The ocellar component of flight equilibrium control in dragonflies
G Stange - Journal of comparative physiology, 1981 - Springer
Journal of comparative physiology, 1981•Springer
This paper describes the dynamics of light-evoked head reflexes in the dragonfly
Hemicordulia tau under light conditions which were selected to optimally address the ocelli.
1. The responses occur only during flight. 2. Stimulation by a light positioned to address the
median ocellus evokes a head movement around the pitch axis. The threshold is in the order
of 10 7 photons· cm− 2· s− 1. With increasing intensity, the responses become progressively
faster but do not increase in amplitude. 3. Stimulation by lights positioned to address the …
Hemicordulia tau under light conditions which were selected to optimally address the ocelli.
1. The responses occur only during flight. 2. Stimulation by a light positioned to address the
median ocellus evokes a head movement around the pitch axis. The threshold is in the order
of 10 7 photons· cm− 2· s− 1. With increasing intensity, the responses become progressively
faster but do not increase in amplitude. 3. Stimulation by lights positioned to address the …
Summary
This paper describes the dynamics of light-evoked head reflexes in the dragonflyHemicordulia tau under light conditions which were selected to optimally address the ocelli.
- 1. The responses occur only during flight.
- 2. Stimulation by a light positioned to address the median ocellus evokes a head movement around the pitch axis. The threshold is in the order of 107 photons · cm−2 · s−1. With increasing intensity, the responses become progressively faster but do not increase in amplitude.
- 3. Stimulation by lights positioned to address the lateral ocelli evokes head movements around the roll axis with a similar threshold and similar dynamics as in the pitch responses. The responses are strongest when two sources at either side of the animal are switched in alternation.
- 4. No evidence is found for interactions between the lateral and the median inputs.
- 5. During sustained illumination from the median source, the head is tilted towards it indefinitely, and increasing the intensity causes only a small additional change of head position. Decreasing the intensity causes a large movement of the head away from the source, and then the system readapts rapidly and the head returns to the on-position (high pass filtering). If increment pulses are superimposed on a steady background, the magnitude of their effect is a function of both their duration and amplitude.
- 6. If the median source is modulated by a square wave of a frequency above the high pass cut-off, the amplitudes of the responses are proportional to modulation depths and independent of average intensity over 4 log units.
- 7. At intensities below 1011 photons cm−2s−1, the spectral sensitivity has a maximum in the green, exceeding the UV-sensitivity by a factor of 5; at higher intensities the responses become more sensitive to UV than to green (reverse Purkinje shift). It is suggested that the reverse Purkinje shift is a functional adaptation to optimize the detectability of the contrast between sky and ground both in dim light and in direct sunlight.
- 8. The dynamics of the behavioural responses can be largely accounted for by known properties of the neuronal elements of ocellar systems.
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