P/S 02 · Classical and operant conditioning
Blinks and Lever Presses
Read data on classical conditioning and reinforcement schedules.
Passage
Learning is a relatively lasting change in behavior that results from experience. In classical conditioning, an organism learns that one stimulus predicts another. A neutral stimulus (NS) that is repeatedly paired with an unconditioned stimulus (US), which triggers a reflex response without any learning, eventually becomes a conditioned stimulus (CS). The reflex response to the US is the unconditioned response (UR), and the learned response to the CS is the conditioned response (CR). In operant conditioning, the consequences of a behavior, such as reinforcement or punishment, change how often the behavior occurs.
Part 1. Researchers study eyeblink conditioning in 90 adult volunteers. A tone is sounded for half a second, and a brief puff of air to the eye is delivered at the end of the tone on some trials. Participants are randomly assigned to three groups of 30. The paired group hears the tone followed by the puff on every trial. The tone-only group hears the tone with no puff. The unpaired group receives tones and puffs at random times, never together. A blink during the tone, before the puff, counts as a CR. Table 1 shows the percentage of tone trials with a CR in successive blocks of 10 trials.
Table 1. Percentage of trials with a blink during the tone.
| Block | Paired group | Tone-only group | Unpaired group |
|---|---|---|---|
| 1 | 4 | 5 | 6 |
| 2 | 18 | 6 | 8 |
| 3 | 45 | 4 | 7 |
| 4 | 70 | 5 | 6 |
| 5 | 82 | 5 | 7 |
After block 5, the paired group is given three more blocks in which the tone is presented without the puff. Their CR percentages in blocks 6, 7 and 8 are 55, 25 and 8. The next day the same participants return, and the tone is presented alone again. In block 9 the CR percentage is 30.
Part 2. In a separate study, hungry rats learn to press a lever for food pellets. Four groups of rats are trained on four reinforcement schedules until their responding is steady: in the fixed-ratio (FR) schedule, a pellet is given after every tenth press; in the variable-ratio (VR) schedule, a pellet is given after an unpredictable number of presses that averages ten; in the fixed-interval (FI) schedule, the first press after a fixed amount of time is reinforced; and in the variable-interval (VI) schedule, the first press after an unpredictable amount of time is reinforced. Food is then stopped completely, and the researchers count the presses made during the first 30 minutes. Table 2 shows the results.
Table 2. Responding on four schedules, and responses during the first 30 minutes without food.
| Schedule | Pattern of responding during training | Presses per minute during training | Presses in first 30 minutes without food |
|---|---|---|---|
| FR | Bursts of presses, short pause after each pellet | 50 | 300 |
| VR | High, steady rate | 60 | 900 |
| FI | Slow after each pellet, faster as the interval ends | 15 | 200 |
| VI | Moderate, steady rate | 25 | 600 |
The researchers describe both parts as examples of how experience changes behavior, but they note that the behaviors differ in kind: the eyeblink is elicited by a stimulus, while lever pressing is emitted by the animal and depends on what follows it. They also point out that participants in Part 1 were told only that they would hear tones and feel air puffs, so most were not aware of the pairing rule when their blinks first began to change.
Questions
Question 1 of 6
In Part 1, why are the tone-only and unpaired groups included?
Random assignment can be used with any number of groups. The control groups answer a specific question about the cause of the change.
Only the puff is the US. The tone starts as a neutral stimulus.
Extinction was tested in the paired group itself, in blocks 6 to 8. Control groups cannot show it.
Why the answer is what it is
The paired group’s CR rate rises from 4% to 82%, but the tone-only and unpaired groups stay near 5%. Hearing the tone alone or getting puffs at random times does not produce blinks to the tone, so the pairing itself is responsible for the learning.
Review: Learning & Memory
Question 2 of 6
After training, a blink in response to the tone alone is best described as:
The blink to the puff is the unconditioned response. A blink to the tone is learned, so it is conditioned.
A response that occurs because of learning is conditioned, not unconditioned.
The tone has become a conditioned stimulus. The unconditioned stimulus is the air puff.
Why the answer is what it is
The air puff is the US and the blink to it is the UR. After pairing, the tone is a CS and the blink to the tone is a CR.
Review: Learning & Memory
Question 3 of 6
In block 9 the CR percentage rises from 8 to 30 after a day without training. This finding is called:
Sensitization would raise the response to many stimuli and does not require earlier pairing.
Generalization is a CR to stimuli that resemble the CS, such as a tone of a slightly different pitch.
Acquisition is the initial learning phase. Here, a response that had faded returns after a delay.
Why the answer is what it is
Blocks 6 to 8 show extinction, in which the CR fades when the CS is no longer followed by the US. The partial return of the CR after a rest is spontaneous recovery, which indicates that the learned association was suppressed, not erased.
Review: Learning & Memory
Question 4 of 6
Based on Table 2, which schedule produces the greatest resistance to extinction?
FR gave 300 presses in the first 30 minutes without food, fewer than VR and VI.
FI gave the smallest number of presses (200) of the four schedules.
VI gave 600 presses, a high number, but less than VR’s 900.
Why the answer is what it is
The VR group made the most presses (900) in the first 30 minutes without food. Unpredictable reinforcement makes it hard for the animal to detect that reinforcement has stopped, and partial reinforcement produces more persistent responding than every-time reinforcement.
Review: Learning & Memory
Question 5 of 6
The FI schedule produces slow responding after each pellet and faster responding as the interval ends. What does this pattern suggest about the rats?
The pressing is emitted behavior controlled by its consequences, which is operant, not a reflex.
The pattern shows that the rats have learned the relationship, because responding is concentrated near the time when pressing pays off.
Habituation is a decline in response to a repeated, harmless stimulus. Here the response rate recovers before each reinforcer.
Why the answer is what it is
In a fixed-interval schedule, pressing right after a pellet is never rewarded, and pressing late in the interval is. The rats learn this and press little at first and more as the time for the next reinforcer approaches.
Review: Learning & Memory
Question 6 of 6
In another condition, pressing the lever turns off a mild floor shock, and the rats come to press more often. This is an example of:
Positive reinforcement adds a pleasant stimulus. Here an unpleasant stimulus is removed.
Punishment lowers behavior. Here the lever pressing increases.
Negative punishment takes away something pleasant to decrease a behavior. Here the behavior increases, so it is reinforcement.
Why the answer is what it is
Reinforcement increases behavior, and ‘negative’ means that a stimulus is removed. Removing the shock when the rat presses the lever makes pressing more likely, which is negative reinforcement.
Review: Learning & Memory
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