Retinal Prosthesis Dissertation - Student Home Pages

Contents
An Address Event Representation (AER) Multicast Router for Colour Vision .................................. i
Acknowledgements ................................................................................................................................ i
Dedication ............................................................................................................................................... i
Abstract\Foreword ................................................................................................................................. ii
Chapter 1 Introduction/research aim ................................................................................................. 10
1.1 Introductory Literature Review ............................................................................................... 10
1.1.1 Sub retinal ..................................................................................................................... 11
1.1.2 Epi retinal ............................................................................................................................. 14
1.2 Conceptual overview ............................................................................................................. 18
1.3 Sub retinal versus Epi-retinal ................................................................................................. 21
1.4 Introduction to stimulators ........................................................................................................... 21
1.5 Thesis structure ..................................................................................................................... 22
Chapter 2 Early directions .................................................................................................................. 24
2.1 Introduction to initially envisaged project ..................................................................................... 24
2.2 Neural network representation .................................................................................................... 25
2.2.1 The first artificial neuron ........................................................................................................... 26
2.2.2 Hebb’s rule ........................................................................................................................... 28
2.2.3 Adaline and the adaptive linear combiner: a bipolar case of above ..................................... 28
2.2.4 Neural Networks –perceptron training .................................................................................. 30
2.2.5 Linear separability ................................................................................................................ 32
2.2.6 The Delta Rule (used to determine separability) .................................................................. 35
2.3 Address Event Representation (AER) ......................................................................................... 37
2.3.1 The message packet ............................................................................................................ 37
2.4 Comparison to Frame Based Representation (FBR) ................................................................... 38
2.4.1 Comparison Criteria ............................................................................................................. 40
2.4.2 Address Event Representation ............................................................................................ 41
2.5 MATLAB sub-retinal simulation ................................................................................................... 42
2.5.1 MATLAB representation ....................................................................................................... 42
2.5.2 Program operation ............................................................................................................... 43
2.5.1 Files in Appendix A ................................................................................................................... 44
2.5.2 Use of the program ................................................................................................................... 44
2.6 Epi-retinal; method of choice ....................................................................................................... 45
2.6.1 MATLAB representation of epi_retinal approach.................................................................. 47
2.6.2 FPGA representation of epi_retinal approach .......................................................................... 48
2.7 Background to stimulators ........................................................................................................... 49
2.7.1 Charge considerations ......................................................................................................... 49
2.7.2 Achromatic current requirements ......................................................................................... 49
Chapter 3 Concepts ............................................................................................................................. 50
3.1 Neural concepts .......................................................................................................................... 52
3.2 Biological Neuron operation ........................................................................................................ 53
3.3 Natural limit for pulse duration ..................................................................................................... 54
3.4 Retinal colour perception ............................................................................................................. 55
3.5 Human visual processing ............................................................................................................ 57
3.6 Current Retinal Implants .............................................................................................................. 61
3.6.1 Retinal structure ................................................................................................................... 61
3.6.2 Retinal operations ................................................................................................................ 62
3.6.3 Commonality of sub retinal and epi retinal approaches ........................................................ 65
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