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Open loop optokinetic responses of the turtle

M Ariel1

  • 1Department of Anatomy and Neurobiology, St. Louis University School of Medicine, MO 63104, USA. ariel@slu.edu

Vision Research
|April 1, 1997
PubMed
Summary

Turtles exhibit limited optokinetic reflex gains at low speeds, differing from mammals. This study electronically opened the optokinetic reflex loop to analyze turtle eye movements.

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Area of Science:

  • Neuroscience
  • Comparative Physiology
  • Vision Science

Background:

  • The optokinetic reflex (OKR) stabilizes gaze during head movements.
  • Understanding the OKR in non-mammalian vertebrates like turtles provides insights into visual system evolution.

Purpose of the Study:

  • To investigate turtle eye movements during horizontal optokinetic stimulation.
  • To characterize the open-loop gain and speed range of the turtle's OKR.

Main Methods:

  • Measured turtle eye movements under closed-loop and open-loop conditions.
  • Electronically opened the optokinetic reflex loop by canceling eye movement effects.
  • Utilized full-field horizontal optokinetic stimulation.

Main Results:

  • The highest open-loop gains (2-3) were observed at low stimulus speeds (< 1 deg/sec).
  • Turtles demonstrated a more limited speed range and lower gain compared to mammalian OKR.
  • Results correlate with in vitro recordings of the turtle's pretectum and accessory optic system.

Conclusions:

  • The turtle's optokinetic system has a restricted speed range and lower gain than mammals.
  • These findings are consistent with the known visual processing capabilities of the turtle's brainstem pathways.
Keywords:
Non-programmatic

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