A Direct Test of Contrast and Delay Reduction Hypotheses:

Why Do Pigeons Prefer Stimuli Following Aversive Events?

Rebecca Singer & Thomas Zentall

University of Kentucky

Justification of Effort

Greater value is placed on the reward that requires greater effort to obtain (i.e., A in organic chemistry vs. A in golf)

Justification of Effort in PigeonsClement, Feltus, Kaiser, and Zentall (2000)

FR1

+

FR20

+

or ?

Train

Test

Contrast Effect

Proposed contrast hypothesis (rather than cognitive dissonance) to explain results

Valu

e

V

-ΔV

+ΔV

Reinforcement

FR1

FR20Aversiveness of task

Relative Value of Reinforcer

Relative Value of Reinforcer

Delay Reduction HypothesisFantino (1969)

Any stimulus that is associated with a reduction in the delay to reinforcement should become a conditional appetitive stimulus

Delay Reduction Hypothesis

Reinforcement

FR20

FR1

Presentation of discriminative stimuli

Overall Purpose

Purpose of current experiments is to provide a direct test of the delay reduction hypothesis by holding trial duration constant

Used two schedules of reinforcement: fixed interval (FI) and differential reinforcement of other behavior (DRO)

Experiment 1a – Training

White White

Horiz Vert

Food Food

DRO FI

Left key = DRO 20 s Right key = FI 20 s

Experiment 1a – Test

Horiz Vert

Food Food

DRO FI

White White White White

Experiment 1a - Results

2 birds demonstrated DRO preference

1 bird demonstrated FI preference

4 birds demonstrated side preference

Experiment 1b: Purpose

Contrast hypothesis states that pigeons will prefer stimuli associated with their non-preferred schedule (or side)

Delay reduction hypothesis states if trial duration is equated there should be no preference for discriminative stimuli

Experiment 1b – Training

White White

Horiz Vert

Food Food

DRO FI

Experiment 1b – Test

DRO , FI, or no initial event

Both S+

Experiment 1b - ResultsTest 4

50

55

60

65

70

75

10017 20835 10050 4335 575 10015 581

Bird #

% P

refe

ren

ce

Conclusions

There was no systematic schedule preference when FI and DRO schedules were used

There was a significant preference for stimuli that followed the aversive schedule