1. an extreme degree of retentiveness and recall, with unusual clarity of memory images. In forensic contexts, eyewitnesses have demonstrated increased recall after undergoing hypnotic induction to help retrieve memories, but such memories have been ruled inadmissible in some U.S. courts (see State v. Mackstate-v-mack).

2. in memory testing, a net increase in the total number of items recalled from one test to another. Hypermnesia usually occurs when information is repeatedly tested in close succession. A net decrease in the total number of items recalled is called forgetting. See reminiscence.