Music discriminations by carp (Cyprinus carpio)
Studies using three koi (Cyprinus carpio) investigated discrimination of musical stimuli. The common protocol used a single manipulandum and a multiple continuous reinforcement-extinction schedule signaled by music of the S+ and S− types in 30-sec presentations separated by a silent 15-sec intertrial interval. In a categorization study, the fish learned to discriminate blues recordings from classical, generalizing from John Lee Hooker (guitar and vocals) and Bach (oboe concertos) to multiple artists and ensembles. A control-by-reversal test developed into a demonstration of progressive improvement in iterated reversal learning. The subjects next learned to discriminate single-timbre synthesized versions of similar music. In the final study, which used melodies with the same order of note-duration values, but with mirror-image orders of pitch values, one fish discriminated melodies with no timbre cues, in contrast to results reported in rats.