FREQUENCY AND PERIODICITY ARE REPRESENTED IN ORTHOGONAL MAPS IN THE HUMAN AUDITORY-CORTEX - EVIDENCE FROM MAGNETOENCEPHALOGRAPHY

Timbre and pitch are two independent perceptual qualities of sounds cl osely related to the spectral envelope and to the fundamental frequenc y of periodic temporal envelope fluctuations, respectively. To a first approximation, the spectral and temporal tuning properties of neurons in the auditory midbrain of various animals are independent, with lay outs of these tuning properties in approximately orthogonal tonotopic and periodotopic maps. For the first time we demonstrate by means of m agnetoencephalography a periodotopic organization of the human auditor y cortex and analyse its spatial relationship to the tonotopic organiz ation by using a range of stimuli with different temporal envelope flu ctuations and spectra and a magnetometer providing high spatial resolu tion. We demonstrate an orthogonal arrangement of tonotopic and period otopic gradients. Our results are in line with the organization of suc h maps in animals and closely match the perceptual orthogonality of ti mbre and pitch in humans.