A visual vigilance experiment was performed in which (a) the effects of monetary incentives, and (b) the effects of removal of these incentives were tested. 20 experimental and 20 control Ss were tested in 2 sessions of 60 and 90 min. each. The experimental group received 20 for every signal correctly detected and had 20 deducted for every signal missed in the 1st session, but received no reward in the 2nd session. The control group was never rewarded. The rewarded group performed better (p < .025) than the controls in the 1st period of the 1st session, and poorer in the final period (p < .025) of the 2nd session. These effects were interpreted as resulting from experimentally induced changes in the motivational level of the reward group. (PsycINFO Database Record (c) 2006 APA, all rights reserved)