Selection by humans searching for computer- generated prey images: the effect of prey density

We investigated the effect of 'prey' density on frequency-dependent selection by human 'predators'. Eighty subjects were presented with computer-generated populations of two cryptically coloured characters on the screen of a colour monitor. Each subject was given the prey at a single combination of one of two frequencies and one of five densities, and was instructed to delete the prey as fast as possible with a light-pen. The results suggested that the degree of selection was inversely proportional to prey density, but there was no evidence that any frequency-dependent component of selection was affected.