| ISLE | Chapter 2
| Experiment: Method of Adjustment: Frequency Discrimination
The method of adjustment means just that. The observer controls the level of the stimulus and adjusts it to be at the perceptual threshold. The participant does so by increasing or decreasing the level of the stimulus until it feels like it is just at the detectable level. This is an intuitive measure for most participants because it mirrors many normal activities like adjusting the volume control on a radio or a dimmer switch on a light. In a light threshold study, the method of adjustment would ask the observer to adjust the light source to be the dimmest light that person can just detect. The advantage of this technique is that it can quickly yield a threshold for each participant, but a disadvantage is that it leads to great variance from one participant to the next and between successive trials for each participant.
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 Trials in the Experiment: how many times you will make your adjustment.
Range of Variation of Relative Dot Luminance: over what range will the starting value of the stimulus
change. The range is a percentage of the total range of values the stimulus can have.
Minimum Value of Frequency Difference: what is the least intense dot that can be displayed.
Maximum Value of Frequency Difference: what is the most intense dot that can be displayed.
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.
As tones play, a slider will appear below the stimulus area. Use the slider to increase
or decrease the frequency difference between the two tones.
Your task is to adjust the frequency difference so that you just hear that the second
tone has a higher pitch. As you adjust the slider, the tones will replay with the new frequency difference.
If you wish to rehear the pair of tones, press the Play Stimuli button in the middle of the screen.
When you have accomplished this goal, click the Done button to the right of the slider to proceed to the next trial.
You can also use the arrow keys to adjust the slider. Up and right arrow keys will increase the frequency difference and
down and left arrow keys will decrease the frequency difference. The enter key will act like the Done button.
When you have finished all of your trials, you will be instructed that you can view your results.
Your data will be presented on this tab. The trials are on the x-axis. On the y-axis will be the value of your dependent measure that you set when you pressed the Match button on that trial. To see your threshold, click the button that says Show Threshold. To display the data for all of the trials, click the Show Data button.
Change the settings below to alter the stimulus parameters in this experiment.