To practice the development of a scientific law using Frequency Discrimination
To test the law that we develop
To gain practice in presenting findings
To design your own experiment
Frequency Discrimination
Observations
If two tones are to close together we hear them as the same
As the frequency moves farther apart, we can eventually hear the difference in frequencies
This is a threshold
There are many frequencies we can hear (20 Hz to 20 KHz, at least for you folks)
It would be nice if there were a rule that would allow us to predict the size of this threshold for each different frequency
Weber's law is one possible rule
k =
ΔI I
But we would need to know the value of k to make predictions.
Eg: threshold at 100 Hz = 9 Hz, threshold at 200 = 21 Hz, threshold at 300 Hz = 30 Hz. So, it looks like Weber's law works, and k = 0.1, so what would the threshold be at 400 Hz? 250 Hz?
Another possible rule is that the threshold never changes.
k =
ΔI
What other sorts of rules are there? This is tough, you are being asked to not just work through a problem but propose a general answer. There are few rules. Start with other ideas and ponder.
Question: What is the rule that would allow us to predict the size of the frequency discrimination threshold? Do not feel bound by Weber's Law.
Developing and testing your law
Last week you collected some data that allowed you to develop your law
After coming up with a proposed law, it needs to be tested
So this week you will collect further data, on other frequencies
Before you can test your law, you must have generated predictions for each of your new frequencies
This will allow you to see how your ideas came out and try for a refinement
Experiments: Reminder
Experiments involve:
Independent Variable(s): the variable(s) the experimenter manipulates, in this case the frequency you are testing for threshold
Dependent Variable: the variable the experimenter measures, in this case the size of the frequency difference at threshold (what type of threshold?)
Use the
Frequency Discrimination version of Method of Limit, Method of Constant Stimuli, or Forced Choice
There are headphones available as well
You will need to use them
Stimulus Settings Tab:
Leave all the same except:
Standard Frequency.
This is your i if you use Weber's law. This is the base comparison frequency
Week 1: Pick 5 frequencies covering a good part of the range of possible frequencies
We typically like to have more values closer together at in the lower part of the range
So we often double each value: 100 Hz, 200 Hz, 400 Hz, etc.
Make sure you cover a good part of the range
Week 2: Pick 4 more frequencies that are between pairs of other frequencies, e.g., a frequency between your lowest and second lowest, then one betweens second and third lowest
Using the list above, you might test 150 Hz, then 300 Hz, etc.
Method Settings Tab:
Pick on of the three methods
Method of Limtis, or
Moethod of Constant Stimuli, or
Forced Choice
Choose the levels on the method settings you think will give you good data
Procedure:
Most will depend upon the nature of your experiment
Read the directions carefully
There is one common element:
two tones will play
Listen carefully
Good data quality is very important
Data
The data will be the frequency differency that is just detected reliably in Hz
What type of threshold is this?
Determine your thresholds using the proper method
Compare your thresholds to your predictions
Presentation
Next week you will give a presentation of your work (about 15-20 minutes)
Expectations:
Clear presentation of the issues and questions
Initial Experiment
Clear presentation of your method (similar structure to writeup)
Focus on and clear presentation of your study to develop your law
Presentation of your law
Presentaion of testing your law
Review of Method
Focus on and clear presentation of your results in comparison to your law
Discussion of how well your law did and what you would do next to improve your law