| ISLE | Chapter 2
| Experiment: Method of Limits: Frequency Discrimination
In the method of limits, stimuli are presented in a graduated scale, and participants must judge whether they detected the stimulus or not. The researcher hopes to pick a value that is readily detected and a value that is never detected and then several values between. These values are then presented in order, going from the most intense to the least intense, a descending staircase, and from least intense to most intense, an ascending staircase.
In this experiment, we will start with a descending staircase. Since the most intense stimulus is readily detectable, you should have no trouble responding with a yes you detected it. The next stimulus to be presented will be the next most intense. If you detect that stimulus, you will again respond with a yes. Then the next most intense stimulus will be presented. This series will be continued until you respond with a no you did not detect the stimulus. This response is called a crossover point as you have crossed from detection over to nondetection.
Then a descending staircase will begin with the least intense stimulus. You should not be able to detect in and respond with a no you did not detect it. Then the next more intense stimulus in the series will be presented. This series will continue until you respond that you did detect the stimulus. This response is also a crossover response as you have crossed from nondetection over to detection.
These two types of staircases, descending and ascending, will continue until you have completed all that the experiment requires. Your threshold is the average of these crossover points.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
On this tab, you can adjust the type of stimulus and the various parameters of the motion of the stimulus to see how this might affect your ability to detect differences in frequency. The settings include the following:
Standard Frequency: the frequency of the standard tone or how fast the sound cycles, in Hertz (Hz) or cycles per second.
Tone Duration: how long the tones in the experiment will play, in seconds.
Gain: the relative intensity of the sound (1.0 is full intensity and 0 is that the sound is off).
Time between Tones: the blank interval between when the first and second tones, in seconds.
Play: allows you to play the current version of the standard tone.
Reset: at the top of the settings page is a Reset button. Pressing this button restores the method settings to their default values.
On this tab, you can adjust how the method will work. The settings include the following:
Number of Levels of Frequency Difference: how many steps there are in the staircase (series).
Number of Staircases: how many staircases (series) will be presented (always an even number).
Minimum Value of Frequency Difference: what is the least frequency difference between the standard (lower frequency tone) and the target (higher frequency tone).
Maximum Value of Frequency Difference: what is the greatest frequency difference between the standard (lower frequency tone) and the target (higher frequency tone).
Reset: at the top of the settings page is a Reset button. Pressing this button restores the stimulus settings to their default values.
On the Experiment tab, press the space bar or the Start button on the screen to start the experiment. Two tones will be played. The first is the standard tone, and the second is the target tone. Click or press Yes (or press the Z key) if you hear that the second tone sounds higher in pitch and No (or press the / key) if you do not hear that the second tone has a higher pitch. When the experiment has been completed, you will be instructed that you can view your results.
You data will be presented on this tab where the trials will be on the x-axis and the intensity value of the stimulus will be displayed on the y -xis. To see your threshold, which is the average of the crossovers, click the button that says Show Threshold. To display the trial by trial data, click the Show Data button.
Change the settings below to alter the stimulus parameters in this experiment.