Elegant‐crested Tinamous Eudromia elegans do not synchronize head and leg movements during head‐bobbing

Head‐bobbing is the fore–aft movement of the head relative to the body during terrestrial locomotion in birds. It is considered to be a behaviour that helps to stabilize images on the retina during locomotion, yet some studies have suggested biomechanical links between the movements of the head and legs. This study analysed terrestrial locomotion and head‐bobbing in the Elegant‐crested Tinamou Eudromia elegans at a range of speeds by synchronously recording high‐speed video and ground reaction forces in a laboratory setting. The results indicate that the timing of head and leg movements are dissociated from one another. Nonetheless, head and neck movements do affect stance duration, ground reaction forces and body pitch and, as a result, the movement of the centre of mass in head‐bobbing birds. This study does not support the hypothesis that head‐bobbing is itself constrained by terrestrial locomotion. Instead, it suggests that visual cues are the primary trigger for head‐bobbing in birds, and locomotion is, in turn, constrained by a need for image stabilization and depth perception.     

Function of head-bobbing behavior in diving little grebes

Most birds show a characteristic head movement that consists of head stabilization and quick displacement. In this movement, which is analogous to saccadic eye movement in mammals, head stabilization plays an important role in stabilizing the retinal image. This head movement, called “head bobbing”, is particularly pronounced during walking. Previous studies focusing on anatomical and behavioral features have pointed out that visual information is also important for diving birds, indicating its significance in the head movements of diving birds. In the present study, the kinematic and behavioral features of head bobbing in diving little grebes were described by motion analysis to identify the head movement in diving birds. The results showed that head-bobbing stroke (HBS) consisted of a thrust phase and a hold phase as is typical for head bobbing during walking birds. This suggests that HBS is related to visual stabilization under water. In HBS, grebes tended to dive with longer stroke length and smaller stroke frequency than in non-bobbing stroke. This suggests that the behavior, which is related to vision, affects the kinematic stroke parameters. This clarification of underwater head movement will help in our understanding not only of vision, but also of the kinematic strategy of diving birds.     

Timing of secondary vestibular neuron responses to a range of rotational head movements

Secondary vestibular neurons exhibit a wide variety of responses to a head movement, with the response of each secondary neuron depending upon the particular primary afferents converging onto it. A single head movement is thereby registered in a distributed manner. This paper focuses on implications of afferent convergence to the relative timing of secondary neuron response modulation during rotational movements about a combination of horizontal axes. In particular, the neurons of interest are those that receive input from afferents innervating the vertical semicircular canals, and the movements of interest are those that have a sinusoidal component about one vertical canal axis and a sinusoidal component about another, approximately orthogonal, vertical canal axis. Under these conditions, the present research shows that it is possible for two or more secondary neurons to have a different relative timing of response (i.e., different relative phase of the periodic modulation in firing rate) for different head movements, and for the neurons to switch their order of response for different movements. For particular head movements, those same neurons will respond in phase. From the point of view of the nervous system, the relative timing of neuron responses may tell which movement is taking place, but with certain restrictions as discussed in the present paper. Shown here is that, among those head movements for which the two components of rotation may be at any phase relative to one another and have any relative amplitude, an in-phase response of just two neurons cannot identify a single motion. Two neurons that respond in phase for one motion must respond in phase for an entire range of motions; all motions in that range are thus response-equivalent, in the sense that the pair of neurons cannot distinguish between the two motions. On the other hand, an in-phase response of three neurons can identify a single motion, for certain patterns of primary afferent convergence. Received: 16 December 1996 / Accepted in revised form: 3 April 1998     

Head bobbing and the body movement of little egrets (<Emphasis Type="Italic">Egretta garzetta</Emphasis>) during walking

Although previous studies have indicated that head bobbing of birds is an optokinetic movement, head bobbing can also be controlled by some biomechanical constraints when it occurs during walking. In the present study, the head bobbing, center of gravity, and body movements of little egrets (Egretta garzetta) during walking were examined by determination of the position of the center of gravity using carcasses and by motion analysis of video films of wild egrets during walking. The results showed that the hold phase occurs while the center of gravity is over the supporting foot during the single support phase. In addition, the peak speed of neck extension was coincident with the peak speed of the center of gravity. These movements are similar to those of pigeons, and suggest the presence of biomechanical constraints on the pattern of head bobbing and body movements during walking.     

Stepping behavior of two-headed kinesin motors

The stepping behavior of the dimeric kinesin is studied by using our model based on previous biochemical, X-ray crystallography and cryo-electron microscopy studies. It is shown that, when a Pi is released from the trailing head, a forward step is made under a backward load smaller than the stall force; while when a Pi is released from the leading head, no stepping is made under a forward load or no load, and a backward step is made under a backward load. The forward stepping time, i.e., the time from the release of Pi in the trailing head to the binding of the ADP head to next binding site, is much smaller than the dwell time even under the backward load near the stall force. Thus the movement velocity of the kinesin dimer can be considered to be only dependent on ATPase rates of the two heads. The duration of the rising phase, i.e., the actual time taken by the ADP head to transit from the trailing to leading positions, is on the time scale of microseconds under any backward load smaller than the stall force. This is consistent with available experimental results.     

Stepping behavior of two-headed kinesin motors

The stepping behavior of the dimeric kinesin is studied by using our model based on previous biochemical, X-ray crystallography and cryo-electron microscopy studies. It is shown that, when a Pi is released from the trailing head, a forward step is made under a backward load smaller than the stall force; while when a Pi is released from the leading head, no stepping is made under a forward load or no load, and a backward step is made under a backward load. The forward stepping time, i.e., the time from the release of Pi in the trailing head to the binding of the ADP head to next binding site, is much smaller than the dwell time even under the backward load near the stall force. Thus the movement velocity of the kinesin dimer can be considered to be only dependent on ATPase rates of the two heads. The duration of the rising phase, i.e., the actual time taken by the ADP head to transit from the trailing to leading positions, is on the time scale of microseconds under any backward load smaller than the stall force. This is consistent with available experimental results.     

Opioid-Induced Nausea Involves a Vestibular Problem Preventable by Head-Rest

Background and Aims

Opioids are indispensable for pain treatment but may cause serious nausea and vomiting. The mechanism leading to these complications is not clear. We investigated whether an opioid effect on the vestibular system resulting in corrupt head motion sensation is causative and, consequently, whether head-rest prevents nausea.

Methods

Thirty-six healthy men (26.6±4.3 years) received an opioid remifentanil infusion (45 min, 0.15 μg/kg/min). Outcome measures were the vestibulo-ocular reflex (VOR) gain determined by video-head-impulse-testing, and nausea. The first experiment (n = 10) assessed outcome measures at rest and after a series of five 1-Hz forward and backward head-trunk movements during one-time remifentanil administration. The second experiment (n = 10) determined outcome measures on two days in a controlled crossover design: (1) without movement and (2) with a series of five 1-Hz forward and backward head-trunk bends 30 min after remifentanil start. Nausea was psychophysically quantified (scale from 0 to 10). The third controlled crossover experiment (n = 16) assessed nausea (1) without movement and (2) with head movement; isolated head movements consisting of the three axes of rotation (pitch, roll, yaw) were imposed 20 times at a frequency of 1 Hz in a random, unpredictable order of each of the three axes. All movements were applied manually, passively with amplitudes of about ± 45 degrees.

Results

The VOR gain decreased during remifentanil administration (p<0.001), averaging 0.92±0.05 (mean±standard deviation) before, 0.60±0.12 with, and 0.91±0.05 after infusion. The average half-life of VOR recovery was 5.3±2.4 min. 32/36 subjects had no nausea at rest (nausea scale 0.00/0.00 median/interquartile range). Head-trunk and isolated head movement triggered nausea in 64% (p<0.01) with no difference between head-trunk and isolated head movements (nausea scale 4.00/7.25 and 1.00/4.5, respectively).

Conclusions

Remifentanil reversibly decreases VOR gain at a half-life reflecting the drug’s pharmacokinetics. We suggest that the decrease in VOR gain leads to a perceptual mismatch of multisensory input with the applied head movement, which results in nausea, and that, consequently, vigorous head movements should be avoided to prevent opioid-induced nausea.     

Types of locomotion in ophiurans

Motion pictures were taken of the locomotion of two species of ophiurans living in the Sea of Japan:Ophiura sarsi vadicoa Djakonov andAmphipholis kochii Lutken.Ophiura sarsi was found to move with the aid of paddling movements of two pairs of arms: The fifth arm (passive) pointed backward. Ophiurans of this species do not use their ambulacral feet. Three main types of locomotor movements were distinguished inAmphipholis kochii, First, locomotion by the "breast stroke" method, in which one arm (the leading) points forward, two point to the side, and two backward. The two side arms are periodically carried forward, after which the disk and the remaining arms are moved with their aid. In this method waves of flexion and extension of the segments spread along the side arms. Second, displacement by pulling with the leading arm pushing with the hind arms, and third, movement by stepping movements of the ambulacral feet. These three methods of locomotion can be used either independently or in various combinations with each other. The ambulacral feet also provide the link between the active arms and the supporting surface by means of which the ophiurans can move forward.Institute of Oceanology, Academy of Sciencs of the USSR, Moscow. Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 521–528, September–October, 1976.     

Hawk Eyes II: Diurnal Raptors Differ in Head Movement Strategies When Scanning from Perches

Background

Relatively little is known about the degree of inter-specific variability in visual scanning strategies in species with laterally placed eyes (e.g., birds). This is relevant because many species detect prey while perching; therefore, head movement behavior may be an indicator of prey detection rate, a central parameter in foraging models. We studied head movement strategies in three diurnal raptors belonging to the Accipitridae and Falconidae families.

Methodology/Principal Findings

We used behavioral recording of individuals under field and captive conditions to calculate the rate of two types of head movements and the interval between consecutive head movements. Cooper''s Hawks had the highest rate of regular head movements, which can facilitate tracking prey items in the visually cluttered environment they inhabit (e.g., forested habitats). On the other hand, Red-tailed Hawks showed long intervals between consecutive head movements, which is consistent with prey searching in less visually obstructed environments (e.g., open habitats) and with detecting prey movement from a distance with their central foveae. Finally, American Kestrels have the highest rates of translational head movements (vertical or frontal displacements of the head keeping the bill in the same direction), which have been associated with depth perception through motion parallax. Higher translational head movement rates may be a strategy to compensate for the reduced degree of eye movement of this species.

Conclusions

Cooper''s Hawks, Red-tailed Hawks, and American Kestrels use both regular and translational head movements, but to different extents. We conclude that these diurnal raptors have species-specific strategies to gather visual information while perching. These strategies may optimize prey search and detection with different visual systems in habitat types with different degrees of visual obstruction.     

The Visual Orientation Strategies of Mantis religiosa and Empusa fasciata Reflect Differences in the Structure of Their Visual Surroundings

In the present study, peering behaviour, which is used to measure distance by the image motion caused by head movement, is examined in two types of mantid. Mantis religiosa inhabits a region of dense grass consisting of uniform, generally uniformly aligned, and closely spaced elements and executes slow, simple peering movements. In contrast, Empusa fasciata climbs about in open regions of shrubs and bushes which consist of irregular, variably aligned and variably spaced elements and it executes comparatively quick, complex peering movements. Hence, it seems that in these two species of mantid, the same orientation mechanism has been adapted to the unique structures of their visual surroundings. Apparently M. religiosa uses motion parallax and E. fasciata uses a combination of motion parallax and forward and backward movements (image expansion/contraction over time) to detect object distances.     

Biomechanical analysis of movement strategies in human forward trunk bending. I. Modeling

 Two behavioral goals are achieved simultaneously during forward trunk bending in humans: the bending movement per se and equilibrium maintenance. The objective of the present study was to understand how the two goals are achieved by using a biomechanical model of this task. Since keeping the center of pressure inside the support area is a crucial condition for equilibrium maintenance during the movement, we decided to model an extreme case, called “optimal bending”, in which the movement is performed without any center of pressure displacement at all, as if standing on an extremely narrow support. The “optimal bending” is used as a reference in the analysis of experimental data in a companion paper. The study is based on a three-joint (ankle, knee, and hip) model of the human body and is performed in terms of “eigenmovements”, i.e., the movements along eigenvectors of the motion equation. They are termed “ankle”, “hip”, and “knee” eigenmovements according to the dominant joint that provides the largest contribution to the corresponding eigenmovement. The advantage of the eigenmovement approach is the presentation of the coupled system of dynamic equations in the form of three independent motion equations. Each of these equations is equivalent to the motion equation for an inverted pendulum. Optimal bending is constructed as a superposition of two (hip and ankle) eigenmovements. The hip eigenmovement contributes the most to the movement kinematics, whereas the contributions of both eigenmovements into the movement dynamics are comparable. The ankle eigenmovement moves the center of gravity forward and compensates for the backward center of gravity shift that is provoked by trunk bending as a result of dynamic interactions between body segments. An important characteristic of the optimal bending is the timing of the onset of each eigenmovement: the ankle eigenmovement onset precedes that of the hip eigenmovement. Without an earlier onset of the ankle eigenmovement, forward bending on the extremely narrow support results in falling backward. This modeling approach suggests that during trunk bending, two motion units – the hip and ankle eigenmovements – are responsible for the movement and for equilibrium maintenance, respectively. Received: 1 July 1999 / Accepted in revised form: 23 October 2000     

Ontogeny of feeding and drinking in the greater rhea (Rhea americana)

Feeding and drinking movements of the greater rhea chick are analyzed. Feeding consists of five movements in the following sequence: orientation, pecking thrust, head lift, forward head jerk and swallow. Drinking is less complex, consisting of a downward movement followed by an upward movement. Adult movements are basically similar; there is a slight trend toward increased variability and decreased energy expenditure. Feeding movements are observed prior to feeding initiation. Drinking movements are first performed during initial water contact. Experience with food and water plays a major role in the development of response efficiency.     

Twist limits for late twisting double somersaults on trampoline

An angle-driven computer simulation model of aerial movement was used to determine the maximum amount of twist that could be produced in the second somersault of a double somersault on trampoline using asymmetrical movements of the arms and hips. Lower bounds were placed on the durations of arm and hip angle changes based on performances of a world trampoline champion whose inertia parameters were used in the simulations. The limiting movements were identified as the largest possible odd number of half twists for forward somersaulting takeoffs and even number of half twists for backward takeoffs. Simulations of these two limiting movements were found using simulated annealing optimisation to produce the required amounts of somersault, tilt and twist at landing after a flight time of 2.0 s. Additional optimisations were then run to seek solutions with the arms less adducted during the twisting phase. It was found that 3½ twists could be produced in the second somersault of a forward piked double somersault with arms abducted 8° from full adduction during the twisting phase and that three twists could be produced in the second somersault of a backward straight double somersault with arms fully adducted to the body. These two movements are at the limits of performance for elite trampolinists.     

The control of twisting somersaults

In the takeoff and early flight phase of a twisting somersault, joint coordination is based on feed-forward control whereas in the late stages of the flight phase configuration adjustments are made using feedback control to ensure accurate completion of the movement and appropriate landing orientation. The aim of this study was to use a computer simulation model of aerial movement to investigate the extent to which arm and hip movements can control twist and somersault rotation in the flight phase of a twisting somersault. Two mechanisms were considered for the control of twist in simulated target trampoline movements with flight times of 1.4 s. In the first case a single symmetrical arm adduction correction was made using delayed feedback control based on the difference between the twist rate in a perturbed simulation and the twist rate in a target movement comprising a forward somersault with 1½ twists. Final corrections were made using symmetrical arm abduction and hip flexion to adjust the twist and somersault angles. In the second case continual asymmetrical arm adduction/abduction adjustments were used to remove the tilt from a perturbed full twisting backward somersault using delayed feedback control based on twist angle and angular velocity. The first method was able to cope with perturbations to a forward somersault with 1½ twists providing the feedback time delay was less than 200 ms. The second method was able to correct a perturbed full twisting backward somersault providing the feedback time delay was less than 125 ms.     

Chemomechanical coupling of the forward and backward steps of single kinesin molecules

The molecular motor kinesin travels processively along a microtubule in a stepwise manner. Here we have studied the chemomechanical coupling of the hydrolysis of ATP to the mechanical work of kinesin by analysing the individual stepwise movements according to the directionality of the movements. Kinesin molecules move primarily in the forward direction and only occasionally in the backward direction. The hydrolysis of a single ATP molecule is coupled to either the forward or the backward movement. This bidirectional movement is well described by a model of Brownian motion assuming an asymmetric potential of activation energy. Thus, the stepwise movement along the microtubule is most probably due to Brownian motion that is biased towards the forward direction by chemical energy stored in ATP molecules.     

A dynamical model for reflex activated head movements in the horizontal plane

 We present a controls systems model of horizontal-plane head movements during perturbations of the trunk, which for the first time interfaces a model of the human head with neural feedback controllers representing the vestibulocollic (VCR) and the cervicocollic (CCR) reflexes. This model is homeomorphic such that model structure and parameters are drawn directly from anthropomorphic, biomechanical and physiological studies. Using control theory we analyzed the system model in the time and frequency domains, simulating neck movement responses to input perturbations of the trunk. Without reflex control, the head and neck system produced a second-order underdamped response with a 5.2 dB resonant peak at 2.1 Hz. Adding the CCR component to the system dampened the response by approximately 7%. Adding the VCR component dampened head oscillations by 75%. The VCR also improved low-frequency compensation by increasing the gain and phase lag, creating a phase minimum at 0.1 Hz and a phase peak at 1.1 Hz. Combining all three components (mechanics, VCR and CCR) linearly in the head and neck system reduced the amplitude of the resonant peak to 1.1 dB and increased the resonant frequency to 2.9 Hz. The closed loop results closely fit human data, and explain quantitatively the characteristic phase peak often observed. Received: 15 April 1996 / Accepted in revised form: 1 July 1996     

The network producing the “active reaction” of stick insects is a functional element of different pattern generating systems

Elongation of the femoral chordotonal organ (signalling a flexion movement of the femur-tibia joint) in stick insects being active releases the active reaction (AR) in the extensor and flexor motor neurones. The AR was released in hindlegs in a situation where free animals would preferentially walk backwards. In most cases the coordination between extensor-flexor and the retractor unguis muscle was like in a stance phase of backward walking. In a situation where free animals would preferentially walk forwards, the percentage of ARs was smaller, and resistance reflexes became more frequent. When campaniform sensilla of the hind leg were destroyed coordinations like in a swing phase of forward walking became more frequent. — Additional stimuli during searching movements in an artificially closed femur-tibia feedback system (Weiland et al. 1986) showed that the AR is expressed also under these conditions and controls velocity and endpoint of a flexion movement. All results support the idea that the neural system producing the AR is a functional element of the pattern generator for forward walking, of the one for backward walking and of the one for searching movements. As far as this system is concerned the three pattern generators only differ in the kind of coordinating pathways between constant functional elements.     

Design and evaluation of head unit for wheelchair control by quadriplegic patients.

A control unit was designed to allow persons who have lost hand and arm function to control the speed, steering, reversal and on-off switching of an electric wheelchair by means of backward movement and rotation of the head. When possible, shoulder movement was used to control both reversal and on-off switching. Clinical evaluation in 10 patients with quadriplegia and 2 with severe neuromuscular disease showed that the unit neither interfered with nor restrained the patients'' residual body movements, permitted use of natural head movements for smooth and fast control of the wheelchair, and was well accepted by and integrated into the life of the patients.     

Vision and the foraging technique of Great Cormorants Phalacrocorax carbo: pursuit or close‐quarter foraging?

Predatory diving birds, such as cormorants (Phalacrocoracidae), have been generally regarded as visually guided pursuit foragers. However, due to their poor visual resolution underwater, it has recently been hypothesized that Great Cormorants do not in fact employ a pursuit-dive foraging technique. They appear capable of detecting typical prey only at short distances, and primarily use a foraging technique in which prey may be detected only at close quarters or flushed from a substratum or hiding place. In birds, visual field parameters, such as the position and extent of the region of binocular vision, and how these are altered by eye movements, appear to be determined primarily by feeding ecology. Therefore, to understand further the feeding technique of Great Cormorants we have determined retinal visual fields and eye movement amplitudes using an ophthalmoscopic reflex technique. We show that visual fields and eye movements in cormorants exhibit close similarity with those of other birds, such as herons (Ardeidae) and hornbills (Bucerotidae), which forage terrestrially typically using a close-quarter prey detection or flushing technique and/or which need to examine items held in the bill before ingestion. We argue that this visual field topography and associated eye movements is a general characteristic of birds whose foraging requires the detection of nearby mobile prey items from within a wide arc around the head, accurate capture of that prey using the bill, and visual examination of the caught prey held in the bill. This supports the idea that cormorants, although visually guided predators, are not primarily pursuit predators, and that their visual fields exhibit convergence towards a set of characteristics that meet the perceptual challenges of close-quarter prey detection or flush foraging in both aquatic and terrestrial environments.     

Foraging movements of Magellanic Penguins Spheniscus magellanicus in the Beagle Channel, Argentina, related to tide and tidal currents

This study investigates the movements of Magellanic Penguins Spheniscus magellanicus breeding on Isla Martillo during the early chick-rearing period. Foraging paths were reconstructed using GPS loggers that registered the penguins′ geographic position, water temperature and depth at regular intervals. The relationship between penguins′ movements and search strategies, tide and tidal currents were assessed. Mean trip duration was on average 14.7 ± 6.9 h (33% overnight), and the maximum distance reached was 24 ± 10 km. All penguins studied foraged to the east of the colony. We identified three phases based on the sinuosity and speed of the trajectory: transit, central and return. Foraging effort was higher during the central phase, followed by the transit phase, and lower in the return phase. Foraging success, measured as the percentage of time at the bottom during each phase, was also highest during the central phase. In all birds studied, the central phase of the foraging trip took place during ebb tide, and birds travelled to the foraging areas with flow tide running in the same direction of displacement. Our study suggests that penguins take advantage of tidal currents to facilitate their movements to and from the main foraging area, thereby reducing the energy expended. Moreover, we suggest that piscivorous diving birds may enhance their catch rate during ebb tide when fish are more concentrated near the channel bed.