The IMI Retinal Implant System - Artificial Sight: Basic Research, Biomedical Engineering, and Clinical Advances - page 124

Figure 6.10. Size of perceived objects (imagined at a distance of 1 meter).
perceived the object immediately in the eye. Based on the description and the
gestures of the subject, the interviewer assumed that the size at a distance of 1m
was about as large as an apple. Most of the subjects had perceptions in the size
of a coin or the head of a match.
It has to be mentioned that the object characteristics described in the postop-
erative interview provide an idea of the overall impression of the subjects. This
includes stimulation at threshold level and also stimulation above threshold.
The stimulation above threshold may be significant as only five intensity levels
from 20 to 380 nC were used. Between one level and the next, the intensity is
approximately doubled.
The brightness of the perceived objects is shown in Figure 6.11. Most of the
subjects had perceptions with brightnesses comparable to a candle or a light
bulb. Objects with very low brightness and extremely bright objects were rare.
One subject saw dark shadows instead of light. The threshold of this subject was
extremely low and stimulation was not applied significantly above threshold. It is
unclear whether the subject would perceive brighter objects if larger stimulation
currents were applied.
Objects appeared in a wide range of colors (Figure 6.12). The predominant
colors were white, yellow, and blue (see Figure 6.12). Red and green were rare.
The perception “black” was reported by the subject who saw shadows instead of
light. In general, one perceived object has one color. Different objects perceived
by the same subject can have different colors. One subject saw an object that
was filled with a mosaic of different colors.
The subjects were asked to categorize the sharpness of the perceived objects.
The results are shown in Figure 6.13. It can be seen that most objects were seen
sharply and clearly.