Summary The use of probe trials to investigate hypothesis-testing behavior was investigated as a variable that may affect the hypothesis-testing process itself. Shift behavior by 96 male and female college students in an optional shift task was used as the dependent variable because it could be evaluated independent of the presence or absence of probe trials. The number of options, two or three, available on the shift task was also manipulated in order to test the hypothesis that, if probe trials cause the adoption of a more efficient shift strategy like Local Consistency, an increase in options would result in a decrease in within-dimension shifts. The data were in support of the hypothesis that probe trials have an effect on an individual's strategy for selecting hypotheses following negative feedback: 89% of the no-probe-trial participants made within-dimension shifts, with no effect following from an increase in options, while 56% of the probe-trial participants made within-dimension shifts, with a de...