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Xiaohua Zhuang, Joel Pokorny, Dingcai Cao; Flicker Adaptation Desensitizes the Magnocellular but Not the Parvocellular Pathway. Invest. Ophthalmol. Vis. Sci. 2015;56(5):2901-2908. doi: https://doi.org/10.1167/iovs.14-16067.
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© ARVO (1962-2015); The Authors (2016-present)
Anatomical and physiological studies show that in primates, visual information is conveyed through two parallel pathways, including the magnocellular (MC-) and parvocellular (PC-) pathways. However, the functional separation between the two pathways remains controversial and challenging. To resolve this, we show a psychophysical approach to desensitize the inferred MC-pathway of human observers independently of the inferred PC-pathway.
The steady-pedestal and pulsed-pedestal paradigms that allow detection and discrimination to be mediated by only the inferred MC- or PC-pathway were used. Three observers (one male, aged 43 years, and two females, aged 33 and 62 years) adapted to either a steadily presented pedestal or a 2- or 10-Hz 50% contrast square-wave modulated luminance flicker. Contrast discrimination thresholds were measured following the flicker adaptation.
Flicker adaptation reduces contrast detection and discrimination of the MC-pathway but not the PC-pathway, with larger MC losses from 10-Hz (∼0.28 log unit loss, P < 0.05 for all observers) than 2-Hz flicker (∼0.13 log unit loss, P < 0.05 for one or two observers depending on stimulus size). Further, our results show that the PC-pathway does not mediate the contrast detection threshold at the background luminance following MC-pathway desensitization.
This study demonstrates the feasibility of independently manipulating sensitivity of the MC-pathway in human observers. Our paradigms provide powerful tools to independently investigate the perceptual functions in the MC- and PC-pathways. This could lead to a better understanding of the perceptual functions of these pathways.
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