| Abstract | [Abstract]: Background:
Baddeley and Hitch’s (1974) multi-component model of working memory (WM) has provided the basis for exploration into the nature of remembering and manipulating information over a short period of time. This model argues
that the passive short-term storage system is not involved in the more dynamic working memory tasks and has formed the basis of much research on clinical populations known to have deficits in WM. However, other models argue that short-term memory and working memory rely on common storage
facilities. The aim of this thesis was to explore whether there is justification for the continued separation of WM into fractionated components. Schizophrenia (SZ) is associated with a wide range of cognitive deficits, including working memory problems. There is also some evidence to suggest that psychotic symptoms exist on a continuum and cognitive deficits similar to those found in SZ have been reported in people endorsing “psychotic-like” symptoms without a formal diagnosis of schizophrenia. It was hypothesized
that the pattern of errors made by the SZ group would help to delineate the nature of deficit shown on WM tasks. Methods:
General Methods
In order to explore the structure of WM and performance of groups hypothesized to be impaired on WM tasks, a range of span and non-span tasks were administered. Forty-two (42) control subjects were recruited for the study. Based on their scores on the Schizotypal Personality Questionnaire (SPQ - Raine, 1991), this group was divided into low scoring (NCL = 27 ) and high scoring (NCH = 15) groups. Thirty (30) people with a DSM-IV diagnosis of schizophrenia were also recruited.
Experiment 1
Experiment one investigated the performance of these groups on simple, complex and delayed span tasks. A simple four-word recall task, with and without interference was used to examine accuracy, error types and any
relationship to symptomatology.
Experiment 2
Experiment two set out to investigate the contributions to span performance. All subjects were administered measures of articulation speed, lexical access ability, and a range of STM, WM and LTM tasks.
Experiment 3
This experiment used a cued-recall paradigm to explore proactive interference effects by manipulating phonological and semantic representations over brief
periods. The task consisted of trials where the subject studied a series of one or two blocks of four words. Results:
Experiment 1
The results of this experiment replicated previous findings (Tehan, Hendry & Kocinski, 2001) of similar patterns of performance across the three tasks with
performance decrements increasing with task difficulty. The SZ group showed significant deficits even on the simple four-word span task. Patterns of errors were similar across the groups once overall levels of performance were taken into account. SZ subjects made more movement (order) errors than the other two groups and movement errors were associated with disorganised symptoms. The association between disorganised symptoms
and loss of items from the end of the list were suggestive of impaired maintenance of item information. The high schizotypy control group performed below that of the low schizotypy controls, but only a few of the differences were significant.
Experiment 2
For both groups articulation and lexical access formed two of the composites. For the control group, all memory tasks contributed to form one single factor. For the SZ group three separate memory composites were needed. Using
regression analyses previous findings (Tehan & Lalor, 2000; Tehan, Fogarty & Ryan, 2004) were replicated for the control group with both lexical access and to a lesser degree, rehearsal speed contributing to memory performance.
Rehearsal speed was a more important predictor for recall of familiar materials (such as letters and digits) in the SZ group. The reverse was true for simple word span, with lexical access making a significant impact and rehearsal speed having little impact. For more complex memory tasks,
neither articulation rate nor access to lexical memory contributed to the performance of the SZ group. Once again poorer performance for the SZ group was associated with disorganised symptoms.
Experiment 3
The findings from this experiment revealed that even on the simple one block trials, the SZ subjects had difficulty accurately recalling the target word with a
category cue, even in the absence of distractor activity. The SZ group made more omissions and significantly more intrusion errors than the control groups. Intrusion errors were associated with disorganised symptoms on the
Positive and Negative Symptom Scale (PANSS). Despite their poorer overall performance, the SZ group did not have significantly more block-1 intrusions than the control groups suggesting that the interference effects for semantic and phonemic information were the same. Conclusions:
This thesis presented evidence which is somewhat supportive of a common storage approach to WM. It calls into question the need to fractionate WM
into components. The multi-component model of WM is often used to investigate performance of SZ subjects, a population know to have WM deficits. Errors across a range of STM, WM and LTM tasks were examined in a SZ group and their performance was compared to two groups of controls: a
group with high scores on a measure of psychometric schizotypy and one with low scores. Implications regarding the purported source of deficits in WM are discussed. |
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