Subject: Re: Definition of masking From: Jont Allen <jba(at)RESEARCH.ATT.COM> Date: Fri, 2 Jul 1999 17:02:19 -0400"Richard J. Fabbri" wrote: > > Chris, > > >The problem then is that to call something "masking" we need to be sure > >of the underlying process. > ...Yes. > ... I have worked on masking along a new physiologic route for > several years and am convinced it is an interactive consequence > occuring DURING the interaction. > > >For example, we shouldn't call the increase in threshold for a tone > >following a masker "forward masking" unless we can be sure that > >the process is one of swamping rather than, say, adaptation. > ... Yes. > ... Masking is a "swamping" interaction and, as such, requires > all signal elements to be present during the same time period. Here is my take on all this: I do not like the term "swamping." This sounds like I am in a swamp;-). "Obscure" is the first term used, and a better term. The obscuring is caused by the stochastic representation of the signal. If it is not such noise that limits the detection, then it is not masking. Turning off the radio, or reducing the volume, is not masking, as it is not stochastic. An important question is: What is the physical mechanism of the masking noise. Is it external noise (i.e., due to roving the signal), or internal noise (i.e., neural noise). In a recent paper (JASA, Dec. 1997, pp 3628-3646), we argue that under many conditions the noise is internal, and due to neural noise. At least it is "Poisson like" since the variance of the signal is equal to the signal mean. In the case of signals like tones, that are not stochastic, the ONLY noise is internal noise. When working with wideband noise signals, it is less clear where the noise comes from. Is it due to the internal representation (yes, we say), or is it due to the stochastic nature of the stimulus? This would apply for the JND of wideband noise, for example (Miller, 1947) Finally, it does not require the masker to be present at the same time. If the noise is internal, and the variance is equal to the mean, then it depends on how large the internal signal is, and that will determine the masking, assuming a threshold at d'=1. If the internal signal decays instantly after the external signal is removed, then one might believe that the masker must be present at the same time. We believe we showed that the masking is due to "loudness noise," namely the internal representation noise of the signal. > ... An effect succeeding a stimulus (not during the stimulus) > reveals a different process and may, in fact, be an adaptation, > possibly a consequence of middle ear (AGC?) time constants: > I agree with this masking qualification. > > Regards, > Rich Comments? Jont B. Allen AT&T Labs-Research, Shannon Laboratory 180 Park Ave., Room E161, Florham Park NJ, 07932-0971 973/360-8545voice, x7111fax, http://www.research.att.com/info/jba -My favorite URL: www-history.mcs.st-and.ac.uk/history -Imagination is more important than knowledge. --Albert Einstein