Acoustic Stimulus Discrimination

The program apcis a simple paired comparison control program for acoustic signals. It presents pairs of acoustic signals and collects binary responses. Adaptive procedures are possible.

Program Features

Sound Signals

There are two signals: the standard and the comparison signal. The subject's task is to select one of the two according to the instructions given. Each of the two signals has its own parameters for frequency, sound intensity and wave type. The sound signal attack and release rate currently is common to both signals. Note that control of intensity, wave type, attack and release rate requires an AdLib compatible sound board to be available. Sound boards are detected automatically.

Response Simulation

The program allows response simulation by giving the command line option -S. In this case responses are simulated according to a logistic psychometric function with parameters pse and jnd.

Program Parameters

compfrequency , stdfrequency (float)
Frequency of comparison and standard signal.

comploudness , stdloudness (float)
Intensity of comparison and standard signal. Intensity is given as a ratio of the maximum intensity. Possible values are between 0.0 and 1.0. The default intensity is 1.0. The actual loudness value strongly depends on the type of sound device used.

compwave , stdwave (int)
Wave type of comparison and standard signal. This parameter is not used currently. The wave type depends on the sound device. On the PC speaker the wave type is similar to a rectangular wave, on the AdLib sound device it is an approximation to a sinusoid.

flags (string)
These are the possible flags:

E
Echo responses on the screen.

R
Randomize sequence of standard and comparison signal.

gaptime (int)
Time gap between successive standard and comparison signal.

soundattack , sounddecay , soundrelease , soundsustain (int)
Sound attack, decay and release rate and sound sustain level. Used only with the AdLib device. Values range between 0 and 15.

stdfirst (int)
True if the standard is presented first. This parameter is set by the program if the flag R is set.

jnd , pse (float)
Parameters of a logistic psychometric function for response simulation.

Example Experiments

Psychometric functions for pitch discrimination: Method of constant stimuli

A standard and a comparison tone are presented. The task is to tell whether the second tone sounds higher than the first one. Presentation is controlled by the method of constant stimuli.


Parameter file pmfk.x from directory \pxl\app\apc

Psychometric functions for pitch discrimination: Adaptive procedures

A standard and a comparison tone are presented. The task is to tell whether the second tone sounds higher than the first one. Stimuli are adjusted by an adaptive procedure.


Parameter file pmfa.x from directory \pxl\app\apc


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Author: Hans Irtel

irtel@psychologie.uni-mannheim.de