Method of Limits

Topics: Sound, Arithmetic mean, Decibel Pages: 3 (918 words) Published: April 7, 2011
Lab 4: Methods of limits
Elizabeth Bryan
Florida State University

Lab 4: Method of limits.
Sound waves are created when an object vibrates. They have two main components: frequency (pitch; measured in Hertz (Hz)) and amplitude (loudness, intensity; measured in decibels (dB)). The method of limits is a psychophysical method in which a particular dimension of a stimulus, or the difference between two stimuli, is varied incrementally until the participant responds differently. The change in stimulus intensity is orderly and regular; so the changes may become predictable to the participant resulting in two types of bias, expectation or habituation. Expectations is when the participant expects the stimulus to change, and thus reports that it has changed, even if it hasn’t. We can tell if the expectation has occurred when the descending mean is greater than the ascending mean. Habituation occurs when the participant hesitates too long to switch the response, responding with a Y or N, even after detection of the stimulus has changed. We can tell this is habituation if the ascending mean is greater than the descending mean. We conducted two total trials at each frequency (i.e., 2 ascending trials and 2 descending trials) to get our information. The purpose of this lab is to determine the participant’s hearing curve using the method of limits. In addition, determining if habituation or expectation occurred is also a goal.

This experiment was conducted using a audiometer that tests hearing using ear position, noise, amplitude, and duration. We first turned the audiometer on, made sure both ears were on, turned the noise (amplitude) off and set the duration for 1/2 second. Then set the frequency (Hz) and the amplitude (db) Levels. The frequencies were pseudo-randomized at the following levels: 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, and 8000 Hz. The participant in this experiment was asked to put on headphones and tell when she could hear a sound...
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