A Real-Time and Portable Bionic Eye Simulator - Biomedical Engineering Systems and Technologies - page 30

A Real-Time and Portable Bionic Eye Simulator

Horace Josh, Benedict Yong, and Lindsay Kleeman

Department of Electrical and Computer Systems Engineering and Monash Vision Group,
Monash University, Wellington Road, Clayton, Australia
{ horace.josh,benedict.yong,lindsay.kleeman } @monash.edu.au

Abstract. The Monash Vision Group is developing a bionic eye based on an im-
plantable cortical visual prosthesis. The visual prosthesis aims to restore vision
to blind people by electrical stimulation of the visual cortex of the brain. Due
to the expected naivety of early prostheses, there is need for the development of
innovative pre-processing of scene information in order to provide the most intu-
itive representation to user. However, in order to explore solutions to this need,
prior to availability of functional implants, a simulator system is required. In this
paper, we present a portable, real-time simulator and psychophysical evaluation
platform that we have developed called the 'HatPack'. It makes use of current
neurophysiological models of visuotopy and overcomes limitations of existing
systems. Using the HatPack, which is compiled into a neat, wearable package,
we have conducted preliminary psychophysics testing, which has shown the sig-
nificance of available greyscale intensity levels and frame rates. A learning effect
associated with repeated trials was also made evident.

Keywords: Visual prosthesis, Portable simulator, Visual cortex, Visuotopic map-
ping, Phosphene, Bionic vision.

1 Introduction

A study conducted in 1968 showed that electrical stimulation of the visual cortex of a
human brain resulted in the elicitation of bright spots of light, called 'phosphenes',
in the visual field of the subject [4]. Supporting results were also found in [1,8,9].
Further studies [14,24] have shown that it is also possible to generate phosphenes via
electrical stimulation of the retina and optic nerve. These early studies provided a basis
for widespread research into the development of functional visual prostheses.
A visual prosthesis, also often referred to as a 'bionic eye', is an implantable biomed-
ical device that aims to restore vision to the blind. The core component of these devices
is an array of electrodes, driven by specialised electronics. The electrodes inject electri-
cal current into a particular section of the patient's visual pathway in order to generate
an 'image' in the visual field.
The term visual pathway refers to the path that signals take from the retina in the eye
where they are generated to the primary visual cortex at the back of the brain. Light that
is incident on photoreceptors in the retina, a layer of cells at the back of the eye, results
in the generation of signals. These signals are passed through the optic nerve and Lat-
eral Geniculate Nucleus (LGN) before arriving at the primary visual cortex (V1), which