Responses of high-frequency movement detector neurons in dragonfly larvae to motion of single objects

Neurons of the class described respond by a discharge with a frequency of 150–250/sec to motion of single objects in a large receptive field. The response depends directly on the size of the object. The neurons are selectively sensitive to motion of dark objects. Widening a dark border (bringing a black disc closer) evokes a stronger response than narrowing a dark border (moving a white disc further away). The response to uniform movement consists of high-frequency volleys of discharges separated by pauses. Repeated movements along the same trajectory induce habituation; after cessation of the movements sensitivity is restored with a time constant of about 30 sec. The role of lateral inhibition and local habituation in the identification of the specific features of optical stimuli is discussed.