Pitch and forward masking

["Brian C. J. Moore" <bcjm@xxxxxxxxxxxxx>]

Dear List members,

In response to the recent email from Chen-Gia Tsai, I wrote to him to ask:

>Why do you think that the pitch strength of a sound (a complex tone in this
>case) should influence its effectiveness as a forward masker of a sinusoid?

He replied:

"Thank you very much for your email. There are two assumptions in my
hypothesis.

First, the grouping rule of harmonicity is modified as that components at
nf0 are grouped only when the pitch sensation of f0 is robust. In the other
words, if the pitch strength of f0 is low, components at nf0 will not be
grouped despite harmonicity.
This assumption appears to be supported by my model of the perception of
roughness induced by subharmonics.

Second, well-grouped components tend to be segregated from other tones.
Effectiveness of masking is influenced by the grouping mechanism
integrating information across auditory channels.
This assumption appears to be supported by the effect of comodulation
masking release."

With regard to the first assumption, it should be noted that the harmonics
in the study of Gockel et al. were all unresolved.  Regardless of the
relative phases of the components, the maskers were heard as strongly fused
single sounds.

With regard to the second assumption, forward masking can be influenced by
across-channel mechanisms when there is a possibility of "confusion" of the
signal with the masker.  See, for example,

Moore, B. C. J., 1980. Detection cues in forward masking. In: van den
Brink, G., Bilson, F. A. (Eds.), Psychophysical, Physiological and
Behavioural Studies in Hearing, Delft University Press, Delft, pp. 222-229.

Moore, B. C. J., Glasberg, B. R., 1982. Contralateral and ipsilateral
cueing in forward masking. J. Acoust. Soc. Am. 71, 942-945.

However, this occurs mainly when the masker is a narrowband sound of the
same centre frequency as the sinusoidal signal.  "Confusion" effects do not
occur when the masker is a broadband sound and the signal is a sinsusoid,
as was the case in the study of Gockel et al.

Gockel, H., Moore, B. C. J., Patterson, R. D., 2003. Louder sounds can
produce less forward masking: Effects of component phase in complex tones.
J. Acoust. Soc. Am. 114, 978-990.

So, I don't think that Chen-Gia Tsai's alternative "explanation" of the
results of Gockel et al. can be correct.

Best wishes,

Brian




Brian C.J. Moore, Ph.D, FMedSci, FRS
Professor of Auditory Perception,
Department of Experimental Psychology,
University of Cambridge,
Downing Street,
Cambridge CB2 3EB,
England

tel. + 44 (0) 1223 333574
fax + 44 (0) 1223 333564
http://hearing.psychol.cam.ac.uk/