Effects of Stimulus Discriminability on Discrimination Acquisition and Stimulus-Equivalence Formation: Assessing the Utility of a Multiple Schedule

Abstract

A multiple schedule was used to examine the effects of stimulus discriminability on discrimination acquisition in baseline and subsequent stimulus-equivalence formation. Six college students were exposed in two experiments to more or less discriminable stimuli across multiple-schedule components (reinforcer magnitude was unequal and equal in Experiments 1 and 2, respectively). For five of the six participants, slower baseline acquisition occurred with the less discriminable stimuli. After high accuracy scores occurred in both components for several sessions, stimulus equivalence was tested across multiple sessions. In terms of accuracy, delayed emergence of equivalence formation only occurred in the component with the less discriminable stimuli for three of the five participants who previously displayed differential acquisition. For one of these other two participants, a 2-week follow-up assessment revealed that stimulus equivalence was disrupted only in the component previously correlated with the slower acquisition period. In terms of response latency, slower responding was obtained in the component with the less discriminable stimuli for all six participants, particularly during initial equivalence testing. These results demonstrate that stimulus discriminability can influence both discrimination acquisition and stimulus-equivalence formation. The results also support the utility of examining stimulus-equivalence formation using a multiple schedule.

Appendix

The following instructions were provided to each participant before the first session of Condition 1 in each experiment:

Welcome to our study on trial-and-error learning! In this study, you will work alone on the computer. The computer will present you with many trials and alternate between red and yellow background screens. On each trial, you will be presented with seven items: one item in the center of the screen surrounded by six items. [In Experiment 2, it noted that there were five items, one in the center surrounded by four others]. Click the mouse over any one of the surrounding items that you think “goes with” the item in the center, and one of two things will occur: (1) oval-shaped stars will appear or (2) the screen will darken. If stars appear then you earned 1 cent if the screen was yellow and 3 cents if the screen was red. [In Experiment 2, it noted that the participant earned 1.5 cents in each component]. If the screen darkened, then you earned 0 cents. You will receive many sessions each day, and each one will last between 20 and 30 min. The computer will tell you when the session is over. Good Luck!

The following instructions were provided to each participant before the single session in Condition 2 in each experiment:

In your next session, there never will be any stars or dark screen. The computer still will record whether your choice is correct or incorrect. You still will receive 1 or 3 cents for each correct choice. [In Experiment 2, it noted that the participant still earned 1.5 cents in each component]. The computer will still tell you that the session is over, and at the end of the session you will be told how much money you earned. Good Luck!”

The following instructions were provided to each participant before the first session of Condition 3 in each experiment (as well as before the third session in Condition 3 in Experiment 2 for Participants 6 and 7):

In your next session, there never will be any stars or dark screen. The computer still will record whether your choice is correct or incorrect. You still will receive 1 or 3 cents for each correct choice. [In Experiment 2, it noted that the participant still earned 1.5 cents in each component]. And, the computer still will tell you that the session is over. The difference in this session is that you will not be told how much money you earned; instead, at the end of the study we will tell you how much you earned in this session. Good Luck!