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Repetitive elicitation of startle-like responses by electrical stimulation of the cochlear nucleus led to sensitization followed by habituation. In contrast, repetitive elicitation of startle-like responses by electrical stimulation of the reticular formation led only to sensitization. Since these different locations represent different points along the acoustic startle circuit, the data suggest that sensitization may be related to the motor side of reflex arcs, whereas habituation may be related to the sensory side.

Modeling of the flight dynamics of unmanned aerial vehicles (UAVs) poses unique challenges that are not present with manned aircraft. The use of analytical modeling methods based on first principles is often difficult for UAVs because of short design cycles, reduced development costs, and many unconventional designs. Also, without the need to carry a pilot, UAVs are often much smaller and lighter than manned aircraft. The lower weights and inertias result in higher natural frequencies and quicker vehicle responses requiring high bandwidth dynamics models. Frequency-domain system identification is especially well suited to the modeling of UAVs. With the availability of flight hardware early in many UAV programs, dynamic response models of the vehicle can be identified and validated rapidly with flight data. The system identification method also allows for rapid updating of vehicle response models as physical changes are made to the vehicle configuration. The use of frequency-domain system identification in the development and operation of a number of UAV programs is discussed. The example aircraft programs include Northrop Grumman's Fire Scout vertical takeoff unmanned air vehicle demonstrator based on the Schweizer 300 helicopter; the broad-area unmanned responsive resupply operations UAV based on Kámán's twin-rotor K-MAX helicopter; AeroVironment's Pathfinder solar-powered stratospheric research aircraft; Yamaha's R-50 small-scale helicopter; and the class of small-scale ducted fan vehicles developed separately by Allied Aerospace (formerly Micro Craft) and Honeywell.Nomenclature F = state matrix G = control matrix H = output state matrix J = output control matrix L = length, body roll moment M = body pitch moment M = descriptor state matrix N = scale ratio, body yaw moment P, Q, R, p, q, r = body angular rates u, v, w = vehicle body velocities u = control vector x = state vector y = output state y = output vector Z = body vertical force δ col = collective stick δ lat = lateral stick δ lon = longitudinal stick δ ped = pedal control input τ = time delay