Re: Threshold of increasing/decreasing tones

[Wolfgang Ellermeier <we@xxxxxxxxxxxxxxxx>]

Dear Stefan Kerber,

while John Neuhoff's response points to true perceptual effects in 
SUPRATHRESHOLD rising and falling levels, you might also want to 
consider simple RESPONSE BIASES. Already in 19th century psychophysics, 
you find discussions of "habituation effects" and "anticipation effects" 
biasing threshold measurements like the one you are using. There is a 
risk that you will never know, in any given subject, what mix of these 
effects will occur, in some circumstances favouring your 'ascending', in 
others your 'descending' runs (as you seem to imply is the case with 
your data).

The standard methodological way out of this dilemma has been to use 
'unbiased', or 'criterion-free' forced-choice (adaptive) procedures, as 
described in Levitt (1971). Of course, they require short tone bursts, 
rather than the continuous tones used in your paradigm.

A discussion of the pros and cons of the 'classical' threshold 
procedures (like the method of limits that you are using) can be found 
in the methods chapter of our (German, sorry list!) textbook on hearing 
[Hellbr\"uck, J. & Ellermeier, W. (2004). // 
<http://www.hogrefe.de/buch/isbn/3-8017-1475-6.html>H\"oren. 
Physiologie, Psychologie - Pathologie. G\"ottingen: Hogrefe.] .

Hope, these hints are helpful,

Regards,

Wolfgang Ellermeier 


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___________________________________________________________
Wolfgang Ellermeier
e-mail: we@xxxxxxxxxxxx
http://www.soundquality.dk
http://www.acoustics.aau.dk
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Forskningsprofessor             Research Professor
Afdeling for Akustik            Departm. of Acoustics
Aalborg Universitet             Aalborg University
Fredrik Bajersvej 7 B5          Fredrik Bajersvej 7 B5
DK-9220 Aalborg Ø               DK-9220 Aalborg O
Danmark                         Denmark
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