Second-order spatial frequency and orientation channels in human vision

D Ellemberg, Harriet Allen, RF Hess

Research output: Contribution to journalArticle

25 Citations (Scopus)


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.
Original languageEnglish
Pages (from-to)2798-803
Number of pages6
JournalVision Research
Publication statusPublished - 1 Sept 2006


  • orientation
  • spatial frequency
  • second-order
  • first-order
  • visual discrimination
  • channels
  • detection threshold


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