Convergent tasks

Transcription

1 CHAPTER 3 METHODS

2 The current study attempted to provide further insights into the debatable role of right hemisphere in lexico-semantic processing. Specifically, it investigated the lexical retrieval skills in a group of subjects with right hemisphere damage (RHD). Additionally, it also attempted to analyze the error patterns in this population, in order to understand the nature of underlying lexico-semantic processing deficit, if any. This study was conducted in two phases. Phase I aimed at the development of a battery of lexical retrieval tasks and Phase II focused on the administration of this battery on two groups of subjects (i.e., clinical subjects with RHD & control normal subjects), which in turn, was followed by the data analysis and interpretation. 3.1.Phase I The review of literature showed that several non-standardized and custom-made batteries have been used to examine the lexical retrieval deficits in subjects with RHD. Although non-standardized tests may be used in the assessment of communication disorders (Coelho, Ylvisaker, &Turkstra, 2005), owing to the heterogeneity of the tasks employed in the previous investigations, a consensus on the role of right hemisphere in lexico-semantic processing had not been arrived at. To circumvent this limitation, in the present study a comprehensive set of tasks to investigate the role of right hemisphere in lexical retrieval skills, was compiled. In addition to the major tasks that were employed in the previous studies on subjects with RHD, certain additional tasks that were commonly employed for other clinical populations such as those with aphasia, dementia, and epilepsy were also included in the battery to make it a comprehensive one. These additional tasks were considered under the assumption that inclusion of such tasks may make the battery more sensitive to the arguably subtle lexico-semantic processing deficits of subjects with RHD (Joanette et al., 1990). Broadly, these tasks were of two types: viz. convergent and divergent. The convergent tasks elicit specific responses to the given stimulus (e.g., visual confrontation naming task), whereas, the divergent tasks elicit multiple responses to a given task (e.g., verbal fluency tasks) (Worrall &Hickson, 2003). 50

3 The development of the convergent tasks, unlike the divergent tasks, involved a few steps starting with the initial pooling of items to the final rating by a group of normal subjects. In the following section, the convergent tasks employed in the present study as well as a brief description of their development are presented Convergent tasks The study included a set of 10 confrontation naming tasks such as noun-retrieval, verb-retrieval, retrieval of the names of famous people, color-naming, naming emotional expressions, definition-naming, responsive-naming, category-naming, synonym-generation, and antonym-generation. Noun retrieval and antonym generation tasks have been used in previous studies on RHD. The remaining tasks were included as they have been frequently used in investigations of subjects with aphasia, dementia, and epilepsy as well as in fmri studies. In the latter set of studies, moderate activations have been reported in the RH in addition to the stronger LH activations. Among the 10 tasks mentioned above, the first five used visual stimuli and the last five used auditory stimuli Construction of the convergent tasks Selection of items For the purpose of generating items under various convergent tasks listed above, a group of five native Kannada speakers (graduate students of Audiology and Speech-Language Pathology) were required to write down as many items as possible under eight subcategories, within approximately 60 minutes for each subcategory. Items for color and definition naming subtests were not pooled as existing materials were used for these tasks. The participants were allowed to list out the items in each of the eight subcategories in multiple sessions across a week. All the items listed out by each participant were considered for rating (described below). The total number of items generated under each subcategory and their representative examples are provided in Table

4 Table 3.1: The convergent tasks: description, examples, and the item selection procedure Subset 1. Nouns 2. Verbs 3. Emotions 4. Famous people 5. *Color naming 6. Responsive naming 7. Synonyms 8. Antonyms 9. Category naming 10. *Definition naming Description of the task Name the object in the picture Name the action in the pictures Name the emotion depicted in the picture Name the person in the picture Name the color Answer the question in single word Provide another word that with same meaning in Kannada Name/provide the opposite of the given word Provide the common word for the category that these belong to Provide the word for what is being described in the definition Example(s) se:bu (apple) vima:na (aeroplane) u:duvudu (blowing) i:juvudu (swimming) sukha(happy) dhukha(sad) Total items generated (& collected**) 215 (90) (68) 20 7 (7) 5 Gandhiji, Nehru 17 (17) 10 Kempu(Red), hasiru(green) aakaashadhallihaaruva vaahanayaavudhu? (vimana) [Which is the vehicle that flies in the air? (aeroplane)] kamala taavare(lotus) sukha(happy) dhukha(sad) hakkigalu kaage, gini, paarivala (birds crow, parrot, & pigeon) sondiluiruvaatidoddapr a:ni aane(a big animal with a trunk elephant) * Existing items were used for these subtests; ** only for visual tasks. Color Naming Task Number of items in the final task For color naming task, the items from the auditory word recognition section of Western Aphasia Battery (Kertesz, 1982) were used. 52

5 Definition naming task A set of 20 items from the auditory definition naming task in Kannada (Jose, 2008) was selected for the present study. Collection of pictures of the selected items Following the initial pooling of items, black and white line drawings of pooled items under the confrontation naming tasks were collected based on their accessibility from available resources. These resources included previous test materials (with the prior permission of the authors), pictures from the International Picture Naming Consortium ( and the Snodgrass and Vanderwart (1980) picture sets. Although names of a large number of nouns and verbs were listed out by the students, the pictures (i.e., B&W line drawings) of all these items could not be retrieved from the resources. This resulted in a smaller set of pictures in these categories (nouns 90; verbs 68). The pictures depicting famous persons were collected from the world wide web through internet browsing. For emotional expressions, the investigator required three students to show six emotions (happy, angry, disgusted, sad, surprised, &afraid) as well as a neutral face and these were photographed (by the investigator) with a high resolution digital camera (Sony Cybershot). During this procedure, the students were reminded to depict the emotions in a natural manner without any exaggerations. The pictures thus collected for various visual subtasks (nouns 90; verbs 68; famous faces 17; emotions - 7) were stored in the computer hard disc in.jpg format for the purpose of familiarity and complexity ratings. The items generated for auditory-based tasks (i.e., responsive naming, category naming, synonym- and antonym-generation tasks) were all audio-recorded in.wav format (with the help of a young female native Kannada speaker at a sampling rate of 44.1 khz) using Adobe Audition 1.5 to ascertain uniformity in stimulus presentation across the participants of the study. These items were stored initially into the hard-drive of the computer and later burnt onto a compact disc (CD), for the purpose of familiarity and complexity ratings. 53

6 Rating of the items Subsequent to the initial pooling and preparation of the items in suitable formats (i.e.,.jpg or.wav) ready for presentation through the computer, the familiarity and complexity of the items were rated. A group of 10 native Kannada-speaking subjects comprising of equal number of literates and semi/illiterates (5 literates with minimum 12 th grade education [mean = 15 years] and 5 semi/illiterates with 12 th grade education [mean = 3.4 years]) were selected for this purpose. The pictures selected under each category (e.gs. nouns & verbs) as well as the items selected under responsive, and category-naming, and those under the antonym and synonym generation tasks were subjected to familiarity and complexity ratings using a 3-point (i.e., familiarity: unfamiliar familiar highly familiar; complexity: simple complex very complex) Likert scale. Distinct from other items, the pictures of faces depicting various emotions and people were rated for percent accurate naming (i.e., 9/10 accurate naming) by the raters. During this rating procedure, the pictures depicting angry, sad, and disgusted did not achieve the predetermined criterion for selection. Therefore, five additional pictures each depicting these three emotions were obtained from the world wide web (www) and these pictures were used for the rating purpose. Among the second set of pictures, one item (each) depicting the expressions angry and sad achieved the selection criterion, whereas, those depicting disgusted failed to meet this criterion, and, thus were eliminated from the subtest. Selection of final items All items (except that of definition and color naming) under the convergent tasks were subjected to the ratings by a group of 10 native speakers as mentioned above. Considering the proposal of Spreen and Risser (2003) that items that are selected based on the normal distribution of their difficulty may yield the floor effect in people with brain damage, the current study, mostly enlisted those items that were rated as highly familiar and simple.however, a few items that achieved familiar and complex ratings (in lieu of highly familiar and simple ) were included in the final list in order to keep the number of test items roughly uniform. Care was taken not to include more than two such items in subtasks with a total item number of 20 and one item in subtasks with total of 10 items. For 54

7 pictures depicting emotional expressions, a criterion of 90% (i.e., 9/10) accurate naming by the 10 raters was used for inclusion. The final battery, thus, included 20 items each under nouns, verbs, antonyms, synonyms, definition, category and 10 items under responsive naming task. The section on famous faces included 10 items and the section on emotions included five items. Additionally, three items were selected as trial items under the noun, verb, definition, responsive, and category-naming tasks as well as the antonym- and synonymgeneration tasks. The lists of all items under various subtests are given in Appendix Divergent (Verbal Fluency) Tasks This study included 11 verbal fluency tasks under two categories (semantic 8; animals, vegetables, birds, fruits, vehicle, clothes, furniture, verbs (concrete action words) & phonemic 3: /p h /, /a/, & /s/). Distinct from the western studies that employ phonemes /f/, /a/, and /s/ under the phoneme fluency tasks, the present study substituted the phoneme /f/ with /p h /, based on two linguists inputs on the apparently limited number of words that begin with /f/ in Kannada. Additionally, the author performed a pilot test in three young native Kannada speakers in the age range of years and found that all of them experienced difficulty in retrieving more than 5-6 words that began with /f/, whereas, the same participants could retrieve around 15 words (on an average) with the phoneme /p h /. Therefore, in the present study, phoneme /f/ was substituted with /p h /. The categories under the semantic fluency criteria included nouns (i.e., animals, vegetables, birds, fruits, vehicles, clothes, &furniture), and verbs (concrete actions) Phase II Phase II of the study was aimed at the administration of the battery on both the clinical and control groups (case-control design) followed by the transcription and analysis of the responses. 55

8 Clinical group Sample size estimation Based on certain established statistical constants (Zα - level of significance of the test [1.96] & Zβ - power of the test [1.282]) and the standard deviation from a representative study in the past (Diggs &Basili, 1987) that employed both convergent (SD = 2.2) and divergent tasks (SD = 4.7), the estimated sample size for the current study was 19. However, owing to the availability, the current study included 22 participants in the clinical group. The subjects in the clinical group were selected based on the following inclusion and exclusion criteria: Inclusion criteria 1. Native/fluent Kannada speakers 2. Age range: years 3. Right-handed (Edinburgh Handedness Inventory; Oldfield, 1971) 4. Alert, oriented to time, place, and person (Addenbrooke s Cognitive Examination Kannada Version, Lokesh, unpublished) 5. Normal or corrected-to-normal vision 6. Etiology: first-ever stroke 7. Site of lesion: right hemispheric cortical or cortical + subcortical areas in the distribution of middle cerebral artery (as evidenced by CT/MRI). 8. Time post-onset: 2 6 months 9. Fair speech intelligibility permitting the examiner to make unambiguous perceptual judgments of the responses Exclusion criteria 1. Severe dysarthria 2. Inadequate attention, poor arousal or coma state 3. Presence of concomitant left hemisphere lesion as evident either from the neurological examination and/or CT/MRI findings 56

9 4. Stroke limited to the right hemispheric subcortical structures without an accompanying cortical lesion in the same hemisphere. 5. Complaint and/or history of epilepsy Selection procedure For the purpose of selection of participants to the clinical group, permission to review the medical case records was obtained from the Medical Superintendent of Kasturba Hospital, Manipal. Subsequent to this, the hospital registration numbers of patients with the International Classification of Diseases 10 (ICD 10) codes I61 to I64 (I61 intracerebral hemorrhage; I62 other nontraumatic intracranial hemorrhage; I63 cerebral infarction; I64 not specified as hemorrhage or infarction) from 2007 to 2010, were periodically recorded. With the help of registration numbers, the CT/MRI reports of a total of 748 patients were reviewed (periodically, for 3 years) through the hospital s intranet portal ( The contact details of those patients with neuroimaging-evidenced right hemispheric cortical or cortical + subcortical lesion were recorded from the Medical Records Department of the hospital, for possible later inclusion in the study, after a minimum post-onset period of two months. The detailed selection procedure used in this study is depicted in a flow chart (see, Figure 3.1). 57

10 Total number of patients with stroke (ICD codes I61-I64) reviewed from August 2007 to February Exclusively right subcortical stroke 32: eliminated from the study Patients with right cortical or cortical + subcortical stroke 105 Patients with left or bi-hemispheric stroke 611: eliminated from the study Non-Kannada speakers 13: eliminated Kannada speakers - 92 Patients from Manipal and neighboring locations- 57 Patients from distant locations - 35 No contact established 20 Contact established - 37 No contact established - 21 Contact established - 14 Deceased - 11 Request accepted - 24 Request rejected - 2 Deceased - 3 Request accepted - 7 Request rejected - 4 Tested at residence - 21 Tested in the department - 3 Not reported for study - 3 Reported for study - 4 Eligible - 16 Ineligible - 5 Eligible - 3 Eligible 3 Ineligible - 1 Figure 3.1: Flowchart depicting the scheme of selection of participants to the clinical group. 58

11 The battery of tests was administered to 16 participants at their residence and six were tested in the institute. Those participants who accepted the investigator s request and reported to the institute for the purpose of participation (including the eligible and ineligible N = 7) were provided with minimal travel allowance. However, those who were tested at their residence were not provided such financial allowance. Table 3.2 provides the demographic information of participants in the clinical group. 59

12 Table 3.2: Demographic and lesion data of the participants in the clinical group Participant Age (years)/ Education RH site of lesion* (see Months Gender (years) Appendix II) post-onset A1 28/Male 13 Posterior temporooccipital infarct in the 3 MCA-PCA distribution A2 75/Male 5 Extensive frontoparietal lesion in the 5 MCA-ACA distribution A3 56/Female 4 Extensive right frontoparietal lesion in the 4 MCA distribution A4 58/Male 10 Fronto-parietal intraparanchymal lesion 4 in the MCA distribution A5 60/Male 12 Fronto-temporal infarct 6 A6 50/Male 3 Frontal infarct 4 A7 77/Female 4 Fronto-temporal infarct 6 A8 63/Male 12 Frontal infarct 4 A9 71/Male - Frontal infarct 6 A10 44/Male 14 Frontal infarct 2 A11 67/Male 7 Fronto-temporo-parietal infarct 6 A12 55/Male 5 Frontal infarct 6 A13 67/Male 15 Frontal infarct 3 A14** 71/Male 4 Frontal infarct 2 A15 62/Female - Fronto-parietal corticosubcortical infarct 6 A16 59/Male 8 Fronto-temporo-parietal 3 A17 77/Male 2 Fronto-parietal including subcortical 4 (BG & internal capsule) A18 68/Male 5 Fronto-parietal including subcortical 4 A19 51/Female 4 Frontal infarct 2 A20 66/Male 7 Fronto-temporo-parietal infarct 5 A21 63/Male 4 Frontal infarct 6 A22 74/Male - Frontal infarct 5 * see Appendix II (Template) for the extent of lesion in all but one participants ** Image not included 60

13 The mean age of the participants in the clinical group was years (SD = 11.73) and the mean years of education was 6 (SD = 4.35) Control group A group of 22 right-handed, age (with a relaxation of 2 years: Mean = years; SD = 11.21), gender, and education-matched (with a relaxation of 1 year: Mean = 5.82 years; SD = 4.32) right-handed normal subjects were recruited to the control group. These participants were matched on a case-to-case basis with the clinical group and they were selected from the hospital premises (caretakers of the in-patients). A detailed interview was conducted to rule out any neurological history (e.g., epilepsy, early head injury, transient ischemic attacks, or recovered stroke) and familial left handedness or forced right handedness. Further, the first five inclusion criteria employed in the clinical group were also employed in the selection of participants in the control group. Table 3.3 provides the demographic data of the control participants. 3.3.Written consent Upon selection and the informal agreement by the subjects to participate in the study, the written consent was obtained from the subjects (i.e., including both clinical and control groups). For the illiterate subjects, a literate proxy (a close family member) was asked to read out the consent letter, and if required, to sign the form on behalf of the participant. 3.4.Institutional Ethical Clearance The study was approved by the Institutional Ethical Committee of Manipal University. 61

14 Table 3.3: Demographic data of the participants in the control group Participants Age Education (years)/gender (years) B1 30/Male 12 B2 74/Male 4 B3 55/Female 4 B4 58/Male 10 B5 60/Male 12 B6 48/Male 4 B7 75/Female 4 B8 61/Male 10 B9 71/Male - B10 45/Male 12 B11 65/Male 7 B12 55/Male 4 B13 68/Male 14 B14 71/Male 4 B15 60/Female - B16 60/Male 7 B17 75/Male 3 B18 66/Male 4 B19 50/Female 4 B20 65/Male 7 B21 64/Male 4 B22 75/Male Procedure The scheme of administration of the test battery was identical for both clinical and control groups. The participants were made to sit comfortably on a chair in a quiet environment. Following this, they were provided with general instructions about the tasks and the expected responses as well as the request for break in the course of the test administration, if needed. 62

15 General instructions Convergent tasks: I am going to present a few tasks where you will either see some pictures or hear a few words and sentences. You shall listen to or watch them carefully and name them accurately and quickly. I will provide you specific instructions and trial items for each task so that it becomes easy for you to perform them. Further, please tell me when you need a break. Divergent tasks: Semantic fluency: I am going to tell you the names of a few categories of words. You are required to name as many items as you can from these categories. You will be provided one minute each for every category. For example, when I say /hu:vugalu/ (flowers), you must name flowers like /gula:bi, tha:vare, mallige../ (rose, lotus, jasmine,..). Try to avoid repetitions. Phoneme fluency: I am going to tell you a few sounds. You are required to name as many items as you can whose names start with these sounds. You will be provided one minute each for every sound. For example, when I say /m/, you must name words like /mane/ (house), /mi:nu/ (fish), /mola/..(rabbit). Avoid repetitions and proper nouns such as names of people (example, mahesha), places (example, mangalu:ru), or sequences (example: mu:vattu(30), mu:vattondu(31), mu:vatteradu(32)/..) Convergent tasks Specific instructions were provided at the commencement of the respective subtasks. The stimuli under the convergent tasks (both auditory & visual) were presented through a laptop (IBM Lenovo R60). The two major tasks (convergent & divergent) as well as the subtasks within them were randomly administered to eliminate the order effect as well as fatigability associated with the phoneme fluency task. The monitor of the laptop was appropriately set to facilitate adequate view of the picture stimuli. Further, before the commencement of trials, a brief sound track (Kannada passage reading by the female speaker 10 seconds) was played back to each participant to set the volume of the speakers of the computer at a comfortable listening level. Each participant was tested individually and the responses were recorded with a portable audio-recorder (Sony P-370) for off-line transcription and analysis Visual convergent tasks: The stimuli were presented one by one and the participants were given 10 seconds response time for each stimulus. Failure to respond during this time period (i.e., 10 seconds) 63

16 led to the provision of phonemic/syllabic/semantic cues [phonemic cue: the initial phoneme of the target (e.g., for a target response na:ji [dog], the phonemic cue would be /n / without the following vowel, whereas, the following syllabic cue would be the combination of /n/ and /a/, i.e., /na../. The semantic cue would provide semantic or functional attributes (e.g., bogaluvapraani)]. After the lapse of initial 10 seconds response time, cues were provided and responses (if any) were recorded for another 10 seconds. No or lack response during the cueing period (i.e., latter 10 seconds) led to the provision of accurate response by the investigator. Some participants were found to be distracted by their inability to name the items and continued their attempts to retrieve the previous response even after the following stimulus was presented, which, in turn, interfered with the continuity of test administration. The provision of accurate response was aimed at eliminating such attempts from the participants Auditory convergent tasks: The auditory convergent tasks followed the similar scheme of stimulus administration as that of the visual convergent tasks. That is, the stimuli were presented one by one and each stimulus was followed by 10 seconds response time (for production of the accurate response). If the subject failed to provide an accurate response within these 10 seconds, it was followed by another 10 seconds during which cues were provided and the response (if any) was recorded. In case of unsuccessful trials, the investigator provided the accurate response at the end of 20 seconds. However, distinct from the visual tasks, owing to the dynamic nature of the auditory stimuli, items were repeated once (whenever required). The criteria of stimulus repetition were: a) lack of response in the first five seconds of the response time; or b) request for repetition by the participant within the first five seconds of the response time. However, the response time (for the accurate responses) remained unchanged (i.e., 10 seconds from the offset of each stimulus presentation) irrespective of the stimulus repetition followed by another 10 seconds for the provision of cues and recording of cued-responses Divergent tasks: All the subtests under the divergent tasks were randomized with convergent tasks (both auditory & visual). The participants were asked to generate as many items as possible 64

17 under each category in one minute (60 seconds). The investigator provided a maximum of three exemplars under each category. The responses from the participants were audiorecorded as in the convergent tasks for later transcription and analysis. All but six participants in the clinical group completed the tasks in a single sitting and the remaining completed it in two sittings. However, all the participants in the control group completed the tasks in a single-sitting. The time of administration in the clinical group ranged approximately from 70 to 120 minutes, whereas, it ranged from minutes in the control group. 3.6.Transcription of the data The responses from both clinical and control groups on the convergent and divergent tasks were presented to three native young adult speakers of Kannada language (SLPs) for the purpose off-line orthographic transcription (de Picciotto&Friedland, 2001). 3.7.Analysis of responses Response analysis: Convergent tasks The transcribed data from the convergent tasks were later coded into different response types by the investigator with the help of a native Kannada speaker (SLP). The responses under the convergent tasks were coded into one of the 13 subtypes (see below). For the purpose of this study, an operational definition for three types of (i.e., correct [response code 1], delayed correct [response code 2] & descriptive [response code 13) responses was employed. That is, under the visual and auditory convergent tasks, the responses that are the correctly retrieved, self-corrected and those retrieved after the stimulusrepetition (for auditory tasks) within the first 10 seconds were considered as accurate responses and these werecoded with one [1]. For both auditory and visual based tasks, the responses that were accurately selfretrieved after the initial response time of 10 seconds and those retrieved subsequent to the provision of cues (phonemic/syllabic/semantic) were considered as delayed correct responses 65

18 (DCR) and these were coded with two [2]. The DCRs were analyzed separately from the accurate responses while comparing the group performance. Further, while analyzing the responses, the necessity for an additional criterion was deemed necessary. That is, a few participants described the pictures (e.g., sitting down holding a plate begging) rather than retrieving the target names of the items depicted in the stimuli. Such responses were considered as descriptive responses and coded with thirteen [13]. For the remaining response types (i.e., 3 12), the present study adopted the response coding criteria compiled by Corina et al. (2010) as provided below: 3. Circumlocutory response responses where the participants describe the attributes or functions of items (e.g., chair sit down) 4. Coordinate response a non-target, within category response (e.g., lion tiger) 5. Associate response a response that is related, but not semantically, to the target (e.g., foot shoe) 6. Superordinate response a hyponym that is, a more general name is produced instead of the target (e.g., pear fruit) 7. Subordinate response a hypernym that is, a more specific response instead of a basic or general one (e.g., flower rose) 8. Visual responses that bore visual similarity with the target item (e.g., nail knife) 9. Phonemic paraphasia 10. Neologism 11. No response 12. Wrong response responses that bore no resemblance to the target item semantically, phonologically, or visually Response analysis: Divergent tasks The responses in the divergent tasks were analyzed according to the guidelines proposed by Troyer et al. (1997) and Joanette et al. (1988). The reason for employing these scoring criteria is that, unlike the traditional means of quantitative analysis such as counting the number of accurate responses, these criteria provide additional insights into the lexical 66

19 retrieval mechanisms by analyzing the switches and clusters as well as the time course of item retrieval. Additionally, the scheme of analysis proposed by Troyer et al., (1997) has been extensively used in subsequent studies in several other languages (e.g., Unsworth, Spillers, & Brewer, 2011). Therefore, in the present study, the data obtained were analyzed in terms of the following measures: 1. Total number of correct exemplars retrieved under each criteria (i.e., semantic & phonemic) 2. Mean cluster size in semantic and phoneme fluency tasks (i.e., one number less than the total number of items in a cluster, where, a cluster is defined as a group of successively generated words belonging to the same subcategories, Troyer et al., 1997) 3. Average number of switches in semantic and phoneme fluency tasks (switch transition from one cluster to another as well as to single words, Troyer et al., 1997) 4. Time-course analysis (the number of category exemplars generated in each quadrant of 60-second duration) (Joanette et al., 1988) Reliability The inter- and intra-transcriber reliability analyses were performed for the data transcriptions. The reason for selection of transcribed data rather than analyzed data for the purpose of reliability assessment was the assumption that reliably transcribed data is likely to be analyzed accurately than an unreliably transcribed data set. To examine the intertranscriber reliability, two tasks each from the convergent (e.gs., noun-retrieval & definitionnaming) and divergent (e.gs., animals & phoneme /a/) conditions were selected. The transcription of the three transcribers for a subset of five participants from the clinical group for the above four tasks were used to test the inter-transcriber reliability. To assess the intra-transcriber reliability, the transcribers were instructed to retranscribe a subset of responses from the convergent (e.gs., verb-retrieval & category-naming) and divergent (e.gs., vehicles & phoneme /s/) tasks between seven to 14 days of initial transcription of five participants in the clinical group. The data, thus collected twice from 67

20 each transcriber was analyzed with intraclass correlation coefficient (ICC) analysis to obtain the intra-transcriber reliability Statistical analyses For the purpose of statistical comparison of the group means, only accurate responses were selected. Paired sample t-test was used for between-group (within-task) comparison of the mean values and for between-task comparison of the groups, repeated measures ANOVA was used. The reliability analyses were performed with intraclass correlation coefficient (ICC). All the statistical analyses were performed with SPSS 16 for Windows. 68