File:Stages of motion processing.jpg

Major processing steps of visual motion computation in insects. (A) Schematic of the visual motion pathway. Images of the moving environment are projected on the array of photoreceptors. The retinal input is spatially and temporally filtered before signals originating from neighboring points in visual space interact with each other. These interactions lead to local motion measurements. The outputs of many retinotopically organized local movement detectors are spatially pooled by LPTCs. (B) Local motion detector in its simplest form. It consists of two mirror-symmetrical subunits and receives input from neighboring points in visual space. In each subunit one of the inputs is delayed (tau), before it interacts with the undelayed signal of the neighboring input channel. A multiplication-like interaction (M) is the lowest order nonlinearity that is sufficient to explain many aspects of motion detection in insects. The subunit outputs contribute to the response of LPTCs with opposite polarity. (C) One of the LPTCs, a so-called FD1-cell, in the third visual neuropile of the blowfly filled with the fluorescent dye Lucifer yellow and visualized in a whole-mount preparation.