Aparicio, C.F. & Baum, W.M. (2009).
Dynamics of choice: relative rate and amount affect local preference at three different time scales.
Journal of the Experimental Analysis of Behavior, 91, 293-317.
To examine extended control over local choice, the present study investigated
preference in transition as food-rate ratio provided by two levers changed across
seven components within daily sessions, and food-amount ratio changed across phases.
Phase 1 arranged a food-amount ratio of 4:1 (i.e., the left lever delivered
four pellets and the right lever one pellet); Phase 2 reversed the
food-amount ratio to 1:4, and in Phase 3 the food-amount ratio was 3:2.
At a relatively extended time scale, preference was described well by a
linear relation between log response ratio and log rate ratio (the
generalized matching law). A small amount of carryover occurred
from one rate ratio to the next but disappeared after four food
deliveries. Estimates of sensitivity to food-amount ratio were
around 1.0 and were independent of rate ratio. Analysis across
food deliveries within rate-ratio components showed that the effect
of a small amount was diminished by the presence of a large
amountÑthat is, when a larger amount was present in the
situation (three or four pellets), the value of a
small amount (one or two pellets) became paltry.
More local analysis of visits to the levers between food
deliveries showed that postfood visits following a large
amount were disproportionately longer than following a
small amount. Continuing food deliveries from the same
source tended to make visits less dependent on relative
amount, but a discontinuation (i.e., food from the
other lever) reinstated dependence on relative amount.
Analysis at a still smaller time scale revealed preference
pulses following food deliveries that confirmed the
tendency toward dependence on absolute amount with
continuing deliveries, and toward dependence on
relative amount following discontinuations. A
mathematical model based on a linear-operator equation
accounts for many of the results. The larger and
longer preference following a switch to a larger amount
is consistent with the idea that local preference
depends on relatively extended variables even on short
time scales.
Key words: food rate, food amount, preference pulse, matching law,
choice, dynamics, rats