Large gaze shift generation whilst standing up - the role of the vestibular system

The functional significance of vestibular information for the generation of gaze shifts is controversial and less well established than the vestibular contribution to gaze stability. Here, we asked seven bilaterally avestibular patients to execute voluntary, whole-body pivot turns to visual targets up to 180° whilst standing. In these conditions not only the demands imposed on gaze transfer mechanisms are more challenging but also neck-proprioceptive input represents an inadequate source of head-in-space motion information. Patients' body segments motion was slower and jerky. In the absence of visual feedback, gaze advanced in small steps, closely resembling normal multiple-step gaze shift patterns but, as a consequence of the slow head motion, target acquisition was delayed. In approximately 25% of trials, however, patients moved faster but the velocity of prematurely emerging slow-phase compensatory eye movements remained lower than head-in-space velocity due to vestibulo-ocular failure. During these trials, therefore, gaze advanced towards the target without interruption but taking again longer than when normal controls use single-step gaze transfers. That is, even when patients attempted faster gaze shifts, exposing themselves to gaze instability they acquired distant targets significantly later than controls. Thus, whilst upright, loss of vestibular information not only disrupts gaze stability but also gaze transfers. The slow and ataxic head and trunk movements introduce significant foveation delays. These deficits explain patients' symptoms during upright activities and show, for the first time, the clinical significance of losing the so called "anti-compensatory" (gaze shifting) function of the vestibulo-ocular reflex

Gaze displacement and inter-segmental coordination during large whole body voluntary rotations

Displacements of the visual axis and multi-segmental (eye-to-foot) coordination in the yaw plane were studied in ten human subjects (Ss) during voluntary reorientations to illuminated targets of eccentricities up to 180°. We also investigated how knowledge of target location modifies the movement pattern. Eccentric targets (outbound trials) elicited eye, head, trunk and foot movements at latencies ca. 0.5, 0.6, 0.7 and 1.1 s, respectively. Knowledge of target location (return trials) reduced latencies for foot and trunk (but not eye and head) thus eye, head and trunk moved more en bloc. In most trials, the initial gaze shift fell short of the target and more than 50% of the visual angle was covered by the sum of vestibular nystagmic fast phases and head-in-space displacement, until target fixation. This indicates that during large gaze shifts the 'anticompensatory' role of the vestibulo-ocular reflex in target acquisition is prominent. During some predictable trials Ss acquired targets with a single large gaze shift, shortening target acquisition time by more than 200 ms. In these, gaze velocity (trunk-in-space + head-on-trunk + eye-in-orbit) remained often fairly constant for durations of up to 500 ms, suggesting that gaze velocity is a controlled parameter. Such pattern occurred during trunk mobilization, thus eye velocity co-varied with head-in-space rather than head-on-trunk velocity. Foot rotations were stereotyped and of constant frequency, suggesting they are generated by locomotor pattern generators. However, knowledge of target location reduced foot latencies indicating that local and supraspinal mechanisms interact for foot control. We propose that a single controller is responsible for the coupling of the multiple body segments and gaze velocity control during gaze shifts. © 2008 Springer-Verlag

Trunk bradykinesia and foveation delays during whole-body turns in spasmodic torticollis

We have investigated how the abnormal head posture and motility in spasmodic torticollis interferes with ecological movements such as combined eye-to-foot whole-body reorientations to visual targets. Eight mildly affected patients and 10 controls voluntarily rotated eyes and body in response to illuminated targets of eccentricities up to ±180. The experimental protocol allowed separate evaluation of the effects of target location, visibility and predictability on movement parameters. Patients' latencies of eye, head, trunk and foot motion were prolonged but showed a normal modification pattern when target location was predictable. Peak head-on-trunk displacement and velocity were reduced both ipsi- and contralaterally with respect to the direction of torticollis. Surprisingly, peak trunk velocity was also reduced, even more than in previously studied patients with Parkinson's disease. As a consequence, patients made short, hypometric gaze saccades and only exceptionally foveated initially nonvisible targets with a single large gaze shift (4 % of predictable trials as opposed to 30 % in controls). Foveation of distant targets was massively delayed by more than half a second on average. Spontaneous dystonic head movements did not interfere with the execution of voluntary gaze shifts. The results show that neck dystonia does not arise from gaze (head-eye) motor centres but the eye-to-foot turning synergy is seriously compromised. For the first time we identify significant 'secondary' complications of torticollis such as trunk bradykinesia and foveation delays, likely to cause additional disability in patients. Eye movements per se are intact and compensate for the reduced head/trunk performance in an adaptive manner. © 2013 The Author(s)

Measuring of distortion product otoacoustic emissions using multiple tone pairs

In order to reduce the examination time of the Distortion Product Otoacoustic Emissions (DPOAE) test, we investigated the applicability of the multiple-tone pairs method by comparing the DPOAE evoked by 4- and 3-tone pairs (Sim) with the conventional 1-tone pair (Seq) in 116 ears of human adults with normal hearing (NH) and 86 ears with sensorineural hearing loss (SNHL). We found that: (1) DPOAE amplitudes in the NH group obtained with the Sim method were strongly correlated with those of Seq. (2) DPOAE amplitude and noise level mean values obtained with the Seq method were significantly higher than those obtained with Sim. (3) DPOAE amplitude was independent of the stimulation side (right vs. left ears). (4) Both methods can equally distinguish ears with NH and a low degree of SNHL from those with higher degrees of SNHL. (5) Examination time was shorter with the Sim method in both groups. In conclusion, the Sim method produces results similar to those of Seq. However, a significant difference between the two methods in relation to DPOAE amplitudes and noise levels was found. Because of this, normal data for both the DPOAE amplitude and noise level are required to improve the sensitivity of the Sim method. The mean examination time in both groups (NH and SNHL) was shorter with the Sim method. Therefore, the multiple-tone pairs stimulation method seems to be more suitable when it is used as an auditory screening test

Altered eye-to-foot coordination in standing parkinsonian patients during large gaze and whole-body reorientations

We investigated whether turning problems in Parkinson's disease may be the result of abnormal horizontal multisegmental angular coordination. Ten mildly affected patients and controls stood upright and voluntarily reoriented eyes and body to illuminated targets of eccentricities up to ±180 degrees. The effects of target location, visibility, and predictability on movement parameters were evaluated. Patients' latencies were normal. Control subjects foveated large eccentricity targets with a single gaze shift in approximately 30% of predictable trials. Patients rarely did so (10% of predictable trials) because of reduced head-in-space and trunk velocity. This resulted in massive foveation delays in patients-an average of half a second for displacements of 180 degrees. The covariation of eye, head, and trunk rotations was quantified statistically by means of principal components analysis. In both groups, the combined movement was initially stereotyped and two principal components accounted for nearly all data variance-the original three mechanical degrees of freedom (i.e., eye-head-trunk) are reduced to two kinematic degrees of freedom. However, in patients, the eye contributed more, and the head and trunk less, to the gaze shift than in control subjects. Although the eye-to-foot turning synergy is preserved in early-stage parkinsonism, quantitative differences are prominent, particularly a larger ocular (and smaller head-trunk) contribution in patients. Turning problems in Parkinson's disease do not result from inability to assemble multisegmental movements, as patients' ability to control numerous degrees of freedom is preserved. However, trunk bradykinesia reduces the frequency of single-step gaze shifts, thus prolonging target acquisition time. Preserved eye motion compensates for trunk slowness. © 2011 Movement Disorder Society

Oral diadochokinetic rates for real words and non-words in Greek-speaking children

This study examined the performance of Greek monolingual typically developing (TD) children on diadochokinetic (DDK) rates in real words and non-words and attempted to establish normative data for Greek. The effects of age, type of stimuli and gender were investigated. A total of 380 children aged 4.0-15.0 years as well as a control group of 313 adults participated in the study. Age significantly affected DDK performance, yet normative data differ from other studies. DDK rates for bisyllabic stimuli were faster than DDK rates for trisyllabic stimuli and real words were articulated faster than non-words. Adolescents aged 13.0-15.0 years were slower than adults both in real word and in non-word /'pataka/ repetition. Additionally, overall boys were significantly faster than girls. These findings show the need to: (a) implement real word stimuli in DDK tasks in order to better depict an individual's oral-motor abilities and (b) establish language-specific normative data for TD children. © 2021 Dionysios Tafiadis et al., published by De Gruyter

Foot rotation contribution to trunk and gaze stability during whole-body mediated gaze shifts: a principal component analysis study

Large gaze displacements are mediated by combined motion of the eye, head, trunk, and foot. We applied principal component analysis (PCA) to examine the degree of variability and linearity in the angular velocity pattern of the various segments involved that participate in this task. Ten normal subjects stood up and had to visually fixate and realign their bodies with LED targets separated 45° apart, ranging from ±45 to 360°. The outbound movement in this paradigm is unpredictable whereas the return (inbound) movement occurs under spatially predictable conditions. Under such predictable conditions, subjects generate in approximately 15% of the trials gaze shifts, with periods of fairly constant high gaze velocity (single-step gaze shifts). PCA showed that gaze velocity variability did not change if the feet were rotating or not. Foot velocity was variable and showed additional PCs suggestive of non-linear motion components. Trunk and head-in-space velocity showed intermediate levels of variability but its variability decreased during the foot stepping movements. The results suggest that the feet, trunk, and head are less tightly controlled by the central nervous system than gaze velocity. Movements of the feet seem to aid trunk stability and motion rather than gaze control. © 2008 Elsevier B.V. All rights reserved