The effects of stimulus degradation after 48 hours of total sleep deprivation

Study objectives: To test the hypothesis that total sleep deprivation (TSD) slows stimulus detection and evaluation processes. Towards that end we manipulate degradation of the imperative stimulus, a manipulation well established to affect the processes of interest, in a delayed letter recognition (DLR) task and the psychomotor vigilance task (PVT), and predicted that after TSD the ordinary reaction time (RT) slowing effect of stimulus degradation would be increased. These hypotheses were only partially confirmed (see below).

Design: Participants were exposed to 48 h of total sleep loss. The PVT and DLR were administered to the same participants. The PVT was administered 8 times -every 6 h from 12:00 on Day 1. The DLR was administered twice, at 09:00 of Day 1 and 48 h later.

Setting: Participants were continuously monitored in a sleep laboratory.

Subjects: 26 healthy young adults enrolled. Due to dropouts and technical failures, the final n's were 20 for the DLR and 21 for the PVT.

Measurements and results: General linear mixed models were employed. In the DLR task there was no interaction between TSD and degradation on any variable. There was, however, a significant interaction between TSD and degradation on mean reaction time in the PVT (P = 0.01).

Conclusions: As in our previous reports, we observe the specificity with which total sleep deprivation affects cognitive processes. One aspect of visual processing, stimulus detection, was affected by total sleep deprivation and made a significant contribution to the performance impairments observed. Another aspect of visual processing, stimulus evaluation, remained unaffected after 2 days and nights of total sleep loss.