The effects of incentive shift as a function of training

Abstract

Five groups of rats were trained and extinguished in an 11 ft runway. Either 0, 10, 20, 30, or 40 trials were given with 1 Noyes pellet followed by the remainder of 40 trials with 10 pellets. The increase in response speed following the incentive shift was positively related to the number of I-pellet trials. Speed during extinction was monotonic with terminal acquisition speed. ProblemSpeed of response in the straight alley duringextinction has been found to be nonmonotonically related to the extent of training when a broad range of acquisition trials is used (lson, 1962; Clifford, 1964). Birch (1961) has attributed this result to the combined effects of goal anticipation and frustration. Theois & Brelsford (1964) account for the finding by hypothesizing that extinction is a positive function ofthe number of responses but a negative function of the strength of goal antiCipation. Under conditions where the total number of trials is held constant increasing strength of goal anticipation is expected to result in nonmonotonicity according to the former flosition and a monotonic negative relation according to the latter. The present experiment was designed to gain information on this point. The design also allows an evaluation of the change in response speed resulting f::om an increase in goal magnitude as a function of the number of preshift trials. Method.Seventy-five male hooded rats, about 90 days old at the beginning of training, were assigned equally to five groups. Three Ss, all from different groups, were eliminated because of illness. A 22-hr. food maintenance schedule was employed throughout the experiment with water always available. Each S was given one trial per day under 22-hr. food deprivation with the order of running randomized across Ss from day to day. Following a run S was returned to his individual home cage where he waited for a minimum of 30 min. before being fed for 1 hr.A straight runway, 4 in wide by 6 in high by 11 ft long, was constructed to be maximally homogeneous. The 1-ft starting section was designed without a door by using two wooden blocks so attached that S had to go under the first and over the second. S's start and running responses were timed by an arrangement of capacitance operated switches wherein S activated the timing device by stepping on copper plates, one of which was hidden under the start section and the other under the runway floor 4 ft down the alley.

Increase in incentive amount with verbal reinforcement

“…This result is consistent with most studies that have increased incentive magnitude with animal Ss (e.g., Ashida & Birch, 1964;Collier et aI, 1961).…”

“…Although reward decrements often produce negative incentive contrast effects in which the performance of the shifted Ss drops significantly below the level of the low-reward control group (e.g., Crespi, 1942;Weinstein, 1970), reward increments usually do not produce positive incentive contrast effects in which the performance of the shifted group rises significantly above the level of the high-reward control group (e.g., Ashida & Birch, 1964;Collier, Knarr, & Marx, 1961). While most studies have investigated the effects of shifting incentive magnitude with infrahuman organisms, few experiments have used human Ss.…”

A test of the “;ceiling effect”; hypothesis of positive contrast

“…Two other experiments have reported similar designs but, unfortunately, their experiments were conducted for other reasons, and the shifts from small to large reward occurred well after the consistently large rewarded group had reached asymptote (Ashida & Birch, 1964;Birch & Valle, 1967). SUBJECTS The Ss were 72 experimentally naive male albino rats of the Sprague-Dawley strain, selected from the colony at Southern Methodist University.…”

Reinforcement magnitude effects with overtraining

“…:r of preshift trials was varied are inconsistt;." in regard to rate and degree of change in running times (Ashida & Birch, 1964;Davis & North, 1968;Rosen, 1966;Spence, 1956; 'The experiment was carried out with the aid of a grant from NIH Biomedical Sciences Support funds to The George Washington University.…”