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Visuomotor operation in transition from object fixation to prey shooting in chameleons

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Abstract

Video-records of the eye and head position of chameleons (two species) in relation to prey targets revealed the following:

  1. 1.

    Foveal fixation is performed monocularly for object identification before chameleons decide to catch the prey.

  2. 2.

    If the chameleon intends to catch the prey, it turns its head towards the prey in preparation for the tongue shoot. While turning its head, the fixating eye does not continue to keep the target fixed foveally. Rather, it adopts a diverging position to the head, the mediosagittal plane of which in the end is target-directed.

  3. 3.

    Ready for tongue shoot, the position of both eyes to the head is definitely adjusted at a fixed diverging angle of 17–19 deg, and this position does not change at all with distance to the target.

  4. 4.

    Chameleons are also able to perform tongue shoots successfully using only one eye (the other being occluded), and they use the same adjustment of prey to eye and eye to head as in the binocular case.

  5. 5.

    Thus, the correct direction of the tongue shoot in chameleons is processed by an extrafoveal retinotopic depiction of the prey image using monocular distance information and a fixed eye in head position.

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References

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Author information

Correspondence to Wolfgang Kirmse.

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Kirmse, W., Kirmse, R. & Milev, E. Visuomotor operation in transition from object fixation to prey shooting in chameleons. Biol. Cybern. 71, 209–214 (1994). https://doi.org/10.1007/BF00202760

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Keywords

  • Head Position
  • Object Identification
  • Distance Information
  • Correct Direction
  • Object Fixation