Development and maintenance of connectivity in the visual system of the frog. I. The effects of eye rotation and visual deprivation

We investigated the influence of stereoscopic vision on the perception of optic flow fields in psychophysical experiments based on the effect of an illusory transformation found by Duffy and Wurtz (1993 Vision Research33 1481 – 1490). Human subjects are not able to determine the centre of an expanding optic flow field correctly if the expansion is transparently superimposed on a unidirectional motion pattern. Its location is rather perceived shifted in the direction of the translational movement. Duffy and Wurtz proposed that this illusory shift is caused by the visual system taking the presented flow pattern as a flow field composed of linear self-motion and an eye rotation. As a consequence, the centre of the expansional movement is determined by compensating for the simulated eye rotation, like determining one's direction of heading (Lappe and Rauschecker, 1994 Vision Research35 1619 – 1631). In our experiments we examined the dependence of the illusory transformation on differences in depth between the superimposed movements. We presented the expansional and translational stimuli with different relative binocular disparities. In the case of zero disparity, we could confirm the results of Duffy and Wurtz. For uncrossed disparities (ie translation behind expansion) we found a small and nonsignificant decrease of the illusory shift. In contrast, there was a strong decrease up to 80% in the case of crossed disparity (ie translation in front of expansion). These findings confirm the assumption that the motion pattern is interpreted as a self-motion flow field: only in the unrealistic case of a large rotational component present in front of an expansion are the superimposed movements interpreted separately by the visual system.

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Eye Movements of the Crab Leptograpsus Variegatus Elicited by Imposed Leg Movements

Journal of Experimental Biology ◽

10.1242/jeb.98.1.151 ◽

1982 ◽

Vol 98 (1) ◽

pp. 151-173

Author(s):

D. VARJÜ ◽

D.C. SANDEMAN

Keyword(s):

Eye Movements ◽

Visual System ◽

Frequency Response ◽

Functional Significance ◽

Horizontal Plane ◽

Vertical Axis ◽

Horizontal Component ◽

Eye Rotation ◽

Freely Moving ◽

Leg Movements

1. The horizontal component of eyestalk movements elicited by moving the legs of blinded crabs is described. 2. The animals' bodies were fixed to a stand and the legs were supported on either a sphere or platform and subjected to movement around the three major axes (yaw, pitch, and roll). Both sinusoidal and stepped movements of the legs were studied. 3. The effect of moving the legs on one side only, homolateral or contralateral to the eyestalk was also studied. 4. The eyestalk excursion elicited by sinusoidal leg excursion around the vertical axis (yaw) is a nearly linear function of the leg excursions over the range of 1–40° peak to peak at 0.1 Hz. The amplification of the system is about 0.4 when the animal's legs are supported on a ball, and 0.8-1.0 when the legs are supported on a platform. 5. The frequency response of the system to yaw is nearly flat for eye excursions of 16° peak to peak, over the range of 0.005-0.1 Hz. 6. The visual system has a powerful braking effect on the eye rotation, when this is generated by the imposed leg movements. 7. Eyestalk responses to yaw can be interpreted to be compensatory in that they stabilize the eyes in space in freely moving animals. 8. Eyestalk movements to pitch and roll are complex. In roll, their horizontal component indicates the presence of considerable rectification in the leg proprioceptor-eye system. 9. The functional significance of the eyestalk movements in the horizontal plane is discussed. Note:

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