Summary of previous chapters

Chapter one started by reviewing the existing literature on learning of linguistic

(Kelly & Armstrong, 2009; Tuomiranta et al.; 2011) and non-linguistic

(Brookshire, 1969; Tikofsky and Reynolds; 1962, 1963) material in PWA, and then moved on to works that looked at four cognitive functions, namely

language, memory, attention, and executive function, and how these functions affected PWA in terms of performing various language tasks. The gap among the existing works mainly lies in a lack of systematic evidence on whether PWA demonstrate ability to learn both linguistic and non-linguistic material in the same learning tasks. Moreover, whether cognitive impairments influence the performance of PWA or whether the deficits observed in cognitive domains stem from their language impairments. In addition, a few methods that have been consistently reported to benefit learning among healthy subjects as well as PWA were discussed as the foundations of the design of the series of

experiments presented in the later chapters (chapter three, four, and five).

Chapter two further extends the discussion on cognitive functions and

assessments to investigate the impact, if any, of reduced cognitive functions on learning was presented, followed by descriptions of the assessments chosen. Finally, a cognitive profile of each individual with aphasia involved in this study was built based on their performance on the cognitive assessments. Brief reports on individual participants with aphasia were given in the end of the chapter, with attention drawn to any outstanding performance on the cognitive assessments. Tables were used to summarise the performance of PWA in various cognitive assessments.

In chapter three, the first two learning tasks of the series of experiments were presented. The non-incremental (experiment 1a) and incremental

(experiment 1b) learning tasks set out to examine one of the fundamental research questions – whether PWA can learn new information. Since the study aims to examine the ability to learn not only linguistic information but also non- linguistic information, the materials involved were varied in terms of ‘linguistic load’. It was expected that, due to the language impairments, PWA would show, most evidently, reduced performance on learning of linguistic-heavy material, in comparison to the control groups; as the linguistic load of the material

decreased (from real words to non-words to animal sounds) control participants lost the benefit of using language knowledge to facilitate learning, and the patterns of learning generated by PWA might be closer to those observed in the control groups, though still at reduced level. What is more, the two approaches employed to direct learning offered further insight into potential influence of memory. If aphasia is accompanied by reduced STM, incremental learning, which is an approach to minimise memory load and to prevent proactive interference, should benefit PWA as well as the two control groups.

The results showed a great range of individual difference among PWA. However, as a group, the learning outcomes of PWA were not sensitive to the manipulation of linguistic load; that is, reduced learning was found across all conditions [linguistic (real words), semi-linguistic (non-words), & non-linguistic (animal sounds)] of the to-be-learnt stimuli. Looking at the two control groups, young participants performed at ceiling level in all linguistic conditions; on the other hand, the learning of older participants was influenced by linguistic conditions, as more visuo-auditory pairs of real words were learnt than non-

words and animal sounds. In addition, none of the groups benefitted from incremental learning.

Chapter four describes a picture recognition task with old-new paradigm

that aimed to detect the potential occurrence of implicit learning in visual modality and to what extent implicit memory is affected by the lag duration between repeated presentations of a visual stimulus. This experiment was inspired by the unexpected main effect of visual stimuli on learning reported in experiment 1a in chapter three. Whether implicit learning happened was determined via observing the change in reaction time toward repeatedly presented pictures, whilst how lag duration might influence outcome(s) of implicit learning was determined by recording the accuracy of the responses. The results suggested that PWA demonstrated the ability to learn implicitly. The patterns of improvement in reaction time and accuracy generated by PWA were similar to the their age-matched control group; each repeated presentation of a picture significantly shortened the participants’ reaction time and increased the accuracy of responses, indicating that implicit memory trace had formed. Also, implicit learning was observed even when the lag durations were extended to up to 20 intervening items, suggesting that the repetition priming effect could last for at least 20 intervening items, or possibly further.

Chapter five comprised massed and spaced learning tasks; it has been

frequently reported that massed practice boosts immediate recollection whilst spaced practice leads to better long-term retention of information. This

experiment set out to look at whether learning outcomes are affected by the manipulation of the way that the to-be-learnt items are practiced during the study phase. What is more, since PWA were capable of learning visually presented items implicitly (reported in chapter four), this experiment further investigated whether massed and spaced practice affects explicit and implicit memory in the same manner regardless of the to-be-learnt material involved, linguistic or non-linguistic.

The experiment (detailed in chapter five) involved learning of visually presented word-pairs as well as picture-pairs in two separate learning tasks of exactly the same experimental design. The experiment consisted of two

sessions: one involved a study phase followed by an immediate cued-recall task (10 minutes after study) and the other, approximately two days apart from the

first one, consisted of a delayed recognition task and a delayed cued-recall task. The findings showed that all three groups of participants generated similar trends in the cued-retrieval practice during the study phase, the two cued-recall tasks, and the delayed recognition task. The benefit of massing over spacing was evident in word-pair/picture-pair learning in the study phase. Spaced- practiced pairs were retained better in the delayed cued-recall task in comparison with massed-practiced pairs; this effect extended to delayed

recognition, in which spaced-practiced items were recognised more accurately. In chapter six, the analysis focused on exploring the relation between the learning outcomes (reported in chapter three, four, & five) and the cognitive functions assessed in this study (reported in chapter two). Prior to the analyses, assessments and learning outcomes were conveyed into z-scores (details in chapter 6.2). Then, a preliminary analysis of Pearson’s correlation coefficient was applied to the dataset, in which scores for each assessment and learning task were considered for individual participants. The results indicated that tests of cognitive functions largely correlated with one another and the same patterns were observed among learning tasks; only minimal correlations were found between cognitive functions and learning outcomes.

To investigate whether lack of correlation between cognitive functions and learning resulted from lack of statistic power of individual tests, composite scores for various cognitive domains and learning tasks were created (detailed description in chapter 6.2.2.). A further Pearson’s correlation coefficient was conducted to examine whether correlation existed among the cognitive variables (language production, verbal STM, non-verbal STM, semantic memory, recognition memory, visual attention, auditory attention, & executive function) and variables of learning (pair-associative learning, implicit learning, massed learning, spaced learning, recognition of massed-practiced items, & recognition of spaced-practiced items). Yet, the results were in line with the preliminary analysis; that is, cognitive functions mostly correlated with one another and some correlations were observed among learning tasks but no correlation was shown across the two types of variable.

7.3. Learning deficit and impaired cognitive functions