation was depicted (e.g., ' 'the woman followed the girl and the girl shouted at the boy"). The third foil in the subject-subject sentences displayed a minimal distance interpretation (e.g., "the woman followed the girl and the girl shouted at the boy"). For the subject-object type, there were two versions of the third foil. One version tested a linear order interpretation (e.g., "the woman followed the girl and the woman shouted at the boy") and the other tested a minimal distance interpretation (e.g., "the girl followed the woman and the girl shouted at the boy''). For the active and passive sentences, one of the foils depicted no action (e.g., the woman, the boy [only in the active sentences], and the girl are standing next to each other), and the second foil depicted a different action (e.g., "the woman followed the girl"). The third foil for the active sentence depicted a minimal distance interpretation (e.g., "the boy shouted at the girl") and for the passive sentence, a linear order interpretation (e.g., ' 'the girl shouted at the woman''). Ten sentences were constructed for each of the six sentence types, for a total of 60 sentences. Within a sentence, animacy and reversibility of nouns were maintained so that interpretation of the sentence could not be made solely on the basis of semantic or pragmatic plausibility. The reversibility of the nouns in each sentence was confirmed by ratings from 10 graduate students. Speech rate. The 60 sentences (along with their 60 paraphrased versions; see Repetition type section), plus six practice trials, were recorded at a normal (180 WPM) and slow (110 WPM) speech rate. The recordings were made by a professional radio announcer directly onto a Macintosh Dsi computer with MacRecorder and SoundEdit Pro. The 40% reduction for the slow rate was selected because previous researchers using smaller reductions (15% or 25%) have found little or no effect of slow speech (Small, 1994; Tomoeda et al., 1990). Repetition type. Two types of repetition were used: verbatim and paraphrase. A verbatim repetition consisted of presenting the same sentence to the participant, A paraphrased version of each sentence simplified the grammatical complexity of the sentence while retaining the meaning of the original sentence. The paraphrased versions of each sentence type are exemplified in Table 2.

test Participants were asked to point to a named item (e.g., woman) displayed with the other two items mentioned in that sentence (boy, girl). The sentence comprehension test was administered after a participant demonstrated comprehension of all test items. After the word comprehension test, participants were instructed to listen to each sentence and point to one of the four pictures that best depicted the meaning of the sentence. They were informed that if they chose a picture that was different from the target, they would hear the sentence again (or, in the case of paraphrased sentences, "another version of the sentence") and then were to make another selection. Sentences were repeated up to two times. Sentence presentation was implemented with the use of PsyScope (Cohen, Flatt, & Provost, 1992) on a Macintosh Classic computer with two external stereo speakers. PsyScope is a computer program for constructing and running psychological experiments. In this study it was used to play back digitally recorded sentences and repeat sentences (verbatim or paraphrased) whenever necessary without any time delay. It also permits the tester to record the accuracy of the participant's response on each trial. The presentation of the cognitive status, naming, and memory tests was distributed around and between the two blocks of the sentence comprehension stimuli. AD patients were paid $25.00 for participating in four sessions, and normal control participants received $10.00 for one session.

Results Participants' scores on tests of general cognitive functioning, confrontation naming, and working memory are presented in Table 1. AD patients showed significant declines in comparison with the normal control group on the Boston Naming Test and across all measures of working memory. Impairments were most noticeable on the digits-backward and sentence-repetition tasks. The sentence comprehension data were analyzed in a repeated-measures analysis of variance. As shown in Figure 2, there was a significant main effect of subject group: AD patients made more errors than did normal control participants, F( 1, 33)

Procedure The sentence comprehension test was administered in two blocks of 38 sentences each, for a total of 76 sentences. The additional 16 sentences included 10 repeated subject-object sentences needed to assess the two versions of the third foil pictures and 6 practice trials, three for each block. One block of sentences was presented at the slow speech rate and the other block at the normal speech rate. The order of blocks and speech rate was counterbalanced across participants. AD patients listened to the 76 sentences in all four Speech Rate x Repetition Type conditions (i.e., normal-verbatim, normal-paraphrase, slow-verbatim, slow-paraphrase). The four blocks of sentences were presented across four sessions approximately 1 week apart. Although it is unlikely that AD patients would experience priming as a result of repeated presentation of the stimuli (Ostergaard, 1990; Salmon, Shimamura, Butters, & Smith, 1988), presenting each block in a different session served to minimize this possibility. Having four sessions also reduced patients' fatigue and distractibility by limiting the amount of testing at one sitting. Because the normal control group would likely experience repetition priming, repetition type was treated as a betweensubjects factor, and the normal control participants were tested in only one session. In order to ensure that AD patients' word comprehension abilities would not interfere with their sentence comprehension, their comprehension of each item (i.e., character or object) appearing in the sentence comprehension pictures was tested before the sentence comprehension

• Normal Control

• AD

1 0

90 80 70

«