Making a Law: Frequency Discrimination II
- Purpose and Goals
- 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
- 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
- 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.
- 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?)
- Control: Change only one thing at a time
Method Settings Tab:
- Back to the Chapter 2 in ISLE Software
- 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.
- 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
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
- 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
- Plot the Standard Frequency on the x-axis. Why?
- Plot your JND on the Y-axis (or ΔI/I) on the y-axis. Why?
- Use differnt symbol/color for each weeks data. Why?
- Indicate your law's predictions for the week 2 data
- Describe your law and how you came up with it
- Indicate if the second week's data fits your law or not