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Although there have been many studies of the effect upon performance of one or more days of complete sleep deprivation, there appear to be no satisfactory data upon the effect of a single night of reduced sleep. There are two main reasons for this: either the scale of the experiment precluded the use of sufficient Ss (Smith, 1916; Husband,1935) or insensitive performance tasks were used (Webb & Agnew, 1965). The present study has sought to remedy these defects. MethodSix enlisted men carried out performance tests from 8 A.M. to 10:30 P.M. (with relatively short breaks for meals) on the Wednesday and Thursday of six successive weeks. On each of the nights preceding the days oftestingtheysiepteitherO,l,2, 3, 5, or 7-1/2 hr. according to the week of testing. Thus by the end of the sixth week each S had met each of these conditions of sleep, the order of their presentation being randomized among Ss with the constraint that on any given night each of the Ss received different amounts of sleep. Where sleep was taken Ss were always wakened at 6:30 A.M., the partial sleep deprivation being achieved by delaying their retirement to bed. They were under constant supervision, except when they were sleeping, from the morning of Tuesday until the end of their second testing day on Thursday. When not carrying out the

A new method for computing form-factors within a progressive radiosity approach is presented. Previously, the progressive radiosity approach has depended on the use of the hemi-cube algorithm to determine form-factors. However, sampling problems inherent in the hemi-cube algorithm limit its usefulness for complex images. A more robust approach is described in which ray tracing is used to perform the numerical integration of the form-factor equation. The approach is tailored to provide good, approximate results for a low number of rays, while still providing a smooth continuum of increasing accuracy for higher numbers of rays. Quantitative comparisons between analytically derived form-factors and ray traced form-factors are presented.