Estimating the gradient direction of a luminance ramp

Roderik G F Erens*, Astrid M L Kappers, Jan J. Koenderink

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


We report on the extent to which human observers are able to indicate the gradient direction of a luminance ramp. In our experiment modulation depth ranged from 1 to 64% and field sizes subtended 0.5 to 47.5° of visual angle. Observers are not able to indicate the gradient direction for modulation depths below 6%. For values above this threshold, the angular standard deviation in the responses decreases proportionally with the logarithm of the modulation depth and is about 11° for a modulation depth of 64%. The angular standard deviations for supra-threshold contrast are slightly increased for the field sizes of 0.5 and 47.5° but are constant over a range of field sizes of 1 to 25°. Thus, size invariance holds well for this range of field sizes.

Original languageEnglish
Pages (from-to)1639-1643
Number of pages5
JournalVision Research
Issue number12
Publication statusPublished - 1993


  • direction
  • Gradient
  • Luminance gradients
  • Shape from shading
  • Spatial contrast
  • Stimulus size


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