Hybrid fitting for a visual prosthesis
The present invention is an improved fitting and training system for a visual prosthesis. Fitting a visual prosthesis through automated means is challenging and fitting a visual prosthesis manually is tedious for clinician and patent, and provides great opportunity for error. A hybrid of computer controlled and manual fitting provides effective, efficient and controlled fitting process. The process includes testing a group of electrodes in random order by providing a prompt followed by stimulation and the patient responding if they saw a percept. After each set, a maximum likelihood algorithm is used to determine the next stimulation level, or if further stimulation is needed for each electrode.
1. A method of brightness fitting for a visual prosthesis comprising:
a. providing an external video processor and an implantable visual neural stimulator including an array of electrodes suitable to contact visual neural tissue;
b. testing the implantable visual neural stimulator to verify function and matching to the external video processor;
c. activating a prompt;
d. activating signals at varying levels on a selected electrode within a subset of electrodes in the array of electrodes;
e. receiving a response from a subject indicating a visual perception;
f. recording the level that elicited the response indicating the visual perception;
g. repeating the steps c through f for each electrode in the subset;
h. determining if a predetermined minimum number of electrodes in the subset elicited responses indicating visual perceptions;
i. if the predetermined minimum number of electrodes did not elicit responses indicating the visual perceptions, activating the subset of electrodes in the array of electrodes simultaneously as a group at varying levels;
j. receiving a subset response from a subject indicating a subset visual perception; and
k. recording the level that elicited the subset response indicating the subset visual perception from stimulating the subset of electrodes.
2. The method according to claim 1 , wherein the subset of electrodes includes four electrodes.
3. The method according to claim 1 , wherein the step of activating a signal includes activating no signal at a pseudorandom interval.
4. The method according to claim 1 , further comprising generating a video configuration file from results of the steps of recording responses indicating visual perception.
5. The method according to claim 1 , further comprising after each response applying a predetermined computer algorithm to determine a next activation level for each selected electrode.
6. The method according to claim 5 , wherein the predetermined algorithm predicts a confidence of a correct answer based upon a consistency of previous answers.
7. The method according to claim 5 , wherein the predetermined algorithm is a maximum likelihood algorithm.
8. The method according to claim 6 , wherein the predetermined algorithm is according to the equation
L
i
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q
=
1
m
(
p
q
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i
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n
yes
,
q
·
(
1
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p
q
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n
no
,
q
Where:
L i is the likelihood that the threshold value is at level i
P q,i is the probability, according to the Psychometric Function, that the patient will perceive a stimulation at level q given that the threshold is at level i
n yes, q is the number of Yes responses in all previous presentations (trials) at level q
n no, q is the number of No responses in all previous presentations (trials) at level q
m is the number of levels in the range-the highest level.