Independent and conjugate eye movements during optokinesis in teleost fish
Kerstin A. Fritsches* and
N. Justin Marshall
Vision, Touch and Hearing Research Centre, Department of Physiology
and Pharmacology, University of Queensland, Brisbane, Queensland, 4072,
Australia
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Fig. 1. (A) Photograph of the experimental set-up using the half-field stimulus
drum. Two of these semicircular constructions are placed around a circular
observation tank, covering 360° of the animal's horizontal and 55° of
its vertical visual fields. The video monitor displays a field of view of 3 mm
and in the photograph shows the eyes and head of a sandlance. (B) Illustration
of one semicircular construction. (C) Diagram to illustrate the position of
the fish relative to the two semicircular parts of the drum. Each half-circle
is powered by a separate power supply, allowing independent variations in
stimulus speed and direction.
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Fig. 2. (A) Tracing of eye movements using `Object Image'. The horizontal eye
position was measured as an angle from the centre of the pupil to the
anterior—posterior axis. (B—D) Dorsal viewing angle of the three
species of fish used in this study: the sandlance (B), the pipefish (C) and
the butterflyfish (D). In all images the animals' nose points towards the top
of the photograph. Scale bars, 2.5 mm.
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Fig. 3. Normal optokinetic response to a whole-field stimulus, displayed as
horizontal eye position (degrees) over time (s). (A) Butterflyfish, (B)
pipefish, (C) sandlance. The stimulus speed varied from 25 to 35°
s-1 between animals and the speed and direction of the stimulus are
indicated by the grey lines. Note the regular and conjugate response in the
butterflyfish while the sandlance shows asynchronous fast phases. In the
pipefish, some linked fast phases can be seen, although the amplitude of the
movement in each eye is mostly different.
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Fig. 4. Optokinetic response to split optokinesis in the temporo-nasal direction
for both eyes with a stimulus speed of 15° s-1 for the left eye
and 5° s-1 for the right eye. Otherwise the conventions are the
same as in Fig. 3. The
butterflyfish (A) does not show a fully developed optokinetic nystagmus in
both eyes; however, some compensatory strategies can be observed. Left:
converging eye movements following the respective stimulus can be observed in
both eyes and independent saccades are shown (example at 5 s). Right: both
eyes move in the same rotational direction (i.e. to the left or the right of
the fish), however, while one eye shows a smooth slow phase in the stimulus
direction, the other eye makes several fast phase movements (1-1.5 s; 2.5-4
s), dissociating slow and fast phases between the two eyes. Pipefish (B) and
sandlances (C) both respond independently to the different stimuli to each
eye.
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Fig. 6. Optokinetic response to split optokinesis in the naso-temporal direction
for both eyes, stimulus speed 15 ° s-1 for the left eye and 5
° s-1 for the right eye. (A) The butterflyfish shows no
response to the stimulus, apart from a potential small following movement in
the left eye (1-3 s). Instead, the eye movements are normal spontaneous ones.
(B,C) Both pipefish and sandlances show independent slow and fast phase
movements to naso-temporal stimulation. In these animals the response to the
slower drum speed (right eye) was not as strong as during temporo-nasal
stimulation.
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Fig. 7. Monocular optokinetic stimulation to the left eye (at 15 °
s-1) while the right eye receives visual input in the form of a
stationary grating. The butterflyfish (A) shows conjugent optokinesis in both
eyes, whereas in both the pipefish (B) and the sandlance (C) the eyes are
unlinked and only the stimulated eye shows a slow phase in the stimulus
direction. However in the pipefish, the eyes are approximately correlated in
the direction in which they are moving, as seen during spontaneous eye
movements.
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Fig. 8. Monocular stimulation to the right eye while the left eye is occluded. The
response in both the butterflyfish (A) and the pipefish (B) is linked, whereas
in the sandlance (C) only the stimulated eye shows optokinesis. Note that in
the pipefish only the slow phase is clearly linked while the fast phase is
frequently asynchronous between eyes.
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Fig. 5. Comparison of eye speeds at stimulus speeds of 5 ° s-1 and
15 ° s-1 during normal optokinesis (white square;
temporo-nasal, TN, direction) and split optokinesis, during which each eye
responds to a different stimulus speed (black square; both eyes are stimulated
in TN direction). Pipefish (left) and sandlances (right) show the appropriate
eye speed to the respective stimulus speeds, suggesting that the slow-phase
response in each eye is independent of that of the other eye.
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© The Company of Biologists Ltd 2002
