Vernier step acuity and bisection acuity for texture-defined form

R. Gray, D. Regan

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Purpose: To compare positional acuity thresholds for orientation-texture defined (OTD) and luminance defiled (LD) boundaries, and to estimate the physiological limit for an OTD boundary. Methods: The stimulus was a texture pattern of short lines. Texture lines had different orientations but the same luminance on either side of the OTD boundary and different luminances but the same orientation on either side of the LD boundary. Vernier acuity and bisection acuity thresholds were measured over a range of spatial sampling frequencies. Results: For the LD boundary, both thresholds were inversely proportional to the sampling frequency over the entire 1.9 to 59 samples/deg r.ange. For the OTD boundary, both thresholds were inversely proporti inal to the sampling frequency for frequencies below 20 samples/detj and were not greatly {1.3 to 4.4 times) higher than thresholds for the LD boundary. Above 20 samples/deg both thresholds rose steeply for the OTD boundary. The lower physiological limits for the OTD boundary were ?.6 arc min for vernier acuity and 1.9 arc min for bisection acuity. Vernier acuity thresholds were significantly lower when both texture contrast and luminance contrast were present than with either type of contrast alone. Conclusions: 1 ) The physiological limit of positional encoding for an OTD be undary is determined by a balance between the improvement of positional acuity caused by increasing the spatial sampling frequency and th 3 reduction in visibility of the OTD boundary caused by a decrease in line length. 2) Observers can combine positional information carried by toxture contrast with positional information carried bv luminance contrast.

Original languageEnglish (US)
Pages (from-to)S635
JournalInvestigative Ophthalmology and Visual Science
Issue number4
StatePublished - Dec 1 1997
Externally publishedYes

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems
  • Cellular and Molecular Neuroscience

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