Second-order spatial frequency and orientation channels in human vision.
We compared the number of spatial frequency and orientation mechanisms underlying first- versus second-order processing by measuring discrimination at detection threshold for first- and second-order Gabors to determine the smallest difference in spatial frequency and orientation that permits accurate discrimination at threshold. For second-order gratings, the number of channels is the same as for first-order gratings for spatial frequencies up to about 2 cpd; however, there are fewer second-order channels at higher spatial frequencies. In contrast, the number of labeled channels for orientation is the same for first- and second-order gratings. In conclusion, our findings provide evidence for distinct spatial frequency and orientation labeled detectors in second-order visual processing. We also show that, relative to first-order, there are fewer second-order channels processing higher spatial frequencies. This is consistent with a filter-rectify-filter scheme for second-order in which the second stage of filtering is at lower spatial frequencies.
Ellemberg
Dave
D
Université de Montréal, Département de Kinésiologie, Canada. dave.ellemberg@umontreal.ca
Allen
Harriet A
HA
Hess
Robert F
RF
D015350:Contrast Sensitivity / Q000502:physiology; D004192:Discrimination, Psychological / Q000502:physiology*; D006801:Humans; D009949:Orientation; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011594:Psychometrics; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology