Green, L., Myerson, J., Shah, A.K., Estle, S.J. & Holt, D.D.(2007).
Do adjusting-amount and Adjusting-delay procedures produce equivalent estimates of subjective value in pigeons?
Journal of the Experimental Analysis of Behavior, 87, 337-347.
The current experiment examined whether adjusting-amount and adjusting-delay procedures provide equivalent
measures of discounting. Pigeons’ discounting on the two procedures was compared using a within-subject yoking
technique in which the indifference point (number of pellets or time until reinforcement) obtained with one
procedure determined the value of the corresponding variable in the yoked condition with the other procedure.
Behavior on each procedure was well described by a hyperbolic discounting function. Results revealed no
systematic differences in the degree of discounting as measured by the discounting rate parameter of the
hyperbola in Experiment 1, which used 20-mg pellets. These results were replicated in Experiment 2 using
smaller, 14-mg pellets, which potentially yield more precise measurement of indifference points on the
adjusting-amount procedure. The finding that estimates of the k parameter in the hyperbolic discounting
function obtained with one procedure did not differ systematically from estimates obtained from the same
subjects with the other procedure represents strong support for the hypothesis that the same process underlies
the discounting of delayed rewards on both adjusting-amount and adjusting-delay procedures.
Key words: discounting, subjective value, adjusting amount, adjusting delay, hyperbolic function, key peck, pigeons