Scalar expectancy

The Scalar timing or scalar expectancy theory (Gibbon 1977) is a model that posits an internal clock, and particular memory and decision processes. This is one of the most popular views of timing in animals. The clock and memory are driven by a discrete pacemaker-accumulator mechanism that yields a linear scale for encoded time. The scalar expectancy theory (SET) posits that animals makes a choices based on a single sample. The animals are posited to make estimates of the time to reinforcement 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.

References

• Gibbon, J. (1977). Scalar expectancy theory and Weber’s law in animal timing. Psychological Review. 84(3), 279-325

• Kacelnik, A., & Brunner, D. (2002). Timing and foraging: Gibbon's scalar expectancy theory and optimal patch exploitation. Learning and Motivation 33 (1), 177-195.

• Killeen, P. R. (1991). Behavior’s time. In G. Bower (Ed.),The psychology of learning and motivation (Vol. 27, pp. 294–334). New York: Academic Press

• Machado, A., & Keen, R. (1999). Learning to Time (LET) or Scalar Expectancy Theory (SET)? A critical test of two models of timing. Psychological Science, 10, 285-290.

• Machado, A., & Pata, P. (2005). Testing the Scalar Expectancy Theory (SET) and the Learning to Time model (LeT) in a double bisection task. Behavior and Learning, 33, 111-122.

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