title: Visual evoked potentials and reaction time measurements to motion-reversal luminance- and texture-defined stimuli.
abstract: OBJECTIVE
  Previous studies have suggested that compared to first-order (FO) motion stimuli, second-order (SO) motion stimuli required more cortical time to be processed. The purpose of this study was: 1- to verify this claim with Visual Evoked Potential (VEP) and eye-hand Reaction Time (RT) measurements and 2- examine if the VEP and RT responses are similarly modulated by the same trigger features of the stimuli.
  
  
  METHODS
  The VEPs and eye-hand RT for motion-reversal luminance- (first-order) and texture-defined (second-order) stimuli were recorded from ten normal human subjects. VEPs and RTs were measured for each motion class at eight different modulation depths (from 3 to 100%).
  
  
  RESULTS
  Our results reveal that for stimuli of low contrast levels, the SO-FO timing differences are approximately 100 ms (RT) or 20 ms (VEP), while for contrasts >or= 15-20% (VEP) or >or= 50% (RT), the SO-FO difference is no longer significant (p < 0.007), suggesting either that the brain can no longer distinguish SO from FO stimuli or that in spite of the added complexity of SO stimuli the brain takes equal time to process both.
  
  
  CONCLUSIONS
  Interestingly, the above contrast discrepancy in SO-FO resolution threshold suggests that, compared to the VEP, the more psychophysical RT measurement can process and thus distinguish a larger spectrum of motion stimuli, thus further confirming the latter measure of the retinocortical processing time as a valid alternative to the VEP.
authors.affiliation: Visual Psychophysics and Perception Laboratory, Ecole d'optométrie, Université de Montréal, Canada.
authors.forename: Hadi
authors.initials: H
authors.lastname: Chakor
authors.forename: Armando
authors.initials: A
authors.lastname: Bertone
authors.forename: Michelle
authors.initials: M
authors.lastname: McKerral
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Faubert
authors.forename: Pierre
authors.initials: P
authors.lastname: Lachapelle
mesh_terms: D000293:Adolescent; D000328:Adult; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values