Fitting of brightness as a function of current amplitude in a visual prosthesis
A visual prosthesis must convey luminance information across a range of brightness levels to accurately represent a visual scene. Thus, the brightness of phosphenes produced by individual electrodes should scale appropriately with luminance, and the same luminance should produce equivalently bright phosphenes across the entire electrode array. Given that the function relating current to brightness varies across electrodes, it is necessary to develop a fitting procedure that will permit brightness to be equated across an entire array. A visual prosthesis that generates stimuli by performing a brightness fitting that normalizes brightness across electrodes is described.
1. A visual prosthesis, comprising:
an array of electrodes suitable to be placed in proximity to visual neural tissue;
a camera for receiving a visual scene; and
a control device coupling said camera to said array of electrodes including
a neural stimulator for applying a plurality of stimuli to visual neural tissue;
means for measuring brightness responses to said stimuli on a first one of said array of electrodes;
means for deriving a first formula comprising a stimulation curve estimating brightness levels not tested on said one electrode based upon said brightness responses to said stimuli on said first one of said array of electrodes;
means for measuring brightness responses to said stimuli on a second one of said array of electrodes;
means for deriving a second formula comprising a stimulation curve estimating brightness levels not tested on said second electrode based upon brightness response to said stimuli on said second one of said electrodes and said first formula;
and
means for generating stimuli by applying said first formula and said second formula to visual input from said camera.
2. The visual prosthesis according to claim 1 , wherein said means for measuring brightness responses is a means for measuring neural activity in the retina.
3. The visual prosthesis according to claim 1 , wherein said means for measuring brightness responses is a means for measuring neural activity in the visual cortex.
4. The visual prosthesis according to claim 1 , wherein said means for measuring brightness responses is a means for measuring a patient's reported responses.
5. The visual prosthesis according to claim 1 , wherein said means for measuring brightness responses is a means for measuring movement of the iris.
6. The visual prosthesis according to claim 1 , wherein said means for generating stimuli varies by applied current.
7. The visual prosthesis according to claim 1 , wherein said means for generating stimuli varies by applied voltage.
8. The visual prosthesis according to claim 1 , wherein said means for generating stimuli varies by applied frequency.
9. The visual prosthesis according to claim 1 , wherein said means for generating stimuli varies by applied pulse duration.