Blackburn & El-Deredy (2013) provide a nice review of the literature on temporal (delay) and probabilistic discounting. They note these features of similarity and difference:

  • Both follow hyperbolic (rather than exponential) discount functions
  • Not correlated: impulsivity might be interpreted as steeper temporal discounting, and shallower probabilistic discounting, but steep temporal discounters don’t appear to be shallow probabilistic discounters
  • Magnitude effect opposite: for probabilistic rewards, larger rewards are more steeply discounted, for delayed rewards, larger rewards are more shallowly discounted
  • Sign effect the same: Gains vs loses effect discounting similarly for temporal and probabilistic discounting (gains are more steeply discounted).

To this list their experiments add a dissociable effect of ‘uncertain outcomes’ (all or nothing) vs ‘uncertain amounts’ (graded reward).

Blackburn, M., & El-Deredy, W. (2013). The future is risky: Discounting of delayed and uncertain outcomes. Behavioural processes, 94, 9-18.