Generative Phenomenology of form perception: Perceptograms and cortical models for amblyopic phantom percepts.

What we see is generated by our cortical neurons processing sensory input. Amblyopia provides a perfect case for studying the neural generation of percepts (Generative Phenomenology) because many amblyopes see phantom forms that contain more features than the stimulus through their amblyopic eye (AE) but not through the fellow eye (FE). Seeing phantom forms is unlike most visual disorders that lead to deficits and requires different types of models. Using computer guided dichoptic displays, we acquired perceptograms (viewable records of perceived images) for single gratings shown to AE. 92.6% of phantom percepts were matched exactly by plaid patterns made of two gratings shown to FE. A formal equation between the cortical signals generated by the gratings seen through AE with the signals generated by their perceptograms seen through FE was used to derive AE receptive fields as linear transforms of FE receptive fields. Passing gratings through the transformed AE model accurately generated the corresponding perceptograms. The transformations reflected complex changes in cortical receptive fields and output combinations. They also explained amblyopic deficits at discerning cyclic distortions from circularity and were validated via reverse-correlation. Changes in neuronal receptive fields thus have profound effects on perception, to the extent that observers can see more features than are present in what is viewed.