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Christoph Teufel, Greg Davis, Paul Fletcher; Psychophysical Assessment of Contrast Adaptation in the Magnocellular Pathway. Journal of Vision 2012;12(9):90. doi: https://doi.org/10.1167/12.9.90.
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© ARVO (1962-2015); The Authors (2016-present)
The functional characteristics of cell populations within the parvo-, magno-, and koniocellular streams have been relatively well characterised in the retina and the lateral geniculate nucleus (LGN) using electrophysiological techniques in animal models. Yet, despite considerable effort, the difficulty in clear-cut assignment of functions to specific neuronal populations impedes the construction of stimuli that specifically affect one pathway in humans. Here, we present results from a novel psychophysical procedure that selectively manipulates magnocellular functioning and not other types of relay neurons within the dorsal LGN. We constructed an adaptation procedure based on the results of recent electrophysiolocial work and classical lesioning studies. The adaptation stimulus used in this procedure has been shown to specifically and profoundly affect the magnocellular pathway in primate LGN with little or no effect on response functions of parvo- and koniocellular populations. Furthermore, the specific spatiotemporal characteristics of this stimulus in combination with monocular adaptation eliminated or minimised any adaptation of cortical cells. We adapted one eye at a time and assessed the effects of this procedure by comparing contrast perception in the observer’s adapted eye with that in the unadapted eye. We used test stimuli that have been shown to rely either on an intact parvo- or magnocellular pathway in primates. The results were consistent with altered responses of the magnocellular LGN layers following exposure to the spatiotemporal characteristics of our adaptation stimulus with no effect on parvocellular functioning. This finding indicates that adaptation of the magnocellular stream affects superthreshold appearance demonstrating its importance to a wide range of perceptual phenomena. We consider the functional significance of contrast adaptation in the magnocellular pathway and discuss the potential of this novel procedure to assess magnocellular contributions to perception in healthy and clinical populations.
Meeting abstract presented at VSS 2012
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