Some interpretations of quantum mechanics assert an active role for human consciousness in actualizing the results of measurements on quantum systems. At the same time, some empirical studies have claimed positive results in testing the abilities of human subjects to bias randomly generated events, i.e., those governed by Gaussian statistics. Experiments have been conducted using a different probability distribution, i.e., the digitally recorded diffracted light intensity from a single slit. This normalized distribution is conventionally interpreted as the probability of locating a photon in a specified lo­cation in the observation plane. Human subjects have been invited to attempt to bias this distribution in a prescribed way. The exper­iment is tightly controlled against any artifacts generating very high data rates with high statistical accuracy. Calibrations show that any displacement of the diffraction pattern relative to the detector of order 1.6 x 10^-5 cms should be detectable. Of twenty subjects tested, none has produced a detectable displacement corresponding to this upper limit.