Processing of emotional material in major depression : cognitive and neuropsychological investigations
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The aim of this thesis was to expand the existing knowledge base concerning the profile of emotional processing that is associated with major depression, particularly in terms of socially important non-verbal stimuli (e.g. emotional facial expressions). Experiment one utilised a face-word variant of the emotional Stroop task and demonstrated that depressed patients (DP) did not exhibit a selective attention bias for sad faces. Conversely, the healthy controls (HC) were shown to selectively attend to happy faces. At recognition memory testing, DP did not exhibit a memory bias for depression-relevant words, but did demonstrate a tendency to falsely recognise depression-relevant words that had not been presented at encoding. Experiment two examined the pattern of autobiographical memory (ABM) retrieval exhibited by DP and HC in response to verbal (words) and non-verbal (images & faces) affective cues. DP were slower than HC to retrieve positive ABMs, but did not differ from HC in their retrieval times for negative ABMs. Overall, DP retrieved fewer specific ABMs than did the HC. Participants retrieved more specific ABMs to image cues than to words or faces, but this pattern was only demonstrated by the HC. Reduced retrieval of specific ABMs by DP was a consequence of increased retrieval of categorical ABMs; this tendency was particularly marked when the participants were cued with faces. During experiment three, DP and HC were presented with a series of faces and were asked to identify the gender of the person featured in each photograph. Overall, gender identification times were not affected by the emotion portrayed by the faces. Furthermore at subsequent recognition memory testing, DP did not exhibit MCM bias for sad faces. During experiment four, DP and HC were presented with videotaped depictions of 'realistic' social interactions and were asked to identify the emotion portrayed by the characters and to make inferences about the thoughts, intentions and beliefs of these individuals. Overall, DP were impaired in their recognition of happiness and in understanding social interactions involving sarcasm and deception. Correct social inference was significantly related to both executive function and depression severity. Experiment five involved assessing a group of eight patients that had undergone neurosurgery for chronic, treatment-refractory depression on the identical emotion recognition and social perception tasks that were utilised in experiment four. Relative to HC, surgery patients (SP) exhibited general deficits on all emotion recognition and social processing tasks. Notably, depression status did not appear to interact with surgery status to worsen these observed deficits. These findings suggest that the anterior cingulate region of the prefrontal cortex may play a role in correct social inference. Summary: Taken together the findings of the five experimental studies of the thesis demonstrate that, in general, biases that have been observed in DP processing of affective verbal material generalise to non-verbal emotional material (e.g. emotional faces). However, there are a number of marked differences that have been highlighted throughout the thesis. There is also evidence that biased emotional processing in DP requires explicit processing of the emotional content of the stimuli. Furthermore, a central theme of the thesis is that deficits in executive function in DP appear to be implicated in the impairments of emotional processing that are exhibited by these patients.
Thesis, PhD Doctor of Philosophy
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