Discrimination of the number of sequential events by rats

Ten rats were trained to press a right lever following two successive sounds and to press a left lever following four successive sounds. Three sound sequences were used in initial discrimination training, such that reliable classification could not be based on the duration of each sound, the interval between sounds, or the total duration of the sound sequence. Classification of seven novel sound sequences suggested that the animals were either using number or the sum of sound durations in a sequence as the relevant cue. When this total sound duration was put in conflict with number, rats classified by number. The conclusion was that rats can discriminate number, even when temporal cues are controlled.