ABSTRACT

Duration and number are attributes of all discrete stimuli. The duration of a stimulus and the number of elements or segments of the stimulus typically covary, so it has been difficult to demonstrate that animals can discriminate between stimuli on the basis of number alone. Animals can discriminate between stimuli on the basis of duration, and both an information-processing model (Gibbon & Church, 1984) and a formal theory (Scalar Timing Theory) (Gibbon, 1981; Gibbon, Church, & Meck, 1984), successfully account for many of the facts of animal timing (Gibbon, 1991). There are now convincing data that animals can discriminate the number of stimuli, even when stimulus durations are uninformative. The chief purpose of this chapter is to review some data suggesting that the same mechanism is used for timing and counting, and to describe how timing models have been extended to account for number discrimination.