Figure Tracking by Flies Is Supported by Parallel Visual Streams

Visual figures may be distinguished based on elementary motion or higher-order non-Fourier features, and flies track both [1]. The canonical elementary motion detector, a compact computation for Fourier motion direction and amplitude, can also encode higher-order signals provided elaborate preprocessing [2-4]. However, the way in which a fly tracks a moving figure containing both elementary and higher-order signals has not been investigated. Using a novel white noise approach, we demonstrate that (1) the composite response to an object containing both elementary motion (EM) and uncorrelated higher-order figure motion (FM) reflects the linear superposition of each component; (2) the EM-driven component is velocity-dependent, whereas the FM component is driven by retinal position; (3) retinotopic variation in EM and FM responses are different from one another; (4) the FM subsystem superimposes saccadic turns upon smooth pursuit; and (5) the two systems in combination are necessary and sufficient to predict the full range of figure tracking behaviors, including those that generate no EM cues at all [1]. This analysis requires an extension of the model that fly motion vision is based on simple elementary motion detectors [5] and provides a novel method to characterize the subsystems responsible for the pursuit of visual figures.