(see AUDIO FILES for information on the *.wav files)
Huggins pitch (see Cramer and Huggins, 1958, reference below) is a faint pitch that can only be heard via stereo or binaural listening. The Figure describes how the stimulus is generated. The amplitudes at each ear are exactly the same. The phases at the two ears are also exactly the same, except in a narrow frequency range (in the demonstration either 400 to 440 Hz, 500 to 550 Hz, or 600 to 660 Hz) where the phases at one ear are advanced by 180 degrees relative to those at the other ear. This process produces a 180-degree interaural phase shift in the narrow frequency regions. A faint pitch is heard which mimics that one would hear if they only listen to the sound of the region of the interaural phase shift. That is, in the demonstration the dichotic Huggins pitch should sound about the same (although fainter) than that produced by narrow bands of noise with bandwidths of 400 to 440 Hz, 500 to 550 Hz, or 600 to 660 Hz.
The 
Huggins
Pitch is produced such that the three pitches are played in
succession (400 to 440 Hz first, 500 to 550 second, and 600 to
660 third), each for one second following a section of noise
without a dichotic pitch. That is, the sounds appear in this
order: noise, 400-440 Hz pitch, 500-550 Hz pitch, 600-660 Hz
pitch.
Listen carefully and you should hear a faint increase in pitch. You may have to listen several times. If you have trouble hearing the pitches (and it does take some listening practice for some people), try listening to the Narrow Band demo below. Also try listening for an image toward one ear or the other.
If you do hear the three pitches, listen again through only one headphone. You will no longer be able to hear the pitches. Try listening through the other headphone. Again, you will not hear the pitches. Thus, only binaural listening allows you to hear the pitches.
The three Narrow
Band noises are played in succession just like the Huggins
pitches were. Listening to these narrow band noises might help
you hear the Huggins pitches, if you had trouble hearing them.
Also if you did hear the Huggins pitches, they should sound a lot
like the narrow band noise pitches.
These narrow band noises were actually generated by subtracting the waveforms presented to the two ears. Since the waveforms are identical at each ear except in the narrow frequency region of the interaural phase shift, subtraction will cancel all frequency components except those in the narrow frequency region, which will then be added together since the phase difference between the two ears was 180 degrees. A type of subtraction model is one model proposed for explaining Huggins pitch (see Yost, 1991, reference below).
The fact that the interaural phase shift makes the Huggins pitch "pop out" from the noise background suggests that spatial separation of sounds is an aid for segregating one sound source from a background of competing sound sources. That is, the narrow band of noise is at one spatial location due to the 180 degree interaural phase shift and the rest of the noise is at another spatial location, making it easier to hear the difference in the two types of waveforms.
Suggested References
Cramer, E. M. and Huggins, W. H., Creation of Pitch through Binaural Interaction, Journal of the Acoustical Society of America 30, 412-417, 1958
Yost, William A., Harder, P. J., and Dye, R. H., Complex Spectral Patterns with Interaural Differences: Dichotic Pitch and the 'Central Spectrum,' in Auditory Processing of Complex Sounds, (edited by W. A. Yost and C. S. Watson), Lawrence Erlbaum, Inc., Publishers, 1987
Yost, William A., Thresholds for Segregating a Narrow Band of Broad Band Noise, Journal of the Acoustical Society of America 89, 834-842, 1991
