ASA 11 - Pulsation Threshold


Perception (e.g.,visual, auditory) is an interpretive process. If our view of one object is obscured by another, for example, our perception may be that of two intact objects even though this information is not present in the visual image. In general, our interpretive processes provide us with an accurate picture of the world; occasionally, they can be fooled (e.g., visual or auditory illusions).

Such interpretive processes can be demonstrated by alternating a sinusoidal signal with bursts of noise. Whether the signal is perceived as pulsating or continuous depends upon the relative intensities of the signal and noise.

In this demonstration, 125-ms bursts of a 2000-Hz tone alternate with 125-ms bursts of noise (1875-2125 Hz), as shown below. The noise level remains constant, while the tone level decreases in 15 steps of -l dB after each 4 tones.

The pulsation threshold is given by the level at which the 2000-Hz to sound continuous.


A.S.Bregman (1978), "Auditory streaming: competition among alternative organizations," Percept. Psychophys. 23, 391-98.

T.Houtgast (1972), "Psychophysical evidence for lateral inhibition in hearing," J. Acoust. Soc. Am. 51, 1885-94.

Time Delay


You will hear a 2000-Hz tone alternating with a band of noise centered around 2000 Hz. The tone intensity decreases one decibel after every four tone presentations. Notice when the tone begins to appear continuous.