Visual Fatigue Visual fatigue may be observed using several different procedures. The fusion frequency of flicker, as stated above, indicates the excitability of the retinocortical system. In office, laboratory and dispensary work the fusion frequency of flicker was lower in the late afternoon than it was in the morning, but the decrement was much more pronounced in laboratory work including three hours' work with the microscope than in laboratory work without the use of the microscope. Reversible visual "illusions" differ before and after vigorous exercise. After two hours of hard inspection work at a very inadequate illumination, the fixation time and the corrective movements increased, while the rate of movements decreased. One manifestation of oculomotor fatigue is a blocking of eye movements for a fraction of a second which enforces involuntary rests. Performance between these blocks is little affected. In very severe stress, such as requiring the eyes to move at the maximum attainable rate for two or more minutes, watering of the eyes may make reading impossible. The secretion of tears is interpreted as a spread of innervation to other effectors. Auditory Fatigue Exposure to noise results in a hearing loss which is proportional to the duration of exposure. The cumulative effect of noise may finally result in permanent hearing loss. The recovery of acoustical threshold in riveters after a full day's work may take fifteen hours. The recovery is considerably accelerated when the lunch pause of one hour is spent in noiseless surroundings; also the increase of threshold at the end of the working day is much less under these conditions. Cotton plugs saturated with mineral oil, to be introduced into the ear canal, are recommended for protection. Typists working under office conditions of high noise level from a busy street had a greater expenditure of energy than when the noise level of the same office had been reduced by acoustical methods. Reduction of the noise level increases the work output and diminishes errors, absenteeism and employee turnover. A varying noise causes a greater drop in work output than a steady noise. Pure tones of uniform loudness reduce output less seriously than does complex noise of equivalent loudness. Tones of frequencies above 512 cps (cycles per second) cut into production more than lower frequencies of the same loudness, and above 512 cps each increase in frequency is followed by further loss in production.		Home Pace Motivation Measures of Endurance Computation of Dietary Requirement Work Efficiency Maximum Steady State Work Inefficiency of Anaerobic Work Estimation of Work Efficiency Efficiency of Grade Climbing Low Economy of Slow Work Maximum Rate of Work Levers of the Body Fatigue and Recovery General Fatigue Symptoms Anxiety State Organic Fatigue Cortical Motor and Sensory Centers Effect of Exercise on Mental Work Visual Fatigue Muscular Fatigue Fatigue Prevention and Recuperation