STIMULUS-CONTROL AND RESPONSE BIAS IN AN ANALOG PREY-DETECTION PROCEDURE

The present study compared the performance of 6 pigeons trained to det ect luminance differences in two different signal-detection procedures . Exposed to a three-key array, the pigeons were trained to peck the l eft key when the brighter of two light intensities had been presented on the center key and to peck the right key when the dimmer of two lig ht intensities had been presented on the center key. Procedure A was a standard signal-detection procedure in which left/bright and right/di m responses produced food reinforcement and left/dim and right/bright responses produced periods of timeout. Procedure B was designed to sim ulate some of the contingencies operating in a prey-detection situatio n. Left-key responses produced reinforcement following the brighter ce nter-key stimulus and a period of timeout following the dimmer center- key stimulus. Right-key responses always produced a short period of ti meout irrespective of the stimulus. Within each procedure, the duratio n of timeout arranged for false alarms (left/dim responses) was varied between 3 s and 120 s. Measures of accuracy and response bias were co mpared between the two procedures. The timeout manipulation produced s ystematic, but relatively small, changes in these measures when right/ dim responses (i.e., correct rejections) produced reinforcement (Proce dure A). Arranging timeout for right/dim responses in Procedure B prod uced greater variability in accuracy and response bias than did arrang ing reinforcement, but this variability was not related to timeout dur ation. Overall, discrimination accuracy was considerably higher when r ight/dim responses produced timeout than when they resulted in reinfor cement, and accuracy was accompanied by a large bias toward the respon se associated with reinforcement. These results are consistent with a recently proposed model of signal detection.