Abstract
Visual perceptual grouping, the process of forming global percepts from discrete elements, is experience-dependent. Here we show that the learning time course in an animal model of artificial vision is predicted primarily from the density of visual elements. Three naïve adult non-human primates were tasked with recognizing the letters of the Roman alphabet presented at variable size and visualized through patterns of discrete visual elements, specifically, simulated phosphenes mimicking a thalamic visual prosthesis. The animals viewed a spatially static letter using a gaze-contingent pattern and then chose, by gaze fixation, between a matching letter and a non-matching distractor. Months of learning were required for the animals to recognize letters using simulated phosphene vision. Learning rates increased in proportion to the mean density of the phosphenes in each pattern. Furthermore, skill acquisition transferred from trained to untrained patterns, not depending on the precise retinal layout of the simulated phosphenes. Taken together, the findings suggest that learning of perceptual grouping in a gaze-contingent visual prosthesis can be described simply by the density of visual activation.
Highlights
< 5,000 ms to learn a relatively simple perceptual grouping task, even after consolidating task rules[21]
Animals were trained with cue stimuli presented in clear view to learn the basic task and to develop their recognition for all 26 letters before the primary training with phosphene view cues was initiated
Before introducing phosphene view cues (Fig. 2), the animals were performing near 100% (94, 81, and 91%) for each of the three animals averaged over all clear conditions
Summary
< 5,000 ms to learn a relatively simple perceptual grouping task, even after consolidating task rules[21]. The potentially longer learning time course in non-human primates permits study of the development of perceptual grouping skills. Psychophysical testing using simulated artificial vision in sighted humans has previously been performed using stimuli, e.g. letters, viewed through patterns of simulated phosphenes[2,4]. We will use the term letter to indicate the conceptual representation of a visual form in an alphabet, like the Platonic ideal of a letter, and glyph to indicate the rendering of a given letter from a given font at a given size for presentation to a subject This latter term from typesetting and computer graphics is similar to optotype that is used in visual acuity testing. After months of training, we tested phosphenes in retinotopic locations that were not previously used and found that acquired skills had transferred to these new visual field locations This transfer appears to constrain the potential neural mechanisms underlying learning to those that are global in nature despite the spatial specificity of discrete islands or clusters of neurons (see paragraph) activated by each phosphene during stimulus presentation. When we use the term clusters of activity, we are referring to the retinotopically fixed but temporally dynamic pattern of neural firing that is created by a given phosphene pattern p p
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