Page 1 |
Save page Remove page | Previous | 1 of 176 | Next |
|
small (250x250 max)
medium (500x500 max)
large ( > 500x500)
Full Resolution
All (PDF)
|
This page
All
Subset |
VIEWING THE PICTURE WE PAINT
by
Matthew R Behrend
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(ELECTRICAL ENGINEERING)
May 2009
Copyright 2009 Matthew R Behrend
Object Description
| Title | Viewing the picture we paint |
| Author | Behrend, Matthew R. |
| Author email | behrend@usc.edu; behrend04@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Electrical Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2009-03-16 |
| Date submitted | 2009 |
| Restricted until | Unrestricted |
| Date published | 2009-04-22 |
| Advisor (committee chair) | Weiland, James D. |
| Advisor (committee member) |
Chow, Robert H. Gundersen, Martin A. Nayak, Krishna |
| Abstract | The aim of this study is to provide guidelines for the design of a retinal prosthesis with specific emphasis on spatial resolution. Optical recordings from retinal ganglion cells (RGCs) using novel methods provide the first clear picture of how the retina sees electrical stimuli. Analysis of the spatial properties of the response show that the site of action potential initiation is not in the soma, but in the initial segment of the axon, ~ 40 um from the soma. Furthermore, 60-us pulses directly stimulate RGCs, while longer pulses target inner retinal neurons. Short pulse widths have a more focal response area than long pulses. The smallest response area was about 100 um, even for electrodes as small as 30 um.; Separation of the electrode array from the retina by a saline gel increases the area of the response and raises stimulation threshold. Spacers with thickness less than 25% of the electrode diameter have little effect on the response size. Therefore, attachment of the array in vivo should have a gap less than 25% of the electrode diameter in order to preserve resolution.; Axonal stimulation remains a problem that threatens to severely limit the perception of pattern stimulation. Recordings at 400−us and 1000-us pulse widths from distant peripheral somata indicate that axons are stimulated at roughly 160% of the threshold for local RGCs, but 60-us pulses avoid axons to at least 200% of the local RGC threshold. Data suggest a means to selectively stimulate RGCs proximal to the electrode at short pulse widths. Bipolar configurations, directing electric field lines transverse to axon bundles, avoided stimulation of those bundles, but could not avoid axons that pass over the cathodic electrode, except for the smallest (10-um) electrodes. Pulse width appears to be the best means of control at the present time. The optimal array configurations are either a grid of electrodes spaced by 100 um, or a conformal array of 10-um bipolar pairs oriented with field lines transverse to the axon bundles. We can expect a resolution of 0.4 degrees of visual field corresponding to Snellen acuity of 20/480. |
| Keyword | retinal prosthesis; retina; artificial vision; retinal implant; electrical stimulation; neural stimulation; calcium imaging |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m2103 |
| Rights | Behrend, Matthew R. |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Behrend-2755 |
| Archival file | uscthesesreloadpub_Volume51/etd-Behrend-2755.pdf |
Description
| Title | Page 1 |
| Full text | VIEWING THE PICTURE WE PAINT by Matthew R Behrend A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (ELECTRICAL ENGINEERING) May 2009 Copyright 2009 Matthew R Behrend |
Comments
Post a Comment for Page 1
