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Emily S. Kachinsky, Vivianne C. Smith, Joel Pokorny; Discrimination and identification of luminance contrast stimuli. Journal of Vision 2003;3(10):2. doi: 10.1167/3.10.2.
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© ARVO (1962-2015); The Authors (2016-present)
The goal of this study was to compare luminance contrast discrimination and polarity identification in the inferred Parvocellular (PC-) and Magnocellular (MC-) pathways. The position identification task tested ability to locate a contrast change within a stimulus. The polarity identification task tested ability to classify the contrast change as either brighter or darker. Three paradigms were employed to find these thresholds for the inferred MC- and PC-pathways: Pulsed-Pedestal, Steady-Pedestal and Pedestal-Δ-Pedestal. Position and polarity identification thresholds were the same for the Pulsed-Pedestal stimuli (inferred PC-pathway). The position identification thresholds were lower than the polarity identification thresholds for Steady-Pedestal stimuli (inferred MC-pathway). The position identification thresholds were lower than the polarity identification thresholds for Pedestal-Δ-Pedestal stimuli when the Δ-Pedestal contrast steps were sub-threshold or close to threshold. When the contrast steps were larger, position identification and polarity identification thresholds were similar for the Pedestal-Δ-Pedestal stimuli. Comparisons were also made between position identification and polarity identification thresholds for a short and a long stimulus presentation. There were no systematic differences dependent on presentation duration.
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