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Recent studies have shown that gait synchronization during natural walking is not merely anecdotal, but it is a repeatable phenomenon that is quantifiable and is apparently related to available sensory feedback modalities. However, the mechanisms underlying this phase-locking of gait have only recently begun to be investigated. For example, it is not known what role, if any, attention plays. We employed a dual tasking paradigm in order to investigate the role attention plays in gait synchronization. Sixteen pairs of subjects walked under six conditions that manipulated the available sensory feedback and the degree of difficulty of the dual task, i.e., the attention. Movement was quantified using a trunk-mounted tri-axial accelerometer. A gait synchronization index (GSI) was calculated in order to quantify the degree of synchronization of the gait pattern. A simple dual task resulted in an increased level of synchronization, whereas a more complex dual task lead to a reduction in synchronization. Handholding increased synchronization, compared to the same attention condition without handholding. These results indicate that in order for two walkers to synchronize, some level of attention is apparently required, such that a relatively complex dual task utilizes enough attentional resources to reduce the occurrence of synchronization.

Complex post-traumatic stress disorder (CPTSD) is a psychiatric diagnosis that includes three additional symptom clusters beyond those necessary for post-traumatic stress disorder (PTSD) diagnosis. CPTSD is typically associated with a prolonged trauma exposure in which a person's destiny is under the control of other people and escape is not an option. Insomnia prevalence in women suffering from CPTSD was compared to the prevalence of insomnia in those with no-PTSD and those with only PTSD. Yazidi women (N = 108, age = 24.41 ± 5.71) former captives of the Islamic State terrorist group were queried about captivity variables, psychological distress, resilience, PTSD, CPTSD, and insomnia. CPTSD prevalence was high (>50%) and was highly correlated with insomnia (95% of those with CPTSD had insomnia). A dichotomous insomnia variable was regressed on age and marital-status (Step 1), captivity-duration and number of fellow captives (Step 2), resilience and psychological distress (Step 3), and group (no-PTSD/PTSD/CPTSD) (Step 4). Insomnia was 18 times more likely in the CPTSD group than in the no-PTSD group. There were no differences in insomnia prevalence between the no-PTSD and PTSD groups. Insomnia levels among Yazidi women released from captivity support an understanding of CPTSD as a separate entity than PTSD. Potential factors linking CPTSD to insomnia, beyond those associated with PTSD are discussed.

OBJECTIVE: Adults diagnosed with attentional deficit disorder (ADHD) are easily distracted in many tasks. Yet ADHD performance on inattentional blindness (IB) tasks has not been examined. Such investigation may aid in discriminating between 3 ADHD models: the neurological model, the perceptual load theory, and the "hunter versus farmer" hypothesis. METHOD: Distractibility was assessed in ADHD and non-ADHD college students using the MOXO task that involves detection of a single attended stimulus that repeatedly appears in the same place and in the well-known IB "gorilla" video which involves tracking of a stimulus moving at a fast pace in a dynamic, complex manner. RESULTS: ADHD college students showed increased distractibility in the MOXO task. By contrast, they performed better than controls in the attended channel of the IB task, while they were also better at noticing the unattended stimuli and thus exhibiting little-to-no inattentional blindness. CONCLUSIONS: As no attentional tradeoffs were evident in the IB task, it appears that the results are most consistent with the "hunter versus farmer" hypothesis, which postulates that ADHD individuals have an alternative cognitive style which is less equipped to deal with detection of repeated stimuli while comprising advantages in the tracking of stimuli moving in a fast dynamic manner. (PsycINFO Database Record (c) 2015 APA, all rights reserved). Language: en

Vestibulo-Ocular Reflex (VOR) abnormalities in cerebellar ataxias are a matter of renewed interest. We have previously reported vestibular areflexia in a group of Yemenite-Jews with Spinocerebellar Ataxia Type 3 (SCA3) who had clear bilateral pathological horizontal Head Impulse Test (HIT). The objective of this study was to evaluate the VOR of ten SCA3 patients who have variable bedside HIT responses by recording their eye movements using magnetic search coils and to correlate these results with their clinical and genetic data. Eight out of the ten patients have abnormal horizontal HIT detected by both clinical bedside examination and laboratory tests. Results of bedside HIT testing were significantly correlated with the VOR gain recorded using magnetic search coils. No significant correlations were found between VOR gain and other clinical or genetic data. Our study confirms the presence of defective VOR in SCA3 patients and corroborates the useful of the HIT as a reliable bedside test for diagnosis of VOR deficits.

International audience; The present study aimed to show that bidirectional reading and language exposure influence the position of egocentric reference (ER), the perceived direction of the body's sagittal axis proposed to act as an anchor for movements in extracorporeal space. Directional factors (e.g., visual scanning bias and reading habits) have been proposed to influence visuospatial performance, such as in line bisection and figure drawing. In past studies, bidirectional readers have been less consistent in demonstrating a bias compared to unidirectional readers. Using a straight-ahead pointing task to assess egocentric reference, we compared 14 unidirectional left-to-right readers (Uni-LR) to three bidirectional reading groups that differed in the reading direction of their native language and/or the level of their second language literacy: 16 low-English literate, native right-to-left, bidirectional readers (Lo-Bi-RL), 13 high-English literate, native right-to-left, bidirectional readers (Hi-Bi-RL), and 15 native left-to-right, bidirectional readers (Bi-LR). Participants were asked to point straight-ahead while blindfolded using either a left-to-right or a right-to-left scanning direction to approach the subjective sagittal midline. Uni-LRs showed left-side spatial bias when scanning left-to-right and right-side bias during right-to-left scanning, Bi-LRs and Lo-Bi-RLs (i.e., intermediate level or less in their second language) demonstrated the opposite pattern, and Hi-Bi-RLs showed left-side spatial bias regardless of scanning direction. Results are discussed in terms of accuracy and spatial bias regarding the interaction between reading direction and spatial cognition based on the level of bidirectional literacy and language exposure.

The present study investigates the performance of persons with reading disabilities (PRD) on a variety of sequential visual-comparison tasks that have different working-memory requirements. In addition, mediating relationships between the sequential comparison process and attention and memory skills were looked for. Our findings suggest that PRD perform worse than normally achieving readers (NAR) when the task requires more than a minimal amount of working memory, unrelated to presentation rate. We also demonstrate high correlations between performance on the task with the most working-memory demands and reading-related skills, suggesting that poor working-memory abilities may be one of the underlying mechanisms of dyslexia. The mediating model analysis indicates that order judgment tasks are mediating to verbal working memory, suggesting that visual sequence memory precedes auditory sequence memory. We further suggest that visual tasks involving sequential comparisons could probe for poor working memory in PRD.

Humans have a special ability to recognize human faces that transcends and is separate from the usual discrimination abilities of the visual system. Schizophrenia patients are known to have an impaired ability to recognize facial affect, a deficit that may stem from a more profound problem of face identification and perception. The special skill of detecting human faces relies upon numerous capabilities, including gestalt perception, "filling-in", and proper gaze scanning, facilities that recent research has shown to be deficient in schizophrenia patients. We therefore hypothesized that schizophrenia patients have a deficit in their perception and structural analysis of human faces that will manifest in their difficulty in detecting faces hidden within neutral pictures. We tested the ability of 35 schizophrenia patients and 32 healthy controls at detecting hidden human faces and animals or animal faces hidden within eight pictures. Overall, the patients recognized fewer items compared to controls, however, it was specifically the human faces in which this difference was significant, suggesting that schizophrenic patients have a specific deficit in their human face recognition system.

Individuals with schizophrenia are known to demonstrate reduced or reversed brain asymmetry. While much is known regarding anatomical brain asymmetry, little is known about how this affects the individual at the functional level. Based on the known leftward bias in normal individuals, the aim of this study was to explore whether any difference in this function would be noted in schizophrenia. This study therefore investigated the phenomenon of functional asymmetry in schizophrenia patients by means of the following tasks: line bisection, line trisection (assessing hemifield spatial neglect) and letter cancellation (assessing contralateral visuospatial exploration). Forty-five schizophrenia inpatients maintained on antipsychotic medication were evaluated. Transections were measured for accuracy, lateralization, and directional bias. In the line bisection task subjects indicated no pseudo-neglect, thus differing from a normal, leftward bias. In the line trisection there was a significant preference to perform the ambiguous instruction on the right side, with no consistent bias in accuracy. Irrespective of conditions, in the letter cancellation task there was always a significant tendency to succeed on the left third compared to the right third. Results may support findings in schizophrenia indicating decreased or altered function of the left hemisphere.

Terror exposure has become commonplace in Israel, with civilians needing to develop appropriate coping mechanisms. This study investigated coping mechanisms of those who are able to return to leisure activity at sites of previous terror attacks. A specially designed questionnaire, exploring knowledge of the terror event, previous terror exposure, coping mechanisms, state of anxiety, and mood, was administered to 93 restaurant attendees at sites of well-known recent terror attacks (2001-2005). Most respondents were aware of the previous terror attack (92.3%) and most reported no fear at revisiting (70.3%), with 20.9% reporting some anxiety and 5.5% reporting moderate or severe anxiety. Sixty percent reported that they have no fear that a terror attack will reoccur at the same place. Some (27.7%) reported change in practices or decrease in one or more activity, especially use of public transport (18%). The most helpful reported resource for facilitating stress coping following a suicide bombing was to "call or be in touch with friends or relatives," and least helpful was "medicines." Over half of respondents (53%) reported that the current security climate affected their mood. Older individuals and females were more affected by terror events. Study observations confirm that resilience develops in the general population in response to ongoing terror attacks. Response to terror is heterogeneous with a range of coping mechanisms expressed.

Presenting a subject with two random-dot flow fields produces a persuasive 3D percept of a rotating cylinder whose perceived direction of rotation is bi-stable and reverses spontaneously. When real reversals are introduced subjects rarely perceive them. It is possible that although these reversals are consciously ignored, they are registered and available to the visual system for potential later use. We tested this prediction by comparing the number of spontaneously perceived reversals with and without real reversals. We found that although the actual reversals were usually not perceived, they nonetheless increased the number of spontaneous flips. The visual system apparently prefers to retain global structure rather than perceive a motion change of every element in the stimulus. However, it does not completely ignore the changes and incorporates them into other emerging interpretations. These findings argue against the fatigue hypothesis of spontaneous reversals which would predict a decrease in the number of reversals and can be interpreted as supporting the information-processing view by noting that due to the real reversals, the visual system continues to accrue data that argues against the current representation and facilitates switching to the rival representation.

Purpose A primary task of the eye care professional is determining the refraction, or optical correction, of a patient. The duochrome red-green test is a standard tool for verification of the final refraction. Traditionally, it is recommended for use both prior to and subsequent to determining the cylindrical or astigmatic component of the refraction. In order for it to be effective when used before correcting the cylinder it is necessary that the COLC (Circle of Least Confusion) be on the retina. This study examined whether it is necessarily true that the duochrome response in uncorrected astigmatism will be as trust-worthy as it is with corrected cylinders. Methods The red-green examination was performed monocularly under the following three conditions: a. fully corrected refraction for the subgroup of eyes that had spherical refractions and for the subgroup of eyes with sphero-cylindrical refractions. b. best sphere-only correction without cylinder correction in sphero-cylindrical eyes c. an induced cylinder error in spherical eyes. The interval between the last “red” response and the first “green” response for the right eyes as a group and separately for the physiological cylinder and induced cylinder correction sub-groups was calculated and compared using a paired, two-tailed t-test. Results The intervals between “red” and “green” responses were not significantly different in the population as a whole and in the uncorrected physiological cylinder and induced cylinder subgroups examined. Conclusion Based on the finding that the interval of red-green equality with fully corrected cylinder and without the cylindrical correction are not significantly different, the red-green duochrome test can indeed be used both before and after cylindrical correction.

Food deprivation has been shown to deleteriously affect human cognition, but findings are equivocal, and few studies have examined several cognitive domains. In this study, the authors used computerized testing to describe the profile of shifts in cognition attributable to short-term religious fasting. Multiple cognitive domains were evaluated at midday and late afternoon following complete abstention from eating and drinking beginning at midnight. Cross-domain, fasting-related deficits were found for tasks requiring perception of spatial relations. Fasting-related information processing deficits were found for response time but not accuracy for test levels of intermediate difficulty. Time-of-day effects often reflected poorer afternoon performance. These findings provide a detailed profile of cognitive consequences of food deprivation, affected by time of day, task demands, and type of outcome.

Gaze-evoked blinks are contractions of the orbicularis oculi (OO)—the lid closing muscle—occurring during rapid movements of the head and eyes and result from a common drive to the gaze and blink motor systems. However, blinks occurring during shifts of gaze are often suppressed when the gaze shift is made to an important visual stimulus, suggesting that the visual system can modulate the occurrence of these blinks. In head-stabilized, human subjects, we tested the hypothesis that the presence of a visual stimulus was sufficient, but not necessary, to modulate OO EMG (OOemg) activity during saccadic eye movements. Rapid, reorienting movements of the eyes (saccades) were made to visual targets that remained illuminated (visually guided trials) or were briefly flashed (memory-guided trials) at different amplitudes along the horizontal meridian. We measured OOemg activity and found that the magnitude and probability of OOemg activity occurrence was reduced when a saccade was made to the memory of the spatial location as well as to the actual visual stimulus. The reduced OOemg activity occurred only when the location of the target was previously cued. OOemg activity occurred reliably with spontaneous saccades that were made to locations with no explicit visual stimulus, generally, back to the fixation location. Thus the modulation of gaze-evoked OOemg activity does not depend on the presence of visual information per se, but rather, results from an extraretinal signal.

There are presently several ongoing clinical trials to provide usable sight to profoundly visually impaired patients by means of electrical stimulation of the retina. Some of the blind patients implanted with retinal prosthesis reported un-patterned perception and yet benefit from the device in many activities of daily living, seemingly because they adopt active scanning strategies. The aim of the present work is to evaluate if and under what conditions a measured visual acuity level is truly an indication that the brain perceived a patterned image from the electrical stimulation of the visual prosthesis. Sighted subjects used a pixelized simulator in which they perceived either a low resolution sub-sampling of the original image (“normal mode” – patterned vision) or an image that was solely a function of the brightness and size of the original image (“brightness mode” – no patterned vision). Results show that subjects were able to adopt a head scanning strategy that enabled acuity beyond the resolution set by a static view of the stimulus. In brightness mode, i.e. without patterned vision, most subjects achieved a measurable acuity level better than the limit set by the geometrical resolution of the entire array but worse than the limit set by the distance between neighboring simulated pixels. In normal mode all subject achieved acuity level that is better than the geometrical resolution of the simulated pixels. Thus, visual acuity levels comparable with the electrodes/pixels resolution implies that the patient perceives an image with spatial patterns.

Eye movements were recorded from three subjects as they initiated tracking of a small circle (“target”) moving leftward or rightward, above or below the horizontal meridian, either alone or in the presence of a small square (“distractor”) moving leftward or rightward on the other side of the horizontal meridian. At the start of each trial, subjects were provided with either a “form” cue (always centrally positioned and having the circular shape and color of the upcoming moving target) or a “location” cue (a small white square positioned where the upcoming target would appear). The latency of pursuit increased in the presence of an oppositely moving distractor when subjects were provided the form cues but not when they were provided the location cues. The latency of saccades showed similar, but smaller, increases when subjects were given the form cues. On many trials with the form cues, pursuit started in the direction of the distractor and then reversed to follow the target. On these trials, the initial saccade often, but not always, also followed the distractor. These results indicate that the mechanisms of target selection for pursuit and saccades are tightly coordinated but not strictly yoked. The shared effects of the distractor on the latencies of pursuit and saccades probably reflect the common role of visual attention in filtering the inputs that guide these two types of eye movements. The differences in the details of the effects on pursuit and saccades suggest that the neural mechanisms that trigger these two movements can be independently regulated.

We compared the accuracy of oblique, memory-guided saccades if the eye is stationary or moves horizontally during the memory period. We studied 11 patients with cerebellar disease and 11 age-matched control subjects. Normal subjects showed similar accuracy of saccades for both conditions. In contrast, all patients showed greater errors if the eye moved horizontally during the memory period; however, errors of both vertical and horizontal components of memory-guided saccades were similar. Thus, inaccuracy of memory-guided saccades could not be simply attributed to failure to internally monitor change in horizontal gaze during the memory period. Instead, we propose that the greater saccadic errors which occurred when gaze changed during the memory period reflected a disruption of predictive mechanisms governing eye movements.

Rottach, Klaus G., Vallabh E. Das, Walter Wohlgemuth, Ari Z. Zivotofsky, and R. John Leigh. Properties of horizontal saccades accompanied by blinks. J. Neurophysiol. 79: 2895–2902, 1998. Using the magnetic search coil technique to record eye and lid movements, we investigated the effect of voluntary blinks on horizontal saccades in five normal human subjects. The main goal of the study was to determine whether changes in the dynamics of saccades with blinks could be accounted for by a superposition of the eye movements induced by blinks as subjects fixated a stationary target and saccadic movements made without a blink. First, subjects made voluntary blinks as they fixed on stationary targets located straight ahead or 20° to the right or left. They then made saccades between two continuously visible targets 20 or 40° apart, while either attempting not to blink, or voluntarily blinking, with each saccade. During fixation of a target located straight ahead, blinks induced brief downward and nasalward deflections of eye position. When subjects looked at targets located at right or left 20°, similar initial movements were made by four of the subjects, but the amplitude of the adducted eye was reduced by 65% and was followed by a larger temporalward movement. Blinks caused substantial changes in the dynamic properties of saccades. For 20° saccades made with blinks, peak velocity and peak acceleration were decreased by ∼20% in all subjects compared with saccades made without blinks. Blinks caused the duration of 20° saccades to increase, on average, by 36%. On the other hand, blinks had only small effects on the gain of saccades. Blinks had little influence on the relative velocities of centrifugal versus centripetal saccades, and abducting versus adducting saccades. Three of five subjects showed a significantly increased incidence of dynamic overshoot in saccades accompanied by blinks, especially for 20° movements. Taken with other evidence, this finding suggests that saccadic omnipause neurons are inhibited by blinks, which have longer duration than the saccades that company them. In conclusion, the changes in dynamic properties of saccades brought about by blinks cannot be accounted for simply by a summation of gaze perturbations produced by blinks during fixation and saccadic eye movements made without blinks. Our findings, especially the appearance of dynamic overshoots, suggest that blinks affect the central programming of saccades. These effects of blinks need to be taken into account during studies of the dynamic properties of saccades.

We measured the eye movements of three sisters with Niemann-Pick type C disease who had a selective defect of vertical saccades, which were slow and hypometric. Horizontal saccades, and horizontal and vertical pursuit and vestibular eye movements were similar to control subjects. The initial movement of oblique saccades was mainly horizontal and most of the vertical component occurred after the horizontal component ended; this resulted in strongly curved trajectories. After completion of the horizontal component of an oblique saccade, the eyes oscillated horizontally at 10–20 Hz until the vertical component ended. These findings are best explained by models that incorporate separate feedback loops for horizontal and vertical burst neurons, and in which the disease selectively affects vertical burst neurons.

We measured torsional eye movements induced by sinusoidal rotation or static tilt, of the head in roll while viewing a far or near target in 4 patients with skew deviation due to brainstem lesions, 4 patients with spasmodic torticollis (ST), 2 patients with unilateral eighth nerve section (VIIIS), and 10 normal subjects. Torsional nystagmus was present in all 4 patients with skew deviation. In subjects and patients, responses to both sinusoidal and static roll were larger while viewing the far target, consistent with factors dictated by geometry. Response gains to sinusoidal roll were abnormal in 3 patients with skew (increased in one, decreased in two), abnormal in 3 with ST (increased in 1, decreased in 2), and in abnormal both VIIIS patients (decreased). Greater abnormalities were evident in 3 skew patients while rolling away from the side of their brainstem lesions and in both VIIIS patients while rolling toward their lesioned ears. There were similar but less pronounced changes during static head roll. We conclude that patients with skew, ST, and VIIIS may all have abnormal ocular counter-rolling that is more evident during dynamic testing while viewing a far target. Such abnormalities endure because of the limited influence exerted by vision on torsional eye movements.

1. Measurements were made in four normal human subjects of the accuracy of saccades to remembered locations of targets that were flashed on a 20 x 30 deg random dot display that was either stationary or moving horizontally and sinusoidally at +/-9 deg at 0.3 Hz. During the interval between the target flash and the memory-guided saccade, the “memory period” (1.4 s), subjects either fixated a stationary spot or pursued a spot moving vertically sinusoidally at +/-9 deg at 0.3 Hz. 2. When saccades were made toward the location of targets previously flashed on a stationary background as subjects fixated the stationary spot, median saccadic error was 0.93 deg horizontally and 1.1 deg vertically. These errors were greater than for saccades to visible targets, which had median values of 0.59 deg horizontally and 0.60 deg vertically. 3. When targets were flashed as subjects smoothly pursued a spot that moved vertically across the stationary background, median saccadic error was 1.1 deg horizontally and 1.2 deg vertically, thus being of similar accuracy to when targets were flashed during fixation. In addition, the vertical component of the memory-guided saccade was much more closely correlated with the “spatial error” than with the “retinal error” this indicated that, when programming the saccade, the brain had taken into account eye movements that occurred during the memory period. 4. When saccades were made to targets flashed during attempted fixation of a stationary spot on a horizontally moving background, a condition that produces a weak Duncker-type illusion of horizontal movement of the primary target, median saccadic error increased horizontally to 3.2 deg but was 1.1 deg vertically. 5. When targets were flashed as subjects smoothly pursued a spot that moved vertically on the horizontally moving background, a condition that induces a strong illusion of diagonal target motion, median saccadic error was 4.0 deg horizontally and 1.5 deg vertically; thus the horizontal error was greater than under any other experimental condition. 6. In most trials, the initial saccade to the remembered target was followed by additional saccades while the subject was still in darkness. These secondary saccades, which were executed in the absence of visual feedback, brought the eye closer to the target location. During paradigms involving horizontal background movement, these corrections were more prominent horizontally than vertically. 7. Further measurements were made in two subjects to determine whether inaccuracy of memory-guided saccades, in the horizontal plane, was due to mislocalization at the time that the target flashed, misrepresentation of the trajectory of the pursuit eye movement during the memory period, or both. 8. The magnitude of the saccadic error, both with and without corrections made in darkness, was mislocalized by approximately 30% of the displacement of the background at the time that the target flashed. The magnitude of the saccadic error also was influenced by net movement of the background during the memory period, corresponding to approximately 25% of net background movement for the initial saccade and approximately 13% for the final eye position achieved in darkness. 9. We formulated simple linear models to test specific hypotheses about which combinations of signals best describe the observed saccadic amplitudes. We tested the possibilities that the brain made an accurate memory of target location and a reliable representation of the eye movement during the memory period, or that one or both of these was corrupted by the illusory visual stimulus. Our data were best accounted for by a model in which both the working memory of target location and the internal representation of the horizontal eye movements were corrupted by the illusory visual stimulus. We conclude that extraretinal signals played only a minor role, in comparison with visual estimates of the direction of gaze, in planning eye movements to remembered targ

Article abstract-We used the magnetic search coil technique to measure horizontal, vertical, and torsional components of convergent-divergent pendular nystagmus in three patients. All showed phase shifts of approximately 180 degrees between the two eyes in the horizontal and torsional planes, but the vertical components were conjugate. Viewing a near target increased the oscillations threefold in one patient and by 60% in a second patient. The waveform was sinusoidal in one patient, but in the other two it was complex, resembling either a sum of several sine waves or a cycloid. When the predominant frequency of the nystagmus was low (1.8 Hz), oscillation of visually mediated vergence might have been responsible; when the frequency was high (6 Hz), the nystagmus might have arisen from an internal instability in connections between nucleus reticularis tegmenti pontis and cerebellar nucleus interpositus, which are important for vergence control.NEUROLOGY 1995;45: 509-515

Purpose The purpose of the current research is to understand if the different eye movement abnormalities in patients with the same neurologic disease are related to varied disease processes or, alternately, do different patients adopt different strategies to overcome a singular brain deficiency. Methods Using a magnetic search coil, we measured saccade dynamics, that is position and velocity waveforms, for patients diagnosed with spinocerebellar ataxia type 3 (SCA-3), also known as Machado-Joseph disease (MJD). Results We observed that the saccadic waveform of the majority of the SCA-3 patients (7 of 10) exhibited dynamic overshoot, with the eye passing the desired endpoint and making a rapid correction before coming to rest. Patients with normal waveforms, that is with no dynamic overshoot, had saccades with relatively low peak velocity. Conclusions Velocity feedback in a closed loop control system is essential for providing a fast response without overshoot. Lack of a velocity feedback or an imbalance between position and velocity gains yields a tradeoff between response time and overshoot. While the goal of a saccade is to get to the desired position, models based on animal research suggest that the saccadic control also incorporates a velocity feedback. Results presented here indicated that all SCA-3 patients had deviations in the saccadic waveform, albeit of two types, either slow saccades or dynamic overshooting saccades. Using saccadic models based on animal research can explain how a single deficit, that is a mismatched velocity control of the motor error due to the disease, can yield these two different abnormalities in human patients.

Calabria and Rossetti (2005) demonstrated that spatial biases related to the mental number line can be seen even when bisecting strings of number words. Strings of smaller magnitude number words were bisected further to the left than strings of larger magnitude number words. The current study investigated whether the left-to-right mental number line associated with number processing will result in similar spatial biases despite a habitual, right-to-left reading direction. Monolingual left-to-right readers were compared to bidirectional readers of English and Hebrew. Strings of Arabic numerals and of number words (e.g., THREE, EIGHT) were presented in separate conditions of English and Hebrew. Significant rightward biases were seen among native Hebrew readers, regardless of English reading level; whereas native English readers (both bidirectional and monodirectional) did not show significant biases to either the left or the right. The spatial bias in bisecting either Arabic numeral strings or number words was related to the habitual reading direction of the participant. There was no difference in spatial bias or for frequency of spatial bias based on numerical magnitude for either condition. We discuss the influence of cultural factors, such as reading direction and proficiency, on the representation of spatial and numerical material.

Prominent formal thought disorder, expressed as unusual language in speech and writing, is often a central feature of Schizophrenia. Since a more comprehensive understanding of phenomenology surrounding thought disorder is needed, this study investigates these processes by examining writing in Schizophrenia by novel computer-aided analysis. Thirty-six patients with DSM-IV criteria chronic Schizophrenia provided a page of writing (300-500 words) on a designated subject. Writing was examined by automated text categorization and compared with nonpsychiatrically ill individuals, investigating any differences with regards to lexical and syntactical features. Computerized methods used included extracting relevant text features, and utilizing machine learning techniques to induce mathematical models distinguishing between texts belonging to different categories. Observations indicated that automated methods distinguish schizophrenia writing with 83.3% accuracy. Results reflect underlying impaired processes including semantic deficit, independently establishing connection between primary pathology and language.

Although of clinical interest, the question is still not fully answered whether antidepressants (AD) can cause or exacerbate restless legs syndrome (RLS). The literature provides contradictory information. This study addresses this problem for the class of second generation AD. In four neurological offices, all patients treated for the first time with an AD were prospectively observed with regard to the question of whether RLS occurred or pre-existing RLS worsened as a result of the medication. Because initial treatment in the participating offices is mainly executed with "modern" selective AD, the study was restricted to these drugs (fluoxetine, paroxetine, citalopram, sertraline, escitalopram, venlafaxine, duloxetine, reboxetine, and mirtazapine). In 9% of patients, RLS was recorded as a side effect related to the administration of AD. The frequency of this side effect varied among the drugs. The problem is most pronounced with mirtazapine provoking or deteriorating RLS in 28% of patients. By contrast, no case occurred during use of reboxetine. As for the other AD, the rate of newly occurred and deteriorated RLS, ranged from 5% to 10%. Typically, RLS occurred during the initial days of treatment.

Developmental dyslexia is a language-based learning disability with frequently associated non-linguistic sensory deficits that have been the basis of various perception-based theories. It remains an open question whether the underlying deficit in dyslexia is a low level impairment that causes speech and orthographic perception deficits that in turn impedes higher phonological and reading processes, or a high level impairment that affects both perceptual and reading related skills.We investigated by means of contrast detection thresholds two low-level theories of developmental dyslexia, the magnocellular and the fast temporal processing hypotheses, as well as a more recent suggestion that dyslexics have difficulties in sequential comparison tasks that can be attributed to a higher-order deficit. It was found that dyslexics had significantly higher thresholds only on a sequential, but not a spatial, detection task, and that this impairment was found to be independent of the inter-stimulus interval. We also found that the poor performance of dyslexics on the temporal task was dependent on the size of the required memory trace of the image rather than on the number of images. Our findings do not support the magnocellular theory and challenge the fast temporal deficit hypothesis. We suggest that dyslexics may have a higher order, dual mechanism impairment. We also discuss the clinical implications of our findings.

Background. Paradoxical diplopia is a condition in which objective eye position contradicts subjective localization in visual space. The term “paradoxical” is usually reserved for instances when known sensory adaptations cannot explain the contradiction. The development of this condition begins with infantile or childhood strabismus, followed by the development of a common sensory adaptation, anomalous retinal correspondence (ARC). ARC causes a reduction in the subjective angle of strabismus compared with the objective angle, and in its completed form the subjective angle decreases to zero. There is no “adaptive” mechanism that would increase the subjective angle such that it would be greater than the objective. In cases of treatment by corrective surgery, the anatomically based motor correction leads to a contradiction between eye position and binocular perception. In this event, the objective angle is less than the subjective, and the result is a paradoxical perception. We encountered a 25-year-old woman who experiences paradoxical localization on cover testing in the absence of a manifest strabismus and with no previous surgical intervention. Methods. Using a magnetic search coil technique, we evaluated eye movements during fixation, smooth pursuit, saccades, and during cover test conditions to determine how these eye movements correlated to the subjective perception in space. Results. Although smooth pursuit and saccades were normal, there were two elements during cover test that could explain the paradoxical projection. One was the phenomenon that during the cover test the paradoxical projection appeared only when the eye was covered for >4 s. The second was that there was a regression from the full exophoria position toward the midline while the eye was under cover that correlated with a possible paradoxical projection situation. Discussion. ARC, usually associated with a beneficial sensorimotor adaptation, can express itself as a detrimental sensorimotor manifestation. Paradoxical perception also can exist without previous surgical intervention and without the influence of prisms and instrumentation such as the synoptophore. Further studies are indicated to explore the sensorimotor feedback mechanism between eye position and spatial perception.

Real-life visual tasks such as tracking jumping objects and scanning visual scenes often require a sequence of saccadic eye movements. The ability of the ocular motor system to parallel process saccades has been previously demonstrated. We recorded the monocular eye movements of five normal human subjects using the magnetic search coil technique in a double step paradigm. Initial target jumps were always purely horizontal or purely vertical. We were interested in the latency to onset of the second saccade as a function of direction in relation to the first saccade. When the inter stimulus interval (ISI) was 150 or 180 ms orthogonal second saccades were of significantly shorter latency than second co-linear saccades. When the ISI was 250 ms the latencies of orthogonal and co-linear second saccades were statistically indistinguishable. Based on these findings it is postulated that the ocular motor system can more readily co-process orthogonal than co-linear saccades.

It might be intuited that a person's reading direction will impact linguistic and/or oculomotor tasks. Whether it also influences nonlanguage tasks, and by what means, is less clear. A novel technique to probe this effect is introduced in this paper, and the affirmative results are presented. The line bisection task has been a standard bedside diagnostic technique for assessing hemifield spatial neglect for many years. In recent years, numerous studies have also examined how normal subjects perform on this task. A recent line of study has focused on the reading habits of the subjects and the effect it has on line bisection. Most European languages are read from left to right, and it is thus postulated that readers of those languages will scan a line from left to right. On the other hand, Hebrew is read from right to left. These previous studies have yielded intriguing results about the role that reading direction plays in nonlanguage tasks. The present study utilized two other line partition tasks, line trisection and line quadrisection, and subjects whose principal reading language was either right-to-left or left-to-right. These tasks are ambiguous when used without instructing the subject on which side to perform the line transection. It was found that principal language was correlated with the side on which the subject chose to trisect or quadrisect the line. However, there was no correlation between preferred side and writing hand and there was no significant difference in accuracy between the preferred side and the secondary side. Thus, the preferred side in this nonlanguage task does not seem to be influenced by writing hand or accuracy but rather would seem to depend exclusively upon the earliest legitimate point, as determined by reading direction.

We compared horizontal and vertical smooth pursuit eye movements in five healthy human subjects. When maintenance of pursuit was tested using predictable waveforms (sinusoidal or triangular target motion), the gain of horizontal pursuit was greater, in all subjects, than that of vertical pursuit; this was also the case for the horizontal and vertical components of diagonal and circular tracking. When initiation of pursuit was tested, four subjects tended to show larger eye accelerations for vertical as opposed to horizontal pursuit; this trend became a consistent finding during diagonal tracking. These findings support the view that different mechanisms govern the onset of smooth pursuit, and its subsequent maintenance when the target moves in a predictable waveform. Since the properties of these two aspects of pursuit differ for horizontal and vertical movements, our findings also point to separate control of horizontal and vertical pursuit. Copyright © 1996 Elsevier Science Ltd.

1. Humans may visually track a moving object either when they are stationary or in motion. To investigate visual-vestibular interaction during both conditions, we compared horizontal smooth pursuit (SP) and active combined eye-head tracking (CEHT) of a target moving sinusoidally at 0.4 Hz in four normal subjects while the subjects were either stationary or vibrated in yaw at 2.8 Hz. We also measured the visually enhanced vestibuloocular reflex (VVOR) during vibration in yaw at 2.8 Hz over a peak head velocity range of 5–40 degrees/s. 2. We found that the gain of the VVOR at 2.8 Hz increased in all four subjects as peak head velocity increased (P < 0.001), with minimal phase changes, such that mean retinal image slip was held below 5 degrees/s. However, no corresponding modulation in vestibuloocular reflex gain occurred with increasing peak head velocity during a control condition when subjects were rotated in darkness. 3. During both horizontal SP and CEHT, tracking gains were similar, and the mean slip speed of the target's image on the retina was held below 5.5 degrees/s whether subjects were stationary or being vibrated at 2.8 Hz. During both horizontal SP and CEHT of target motion at 0.4 Hz, while subjects were vibrated in yaw, VVOR gain for the 2.8-Hz head rotations was similar to or higher than that achieved during fixation of a stationary target. This is in contrast to the decrease of VVOR gain that is reported while stationary subjects perform CEHT.(ABSTRACT TRUNCATED AT 250 WORDS)

We investigated the pathogenesis of acquired pendular nystagmus (APN) in six patients, three of whom had multiple sclerosis. First, we tested the hypothesis that the oscillations of APN are due to a delay in visual feedback secondary, for example, to demyelination of the optic nerves. We manipulated the latency to onset of visually guided eye movements using an electronic technique that induces sinusoidal oscillations in normal subjects. This manipulation did not change the characteristics of the APN, but did superimpose lower-frequency oscillations similar to those induced in normal subjects. These results are consistent with current models for smooth (non-saccadic) eye movements, which predict that prolongation of visual feedback could not account for the high-frequency oscillations that often characterize APN. Secondly, we attempted to determine whether an increase in the gain of the visually-enhanced vestibulo-ocular reflex (VOR), produced by viewing a near target, was accompanied by a commensurate increase in the amplitude of APN. Increases in horizontal or vertical VOR gain during near viewing occurred in four patients, but only two of them showed a parallel increase in APN amplitude. On the other hand, APN amplitude decreased during viewing of the near target in the two patients who showed no change in VOR gain. Taken together, these data suggest that neither delayed visual feedback nor a disorder of central vestibular mechanisms is primarily responsible for APN. More likely, these ocular oscillations are produced by abnormalities of internal feedback circuits, such as the reciprocal connections between brainstem nuclei and cerebellum.

PURPOSE. Dyslexia is a language-based learning disability characterized by difficulties with reading, spelling, and writing. Persons with dyslexia often have deficits in processing rapid temporal sensory information. There is also evidence of sensorimotor deficits in persons with dyslexia. Whether these deficits include ocular motor problems is still an open question. Some previous studies have shown an increased saccadic latency in dyslexics, whereas others have not reproduced this finding. The purpose of the present study was to investigate saccadic latency in young adults with dyslexia during the double-step paradigm, a task that requires rapid sequential visual information processing and saccade generation. The study hypothesis was that dyslexics have a longer saccadic latency in the second orthogonal saccade, a task that nondyslexics parallel process and perform rapidly. METHODS. Eight students with dyslexia and eight age-matched control subjects participated in the study. Their eye movements were monitored with the scleral search coil technique in simple saccade trials and in the double-step paradigm. The second saccade was either orthogonal or colinear to the first. Intersaccadic interval and latency were calculated for the second saccade. RESULTS. No difference in saccadic latency was found for colinear second saccades; however, dyslexics had significantly longer latencies for orthogonal second saccades. This included a subset of subjects who had longer latencies for orthogonal than for colinear saccades. CONCLUSIONS. The findings indicate that under certain conditions, when the demand for rapid visual information processing is high and a rapid saccade sequence is required, some persons with dyslexia show ocular motor deficits manifested by longer saccadic latencies.

In 10 human subjects, we measured the accuracy of saccades to remembered locations of targets that were flashed on a 20 × 30 deg random dot display, while they tracked a spot of light that stepped between three vertical locations. The background was either stationary or stepping horizontally in synchrony with vertical motion of the spot of light, a condition that induced a strong illusion of diagonal target motion. Memory-guided saccades were less accurate horizontally, but not vertically, when the background moved compared with when it was stationary. The horizontal component of memory-guided saccades correlated better with the position of the background when the target was flashed than with the position of the background at the end of the memory period. We conclude that the visual illusion corrupted the working memory of target location, but had a lesser effect on the estimate of gaze at the end of the memory period, which seemed to depend more on extraretinal signals.