Conditioning afterimages: a procedure minimizing the extinction effect of normal test trials

Six subjects were trained on a conditioning schedule of ten trials a day for 25 days: a further 18 CS-US pairings were presented on 4 subsequent days. The tone employed as the CS was put on 30 sec before the presentation of a briefly illuminated visual target (the US) and maintained until terminated by the subject when his afterimages disappeared. This procedure allowed continuous monitoring of the evolution of the conditioned response (conditioned afterimages): directly for CRs with a latency of less than 30 sec which could occur on every training trial before the US was presented; indirectly from the changes in the duration of afterimagery following the presentation of the US. As every trial yielded some evidence about the evolution of the CR, unreinforced test trials were not necessary after every block of training trials so minimizing the extinction effect attributable to the presentation of an unreinforced CS. In the course of the experiment the mean duration of afterimagery increased almost fivefold with one subject showing a tenfold increase. Five of the subjects experienced visual images in response to the tone alone and were judged to be conditioned. The data are discussed in relation to the evolving levels of conditioning identified by Bzhalava (1958, 1965).