Sensitivity to contrast modulations: the spatial frequency dependence of second-order vision

Andrew Schofield, Mark Georgeson

Research output: Contribution to journalArticle

60 Citations (Scopus)


We consider the overall shape of the second-order modulation sensitivity function (MSF). Because second-order modulations of local contrast or orientation require a carrier signal, it is necessary to evaluate modulation sensitivity against a variety of carriers before reaching a general conclusion about second-order sensitivity. Here we present second-order sensitivity functions for new carrier types (low pass (1/f) noise, and high pass noise) and demonstrate that, when first-order artefacts have been accounted for, the shape of the resulting MSFs are similar to one another and to those for white and broad band noise. They are all low pass with a likely upper frequency limit in the range 10-20 c/deg, suggesting that detection of second-order stimuli is relatively insensitive to the structure of the carrier signal. This result contrasts strongly with that found for (first-order) luminance modulations of the same noise types. Here the noise acts as mask and each noise type masks most those frequencies that are dominant in its spectrum. Thus the shape of second-order MSFs are largely independent of the spectrum of their noise carrier, but first-order CSFs depend on the spectrum of an additive noise mask. This provides further evidence for the separation of first- and second-order vision and characterises second-order vision as a low pass mechanism. (C) 2002 Elsevier Science Ltd. All rights reserved.
Original languageEnglish
Pages (from-to)243-259
Number of pages17
JournalVision Research
Publication statusPublished - 1 Feb 2003


  • first order
  • contrast
  • luminance
  • sensitivity function
  • second order


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