Biological and Psychological Description of an Internal Clock
Russell M. Church Hilary A. Broadbent Brown University
John Gibbon New York State Psychiatric Institute and Columbia University
Studies of time perception demonstrate that animals can discriminate the duration of external stimuli. For example, an animal can be trained to make different responses depending on the duration of a stimulus ( Church, 1989; Gibbon & Allan, 1984). An animal can also be trained to respond at regular intervals ( Weiss & Laties, 1965).
The data of time perception and time production experiments can be described without postulating an internal clock or any intervening variables. With such an approach, functional relationships between independent variables and the behavior of the animal can be established and general principles, such as Weber's law, can be applied to animal timing ( Gibbon, 1977). But to explain the psychophysical data, many investigators have found it useful to assume the existence of an internal timing mechanism and other processes intervening between the input and output variables. One goal is to use the postulated intervening processes to obtain a greater understanding of time discrimination and timed performance. At a minimum, intervening variables have provided convenient metaphors to guide thinking about the influence of the conditions of stimulation and reinforcement on responding. An alternative goal is to use information about time discrimination and timed performance to obtain a greater understanding of fundamental psychological processes. These intervening variables may represent psychological processes that translate the input into behavior. A still more ambitious goal is to describe the biological realization of these mental processes. A quantitative specification of the intervening variables may provide a needed roadmap for identifying the biological basis of timing.
The concept of an internal clock was used by Hoagland ( 1933) as a physiological concept to account for changes in human time discrimination as a function of