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Updated: May 10, 2026
04:43
Visualizing Visual Adaptation
Published on: April 24, 2017
What has driven the evolution of multiple cone classes in visual systems: object contrast enhancement or light
Shai Sabbah1, Craig W Hawryshyn
1Department of Biology, Queen's University, Kingston, Ontario K7L 3N6, Canada. shai_sabbah@brown.edu
BMC Biology
|July 6, 2013
Summary
The contrast theory, not the flicker theory, best explains how multiple cone classes evolved in fish eyes to maximize visual contrast against varied backgrounds, challenging previous assumptions.
Area of Science:
- Vision Science
- Evolutionary Biology
- Comparative Physiology
Background:
- Two theories explain the evolution of multiple cone classes in vertebrate eyes: the contrast theory and the flicker theory.
- The contrast theory posits evolution for maximizing object contrast against diverse backgrounds.
- The flicker theory suggests evolution to eliminate shallow-water light flicker for enhanced object detection.
Purpose of the Study:
- To investigate the selective pressures driving the evolution of multiple cone classes in vertebrate eyes.
- To test the validity of the flicker theory's assumptions regarding flicker cancellation and object detection.
- To compare the predictive power of the contrast and flicker theories for visual system tuning.
Main Methods:
- Analysis of flicker amplitude and temporal frequency across the visible spectrum.
- Assessment of flicker temporal frequency in relation to fish visual sensitivity.
- Modeling of chromatic contrast between fish patterns and backgrounds under flickering illumination.
Main Results:
- Flicker characteristics vary spectrally, precluding simple cancellation by cone output antagonism.
- Flicker temporal frequency aligns with maximal visual sensitivity in many fish, suggesting a role in detection.
- Cone spectral sensitivity in a cichlid species is tuned to maximize chromatic contrast, not eliminate flicker.
Conclusions:
- The flicker theory's core assumptions are violated, significantly weakening its support.
- Findings indicate that the contrast theory provides a more parsimonious explanation for the evolution of multiple cone classes.
- The visual system of the studied cichlid is optimally tuned for contrast, supporting the contrast theory over the flicker theory.
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