Moritz, S., Glascher, J., & Brassen, S.
(2005). Investigation
of mood-congruent false and true memory recognition in depression. Depression
and Anxiety, 21, 9-17.
Introduction
Past research has shown that depressed patients have general memory impairment. Further, they have a tendency to exhibit a mood-congruent bias where they show higher recall and recognition of negatively-valenced words in memory tests, as well as a mood-congruent processing bias in attention tasks such as the Stroop paradigm. An examination of memory lacking in the literature is that of memory errors, the focus of this study. Depressed participants may exhibit two possible processing patterns which offer very different predictions about false memories. The first is a familiarity-based retrieval strategy where the same mechanism for recognizing negatively-valenced studied items is applied to negatively-valenced non-studied items, and thus a higher rate of false recognition of valenced items would be predicted. The second strategy is item-based where depressed participants have enhanced accuracy for retrieval of negatively-valenced items but a conservative threshold for non-studied items, and thus a lower rate for false memories. The identification of false memory rates for negatively-valenced items is of clinical relevance because of its contribution to the pathogenesis of depression. Depressive thoughts could be formed because of the increased presence of negative life events, the elevated accessibility of memories for these events, and the elevated presence of negatively-valenced false memories.
Methods
25 inpatients diagnosed with major depression or dysthymia served as the patient group, and the healthy control group consisted of 28 individuals recruited via advertisements and general word-of-mouth from the general population. The materials consisted of four DRM-style lists oriented around a depressed theme (loneliness), delusion theme (betrayal), positive theme (holidays), and neutral theme (window). Each was constructed through a norming study using 75 healthy subjects. 12-word lists were constructed with decreasing associative strengths. In each list, words were categorized as ‘strong’, ‘moderate’, and ‘weak’ according to associative strength and one of each was removed to serve as a lure word on the recognition test in addition to the critical lure. Also on the recognition test were two words from each of the four lists to serve as ‘old’ items, and eight new, unrelated words. Thus, the encoding list contained a total of 36 words (four 9-word lists), and the recognition test contained a total of 48 items. The encoding list was read in blocked fashion out-loud in a randomized order to each subject. Immediately following presentation, the recognition test was presented orally in semi-randomized fashion asking for ‘old’/’new’ responses and ‘confident’/’not confident’ follow-up responses.
Results
There was a lower number of ‘old’ responses for neutral words than for emotionally charged words across groups. A higher number of ‘old’ responses were given for words with greater relatedness to the central theme of lists. True recognition exceeded false recognition, and this effect was equal for both groups. Group X Item Type interaction showed that patients had worse true recognition than healthy controls, but false recognition did not differ. Depressed patients recognized words, both true and false, for emotional lists significantly more than healthy controls; showed decreased true recognition for neutral list words than emotional list words relative to controls; and showed a higher error rate for false recognition on emotional lists relative to neutral lists than controls, particularly depression-relevant unrelated words. Healthy controls also showed improved true recognition of emotional list items, but primarily due to the positive theme list items. In an analysis of ‘core’ list items, depressed subjects had significantly lower true recognition of neutral list items than healthy controls. Using depression assessment scores, a positive correlation was found between lower true recognition and severity of depression. Confidence ratings replicate findings of ‘old’/’new’ responses. No effect of age was found, even though the patient and control groups differed significantly on this demographic measure. The patient group showed a nearly significant (p=.06) correlation between true and false recognition, while the healthy controls showed no such relationship.
Discussion
The above results failed to show the typical mood-congruent bias that has been shown in past research, but is consistent with more recent research. The authors elaborate on memory-relevant neurological abnormalities identified in depression as they relate to the above findings, and how they may offer explanations for the inconsistent findings in the literature. Also, they argue how their use of recognition vs. recall test format may have resulted in the lack of clear mood-congruent bias obtainment. The correlation noted in the patient group is also argued as evidence for familiarity-based processing rather than item-based processing.
Important Legal Disclaimer: The preceding are articles we read together in the Lampinen Lab Spring 2006 false memory reading group. By clicking on the button next to the article you can see the summary of that article. The summary was prepared by the student presenting that article and it is of course the case that the views expressed in the summary do not necessarily represent the views of the reading group as a whole, Dr. Lampinen, the Lampinen Lab, Hugo's, the University of Arkansas, the Razorback Football or Basketball teams (although we're not sure about cross country), people living down the street from us, Bob Dylan, Jack Fate, our extended families, or anyone else for that matter except for the student who wrote the summary (and they don't necessarily believe what they wrote either).