Discourse processing abilities in ageing : influence of working memory capacity on reference resolution.
Thesis DisciplineSpeech and Language Sciences
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Maintaining health and quality of life into old age is a critical issue facing society today. Language, and in particular language comprehension, is vulnerable to the processes of ageing (Au, Albert, & Obler, 1989; Kynette & Kemper, 1986; Nicholas, Obler, Albert, & Goodglass, 1985; Shewan & Henderson, 1988). An improved understanding of language processing and ageing will assist in distinguishing language difficulties in normal ageing from those in pathological ageing and aphasia (Maxim & Bryan, 1994) and, potentially, optimises communication throughout life. The current thesis focuses on a specific component of language comprehension - anaphora resolution . Anaphora resolution occurs frequently in everyday discourse and has been reported to decline with ageing (Cohen, 1979; Light & Capps, 1986; Ulatowska, Hayashi, Cannito, & Fleming, 1986). This thesis explored anaphora resolution relative to two key variables: ageing and working memory. Ageing was chosen as a variable as anaphora resolution has been shown to be affected by age (Cohen, 1979; Light & Capps, 1986; Ulatowska et al., 1986). Working memory was chosen as working memory is thought to underlie key aspects of discourse comprehension such as building a mental structure of discourse and updating the information (Brébion, 2003; Hasher & Zacks, 1988; Radvansky, Copeland, & Hippel, 2010; Radvansky, Lynchard, & von Hippel, 2009). Anaphora resolution was investigated using two key paradigms. The first focussed on anaphora resolution in a reading comprehension task. Performance was assessed using accuracy of response. The second employed Gernsbacher's (1989) probe-response paradigm. The probe- response paradigm allowed examination of specific working memory processes underlying discourse comprehension, namely; a) storing and maintaining information in working memory (i.e., laying the foundation of the discourse structure); and b) updating information stored in working memory through suppressing the irrelevant discourse information. Storage and maintenance of the information was assessed by examining whether participants utilised “advantage of first mention” (Gernsbacher, 1990). Suppression was evaluated by investigating whether the accessibility of nonreferent names decreased in participants' working memory after they read anaphoric pronouns in sentences. This approach aimed to answer the following questions: 1) Do age and working memory capacity affect anaphora resolution in a comprehension task?; 2) Do age and working memory affect advantage of first mention in a probe recognition task?; and 3) Does age affect suppression of irrelevant information in an anaphora resolution task? In Chapter 3, Gernsbacher's (1989) original study was replicated. In Chapter 4 the same questions were examined, with the addition of a higher working memory load. For both studies, 30 younger and 30 older participants completed two comprehension experiments followed by an assessment of working memory capacity (reading span task). The comprehension experiments each contained a reading comprehension task and a probe recognition task. The reading comprehension task introduced two discourse characters (either a male or female name), one of which was referred to later in the text, using an anaphoric pronoun. Comprehension questions always asked about the referents of the anaphoric pronouns. Participants' accuracy in answering each comprehension question was indicative of their ability to resolve anaphora. Response times in the recognition task provided measures of the accessibility of: a) first and second mentioned names, and b) referent and nonreferent names. Chapters 3 and 4 found that, regardless of the tasks' working memory storage demands, older adults were less accurate than younger adults in the comprehension of anaphoric pronouns. Comprehension accuracy was related to working memory capacity, such that individuals with higher working memory capacity exhibited higher accuracy of response in the comprehension task. In addition, working memory capacity affected the accessibility of first and second mentioned names in the discourse suggesting that working memory capacity might influence the process of laying the foundation for the mental representation of comprehension. An ageing effect was observed on the suppression process during anaphora resolution under high working memory load only. When working memory load was low, neither younger nor older participants suppressed the accessibility of the nonreferents by the time they finished reading the sentences. This suggested that anaphora resolution might be postponed in less demanding tasks. However, under higher working memory load, younger adults, but not older adults, suppressed the accessibility of the nonreferents by the time they finished reading the sentence. It was therefore suggested that age-related changes in anaphora resolution abilities might be mediated by a decline in inhibitory functions that are responsible for suppressing the already-activated information that are no longer relevant to the task goals. The final study of the thesis (Chapter 5) aimed to determine why younger adults delayed the process of anaphora resolution in Experiment 1 (See Chapter 3), but completed the process by the time they finished reading the sentences in Experiment 2 (See Chapter 4). Specific questions addressed were: 1) Was comprehension accuracy affected by working memory storage load and the syntactic structure of the sentences?; 2) Do younger adults suppress the accessibility of the nonreferents by the time they reach the end of the sentence, in simpler sentences with increased storage load and late disambiguation?; and, 3) Do younger adults suppress the accessibility of nonreferents by the time they reach the end of the sentence, in more syntactically complex sentences with low storage load and prior disambiguation?. Forty younger participants completed four separate comprehension experimental tasks followed by a reading span test. A similar experimental approach was employed to that described in Chapters 3 and 4; however working memory storage load, syntactic complexity, and time-course for providing contextual information were manipulated. Results of Chapter 5 found that participants' accuracy declined in more syntactically complex sentences. A decline in accuracy appeared indicative of the tasks' higher processing demands and demonstrated that prior disambiguation was not facilitating the resolution of anaphora. Results from the recognition task showed that in sentences of increased syntactic complexity, participants suppressed the accessibility of nonreferents by the time they finished reading the sentence. It was suggested that higher processing demands of syntactically complex sentences, rather than a facilitating effect of earlier disambiguation in these sentences, contributed to the earlier suppression of nonreferents. In summary, this thesis demonstrated that older adults were less accurate than younger adults in comprehending anaphoric pronouns. Moreover, working memory capacity positively influenced comprehension accuracy and affected the advantage of first mention of discourse entities. It was suggested that individual differences in working memory capacity might affect the ability to lay foundations for discourse comprehension. Furthermore, older adults showed no suppression of nonreferents during processing of anaphora, regardless of working memory storage load. It appears possible that older adults' difficulty in anaphora resolution might be due to an inability to suppress irrelevant discourse information. Findings from the present study suggest that ageing may negatively affect the comprehension of linguistic structures for which more than one meaning could be inferred. While further exploration of this finding is required, it is possible that communication strategies could be devised to minimise the use of structures with more than one meaning - with the aim of improving and maintaining communication in older adults. Ultimately, determining the underlying causes of language impairments in both healthy ageing and neurological disease will help to improve speech-language therapy methods for these populations.