Spatial generalization and peak shift in humans

Using a computer betting game, five experiments tested university students on spatial generalization and peak shift. On each trial, one location was marked and the subject was invited to bet 0-4 points. At the winning location (S+), bets won four times the points betted. At nearby losing locations (S−s), points betted were lost. Generalization gradients were exponential in shape, supporting Shepard's (1987), law (Experiment 1). With peak shift manipulations, three kinds of peak shift or area shift were found. (1) Subjects betted more on the S+ side than on the S− side (Experiments 2-4). (2) When asked if a location was the winning location, subjects responded “yes” more often to locations on the S+ side than to locations on the S− side (Experiments 3-5). (3) When asked to point to the winning location on the screen, subjects' errors indicated peak shift (Experiment 5).