Recall of mental sleep experience with or without prior verbalization

We investigated whether verbalization of contents of mental sleep experience (MSE), just after awakening provoked during rapid eye movement (REM) sleep, facilitates subsequent recall in the morning. Twelve subjects were awakened four times in each of two experimental nights and alternately asked to recall, with or without concurrent verbalization, MSE contents preceding the awakening. In the morning, the subjects were asked to report MSEs both verbalized and nonverbalized during the night. If subjects were unable to provide a spontaneous morning report, they were prompted using a probe, which was the title given by the subjects to each MSE at the end of its verbalization or covert recall at night. Frequencies of spontaneous reports were high, regardless of whether MSEs had been previously verbalized or not. The proportions of spontaneous and probed reports were similar for verbalized and nonverbalized MSEs, but spontaneous morning reports were longer than probed ones, regardless of their previous verbalization. Spontaneous and probed morning reports corresponding to night reports shared similar linguistic structures (i.e., length of sentences and proportions of waking-related utterances, which are indicative of difficulty of retrieval for MSE contents) and had similar percentages of contents common to night and morning reports. These findings support the hypothesis that verbalization does not directly influence the further accessibility of MSE contents.