University of Western Ontario, London, Ontario CANADA. INTRODUCTION ... The Alzheimer's Society of London-Middlesex and the. Aging Brain Clinic at St.
PROCESSING OF NOUNS AND VERBS BY INDIVIDUALS WITH DEMENTIA OF ALZHEIMER’S TYPE (DAT)
1
Aneta Kielar1 and J.B. Orange2 Department of Psychology and 2School of Communication Sciences and Disorders, University of Western Ontario, London, Ontario CANADA INTRODUCTION
Naming problems are common in individuals with dementia of Alzheimer’s type (DAT) [6, 13]. The naming errors are attributed often to the degradation of representations in semantic memory [7, 8, 23]. Previous studies of confrontational naming of pictures and objects by individuals with DAT focused primarily on naming nouns [1, 16]. More recently, there has been increased interest in verb naming in DAT. These studies indicate that individuals with DAT are more impaired in naming verbs than naming nouns [5, 22, 25]. Participants with DAT experience problems judging verb meaning [22], identifying semantic relations among verbs, and determining the coherence of sentences containing verbs [11]. In addition, patients with DAT have difficulty learning the meanings of new verbs [12] and produce more semantically unrelated errors relative to controls on the Action Naming Test – a test of verbs [4]. Collectively, these results indicate that the naming difficulties of individuals with DAT include nouns as well as verbs. It is hypothesized that the verb naming impairments in DAT might be due to differences in the mental representation of verb meaning compared to noun meaning [5, 6, 10, 22, 25]. However, none of the previous studies of confrontational naming in DAT investigated differences in naming among different verb types. Nouns and verbs differ in several important ways, such as the type of associated grammatical information (e.g., plurality of nouns, tense of the verb), their differential influences in sentence comprehension, and in the amount of language processing required to interpret their meaning. It is speculated that nouns and verbs are retrieved differently and that they differ in their mental representation within semantic memory [9]. Moreover, they possess unique semantic representations and sound structures. However, the relative contributions of these pieces of information to their differential mental organization in semantic memory are not clear. For example, it has been suggested that different kinds of information are used to process regular versus irregular verbs (e.g., walk – walked vs. run – ran) [3, 14, 21]. Generation of regular past tense depends more on phonological processes and
computational rules because regularity involves phonological factors. That is, the past tense suffix –ed is pronounced as /t/, /d/ or /Id/ depending on phonological characteristic of the stem of a word. In contrast, generating an irregular past tense depends more on semantic information and lexical processes because irregular past forms are associated with their present tense forms in meaning and changes are not phonologically predictable (e.g. meaning of “take” is associated with past tense “took”). Thus, damage to the phonological or semantic components of language has differential consequences for regular vs. irregular verbs [17]. In particular, damage to frontal brain regions that are involved in phonological computational processing should lead to deficits in naming of regular verbs, whereas damage to temporal brain regions involved in storing semantic representation of words should lead to the impairment in processing irregular past tense verbs and nouns. The objective of this study was to measure changes in noun and verb confrontation and generative naming in individuals with early clinical stage DAT. Comparison of noun and verb processing can provide insight into the nature of emerging naming deficits observed in individuals with DAT. The overall purpose of the study was to determine whether patients with early clinical stage DAT exhibit difficulties processing nouns and verbs relative to normal controls. The study aimed to answer two research questions. The first is whether processing of nouns and verbs differ in participants with DAT vs. normal controls, and second is whether there are differences in processing regular vs. irregular verbs in participants with DAT. METHOD Participants Data were collected from 10 participants with the early stage dementia of Alzheimer’s type (DAT) using widely accepted research criteria for the clinical diagnosis of DAT [18]. Participants were recruited from the Alzheimer’s Outreach Service in London Canada, The Alzheimer’s Society of London-Middlesex and the Aging Brain Clinic at St. Joseph’s Health CareParkwood Hospital at London Canada. DAT participants were screened for severity of dementia and participation was restricted to those with mild
clinical stage DAT according to scores obtained on the Standardized Mini Mental State Examination (SMMSE) [19]. Participants with DAT were classified as mildly demented if their SMMSE scores ranged from 19 to 25 out of maximum 30. SMMSE scores of 26 or more out of 30 indicated normal performance. Participants with DAT were matched on education, gender and age with their spouses who acted as the 10 controls. All participants were screened for medication use and health status. The control participants had no chronic medical conditions, and no history of neurological or psychiatric illness. None of the participants were taking medications that interfere with speech, language, hearing or cognitive performance (e.g. anti-depressants, anti-psychotics, sedatives etc.) other than participants with DAT who were taking medications for DAT (e.g. Aryceptyl, Reminyl). Participants with a history or a diagnosis of primary psychiatric disorder such as major depression or schizophrenia were excluded. Participants with other causes of dementia such as vascular disease, stroke, metabolic conditions, or infectious diseases or other neurological conditions that might affect cognitive performance also were excluded form the study. None of the participants were depressed at the time of testing based on their performance on the Geriatric Depression Scale (cut-off score of 14/30) [24]. All participants possessed functional hearing and vision skills necessary to complete language tasks as screened by the perceptual subtests of Arizona Battery for Communication Disorders of Dementia (ABCD) [2]. English was the native language of all participants. The clinical and demographic characteristics of all participants are summarized in Table 1. Materials and Procedure After completing screening measures of general cognitive skills, memory, language and perceptual ability (SMMSE, GDS, ABCD) both the DAT and normal control participants were administered verbal fluency test consisting of category (i.e., “Name as many animals in one minute as you can.”) and letter fluency tasks (e.g., “Name as many words as you can in one minute that begin with the letter ‘F’.). The letter and category fluency test were administered to measure word retrieval ability and assess any attention difficulties. The category fluency task consisted of 8 categories, four of which included living items (animals, birds, water creatures, dogs) and 4 non-living items (household items, vehicles, musical instruments and tools). Participants were asked to provide as many exemplars as they could from each category in 60 seconds. For the letter fluency task, participants were asked to say as many words as they could think of beginning with the letters “F”, “A”, and “S”, again with 60 seconds allowed for each letter.
Proper nouns, numbers or the same word with different endings were not accepted. The scores used for analysis were the total number of correct responses on the two tasks and the total number correct for living and non-living categories (e.g. animals + birds + tools + vehicles = category fluency; animals + birds = living; tools + vehicles = non-living; F words + A words + S words = letter fluency). Category fluency tasks were administered before letter fluency tasks. Noun naming was assessed using a shortened, 30-item version of the Boston Naming Test (BNT) [15]. This version of BNT consists of 30 black and white line drawings of items ranging from highly frequent at the beginning of the list to less frequent at the end of the list. Participants were asked to name each item. If a participant was unable to name the item the experimenter provided a semantic or phonological cue. Verb naming was assessed using a sentence completion task modified form the Action Naming Test (ANT) [20]. The modified administration was designed to elicit production of regular and irregular past tense verb forms. This test consists of 55 black and white line drawings depicting frequently and infrequently occurring actions (e.g., swimming vs. curtsying). Sentence completion pairs were created for each drawing such that the present tense form of the verb was provided by the examiner in the stem sentence and the participant then was required to produce the past tense form in the second sentence (e.g., “In this picture the man is swimming. Yesterday, the man ….”). The drawing remained in view while participants completed the sentence. In total there were 17 irregular and 38 regular verbs. The responses were coded for the ANT total correct and separate ANT scores for regular and irregular verbs. Testing was conducted in a quite room in participants’ homes in approximately 45 minutes. RESULTS Data from two DAT participants were excluded from the analysis. One of the participants could not perform many of the ANT sentence completion tasks which resulted in half of the data set missing for this participant. The second patient was excluded due to the conflict between clinical diagnosis of DAT and his SMMSE score. This patient achieved SMMSE score of 30 which suggested unclear clinical cause for presentation of dementia. Raw scores on BNT naming test and sentence completion version of ANT test were converted to percentages for the purpose of comparisons. The percentage accuracy scores of control and DAT participants on both tests are reported in Table 2.The one-way ANOVA that assessed raw score SMMSE performance revealed
that the patients with DAT scored significantly lower that controls, F (1, 16) = 89, p < .01, confirming the difference between two groups in the cognitive functioning (DAT: M = 23 SE = .42; Controls: M = 29 SD = .42). There were no significant differences between patients and controls in age, F(1, 16) = 1.27, p > .05, years of education, F(1, 16) = 1.00, p > .05 or geriatric depression scale, F(1, 16) = 2.30, p > .05.
at naming exemplars from living than non-living categories, t(7) = 2.80, p < .05. There was no significant difference between groups on the letter fluency test, F(1, 16) = 4.00, p > .05, indicating that compared to the semantic representation of concepts, the retrieval ability and phonological/orthographic word knowledge is relatively preserved in early stage DAT. CONCLUSION
Verb and Noun Naming The noun and verb naming scores of participants with DAT and normal controls are presented in Table 2. Verb and noun naming data were analyzed using mixed design repeated measures ANOVA with Group (Controls, DAT) as a between-participant variable and Test as a within-participant variable (BNT, ANT_total, ANT_ regular, ANT_ irregular). There was a significant main effect of group, F(1, 16) = 15, p < .01, indicating that overall controls performed better than patients (Controls: M = 91%, SE = 2.1%; DAT: M = 80%, SE = 2.3%). The main effect of test also was significant, F(3, 48) = 50, p < .01, revealing that the performance on the BNT was significantly lower (M = 65%, SE = 3% ) than on the ANT_total (M = 93%, SE = 2%), ANT_regular (M = 94%, SE = 2% ) and ANT_irregular (M = 91%, SE = 3%) formats (p .05). There was a significant group by test interaction, F (3, 48) = 20, p < .01. The post-hoc tests using Tukey’s Honestly Significant Difference (HSD) revealed that controls performed equally well on both nouns and verbs (p > .05) whereas participants with DAT were more impaired on naming nouns than verbs (p < .01). The analyses indicated that the naming of regular and irregular verbs did not differ from each other neither for controls or for participants with DAT (p > .05). Moreover, the intra-test analysis using one-way ANOVAs revealed that patients with DAT were significantly more impaired than control participants at naming nouns, F(1, 16) = 41, p < .01 (DAT: M = 45%, SE = 4%; Controls: M = 84%, SE = 4%). However, the two groups were not significantly different at naming verbs (ANT total, F(1, 16) = .87, p > .05; ANT_regulars, F(1,16) = 1.13, p > .05; ANT_irregulars, F(1, 16) = .26, p > .05). Other Neuropsychological Measures One-way ANOVAs revealed that the word retrieval ability of participants with DAT was significantly more impaired than that of controls for both living and nonliving categories (living: F(1, 16) = 18 , p < .01; nonliving; F(1, 16) = 10, p < .01) (See Table 3). The comparisons of performance on living vs. non-living categories using paired t-tests indicated that participants with DAT were significantly more impaired
The processing of nouns and verbs in participants with DAT and normal controls was assessed using pictured objects and action naming tests. Participants with DAT as a group were more impaired on naming nouns than verbs. They also were equally accurate on naming regular and irregular verbs and their naming accuracy on all verb types did not significantly differ from controls. The finding of the impaired noun naming on the BNT is consistent with the previous reports of naming deficit observed in the individuals with DAT [7, 13]. This research has implications for understanding psycholinguistic problems in DAT. Moreover, our findings have relevance to both neuroscientists and clinical/applied researchers by helping them advance their understanding of the differential effects of DAT on linguistic elements. Table 1: Participant Demographic and Clinical Characteristics (Mean + SD)
Age (yrs) Education (yrs) Gender (male/female) SMMSE (max=30) Geriatric Depression Score (max=30)
DAT (N=8) M Range (SD) 78 (6) 66-86 12 (4) 8-17 8/2 23 (1.2) 3.3 (3.5)
22-25 0-9
Controls (N=10) M (SD) Range 74(8) 54-83 13.5(3) 8-17 2/8 29 (1.3) 5.8 (3.6)
26-30 2-14
Table 2: Participant Percent (Mean+ SD) Correct Scored for Naming Nouns (BNT) and Verbs (ANT) DAT (N=8)
Boston Naming Test Action Naming Test_total ANT_regular ANT_irregular
M (SD) 45 (11) 91 (11)
Controls (N=10) M (SD) 84 (14) 94 (3)
92 (10) 90 (16)
95 (2) 92 (5)
Table 3: Participant Mean (+ SD) Scores for Category and Letter Fluency Tasks
Category Fluency – Living Category Fluency – NonLiving Category Fluency – Total Letter Fluency (total FAS)
DAT (N=8) M (SD) 25 (7)
Controls (N=10) M (SD) 47 (14)
p
< .01
31 (11)
48 (12)
< .01
56 (18)
95 (25)
< .01
19 (13)
31 (13)
ns
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