Fitting of brightness as a function of current amplitude in a visual prosthesis
To accurately represent a visual scene a visual prosthesis must convey luminance information across a range of brightness levels. To do this, the brightness of phosphenes produced by an individual electrode 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. The current invention describes a method of performing a brightness fitting that normalizes brightness across electrodes. The method determines a set of parameters that are stored in the subjects Video Configuration File—the look-up table that converts the video camera input to stimulation profiles for each electrode. One electrode would be specified as the standard. Brightness rating would be carried out on that electrode so “rating” as a function of current amplitude was known for that electrode.
1. A method of fitting a visual prosthesis, comprising:
applying a plurality of stimuli via a first selected electrode to visual neural tissue;
measuring brightness responses to said stimuli;
deriving a formula based upon said brightness responses;
applying a stimuli via a second selected electrode;
measuring a brightness response to said stimulus applied to said second electrode;
deriving a constant based on brightness matching measurement of said reference stimulus on said first selected electrode and said stimulus on said second selected electrode; and
generating further stimuli on said second electrode by applying said formula offset by said constant to visual input.
2. The method according to claim 1 , wherein said stimuli vary according to applied current.
3. The method according to claim 1 , wherein said stimuli vary according to applied voltage.
4. The method according to claim 1 , wherein said stimuli vary according to applied frequency.
5. The method according to claim 1 , wherein said stimuli vary according to applied pulse width.
6. The method according to claim 1 , wherein said brightness responses are perceptions of brightness reported by a user.
7. The method according to claim 1 , wherein said responses are neural responses recorded from the visual neural tissue of the user.
8. The method according to claim 1 , wherein said responses are recorded physiological changes in the iris of a user.
9. The method according to claim 1 , wherein said responses are recorded neural activity of the user.
10. The method according to claim 1 , further comprising creating a table based on said formula.
11. The method according to claim 10 , wherein said step of generating stimuli by applying said formula comprises applying values from said table.
12. The method according to claim 1 , wherein said formula defines brightness as slope times current to the power of shape where slope and shape are derived terms.