Translatory Component Research Articles

Anterior crowding--just an esthetic problem?

One frequent late sequel of frontal crowding is the development of gingival recessions manifesting themselves especially at rotated anterior teeth. This correlation is discussed with regard to the literature and to the authors' own clinical findings and experimental studies. According to present-day knowledge the following statements can be made: In cases with frontal crowding the tangential stiffening of the anterior teeth is inadequate. Thus translatory and rotational force components resulting from the elastic deformation of the mandible under functional loading effect the movement of rotated front teeth during maximum jaw opening and mandibular protrusion. Also tongue thrusting and frontolateral bruxism lead to force vectors in vestibular direction affecting the delicate periodontal tissues. These statements are confirmed by the authors' own in-vivo experimental studies measuring the amount of tooth displacement during test persons' functional movements. Furthermore, in the long-term anterior crowding will mostly trigger incorrect anterior guidance, i.e. guidance predominantly by the rotated or ectopically positioned front tooth with subsequent overloading of the antagonist. Orthodontic therapy of frontal crowding is not just an esthetic problem but can be of special importance in the prevention of stress-related reactions in the masticatory system.

Idiothetic navigation in humans: estimation of path length.

When vision is excluded humans are still able to walk back to a starting point or to a previously seen target. This performance may be mediated by path integration, based on information about movement with respect to the ground or to inertial space, that is, on substratal or inertial idiothetic cues. We intend to unravel whether, and how accurately, these two inputs act and interact on the translatory component of this navigation performance. Subjects were asked 1) to reproduce a path they had walked, and 2) to indicate the location of a target they had seen before being blindfolded by (i) walking there, (ii) treading a motor-driven conveyor belt until they imagine they are there, and (iii) reporting, while being driven in a trolley, when they seem to pass the target. The estimation of path length turns out to vary as a function of walking velocity, step length, and step rate. The estimate becomes virtually veridical when subjects walk at their normal pace, but it overshoots at lower and undershoots at higher values of these variables. Veridicality at near normal speeds is also found with passive transport (iii), but with a reverse dependence on velocity. It is concluded that in these paradigms path control and perception are mediated by an open-loop performance of the underlying path integration system, calibrated in such a way as to yield veridical estimates during normal walking. Either inertial or substratal idiothetic information is sufficient for this performance. However, the quantitative relations found argue in favor of the hypothesis that substratal idiothetic information predominates when both are available. In spite of its limitations the capability shown here may serve as an essential constituent of navigation by path integration in humans.

How locusts separate pattern flow into its rotatory and translatory components (Orthoptera: Acrididae)

The ability of desert locusts,Schistocerca gregaria, to separate pattern flow within the lateral visual fields into its rotatory and translatory components was studied in tethered flight under open-loop conditions. The optomotor turning behavior results from the sum of compensatory steering and upwind/downwind turning induced by the rotatory and translatory component of pattern flow, respectively. Thereby, the analysis of the visual stimulus is supposedly achieved by linear binocular interaction, i.e., by summation and subtraction of the optomotor effectiveness of the pattern flow on either side. Our results indicate that, in addition, locusts take into account the relative contribution of the rotatory and the translatory stimulus component to the sum total of pattern flow. This yields a factor which modifies the gain of the control loop of either of the response components to give a nonlinear response. It results in a weakening of the behavior upon stimuli composed of rotatory and translatory components. We discuss our results as an adaptation by which an animal avoids inappropriate behavior upon ambiguous stimulus situations.

Humans combine the optic flow with static depth cues for robust perception of heading

The retinal flow during normal locomotion contains components due to rotation and translation of the observer. The translatory part of the flow-pattern is informative of heading, because it radiates outward from the direction of heading. However, it is not directly accessible from the retinal flow. Nevertheless, humans can perceive their direction of heading from the compound retinal flow without need for extra-retinal signals that indicate the rotation. Two classes of models have been proposed to explain the visual decomposition of the retinal flow into its constituent parts. One type relies on local operations to remove the rotational part of the flow field. The other type explicitly determines the direction and magnitude of the rotation from the global retinal flow, for subsequent removal. According to the former model, nearby points are most reliable for estimating one's heading. In the latter type of model the quality of the heading estimate depends on the accuracy with which the ego-rotation is determined and is therefore most reliable when based on the most distant points. We report that subjects underestimate the eccentricity of heading, relative to the fixated point in the ground plane, when the visible range of the ground plane is reduced. Moreover we find that in perception of heading, humans can tolerate more noise than the optimal observer (in the least squares sense) would do if only using optic flow. The latter finding argues against both schemes because ultimately both classes of model are limited in their noise tolerance to that of the optimal observer, which uses all information available in the optic flow. Apparently humans use more information than is present in the optic flow. Both aspects of human performance are consistent with the use of static depth information in addition to the optic flow to select the most distant points. Processing of the flow of these selected points provides the most reliable estimate of the ego-rotation. Subsequent estimates of the heading direction, obtained from the translatory component of the flow, are robust with respect to noise. In such a scheme heading estimates are subject to systematic errors, similar to those reported, if the most distant points are not much further away than the fixation point, because the ego-rotation is underestimated.

Eye movements in freely moving crabs: Their sensory basis and possible role in flow-field analysis

1. 1. Multisensory control of eyestalk orientation is reviewed in the light of studies of eye movements of freely moving crabs. 2. 2. During locomotion, the eyes of freely moving crabs compensate for the rotatory but not the translatory components of visual flow. 3. 3. It is argued that, since only the rotatory component can be used for course control, while only the translatory component provides information on ground speed and the three dimensional layout of the environment by means of motion parallax, this separation of flow field components makes good functional sense.

Sensory Basis and Functional Role of Eye Movements Elicited During Locomotion in the Land Crab Cardisoma Guanhumi

ABSTRACT Eye movements in the horizontal plane and the rotatory component of body movement have been continuously recorded in land crabs, Cardisoma guanhumi Latreille, walking freely in an arena. The results show that the eyes compensate for locomotor turns by moving in the opposite direction to the body, thus reducing the image motion of surrounding objects on the retina. Gains often approach unity, so that stabilization of the rotatory component of self-generated image motion is good. Of the three compensatory eye reflexes that could contribute to these responses, optokinetic responses play a major role, since the gain of the responses of freely walking blinded crabs was about half that of crabs that could see. Since blinded crabs held above a ball moved their eyes whenever they rotated the ball about a vertical axis (i.e. turned), a significant role for leg proprioceptor-driven eye movements is also presumed. It is unclear whether vestibular nystagmus, driven by the statocysts, also has a role to play. In contrast to the high-gain compensatory responses that accompany turns, the translatory component of locomotion elicits compensatory eye movements only under the most favourable circumstances, when the crab walks along a runway facing a set of stripes. Even then, the responses are of very low gain (0.02-0.09). Amongst several possible factors, this is partly because lateral ommatidia, which drive the optokinetic responses, will face the poles of the flow field during sideways walking, and partly because stationary contrasts (as occur at the poles of the flow field) reduce the gain of optokinetic responses. It is argued that, by compensating for turns but not translatory locomotor movements, crabs effectively separate the rotatory from the translatory components of the visual flow field around them. Since only the former can be used in course control, while only the latter provides information on ground speed and the three-dimensional layout of the environment, such a separation makes good functional sense.

Coordination of legs during straight walking and turning in Drosophila melanogaster

Leg coordination of Drosophila melanogaster was studied using frame-by-frame film analysis. 1. For fastest walking alternating tripod coordination is observed which slightly deviates towards tetrapody as a function of step period. During acceleration or deceleration legs may transiently recover in diagonal pairs. 2. Mean step length increases with step frequency. 3. Mean recovery stroke duration increases with step period and plateaus beyond a period of about 110 ms. Middle legs recover significantly faster than others. 4. Ipsilateral footprints are transversally separated. 5. Walking is usually initiated in tripod coordination (frequently in combination with a turn), otherwise in an accelerating sequence which rapidly shifts towards tripod pattern. Flies can stop abruptly or decelerate over about one metachronal wave. 6. Short interruptions in walking are observed. Legs interrupted during swing phase stay lifted and finish recovery thereafter. 7. Slight changes in walking direction are obtained by altering step lengths only. Tight turns are composed of two or three phases with backward, zero and forward translatory components. In fast turning tripod coordination is maintained. Otherwise body sides can decouple widely. In all turns numbers of contralateral metachronal waves were equal. Results are compared to those for other walking insects and their relevance in screens for locomotor mutants is discussed.

Investigation of the effect of a variable anterior guidance incline on the graphic registration of mandibular border movement: Part I

Lateral mandibular movement occurs as a combination of rotational movements around the working condyle with forward, medial, and inferior movement of the nonworking condyle and a small amount of lateral translation. The lateral translator-y component, the Bennett movement, has been reported and discussed extensively.‘-’ The principal element cited as responsible for the Bennett movement is the anatomy of the temporomandibular joints.*-‘3 The muscles of mastication have been shown to affect the nature of mandibular border movements as they appear on graphic or pantographic registrations. The functional anatomy of the musculature has been described by many authors.“, I23 14-19 Several investigators have reported the effects of medication on the registration of lateral border movements.20‘27 Many of these showed differences between the graphic registrations of medicated and nonmedicated subjects and concluded that muscles play a significant role as limiting factors of border movements. This is further illustrated by studies that showed that the mandibular dysfunction syndrome causes variations in the nature and reproducibility of registrations of mandibular border movement.27-33 A difference in graphic registrations has been shown to occur between voluntary and induced lateral border movements.3’a 34 The effect of a variable anterior guiding plane on the graphic and pantographic registration of mandibular border movements was studied by Cohen,35 Kotowitz et a1.,36 and Clayton et al. 37 They all reported that there was no effect. The influence of anterior guidance on lateral mandibular movement was also reported by Hickey et al.:* Prieskel,39 Kitschenberg,4O and Kamimura.41 With different methods, their findings suggest that a variable anterior guidance could affect the condylar movement pattern. KitschenbergN used a modified pantograph with interchangeable bearing surfaces on five subjects and concluded that “an increase of lateral guidance effects

Courtship-Like Tracking Behaviour in Wild-Type Female Drosophila melanogaster

Abstract Both male and female Drosophila melanogaster possess systems which enable them to track other walking flies visually. Males use this system predominantly in courtship; females, when of sufficient age but still unmated, have been observed to track other flies, at rates of up to 18 bouts per hour. This behaviour is most conveniently studied in groups of females. Although similar to the courtship tracking of males, fem ale/female tracking lacks the “circling” component of courtship. The data suggest a functional relationship of female/female tracking to reproductive behaviour, although none has yet been identified. Bouts of tracking by females are most frequently terminated by the following female, especially when the target female remains motionless. Comparison of the tracking parameters of males and females has revealed differences in the velocity and pathlength of tracking bouts, and in the position of the fly with respect to the target. Males of Canton and Kapelle strains differ in the translatory component of their courtship tracking, but such a difference was not evident between females of these strains. Furthermore, tracking females do not allow their distance to the target to rise to that permissible in males, which suggests some sex-specificity in a part of the control system for tracking.

The courtship tracking of Drosophila melanogaster

The courtship of male Drosophila melanogaster, which occurs so far as is known exclusively on the ground, may be regarded as a tracking process upon which are superimposed specific elements of courtship behaviour. Two methods were utilised to study this process, both of which involved the use of a fixed female courtship stimulus. The male courted this female whilst 1. running on the moving floor of a revolving chamber (female stationary) and 2. tracking her as she was rotated on a radius in a stationary chamber. Behaviour in the first apparatus was recorded via an electronic eye watching the flies and a keyboard operated by the experimenter. Behaviour in the second apparatus was filmed and subsequently analysed frame by frame. The patterning of courtship around the female was shown to be limited by the velocity at which the male had to run in order to court the female. At lower velocities more excursions ("circling") to the side of the female were made. The mean distance of the male behind the female increased with velocity. The slope of this effect provides an estimate of the reciprocal feedback gain of the control system for tracking. Strain and velocity dependent differences in courtship variables were revealed. The proportion of wing extension emitted in tracking varied widely, the lowest value being shown by the strain which tracked the fastest (WT Kapelle). It is proposed that the relation between these two variables is of fundamental importance in determining the outcome of courtship. Using females moving sideways it was demonstrated that males orientate to the abdomen in close range of the female (<4 mm centre to centre), and more centrally at greater distance, where visual stimuli probably dominate as cues to orientation. Sinusoidal modulation of the female's velocity enabled a preliminary stimulus-response analysis of the linear aspects of courtship tracking. For males tracking females whose speed was modulated at a mean of 1.2 Hz a phase lag of 148±30ms was determined for the translatory component and 21±55ms for the rotatory component of the male's response. A strain difference between wild type Kapelle and Canton-S strains in tracking efficiency permits the conclusion that courtship tracking ability may provide a basis for selective mating in Drosophila.

The mechanism of object fixation and its relation to spontaneous pattern preferences in Drosophila melanogaster.

The orientation behavior of walking flies, Drosophila melanogaster, towards a single 6 degrees wide black vertical stripe (elementary stripe) can be explained by use of the turning tendency function H(beta). This function is characterized by maximal values at an angular distance of beta = 25 degrees from the stable zero position (= orienting direction), a sharp decline from this maximum to beta = 60 degrees, and a very slow approach to the unstable zero position (Horn and Wehner, 1975). The shape of this function is influenced by both translatory and rotatory components of movement. If the translatory component is minimized by measuring the turning function W(beta) (see 2.3) at a distance of 10 mm (C1) from the center of the arena, a change in the strength of this decline is caused. But with increasing translatory component, i.e. at a greater distance from the center of the arena, W(beta) approximates the heuristical function H(beta) (Fig. 12). The turning functions W(beta) are pattern-specific; the angular positions of the maximum responses shift to greater angles with increasing width of the patterns (Fig. 2). In the two-pattern configuration with double or single stripes, there is always a coincidence between the stable zero positions of Wsigma(beta), the mean of the frequency distributions P(beta) of the flies' positions and ng(beta) of the straight courses, and the stable zero positions of Hsigma(beta) obtained from an additive superposition of two or more angular shifted turning tendency functions H(beta) (Fig. 5, 7). Therefore, the mean positions of the flies in a multi-stripe experiment composed of elementary stripes can be predicted from the addition of many angular shifted turning tendency functions H(beta). Between H(beta) and the frequency distribution P(beta) of the flies' positions beta, the following formula holds: P(beta) = C.intregal of H(beta)dbeta (Fig. 13). With this equation, the spontaneous preference of the broader of two double stripes can be explained presuming lateral interactions between the components of the patterns (Fig. 8, 10). The strength chii of this lateral interaction depends on the width delta of the double stripes. The greater delta, the smaller is chii. chii is a pattern-specific value (Table 1, 2).

The optomotor equilibrium of theDrosophila navigation system

In his discussion of the optomotor behaviour Kalmus claimed in 1964 that the visual systems of insects continuously resolve horizontal displacements relative to the surroundings into rotatory and translatory components, each associated with optomotor feedback of particular quality and sign. The feedback is supposed to achieve, simultaneously, minimization of the rotatory movements and maximization of the translatory movements, a behaviour repeatedly observed with actively moving insects such as the fruitflyDrosophila melanogaster. The present approach takes into account that the output of movement detectors in the visual system of insects is necessarily equivocal with respect to the speed of the stimulus (e.g. zero output at both zero and infinite speed). Decomposition of the stimulus is not feasible under these conditions. It is obviously the composite stimulus to which the insects respond. Moreover, there is experimental evidence that optomotor feedback on the translatory movement is not necessarily a response-determining factor in insects. The optomotor behaviour of the walking fruitfly is sufficiently described by the sum of itsrotatory responses to the composite stimuli on either side. A diagram representing the expected rotatory response of the walking fruitfly as a function of both the rotatory and the translatory stimulus component is used to derive the prevailing traits of the behaviour in resting, rotating and floating environments, respectively. Most conspicuous is the inversion of the course-control response in about one half of the possible states of stimulation. This effect gives rise to at least some of the apparently spontaneous turns of actively moving insects which have been ascribed by v. Holst and Mittelstaedt to efferent commands from higher centres of the brain, according to their principle of reafference. The present results merely disprove the necessity of these commands. Inversion of the response is also an inherent property of the course-control systems of the optomotorically active insects. The expected increase of these inversions with closer proximity of the visual environment is found by observation of walking fruitflies. The relation between the rotatory and translatory movements of the freely walking fly and its state of stimulation in a given environment is used to describe the expected behaviour in terms of the most probable transition of state. The approach is based on estimates of the power required by the fly in order to maintain a given state against the torque that is produced by its course-control system in response to the optomotor stimulation. The most probable transition of state is apparently determined by the tendency of the fly to decrease the power requirement by appropriate adaptation of its rotatory movement. The transition may come to an end in one of the states of minimum power requirement where the speed of the rotating fly is held in a stable optomotor equilibrium.

Lateral jaw movements in mammalian dentitions

A study was made of the masticatory apparatus of two groups of mammals with very different dietary needs and chewing habits. Lateral chewing movements were considered in terms of their rotational and translatory components. Carnivores have a lateral jaw movement that has only a rotational component. Translatory movements seem to be associated with shearing action while rotational movements are associated with grinding. In all of the animals studied, some accommodation was observed to prevent so-called balanced occlusion in which tooth contacts occur on both sides of the mouth at the same time. Dentists who compare cuspless artificial teeth with those of herbivorous animals are probably unaware of the masticatory requirements of these animals.