title: Low-spatial-frequency channels and the spatial frequency-doubling illusion.
abstract: OBJECTIVE
  This study examined the number and nature of spatiotemporal channels in the region where the frequency-doubling (FD) illusion would be expected to occur at eight locations spanning the central 30 degrees of the visual field.
  
  
  METHODS
  The probability of seeing the FD illusion was examined in 17 subjects. Stimuli were presented at 5 octaves of low spatial frequencies, at each of seven flicker frequencies in the range 5.65 to 27.95 Hz. In a single trial, subjects matched the apparent spatial frequency of the flickering test pattern using a two-alternative, forced-choice method. Thirteen subjects were examined for stimuli presented at contrast 0.95. Three or four subjects were examined at each of the contrasts 0.2, 0.4, and 0.8. A factor analysis was conducted on the psychometric functions, quantifying the number and possible spatiotemporal tuning of neural channels present.
  
  
  RESULTS
  At contrast 0.95, three factors were able to explain 79.3% of the total variance in the psychometric responses to the 35 test conditions. This simple form of three broad spatiotemporal channels was also found at the other contrasts and in different subjects. The factor scores showed differential distribution of the factors onto the eight different visual field locations. Thus the expression of the three channels differed somewhat across the visual field.
  
  
  CONCLUSIONS
  The results support earlier reports, that there are several low-spatial-frequency channels below 1 cyc/deg in the periphery. The results may have implications for the FDT and matrix perimeters.
authors.affiliation: Department of Biomedical Sciences, Faculty of Applied Health Sciences, Universiti Kebangsaan Malaysia, Wilayah Persekutuan, Kuala Lumpur, Malaysia.
authors.forename: Yanti
authors.initials: Y
authors.lastname: Rosli
authors.forename: Suzanne M
authors.initials: SM
authors.lastname: Bedford
authors.forename: Ted
authors.initials: T
authors.lastname: Maddess
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011594:Psychometrics; D013028:Space Perception / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology*; D055815:Young Adult