Referential processing during reading: concurrent recordings of eye movements and head motion.

Patients with Parkinson's disease (PD patients) have been shown to exhibit abnormally low levels of synergy in their posture control. The goal of this study was to determine how synergic interactions between vision and posture are affected in PD patients. These synergic interactions were expected to be impaired because PD affects the basal ganglia, which are involved in the modulation of both types of movement. Twenty patients (mean age: 60) on levodopa and 20 age-matched-controls (mean age: 61) performed a precise visual task (searching for targets in an image) and an unprecise control task (randomly looking at an image) in which images were projected onto a large panoramic display. Lower back, upper back, head and eye movements were recorded simultaneously. To test behavioural synergies, Pearson correlations between eye and postural movements were analysed. The relationships between eye movements and upper and lower back movements were impaired in the patients. The age-matched controls did not show any significant correlations between eye and postural movements. Overall, our results showed that the PD patients failed to adjust and control their postural stability for success in the visual task. The impaired synergy between eye and postural movements was not related to clinical variables-probably because our patients had early-stage PD. Our results showed that impairments in synergy can occur very early in PD. Hence, the analysis of this synergy might provide a better understanding of postural instability, visual task performance in the upright stance, and perhaps the risk of falls in PD patients.

The relationships between eye and head movements during the viewing of various visual stimuli using a head mounted display (HMD) and a large flat display were compared. The visual sizes of the images displayed were adjusted virtually, using an image processing technique. The negative correlations between head and eye movements in a horizontal direction were significant for some visual stimuli using an HMD and after some practice viewing images. Also, scores of two factors for subjective assessment of viewing stimuli positively correlated with horizontal head movements when certain visual stimuli were used. The result suggests that under certain conditions the viewing of tasks promotes head movements and stimulates correlational relationships between eye and head movements.

The role of compensatory eye and head movements for gaze stabilization in the unrestrained frog

We investigated coordinated saccadic eye and head movements following predictive horizontal visual targets at - 30° by applying transcranial magnetic stimulation (TMS) over the cerebellum before the start of the gaze movement in 10 young subjects. We found three effects of TMS on eye-head movements: 1. Saccadic latency effect. When stimulation took place shortly before movements commenced (75-25 ms before), significantly shorter latencies were found between predictive target presentation and initiation of saccades. Eye latencies were significantly decreased by 45 ms on average, but head latencies were not. 2. Gaze amplitude effect. Without TMS, for the 60° target amplitudes, head movements usually preceded eye movements, as expected (predictive gaze type 3). With TMS 5-75 ms before the gaze movement, the number of eye movements preceding head movements by 20-50 ms was significantly increased ( p < 0.001) and the delay between eye and head movements was reversed ( p < 0.001), i.e. we found eye-predictive gaze type 1. 3. Saccadic peak velocity effect. For TMS 5-25 s before the start of head movement, mean peak velocity of synkinetic eye saccades increased by 20-30% up to 600°/s, compared to 350-400°/s without TMS. We conclude that transient functional cerebellar deficits exerted by means of TMS can change the central synkinesis of eye-head coordination, including the preprogramming of the saccadic pulse and step of a coordinated gaze movement.

Relationship between eye acceleration and retinal image velocity during foveal smooth pursuit in man and monkey.

Owing to several reasons (e.g. changing light conditions) the measurement of eye movement behaviour is often unstable and data loss can occur. It is investigated whether head movement recording could be an alternative to eye movement analysis for measuring distraction through visual secondary tasks in driving. During a 1-h drive in the driving simulator, 16 participants conducted a self-paced menu system task that was designed according to design principles for commercial in-vehicle information systems. Influence of visual distraction was analysed and compared for parameters of eye and head movement. Parameters like percent road centre for head and eye movement and proportion of head movement were calculated. The results show that head movement analysis can differentiate nearly as well between distracted and attentive driving as parameters based on eye movement recording in this task context. It is concluded that head movement analysis seems to be a promising alternative for assessing drivers’ distraction under certain circumstances.

This study explored the dynamics of steady-state visual evoked potentials (SSVEPs) amid unrestricted head and eye movements using immersive virtual reality (VR) to concurrently record eye and head movement data with a 64-channel electroencephalogram (EEG) during a visual fixation task. Employing a dual-condition approach-eye-shifting and head-turning-the trials were time-locked to stimulus onset, Gaze Intersection Point (GIP) onset, and fixation onset. Eye and head velocity, Canonical Correlation Analysis (CCA) correlation, and Inter-Trial Coherence (ITC) were computed across the trial duration. SSVEP signal detection (reflected in CCA scores) was most closely aligned with the GIP onset. The CCA score increase before fixation suggests that visual processing is not fully suppressed during simultaneous head and eye movements. These findings support the potential of SSVEP for tracking the time course of visual processing in naturalistic settings where research participants are free to move their heads and eyes as they explore their three-dimensional environment.

To investigate the characteristics of the head movements and the mechanisms of gaze, stabilization during walking and running, eye and head movements were recorded in 10 normal subjects and 8 patients with labyrinthine lesions, who repeated stepping (1.OHz) and running (1.5Hz) on the same spot. 1. In normal subjects, head displacements during stepping were limited in the vertical, right-left and anteroposterior directions (0.8, 1.5 and 1.5cm on average, respectively), and the head rotations and the eye movements were also small. During running, the increase in the vertical head displacement (5.5cm on average) induced rhythmical pitching motions of the head and vertical eye movements. 2. In patients with labyrinthine lesions, both the horizontal head displacement and the rotation amplitude became twice as large as those in normal subjects during either locomotion, however, horizontal eye movements did not correspondingly increase. The vertical head displacements during running resembled those of normal subjects, but the amplitude of pitching motion of the head significantly decreased. 3) The spatial stabilization of the head during stepping in normal subjects indicated that walking is a suitable locomotion for gaze stabilization. On the other hand, the head was more unstable during running, however, the pitching motions of the head resulting from vertical head displacements seemed to reduce the concussion of the head and produce vertical compensatory eye movements which maintained the gaze stabilization. 4) In patients with labyrinthine lesions, the horizontal eye movements did not compensate the horizontal head movements during walking and running. Furthermore, since the pitching motions of the head could not be produced rhythmically during running, the vertical body oscillations were directly conducted to the head. The abnormalities of the head movements in addition to the insufficient compensations may cause oscillopsia in these patients. 5) The present study indicated that the head stabilization is essential to maintain the gaze stabilization during walking and running and that the semicircular canals-ocular reflexes act a major role in these mechanisms.

Deciphering and analyzing the neural correlates of different movements from the same limb using electroencephalography (EEG) would represent a notable breakthrough in the field of sensorimotor neurophysiology. Functional movements involve concurrent posture co-ordination and head and eye movements, which create electrical activity that affects EEG recordings. In this paper, we revisit the identification of brain signatures of different reaching movements using EEG and present, test, and validate a protocol to separate the effect of head and eye movements from a reaching task-related visuomotor brain activity. Ten healthy participants performed reaching movements under two different conditions: avoiding head and eye movements and moving with no constrains. Reaching movements can be identified from EEG with unconstrained eye and head movement, whereas the discriminability of the signals drops to chance level otherwise. These results show that neural patterns associated with different arm movements could only be extracted from EEG if the eye and head movements occurred concurrently with the task, polluting the recordings. Although these findings do not imply that brain correlates of reaching directions cannot be identified from EEG, they show the consequences that ignoring these events can have in any EEG study that includes a visuomotor task.

Although beamforming algorithms for hearing aids can enhance performance, the wearer's head may not always face the target talker, potentially limiting real-world benefits. This study aimed to determine the extent to which eye tracking improves the accuracy of locating the current talker in three-way conversations and to test the hypothesis that eye movements become more likely to track the target talker with increasing background noise levels, particularly in older and/or hearing-impaired listeners. Conversations between a participant and two confederates were held around a small table in quiet and with background noise levels of 50, 60, and 70 dB sound pressure level, while the participant's eye and head movements were recorded. Ten young normal-hearing listeners were tested, along with ten older normal-hearing listeners and eight hearing-impaired listeners. Head movements generally undershot the talker's position by 10°-15°, but head and eye movements together predicted the talker's position well. Contrary to our original hypothesis, no major differences in listening behavior were observed between the groups or between noise levels, although the hearing-impaired listeners tended to spend less time looking at the current talker than the other groups, especially at the highest noise level.

Saccadic eye movements are extremely rapid and jerk-like shifts of the eyes (up to 900 deg s−1) with which we explore our environment between periods of fixation, and other oculomotor tasks. We perform about 20 000–25 000 of such highly accurate eye movements per day to bring visual targets of interest onto our foveae. To achieve such precision, eye movements in general, and saccades in particular, need to be space–time coordinated. An article by Cromer & Waitzman (2006) in this issue of The Journal of Physiology suggests one mechanism of how space–time coordination of saccadic eye movements in the horizontal plane could be achieved by a little known and little studied area in the brainstem, the central mesencephalic reticular formation (cMRF). Although discovered years ago by the Cohen group (Cohen & Büttner-Ennever, 1984; Cohen et al. 1985, 1986), its existence had been largely neglected until the Waitzman group recently unearthed it. The classically defined cMRF is located lateral to the oculomotor nucleus (Fig. 1), dorsal to the caudal pole of the red nucleus and ventral to the posterior commissure. Different cMRF regions receive projections from small and large saccade areas of the superior colliculus (Cohen & Büttner-Ennever, 1984; Cohen et al. 1986). Stimulation of the dorsal cMRF induces fixed vector saccades (‘retinocentric’), i.e. of constant amplitude and direction regardless of the initial eye position, whereas in the ventral cMRF saccade amplitude varies depending on eye position (Cohen et al. 1985). Summary of connections of the central mesencephalic reticular formation (cMRF) The cMRF receives input from the frontal eye fields (FEFs), supplementary eye fields (SEFs) and superior colliculus (SC). Reciprocal ‘feed-back’ projections reach the SC from the cMRF. ‘Feed-forward’ projections from the cMRF target populations involved in head movements (brainstem head movement centres and cervical spinal cord) and eye movements (e.g. horizontal saccade generator network containing excitatory burst neurones (EBNs) in the paramedian pontine reticular formation (PPRF), inhibitory burst neurones (IBNs) and omnipause neurones (OPNs). Bilateral monosynaptic projections exist both to medial rectus (MR) motoneurones in the oculomotor nucleus (III) and to ‘slow’ and ‘fast’ abducens (VI) motoneurones (MNs), which innervate the lateral rectus muscle (LR). While feed-back projections from the cMRF to the SC and feed-forward projections (e.g. to PPRF) are mediated by separate neurone populations, it is unknown whether the same applies to the various other efferent projections from the cMRF. Direct projections from the cMRF to fast LR and MR MNs represent another pathway for horizontal saccade generation, in addition to traditional saccade generation pathways (involving projections from the FEFs via the SC to the PPRF, and from the PPRF to ipsilateral LR MNs and abducens internuclear neurones, AIN, and subsequently contralateral MR MNs for the production of horizontal conjugate eye movements). In addition, the cMRF plays a role in the coordination of eye and head movements, i.e. in gaze control. INC, interstitial nucleus of Cajal. The important role the cMRF is playing for space–time coordinated rapid eye movements, as shown in the article by Cromer & Waitzman (2006), has to be seen in the following context. While we may be looking anywhere at a given moment in time when an object of interest appears in our visual field, we are able to capture such a target immediately with a saccadic eye movement. The superior colliculus provides a spatial map of the visual environment of interest. The spatial code for target-selecting saccadic eye movements exists in the form of a vector representation of a given target location that allows us to shift gaze from one place to any other place in the visual field. However, up to now, it has been unclear which neuronal circuits are actually involved in performing such a movement vector calculation, since the superior colliculus only offers a spatial map but not the temporal aspect of the required eye movement. Cromer & Waitzman (2006) now offer the suggestion that various feed-back and feed-forward loops between the cMRF, the superior colliculus and the premotor saccade generator network (Fig. 1), including neurones within the cMRF, constitute a network that allows the space–time coordination of target-selecting rapid eye movements. They have identified eight different neurone types within the cMRF related to one or more saccade metric parameters and combinations thereof, e.g. velocity, duration, amplitude, etc. They argue that these different neurone types indicate different processing stages of spatial–temporal transformations via multiple anatomical pathways and physiological mechanisms. Projections from the cMRF to the premotor saccade generator network (EBNs, IBNs, OPNs) would serve as the feed-forward signals of the now time-coordinated and space-coded collicular outflow, whereas the projections from the cMRF to the superior colliculus would provide the necessary feed-back flow. Neuroanatomical tract tracing results with a retrograde transneuronal marker have shown that the cMRF also innervates directly, i.e. monosynaptically, lateral rectus (Graf et al. 2000; Ugolini et al. 2001, and submitted) and medial rectus motoneurones (Graf et al. 2002). These direct projections may be part of the network involved in generation of combined eye and head movements, i.e. gaze control, since the cMRF also innervates the cervical spinal cord (Robinson et al. 1994; Scudder et al. 1996) and brainstem head movement centres (May et al. 2005; Perkins et al. 2005). Furthermore, the cMRF, like the superior colliculus, receives direct projections from the cortical frontal eye fields (FEFs) (Huerta et al. 1986; Stanton et al. 1988) and the supplementary eye fields (SEFs) (Huerta & Kaas, 1990; Shook et al. 1990) (Fig. 1). This makes the cMRF also a potential relay to transmit information related to saccade metrics from the FEFs and SEFs to horizontal extraocular motoneurones. Finally, the cMRF may even play a role in maintaining eye position, gaze holding and fixation. Monosynaptic projections from the caudal (horizontal) cMRF to lateral rectus and medial rectus motoneurones support such an idea of participation in stabilizing eye position and fixation, particularly as such projections also target the so-called ‘slow’ lateral rectus motoneurones (Ugolini et al. 2001, and submitted), and bilateral stimulation of the cMRF promotes fixation (Cohen et al. 1985). The bilateral monosynaptic projections from the cMRF to lateral rectus motoneurones are also a potential substrate for the transmission to these motoneurones of vergence signals (Mays & Gamlin, 1995). To summarize, the cMRF is embedded in an interconnected and complex network of eye movement circuits for the production of saccades, fixation, gaze holding and vergence (Fig. 1). It receives direct input from the cortical eye movement centres, the FEFs and SEFs, and it projects directly to horizontal, i.e. lateral and medial rectus, motoneurones. There it contacts both ‘fast’ and ‘slow’ motoneurones. Besides ocular motoneurones, the cMRF also contacts the horizontal saccade generator network (EBNs, IBNs, OPNs) and head movement related brainstem centres, and maintains reciprocal connections with the superior colliculus.

Coordination of eye and head movements on nonreading tasks was investigated in 16 reading-disabled and 18 normal children aged 6 to 11 years. Types of eye movements are described and mechanisms controlling eye and head movement are reviewed. Significant differences were found between the two groups in sequencing of eye and head movements that were made in response to the appearance of visual stimuli at unexpected times and positions. Some reading-disabled children also were found to require more eye movements to achieve fixation on targets at known positions. It is suggested that the vestibular system may be implicated as a factor in the results obtained from the reading-disabled children and that the atypical eye-head movement patterns observed may did in stabilizing their visual world.

Effects of lesion of paramedian pontomedullary reticular formation by kainic acid injection on the visually triggered horizontal orienting movements in the cat

1. Monkeys were trained to look to brief visual targets presented in a completely darkened room. On some trials, after the visual target disappeared but before a saccade to the target could be initiated, the eyes were driven to another position in the orbit by electrical stimulation of the superior colliculus. Retinocentric models of the saccadic system predict that a saccade with a predetermined distance and direction based entirely on retinal error will occur. If this were the case, gaze would miss the target location by a distance and direction equal to the vector of the stimulation-induced movement. Spatial models assume that the retinal error signal will be combined with information about the change in eye position produced by stimulation and predict that the animal will look to the position of the target in space. 2. Results confirm the predictions of spatial models. Animals compensated for the stimulation-induced perturbation by looking to the position of the target in space. The result predicted by retinocentric models-a saccade with a direction and amplitude based on retinal error alone-was never observed. 3. The eye movement that compensated for the change in eye position produced by stimulation was a saccade, not a passive, lowvelocity movement to an orbital position of mechanical equilibrium established by a tonic pattern of motoneuron activation specified by the visual target. This indicates that a new saccade command, based on stored information about the location of the retinal image and information about the new position of the eyes, had been issued. Computation of the vector of the compensatory saccade does not necessarily increase the latency of target acquisition. The interval between the end of a stimulation-induced saccade and the beginning of the compensatory saccade was frequently 20 ms or less, permitting the animal to acquire the target with a normal latency.

Walking and turning is a movement that places individuals with Parkinson's disease (PD) at increased risk for fall-related injury. However, turning is an essential movement in activities of daily living, making up to 45% of the total steps taken in a given day. Hypotheses regarding how turning is controlled suggest an essential role of anticipatory eye movements to provide feedforward information for body coordination. However, little research has investigated control of turning in individuals with PD with specific consideration for eye movements. The purpose of this study was to examine eye movement behavior and body segment coordination in individuals with PD during walking turns. Three experimental groups, a group of individuals with PD, a group of healthy young adults (YAC), and a group of healthy older adults (OAC), performed walking and turning tasks under two visual conditions: free gaze and fixed gaze. Whole-body motion capture and eye tracking characterized body segment coordination and eye movement behavior during walking trials. Statistical analysis revealed significant main effects of group (PD, YAC, and OAC) and visual condition (free and fixed gaze) on timing of segment rotation and horizontal eye movement. Within group comparisons, revealed timing of eye and head movement was significantly different between the free and fixed gaze conditions for YAC (p<0.001) and OAC (p<0.05), but not for the PD group (p>0.05). In addition, while intersegment timings (reflecting segment coordination) were significantly different for YAC and OAC during free gaze (p<0.05), they were not significantly different in PD. These results suggest individuals with PD do not make anticipatory eye and head movements ahead of turning and that this may result in altered segment coordination during turning. As such, eye movements may be an important addition to training programs for those with PD, possibly promoting better coordination during turning and potentially reducing the risk of falls.