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We studied the number, valence, and vividness of intrusive and non-intrusive memories in two groups (N = 20) of pre-screened non-depressed mood and depressed mood undergraduate participants. They were asked to generate as many intrusive memories (IMs) as possible from the prior 2 weeks, together with pleasant and unpleasant non-intrusive memories from the same period. They subsequently formed images of these memories and rated them on measures of vividness, valence, arousal, and overall affect, while having their heart rate, skin conductance, and electromyogram monitored. IMs were common, with participants generating a mean of 1.15 pleasant IMs and 1.60 unpleasant IMs, and there was some evidence that they were mood-congruent. IMs were more vivid than non-intrusive memories, a difference not due to either valence or arousal. We conclude that IMs are a general feature of human memory rather than just a symptom of certain clinical disorders.
Bywaters et al. (Mon,) studied this question.