Interaction of substrate, gravity and visual cues in the control of compensatory eye responses in the spiny lobster,Palinurus vulgaris

Summary

• 1. The compensatory eyestalk movements ofPalinurus vulgaris have been measured in response to oscillations of the body, substrate and patterned visual surround about a body-parallel horizontal axis. The stimuli were delivered alone, and in fourteen different combinations (Fig. 2).

• 2. Responses are greatest (amplitude gain ca. 1.5) when the mechanical inputs, substrate and gravity, are combined synergistically (Fig. 3 a). The effect of the optokinetic stimulus is gain-limiting (Fig. 3b, c).

• 3. When analysed over a wide frequency range (0.001–0.4 Hz), substrate and optokinetic drum movements result in quite different response curves (Figs. 4a, c), combinations of these stimuli produce responses at an intermediate level when synergistic (Fig. 4b), but at a low level when antagonistic (Fig. 4d).

• 4. Turning the animal inside a stationary optokinetic drum, to produce synergistic action of vision and statocyst input, improves the compensatory response (Fig. 5: P8).

• 5. The threefold stimulus combination which simulates an external disturbance (condition 3, Fig. 2) elicits eye responses which are exactly compensatory at all frequencies tested (Fig. 6).

• 6. When the visual surround is devoid of pattern (but presents a gradient of light intensity, centred above) the eye response to substrate movement is attenuated (Fig. 7), whereas the gravity response is enhanced (Fig. 8).

• 7. Timing relationships display consistent phase advances with decreasing frequency (Fig. 9, Fig. 10).

• 8. These results are discussed in terms of the gain-limiting properties of the optokinetic system, and the action of a visual factor responsive to the vectorial component of the stimulating light.