PUB - Publikationen an der Universität Bielefeld

As nocturnal animals, stick insects sample near-range information by active tactile exploration using their antennae. A previous study on the use of visual and tactile cues showed that antennectomy in stick insects strongly affects climbing efficiency, whereas blindfolding does not (Dürr et al., 2003, Int.J.Robot.Res., 22:151-167). However, this study used a setup with very low luminance and visual contrast. Since it is known that stick insects reliably orient themselves towards visual landmarks (Kalmus, 1937, Z.vergl.Physiol., 25:494-508), we wondered whether stick insects can exploit visual cues during climbing, provided that visual contrast and luminance were similar to experimental conditions of visual orientation experiments.To test this, we let animals climb an obstacle (height: 24 mm). On the front of the obstacle we placed one of three visual patterns (a horizontal or vertical black bar on white background, or a checkerboard). Stick insects were first tested intact and then grouped into two cohorts: In cohort 1 animals were tested with both antennae cut, then retested after blindfolding. In cohort 2, animals were tested blindfolded first, then with additional antennectomy. For each cohort and test session, we analysed the minimum distance to the obstacle, head orientation, and foot placement. Our expectation was that sighted animals with cut antennae would react similarly to intact animals, and differently from blindfolded, antennectomized animals. Our results proved both expectations wrong in that blindfolding had little or no effect on the parameters observed. We conclude that stick insects make little or no use of visual cues during climbing.