This outline summarizes major points covered in lecture. It is not intended to replace your own lecture notes.
Detection Versus Discrimination
Absolute detection thresholds tell psychoacousticians what the limits of detection are for sound
parameters (e.g. frequency, amplitude and time).
Often we are interested in the sensitivity of a listener to changes in an acoustic parameter.
Discrimination procedures measure what a listener can respond to or just detect.
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.
We want testing procedures that provide a measure of listener sensitivity that does not change with
the Subject’s (S’s) response criterion.
Psychophysical Testing Procedures
Psychoacousticians employ different measurement (testing) procedures to quantify a Subject’s
(S’s) perceptual sensitivity.
Detection procedures measure absolute performance of S.
Discrimination procedures measure relative performance of S.
Scaling procedures allow S to quantify subjective magnitude of stimulus.
Matching procedures determine physical aspects of stimuli that Ss use to equate different stimuli.
Detection testing procedures measure absolute performance of Subject (S) such as Threshold of
Audibility or Absolute Limen (AL).
Discrimination testing procedures measure relative performance. Ss judge if stimuli are different
from each other; can use this to determine Just Noticeable Difference (JND) threshold or Difference
Limens (DL) threshold.
Scaling procedures ask S to quantify stimulus magnitude on a defined scale; Ss are given a “rule”
that is used to assign a number quantity to the perceptual magnitude of a stimulus.
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).
Most psychophysical experiments are designed to obtain a psychometric function from S.
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 of the range of total possible “YES” responses.
Thresholds of Audibility
In measuring or quantifying perceptual sensitivity to auditory signals, psychoacousticians adopt one
of two basic threshold testing procedures.
Detection Performance (Absolute)
o Detection Threshold or Absolute Limen (AL)
E.g. Audibility Thresholds: Minimum Audible Field (MAF) threshold in room at 1m using
method of constant stimuli.
o Threshold obtained using Method of Constant Stimuli
o Minimum Audible Field (MAF) thresholds are SPLs for pure tones measured in open space
(free field) with loudspeaker positioned at fixed distance from S (e.g. at 1 m).
o Minimum Audible Pressure (MAP) threshold at S’s tympanic membrane measured with
headphones that have been calibrated with a coupler device for airspace in external auditory
Discrimination Performance (Relative)
o “Ask” listener if stimuli are different.
o Can measure Just Noticeable Difference (JND) Threshold
E.g. Frequency discrimination
Beware of Response Bias
Experimenters assess the performance of subjects (Ss) on a variety of psychophysical tasks.
Experimenter is interested in determining the subject’s sensitivity to changes in the stimulus.
Psych 3A03 1 November 2012
Week 9 Dr. Paul A. Faure Experimenter is NOT interested in the subject’s ability to respond in the experiment (response
Thus, the experimenter wants a measure of response sensitivity that is bias free (very difficult).
Many sources of bias (e.g. listener motivation, testing conditions, test instructions & feedback,
Response bias assessed in method of constant stimuli procedure by inserting “blank” or “catch”
trials in testing sequence, and then looking for false alarm responses.
Theory of Signal Detection (TSD)
Theory of Signal Detection (TSD) is used to measure the ability of a