Steering Correction Research Articles

Octopaminergic Innervation and Modulation of a Locust Flight Steering Muscle

We demonstrate that the meso- and metathoracic pleuroaxillary flight steering muscle (M85 mesothorax, M114 metathorax) of the migratory locust are each innervated by a single dorsal unpaired median neurone (DUM3,4,5a). The soma of this neurone can be localized by retrograde staining of the motor nerve with Neurobiotin, but not with cobalt salts. The primary neurite projects in the superficial DUM cell tract, and the axons run in nerve roots 3, 4 and 5 and in all their secondary branches. Other muscle targets include the second tergal remotor coxa (M120) and the posterior rotator coxae (M122, M123, M124), but not the first tergal remotor coxa (M119) and subalar (M129) flight muscles. Octopamine-like immunoreactive varicosities occur on the pleuroaxillary muscles. Stimulation of DUM3,4,5a and octopamine (10(-6) mol l-1) superfusion increased the amplitude and the relaxation velocity of neurally evoked twitch contractions of this muscle. Octopamine also significantly reduced the tonic tension that this muscle develops when stimulated at flight frequency (20 Hz), while increasing the amplitude of each phasic twitch. A catch-like tension is also reduced in the presence of octopamine. Simulations of the motor pattern experienced by the pleuroaxillary muscles during roll manoeuvres suggest that transient changes in tension underlying corrective steering could be doubled in the presence of octopamine.

A new approach to robust beamforming in the presence of steering vector errors

This correspondence presents a new approach to array beamforming in the presence of steering vector errors, such as steering angle and carrier frequency errors. The basic idea is based on the principle that the output power of an optimized beamformer achieves a local maximum if the steering vector coincides with that of the desired signal. The proposed approach iteratively searches for the correct steering vector by maximizing the array mean output power using a first-order Taylor series approximation of the steering vector in terms of the steering errors. This method has the advantages of easy implementation and suffers no loss in the degrees of freedom for interference rejection. Furthermore, the method is independent of the choice of the phase center coordinate origin contrary to derivative constraint methods. Conditions for the existence of a solution using the proposed method are also established. >

Intersegmental coordination of flight steering in locusts

Correctional steering during flight involves the neuromuscular apparatus of nine segments and some 10% of the extracerebral CNS. Steering is initiated and coordinated intersegmentally by pleurisegmental sensory interneurons that report course deviation. These traverse the participating ganglia and contact a similar post-synaptic circuitry in each segment. The musculature and motor neurons involved are segmentally homologous, and so probably are the local circuits producing the different behaviours. In these circuits, exteroceptive sensory information sums with tonic or rhythmic drive from the flight motor. This summation is responsible for the context specificity of behaviour, and for recruitment, phase shifting within the wing-beat cycle and other motor effects.

Locust flight steering

Locusts, Locusta migratoria, flying under closed-loop conditions in a flight simulator, control the stability of their visual environment by means of correctional steering and so minimize retinal slip (the optomotor reaction). Correctional steering includes modulation of the wingbeat, ruddering with abdomen and legs and compensatory head movements. Pulsed ultrasounds that simulate bat echolocation signals elicit avoidance steering in flying locusts: ruddering and yaw torque are directed away from the sound source. In this article the two modes of steering are compared and their interaction is studied. 1. In both correctional and avoidance steering ruddering is directed to the side of the turn. However, during correctional manoeuvres, head movements are also directed to the side of the turn, while during avoidance steering the head moves in the direction opposite to that of the turn (Fig. 4). 2. The components and temporal organization of both sorts of steering are similar. Head movements occur some 30–40 ms after torque production begins (Fig. 5). Thus, neither correctional nor avoidance steering is initiated by head movements. 3. Under closed-loop conditions, avoidance steering generates pronounced rotation of the panorama (Figs. 6, 7) that is not counteracted by the compensatory optomotor reflex. 4. Acoustically elicited head turns are also performed in darkness (Fig. 4a), and irrespective of the sign of the visual reafference (Fig. 9), which indicates that they are temporarily independent of visual information. A mechanism is proposed in which optomotor interference is prevented by an inhibitory corollary discharge of acoustic origin. 5. Locusts prevented from moving their heads still perform avoidance turns (Fig. 8), but these are of shorter duration than when the head is free. 6. The role of head movements in steering is discussed. It is proposed that neck proprioception assists visual and acoustic information in adaptive flight steering. Head movements in closed-loop corrective steering reduce steering overshoot; during avoidance steering opposite head movements may in turn favor steering overshoot.

Intracellular Recordings From Intact Locusts Flying Under Closed-Loop Visual Conditions

ABSTRACT The flight path of locusts is under permanent visual and mechanoreceptive control (the latter evaluates changes in wind direction). Involuntary course deviations are compensated immediately by a neuronal feedback system or ‘autopilot’, which induces corrective steering movements of the wings, abdomen and legs and which are generally accompanied by compensatory head movements (Taylor, 1981; Hensler and Robert, 1990). During apparently straight flight the flight path is not perfectly straight, but instead the insect oscillates slightly along a mean course (Robert, 1988; Hensler and Robert, 1990).

Time-of-day effects of alcohol intake on simulated driving performance in women

There is a circadian propensity for sleepiness in the early afternoon (contrasting with an alertness peak early evening) which potentiates the sedating effects of alcohol. However, little research has been done to examine these effects on driving performance. Four units of alcohol (95 ml of 40% spirit) or placebo were given double blind, with a snack to two groups ('early afternoon' and 'early evening') of 12 young women, at either 1310 h or 1810 h. Blood alcohol levels (BACs) were estimated by breathalyser. BACs were within the UK legal driving maximum. Subjects underwent 40 min of monotonous motorway driving in a car simulator. Self-ratings on sleepiness and alcohol effects showed a significantly greater impact of alcohol in the early afternoon relative to the early evening. Whilst neither time of day nor alcohol affected lateral corrective steering movements, alcohol significantly increased the average following-distance and the variability in this distance, especially during the early afternoon. In some subjects from the early afternoon group, this impairment seemed to be to dangerous levels following alcohol.

Mesothoracic interneurons involved in flight steering in the locust

1. 1. Twenty-eight interneurons with somata in the mesothoracic ganglion of the locust Locusta appear to be involved in steering in flight. All have their arborizations in the dorsal (flight) neuropil. All make directionally selective responses to visual, ocellar or wind stimuli corresponding to simulated deviations from course in flight. All are directly and/or indirectly postsynaptic to one or more sensory descending neurons (DNs) of the brain, which have been shown to produce steering behaviour when electrically stimulated. Convergence of DNs leads to complex responses by the interneurons. Some receive a variety of additional sensory information derived from thoracic receptors, especially wing proprioceptors and the ear. 2. 2. The membrane potentials of all these interneurons are modulated at flight frequency during fictive flight in deafferented preparations. Nineteen are depolarised in depressor phase (and/ or hyperpolarised in elevator phase); nine are depolarised in elevator phase (and/or hyperpolarised in depressor phase). The modulation derives in at least one case (neuron 016), and presumably in all, from synaptic drive from oscillator or oscillator-follower interneurons. None of the described cells, with the possible exception of IN 313, is thought to be part of the oscillator itself. 3. 3. The 28 ‘steering interneurons’ are characterised and named. Five (016, 035, 036, 302, 313) have been previously described in other contexts. Of these, the first 3 have been renamed; they were previously 116, 135 and 136 of Rowell and Pearson (1983). Four other previously named units are synonomized: 318 of Rowell and Pearson (1983) becomes 302 of Robertson and Pearson (1983), and 120 and 119 of Rowell and Pearson (1983), and 1AA of Elson (1987), all become 016. Two new modifications of the numbering system for locust interneurons are introduced. 4. 4. Five steering neurons are known to make monosynaptic, excitatory or inhibitory connections with flight motor neurons. Individual steering interneurons contribute between 25% and 10% of the total oscillatory drive to individual FMNs. 5. 5. The population of steering interneurons is the site of convergence of oscillator drive and sensory input prior to reaching the motor neuron: this allows sensory modulation of the strength and timing of drive to the individual motor neuron in the appropriate phase of the wing beat cycle, which is required for corrective steering. They are also a point at which the motor drive to the motor neuron is modified by proprioceptive reafference.

Development of a 10-meter wedged-pole undulator

A permanent magnet hybrid undulator of 10-m length is under construction at Spectra Technology, Inc. for use in free electron laser experiments at the Boeing Aerospace Company. The undulator system includes a remotely-adjustable compound taper as needed to explore simultaneous achievement of high extraction and high optical gain in the 1 μm wavelength range. Notable improvements relative to the earlier tapered hybrid undulator (THUNDER) include the use of wedged poles for higher field strength and a magnetically seamless structure which accommodates frequent two-plane steering correction without drift spaces. An important development is the finding that magnetic field errors can be substantially reduced using thin iron shims attached to the permanent magnets.

Descending Interneurones of the Locust Reporting Deviation from Flight Course: What is their role in Steering

ABSTRACT Some descending intemeurones (DNs) in insects encode deviation from flight course. Intracellular recording reveals their inputs (from eyes, wind hairs, proprioceptive information from the neck and in some cases ocelli). Intracellular stimulation during flight reveals their motor effects. All components of steering (modification of wing stroke, ruddering with the hind legs, ruddering with the abdomen and head rotation) can be initiated by single DNs. Steering in flight involves the concerted action of at least 10 pairs of DNs synapsing with motor neurones and premotor intemeurones. The whole system forms an autopilot, well suited for corrective steering. It is modulated principally by head movements, which have both optical and proprioceptive effects: compensatory head move-ments increase the accuracy of correctional steering by reducing overshoot, and disable the autopilot during turns evoked by directional pulsed ultrasound for purposes of bat-evasion. DNs responding specifically to visual flow fields are also known, but appear to be related to control of velocity rather than to steering.

Mechanisms of flight steering in locusts

Steering in flight by locusts provides a well-studied example of the modulation of a rhythmic motor output by unpredictable inputs from outside to produce adaptive behaviour, in this case a form of locomotion. The simplest form, correctional steering, allows the animal to compensate for unintentional deviations from course. Its mechanisms are relatively well understood. The central nervous circuitry which makes this behaviour possible can be thought of as an autopilot. The entire process, from sensory input to the aerodynamic effects of changed motor outputs, is here reviewed. Intentional change of course, either spontaneous or induced by a change in the outside world, is more complex: it demands not only active steering, but also the temporary disablement of the autopilot. The mechanisms by which this could be achieved are discussed.

Visual steering under closed-loop conditions by flying locusts: flexibility of optomotor response and mechanisms of correctional steering

1. Tethered locusts,Locusta migratoria, flying in a laminar air flow react to motion of the visual world with compensatory steering. 2. Vertical gratings surrounding the animal and rotating around the yaw axis elicit an optomotor yaw response. At the low light level used, gratings of spatial periods (λ) below 10° or of contrast frequency (CF) above 15 Hz are less effective. 3. In a flight simulator which converts torque into angular velocity of the vertical grating, the locust can control the motion of its visual surroundings. When the negative feedback loop is closed, locusts stabilize a vertical grating by modulation of their yaw torque. This indicates that the correctional steering behaviour described under open loop conditions is functionally relevant. 4. Under the same conditions, the optomotor reactions lead to the stabilization of a single vertical stripe in the frontal visual area (fixation). 5. With positive feedback (i.e. the pattern turns in the same direction as the torque), no corresponding inversion of steering is observed, and stabilization around the yaw axis fails. 6. Under similar negative feedback conditions, locusts stabilize the position of the visual horizon around the roll axis by modulating their roll torque. Positive feedback leads, however, to the stabilization of the horizon in the inverted position (reverse albedo). 7. The results suggest the existence of two steering strategies, one based on the parameters of visual movement and the other on position in the visual field and relative luminance. The use of these strategies is discussed.

Integration of nonphaselocked exteroceptive information in the control of rhythmic flight in the locust.

The integration of exteroceptive information in the flight control system of the locust was studied by determining the cellular basis of ocellar- (simple eye) mediated control of flight. Neural interactions that transform phase-independent sensory input into phase-specific motor output were characterized. Ocellar information about course deviations during flight was conveyed to the segmental thoracic ganglia by three pairs of large fast multimodal descending neurons. These made connections with thoracic motoneurons directly, via short-latency mono-or disynaptic pathways, and indirectly, via a population of intercalated thoracic interneurons. The synaptic potentials caused in the motoneurons by the direct pathway occurred at short latency and were adequate for summation with other types of sensory input. However, the strength of the synaptic effects of this pathway was weak compared with the central flight oscillator drive to the same motoneurons. In contrast, synaptic potentials evoked by the descending neurons in the thoracic interneurons were often large and brought these cells close to threshold. In turn, these interneurons always had stronger synaptic effects on postsynaptic flight motoneurons than did the descending neurons alone. We conclude that the indirect interneuronal pathway is more powerful in its effects on motoneurons than the direct pathway. Premotor thoracic interneurons, which received ocellar input appropriate for a role in correctional steering, were also rhythmically modulated during flight motor activity in phase with either depressor or elevator motoneurons. This phasic modulatory drive occurred in deafferented preparations, indicating that its source is the central oscillator for flight. Presentation of ocellar stimulation during flight motor activity showed that the central oscillatory modulation of the thoracic interneurons gated the transmission of sensory information through these interneurons. Ocellar-mediated postsynaptic potentials influenced the firing of thoracic interneurons only if they arrived during the proper phase of rhythmic drive. Thus the transmission of ocellar information from interneuron to motor neuron is possible only during appropriate phases of the flight cycle.

A Vehicle Guidance Controller

ABSTRACT A microcomputer-based vehicle guidance controller used to control a tractor in the field is discussed. The microcomputer detects positional errors using signals from an antenna mounted on the tractor, determines the correct steering action, and steers the tractor using the hydraulic steering system of the tractor. The performance was evaluated by measuring the steering response to various paths negotiated at different speeds. The data were analyzed statistically and the performance of the two steering algorithms tested was compared. Results indicated that the steering accuracy was satisfactory for most field operations. Ninety-five percent of the microcomputer's time is available to perform functions other than guidance.

Automatic Tuning of the LBL Bevalac Transfer Line

Automatic tuning of a beam transport line has been accomplished successfully with the Bevalac control computer. Both steering and focusing corrections are made. New magnet currents are computed from equations governing beam optics in a real-time simulation of the beam line. This approach requires iteration although it converges quite rapidly. Computer automatic tuning is comparable to the most time efficient manual tuning operation.

Diver navigation system

An underwater navigation device wherein a flux gate compass provides head difference signals, a doppler navigation sonar provides drift angle signals, which signals are combined by a summer to provide steering correction signals that are displayed by a steering null meter.

Errors in time delay measurements

Simple delay and sum of sensors in a seismic array is an effective method for noise suppression. However, unless we have precise steering delays, much of the signal energy is lost during the beam forming process too. We have investigated possible error sources in time delay measurements, using a computerized cross-correlation procedure. Parameters perturbed are correlation window length and positioning, signal frequency content and signal to noise ratio (SNR). Our results indicate that relative low frequency waves and using the very first part of theP-signals give the most reliable and stable time delay values. High frequency bandpass filtering improves SNR, but signal correlation and the precision in beam steering corrections decrease. Significant loss of high frequency energy during beamforming seems to be unavoidable.