March 2012
Volume 53, Issue 14
ARVO Annual Meeting Abstract  |   March 2012
Crowding in the S-cone pathway
Author Affiliations & Notes
  • Daniel R. Coates
    Vision Science Graduate Program, UC Berkeley, Berkeley, California
  • Susana T. L. Chung
    Vision Science Graduate Program, UC Berkeley, Berkeley, California
  • Footnotes
    Commercial Relationships  Daniel R. Coates, None; Susana T. L. Chung, None
  • Footnotes
    Support  NIH/NEI T32-EY007043, R01-EY012810
Investigative Ophthalmology & Visual Science March 2012, Vol.53, 4139. doi:
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      Daniel R. Coates, Susana T. L. Chung; Crowding in the S-cone pathway. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4139.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : It has been known for some time that the pathway mediated by short-wavelength sensitive cones (SWS) has significant functional differences from the standard red/green and achromatic luminance channels, including reduced acuity, differing temporal response, and hemispheric asymmetries at varying eccentricities. As clinicians and researchers begin to utilize information from SWS-isolated resolution tasks to study ocular disease such as glaucoma, diabetes, and age-related maculopathy, it is necessary to understand how nearby contours interact with targets during spatial recognition tasks, a phenomenon known as lateral masking, or 'crowding.' In this study we quantify the crowding effect in this pathway, showing how its magnitude compares to that in the more typical visual processing channels.

Methods: : We used the standard technique of selective chromatic adaptation to isolate the S-cone pathway, in conjunction with a tumbling-E acuity task in flanked and unflanked conditions at 3, 8, and 15 degrees eccentricity. Specifically, subjects (N=4) monocularly viewed computer-generated stimuli on a CRT monitor through a narrow-band blue filter, while a beam splitter overlaid a bright yellow background designed to saturate the long- and medium-wavelength sensitive cones. A staircase procedure determined the minimum acuity for flanked and unflanked stimuli with a variety of flanker spacings (1.5-4x letter size) and background intensities (100-1000 cd/m2). Per typical crowding studies, stimuli were shown for 150 ms.

Results: : Unflanked S-cone whole-letter acuities (1.12 deg +/-0.2 deg at 8 deg eccentricity) for our subjects at the tested eccentricity agreed with those measured previously by other researchers. Interestingly, we found that when flanked acuity (e.g., at the closest flanker spacing, 2.2 deg +/- 0.3 deg at 8 deg eccentricity) is plotted versus flanker spacing, the slope of the crowded portion is steeper than results from other stimulus manipulations that have been studied. For the large size optotype required to reach threshold for the acuity limitations of the S-cone pathway, crowding has a less deleterious effect than acuity.

Conclusions: : Our results show that crowding, although clearly evident when measuring peripheral acuity in the condition of S-cone isolation, will impact acuity measurements less than during traditional testing conditions. This confirms a theoretical idea that crowding is based on cortical distance. Since S-cones are more sparsely represented in the cortex, the scaling necessary to achieve acuity measurements will place adjacent stimuli outside the range of crowding interference zones.

Keywords: visual acuity 

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