A method for applying time-of-flight (TOF) information to the three-dimensional (3-D) localization of multiple-photon-emitting radionuclides is presented. The same principle used for TOF imaging of positron annihilation photons is suggested for use with nuclides that emit two photons (gamma or x rays) in near coincidence. Two photons originating from the same decay event are detected. The locations at which they are detected become the foci of a hyperbola described by the difference in their path length. If one detector is collimated a line is established by the photon it detects, which intersects the hyperbola at the origin of the event. Should TOF imaging become a reality, this technique would extend its usefulness to nuclides that do not emit positrons.

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216 Ss were given a concept-identification problem wherein Ss were required to make an overt button-pressing response, as an observing response, in order to view each dimension of an instance. On each trial, Ss were allowed to view any dimensions they desired with the constraint that they were allowed to view only half of the available dimensions. On those trials in which the one relevant dimension was not observed, Ss were given misinformative feedback. Three levels of misinformative feedback, designed to vary the probability of S's classification response being called correct ( p), were used. It was found that mean number of errors to solution was a function of problem difficulty and saliency but independent of variations in p as predicted by Trabasso and Bower (1968). The results did not support the strength theories in concept identification.