title: Temporal properties of visual perception on electrical stimulation of the retina.
abstract: OBJECTIVE
  To investigate the elementary temporal properties of electrically evoked percepts in blind patients chronically implanted with an epiretinal prosthesis.
  
  
  METHODS
  Nine subjects were presented with isolated stimuli of variable duration and pulse rate. Stimulation amplitude was set to the upper comfortable level and a group of 2 × 2 adjacent electrodes was simultaneously activated. First, subjects were asked to verbally describe their visual perception paying particular attention to the time-course of brightness. Then, in subsequent trials, they described the brightness time dependence using a joystick while auditory feedback of joystick position was provided.
  
  
  RESULTS
  All subjects described a bright, well-localized percept at stimulus onset. Only one subject reported such a bright, well-localized visual sensation during an entire 10-second stimulation trial. For the remaining eight subjects, it faded more or less rapidly (in four cases <0.5 second) and was often followed by a percept described as less bright, poorly localized, and having different color. Only initial percepts at stimulation onset seemed bright and localized enough to reconstruct a patterned image. Changing stimulation pulse rate influenced the time course of perception only in some cases but the effect was not systematic.
  
  
  CONCLUSIONS
  Percepts differed considerably across subjects, probably because of the considerable variations in the progression and remodeling processes associated with the disease. Appropriate coding of a patterned image under such conditions appears challenging. Further research of the underlying mechanisms of visual perception upon electrical stimulation of the retina is required to optimize stimulation paradigms and to better establish patient selection criteria.
authors.affiliation: Ophthalmology Clinic, Geneva University Hospitals, 4 Rue Gabrielle-Perret-Gentil, Geneva 14, Switzerland. Angelica.Perez-Fornos@hcuge.ch
authors.forename: Angélica
authors.initials: A
authors.lastname: Pérez Fornos
authors.forename: Jörg
authors.initials: J
authors.lastname: Sommerhalder
authors.forename: Lyndon
authors.initials: L
authors.lastname: da Cruz
authors.forename: Jose Alain
authors.initials: JA
authors.lastname: Sahel
authors.forename: Saddek
authors.initials: S
authors.lastname: Mohand-Said
authors.forename: Farhad
authors.initials: F
authors.lastname: Hafezi
authors.forename: Marco
authors.initials: M
authors.lastname: Pelizzone
mesh_terms: D000328:Adult; D000368:Aged; D001766:Blindness / Q000503:physiopathology; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D008839:Microelectrodes; D008875:Middle Aged; D010719:Phosphenes / Q000502:physiology*; D019919:Prosthesis Implantation; D012160:Retina / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D057488:Visual Prosthesis