Abstracts of research publications by Klaus A J Riederer

Society for Neuroscience 31st Annual Meeting , San Diego, CA, USA, 10.-15.11.2001.

Human Cortical represenation of 3-dimensional sounds: differences between azimuth and elevation

Nobuya Fujiki, Klaus A J Riederer(*), Veikko Jousmäki, Jyrki Mäkelä & Riitta Hari

Brain Research Unit, Low Temperature Laboratory

(*) Laboratory of Computational Engineering Helsinki University of Technology (HUT)
P.O. Box 2200 (* 9400), FIN-02015 HUT, Finland
Tel: +358 9 4510;
URL: http://www.hut.fi/

Brain mechanisms of directional hearing have been mainly studied in the subcortical auditory pathways of animals. However, several lesion studies indicate that also the auditory cortex is essential for sound localization. In human brain imaging studies, sounds are usually presented through headphones and the lateralization of sounds is created by interaural time and intensity differences (ITDs and IIDs). Although these stimuli can produce percepts of different sound locations in the horizontal plane, they can represent neither sound elevation nor back-front differences. We recorded cortical magnetic signals from eight subjects to 3-dimensional sounds, convolved with individual head-related transfer functions; in addition to ITDs and IIDs, these sounds also include monaural spectral cues. Responses of the auditory cortices were recorded to infrequent changes in azimuth and elevation in the anterior and in the right lateral space.

In the anterior space, the 90-200 ms response was 27-52 ms earlier (p = 0.001) and the 150-320 ms response 7-84% stronger (p = 0.03) to azimuth than elevation differences. The responses to azimuth changes were significantly earlier and stronger in the anterior than in the lateral space; the differences were larger in the right than the left hemisphere. These findings indicate that the human auditory cortex represents most extensively sound azimuth in the anterior space.

Supported by: the Academy of Finland, Sigrid Juselius Foundation, the Japan Society for the Promotion of Science and the Ministry of Education, Finland.