title: Simulation of artificial vision, III: do the spatial or temporal characteristics of stimulus pixelization really matter?
abstract: OBJECTIVE
  In preceding studies, simulations of artificial vision were used to determine the basic parameters for visual prostheses to restore useful reading abilities. These simulations were based on a simplified procedure to reduce stimuli information content by preprocessing images with a block-averaging algorithm (square pixelization). In the present study, how such a simplified algorithm affects reading performance was examined.
  
  
  METHODS
  Five to six volunteers with normal vision were asked to read full pages of text with a 10 degrees x 7 degrees viewing window stabilized in central vision. In a first experiment, reading performance with off-line and real-time square pixelizations was compared at different resolutions. In a second experiment, off-line square pixelization was compared with off-line Gaussian pixelization with various degrees of overlap. In a third experiment, real-time square pixelization was compared with real-time Gaussian pixelization.
  
  
  RESULTS
  Results from the first experiment showed that real-time square pixelization required approximately 30% less information (pixels) than its off-line counterpart. Results from the second experiment, using off-line processing, revealed a restricted range of Gaussian widths for which performances were equivalent or significantly better than that obtained with square pixelization. The third experiment demonstrated, however, that reading performances were similar in both real-time pixelization conditions.
  
  
  CONCLUSIONS
  This study reveals that real-time stimulus pixelization favors reading performance. Performance gains were moderate, however, and did not allow for a significant (e.g., twofold) reduction of the minimum resolution (400-500 pixels) needed to achieve useful reading abilities.
authors.affiliation: Ophthalmology Clinic, Department of Clinical Neurosciences, Geneva University Hospitals, Switzerland.
authors.forename: Angélica Pérez
authors.initials: AP
authors.lastname: Fornos
authors.forename: Jörg
authors.initials: J
authors.lastname: Sommerhalder
authors.forename: Benjamin
authors.initials: B
authors.lastname: Rappaz
authors.forename: Avinoam B
authors.initials: AB
authors.lastname: Safran
authors.forename: Marco
authors.initials: M
authors.lastname: Pelizzone
mesh_terms: D000328:Adult; D003198:Computer Simulation; D003199:Computer Systems; D005133:Eye Movements / Q000502:physiology; D005137:Eye, Artificial; D006801:Humans; D011932:Reading; D015348:Vision, Binocular / Q000502:physiology*