Behavioral measures of the transition from wakefulness to sleep: which task interferes less with the sleep onset process?

Reaction Time Taaks OU") have revealed that during the sleep onset period (SOP) there is an intermittent pattern of response failure; this could reflect a vigilance discontinuity intrinsic to the SO process or a disturbing effect of the amustic stimuli on sleep. Recently, we have ahown that during the SOP a Tapping Task ('IT) is aseociated to earlier response cessation and to a greater proportion of periods of response failure compared to R1T. In this study somnopoligraphic and subjective data were analysed to confirm that TT compared to a R'IT is a less interfering behavioural measure of the transition from wakefulness to sleep. 6 Ss slept for 4 consecutive nights in the sleep lab with standard somnopoligraphic recordings. In the nights 3 and 4, Ss. were required to fall asleep performing bimanualy either a TT or a RTT. Upon the morning awakening Ss. were required to fill a questionnaire reporting subjective sleep timing. The results show that: a) compared to RTT, TT ie associated with significantly greater proportions of slow wavee sleep (i.e. EEG sleep) and oftime ofresponse failure (i.e. behavioural sleep) duringthe SOP b) both the latencies of behavioural and EEG sleep are shorter during TT; c) intercorrelations among subjective, behavioural and EGG latencies are greater with 'IT compared to R1T. Results confirm that R I T interfere more with the SO process compared to TT and suggest that the TT provides a better behavioural measure of transition from wakefulness to sleep.