Outcome Devaluation
Outcome devaluation means decreasing the value of a reward or other consequence. The experiment separated learning the action, changing the value of the outcome, and measuring the action when the outcome was no longer delivered.
Why the Outcome Matters
A rat can learn an action because that action produces a desirable consequence. In the Adams and Dickinson experiment, rats learned to press a lever for sucrose pellets. The central question was not only whether the rats had learned to press the lever. It was whether later pressing would still depend on the current value of the sucrose pellets.
Outcome devaluation means decreasing the value of a reward or other consequence. The experiment separated learning the action, changing the value of the outcome, and measuring the action when the outcome was no longer delivered.
Training the Lever Response
During instrumental conditioning, lever pressing was established as a behavior that produced sucrose pellets. This training stage shows that the rats learned the response. However, training alone does not show why the rats would continue pressing later. Pressing might be controlled by the learned relationship between the action and its outcome, or it might continue simply because pressing had become familiar.
Separating the Action from the Outcome
What has been established after rats learn to press a lever for sucrose pellets, and what remains unknown?
- 1Action learned
The rats have learned the lever-press response because pressing produces sucrose pellets.
- 2Outcome identified
Sucrose pellets are the consequence associated with the lever press.
- 3Question left open
Training does not by itself reveal whether later pressing depends on the current value of the sucrose pellets.
The experiment needs a separate procedure that changes the value of the pellets before lever pressing is tested.
Changing Pellet Value
The researchers devalued the sucrose pellets without requiring the rats to press the lever. Rats received free access to the pellets, so the food was available independently of their actions. After 15 minutes of access, one group received lithium chloride, a nausea-inducing poison. This procedure was repeated for three sessions. By the final session, the injected rats consumed none of the freely available pellets, indicating that the pellets had lost value for them.
Testing During Extinction
After the pellet value was changed for one group, both groups were tested with extinction trials. During extinction, the lever was disconnected from the pellet dispenser. Rats could still press the lever, but pressing no longer delivered sucrose pellets. This allowed researchers to measure lever pressing without giving the outcome again.
The order of operations is essential: first the rats learn that pressing produces pellets, then the pellet value is changed for one group, and finally both groups press while pellets are withheld. Because the test does not provide pellets, a difference in response rate shows how the changed outcome affected performance of the learned action.
Predicted Group Difference
What do you think happens?
During extinction, which group should show the lower lever-press response rate: rats whose pellets were devalued or non-injected rats?
Reveal answer
Rats whose pellets were devalued should show the lower response rate.
The source reports that rats with devalued pellets showed lower response rates than non-injected rats from the start of extinction.
The devalued group pressed the lever at a lower rate than the non-injected group from the start of extinction. This result shows that changing the value of the sucrose outcome affected performance of the learned action, even though the rats had already learned how to press the lever.
Common Interpretation Errors
Common mistake Treating training as proof that the outcome will always control the behavior.
What it looks likeThe rats learned to press the lever for sucrose pellets, so their later pressing must be controlled by the pellets in the same way.
Why it failsTraining establishes the response but does not reveal whether later pressing depends on the current value of the outcome or merely on familiarity with the response.
Do this insteadUse devaluation followed by an extinction test to examine the effect of the outcome's current value.
Common mistake Saying that devaluation occurred because the rats had to press the lever repeatedly.
What it looks likeThe pellets became less valuable because lever pressing was repeated during the devaluation stage.
Why it failsThe rats received free access to pellets independently of their actions.
Do this insteadIdentify the devaluation procedure as free pellet access followed by lithium chloride-induced nausea.
Common mistake Assuming that extinction means the rats cannot press the lever.
What it looks likeThe lever was disconnected, so the rats could not perform the response.
Why it failsThe lever remained available for pressing; it was disconnected from the pellet dispenser.
Do this insteadExtinction measured pressing while withholding the sucrose-pellet outcome.
Common mistake Predicting that the devalued group should press more because it had received more experience with pellets.
What it looks likeThe injected rats had free pellet access, so they should show the highest response rate.
Why it failsBy the final devaluation session, the injected rats consumed none of the freely available pellets, indicating that the pellets had lost value.
Do this insteadPredict a lower response rate for the devalued group than for the non-injected group during extinction.
Apply the Experimental Logic
A group of rats has learned that pressing a lever produces sucrose pellets. Before testing, the pellets are provided freely for 15 minutes, followed by lithium chloride-induced nausea across the devaluation procedure. During the final test, the lever is disconnected from the pellet dispenser. Predict how this group should compare with non-injected rats in lever pressing from the start of extinction, and explain why the test can reveal an effect of pellet value.
Hints
- Identify what happened to the value of the sucrose pellets.
- Remember that the extinction test measures pressing without delivering pellets.
- Compare the response rates of the devalued and non-injected groups.
Practice Answer
How should the devalued group perform during the extinction test?
- 1Value changed
Free access to sucrose pellets followed by lithium chloride-induced nausea reduced the value of the pellets for the injected rats.
- 2Outcome withheld
The lever was disconnected from the pellet dispenser, so pressing no longer produced sucrose pellets.
- 3Groups compared
The devalued rats' response rate was compared with the response rate of non-injected rats.
The devalued rats should show a lower lever-press response rate than the non-injected rats from the start of extinction.
Key Takeaways
- 1Instrumental conditioning established lever pressing as a behavior that produced sucrose pellets.
- 2Pellet value was reduced through free access to pellets followed by lithium chloride-induced nausea, repeated across three sessions.
- 3Extinction disconnected the lever from the pellet dispenser, allowing pressing to be measured without delivering pellets.
- 4Rats with devalued pellets showed lower response rates than non-injected rats from the start of extinction.
- 5The group difference shows that changing the value of the outcome affected performance of the learned action.
At a glance
- Lever pressing was learned because it produced sucrose pellets.
- Outcome devaluation reduced the pellets' value through free access followed by lithium chloride-induced nausea.
- Extinction tested lever pressing while the lever was disconnected from the pellet dispenser.
- The devalued rats pressed at a lower rate than non-injected rats from the start of extinction.