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The aims of the experiment were: (1) to establish the proportion of sleep stages in morning spontaneous awakening and to observe whether any stage-dependent differences can be found in the mentation reports; and (2) to compare the characteristics of mental activity during sleep onset (SO) and during the latest sleep period. One hundred forty-four dream reports and their association reports were collected from 36 subjects in a lab experimental design. Dream reports were analyzed as to structure (length, narrative continuity), content (self, setting, lab references, nonself characters, dimensional distortions, body feelings, bizarreness and emotions), and awareness (reality testing). Associations were classified as episodic, abstract self-referred, and semantic memories. The morning awakenings results were not affected by the stage of sleep during which dreaming occurs. SO reports prevalently show a lifelike nature, while sleep-offset reports are prevalently dreamlike. On the other hand, there seems to be a similar availability of mnemonic systems in the two sleep conditions.

Upon nighttime experimental awakening of 27 subjects in four sleep conditions (sleep onset early; sleep onset late; Stage 2; and rapid eye movement, REM, sleep), 108 dream reports and their association reports were collected. Dream reports were analyzed for length (temporal units) and content categories (continuity; implausibility; presence of the dreamer [i.e., "the self"], a setting, characters). Associations were classified as episodic, abstract self-referred, and semantic memories. The two sets of results tend to show a basic homogeneity among mentation reports in the four sleep conditions considered. These findings are interpreted as supporting the hypothesis that the same cognitive mechanisms operate, at different levels of engagement, in dream generation rather than the hypothesis of multiple dream-generation systems dependent upon the physiological characteristics of the various sleep stages.

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