Psychophysical test of a tunable retina encoder for retina implants

The perception-based tuning procedure of a learning retina implant as a visual prosthesis for blind subjects with retinal degeneration was tested in subjects with normal vision. A simulated retina encoder (RE) with 256 tunable spatiotemporal receptive field (RF) filters was stimulated by spatiotemporal visual patterns. RE output impulse rate was fed into an inversion module (IM) to reproduce the corresponding input pattern in real time. Initially, IM was trained to generate an approximation of the inverse of the RE mapping for a given RE state S, so as to yield a close similarity between spatiotemporal RE input and IM output patterns. Subsequently, S was arbitrarily changed thus drastically increasing the difference between desired and perceived pattern. A learning algorithm based on evolution strategies was developed to adjust RE iteratively with human feedback