| ISLE | Chapter 2
| Experiment: Magnitude Estimation: Tone Loudness
Magnitude Estimation is a psychophysical method in which participants judge and assign numerical estimates to the perceived strength of a stimulus. This technique was developed by S. S. Stevens in the 1950s (e.g., Stevens, 1956). Magnitude estimation usually works in the following way. A stimulus is presented, and the participant simply gives a number that indicates how intense she perceive that stimulus. In a common variation, an experimenter presents a standard stimulus, which is often called the modulus, and assigns it a particular value, say 20. Then the participant must judge subsequent stimuli and give them a numerical value comparing it to the standard stimulus or modulus. So if the participant thinks the new stimulus is twice as intense as the standard, it should be assigned a 40. If the next tone is just a bit less intense than the standard, it will be assigned a 15. If the tone is heard to be much less intense than the standard, it might receive a 5 on this hypothetical scale.
In this version of magnitude estimation, you will be judging the loudness of a tone.
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 effect the aftereffect. The settings include the following:
Frequency: the frequency of the 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.
Frequency Difference: the difference of the frequency between the modulus (the value given above) and the frequency of the tone you are judging, in Hz.
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 Gain: how many different levels of intensity of your stimulus.
Number of Repetitions: how many times each stimulus will be presented.
Use Modulus: controls if a comparison stimulus (the modulus) be presented.
Enter the
value for this standard stimulus. A value of 50 is the default.
Minimum Value of Gain: What is the least intense tone that will be played.
Maximum Value of Gain: What is the most intense
tone that will be played.
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.
Listen carefuly. If you use the modulus,
it will be the first tone played. The value of the modulus will be shown below
the fixation mark. Then the target stimulus will be presented. This stimulus, a tone,
will be played shortly after the modulus.
After the target tone has been played, a box will appear for you to type your judgment.
If
you have a keyboard, you can use the numbers to type your estimate of the stimulus. Back space
will remove the last
number typed and the delete key will clear the stimulus. Press the enter key when you are done. If you do not have a keyboard or wish to use your mouse,
you can use the number buttons after the Done button to enter the numbers. The B button is the back space and the
C button will act as the delete button. You can press the done button to go to the next trial.
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. On the x-axis will be the different levels of intensity of the stimulus. On the y-axis will be the average magitude estimation of that intensity. To display the data showing the average magnitude estimation for each stimulus level, click or tap the Show Data button.
Change the settings below to alter the stimulus parameters in this experiment.