Auditory Binaural Pathway Neural Auditory pathway Auditory Nerve

Auditory Binaural Pathway

Neural Auditory pathway • • Auditory Nerve Cochlear Nucleus Medial Superior Olive Lateral lemniscus Inferior Colliculus Medial geniculate nucleus • Primary auditory cortex

Schematic Representation of the Brainstem Auditory Pathway

Brainstem MRI & f. MRI Scans Axial Coronal Sagittal

Auditory Pathway and Brainstem Outline Overlapped on f. MRI Scans

Binaural Stimulation Axial cut (6/12) -SOC Coronal cut (6/11) - AC Coronal cut (2/11) - MGB 0. 025 0 Axial cut (2/12) - CN Axial cut (10/12) - LL

Auditory Lateralization Cues • Interaural Time delay – The sound reaches the closest ear before the other • Interaural Level delay – The sound at the closest ear is louder

LATERALIZATION Perception Stimulus R ILD 2 1 3 4 5 L 6 7 8 9 R ITD=ILD=0 L L

Normal Performance Histograms = number of times a subject reported perceiving a position when ITD or ILD presented

Abnormal Performance Side --Oriented 9 9 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 -1 1 - 10 1 -1 0 ITD(msec) 1 position Center-Oriented 0 ILD(d. B) 10 0 ITD(msec) 1 1 - 10 0 ILD(d. B) 1 0

Lesion Detection

Correlation between MRI and Lateralization Normal Lateralization MS 10 MS 20 MS 52 CVA 23

Correlation between MRI and Lateralization Center-Oriented Lateralization

Correlation between MRI and Lateralization Side-Oriented Lateralization

Correlation between MRI and Lateralization

Monaural & Binaural Activation in a Right Sagittal Section Left Ear Stimulation Right & Left Ears Stimulation Right Ear Stimulation

Monaural & Binaural Activation in a Left Sagittal Section Left ear stimulation Both ears stimulation Right ear stimulation

Find the minimum ITD/ILD • We will conduct an experiment to measure the minimum ILD/ITD. t. Right , LRight t. Left , LLeft

Superior Olive Complex

Coincidence Detection Cells • Coincidence detection (CD) is one of the common ways to describe the functionality of a single neural cell. • Correlation • There are several type of such cells: – Excitatory Inhibitory (EI) – Excitatory (EE) – Cumulative

Neural mechanisms – EE Type cells n Spikes when inputs coincide.

EE Formulation

Neural mechanisms – EI Type cells n Spikes with excitatory input unless inhibited.

EI Formulation

Complex Cells

EI Cells Signal Separation n Signal separation ability is considered as most important in tasks such as cocktail party, BMLD.

EE Cells spontaneous rate n The spontaneous rate of cells that results from external noise reduced at higher levels

ITD Mean Rate From Agmon-Snir et al. (1998), Nature 293, 268 -272 Model Predictions

ILD Mean Rate

JND(ITD) All Information: Rate & Timing Rate Only

Phase Delay in EE Cells Inputs

Prediction of JND(ITD) from EE Cell N Excitatory Inputs E E N=6 EE N Excitatory Inputs N=20 N=6 N=20

Prediction of JND(ILD) from EI Cell 1 Excitatory Inputs E E EI M=3 M Inhibitory Inputs M=3 • Rate Coding and All Information Coding provided similar results M=15