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Depressed patients show cognitive deficits along with mood disturbances. Growing evidence suggests an impairment at the level of executive control, which might account in part for patients' difficulties in everyday activities and cognitive performance. Furthermore, there is evidence that depressive patients show information processing biases for emotional information which are thought to play a role in the etiology and maintenance of the disorder. Attentional bias occurs in an early stage of information processing, while memory bias occurs in a later stage of processing (strategic elaboration). The goal of this study was to investigate executive control (the Stroop test) and information processing biases for emotional information in an early stage of processing (the emotional Stroop test) and in a later stage of processing (memory recognition test) in healthy subjects and depressive patients. A further objective of this study was to compare the performance of melancholic and non-melancholic depressive patients in the Stroop test, in the emotional Stroop test and in the memory recognition test. Last, we wanted to investigate the relationship between the performance in an executive control task (the Stroop effect) and information processing bias measures for emotional information. This study is the first to investigate the Stroop test, the emotional Stroop test and the memory recognition test in the same healthy subjects and depressed patients. Furthermore, this is the first study investigating information processing biases for emotional information in the melancholic and non-melancholic patients.

Executive control was investigated using the Stroop task, which has been extensively used to study executive control. The emotional Stroop task has widely been used to investigate attentional biases in anxiety and depression and was therefore employed also in this study. Memory bias was examined with the memory recognition test since it allowed us to study both “pure” memory and response bias. Response accuracy d’ and response bias beta were calculated according to the signal-detection model. Twenty-three depressive patients and 27 healthy subjects performed computerized mixed trial
Stroop and emotional Stroop tests. Afterwards, the subjects performed the memory recognition task. Depressive patients were divided according to DSM-IV diagnosis into melancholic and non-melancholic subgroups. Furthermore the level of anxiety and depression was assessed in all subjects.

Results of the Stroop task showed that when the depressed patients were analyzed as a whole group, they showed only a trend toward a larger Stroop effect at the beginning of the task. When the analysis was performed with the melancholic and non-melancholic subgroups, contrary to the expectations, only the non-melancholic patients were impaired in the Stroop task compared to the melancholic patients and healthy subjects. Furthermore, we failed to find evidence for an attentional bias in the depressed patients in the emotional Stroop task measured as longer RTs to the emotional compared to neutral stimuli. However, both groups committed more errors in the negative compared to the neutral and positive condition. We also failed to find evidence for a memory bias in depressed patients measured as discrimination accuracy d’. Considering the response bias measure beta, the analysis showed that the healthy subjects had a more conservative response bias toward positive stimuli. This means that healthy subjects were less likely to answer “yes” to the positive stimuli than to other stimuli. The patients on the other hand had a more conservative response bias toward both emotional stimuli (negative and positive) compared to neutral stimuli. Contrary to the expectations, there were no differences in the response bias between the melancholic and non-melancholic patients. The results of the correlational analysis provide evidence that the executive control and emotional information processing are connected phenomena in the healthy subjects but not in the depressed patients. The healthy subjects with poor executive control are paying more attention to the negative stimuli compared to neutral stimuli. This was not the case in the depressed patients. We suggest that the unexpected result of melancholic patients performing better than non-melancholic ones in the Stroop task may be due to their more pronounced rigidity, which makes them more resistant to distraction. Hence, more detailed psychopathological assessment is desirable for future investigations of the melancholic patients. Furthermore, since we failed to find attentional bias in the depressed patients toward the emotional stimuli in the emotional Stroop test, we are concluding that besides methodological issues there are more important clinical factors than diagnosis (i.e. trait anxiety). We are suggesting that memory bias is impossible or difficult to demonstrate in the depressed patients when stimulus exposure occurs under sets that are explicitly antithetical to self-referencing. The relationship found between the Stroop effect and the emotional Stroop effect in the healthy subjects is suggesting that healthy individuals with lower levels of executive control may be more vulnerable to depression.

contents
1. Abstract
2. Theory

2.1. Depressive disorder
2.2. Executive control
2.2.1. Stroop test
2.2.2. Stroop test and depression

2.3. Emotional information processing

2.3.1. Individual differences influencing emotional information processing
2.3.1.1. Behavioral data
2.3.1.2. Neuroimaging data

2.4. Information processing bias for emotional information

2.4.1. Emotional Stroop test and depression
2.4.2. Memory bias
2.4.3. Cognitive factors and melancholic depression

2.5. Executive control and emotional information processing

2.5.1. Investigations of Stroop and emotional Stroop task in same subjects
2.5.2. Executive control and emotional information processing in depression

2.6. Objective and hypotheses

2.6.1. Objective of the study
2.6.2. Hypotheses of the study
2.6.2.1. Stroop test
2.6.2.2. Emotional Stroop test
2.6.2.3. Memory recognition test
2.6.2.4. Correlations between clinical symptomatology and the Stroop effect
2.6.2.5. Correlations between clinical symptomatology and the emotional Stroop effect
2.6.2.6. Relationship between the Stroop and the emotional Stroop effect
2.6.2.7. Relationship between different emotional bias measures

3. Methods

3.1. Subjects
3.2. Task and procedure
3.2.1. Stroop test
3.2.2. Emotional Stroop test
3.2.3. Memory recognition test
3.2.4. Procedure

3.3. Data analysis

3.3.1. Stroop test
3.3.2. Emotional Stroop test
3.3.3. Memory recognition test
3.3.4. Correlations

4. Results

4.1. Stroop test
4.1.1. Analysis of total depressed sample
4.1.2. Analysis of depressive subgroups: melancholic vs. non-melancholic
4.1.3. Correlations

4.2. Emotional Stroop test

4.2.1. Analysis of total depressed sample
4.2.2. Analysis of depressive subgroups: melancholic vs. non-melancholic
4.2.3. Regression analysis of the emotional Stroop effect
4.2.4. Correlations

4.3. Correlations between the Stroop and the emotional Stroop test

4.3.1. Correlations between the runs
4.3.2. Correlations between the “sad” and “happy” Stroop

4.4. Memory recognition test

4.4.1. Response accuracy
4.4.2. Response bias
4.4.3. Analysis of depressive subgroups: melancholic vs. non-melancholic
4.4.4. Correlations
4.4.4.1. Response accuracy
4.4.4.2. Response bias
4.4.4.3. Correlations between response accuracy, response bias, Stroop effect and emotional Stroop effect

5. Discussion

5.1. Stroop test
5.2. Emotional Stroop test
5.3. Memory recognition test
5.4. Relationship between the Stroop and emotional Stroop test
5.4.1. Future research

5.5. Relationship between different emotional bias measures
5.6. Relationship between memory test, Stroop effect and emotional Stroop effect
5.7. Cognitive factors and melancholic depression
5.8. Limitations of the study
5.9. Conclusions

6. Fazit
7. References
8. Appendix

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