Motor Constraints Research Articles

MORPHOLOGICAL ADAPTATION INFLUENCES THE EVOLUTION OF A MATING SIGNAL

Theory predicts that forces of natural selection can reduce the intensity of sexually selected traits. In this study, I investigate how morphological adaptation to feeding ecology influences a mating signal. In birds, changes in feeding ecology can cause rapid divergence in bill morphology. Because bills are also important for song production, feeding ecology may influence song divergence. During song, birds can rapidly change vocal tract resonance using bill movement, yet are constrained in rate and magnitude of bill movements resulting in a trade-off between trill rate and frequency bandwidth. Male swamp sparrows vary in their ability to produce rapid, broad-band trills and females prefer more physically demanding songs. Populations of swamp sparrows adapted to the feeding ecology of tidal marshes have larger bills than inland populations. Larger bills should increase the constraints of producing rapid, broad-band trills allowing for a test of how changes in feeding ecology affect a feature of song used in mate choice. I found significant differences in acoustic features of song consistent with the hypothesis that coastal males are less able to meet the physical demands of song production because of the constraints of having larger bills. As possible compensation for decreases in song performance, coastal populations exhibit an increase in song complexity. These changes support the current model of how motor constraints influence song production and suggest a mechanism by which feeding ecology can influence signal evolution.

Ambient noise, motor fatigue, and serial redundancy in chaffinch song

Many animal signals are performed in a highly redundant manner as in some bird species where males sing several renditions of one song type before switching to another. However, differences in signal redundancy between contexts and between individuals are only poorly understood. We found that chaffinches (Fringilla coelebs) in noisier areas (i.e., close to waterfalls and torrents) sang longer bouts of the same song type before switching to a new type, suggesting that they use increased serial redundancy to get the message across in noisy conditions. This is the first evidence of a noise-dependent adjustment of signal redundancy in a songbird. In addition, we found that song types with faster trills were sung in shorter bouts suggesting that the performance of highly redundant song series is probably limited by motor constraints. Thus, in noisy environments, serial redundancy in bird song may reflect a trade-off between successful signal transmission and preventing motor fatigue.

Bimanual Interference in Rapid Discrete Movements Is Task Specific and Occurs at Multiple Levels of Processing

It has been suggested that interference in symbolically cued bimanual reaction time tasks is caused primarily by the perceptual processing of stimuli and not by motor preparation of the required movements. Here subjects made movements of the right and left index fingers that varied in their spatial and motor congruence. Spatial congruence was manipulated by presenting symbolic cues (i.e., pairs of letters) on a computer screen cueing the required movement directions. Motor congruence was manipulated by altering hand orientation. Results showed that interference occurs at both the stage of stimulus processing and the stage of motor preparation. These effects were reflected in the latencies of the different bimanual movements with both motor incongruence and spatial incongruence causing significant increases in reaction time. However, spatially incongruent movements that were made in response to incongruent visual cues demonstrated changes in reaction time that were more than double those of movements that required simultaneous activation of nonhomologous muscles. Therefore in symbolically cued bimanual reaction-time tasks, although both motor and spatial constraints operate, there is a clear dominance of spatial incongruence on performance. While motor congruence effects are likely due to cross-facilitation in corticospinal pathways, spatial incongruence effects are probably due to interference between the mechanisms that identify incongruent stimuli and translate these cues into the appropriate movements.

Compensation for and adaptation to changes in the environment

Human motor behavior is remarkably accurate, even though many everyday skills require flexible adjustments between motor activity and its consequences in extracorporeal space. The present study addressed two questions: first, how do people compensate for unpredictable changes in the environment, and second, how do they adapt to such changes? In Experiment 1, participants repeatedly and continuously drew up and down strokes on a writing pad. After drawing under a base mapping, either (a) a change of target position, or (b) a change of gain, or (c) both occurred. Compensation for gain changes occurred later than compensation for changes in target position. In addition, there were aftereffects of the previous movement in accuracy and movement time. Adaptation to changes occurred in reference to extracorporeal space, with motor constraints as a limiting factor. In Experiment 2 we obtained similar effects when participants had more time to adapt. The view that movements are planned in reference to their goals in extracorporeal space is supported.

Motion Generation and Adaptive Control Method of Automated Guided Vehicles in Road Following

Dynamics of automated guided vehicles (AGVs) are described by a nonlinear nonholonomic model with two inputs: the rear axle torque and the steering angle torque. This model uses integrated longitudinal and lateral behavior. The first part of this paper is concerned with motion generation, taking into account kinodynamics and motor's constraints. Usual kinematics constraints are not always sufficient to provide feasible trajectories; thus, we focus on velocity limitation and the motor's current and slew rate constraints. Optimal velocity is determined for AGVs along a specified path with a known curvature. The main result concerns the realistic situation when the parameters of the model describing the movement of the vehicle are not well known. A nonlinear strategy is proposed to ensure control of the vehicle even if the knowledge of the AGV's constant parameters is not perfect. The proof of the main result is based on the Lyapunov concept and the proposed results are illustrated by simulations and some comments.

Influence of the palate shape on articulatory token-to-token variability

Articulatory token-to-token variability not only depends on linguistic aspects like the phoneme inventory of a given language but also on speaker specific morphological and motor constraints. As has been noted previously (Perkell (1997), Mooshammer et al. (2004)), speakers with coronally high "domeshaped" palates exhibit more articulatory variability than speakers with coronally low "flat" palates. One explanation for that is based on perception oriented control by the speaker. The influence of articulatory variation on the cross sectional area and consequently on the acoustics should be greater for flat palates than for domeshaped ones. This should force speakers with flat palates to place their tongue very precisely whereas speakers with domeshaped palates might tolerate a greater variability. A second explanation could be a greater amount of lateral linguo-palatal contact for flat palates holding the tongue in position. In this study both hypotheses were tested.
 
 In order to investigate the influence of the palate shape on the variability of the acoustic output a modelling study was carried out. Parallely, an EPG experiment was conducted in order to investigate the relationship between palate shape, articulatory variability and linguo-palatal contact.
 
 Results from the modelling study suggest that the acoustic variability resulting from a certain amount of articulatory variability is higher for flat palates than for domeshaped ones. Results from the EPG experiment with 20 speakers show that (1.) speakers with a flat palate exhibit a very low articulatory variability whereas speakers with a domeshaped palate vary, (2.) there is less articulatory variability if there is lots of linguo-palatal contact and (3.) there is no relationship between the amount of lateral linguo-palatal contact and palate shape. The results suggest that there is a relationship between token-to-token variability and palate shape, however, it is not that the two parameters correlate, but that speakers with a flat palate always have a low variability because of constraints of the variability range of the acoustic output whereas speakers with a domeshaped palate may choose the degree of variability. Since linguo-palatal contact and variability correlate it is assumed that linguo-palatal contact is a means for reducing the articulatory variability.

Neural Substrates of Real and Imagined Sensorimotor Coordination

Much debate in the behavioral literature focuses on the relative contribution of motor and perceptual processes in mediating coordinative stability. To a large degree, such debate has proceeded independently of what is going on in the brain. Here, using blood oxygen level-dependent measures of neural activation, we compare physically executed and imagined rhythmic coordination in order to better assess the relative contribution of hypothesized neuromusculoskeletal mechanisms in modulating behavioral stability. The executed tasks were to coordinate index finger to thumb opposition movements of the right hand with an auditory metronome in either a synchronized (on the beat) or syncopated (off the beat) pattern. Imagination involved the same tasks, except without physical movement. Thus, the sensory stimulus and coordination constraints were the same in both physical and imagination tasks, but the motoric requirements were not. Results showed that neural differences between executed synchronization and syncopation found in premotor cortex, supplementary motor area, basal ganglia and lateral cerebellum persist even when the coordinative patterns were only imagined. Neural indices reflecting behavioral stability were not abolished by the absence of overt movement suggesting that coordination phenomena are not exclusively rooted in purely motoric constraints. On the other hand, activity in the superior temporal gyrus was modulated by both the presence of movement and the nature of the coordination, attesting to the intimacy between perceptual and motoric processes in coordination dynamics.

Visual and motor constraints on trajectory planning in pointing movements

The aim of the present study was to show that planning and controlling the trajectory of a pointing movement is influenced not solely by physical constraints but also by visual constraints. Subjects were required to point towards different targets located at 20°, 40°, 60° and 80° of eccentricity. Movements were either constrained (i.e. two-dimensional movements) or unconstrained (i.e. three-dimensional movements). Furthermore, movements were carried out either under a direct or a remote visual control (use of a video system). Results revealed that trajectories of constrained movements were nearly straight whatever the eccentricity of the target and the type of visual control. A different pattern was revealed for unconstrained movements. Indeed, under direct vision the trajectory curvature increased as the eccentricity augmented, whereas under indirect vision, trajectories remained nearly straight whatever the eccentricity of the target. Thus, movements controlled through a remote visual feedback appear to be planned in extrinsic space as constrained movements.

Timing variations in music performance: musical communication, perceptual compensation, and/or motor control?

A perceptual performance paradigm was designed to disentangle the timing variations in music performance that are due to perceptual compensation, motor control, and musical communication. First, pianists perceptually adjusted the interonset intervals of three excerpts so that they sounded regular. These adjustments deviated systematically from regularity, highlighting two sources of perceptual biases in time perception: rhythmic grouping and a psychoacoustic intensity effect. Then the participants performed the excerpts on the piano in the same regular way. The intensity effect disappeared, and some variations due to motor constraints were observed in relation to rhythmic groups. Finally, the participants performed the excerpts musically. Variations due to musical communication involved additional group-final lengthening that reflected the hierarchical grouping structure of the excerpts. These results underline the nuclear role of grouping in musical time perception and production.

Vocal performance influences female response to male bird song: an experimental test

Female songbirds are thought to assess males based on aspects of song, such as repertoire size or amount of singing, that could potentially provide information about male quality. A relatively unexplored aspect of song that also might serve as an assessment signal is a male’s ability to perform physically challenging songs. Trilled songs, such as those produced by swamp sparrows (Melospiza georgiana), present males with a performance challenge because trills require rapid and precise coordination of vocal tract movements, resulting in a trade-off between trill rate and frequency bandwidth. This trade-off defines a constraint on song production observed as a triangular distribution in acoustic space of trill rate by frequency bandwidth, with an upper boundary that represents a performance limit. Given this background on song production constraints, we are able to identify a priori which songs are performed with a higher degree of proficiency and, thus, which songs should be more attractive to females. We determined the performance limit for a population of swamp sparrows and measured how well individual males performed songs relative to this limit (‘‘vocal performance’’). We then compared female solicitation responses to high-performance versus lowperformance versions of the same song type produced by different males. Females displayed significantly more to highperformance songs than to low-performance songs, supporting the hypothesis that females use vocal performance to assess males. Key words: bird song, female choice, indicator mechanism, Melospiza georgiana, motor constraint, sexual selection, vocal performance. [Behav Ecol 15:163–168 (2004)]

Impaired recovery of syllable repertoires after unilateral lesions of the HVC of male domesticated canaries

Abstract Particular features of the song of adult male canaries such as a large syllable repertoire resulting in a great diversity of song phrases and special so-called 'complex' syllables enhance various features of female reproductive behaviour. These features are produced in a species or strain dependent manner during expiration by the left, the right, or the sequential activity of the left and right syrinx halves, independently working sound sources of songbirds. The activity of each syrinx half appears to be controlled by an ipsilateral, anatomically symmetric network of interconnected brain nuclei involving the High Vocal Centre (HVC), while expiration appears to involve both the left and right descending motor pathway. Waterschlager canaries with a left-sided syringeal dominance recover their repertoire size after unilateral left-sided lesion of the HVC over several months and do not experience syllable deficiency after unilateral right-sided HVC lesions. Here we report on the recovery of the syllable repertoire of domesticated Non-Waterschlager canaries during several months after lesion of either the left or right HVC. Despite the recovery of the initially degenerated song structure after either lesion, the males show a permanent reduction of about 60% of their syllable repertoire size in relation to the permanent loss of HVC neurons. In particular, most complex syllables and all of the sexually attractive sub-type are lost and not recovered. Since our canaries do not show peripheral syringeal dominance, these data suggest that (1) only about 40% of the syllables can be produced by only the left or only the right vocal pathway; (2) that the left or right vocal pathway cannot take over the function of the contralateral one; (3) that large repertoires as well as complex syllables requires both vocal pathways; and (4) that the degree of vocal learning appears to be restricted by peripheral motor constraints in adulthood.

Directional female preference for an exaggerated male trait in canary (Serinus canaria) song.

Motor constraints on vocal production impose a trade-off between trill rate and frequency bandwidth within birdsong. We tested whether domesticated canary (Serinus canaria) females, reared either in acoustic isolation or in aviary conditions, had a preference for broad bandwidth songs with artificially increased syllable rates. The copulation solicitation display (CSD) was used as an index of female preference. As predicted, both naive and experienced females were especially responsive to syllables with a broad bandwidth emitted at an artificially increased rate. Female preference for supernormal stimuli provide support for the honest-signalling hypothesis and our results are consistent with recent findings indicating that production of song phrases maximizing both bandwidth and syllable rate may be a reliable indicator of male physical or behavioural qualities. We suggest that female preference for vocal emissions, which simultaneously maximize these two parameters, could be a widespread pattern within songbirds.

The Timing of Grace Notes in Skilled Musical Performance at Different Tempi: A Preliminary Case Study

An empirical study is reported which investigates the relationship between musical structure and the timing of 11 grace notes in 45 performances by the same performer of a short Beethoven piano piece at a range of tempi. These performances were recorded and analysed so as to extract timing measurements, and the pianist was interviewed to gain insights into his conscious performing strategies. Significant differences in the relative length of different grace notes were found: the two grace notes with a large descending pitch interval were played significantly longer than the others. Additionally, the grace notes were timed such that they did not "take time" from the note they are nominally attached to, but from the preceding time interval. Close attention to interview data provided by the pianist reveals that the relative timing of the grace notes corresponds to his claims that he was mimicking the motor constraints of vocalists and string players. Lastly, the data provided additional evidence against the notion that changes in overall tempo always leave the relative proportion of adjacent events invariant. Grace notes with a longer mean duration tended to deviate significantly from proportional duration, whilst shorter grace notes were roughly invariant over tempo.

A species-specific acoustic cue for selective song learning in the white-crowned sparrow

Song learning in birds is paradoxical. Without tutoring, songbirds do not develop normal songs. Yet despite this inability, birds possess extensive foreknowledge, in a mechanistic sense, about the normal song of their species. When given a choice of tape recordings, young, naıve songbirds select sounds of their own species for imitation. We tape-tutored white-crowned sparrows, Zonotrichia leucophrys oriantha, with a set of manipulated songs to investigate whether the introductory whistle universally present in white-crowned sparrow song guides selective song learning in this species. Our results confirm that this whistle serves as a cue for song learning, enabling acquisition of normally rejected sounds of other species, including hermit thrush, Catharus guttatus, notes, which have a sound quality distinct from that of natural white-crowned sparrow phrases. Our results support the conclusion that sensory mechanisms rather than motor constraints are primarily responsible for the selectivity seen in song learning.

Motor constraints on the development of perception-action matching in infant reaching

Previous studies on reaching and grasping have suggested that infants need considerable experience at both seeing and touching in order to develop responses adapted to the environment. Such an account, however, does not reveal how appropriate perception-action matching emerges from these repeated experiences at seeing and touching. The present research addresses this issue by investigating the dynamics of perceiving and acting in 5- to 9-month-old infants as they saw, reached for, touched, and grasped objects of different sizes and texture. To gain insights into the mechanisms of change that underlie pattern formation, we observed infants’ responses as a function of time, as infants reached for and manipulated objects successively. We found that the developmental process by which appropriate perception-action matching emerges is tied to important changes in the motor system. Before 8 months, infants’ reaching responses are constrained by systemic motor tendencies that conflict with the process of perceptual-motor mapping. When these motor tendencies disappear, infants are able to use and integrate visual and haptic information to scale their actions to objects. These results are consistent with a dynamic systems approach, which views behavioral changes and their underlying psychological processes as the product of continuous tensions and interactions between the organism’s own constraints and the characteristics of the task at hand.

A new control strategy for induction motor based on non-linear predictive control and feedback linearization

Proposed in this paper is a new approach of design using a monovariable generalized predictive control law, with multiple reference model (GPC/MRM) to control, firstly, rotor speed and rotor flux amplitude of an induction machine. The control law will be extended and applied, secondly, to answer a second objective which is the control of the rotor position and rotor flux amplitude of the same machine. The non-linear dynamical model of the machine is described in the stator fixed reference frame. The GPC algorithm is combined with the non-linear input–output linearizing control properties; moreover, we establish a new formulation of the reference signals, which enables one to track flux and speed/position nominal profiles, satisfying motor constraints. The global controller synthesis is given under an RST form which introduces a novel definition of the prefiltering polynomial. Copyright © 2000 John Wiley & Sons, Ltd.

Undifferentiated lingual gestures in children with articulation/phonological disorders.

Previous research using electropalatography (EPG) has shown that a distinctive articulatory characteristic of lingual consonants in the speech of school-age children with articulation/phonological disorders (APD) is a high amount of tongue-palate contact. Consonants produced in this way have been referred to as undifferentiated lingual gestures. This article reviews the EPG literature on undifferentiated gestures with 4 overarching goals: (a) to provide a precise articulatory description of undifferentiated gestures, (b) to estimate the rate of occurrence of undifferentiated gestures in children with APD, (c) to propose an original.interpretation of undifferentiated gestures, and (d) to discuss the significance of the gestures in the light of current theories of APD. Undifferentiated gestures typically occur during productions of lingual consonant targets and are characterized by contact that lacks clear differentiation between the tongue apex, tongue body, and lateral margins of the tongue. The EPG literature reports 17 school-age children with APD, of whom 12 (71%) show evidence of undifferentiated gestures. Standard transcriptions do not reliably detect undifferentiated gestures, which are transcribed as speech errors (e.g., phonological substitutions, phonetic distortions) in some contexts, but are transcribed as correct productions in other contexts. Undifferentiated gestures are interpreted as reflecting a speech motor constraint involving either delayed or deviant control of functionally independent regions of the tongue. The limitations of the current EPG literature are stated, and the need for research into undifferentiated gestures in preschool children is discussed.

Visual activity in relation to head movement in infants with leukomalacia

Leukomalacies are supposed to have consequences for visual and cognitive development. However, authors describe opposite changes with age : for instance, both increasing and decreasing acuity have been reported (Levene and al. 1992; Dubowitz and al. 1996;). There is also no general agreement about performance in visual detection and attention. Moreover, some motor impairment often accompany perceptual defects. Because the patietal areas are touched by these lesions, it is assumed that specific motor constraints influence the perceptual behavior of leukomalacic infants. In order to detect caracteristic visual-motor features, we have studied the orienting reaction to visual stimuli and the capacity of visual detection in leukomalacic infants.

Motoric constraints link manual babbling and early signs

Motoric constraints link manual babbling and early signs

Motor constraints on vocal development in a songbird

The development and evolution of bird songs may be influenced by the mechanisms that underlie sound production, although the nature of this influence is not well understood. Here it is shown experimentally that vocal development in songbirds can be affected by physical limits on how birds are able to sing. Young swamp sparrows, Melospiza georgiana, were presented with conspecific song models modified such that rates of syllable repetition were increased above normal rates. Imitations of these songs were inaccurate in ways that indicated motor constraints on vocal performance and that did not indicate perceptual or memory-based constraints. Some song imitations were deficient in trill tempo and/or syllable composition, and others were produced with a species-atypical ‘broken’ syntax, in which pauses were interspersed within songs. These results illustrate how the development and evolution of trill structure can be limited by motor constraints on vocal production, and also identify a possible mechanism for the evolution of a novel form of song syntax.