The electrophysiological net response ('F-complex') to spatial fusion of speech elements forming an auditory object.
OBJECTIVE
The purpose of this study was to define and analyze the brain activity associated with fusion of speech elements to form an auditory object and to study the effects of presenting the elements at different spatial locations (duplex stimulus).


METHODS
Stimuli were formant transitions (presented to the front, left or right of the subject) and base (presented to the front), that fused to result in V-C-V sequences /aga/ and /ada/. Ten right-handed, adult, native Hebrew speakers discriminated each fused stimulus, and the brain potentials associated with performance of the task were recorded from 21 electrodes. The net-fusion response, the 'F(fusion)-complex', was extracted by subtracting the sum of potentials to the base and formant transitions from the potentials to the fused sound. Low resolution electromagnetic tomography analysis (LORETA) was performed to assess the timing and brain location of the fusion process.


RESULTS
The 'F-complex', comprising of the difference N(1), P(2), N(2b) (FN(1), FP(2), FN(2b)) components could be identified for each of the stimuli and reflected a process indicating inhibition, occlusion or both, with right ear advantage in fusion. LORETA analyses indicate sequential processing of speech fusion in the temporal lobes, beginning with right prominence in FN(1) and FP(2) shifting to a more symmetrical pattern in FN(2).


CONCLUSIONS
The electrophysiological correlates of speech fusion highlight the uniqueness of speech perception and the brain areas involved in its analysis.
Laufer
Ilan
I
Evoked Potentials Laboratory, Gutwirth Building, Technion - Israel Institute of Technology, Haifa 32000, Israel.
Pratt
Hillel
H
D000161:Acoustic Stimulation; D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000502:physiology*; D004594:Electrophysiology; D005072:Evoked Potentials, Auditory; D006801:Humans; D011930:Reaction Time / Q000502:physiology; D013017:Sound Localization / Q000502:physiology*; D013067:Speech Perception / Q000502:physiology*