Timing ability and numerical competence in rats.

Counting and timing ability in Wistar rats was tested in 4 psychophysical choice experiments. After training naive rats with discrete sound sequences that confounded time and number, only time gained control of behavior; control by time was stronger and acquired more rapidly after training with separate time- and number-relevant signals. Two nonnumeric cues associated with periodic sequences, temporal ratio and sequence pattern, did not appear to provide the basis for numerical discrimination, as performance was unaffected by a sudden change from periodic signals to signals with unique temporal patterns. Even after highly accurate performance with number, time showed exclusive control of behavior for signals with conflicting time and number cues. This study provides an unequivocal demonstration that rats can count, but they do so according to H. Davis and J. Memmott's (1983) "last resort" hypothesis.