Logan Bell

Date of Award

2024

Document Type

Thesis

Degree Name

Bachelors

Department

Social Sciences

First Advisor

Harley, Heidi

Area of Concentration

Biopsychology

Abstract

The instrumental learning process, explored through studies on animals like rats and goldfish, investigates how behavior is influenced by consequences. While Thorndike and Skinner laid the groundwork, research has shown differences in responses to changes in reward magnitude between species. Rats have demonstrated the depression effect, a decline in the rate of performance due to a reduction in the size of reward, however, goldfish studies have faced challenges in replicating findings on this effect. The current study aims to investigate whether goldfish exhibit the depression effect in variable magnitude downshifts. The study involved six common freshwater goldfish (Carassius auratus) randomly assigned to three experimental groups, in which all began with 0.3 mL fish paste reward and each group downshifted to 0.15 mL, 0.05 mL, and 0.10 mL. Trials were conducted over 14 non-consecutive days, with the pre-shift phase (i.e., the phase before any shift in reward magnitude) lasting 24 trials and the post-shift phase (i.e., the phase after a shift in reward magnitude) lasting 12 trials. The anticipated depression effect did not occur with the goldfish: Analyses showed no significant sustained decrease in running speeds from pre-shift to post-shift phases for all groups. On the other hand, the running speeds of the fish were more erratic post-shift than pre-shift suggesting that the fish noticed a difference in the reinforcement values. The challenge of obtaining consistent results in goldfish experiments may stem from the ratio between initial reward magnitude and the number of trials, as a small pre-shift reward may not be differentiable from a smaller post-shift reward, and too few trials leads to a weaker association built between the goal behavior and the reward. Suggestions for future research include increasing both the trial number and the initial reward magnitude, as well as considering frustration theory to understand the impact of reward magnitude reduction on animal behavior and learning.

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