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Radhika Gulati, Hannah Roche, Kavitha Thayaparan, Ralf Hornig, Gary S. Rubin; The Development of a Picture Discrimination Test for People with Very Poor Vision. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1197.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a picture discrimination test that quantifies ability to locate objects in natural scenes, for patients implanted with IMI’s Intelligent Retinal Implant System.
100 images of everyday urban scenes were photographed with a digital camera. Each scene had an object of interest (e.g. doorway, staircase, obstacle on the walking path) on the left or right side. Subjects 18-45 years old with normal vision viewed the pictures through a camera driven virtual reality headset. The images were projected on a screen at a fixed size and luminance and viewed with the camera mounted on the headset. The camera image was rendered on a 7 x 7 grid of Gaussian shaped pixels to simulate phosphene vision as it might be experienced with a retinal implant. Subjects had to indicate whether the object of interest was on the left or right side. All 100 pictures were shown twice in random order. In the first experiment no feedback was given to the participants. In the second experiment feedback was given during the first run only. 60 subjects participated in the study, 30 for each experiment.
In the first experiment, without feedback, the median scores were 64% and 66% correct on the two runs with 20 subjects scoring 80-90% correct and 10 subjects scoring 10-30% correct. Clearly, the low scoring group was responding to something in the pictures; they were just interpreting the information incorrectly. In the second experiment, with feedback during the first run, the median scores were 85% and 86% correct on runs 1 and 2. All subjects performed at or above chance. The pictures are currently undergoing Rasch analysis which suggests that there are at least 2 dimensions underlying performance, one related to contrast polarity (bright vs dark objects) and the other possibly related to symmetry of the scene.
The results of these experiments indicate that subjects can locate an object of interest in everyday scenes even with extremely impoverished visual resolution. But to obtain stable and reliable measurements, the subjects must be given feedback to allow them to establish a useful strategy.
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