Discussion about "place pitch" concept

["Dr. Uwe Baumann" <uwe.baumann@xxxxxxxxxxxxxxxxxxxxxxx>]

Dear Martin, Christian, Dick, Roy, and others -

The ongoing discussion about temporal pitch emerged the statement 

"There is no physiology of a "place pitch", and this concept should be given up." by Martin Braun, which was supported by several others.

I would like to point the discussion to electrical excitation of the spiral ganglion cells by means of a cochlear implant electrode array.
With direkt pulsatile stimulation of the auditory nerve, Zengs' (2002) as well as our own results (Baumann & Nobbe, submitted) do clearly show, that:

a) the upper limit for temporal pitch with pulsatile stimulation is 300 pulses per second

b) pure temporal pitch discrimination (without place cues) is astonishingly worse: depending on base rate an average rate change of 23% to 33% pulse rate is required to elicit a just noticeable difference in terms of pitch perception.

c) The absence of a difference in terms of repetition rate discrimination between apical and basal electrode locations indicates that a reduction of the base rate/place mismatch does not improve discrimination performance.

d) Concerning autocorelation based models of pitch perception:
"With electrical stimulation, identical temporal information can be provided to different channels by independently stimulating basal and apical electrodes. The summed autocorrelation function should be identical between basal and apical stimulation, predicting an independence of rate pitch on the place of stimulation. This prediction is clearly inconsistent with the observed joint dependence
of pitch perception on rate and place [by pulsatile electrical stimulation]." (Zeng, 2002)

There have been discussions about the reasons of the poor contribution of temporal information to pitch perception in electrical hearing. Poor neural survival  is one major argument. But even in case of a reduced number of fibers, the rate code will be transmitted more accurately in electrical hearing than by normal acoustical stimulation (Hartmann, 1984).

These and several other arguments will be discused in our alredy mentioned (presumably upcoming) paper.

The outlined observations are not able to counter the notion "There is no physiology of place pitch", but they clearly indicate that there is a place pitch in psychophysical electrical stimulation of the cochlea by means of intracochlear electrode arrays.

Uwe

Dr.-Ing. Uwe Baumann
Electrical Engineer/Medical Physicist/Audiologist
University of Munich
Dept. Otolaryngology/Audiology
Marchioninistr. 15
D-81377 München
Tel: ++49-89-7095-3878
Fax: ++49-89-7095-6869
email: uwe.baumann@med.uni-muenchen.de
www: http://ghn86x.hno.med.uni-muenchen.de/bau

References:

Baumann U, Nobbe A (2004) Pulse rate discrimination with deeply inserted electrodes. Hearing Research submitted

Hartmann R, Topp G, Klinke R (1984) Discharge patterns of cat primary auditory fibers with electrical stimulation of the cochlea. Hear. Res.13:47-62

Zeng, F.-G. (2002) Temporal pitch in electric hearing. Hear.Res. 174, 101-106.