Figure 1.

Illustration of the experimental set-up and procedure

(A) Tactile stimulations (Haptic) were delivered by a texture simulator: the StimTac. The participants actively explored the surface of a touchpad delivering a simulated texture while their finger movement was recorded with an optical sensor. Auditory stimulations (Audio) were sonified movements generated by a sound synthesizer. Rough or Smooth sounds were produced. Audio-Haptic stimulations (Bimodal) were generated by synchronizing the StimTac and the sound synthesizer. In these conditions, the velocity of the participant’s finger was sent to the synthesizer to modulate the sounds in real time. A custom program implemented in the NI LabView environment was used to monitor tactile and auditory stimulations in synchronization with MRI acquisitions.

(B) Experimental procedure. The functional acquisitions consisted of 5 runs each including 4 blocks: Haptic (H), Audio (A), Bimodal (AH) and Rest blocks. The 3 stimulation conditions had two textural levels: Smooth (H_Smooth, A_Smooth, AH_Smooth) or Rough (H_Rough, A_Rough, AH_Rough). Each modality was always presented as a ‘block’ with 6 consecutive stimuli of the same modality (3x2 textures). Four blocks for each modality were presented in a pseudo-random way including also Rest blocks. In total, a run lasted 8 min.