Propositional Idea Density in aphasic discourse

Abstract

Background: Measuring and describing the effects of aphasia on the informativeness of language is a complex process. Due to technological advances in the recent years, the processes involved in the measurement of language can be automated through the use of computerised analyses. In the present research, the Computerized Propositional Idea Density Rater (CPIDR 3.2) provides an automated method for calculating Propositional Idea Density (PD), a measure which has been shown to be sensitive to the effects of ageing and dementia. The measure of PD quantifies the proportion of words within a text that are semantically intrinsic to its overall meaning. Aims: This research investigated the extent to which PD measures were different in aphasic and non-aphasic discourse, and the extent to which PD correlated with the severity of aphasia and with the established measures of other aspects of informativeness. Given the previously reported high levels of agreement between the computerised analysis and human raters, it was hypothesised that there would be high levels of agreement between the computerised analysis and human judgements for aphasic (as well as non-aphasic) discourse. Methods & Procedures: Data from the Goals in Aphasia Project were analysed for the purposes of the present research. De-identified transcriptions of 50 interviews with individuals with aphasia and 49 interviews with their family members were stripped of all interviewer data, leaving only conversational contributions made by the participants. These formatted transcripts were analysed using two automated, computerised language analysis tools: CPIDR 3.2) and Systematic Analysis of Language Transcripts (SALT Version 8) for a range of other discourse measures. Outcomes & Results: Results showed a significant difference in PD (p < .001) between aphasic and non-aphasic discourse, and PD decreased significantly as aphasia increased in severity (p < .001). The concurrent validity of these findings was supported by the findings of relationships with established discourse measures. The total percent agreement between the computerised analysis and human judgments for aphasic discourse was 99.57% and for non-aphasic discourse was 99.74%. Conclusions: The findings indicated that PD has the potential to be used as a measure of discourse informativeness in aphasia and that further research into this approach to analysis is warranted.