Re: multidimensional scaling of timbre

[Paul Iverson <p.iverson@xxxxxxxxx>]

I don't know of a paper on this topic, but here are some impressions.

It is clear that people change their attention to dimensions depending  
on the set. For example, if there are large pitch variations among the  
stimuli, listeners' ratings are dominated by that dimension,  whereas  
they attend more specifically to timbre dimensions if that pitch  
variation is removed. On the face of it, it thus seems very plausible  
that listeners can only attend to a small number of dimensions at a  
time. It is certainly the case that higher dimensions in MDS solutions  
become progressively less interpretable, which suggests that they may  
just be modeling noise.

That being said, it is hard to say whether this reveals an attentional  
limitation or is a measurement issue with rating scales and the MDS  
procedure. For example, I find that there is always much more  
unaccounted variance when I am using real recordings than when I am  
using a set (usually speech stimuli) that have been synthesized to  
vary on only a small number of dimensions. For example, a set that has  
been synthesized to be two dimensional will fit into a two-dimensional  
solution far better than a set of natural recordings will fit into a  
two-dimensional solution. I think that this indicates that listeners  
are indeed sensitive to higher dimensions in the natural stimuli; the  
unaccounted variance in such MDS experiments is not just noise.  
However, the relative contribution of those dimensions begins to be  
small enough to merge with the level of noise in the data, such that  
they can no longer be modeled very well by MDS. That is, there is  
usually enough gain to measure only a few of the most influential  
dimensions that drove the rating-scale judgements.

Best regards,

Paul

Paul Iverson, Ph.D.
UCL Division of Psychology & Language Sciences
Chandler House
2 Wakefield Street
London WC1N 1PF
UK

http://www.langsci.ucl.ac.uk/people/person.php?id=36


> ----------------------------------------------------------------------
>
> Date:    Sun, 19 Oct 2008 16:17:32 +0200
> From:    Christian Kaernbach <auditorylist@xxxxxxxxxxxx>
> Subject: multidimensional scaling of timbre
>
> Dear list,
>
> I seem to remember that one lesson from multidimensional scaling of
> timbres was that the type of dimensions found depends strongly on the
> selection of the stimuli. If my memory serves me right, the similarity
> data would alway yield two- to three-dimensional spaces, regardless of
> whether the stimuli were quite divers (all types of instruments of the
> classical orchestra) or from a narrow subgroup (say, all woodwinds).  
> In
> other words, people seem to be able to manage two to three  
> dimensions in
> their cognitive space representing the entirety of the stimuli of a
> certain experiment. Is that correct, and is there a reference  
> referring
> to this phenomenon?
>
> Thanks in advance,
> Chris
>
> --
> Christian Kaernbach
> Kiel University
> Germany
> www.kaernbach.de