Stimulus Degradation and Sleep Deprivation 1 THE EFFECTS OF STIMULUS DEGRADATION AFTER 48 HOURS OF SLEEP DEPRIVATION Running Head: Stimulus Degradation and Sleep Deprivation

Study Objectives: To test the hypothesis that total sleep deprivation (SD) 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 SD 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 hours of total sleep loss. The PVT and DLR were administered to the same participants. The PVT was administered eight times every six hours from 12pm on Day 1. The DLR was administered twice, at 9am of Day 1 and 48 hours later. Setting: Participants were continuously monitored in a sleep laboratory. Subjects: 26 Healthy young adults enrolled. Due to drop out 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 SD and degradation on any variable. There was, however, a significant interaction between SD and degradation on mean reaction time in the PVT (p=0.01). Conclusions: As in our previous reports, we observe the specificity with which sleep deprivation affects cognitive processes. One aspect of visual processing, stimulus detection, was affected by sleep deprivation and made a significant contribution to the performance impairments observed. Another aspect of visual processing, stimulus evaluation, remained unaffected after two days and nights of total sleep loss.