Prosthetic Vision Simulation in Fully and Partially Sighted Individuals - Artificial Sight: Basic Research, Biomedical Engineering, and Clinical Advances - page 73

view (8mm exit pupil) and is capable of monochrome VGA resolution (640 480

pixels). The headset has built-in refractive correction, IR pupil illumination, and
a charge coupled device (CCD) camera allowing recording of the test subject's
eye movements. The scene in front of the HMD wearer was captured by a
CCD camera, Watec model WAT-660D (Genwac, Orangeburg, NY), mounted
centrally on the front cover of the headset, as shown in Figure 4.1. The optical
axis of the camera is at a 90 downward angle to the subject's line of sight. The
test subject was allowed to use just the left eye (the right eye monitor of the
headset was switched off), hence there was an offset of about 3.2 cm between the
axis of the camera view and the subject's eye position, the camera position did
correspond to the subject's cyclopean eye and body axis. The video feed from
the downward-looking camera was processed by a Dell Inspiron 8200 laptop
computer with a dedicated filter implemented under the DirectShow operating
environment.

×

Stimulus
The DirectShow filter program allowed many different settings such as size
of the phosphene grid and of each phosphene, gray levels of phosphenes and
background, etc. In our experiments we used a grid of 6 × 10 dots with 1
effective diameter and 2 center-to-center spacing, representative of prosthesis
resolutions that may be achieved in the near future. The dots had a Gaussian
intensity profile on a black background. The dot raster was shown to subjects
only while they were allowed to perform the experimental task.

Figure 4.1. Angle between the view planes of the camera and the test subject and the
offset between the middle of the camera view and the middle of the test subjects view.