Long-term Retention of Many Visual Patterns by Pigeon~

Using a simultaneaus discrimination procedure it was shown that pigeons were capable of learning to discriminate 100 different black and white visual patterns from a further 625 similar stimuli, where responses to the former were rewarded and responses to the latter were not rewarded. Tests in which novel stimuli replaced either the rewarded or nonrewarded stimuli showed that the pigeons had not only learned about the 100 positive stimuli but also about the 625 negative sti~uli. The fact that novel stimu li enbanced discrimination performance when they replaced the many negative stimuli indicated that the pigeons had categorized the stimuli into two classes, famili~r and less familiar. Long-term retention was examined after a 6-montb interval. To begin witb it seemed poor but a recognition test performed after the subjects had been retrained with a subset of the stimuli after an interval of 7 months confirmed that pigeons are capable of retaining in memory several 100 visual items over an extended period. It is proposed tbat the initial retrieval weakness was due to a forgetting of tbe contingencies between Stimulus categories and response outcomes. Further tests involving variously modified stimuli indicated tbat wbile Stimulus size variations had a negative effect on performance, orientation changes did not interfere with recognition, supporting tbe view that small visual stimuli are memorized by pigeons largely free of orientation Iabels. Tbe experiment generally confirms tbat pigeons have tbe capacity of storing information about a !arge number of visual Stimuli over long periods of time. Corresponding author: Prof. Dr.]. D. DELIUS, Allgemeine Psychologie, Universität Konstanz, Postfach 5560, D-7750 Konstanz.