Abstract

There is considerable evidence that animals can time multiple intervals that occur separately or concurrently. Such simultaneous temporal processing occurs both in temporal discrimination procedures and in classical conditioning procedures. The first part of the chapter will consist of the review of the evidence for simultaneous temporal processing, and the conditions under which the different intervals have influences on each other. The second part of the chapter will be a brief description of two timing theories: Scalar Timing Theory and a Packet Theory of Timing. Scalar Timing Theory consists of a pacemaker-switch-accumulator system that serves as a clock, a memory that consists of examples of previously reinforced intervals, and a decision process that involves a comparison of ratios to a criterion; the Packet Theory of Timing consists of a conditional expected time function that serves as a clock, a memory that consists of weighted sums of these values, and a probabilistic decision process that produces packets of responses. Both of these theories will be applied to an example of simultaneous temporal processing by rats, and will serve as the basis for some general comments about the basis for selecting and evaluating quantitative theories of timing.