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Experiment 5: Discrimination
Purpose:
To train the animal to discriminate between the presence and absence of
the cue light. This is achieved by reinforcing lever responses in the presence of light
and by not reinforcing responses during the absence of light, thereby extinguishing
responses in the latter condition. The presence of light is called the discriminative
stimulus (SD) for the lever response; the absence of light is called the
S-Delta (S D).
Procedure:
- Do an equipment test.
- Notify the TF when you are ready to begin the experiment.
- As light is being used as the discriminative stimulus, it is important to minimize all
other sources of light so as not to confuse your animal.
- Place your subject in the operant chamber and turn on the cue light (SD) by
pressing the hand switch. The first response emitted will be reinforced.
- Immediately after the delivery of the reinforcer, the cue light will go off and must
remain off for one minute (S
D). You are required to time this minute, during which time responses will
not be reinforced.
At the end of the minute click the hand switch to turn the cue light on again (SD)
Continue with the sequence. The first response during SD will be reinforced.
The cue light will then go off (SD). During SD responses will not be reinforced. Time the one-minute duration of SD then click the hand switch to turn
on the cue light.
Data: There are two sets of data that you will need to record: (a) the number of seconds
until the response during SD (when the light is on) and (b) the number of
responses during SD
(when the light is off)
The pattern described in point 5 should continue until responses during SD have dropped to a very low level
(to zero or close to zero).
The house light will so off and the experiment will end at the completion of the 120th
delta trial.
. At this stage we might say that the animal is discriminating between the presence and
absence of light - or can we? Do we have stimulus discrimination, or do we simply have an
FI pattern of responding? How would you test for it? Do so in a second session.
Data Collection:
Before coming to class prepare a data sheet.
You will be collecting two sets of data.
- the number of seconds until the response during responses during SD (when the
light is on)
- the number of responses during S
D (when the light is off)
Group Data
Submit your group data before leaving class.
| Latencies - One Minute
Interval |
Latencies - Variable
Interval |
| First Five Trials |
Last Five Trials |
First Five Trials |
Last Five Trials |
1 |
2 |
3 |
4 |
5 |
1 |
2 |
3 |
4 |
5 |
1 |
2 |
3 |
4 |
5 |
1 |
2 |
3 |
4 |
5 |
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| Resp. per min - One minute
Interval |
Latencies - Variable
Interval |
| First Five Trials |
Last Five Trials |
First Five Trials |
Last Five Trials |
1 |
2 |
3 |
4 |
5 |
1 |
2 |
3 |
4 |
5 |
1 |
2 |
3 |
4 |
5 |
1 |
2 |
3 |
4 |
5 |
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Lab Report # 3 :
You will be required to present your data graphically with a view to
answering the following questions:
- What was the pattern of latencies across all trials for your subject? Is there a
difference between latencies during the one-minute interval and during the variable
interval?
- What was the pattern of responding over all trials for your subject? Is there a
difference in response rates during the one-minute interval and during variable interval?
- How could one summarize the latencies across trials for your subject?
- How could one summarize the responses per minute made by your subject?
- How does your subject compare to the group with regard to latencies?
- How does your subject compare to the group with regard to the number of responses per
minute?
Statistical Analysis:
- Does the group show a significant difference between the latencies during fixed interval
and variable interval?
- Does the group show a significant difference between the number of responses during
fixed interval and variable interval?
MED-PC Output
Array A – latencies to respond during SD
Array B – the number of responses during SD
Array D – the duration (in seconds) of SD
Discrimination Program.
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