Review: steady and pulsed pedestals, the how and why of post-receptoral pathway separation

In the mid-1990s, the Pokorny and Smith research group began a series of psychophysical experiments with the aim of separately measuring magnocellular (MC)- and parvocellular (PC)-pathway mediated achromatic contrast discrimination. Three paradigms provide complementary information: The pulsed-pedestal paradigm reveals PC contrast gain, the steady-pedestal paradigm reveals steady-state MC-pathway sensitivity, and the pedestal-Δ-pedestal paradigm reveals MC contrast gain. Further studies investigated the temporal and spatial summation properties of the underlying mechanisms and extended the work to include measures of spatial resolution, chromatic contrast discrimination, the detection and identification of stimulus polarity, and the inferred retinal mechanisms mediating illusory distortions. Other laboratories have also applied the methods to the study of normal and clinically impaired vision. This review describes the pedestal methodologies, how they relate to physiology, and how they have been and should be employed.