Meeting Abstract
Insects exhibit robust goal-tracking behavior in a range of environmental conditions. In the presence of redundant, parallel sensory information, how does multimodal integration depend on environmental conditions, such as light-level? Manduca sexta (tobacco hawk moths) hover-feed under conditions ranging from moonlit nights (0.3 lux) to early twilight (300 lux). From earlier work on hover-feeding hawk moths at 0.3 lux, we know that mechanical and visual cues sum linearly in tracking, but mechanosensory gain is higher for slow movements and visual gain is higher for fast movements, an example of bandwidth separation. Visual processing delays depend on light level. Whether this bandwidth separation and linear integration remain true under high illuminance, or changes to accommodate the more salient visual inputs, was unknown. Hence, we studied hover-feeding behavior of Manduca sexta under high illuminance conditions (300 lux). Mechanical cues (to the proboscis) and visual cues (to the eyes) were provided, together and in conflict, using a two-part robotic flower. Frequency-domain system identification analysis showed that the high visual gain shifts the frequency crossover point between mechanical and visual modalities to lower frequencies. Nonetheless, the linear sum of the two conflict-responses matches the response to coherent flower motion. Hence, linearity is conserved irrespective of illuminance level, and the internal gain of visual cues is enhanced in the presence of a more salient visual environment. Parallel sensory inputs are modulated to achieve performance requirements, while maintaining linearity of the resulting behavior. This suggests that the underlying neural circuits are flexible, accommodating variable delays and sensitivity as light level changes, and robust in their integration.
