(Hint: Drawing a graph might help here.) We reinforce a rat’s bar-press on the “drug” lever when he has 5 mg/kg of heroin in his system, but punish bar-presses on the drug lever when he has 10 mg/kg of heroin in his system. We then test whether the rat will hit the “drug” lever under different levels of the drug (from 0 to 20); ie, we test for generalization. Under these conditions, the peak of the generalization gradient should:
Select one
a. reside at the 5 mg/kg dose, since that is the discriminative stimulus
b. shift toward the left (toward 0 mg/kg).
c. shift toward the right (toward 20 mg/kg)
d. reside at the 10 mg/kg dose, since that is the discriminative stimulus
The Correct Answer and Explanation is :
The correct answer is: a. reside at the 5 mg/kg dose, since that is the discriminative stimulus
Explanation:
In behavioral psychology, a discriminative stimulus is a cue or event that indicates the availability of reinforcement or punishment, depending on the response made. In the case described, the rat learns to associate pressing the “drug” lever with reinforcement (a positive outcome) when it has 5 mg/kg of heroin in its system. Conversely, pressing the same lever when the rat has 10 mg/kg of heroin leads to punishment (a negative outcome).
Generalization occurs when an organism responds to new stimuli that are similar to the original conditioned stimulus without prior training on these new stimuli. The peak of the generalization gradient typically occurs at the value of the stimulus that was reinforced, not the one that was punished. This is because the reinforced stimulus becomes the strongest cue for the desired behavior due to its positive association.
In your scenario, since the rat was reinforced for pressing the lever at 5 mg/kg, it is most likely to generalize this behavior to similar doses. This means that the peak of the generalization gradient will most likely reside at 5 mg/kg. The rat’s responses will tend to decrease as the dosage diverges from this point, either higher or lower, because these doses are less similar to the conditioned 5 mg/kg dose and carry different consequences (punishment or no reinforcement).
The gradient will not peak at 0 mg/kg or 20 mg/kg because these doses are farther from the reinforced dose and were not associated with positive outcomes. Similarly, the gradient will not peak at 10 mg/kg, even though this dose was used during training, because it was associated with punishment, making it an unlikely choice for the rat when seeking reinforcement.
To help visualize this concept, let’s create a graph of the expected generalization gradient:
- The x-axis will represent the doses of heroin from 0 to 20 mg/kg.
- The y-axis will represent the likelihood of the rat pressing the “drug” lever.
- The peak of the curve will be at 5 mg/kg, decreasing as the doses move away from this point.
The graph above illustrates the generalization gradient for the rat’s lever-pressing behavior. The peak of the gradient resides at 5 mg/kg, marked by the red dashed line, which is the dose where the rat was reinforced. This indicates the highest likelihood that the rat will press the lever. As the doses move away from this peak, the likelihood of lever pressing decreases, shown by the curve tapering off.
The green dashed line at 10 mg/kg, where the rat was punished, does not peak because this dose discourages the behavior rather than encourages it. This visual helps clarify why the behavior is most likely to occur at the reinforced dose rather than at any other dose.
