The display screen is surrounded by photocells, which sense the location of the pigeon's peck. The target letter (here the letter 'P') can appear in any location; when the bird pecks at a location the display goes blank, and a new display appears after a brief interval. Reaction time is the time between display onset and a peck response. 

This approach permits precise manipulations of  perceptual and memory variables. For example, the present display provides a difficult perceptual task, because there is a large and heterogeneous set of distractors. The memory task would be easy if the target was always the same letter. In many experiments, however, memory is burdened by training the bird to peck any of several letters, only one of which appears on a given trial. 
 
The equipment permits the measurement of search speed (RT) as well as accuracy. As noted above, RT provides a useful measure of information-processing style. However, this measure and other aspects of our method simulate less well the natural foraging situation.