Audio-tactile integration of meaningful objects in the human brain

Andrea Polony, Institute of Medical Psychology (IMP), and Brain Imaging Center (BIC), Johann Wolfgang Goethe-University, Frankfurt am Main, Germany

Abstract
Functional imaging studies of audio-tactile (AT) processing revealed caudal auditory belt areas as the prime candidate region for AT integration (Foxe et al., 2002; Kayser et al., 2005; Murray et al., 2005; Schuermann et al., 2006). However, these studies employed rather low-level stimulus material. Here, we used fMRI to test for AT integration of meaningful natural objects (animals). While controlling for potential cue and motor confounds using a ‘no-stimulus’ baseline condition (M), we searched for regions that were activated by each of the unimodal conditions (i.e., A>M as well as T>M), and additionally responded more strongly to bimodal AT stimulation than to each of the unimodal conditions. Although tactile stimulation was restricted to the right hand, we were able to reveal a bilateral temporo-parietal region located between the secondary auditory and somatosensory cortices. Motivated by recent findings on audio-visual (AV) integration in potential homologue regions of the non-human primate (Kayser et al., 2007), we further tested this region for audio-visuo-tactile (AVT) integration. However, employing strict criteria for AVT integration we neither found the V>M nor the AVT>AT criteria to be fulfilled. We thus conclude that the integrative role of this bilateral temporo-parietal region might be specific to AT integration.

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