Making a Law: Frequency Discrimination II



  1. Purpose and Goals
    1. To practice the development of a scientific law using Frequency Discrimination
    2. To test the law that we develop
    3. To gain practice in presenting findings
    4. To design your own experiment
  2. Frequency Discrimination
    1. Observations
      1. If two tones are to close together we hear them as the same
      2. As the frequency moves farther apart, we can eventually hear the difference in frequencies
      3. This is a threshold
      4. There are many frequencies we can hear (20 Hz to 20 KHz, at least for you folks)
      5. It would be nice if there were a rule that would allow us to predict the size of this threshold for each different frequency
      6. Weber's law is one possible rule



        1. 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?
      7. Another possible rule is that the threshold never changes.



      8. 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.
    2. 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.
  3. Developing and testing your law
    1. Last week you collected some data that allowed you to develop your law
    2. After coming up with a proposed law, it needs to be tested
      1. So this week you will collect further data, on other frequencies
      2. Before you can test your law, you must have generated predictions for each of your new frequencies
    3. This will allow you to see how your ideas came out and try for a refinement
  4. Experiments: Reminder
    1. Experiments involve:
      1. Independent Variable(s): the variable(s) the experimenter manipulates, in this case the frequency you are testing for threshold
      2. Dependent Variable: the variable the experimenter measures, in this case the size of the frequency difference at threshold (what type of threshold?)
      3. Control: Change only one thing at a time

The Experiment:

  1. Equipment
    1. Back to the Chapter 2 in ISLE Software
    2. Use the Frequency Discrimination version of Method of Limit, Method of Constant Stimuli, or Forced Choice
    3. There are headphones available as well 
      1. You will need to use them
  2. Stimulus Settings Tab:
    1. Leave all the same except:
    2. Standard Frequency.
      1. This is your i if you use Weber's law. This is the base comparison frequency
      2. 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
      3. 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.
  3. Method Settings Tab:
    1. Pick on of the three methods
      1. Method of Limtis, or
      2. Moethod of Constant Stimuli, or
      3. Forced Choice
    2. Choose the levels on the method settings you think will give you good data
  4. Procedure:
    1. Most will depend upon the nature of your experiment
    2. Read the directions carefully
    3. There is one common element:
      1. two tones will play
    4. Listen carefully
    5. Good data quality is very important
  5. Data
    1. The data will be the frequency differency that is just detected reliably in Hz
    2. What type of threshold is this?
    3. Determine your thresholds using the proper method
    4. Compare your thresholds to your predictions
  6. Write-up
    1. Graph:
      1. Plot the Standard Frequency on the x-axis. Why?
      2. Plot your JND on the Y-axis (or ΔI/I) on the y-axis. Why?
      3. Use differnt symbol/color for each weeks data. Why?
      4. Indicate your law's predictions for the week 2 data
    2. Paragraph:
      1. Describe your law and how you came up with it
      2. Indicate if the second week's data fits your law or not