Visual Neuroscience (2003), 20:543-555 Cambridge University Press Copyright © 2003 Cambridge University Press DOI 10.1017/S0952523803205083
Visual resolution with epi-retinal electrical stimulation estimated
from activation profiles in cat visual cortex
MARCUS
WILMS
a1
c1
, MARCUS
EGER
a1
, THOMAS
SCHANZE
a1
and REINHARD
ECKHORN†
a1
c2
a1 Institute of Neurophysics,
Philipps–University Marburg, 35032 Marburg,
Germany
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AbstractBlinds with receptor degeneration can perceive localized phosphenes
in response to focal electrical epi-retinal stimuli. To avoid extensive
basic stimulation tests in human patients, we developed techniques for
estimating visual spatial resolution in anesthetized cats. Electrical
epi-retinal and visual stimulation was combined with multiple-site
retinal and cortical microelectrode recordings of local field
potentials (LFPs) from visual areas 17 and 18. Classical visual
receptive fields were characterized for retinal and cortical recording
sites using multifocal visual stimulation combined with
stimulus–response cross-correlation. We estimated visual spatial
resolution from the size of the cortical activation profiles in
response to single focal stimuli. For comparison, we determined
activation profiles in response to visual stimuli at the same retinal
location. Activation profiles were single peaked or multipeaked. In
multipeaked profiles, the peak locations coincided with discontinuities
in cortical retinotopy. Location and width of cortical activation
profiles were distinct for retinal stimulation sites. On average, the
activation profiles had a size of 1.28 ± 0.03 mm cortex.
Projected to visual space this corresponds to a spatial resolution of
1.49 deg ± 0.04 deg visual angle. Best resolutions were 0.5 deg
at low and medium stimulation currents corresponding to a visus of
1/30. Higher stimulation currents caused lower spatial, but higher
temporal resolution (up to 70 stimuli/s). In analogy to the
receptive-field concept in visual space, we defined and characterized
electrical receptive fields. As our estimates of visual resolutions are
conservative, we assume that a visual prosthesis will induce phosphenes
at least at this resolution. This would enable visuomotor coordinations
and object recognition in many indoor and outdoor situations of daily
life.
(Received April 15 2003) (Accepted August 15 2003)
Key Words: Electrical retina stimulation; Visual cortex; Visual resolution; Retina implant.
Correspondence: c1 Address correspondence to: Marcus Wilms,
Renthof 7, 35032 Marburg, Germany. E-mail:
marcus.wilms@physik.uni-marburg.de c2 Address reprint requests to: Reinhard
Eckhorn, Renthof 7, 35032 Marburg, Germany. E-mail:
reinhard.eckhorn@physik.uni-marburg.de
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