Scalar expectancy

The Scalar timing or scalar expectancy theory (SET) is a model that posits an internal clock, and particular memory and decision processes.[1] SET is the predominate model of animal timing behavior.[2]

History

John Gibbon originally proposed the scalar expectancy model, an extension of Weber's Law, as a quantitative model used to explain the temporally controlled behavior on non-human subjects.[1] SET in its early version was primarily used to explain the break-run pattern, a common response pattern on fixed-interval reinforcement schedules.[3] In a break-run pattern, an animal does not start responding to the stimulus upon representation. However, as the target duration approaches, the subject switches to a high rate of responding; this switch occurs at approximately two-thirds of the target duration.[1]

Animal mechanism

The clock and memory are driven by a discrete pacemaker-accumulator mechanism that yields a linear scale for encoded time. The scalar expectancy theory posits that animals make 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 Behavioral Theory of timing (BeT) model[4] and Machado’s learning-to-time (LeT) model.[5]

Human mechanism

In 1993, Wearden claimed that human behavior exhibits appropriate scalar properties, as was indicated by experiments on internal production with concurrent chronometric counting.[6] However, human timing behavior is undoubtedly more varied than animal timing behavior. A major factor responsible for this variability is attentional allocation.[6]

References

  1. 1 2 3 Gibbon, J. (1977). Scalar expectancy theory and Weber’s law in animal timing. Psychological Review. 84(3), 279-325
  2. ↑ Joshua S. Beckmann (2007). The Effects of Stimulus Dynamics on Temporal Discrimination: Implications for Change and Internal Clock Models of Timing. ProQuest. pp. 5–. ISBN 978-0-549-22213-2. Retrieved 11 January 2013.
  3. ↑ Christopher Michael Magaro (2008). Dissociating Clock Speed and Attention in the Modality Effect. ProQuest. pp. 7–. ISBN 978-0-549-47717-4. Retrieved 11 January 2013.
  4. ↑ 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
  5. ↑ 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.
  6. 1 2 M.A. Pastor; J. Artieda (10 June 1996). Time, Internal Clocks and Movement. Elsevier. pp. 148–. ISBN 978-0-08-054304-8. Retrieved 11 January 2013.
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