Retinal Prosthesis Dissertation - Student Home Pages

Typically AER is used as a multi sender, multi receiver asynchronous protocol
whereas however in this epiretinal approach to a retinal prosthesis application its
neuromorphic capability is as a timed synchronous protocol. In other words as there
is only a single image to be transmitted; although each image is composed of
multiple pixels, then this time multiplexed synchronous protocol will not have
contention between AER packets. So despite the image signal eventually being
multicast to many electrodes an asynchronous protocol enabling handshaking and
avoiding contention is not necessary or warranted and will eliminate overheads
associated with such extra processing.
1.2 Conceptual overview
To accommodate the initial test setup described in the abstract a frame rate of 25
frames per second (fps) was chosen, this corresponds to the UK TV camera standard.
The UK TV standard; as with the 25p video format, deals with persistence of vision
where an after image of a stimulus remains long enough for the phi phenomenon (an
optical illusion) to occur i.e. the perception of movement. At 1fps to transmit each
pixels worth of information would take 1s divided by the pixel size of the image. So
for a four by four image i.e. sixteen pixels, pixel time would equal 1/16 i.e. 0.0625s
meaning 16Hz for the frequency of AER packets i.e. synonymous with pixel
frequency. Each AER packet contains the pixel address and payload e.g. pulse count,
corresponding to the colour information, during the AER transmission. At 25 fps the
frequency of AER packets, for this example, would be 25*16=400Hz. The frequency
of AER packets (f packet ) is the frame rate multiplied by the image size in pixels. There
is a linear relationship between the frame rate for any particular image size and AER
packet frequency that needs to be set e.g. 50*16=800Hz and for a 1024 pixel image
@ 25fps, AER packet frequency would equal 25.6kHz.
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