A Comprehensive Three-dimensional Cortical Map of Vowel Space

摘要

Mammalian cortex is known to contain various kinds of spatialnencoding schemes for sensory information including retinotopic,nsomatosensory, and tonotopic maps. Tonotopic maps are especiallyninteresting for human speech sound processing becausenthey encode linguistically salient acoustic properties. In this study,nwe mapped the entire vowel space of a language (Turkish) ontoncortical locations by using the magnetic N1 (M100), an auditoryevokedncomponent that peaks approximately 100msec after auditorynstimulus onset. We found that dipole locations could benstructured into two distinct maps, one for vowels produced withnthe tongue positioned toward the front of the mouth (frontnvowels) and one for vowels produced in the back of the mouthn(back vowels). Furthermore, we found spatial gradients in lateral–nmedial, anterior–posterior, and inferior–superior dimensionsnthat encoded the phonetic, categorical distinctions between allnthe vowels of Turkish. Statisticalmodel comparisons of the dipolenlocations suggest that the spatial encoding scheme is not entirelynbased on acoustic bottom–up information but crucially involvesnfeatural–phonetic top–down modulation. Thus, multiple areasnof excitation along the unidimensional basilar membranenare mapped into higher dimensional representations in auditoryncortex.