title: Flicker adaptation desensitizes the magnocellular but not the parvocellular pathway.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Institute for Mind and Biology University of Chicago, Chicago, Illinois, United States.
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Zhuang
authors.affiliation: Visual Science Laboratories, University of Chicago, Chicago, Illinois, United States.
authors.forename: Joel
authors.initials: J
authors.lastname: Pokorny
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States.
authors.forename: Dingcai
authors.initials: D
authors.lastname: Cao
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology; D004192:Discrimination, Psychological / Q000502:physiology; D005260:Female; D005829:Geniculate Bodies / Q000166:cytology / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology*