July 2019
Volume 60, Issue 9
Open Access
ARVO Annual Meeting Abstract  |   July 2019
Determining the Isoluminant Point in Chicks
Author Affiliations & Notes
  • Alex Hentschel
    Vision Science, New England College of Optometry, Boston, Massachusetts, United States
  • Footnotes
    Commercial Relationships   Alex Hentschel, None
  • Footnotes
    Support  NIH Grant RO1 EY023281
Investigative Ophthalmology & Visual Science July 2019, Vol.60, 3156. doi:
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      Alex Hentschel; Determining the Isoluminant Point in Chicks. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3156.

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

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Abstract

Purpose : The isoluminant point is where the visual system perceives a modulating stimulus as changing only in chromatic contrast but not luminance contrast. In humans, the isoluminant point has been measured with ERGs and has been used to study the chromatic responses of the retina. ERG luminance responses have been studied in chicks, however, little is known about the chromatic responses of the chick’s retina and the contribution of the long- (L), middle- (M), and double- (D) cones. In this study we quantified the chick’s isoluminant point electrophysiologically for use in studying the properties of the chick’s chromatic system.

Methods : Full-field photopic flicker ERGs were recorded monocularly from 2-week old, dilated, White Leghorn chicks using a four primary full-field Ganzfeld stimulator (Diagnosys, LLC). First, we established that 36 Hz sinusoidal luminance modulation generated the highest retinal response that corresponds to the peak frequency of the chick’s luminance system. Then, using stimuli comprised of counterphase red (R) and green (G) 36 Hz sinewaves (mean 250 cd/m2) we recorded ERGs to find the ratio of R and G that produced a minimal retinal response (isoluminant point). A range of R/(R+G) ratios were tested from zero, where there is no red modulation and only green modulation, to 1, where there is only red modulation and no green modulation. In a follow up experiment, we silenced the chick’s D-cone using silent substitution, and ERGs were recorded to a 36 Hz sinusoidal stimulus that generated different ratios of L- and M-cone contrasts.

Results : Our results showed that chicks have an isoluminant point at a R/(R+G) ratio of 0.04. In terms of cone contrast, this isoluminant point was achieved with 7% L-cone contrast, 93% M-cone contrast and 40% D-cone contrast. When the D-cone was silenced (0% contrast), the isoluminant point was achieved with an L-cone contrast of 23% and M-cone contrast of 19%.

Conclusions : With an active D-cone, the isoluminant point is strongly influenced by the long-wavelength sensitive photopigment in the D- and L-cone. When the D-cone is silenced, the L- and M-cone contribution to the isoluminant point is more balanced and more similar to that found in humans. Therefore, it appears that the D-cone adds additional long-wavelength bias in the chick’s visual system.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

 

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