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Threshold Detection.docx

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Paul Faure

November 12 , 2013 Psych 3A03: Audition Threshold Detection Auditory Perception and Psychophysics - Now that we understand the fundamentals of the hearing, we will next focus on the perception of simple and complex sounds during audition - We have examined how sound frequency, amplitude, and starting phase (time) and received and processed by the auditory system, but now we want to examine our perceptual sensitivity to these same physical parameters - Psychophysics is the branch of science that examines the relationship between the perceptual and physical aspects of a stimulus - Auditory stimulus = psychoacoustics Detection versus Discrimination - Absolute detection thresholds tell psychoacousticians what the limits of detection are for sound parameters (e.g. frequency, amplitude and time) - Often researchers are interested in the sensitivity of a listener to changes in an acoustic parameter - In these cases discrimination procedures are employed to measure what a listener can respond to or just detect - Sensitivity = discrimination - S.S> Stevens correctly pointed out that psychophysicists measure what a listener does respond to, and often, this measure corresponds to what a listener can respond to, but not necessarily - Want testing procedures where measure of sensitivity does nto change with subject’s response criterion - Absolute vs. relative Psychophysical Testing Procedures - Psychoacousticians employ different measurement or testing procedures to quantify a Subject’s (S’s) perceptual sensitivity 1. Detection procedures measure absolute performance of S. methods vary but include: a. Method of constant stimuli b. Method of limits c. Method of adjustment d. Method of adaptive testing e. Signal detection theory 2. Discrimination procedures measure relative performance 3. Scaling procedures allow S to quantify subjective magnitude of stimulus 4. Matching procedures determine the physical aspects of stimuli that Ss use to equate different stimuli Psychophysical Testing 1. Detection testing procedures measure absolute performance of subject (S) such as threshold of audibility or absolute limen (AL) 2. Discrimination testing procedures measure relative performance. Ss judge if stimuli are different from each other to determine the just noticeable difference (JND) threshold or difference limens (DL) threshold 3. Scaling procedures ask S to quantify stimulus. The Ss are given a rule that is used to assign a number quantity to the perceptual magnitude of a stimulus 4. Matching procedures ask Ss to equate different stimuli by adjusting a physical parameter of one stimulus until it appears perceptually equal to another stimulus (e.g. equal loudness matching) The Psychometric Function - Sigmoid function - X-axis: magnitude of stimulus intensity - Y-axis: percent of stimuli detected from 0-100% - Most psychophysical experiments are designed to obtain a psychometric function from S – shows saturation at both ends, change in a non-linear manner - Psychometric function relates measure of S performance to physical value of stimulus - Estimate of a S’s threshold is obtained directly from the psychometric curve - Threshold is often chosen to be the midpoint in the range of total possible YES responses - E.g. threshold = 50% detection Thresholds of Audibility - In measuring or quantifying perceptual sensitivity to auditory signals, pshycoacousticians adopt one of two basic threshold testing procedures 1. Detection performance (absolute)  Detection threshold or absolute Limen (AL)  E.g. audibility thresholds, minimum audible field (MAF) threshold in room @ 1m using method of constant stimuli  Thresholds obtained using the method of constant stimuli  Showing the proportion o
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