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Related Experiment Videos

Psychophysically derived visual mechanisms in turtle. II--Spatial properties.

D F Sisson1, A M Granda

  • 1School of Life and Health Sciences, University of Delaware, Newark 19716.

Vision Research
|January 1, 1989
PubMed
Summary
This summary is machine-generated.

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Refractive state, contrast sensitivity, and resolution in the freshwater turtle, Pseudemys scripta elegans, determined by tectal visual-evoked potentials.

Visual neuroscience·1991

This study reveals that turtle vision relies on red and green light-sensitive cones. Under low light, rods pool signals, while cones require individual photon detection for vision.

Area of Science:

  • Comparative physiology
  • Vision science
  • Retinal mechanisms

Background:

  • Understanding visual perception in reptiles provides insights into vertebrate evolution.
  • Investigating photoreceptor function under varying light conditions is crucial for visual ecology.

Purpose of the Study:

  • To determine the peak wavelength sensitivities of visual mechanisms in Pseudemys turtles.
  • To measure Ricco's critical areas under different light adaptation states (dark, moderate, intense).
  • To elucidate the roles of rods and cones in visual thresholds under varying luminance.

Main Methods:

  • Utilized Stiles' two-color threshold technique to isolate visual mechanisms.
  • Measured Ricco's critical spatial summation areas for red (650 nm) and green (540 nm) light.

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  • Assessed visual thresholds across dark-adapted, moderately light-adapted, and intensely light-adapted states.

    • Main Results:

    • Peak sensitivities were identified at 650 nm (red) and 540 nm (green).
    • Critical spatial areas decreased with increasing light adaptation.
    • In dark adaptation, one photon per 12 rods sufficed for green threshold, and one photon per four red-sensitive cones for red threshold, indicating rod pooling.
    • In light adaptation, rods were non-functional; cones required approximately one photon per receptor, showing minimal pooling.

    Conclusions:

    • Pseudemys turtles possess distinct red and green sensitive cone mechanisms.
    • Rods exhibit significant spatial summation (pooling) in low light, while cones demonstrate limited summation, requiring near-single photon detection at threshold.
    • Light adaptation drastically alters the contribution and summation properties of photoreceptor types in Pseudemys vision.