CHAPTER 4 RESULTS
The primary objective of the current study was to investigate lexical retrieval skills in subjects with right hemisphere damage (RHD). Additionally, the scrutiny of the error pattern in these subjects was considered as a subsidiary aim. For this purpose, a group of 22 subjects with RHD as well as an equal number of age-, gender- and education-matched neurologically normal subjects were selected for the present study. These subjects were administered a custom-made battery of lexical retrieval tasks. Before proceeding to the presentation of the results of between-group comparisons and the subsequent error analyses, the results of group comparison on various domains of Kannada version of Addenbrooke s Cognitive Examination (Lokesh, unpublished) is presented to ascertain that both groups exhibited comparable cognitive skills. Table 4.1: The descriptive statistics and the between-group comparisons of clinical and control groups across five domains of Addenbrooke s Cognitive Examination (Kannada). Values in parentheses indicate the maximum possible score under each domain. Independent groups Group comparison Domain Group Mean SD CI (95%) Lower Upper df t- value P Attention & Orientation (18) Memory (26) Fluency (14) Language (26) Visuospatial (16) * significant Clinical 16.73 0.7 Control 16.91.97 Clinical 23.95 1.36 Control 24.32 1.28 Clinical 6 1.41 Control 9.32 1.84 Clinical 21.86 2.71 Control 22.91 2.33 Clinical 14.32 1.17 Control 15.36 0.66-0.56 0.19 21-1.00 <.05-0.78 0.06 21-1.78 <.05-3.74-2.9 21-16.46 >.05 * -1.39-0.69 21-6.24 >.05 * -1.58-0.51 21-4.04 <.05 The comparison of performance on Addenbrooke s Cognitive Examination Kannada version (Lokesh, unpublished) showed no significant difference in the three domains of attention and orientation, memory, and visuospatial functions between the two 69
groups. However, these groups differed significantly in the language and (verbal) fluency domains. 4.1.Reliability analysis The reliability of transcriptions was analyzed both among and within transcribers for a set of selected tasks in the battery. For this purpose, each consistently transcribed item was given a point of one (1) and two (2) for each inaccurately transcribed item. Table 4.2 shows the tasks and the intra-class correlation coefficient (ICC) for each of these comparisons. Table 4.2: Inter-transcriber intra-class correlation coefficient (ICC) for four selected tasks Tasks ICC Noun-retrieval.718 Definition-naming.81 Animals.762 Phoneme /a/.778 The comparison of transcriptions across the three transcribers showed good agreement (i.e., >.7) confirming the reliability of the transcriptions. The intra-transcriber reliability was also examined by ICC analysis for a set of selected tasks from the convergent and divergent conditions. Table 4.3 provides the ICC of intra-transcriber reliability analysis. 70
Table 4.3: Intra-transcriber intra-class correlation coefficient (ICC) for four selected tasks Tasks Transcriber ICC 1.8 Verb-retrieval 2.864 3.864 1 - Category-naming 2-3.864 1.9 Vehicles 2.9 3.864 1 - Phoneme /s/ 2-3 - The empty cells in Table 4.3 indicate that the two transcriptions were identical. It is, thus apparent from the ICC analyses that the transcriptions of the responses showed good agreement (i.e., >.7), and therefore reliable. 4.2. Convergent tasks In the following section, the results of between-group (clinical & control) comparisons are presented. For representational clarity, the results of all between-group (within-task) comparisons of the scores from the convergent tasks are presented in Table 4.4. However, wherever appropriate, repeated measures ANOVA were used for betweentask, between-group comparisons. 71
4.2.1. Comparison of accurate responses Table 4.4: Descriptive statistics and the results of between-group comparisons on various convergent tasks. Values in parentheses indicate the maximum possible score under each subtask. Convergent tasks Independent groups Group Mean SD CI (95%) Lower Upper Group comparison df t- value p Nouns (20) Verbs (20) Antonyms (20) Synonyms (20) Definitions (20) Category (20) Responsive (10) Faces (10) Colors (6) Emotions (5) Clinical 17.23 2.31 Control 19.09 1.06 Clinical 14.14 2.9 Control 17.73 1.72 Clinical 13.41 2.72 Control 18.18 1.7 Clinical 11.5 3.22 Control 17.23 2.09 Clinical 17.04 1.86 Control 17.55 2.21 Clinical 10.77 3.62 Control 17.27 2.57 Clinical 5.91 1.99 Control 8.86 1.36 Clinical 5.5 1.71 Control 7.32 2.23 Clinical 3.5 1.76 Control 4.73 1.2 Clinical 1.95 1.04 Control 2.64 1.21-2.62-1.11 21-5.16 <.001-4.44-2.74 21-8.78 <.001-5.55-3.98 21-12.64 <.001-6.91-4.55 21-10.11 <.001-1.02 0.03 21-1.98.061 NS -7.65-5.35 21-11.74 <.001-3.57-2.33 21-9.92 <.001-2.28-1.62 21-7.21 <.001-1.89-0.55 21-3.81 <.05-0.99-0.36 21-4.46 <.001 NS not significant 72
Table 4.4 shows that the clinical population showed significantly poorer performance in all but one task (i.e., definition-naming) when compared to the control group. On the task of definition-naming, the difference in means between the groups (0.51) failed to reach statistical significance. Although it is apparent from the comparisons of the mean scores that the control group outperformed the clinical group in most of the tasks, the differences in mean scores in certain tasks were of academic interest. For instance, the control group scored high on retrieving nouns, but not the clinical group. Both groups however, had low scores on retrieving verbs (see Table 4.4). Verbs are considered to be more difficult to process as they are inherently complex, more abstract, and less imageable compared to nouns (Bird, Howard, & Franklin, 2003). In order to examine if the extremely poor performance on verb-retrieval task by the clinical group was due to the inherent processing difficulty associated with this grammatical class alone or to the combined effects of brain damage and verb processing difficulty, the repeated measures ANOVA was performed with the Group as the independent variable and noun- and verb-retrieval tasks as the factors. The results of this comparison showed a significant main effect for the tasks (F (1, 42) = 46.56, p < 0.001) (η 2 =.526) as well as for the interaction between groups and tasks (F (1, 42) = 7.00, p <.05) (η 2 =.143). This result, therefore, confirmed that the brain damage in the clinical group resulted in disproportionate impairment in retrieving verbs. Figure 4.1 depicts the distribution of the mean scores of the two groups as a function of the tasks under comparison. 73
Figure 4.1: Performance of clinical and control groups as a function of noun and verb retrieval tasks Yet another observation that triggered additional analysis was the better performance of control subjects on the antonym-generation task compared to their performance on synonym-generation task. Although the scores were poorer, the participants in the clinical group too showed a similar trend (i.e., higher scores on antonym- than on synonym-generation task). Together these results showed that antonyms were generated more accurately than synonyms. Some studies (e.g., Jeon et al., 2009) have reported of both shared and separate neural substrates while processing these two classes of lexical items. In this context, it was interesting to examine if the brain damage caused any disproportionate processing deficits in either antonyms or synonyms. For this purpose, the repeated measure ANOVA was performed with the Group as the independent variable and the two tasks (i.e., antonym- & synonym-generation) as the factors. The results of this comparison showed a significant main effect for the tasks (F (1, 42) = 14.87, p < 0.001) (η 2 =.261), but not for the interaction between the groups and tasks (F (1, 42) = 1.65, p >.05) (η 2 =.038). This result, therefore, confirmed that the brain damage did not result in any specific disadvantage in processing antonyms or synonyms. 74
Figure 4.2 depicts the distribution of the mean scores of the two groups as a function of the tasks under comparison. Figure 4.2: Performance of clinical and control groups as a function of antonym- and synonym-generation tasks. In essence, the analysis of responses from the convergent tasks, which mainly focused on the between-group comparison showed significantly poor performance in the clinical group in all but one (definition-naming) task (see Table 4.4). Further, certain between-task comparisons performed based either on the past research evidence (e.g., noun-verb comparison) or on academic interest (e.g., antonyms-synonyms) showed that the subjects in the clinical group exhibited disproportionate impairment while retrieving verbs compared to nouns, whereas such processing disadvantage was not seen in the case of antonyms or synonyms. In the following section, the results of error analysis from the convergent tasks are presented. 75
4.2.2. Error analysis: Convergent tasks In the convergent tasks, the distribution of error types (see Table 4.5) showed a predominance of the delayed correct responses (DCR) in both clinical and control groups. They constituted 13.91% of the overall responses and 39.87% of the error responses in the clinical group. In the control group, the DCR constituted 7.21% of the total number of responses and 55.4% of the total number of error responses. The next predominant type of error, as is apparent from Table 4.5, was no response. They constituted 9.36% of the total number of responses and 26.84% of the total error responses in the clinical group. In the control group, 3.14% of the total number of responses and 24.13% of the overall error responses were no responses. The circumlocutions, coordinate, associate, superordinate, subordinate error types as well as the descriptive responses were indicative of the underlying lexico-semantic deficits and these errors together constituted 295 responses, which in turn, was 8.83% of the total number of responses and 25.31% of the total number of error responses in the clinical group. The control group produced a smaller number of such errors. That is, only 52 responses that constituted 1.56% of the overall number of responses and 11.95% of the total number of error responses belonged to the semantic type. Yet another category of errors (i.e., wrong responses) that bore no resemblance to the target items semantically, phonemically, or visually constituted 2.3% of the total responses and 6.6% of the overall error responses in the clinical group. The control group showed a total number of 34 responses under this category contributing to 1.01% of the total number of responses and 7.82% of the overall number of error responses. 76
Clinical Control Clinical Control Clinical Control Clinical Control Clinical Control Clinical Control Clinical Control Clinical Control Clinical Control Clinical Control Chapter 4 Table 4.5: Types and distribution of error responses across the convergent tasks and participant groups Tasks Nouns Verbs Antonym Synonym Responsive Definition Category Emotions Faces Colors Error types DCR 23 14 55 25 70 25 31 23 53 20 80 26 48 28 11 18 52 36 42 26 Circumlocution 2 0 1 0 0 0 2 1 0 0 3 0 21 6 0 0 0 0 0 0 Coordinate 9 2 4 0 5 0 1 1 1 0 11 1 0 0 0 0 0 0 0 0 Associate 1 0 2 0 29 4 40 5 4 1 6 0 14 4 0 0 0 0 0 0 Superordinate 12 0 0 0 0 0 1 0 1 0 0 0 63 12 0 0 0 0 0 0 Subordinate 0 0 5 0 0 0 5 0 3 0 0 0 2 0 0 0 0 0 0 0 Descriptive 0 0 22 13 2 1 2 0 0 0 4 0 0 0 17 1 0 0 0 0 Visual 7 3 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Paraphasia (phonemic) DCR - Delayed Correct Response 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Neologism 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 No response 7 1 32 10 38 11 90 33 25 4 31 9 55 10 4 9 28 18 3 0 Wrong response 0 0 5 2 1 1 14 3 0 0 1 0 1 0 21 15 22 11 12 2 77
Each error type across the 10 convergent tasks was compared between the two groups to examine if the clinical group and control groups varied significantly on them using paired sample t-test. Table 4.6 shows the results of between-group comparison of the errors (within-type). Table 4.6: Types and distribution as well as the between-group comparison of error types in the convergent tasks Error type Independent groups Population Mean SD Group comparison CI (95%) df t-value p Lower Upper DCR a Clinical 46.5 20.8 Control 24.1 5.99 9.3 35.5 9 3.87 <.05* No response Semantic Visual Wrong response Clinical 31.3 26.33 Control 10.5 9.49 Clinical 29.5 29.58 Control 5.2 7.17 Clinical 1.6 3.4 Control 0.3 0.95 Clinical 7.7 8.82 Control 3.4 5.25 7.19 34.46 9 3.46 <.05* 7.69 40.9 9 3.31 <.05* -0.83 3.43 9 1.35 >.05 NS 0.89 7.71 9 2.85 <.05* a Delayed correct response; NS not significant; * - significant The comparison of error types between the groups showed that the clinical group showed significantly larger number of errors except for the visual errors. It is apparent from Table 4.6 that the different error types showed extreme dispersion (i.e., SD) in their distribution across the tasks in the clinical group. The distribution of the visual errors across the tasks between the two groups did not significantly differ, indicative of the fact that visual processing in the clinical group was similar to that of the control group. 78
4.3. Divergent tasks 4.3.1. Accurate scores, cluster size, and switches In the divergent tasks, the participants were instructed to retrieve maximum number of exemplars under each given criterion within 60 seconds duration. This task included both semantic and phoneme criteria. The former criterion had eight semantic categories (i.e., animals, vegetables, birds, fruits, vehicles, clothes, furniture, & verbs) and the latter had three categories (/p h /, /a/, & /s/). The transcribed data were analyzed in several ways based on the proposals of Troyer et al. (1997) and Joanette et al. (1988). First, the accurate score (excluding repetitions & unrelated items) under each criterion was calculated for every participant. Subsequent to this, the mean accurate scores were determined by averaging the total scores, separately for each major task (i.e., semantic & phonemic). The mean scores obtained from the clinical and control groups were compared using paired sample t-test under each criterion (see Table 4.7). The results of this comparison revealed significant difference between the two groups in terms of both semantic and phonemic fluency tasks. Additionally, the mean cluster size and switches were also compared between the two groups. The comparison of cluster size showed significant difference only in the semantic, but not in the phonemic criterion. However, the between-group comparison of switches failed to show any significant difference under both semantic and phonemic criteria (see Table 4.7 for the details of these comparisons). 79
Switches Cluster size Accurate score Variables Chapter 4 Table 4.7: Descriptive statistics as well as the results of between-group comparisons of the mean accurate score, clusters, and switches under the divergent (verbal fluency) tasks Independent groups Group comparison Criterion Group Mean SD CI (95%) Lower Upper df t- value p Semantic Clinical 9.4 1.35 Control 12.5 1.8-3.63-2.57 21-12.9 <.001 Phonemic Clinical 6.98 2.09 Control 8.38 2.74-2.1-0.68 21-4.09 <.05 Semantic Clinical 1.80 0.29 Control 1.99 0.28-0.37-0.02 21-2.27 <.05 Phonemic Clinical 1.81 0.98 Control 1.94 0.89-0.88 0.45 21-0.66 >.05 Semantic Clinical 26.68 4.26 Control 26.82 4.00-0.98 0.71 21-0.34 >.05 Phonemic Clinical 3.68 1.86 Control 4.36 2.06-1.52 0.16 21-1.69 >.05 4.3.2. Time course analysis The time course analysis was performed on both semantic and phonemic fluency tasks, where, the average number of accurately identified items in each quadrant of the 60 seconds period was calculated. Table 4.8 provides the descriptive statistics of the two groups across the four quadrants under each criterion. 80
Phonemic Semantic Chapter 4 Table 4.8: Descriptive statistics (Mean & SD) of the clinical and control groups across the time quadrants under semantic and phoneme fluency tasks Criterion Quadrant (seconds) 1 (0-15) 2 (16-30) 3 (31-45) 4 (46-60) 1 (0-15) 2 (16-30) 3 (31-45) 4 (46-60) Group Mean SD Clinical 4.76 0.97 Control 5.29 0.73 Clinical 3.05 0.54 Control 3.78 0.79 Clinical 1.19 0.43 Control 2.02 0.67 Clinical 0.27 0.18 Control 0.93 0.47 Clinical 3.55 1.08 Control 4.03 1.25 Clinical 2.3 0.66 Control 2.48 0.88 Clinical 0.79 0.65 Control 1.12 0.58 Clinical 0.35 0.33 Control 0.68 0.42 Additionally, the repeated measures ANOVAs were performed under each criterion to examine if the clinical and control groups performance varied as a function of time. Under the semantic criterion, the comparison of scores across the quadrants (Figure 4.3) showed a significant main effect for the groups (F (3, 126) = 469.99, p < 0.001) (η 2 =.918), but not for the interaction between the groups and time quadrants (F (3, 126) = 0.482, p > 0.5) (η 2 =.011). 81
Figure 4.3: Mean scores of the clinical and control groups as a function of the time quadrants in the semantic fluency task Similarly, the phonemic condition (Figure 4.4) also showed a significant main effect only for the groups (F (3, 126) = 291.64, p < 0.001) (η 2 =.874), but not for the interaction between the groups and time quadrants (F (3, 126) = 0.506, p > 0.5) (η 2 =.012). Thus, the time-course analysis revealed that the two groups showed a similar pattern of performance under both semantic and phonemic criteria. 82
Figure 4.4: Mean scores of the clinical and control groups as a function of the time quadrants in the phoneme fluency task 4.4. Literacy and lexical retrieval While collecting the data from the participants, it was apparent to the investigator that subjects from both groups with moderate to high levels of education (i.e., 12 years) performed better in most of the tasks. Although, the apparently small number of participants (n = 5) in this operationally-defined literate group (i.e., education 12 years) did not permit the use of any statistical test of significance on the current data, to highlight the influence of literacy on the overall test performance, the descriptive statistics (Mean & SD) of both groups (i.e., literate & semi-/illiterate) across the subtests are provided in Table 4.9. 83
Verbal fluency task Convergent task Chapter 4 Table 4.9: The Mean and SD of accurate responses across the tasks between clinical and control groups as a function of literacy (literate: 12 years of education) Task Subtask Group Literate (n = 5) Semi-/Illiterate (n = 17) Mean SD Mean SD Nouns Verbs Antonyms Synonyms Definitions Category Responsive Faces Colors Emotions Semantic Phonemic Clinical 19.2 1.79 16.65 2.15 Control 19.8 0.45 18.88 1.11 Clinical 17.00 1.58 13.29 2.67 Control 19.6 0.55 17.17 1.55 Clinical 15.2 2.17 12.88 2.69 Control 19.6 0.55 17.76 1.71 Clinical 12.8 4.15 11.12 2.93 Control 19.00 1.00 16.71 2.05 Clinical 18.4 1.14 16.65 1.87 Control 19.2 0.84 17.06 2.28 Clinical 15.2 1.09 9.47 3.00 Control 19.8 0.45 16.53 2.45 Clinical 8 0.71 5.29 1.83 Control 9.8 0.45 8.58 1.42 Clinical 7.8 0.84 4.53 1.46 Control 10 0.00 6.12 1.99 Clinical 5.00 1.0 3.06 1.71 Control 5.8 0.45 4.41 1.18 Clinical 3.4 0.55 1.53 0.72 Control 3.5 0.87 2.24 0.97 Clinical 11.13 0.65 8.89 1.03 Control 14.33 0.88 11.97 1.65 Clinical 9.46 0.93 6.26 1.75 Control 12.38 1.48 7.2 1.68 84
Figure 4.5: Scatter plots depicting the distribution of total scores on: (A) convergent tasks, (B) divergent semantic fluency, and (C) divergent phoneme fluency tasks for individual participants as functions of their literacy and group (i.e., clinical & control) membership. It is obvious from both Table 4.9 and Figure 4.5 that the performance of the literate group was always better on all the tasks. The implications of this observation are discussed in the following chapter (Discussion). 85
4.5. Site and extent of lesion and lexical retrieval In the present study, all participants in the clinical group (except A1) exhibited lesion in the right frontal lobe (see Appendix 2). Among them, 10 participants (A6, A8, A9, A10, A12, A13, A14, A19, A21, & A22) showed lesions confined to the frontal lobe, whereas, remaining exhibited lesion in the frontal and adjacent parietal (A2, A3, A4, A15, A17, & A18), temporal (A5 & A7) or temporo-parietal (A11, A16, & A20) lobes. For the purpose of comparison, these subjects were categorized into frontal (N = 10) and frontal plus (N = 11; fronto-parietal + fronto-temporal + fronto-temporo-parietal) groups. Owing to the smaller number of subjects in each group, a statistical test of significance was not performed. However, the descriptive results are provided in Table 4.10. 86
Divergent tasks Convergent tasks Chapter 4 Table 4.10: The Mean and SD of accurate responses across the lexical retrieval tasks between Frontal (N = 10) and Frontal plus (N = 11) groups Tasks Subtasks Group Mean SD Nouns Verbs Antonyms Synonyms Definitions Category Responsive Faces Colors Emotions Semantic Phonemic Frontal 17.9 2.08 Frontal plus 16.36 2.29 Frontal 14.00 2.76 Frontal plus 13.8 2.82 Frontal 13.45 2.73 Frontal plus 13.3 2.98 Frontal 11.45 3.27 Frontal plus 11.9 3.46 Frontal 16.82 1.6 Frontal plus 17.00 2.05 Frontal 10.73 3.69 Frontal plus 10.51 3.78 Frontal 6.00 1.73 Frontal plus 5.6 2.32 Frontal 5.27 1.41 Frontal plus 5.6 1.96 Frontal 3.73 1.95 Frontal plus 3.2 1.68 Frontal 1.91 1.04 Frontal plus 1.9 1.1 Frontal 9.2 1.4 Frontal plus 9.35 1.15 Frontal 7.2 2.15 Frontal plus 6.63 2.13 87
It is apparent from Table 4.10 that, in general, both groups exhibited comparable performance across the tasks. The implications of these results are discussed in the following chapter (Discussion). In sum, the foregoing sections presented the results of comparisons of scores on various tasks used in the current study. The results, in general, showed an overall poor performance in the clinical group. The comparison of the group performance on convergent tasks showed significantly poor performance in the clinical group in all but one task (i.e., definition-naming). Similarly, the clinical group performed poorly on both divergent (i.e., semantic & phonemic verbal fluency) tasks compared to the control group. Additional analyses (i.e., switches, clusters, & time course of lexical retrieval) were performed between the two groups in the divergent tasks. The results of these analyses showed that the clinical group produced significantly smaller mean cluster size in the semantic condition, whereas the cluster size in the phonemic criterion was similar to that of the control participants. Additionally, the two groups of participants did not differ in terms of the number of switches in the semantic and phonemic criteria. Finally, the time course analysis of responses from the divergent tasks showed that although the two groups differed in terms of the number of exemplars generated across the four quadrants of 60 seconds duration, their performance showed a similar trend during this period. In the following section, the results of various comparisons are discussed in the light of evidences from previous research. 88