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Qasim Zaidi; Phenomenology and neurons. Journal of Vision 2013;13(9):1395. doi: 10.1167/13.9.1395.
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© ARVO (1962-2015); The Authors (2016-present)
Frequent pitfalls of relying solely on visual appearances are theories that confuse the products of perception with the processes of perception. Being blatantly reductionist and seeking cell-level explanations helps to conceive of underlying mechanisms and avoid this pitfall. Sometimes the best way to uncover a neural substrate is to find physically distinct stimuli that appear identical, while ignoring absolute appearance. The prime example was Maxwell's use of color metamers to critically test for trichromacy and estimate the spectral sensitivities of three classes of receptors. Sometimes it is better to link neural substrates to particular variations in appearance. The prime example was Mach's inference of the spatial gradation of lateral inhibition between neurons, from what are now called Mach-bands. In both cases, a theory based on neural properties was tested by its perceptual predictions, and both strategies continue to be useful. I will first demonstrate a new method of uncovering the neural locus of color afterimages. The method relies on linking metamers created by opposite adaptations to shifts in the zero-crossings of retinal ganglion cell responses. I will then use variations in appearance to show how 3-D shape is inferred from orientation flows, relative distance from spatial-frequency gradients, and material qualities from relative energy in spatial-frequency bands. These results elucidate the advantages of the parallel extraction of orientations and spatial frequencies by striate cortex neurons, and suggest models of extra-striate neural processes. Phenomenology is thus made useful by playing with identities and variations, and considering theories that go below the surface.
Meeting abstract presented at VSS 2013
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