|
| Delay Discounting: Does the Procedure and/or Experience Matter? |
| Tuesday, June 1, 2010 |
| 9:00 AM–10:20 AM |
| Republic C (Grand Hyatt) |
| Area: EAB/BPH; Domain: Experimental Analysis |
| Chair: Christine E. Hughes (University of North Carolina, Wilmington) |
| Abstract: Delay-discounting research has increased dramatically over the last decade. A lot of research has involved nonhumans responding on a typical self-control/impulsivity task in which subjects are given choices between smaller-sooner and larger-later reinforcers. Typically, the delays are varied either within or across session, often in a regular order, and delay-discount functions are obtained. In this symposium, the four presenters will discuss research in which aspects of the procedure or living environment are varied. The reliability of the delay-discount functions is assessed, and the usefulness of these functions as baselines for assessing drug effects or species differences is discussed. Could delay-discount functions obtained via the typical methods be controlled by variables other than delay? If so, what does that say about conclusions about self-control and impulsivity made based on data obtained from these procedures? |
| |
| Within-Session Discount Functions in Rats Using Randomly Ordered and Ascending Delays |
| ELIZABETH WATTERSON (University of North Carolina, Wilmington), A. Scott Handford (University of North Carolina, Wilmington), Carla Pruitt (California State University, Long Beach), Raymond C. Pitts (University of North Carolina, Wilmington), Christine E. Hughes (University of North Carolina, Wilmington) |
| Abstract: Seven Sprague-Dawley rats responded in a “self-control” experiment. Sessions included five, 12-trial blocks. Within each block, there were six forced-choice and six free-choice trials. Responses on one retractable lever produced 0.02 ml of sugar water immediately (i.e., the small reinforcer) whereas responses on the other retractable lever produced 0.08 ml of sugar water after a delay (i.e., the large reinforcer). In the first half of the study, delays to the larger reinforcer ranged between 0 and 40 s and were presented randomly across blocks within a session. After substantial exposure to the random-delay sequence all rats showed stable delay-discount functions. In the second half of the study delays to the larger reinforcer increased across blocks of trials. Stable discount-curves were again established. In both portions of the study administration of saline and d-amphetamine followed stability of discount-functions. Results show that ascending delays lead to a slightly steeper curve than randomly-ordered delays. Further examination of the data revealed that when delays were randomly presented larger reinforcer choices decreased across blocks regardless of the order in which the delays were arranged. This suggests larger reinforcer choice is at least partially controlled by time spent in the session. |
| |
| Housing Enrichment Decreases Impulsive Choice in Spontaneously Hypertensive, but Not Sprague-Dawley Rats |
| DENNIS J. HAND (Central Michigan University), Jim I. Gerhart (Central Michigan University), Mark P. Reilly (Central Michigan University) |
| Abstract: Variables outside an experimental context, such as housing conditions, can influence dependent measures. The present study examined how enriched and impoverished housing conditions change impulsive choice in two rat strains, Spontaneously Hypertensive Rats (SHRs), a model of impulsive behavior, and Sprague-Dawley (SD). Rats were presented with two reinforcer alternatives in a discrete-trials format. A single press on one lever produced one food pellet immediately while another lever produced three food pellets following a signaled delay which increased within each session. Choice data were gathered first with the rats housed individually in hanging wire cages (impoverished condition), second with the rats housed in a group of six (strains not mixed) in a large cage with bedding and three toys that were changed daily (enriched condition), and finally back in the individual wire cages. The SHRs chose the large, delayed alternative more often in the enriched condition than the impoverished condition. Choice by the SDs was unchanged by any housing condition. These results suggest that housing conditions can affect impulsive choice, however the reasons for the lack of an enrichment effect in the SD rats is at present unknown. |
| |
| Inter-Trial Interval Duration Modulates Impulsivity in Rats and Pigeons During an Intertemporal Choice Procedure |
| JACK SMETHELLS (Central Michigan University), Mark P. Reilly (Central Michigan University) |
| Abstract: Impulsivity can be defined as a preference for small-immediate reinforcers over larger-delayed ones. Various discrete-trials intertemporal choice procedures have been developed to investigate variables that modulate impulsivity. Within these procedures, choice trials are usually separated by a compensating intertrial interval (ITI) that maintains a consistent trial presentation rate irrespective of the alternative chosen. Previous research has indicated that the length of the ITI can affect risky choice (Kaminski & Ator, 2001), however, research has yet to establish how it may impact impulsivity in an intertemporal choice procedure. The present experiment employed rats and pigeons responding in an intertemporal choice procedure that employed either 45-s or 10-s compensating ITI and delays of 3 s (pigeons) or 3 and 6 s (rats). Preference for the small-immediate reinforcer increased (impulsivity increased) at all delay values when the ITI was reduced from 45 s to 10 s. Research has shown that increased exposure to a reinforcer has generally resulted in increased impulsivity (Grosh & Neuringer, 1981), which could be one of several possible mechanisms underlying the ITI effect seen in the present study. |
| |
| Experience With a Novel Task Reverses Differences in Impulsivity between Lewis and Fischer 344 Rats |
| CARLOS F. APARICIO (The Aurora School), Carla Pruitt (California State University, Long Beach), Christine E. Hughes (University of North Carolina, Wilmington), Raymond C. Pitts (University of North Carolina, Wilmington) |
| Abstract: Often, Lewis rats show steeper delay-discount functions than Fischer 344 rats in impulsivity tasks. But does an extended experience with the impulsivity task reverse this difference between Lewis and Fischer 344? In this experiment, 8 Lewis and 8 Fischer 344 rats’ lever pressing was maintained by a concurrent-chains procedure. Trials began by turning on the light above a back-wall-lever, pressing that lever started the initial-link by inserting two front-levers into the chamber. Pressing these levers gave access to the terminal-link according to a random interval schedule 10 s. The left lever provided 1 food-pellet according to a fixed interval (FI) schedule 5 s. The right lever provided 4 food-pellets according to either an FI 5-, 10-, 20-, 40, or 80-s across blocks of the session. The delays were presented randomly. Each pair of FIs was in effect for 10 food deliveries. Each food-delivery retracted the corresponding front-lever, signaling the end of the trial. When training began, Lewis rats were more impulsive than Fischer 344 rats. But with experience in the task, Fischer 344 rats became more impulse than Lewis rats. We will discuss the implications of these results with respect to differences between Lewis and Fischer 344 rats. |
|
| |