Purchase this article with an account.
Oliver Flynn, Brett Jeffrey; Rod-mediated contour integration measured under scotopic conditions using radial frequency patterns. Journal of Vision 2018;18(10):411. doi: 10.1167/18.10.411.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Photopic shape discrimination tasks using radial frequency (RF) deformation patterns are useful for measuring contour integration and judgments of circularity. Here, we measure shape discrimination using RF patterns under scotopic conditions to investigate rod-mediated contour integration. An RF pattern is a ring with a luminance profile defined by a fourth-derivative Gaussian and a radius deformed by a sine wave. A temporal 2-AFC staircase paradigm was used to measure observers' threshold deformation from circularity using stimuli on a monitor dimmed with neutral density filters to scotopic levels. Radius of the rings (2°-6°), number of radial cycles (5-13), and portion of the stimulus visible (as low as one cycle; 4° and 8° radii; 4, 8, and 16 radial cycles) were manipulated in separate experiments. Two trained observers were tested. Thresholds of approximately 2 minutes of arc were measured consistently across all radii (127 +/- 46 arc sec) and radial cycles (126 +/- 42 arc sec). When large portions of the stimuli were occluded, thresholds improved as visible cycles were added, from one to three cycles, after which thresholds remained constant. This pattern of data was seen regardless of the radius or radial cycles present in the full stimulus. Contour frequency was defined as a measure of the number of cycles per degree of circumference. When only 1 cycle was visible, thresholds decreased as contour frequency increased, from approximately 5 to 3 minutes of arc. In conclusion, under scotopic conditions, contour integration occurs across only a small proportion of the RF pattern stimulus. This is in contrast with photopic data, which finds elevated thresholds even when small portions of the stimulus are occluded. Thresholds are approximately constant across the range of stimulus radii tested, which is consistent with histological measures of rod density as a function of retinal eccentricity.
Meeting abstract presented at VSS 2018
This PDF is available to Subscribers Only