Memory for unconsciously perceived events: Evidence from anesthetized patients

Studies investigating memory for events during anesthesia show a confusing pattern of positive and negative results. To establish whether there are any consistent patterns of findings across studies, we conducted a meta-analysis of the data from 2517 patients in 44 studies. The meta-analysis included two measures of the effects of positive suggestions on postoperative recovery: (a) the duration of postoperative hospitalization and (b) the amount of morphine administered via patient-controlled anesthesia, as well as two measures of memory for specific information presented during anesthesia: (c) direct tests and (d) indirect tests. The meta-analysis indicated that positive suggestions presented during anesthesia have little or no effect on postoperative recovery. On the other hand, the metaanalysis showed that specific information is remembered following surgery, as long as testing is not delayed longer than 36 h. Studies of memory for events during anesthesia provide a useful avenue for exploring unconscious cognition. (C) 1996 Academic Press.