The study was approved by the University Institutional Review Board, and informed consent was obtained for each participant. Subjects were tested individually in a quiet room in the laboratory. Experimental design Baseline expressive language tasks counting and formulation of single sentences were used to differentiate discourse-level neurovascular activation from sentence-level activation.
Participants were requested to count aloud from 1—, and to formulate single sentences. Use each picture to create a sentence that describes the picture. You are traveling to New York City for a two-week stay. Participants were allowed as much time as needed to complete the task. Personal narratives were elicited with the conversational map procedure, as described in McCabe et al. Both experiences were elicited in order to compare discourse from experiences with positive vacation versus negative injury valences: the participant was asked to tell about two such episodes in their life.
The elicitation procedure for the fictional narrative was described in Berman and Slobin [ 53 ]. The scene in this picture represents a moment in time. Something happened to cause the pictured event, and something is going to happen afterwards. When the slide changes, please tell me the whole story from what happened before the pictured event through what will happen after this scene. A schematic illustration of the overall experimental structure is presented in Figure 1. Narrative content analysis All discourse was transcribed verbatim by two trained students in the Communication Sciences and Disorders BS program at UVM: there were a total of 60 discourse transcripts 6 per participant: 2 procedural, 2 personal, 1 fictional, 1 conversation.
Data were analyzed and results presented graphically using Stata version Efficiency was analyzed using the number of correct information units CIUs per minute, as described in Nicholas and Brookshire [ 29 ] and Matsuoka, Kotani, and Yamasato [ 28 ]. This measure has the advantage of presenting information about speed, grammatical accuracy and content accuracy in a single score.
High Point Analysis and the MCAS were combined because unlike High Point Analysis, the MCAS includes indicators of discourse quality, which in most educational and vocational contexts is more functionally relevant than adherence to a conventional narrative structure. Conversation was analyzed using a modification of the Clinical Discourse Analysis tool [ 50 , 54 ], a conversational sampling procedure providing a descriptive analysis of functional aspects of social interaction.
Each utterance was gauged as to whether it contained an error in any of the domains errors in two or more different areas were not counted twice: an utterance was simply gauged as having an error or not.
The number of error-free t-units was divided by the total number of t-units in the sample, yielding a percentage. The fNIRS device uses 16 optodes optical sensors positioned over the frontal cortex to measure changes in optical density in cerebral bloodflow during task-related activity. On the vertical z axis, the sensor was positioned at Fpz, with Fp1 and Fp2 marker locations positioned at the bottom voxel row [ 57 ]. The lower row of channels is then aligned with Fp1, Fpz and Fp2. Soft foam tape was used to cover the outer surface of the device and prevent the intrusion of ambient light to the detectors.
Participants were asked to refrain from large head movements or forehead movements. Activation was measured during the first 60 seconds of each task, and recorded as average oxyhemoglobin HbO 2 levels for each optode. These values were transformed to beta-weights to eliminate nonsignificant activations i.
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HbO 2 data was derived from the 16 optodes at a sampling rate of 2 Hz. All recordings were made following a short device testing period to ensure adequate signal characteristics for the OD data i. To remove signal contamination related to nonrelevant biological signals e. This facilitated comparison of neurovascular activation between genres across participants. Analysis of neurovascular activation during Procedural discourse was narrowed to just the NYC task, because preliminary results indicated significant ceiling effects for the ATM task, and the NYC task was gauged to be a more realistic proxy for real-world moderate complexity planning.
Among Personal narratives the Injury task rather than the Vacation task was selected for comparison with neurovascular activation. Correlations between behavioral data and neurovascular activation were explored using pairwise Pearson product-moment coefficients. A paired-samples Hotelling t -squared test t 2 was used to compare differences in means between the genres, as noted in Table 2. Multiple comparison correction Bonferroni was not applied, following recommendations in Perneger [ 62 ], because of its assumption of a universal null hypothesis and because of the risk of such correction yielding type II error in preliminary research designs.
The six conditions i. Medians and variance for the efficiency measure are presented in boxplots in Figure 2A , and for informativeness in Figure 2B. Differences between genres were tested using two-sample t -tests using variables with unequal variances Table 3 , Figure 3. There were no significant differences in cortical neurovascular activation pattern amplitudes between the four genres. Pairwise Pearson product-moment correlations were calculated between both behavioral measures efficiency and informativeness and neurovascular activation Table 4 for each of the four genres.
As noted above, the NYC task was chosen to represent procedural discourse, and the Injury task was chosen to represent personal narratives.
There was a significant negative correlation between behavioral performance in Fictional narrative and neurovascular activation Figure 4. However, there are certain genres of discourse that are critically important in vocational, social, and other familiar contexts. Past research has primarily focused on production of short, simple fictional narratives often 5 sentences or fewer , despite the low frequency and weak functional relevance of that type of discourse in common vocational and social contexts.
The genre of fictional narratives alone may be too coarse a measure to sensitively and reliably gauge impairment in discourse. Hypothesis one was supported: there was no difference between the efficiency of the four genres. Given this finding, it may be valid when studying discourse efficiency to measure only the most ecologically relevant discourse genres.
Hypothesis two was also supported, that there were significant differences in informativeness between the genres. Among procedural discourse tasks, the more complex NYC task likely would have higher social and vocational relevance than the ATM task, and it evoked slightly lower efficiency and significantly lower informativeness.
It is reasonable to expect that discourse tasks with the highest complexity and lowest behavioral performance characteristics would be most susceptible to impairment with brain injury. There were no significant differences in neurovascular activation between the genres.
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It is worth noting that there appears to be a nonsignificant trend toward higher activation in the Personal injury genre. If that is the case, it may be related to the emotional salience of stories of personal injury, or because of the complexity of representing an injury to an unfamiliar listener. There were no significant correlations between behavior Efficiency and neurovascular activation in any of the genres.
There was a nonsignificant trend for increases in efficiency to be associated with decreases in neurovascular activation in personal and fiction narratives.
This seemingly counterintuitive observation of better performance with lower mental effort has been extensively reported in studies of physical movement efficiency, and as noted above, in discourse formulation where adherence to a predictable narrative structure lowers task-related neurovascular activation. It is plausible to consider that greater efficiency in particular as opposed to other microstructural measures such as productivity or grammaticality may in fact be evoked with lower neurovascular activation, and that in individuals with TBI the opposite pattern may be expected: higher activation resulting in lower performance.
This study was limited by its relatively small sample size, as well as by the high variability in both behavioral measures and neurovascular activation.
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Future research will observe discourse behavior and neurovascular activation among individuals with TBI. Larger sample sizes will likely resolve these issues, but relatively high variability in both discourse formulation and in neurovascular activation is likely to remain the rule. This may require use of single case research designs, and such designs also work well for intervention research where there is a high degree of individual tailoring of therapy to the individual [ 63 ]. Recent research has noted that differences in performance between sentence-based tasks versus discourse tasks appear to be the result of variation in the executive processes that support microstructural processing, such as attention, planning, monitoring, perspective-taking, and incorporating pragmatics or context into discourse [ 19 ].
The same researchers also noted deficits in timing more pauses and mazes within sentences, and errors of cohesion between sentences in individuals with TBI but without aphasia, leading to the plausible proposal that microstructural and macrostructural processes are not independent, but share foundational cognitive resources. It is important to continue to refine measurement and treatment of both types of deficit in ecologically relevant genres of discourse. Gray bar represents instructions to participants; white bar is 20 second fixation cross between tasks. Personal narratives are represented by the Vacation task and Injury task.
Median indicated by dashed lines. B Discourse informativeness by genre. For each genre, blue bar is left lateral activation, green bar is left medial activation, purple bar is right medial activation, and red bar is right lateral activation. CIU, correct information units. Discourse production following injury to the dorsolateral prefrontal cortex.