Psychophysics of Prosthetic Vision: II. Stochastic Sampling, the Phosphene Image, and Noise

Abstract

Stimulation of the diseased retina via an intraocular electrode array is a proposed means of restoring some vision to the profoundly blind. A prosthetic device to this end would involve post-implantation calibration (analogous to cochlear implant fitting), wherein the subject indicates those discrete positions in the visual field where luminous percepts are elicited. This procedure would be a source of noise, because the indicated positions would only approximate the actual positions in the visual field. Put differently, the procedure introduces sampling jitter, and would therefore affect clinical outcomes such as mobility and reading speeds. The nature of this noise is the concern of the present paper; we derive an expression for the noise power spectrum as it relates to the statistical nature of the sampling jitter. We show that, generally, jitter has greater effect on higher spatial-frequencies, that is, those areas of the implantee's visual perception that represent fine detail are more prone to noise. More specifically, the noise spectrum depends on the characteristic function of the random variable describing the sampling jitter. Our results signal the need for experimental work that characterizes sampling jitter in implantees, plus the need for simulations that allow a better understanding of perception and the noisy phosphene image.

An Intrinsic Neural Oscillator in the Degenerating Mouse Retina

“…Moreover, membrane oscillations could favor the transfer of a specific bandwidth of information to higher visual centers. Nonetheless, when artificial methods are applied with prosthetic devices and signals are suprathreshold, increased background noise would likely degrade quality of the restored image (Powers et al, 1995;Hallum et al, 2006). Our current study provides direct evidence that a principal component of the spontaneous activity in the rd1 retina arises from intrinsic activity in networks of ON cone bipolar and AII amacrine cells.…”

An update on retinal prostheses

“…Early work in this area, performed in a significant number of studies with normally-sighted participants viewing a retinal implant simulator, have demonstrated the benefits of image filtering. Hayes et al incorporated regional averaging (calculating the average value over a surrounding neighbourhood of pixels) and Gaussian filtering (where a Gaussian profiled weighted average is applied) which was demonstrated to result in a sharper downsampled image and hence improved visual performance in tasks such as visual pursuit (Hayes et al, 2003;Hallum et al, 2006). An early report of image processing in Argus II recipients stated that several image filtering methods were available to users, including edge detection, contrast enhancement, and difference of Gaussian (Humayun et al, 2009).…”