Re: 40 Hz RIP (Neil Todd )

Subject: Re: 40 Hz RIP
From:    Neil Todd  <todd(at)HERA.PSY.MAN.AC.UK>
Date:    Tue, 27 May 1997 21:40:16 +0100

Dear DeLiang > I meant how many experimentalists have looked for oscillations in the > auditory system (not the literature). Galambos, R. Makeig S, Talmachoff PJ (1981) A 40 Hz auditory potential recorded from the human scalp. Proc. Natl. Acad. Sci. USA 78: 2643-47. Basar, E. (1988) EEG - dynamics and evoked potentials in sensory and cognitive processes in the brain. In Dynamics of sensory and cognitive processing by the Brain (E Basar ed). Springer-Verlag Sheer, DE (1989) Sensory and cognitive 40 Hz event-related potentials. In Brain Dynamics (Ed E Basar). Springer: Berlin. Pantev et al (1991) Human auditory evoked gamma-band magnetic fields. Proc. Natl. Acad. Sci. 88: 8996-9000. Pantev et al (1994) Oscillatory Event-Related Brain Dynamics. New-York: Plenum. > The vision community is a better place to voice your complaints, Now hang on just a minute DeLiang. You have made some grand claims concerning the application of the "oscillatory framework" to both visual and auditory processing. Also, as you will admit, apart from the references I have given above, the experimental literature you have been using to support your auditory models is *visual*. It is therefore perfectly legitimate for us to question the nature of that visual evidence. We have some very good vision people here in Manchester with whom I am in regular contact. If I may remind you, on May 20th you wrote: > Al writes: > > Since one table is red, the firing of RED and TABLE must be synchronized. > > Since the other table is blue, BLUE and TABLE must also be synchronized. > > Following the argument to completion implies that all four concepts must > > be synchronized. What we need is two separate instantiations of RED, one > > bound to TABLE, the other bound to BALL. > This isn't really a problem for the oscillatory framework. The > idea is the following: to have an oscillator assembly > corresponding to > TABLE oscillate with double frequency so that this assembly > synchronizes with > both the BLUE assembly and the RED assembly. At the same time > the synchronized > assembly for BLUE TABLE and that for RED TABLE are > desynchronized. > The above idea was used in an early paper on oscillatory > associative memory > (Wang, Buhmann, and von der Malsburg, 1990, refs. below) to handle the > overlap problem, essentially the same as the above problem. > But the oscillator > model used there proves to be too clumpsy. A recent model by > Brown and Wang > (1996) explicitly addressed the problem of "duplex > perception" in audition > using the same idea. But the Brown/Wang model is based on > relaxation > oscillator networks, which have an elegant theory and > computational properties > behind (see below). It is clear that the in the first scheme you envisaged the frequency of the oscillators had only an arbitrary relationship to the objects or features they were binding, i.e. there is nothing double about the relationship between TABLE and BALL. In the second case, as I said, Guy advocated a chaotic oscillator which has only a remote relationship if any (see previous message, but see also forthcoming message from Martin Cooke). It is certainly not the case that I have a problem with "a specific point in a specific paper". I have a fundamental problem with a major aspect of the architecture of the "oscillatory framework" which is to do with the arbitraryness of the relationship between the oscillator activity and the objects or features they bind. In other words whether it is itself a signal or whether it is a sign (to use semiotic jargon). You are right that there is no point repeating arguments on the list, and I am sure that most list readers will have become bored by now, but let me try once more to make clear what my problem is. We are agreed that the information for binding is in the commonality of temporal structure of RF inputs. Now, in the auditory case the simplest way to measure that commonality is to keep a copy or memory of each "frame" of the auditory spectrum over a certain time-window, say 1 second, and compute a cross-correlation matrix over "channels" in the memory. This scheme involves no oscillations whatsoever, but it does require some "delay lines" in order to keep a memory. An alternative is to first transform the input into the fourier domain, i.e. sample the power spectrum, and then compute the correlation between the power spectra for each channel. The advantage of the second scheme is that it does away with the need for "delay lines" and the overwhelming evidence is that the cortex, especially visual cortex, does indeed represent its inputs by sampling its power spectrum. In order to sample the power spectrum we do require a set of filters which do have a damped oscillatory impulse response, but the frequency of the filter response is directly related to the signal that is driving it, i.e. it is itself a signal. Any further oscillatory computation is entirely redundent. I rest my case. Cheers Neil

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