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Re: Sound localization standard model question and confusion

Dear Piotr

Thank you for the comment and the references (I was however, already familiar with them).
For me, the problem on the statistical anaylsis is simple:  what null hypotheses are being rejected by the result's statistical significance.
To me, the two null hypotheses as formulated in the analysis are: 1) the DCN has no effect on sound localization; and 2) the DCN's effect on sound localization is equal in both azimuth and elevation.  Both of these null hypotheses can be rejected (no surprise here).
The difficulty here is that the null hypotheses do not match to the actual desired hypothesis; the desired hypothesis is not that the DCN has some effect on localization, but rather that the DCN is in the critical path for elevation localization.  To match that actual desired hypothesis, the null hypothesis would then be formulated as something like: there is SOME elevation localization if the DCN output is disabled. 

OK, determining the statistical level of "SOME elevation localization" may be problematic, except in this case for the (-30, 0, +30) elevations.  The (for me, the correctly formulated) null hypothesis cannot reasonably be rejected -- there is still a lot of elevation localization occurring.   [Even for the other cat, this still holds.]

Is this an incorrect analysis? 

If my analysis is correct, then the experiment still has an extremely important result; it's conclusion is just the opposite of what has been interpreted: Localization based on spectral cues is processed someplace else other than the DCN.  For higher elevations the DCN may play a role. 

Best regards,

On 10/7/2011 11:50 AM, Piotr Majdak wrote:
Dear Mark,

When I look only at a single spatial position in your document, I agree, the statistical evidence is also not obvious to me. But when you average over all the tested positions, the statistical variance would decrease and the decrease in the elevation slopes (response vs. target) after the lesion would be more prominent. Looking at the statistical results in Table I of May (2000) - it seems like the average effects (column EL error) are significant.

BTW, the data in your document show the results for the cat having less effect (p < 0.05). The other cat showed even more statistical significance (p < 0.01).

I think that the common assumption is that DCN is an important stage in the localization process but also other stages are also involved. The DCN type IV cells have been shown to be tuned to spectral notches also by others [1, 2]. The type IV cells project to the inferior colliculus (ICC), where further neural basis for sound localization has been found [3]. The ICC projects further (but not only) to the superior colliculus (SC), where a systematic map of auditory space could be confirmed in birds (in their SC's equivalent, optic tectum) but the situation seems to be more complicated for mammals [4]. If you'd like to read more, I'd like to suggest you this excellent review: Grothe, B., Pecka, M., and McAlpine, D. (2010). "Mechanisms of sound localization in mammals," Physiol Rev 90, 983-1012. 

[1] Imig, T. J., Bibikov, N. G., Poirier, P., and Samson, F. K. (2000). "Directionality derived from pinna-cue spectral notches in cat dorsal cochlear nucleus," J Neurophysiol 83, 907-925.
[2] Hancock, K. E., and Voigt, H. F. (1999). "Wideband inhibition of dorsal cochlear nucleus type IV units in cat: a computational model," Ann Biomed Eng 27, 73-87.
[3] Davis, K. A., Ramachandran, R., and May, B. J. (2003). "Auditory processing of spectral cues for sound localization in the inferior colliculus," J Assoc Res Otolaryngol 4, 148-163.
[4] King, A. J. (2004). "The superior colliculus," Curr Biol 14, R335-8.

Best regards,

Piotr Majdak

Piotr Majdak
Psychoakustik und Experimentelle Audiologie
Institut für Schallforschung
Österreichische Akademie der Wissenschaften
Wohllebengasse 12-14, 1040 Wien
Tel.: +43 1 51581-2511
Fax: +43 1 51581-2530