Search Results

The differential effects of voluntary head movements (horizontal oscillations about the z axis) and varying head positions on postural sway are investigated in this chapter. The methods of the experiments are presented here. Ten subjects took part in the experiments, where their head movements were recorded using a head-fixed angular accelerometer. The main finding of the experiment is that the differential effects of varying head positions were surprisingly small. Moreover, the body sway does not significantly increase with head rotation and that indicated the precise reevaluation of head sway with respect to the head position relative to the trunk.

This chapter presents results concerning AH's head and eye movements and the consequences of these movements for her visual location perception. It shows that AH often moved her head and eyes in the wrong direction when attempting to orient toward a visual stimulus. It then reports a far more surprising result: AH's misperceptions of object location often remained stable across head and eye movements. For this latter result, the chapter offers a speculative interpretation concerning the processes that generate high-level visual location representations. Finally, it discusses the implications of AH's performance for issues concerning the levels of the visual system implicated in conscious visual experience.

The vestibular nuclei receive vestibular-related information from canal and otolith afferents as well as from the vestibulocerebellum. In addition and in contrast to other sensory systems, early vestibular processing is highly convergent and strongly multimodal. Notably, the vestibular nuclei receive substantial visual, somatosensory, and oculomotor inputs. Multimodal interactions, which also occur elsewhere in the central vestibular pathways, are vital for spatial perception and for gaze and postural stabilization. Because oculomotor signals play an important role in shaping the information encoded centrally, knowledge of how the brain controls eye movements is crucial for understanding vestibular processing. This chapter provides an overview of oculomotor processing. Topics discussed include an overview and classification of eye movement types, ocular structure and functional implications, gaze redirection, gaze stabilization, and interactions between eye and head movements.

This chapter begins by examining the connections between remnant movement, scrambling, and restructuring. It introduces a number of phenomena and concepts essential for the description of the syntactic structure of West Germanic as well as for the understanding of the discussion of restructuring infinitives. It discusses the essential properties of and the relevant restrictions on remnant movement. It also talks about the interaction between remnant movement and head movement. It argues that remnant categories created by head movement cannot undergo further movement and show how this restriction can be derived from Attract Closest as well. It demonstrates that the original account by Den Besten and Webelhuth is flawed. It argues that remnant VPs in German are created by licensing movement of VP-internal material into dedicated licensing positions in the lower middle field. It outlines the core ideas and concepts that were adopted and indicates the account of individual phenomena.

In this chapter, a variety of saccadic eye-head movements evoked by visual and auditory stimuli are reviewed. Variation in head movement strategies resulting from methodology as well as the subject's own biases are considered alongside factors already known to affect eye-head movements. Search strategies are compared in different tasks. First, in the relatively simple situation in which the head is immobilized; second, in the more complicated situation when the head is free to move. The variables of movement amplitude and sensory modality are compared at the same time. In the studies of Guitton and Volle as well as Bizzi et al., saccadic latency was majorly affected by the predictability of the fixation-saccade interval and the saccade amplitude and direction.

According to Lashley, the key in achieving coordinated patterns of action was to program diverse motor responses with reference to a single, central spatial map and a single internal clock. This chapter studies the coordinated head and eye movements during natural and unusual performance of visual tasks, and the results of the investigations in scanning the unusual head-eye movement combinations. Three characteristics were revealed regarding the normal coordination of head and eye movements. The first one is that moving the head can increase saccades rate. The second is that the ability to perform unusual patterns of head and eye movements is different during a task with clear cognitive components than during less natural tasks when the observer tries to direct the eye to an eccentric target without cognitive significance. Lastly, there is a natural tendency to program head and eye movements concurrently in similar spatial and temporal patterns.

In this chapter, the authors addressed the question of the degree to which gaze saccades executed under natural conditions are modulated by concomitant head movements by creating a “quasi-natural” situation. Head-fixed saccades were compared to head-free saccades. The first experiment in this study cannot prove or disprove the validity of Bizzi's classical summation hypothesis for human gaze saccades confined to the oculomotor range. It rather demonstrates that the presence of a classical VOR is irrelevant for the velocity of such gaze saccades since the concurrent head movement starts too late and is too slow to impart to the saccade a significant gain in velocity in the event of a disconnected VOR. The second experiment confirms that the factor of greater importance for the dynamics of head-free saccades is the orbital eccentricity and direction of the EiH contribution to saccades.

Gaze is defined as the coordinated sum of eye and head movements and gaze position is the position of the eye in space, while eye position is the position of the eye in the orbit. In this chapter, the authors discuss how several causal factors (protocol conditions including desired gaze amplitude and pathologic situations including reduced inclination to move the head in hemianopia) influence the selection of a gaze mode despite statistical selection. The results of the methods employed in this study show that there is a strong connection between the gaze type as defined by relative latency of eye and head movement and the VOR gain and gaze amplitude. It is also evident that some motor brain mechanism organizes a relative latency between head and eye movement.

This chapter discusses phenomena that have been appealed to in work advocating ‘head‐to‐head movement’. It is argued that such a mechanism further weakens the restrictiveness of syntax, despite introducing further tracking-devices. On the basis of a discussion of English and French, an alternative analysis of ‘movement to Infl’ and ‘movement to Comp’ is offered. The latter is provided with the non‐movement lexical account already appealed to in the discussion of interrogatives in Chapter 4. Analysis of the former invokes differences between languages in how much argument incorporation they permit in the lexicon, and this is illustrated from a range of languages. French is interpreted as involving incorporation of pronominal complements that may be coreferential with an adjunct, where English has a complement. This accounts for various differences between the languages in adverb position.

Some of the functional properties of different otolith-ocular reflexes are discussed in this chapter, such as the linear vestibulo-ocular reflexes, which are activated by linear acceleration. The latter part of the chapter focuses on the interaction of otolith and canal signals during rotatory head movements. Stabilization of the line of sight and maintenance of spatial orientation requires appropriate transformation of sensory inputs of different modalities to oculomotor output. Rapid information about head movements and orientation in space is provided by the vestibular organs. The utricular and saccular otolith organs detect linear accelerations of the head, and hence convey information about translatory head movements as well as about head orientation relative to gravity, while the semicircular canals, activated by head angular accelerations, provide afferent information. Otolith signals interact with semicircular canal signals in at least two important ways involving the velocity storage system. First, otolith signals are processed to complement the canal-ocular reflexes at frequencies of head rotations below 0.1 Hz. Second, static otolith input interacts through the velocity storage integrator with head velocity signals to provide a spatial reference about head angular velocity. The otolith organs provide complementary signals that are used to detect the direction of the head rotation in space, i.e. relative to gravity, as well as eccentricity of rotation during fast head movements. Dynamic otolith signals can initiate appropriate transformations of canal-driven head velocity signals to account for eccentricity of ocular rotation and target distance.

This chapter clarifies that “Listing's Law”, which governs the rotations of voluntary eye movements, also governs specific types of voluntary head movements. Listing's law for the eye states that there is a “displacement plane” associated with the orientation assumed by the eye, and there is exactly one eye position p in which the displacement plane is orthogonal to the line of sight. The analogy of Listing's law for the head states that there is an associated displacement plane DPh such that the head assumes only those positions from the reference position by rotating about the axis lying on DPh. This chapter also presents the methods of the experiments performed on seven human subjects where their three-dimensional head position and velocity vectors were measured using Robinson's magnetic field-search coil technique. The primary finding of this study is the Listing's Law for the head.

The objective of this chapter is to present the effects of voluntary control and stimulus conditions on three types of oculomotor behavior that were previously regarded as different subsystems. Examples are given in this chapter to illustrate that performance is determined by stimulus conditions and voluntary processes. The primary contribution of head movements to saccadic gaze shifts is a reduction of the duration of the gaze shift that results in different characteristics of the velocity profile. These experiments aim to study interactions between saccades and vergence or pursuit and vergence, and to give more insight into the degree to which the performance of the head motor systems and oculomotor behavior is determined by processing in modular subsystems.

This chapter describes a case of putative head movement where the A-over-A Condition is irrelevant: The movement of simultaneously minimal and maximal categories. It focuses on Romance clitics, which show at least some properties of head movement and, by treating them as simultaneously maximal and minimal elements, are able to move both as XPs and as heads. The chapter argues that cliticization is head movement and explains why that is both allowed and required based on two central ideas: That of a word as phase and that of defective goal. It shows that cliticization can have semantic effects and that it cannot be reduced to A-movement combined with some special morphophonological operation by comparing cliticization and Scandinavian object shift. The chapter also considers cliticization as head-to-head incorporation and offers a general account of verb movement.

This book has explored head movement based on the central idea of minimal phases, and has argued that it cannot and should not be eliminated from narrow syntax, therefore implying a reconsideration of recent suggestions to replace certain cases of head movement with remnant movement and/or PF-movement. This concluding chapter reexamines Noam Chomsky’s objections to head movement, and considers the Extension Condition, which Chomsky claims is violated by the derived structure of head movement. The book has argued that its effects derive from Edge Features, in which case it is satisfied by some cases of head movement, but not by other types of head movement (those triggered by Agree and defectivity). This is similar to what can be observed with XP-movement: EF triggers A0-movement but not A-movement; the former thus obeys the Extension Condition, while the latter does not.

This study concentrates on motor strategies performed by the monkey (Macaca mulatta) for orienting movements in the head-free condition during visual tracking and visual pursuit. This study is based on the assumption that the CNS would induce motor strategies that would reduce the number of degrees of freedom. This is to simplify the central control of movements. The materials and methods of the study include the experimental procedure, the surgery techniques, the electromyographic recording, and the recording of head movements. The results present the involvement of the head in gaze shifts, the head trajectory and muscular synergy, the notable elements of head trajectories, and the kinematic variability and similarity. It is concluded that muscular synergies could be used by the CNS to simply the control of complex structure through motor programs with few independent parameters.

The primary objective of this study is to describe the qualitative and quantitative relationships between head and forelimb movements in intact dogs during the early stage of instrumental learning, and in trained dogs after motor cortex ablations. The acquisition of instrumental reactions includes the stages of training, the correlation of limb and head movements, and the stability of head and limb position. The disturbance of the acquired skill after motor cortex lesions is also discussed in this chapter. The results show that there is an innate coordination of head and forelimb movements in the dog that interfere with the performance of instrumental reactions. This coordination is also displaced in head extension preceding limb flexion.

The objective of this study is to evaluate the remaining range of head movement after surgery and to account for the behavior of the intervertebral levels beyond the site of arthrodesis. There is an accurate reduction of the fracture and/or dislocation. Moreover, compensatory motion can take place on either side of the site of operation. It is concluded that any surgical intervertebral fusion jeopardizes the range of motion of the cervical spine.