Figure 1.
Swimming traces of wt and bel rev larvae in a 22-mm-diameter dish exposed to a projected still grating (spatial frequency = 0.06 cycles/deg, contrast = 100%).
A, wt swims in random direction or stays still near the dish edge (recording duration = 236 s). B, bel rev displays the characteristic looping behavior (recording duration = 55 s).
Figure 2.
Contrast and visual input dependence of looping.
The panels show the swimming traces of a single bel rev larva in a 22-mm-diameter dish across 12 subsequent (from a to l) visual stimulus conditions (each panel corresponds to one condition with 60 s recording duration). A, Only few circles were observed when bel rev was exposed to a projected gray uniform background (minimal contrast, gray-black bar). A projected black and white grating consistently evoked strong looping (maximum contrast, black-and-white bar). Swimming activity almost completely ceased in the absence of light (darkness, black bar). B, Quantitative analysis of looping in bel rev (N = 7). Overall, the number of circles per minute differed across conditions, F(2,12) = 57.55, p<0.0001. Looping was much more pronounced at maximum contrast compared to minimal contrast, t(6) = 7.89, p = 0.0002, and darkness, t(6) = 8.13, p = 0.0002. The rate of looping was similar at minimal contrast and in darkness, t(6) = 2.13, p = 0.0767. ns, non significant. ***, significant at p<0.001.
Figure 3.
Eye movements before and during looping.
A, When presented a stationary stimulus, bel rev always showed several instances of congenital nystagmus prior to the onset of looping. B, C, The larva began to loop in the same direction as the preceding eye movements. D, During looping, the eyes stopped moving, assuming a peripheral position toward the looping direction.
Figure 4.
Schematic view of the visual-postural control system.
The perceived retinal slip velocity (vr) is the main afference input signal to the optokinetic response and the postural control system. vr is physically determined by stimulus velocity (vs), head/body movement (vp), and eye velocity (ve). A non-zero retinal slip velocity serves as the error signal for the optokinetic and the postural feedback loop, evoking either eye movement (Δve) and/or postural adjustment (Δvp) in order to compensate the error signal. Eye movements are additionally influenced by the vestibulo-ocular system that triggers eye movement in opposite direction of head/body movement. In addition to the afference signal, the postural control system also receives input from eye movement-related signals (efference copy and reafference signal from the eye muscle). Hence, the stability of the body in space and the visual world on the retina is accomplished through the interplay of both an afference-based feedback system and an eye movement-related feedforward mechanism.