Retinal Prosthesis Dissertation - Student Home Pages

(Where * is the convolution operator and I refers to the intensity of the point)
Similarly g outer (x,y,βσ) =
( ) ( )
( )
(3)
So DOG = g inner (x,y,σ) - g outer (x,y,βσ)
(4)
Typically finite impulse response filters (FIRs) are used to implement these concepts
within FPGA fabric.
3.6 AER concept in context
AER is a time division multiplexing system, therefore signals are sent in one
complex transmission and the receiving end has to separate the individual signals.
This gives an opportunity to emulate the many wires that would otherwise be
required to transmit the values of pixel intensity of each pixel of a scene. So for a
1024 by 1024 scene: required at the fovea of the eye, 1,048,576 wires would need to
be emulated. In the case of a scene of 32 by 32 the connectivity of 1024 wires would
need to be emulated and for a scene of 4 by 4 the connectivity of 16 wires would
need to be emulated. At 25 fps the time for each frame would be 0.04s (40ms) such
timing would be appropriate for the initial test setup to display on a monitor. A spike
plus interval occurs in 20ms at maximum pulsing and in 200ms for minimal pulsing.
Pulses per second can be determined from interspike time, within this time frame;
see figure 27:
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