עבוד אותות במערכת החושים סמסטר א' תשס"ז Cochlear Implant Binaural Hearing

Cochlear Implant

1. Sound Processor captures sound from the environment processes sound into digital information transmits to the implant over a transmitting antenna, or headpiece, held in place by magnets in both the headpiece and implant 2. Implant converts digital information into electrical signals sends signals down tiny wires to the electrode array in the inner ear delivers electrical signals through tiny contacts, or electrodes, to the hearing nerve the hearing nerve carries the sound information to the brain, where it is heard 3. Electrode Array

Localization = judgment of the direction and distance of a sound source Lateralization = the apparent location of the sound source within the head when headphones are used

Binaural Hearing: Interaural Differences We will conduct an experiment to measure the minimum ILD/ITD. t Left, L Left t Right, L Right

Masking Level Difference MLD=0 dB MLD=15 dB MLD=0 dB MLD=9dB

The Pina

Head Related Transfer Function

“”Cone of confusion בתוך הקונוס התלת ממדי ישנם צרופים שונים של מקומות שלהם יש אותו ITD ואותו ILD היוצרים אזור של קושי בהחלטה של מיקום הקול. תנועות הראש משנות את מיקום הקונוס ומקטינות את אזור חוסר הוודאות

Minimal Audible Angle - MAA מהו ההפרש הקטן ביותר בשינוי מיקום הקול המאפשר הבחנה בשינוי זה ? היכולת שלנו להבחין בהפרש במיקום מקור הקול היא טובה ביותר כשהקול מגיע מלפנים בחזית הראש. יכולת זו הולכת ופוחתת כשמקור הקול נמצא בצדי הראש או מאחור. שינויים קטנים בכיוון הקול מלפנים יוצרים הבדלים גדולים ב - ITD.

LATERALIZATION Perception Stimulus R L R R L L ILD ITD ITD=ILD=0

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

Center-OrientedSide --Oriented position ITD(msec) ILD(dB) Abnormal Performance

Patients’ Performance

Auditory Pathway in the Human Brain

Neural Response to Interaural Differences

Lesion Detection on MRI Scans

Brainstem MRI Scans AxialCoronal Sagittal

Auditory Pathway in the Human Brain

Schematic Representation of the Brainstem Auditory Pathway

Auditory Pathway and Brainstem Outline Overlapped on fMRI Scans

Lesion Detection

Overlap of Auditory Pathway on MRI Scans

Correlation between MRI and Lateralization Normal Lateralization MS10 MS20 MS50 MS52 CVA23

Correlation between MRI and Lateralization Side-Oriented Lateralization

Correlation between MRI and Lateralization Center-Oriented Lateralization

Correlation between MRI and Lateralization

Experimental Summary and Conclusions Two types of abnormal lateralization performance were found : center-oriented and side-oriented. Both types of abnormalities were found in patients with either MS or Stroke Center-oriented lateralization is correlated with TB/SOC lesions Side-oriented lateralization is correlated with LL/IC lesions

fMRI Study with Binaural Stimulation Coronal cut (2/11) - MGBAxial cut (6/12) -SOC Axial cut (10/12) - LL Axial cut (2/12) - CN Coronal cut (6/11) - AC

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

Interaural Discrimination A model that correctly estimates the human’s ability to distinguish between azimuth of two close identical tone signals. t Left, L Left t Right, L Right ITD = t Right – t Left [Sec] ILD = L Right – L Left [dB] Min(ITD)=? ~20µSec Min(ILD)=? ~1dB

Experimental results Time JND [µSec]Level JND [dB]

Simulation results N =32N =2 Time JND [µSec]Level JND [dB] Simulation Mean of Experimental results