The Scalar timing or scalar expectancy theory (Gibbon 1977) is a model that posits an internal clock

Clock

A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

, and particular memory

Memory

In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....

 and decision

Decision making

Decision making can be regarded as the mental processes resulting in the selection of a course of action among several alternative scenarios. Every decision making process produces a final choice. The output can be an action or an opinion of choice.- Overview :Human performance in decision terms...

 processes. This is one of the most popular views of timing

Timing

Timing is the time when something happens or the spacing of events in time. Some typical uses are:* The act of measuring the elapsed time of something or someone, often at athletic events such as swimming or running, where participants are timed with a device such as a stopwatch...

 in animals. The clock and memory are driven by a discrete pacemaker

Cardiac pacemaker

right|thumb|350px|Image showing the cardiac pacemaker which is the SA nodeThe contraction of heart muscle in all animals with hearts is initiated by chemical impulses. The rate at which these impulses fire controls the heart rate...

-accumulator

Accumulator

Accumulator may refer to:* Accumulator , in a CPU, a processor register for storing intermediate results* Accumulator , an apparatus for storing energy or power...

 mechanism that yields a linear scale

Scale (ratio)

The scale ratio of some sort of model which represents an original proportionally is the ratio of a linear dimension of the model to the same dimension of the original. Examples include a 3-dimensional scale model of a building or the scale drawings of the elevations or plans of a building. In such...

 for encoded time. The scalar expectancy theory (SET) posits that animals make choices based on a single sample. The animals are posited to make estimates of the time to reinforcement

Reinforcement

Reinforcement is a term in operant conditioning and behavior analysis for the process of increasing the rate or probability of a behavior in the form of a "response" by the delivery or emergence of a stimulus Reinforcement is a term in operant conditioning and behavior analysis for the process of...

delivery using a scalar-timing process. This scalar-timing process rescales estimates for different values of the interval being timed. Scalar-timing implies a constant coefficient of variation. Expectations or reinforcement are based on these estimates are formed from these sample. The animal discriminates between response alternatives by taking the ratio of their expectancies. A number of alternatives have been developed over the years. These include Killeen’s (1991) Behavioral Theory of timing (BeT) model and Machado’s (2005) learning-to-time (LeT) model.