1. Single reward vs. two different rewards:
Are two different rewards preferred over one consistent reward in odor discrimination by rats?
Anu Thapa
Randolph College
Lynchburg, VA 24503
Introduction
According to operant conditioning, theory, reinforcers work while they are provided consistently. The contiguity as well as contingency of the reinforcers with the behavior affects how quickly a behavior is learnt or lost (Chance, 2005). Much research has been conducted to examine these effects on operant conditioning.
However, there is not much literature available that examines the effect of using two different kinds of rewards to reinforce the same behavior. . This experiments examines the effectiveness of using two different rewards to reinforce a behavior to that of using a consistent reward to reinforce the same behavior. I hypothesized that there would be a difference between the effectiveness of using one reward over two different rewards in odor discrimination for rats.
Figure 1
Results
Because the subject for this experiment was a single rat, it was not possible to run a dependent sample t-test on the data collected.
However, the average latency to dig for the cocoa vs. cinnamon condition was 2.58 seconds, and that for the cumin vs. cardamom condition was 1.70 seconds.
Latency to dig (sec):
Cocoa vs. Cinnamon: 4.98, 3.51, 4.92, 2.20, 1.40, 1.42, 1.45, 1.48, 1.47.
Cumin vs. Cardamom: 1.25, 1.84, 2.49, 0.96, 1.82, 0.96, 1.54, 2.71
The results for the testing day are unavailable because the rat refused to dig.
Shaping (Day 1)
Two cups of unscented sand (three trials)
Shaping (Day 2)
Two cups of unscented sand (six trials)
Figure 2
Training (Day 1)
Two cups of scented sand (cocoa/ cinnamon)
(ten trials) with 75% correct.
Discussion
The results are inconclusive because the rat did not dig during the crucial testing period.
The fact that the rat took less time to dig during the cumin vs. cardamom condition can be attributed to the rat’s memory rather than preference over two different rewards.
The latency to dig of the rat during the very first trial of the cumin/cardamom condition shows that the speed was due to memory.
For future purposes it would be prudent to use more than one rat as subject.
Method
Subjects
A hundred and twenty-days old, male Long-Evans rat (N=1) was reduced to and maintained at 85% of his free-feeding weights one week prior to and during experimentation. Water was available ad libitum.
Apparatus
All shaping, training, and testing took place in the rats’ home cages. Plastic Nalgene® cups (125 ml size) were used for the odor discriminations and were mounted using Velcro® onto rectangular Plexiglas® bases. Odor discriminations were created by mixing play sand (148 grams & 149 grams) with different dried spices (i.e., 2 grams of cocoa or cinnamon and 1 gram of cumin or cardamom).
Procedure
The rat was shaped to dig in unscented cups of sand for two days prior to training He received one day of training for each odor discrimination. For the cocoa/cinnamon discrimination, the distinction was made by adding corn puffs in the cocoa cup. Whereas, for the cumin/cardamom discrimination, the cup containing cumin contained either four fruit loops or four corn puffs in random order. The position of the cups were also randomly changed (left vs. right). The rat’s latency to dig in either of the cup was measured by a stop watch.
On the day of the testing the rat was presented with cups containing cocoa and cinnamon sans the rewards. His latency to dig and the time spent digging on each cup was to be recorded using the stop watch.
The cup preference was to be calculated using the following formula:
Cup preference = time spent digging on each cup/ total time (300 seconds)
Training (Day 2)
Two cups of scented sand (cumin vs. cinnamon) eight trials with 75% correct total)
Testing (Day 5)
Two scented cups (cocoa/cumin) presented without rewards.
References
Chance, P. (2006). Learning and behavior: Active learning edition (5th ed.). Belmont, CA: Thomson/Wadsworth.