Human factors in operating systems related to delay and displacement of retinal feedback.

Evaluated theories of response to altered retinal feedback i.e., associative learning doctrines and the feedback-compensation hypothesis in relation to their application in defining human factors principles in machine and perceptual training designs. Using 12 Ss, controlled comparisons were made of the relative effects of reversed and delayed feedback of head and eye movements under conditions in which head movements could not compensate altered feedback of eye movements and vice versa. Findings, e.g., the accuracy of ocular tracking, etc., are discussed. Some results indicate that there was little or no learned adaptation to the reversed and delayed vision produced by head and eye movements. Findings support a behavioral cybernetic interpretation of the guidance factors in man-machine and perceptual systems relationships by showing that the effects of altered feedback in machine and systems operation are determined by movement capabilities in compensating displacements and delays in sensory input. Results also suggest that visual impairments may be produced by delays in the retinal feedback effects of eye and head movements and that these defects may require dynamic methods of optometric diagnosis and training for their measurement and correction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Binocular coordination in reading.

Measured the differences in time between the 2 eyes, using laboratory real-time computer methods to detect and measure the time between velocity peaks of binocular saccadic movements in reading. The hypothesis was that instead of being completely conjugate as indicated by prior methods of ocular measurement, the eyes must be coordinated in directional motion by small time differences that govern their feedback guidance and relative velocity. Results with 3 Ss indicate that the time differences between the eyes clustered around 3 values: (a) near synchrony, including no difference and left eye leading by 1 msec.; (b) left eye leading by 7-9 msec.; and (c) left eye leading by 14 msec. These time differences were not related to the difficulty of the reading material, but were changed significantly by 15– horizontal rotation of the reading display. Results change the established views that the eyes are perfectly conjugate in saccadic motion and provide initial suggestive data toward a dynamic feedback doctrine of coordinate eye motion and functional disabilities in visual perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feedback factors in steering and tracking behavior.

Investigated the assumption that, in self-produced behavior, steering and target represent distinctive modes of reponse which are based, respectively, on perception and guidance of body movements in relation to the environment (steering) and on perception and guidance in relation to movement of environmental targets (stimulus tracking). These 2 modes of guided performance were compared using 7 Ss under controlled conditions in relation to the effects of feedback delay. Steering was degraded as much if not more than stimulus tracking by feedback delays between hand motion and the visual display involved in the different tasks. Steering performance, as in control of vehicles, thus may be affected seriously be feedback delays produced by powered steering and tracking devices and by inertia of action of a vehicle in relation to steering action at different speeds. Results theoretically clarify the feedback relations between self-produced and stimulus-response patterns of performance and learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of feedback delay on eye-hand synchronism in steering behavior.

Used real-time computer methods of controlling feedback factors in eye tracking to compare accuracy in tracking environmentally-generated and hand-generated visual targets in steering behavior of 5 undergraduates. Feedback delays of .1 and .2 sec. between hand and target movement produced a time lag of eye motion with respect to the hand-produced target action. Results confirm the assumption that steering and stimulus tracking represent different modes of response and are subject to different conditions of delay and displacement of action feedback of body movements. The main effect of feedback delays on eye tracking in steering was to restrict the normal capability of the eye to predict the course of self-generated stimulus movements by reducing the interval of time between hand action and eye response beyond the magnitude of the actual delay interval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Infant attention and the development of smooth pursuit tracking.

The effect of attention on smooth pursuit and saccadic tracking was studied in infants at 8, 14, 20, and 26 weeks of age. A small rectangle was presented moving in a sinusoidal pattern in either the horizontal or vertical direction. Attention level was distinguished with a recording of heart rate. There was an increase across age in overall tracking, the gain of the smooth pursuit eye movements, and an increase in the amplitude of compensatory saccades at faster tracking speeds. One age change was an increase in the preservation of smooth pursuit tracking ability as stimulus speed increased. A second change was the increasing tendency during attentive tracking to shift from smooth pursuit to saccadic tracking when the stimulus speed increased to the highest velocities. This study shows that the development of smooth pursuit and targeted saccadic eye movements is closely related to the development of sustained attention in this age range. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Detection of cortical activities on eye movement using functional magnetic resonance imaging

Cortical activity during eye movement was examined with functional magnetic resonance imaging. Horizontal saccadic eye movements and smooth pursuit eye movements were elicited in normal subjects. Activity in the frontal eye field was found during both saccadic and smooth pursuit eye movements at the posterior margin of the middle frontal gyrus and in parts of the precentral sulcus and precentral gyrus bordering the middle frontal gyrus (Brodmann's areas 8, 6, and 9). In addition, activity in the parietal eye field was found in the deep, upper margin of the angular gyrus and of the supramarginal gyrus (Brodmann's areas 39 and 40) during saccadic eye movement. Activity of V5 was found at the intersection of the ascending limb of the inferior temporal sulcus and the lateral occipital sulcus during smooth pursuit eye movement. Our results suggest that functional magnetic resonance imaging is useful for detecting cortical activity during eye movement.     

Delayed feedback in steering during learning and transfer of learning.

Compares accuracy in steering behavior as a characteristic mode of dynamic self-generation of stimuli by movement, with stimulus tracking in which response guidance is determined primarily by movements of environmental stimuli. Breath-generated variations in a visual target were used to measure steering of 24 female undergraduates. The hypotheses were that learning in tracking the respiration-generated targets would proceed more rapidly than that of tracking an environmental stimulus and that transfer of performance with the self-generated targets also would be superior. Results based on exact calibration of the equality of error control of the 2 modes of tracking confirm these assumptions. It was also found that steering and stimulus tracking were differentially affected in the learning and transfer trial series by manual-visual feedback delays between 0-1.5 sec. Results are explained theoretically by the assumption that steering reactions involved built-in stereotypical spatial and temporal coordinations between eye, hand, and body movements which were not present in the stimulus tracking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Saccade latency toward auditory targets depends on the relative position of the sound source with respect to the eyes

The latency of saccadic eye movements evoked by the presentation of auditory and visual targets was studied while starting eye position was either 0 or 20 deg right, or 20 deg left. The results show that for any starting position the latency of visually elicited saccades increases with target eccentricity with respect to the eyes. For auditory elicited saccades and for any starting position the latency decreases with target eccentricity with respect to the eyes. Therefore auditory latency depends on a retinotopic motor error, as in the case of visual target presentation.     

When is it best to hear a verb? The effects of the timing and focus of verb models on children''s learning of verbs

Recent neurophysiological studies of the saccadic ocular motor system have lent support to the hypothesis that this system uses a motor error signal in retinotopic coordinates to direct saccades to both visual and auditory targets. With visual targets, the coordinates of the sensory and motor error signals will be identical unless the eyes move between the time of target presentation and the time of saccade onset. However, targets from other modalities must undergo different sensory-motor transformations to access the same motor error map. Because auditory targets are initially localized in head-centered coordinates, analyzing the metrics of saccades from different starting positions allows a determination of whether the coordinates of the motor signals are those of the sensory system. We studied six human subjects who made saccades to visual or auditory targets from a central fixation point or from one at 10 degrees to the right or left of the midline of the head. Although the latencies of saccades to visual targets increased as stimulus eccentricity increased, the latencies of saccades to auditory targets decreased as stimulus eccentricity increased. The longest auditory latencies were for the smallest values of motor error (the difference between target position and fixation eye position) or desired saccade size, regardless of the position of the auditory target relative to the head or the amplitude of the executed saccade. Similarly, differences in initial eye position did not affect the accuracy of saccades of the same desired size. When saccadic error was plotted as a function of motor error, the curves obtained at the different fixation positions overlapped completely. Thus, saccadic programs in the central nervous system compensated for eye position regardless of the modality of the saccade target, supporting the hypothesis that the saccadic ocular motor system uses motor error signals to direct saccades to auditory targets.     

Smooth pursuit in 1- to 4-month-old human infants

The ability of human infants < or = 4 months of age to pursue objects smoothly with their eyes was assessed by presenting small target spots moving with hold-ramp-hold trajectories at ramp velocities of 4-32 deg/sec. Infants as young as 1 month old followed such target motions with a combination of smooth-pursuit and saccadic eye movements interrupted occasionally by periods when the eyes remained stationary. The slowest targets produced variable performance, but targets moving 8-32 deg/sec produced consistent pursuit behavior, even in the youngest infants. By the fourth month, eye-movement latency decreased and smooth-pursuit gain and the percentage of smooth pursuit per trial increased for all target velocities, though these measures had not yet reached adult levels.     

Eye tracking dysfunction in schizophrenia: Characterization of component eye movement abnormalities, diagnostic specificity, and the role of attention.

To characterize oculomotor components and diagnostic specificity of eye tracking abnormalities in schizophrenia, we examined a large consecutively admitted series of psychotic patients and matched controls. The most common abnormality in schizophrenic patients was low gain (slow) pursuit eye movements (47% of cases). Pursuit and saccadic eye movement abnormalities were no more severe in schizophrenic Ss than in those with affective psychoses, except that high rates of catch-up saccades were unique to schizophrenic Ss (17% of cases). These findings indicate that impaired pursuit eye movements are a major cause of eye tracking impairments in schizophrenia, that tracking dysfunctions commonly occur in affective psychoses, and that markedly high rates of catch-up saccades during eye tracking may be specific to schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Review of Eye Movements and Vision.

Reviews the book, Eye Movements and Vision by A. L. Yarbus (Lorrin A. Riggs, translation editor; Basil Haigh, translator) (1967). As Riggs says in the introduction to Yarbus's book: The "book is primarily a monograph describing the original researches of the author." The book offers considerably more to the researcher in other areas of vision or visual perception. It discusses major considerations involved in the state of the art of performing eye movement studies. The range of the topics studied is extensive, including work on flicker, color, empty fields, stationary pictures, saccadic movements, nystagmus, visual pursuit of objects, to name a few. The book relates eye movement to a broad spectrum of visual phenomena. There are other plusses on the side of the book--the art work is very good, the translation by Basil Haigh, I found easy to read. In addition, there is a bibliography containing over a hundred and fifty references. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eye-hand coordination: Oculomotor control in rapid aimed limb movements.

Three experiments are reported in which Ss produced rapid wrist rotations to a target while the position of their eyes was being monitored. In Experiment 1, Ss spontaneously executed a saccadic eye movement to the target around the same time as the wrist began to move. Experiment 2 revealed that wrist-rotation accuracy suffered if Ss were not allowed to move their eyes to the target, even when visual feedback about the moving wrist was unavailable. In Experiment 3, wrist rotations were equally accurate when Ss produced either a saccadic or a smooth-pursuit eye movement to the target. However, differences were observed in the initial-impulse and error-correction phases of the wrist rotations, depending on the type of eye movement involved. The results suggest that aimed limb movements use information from the oculomotor system about both the static position of the eyes and the dynamic characteristics of eye movements. Furthermore, the information that governs the initial impulse is different from that which guides final error corrections. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial localization with paralyzed eye muscles

Four subjects suffering from a unilateral peripheral paralysis of the 3rd or the 6th nerves have been studied in spatial localization tasks, with their normal eye occluded. When peripheral targets were presented in the hemifield corresponding to the paralysis, the saccadic eye movements (recorded from the normal occluded eye) were of an exaggerated amplitude. 'Staircase' oculomotor patterns, closely similar to those occurring in 'open-loop' visual stimulation, could also be observed. Our patients also presented the classical hypermetric misreaching when attempting to point by hand at visual targets in an otherwise dark room. This effect (past-pointing) was likely to be due to a monitoring of the exaggerated oculomotor signal: in one subject past-pointing disappeared when reaching at the targets on the basis of the sole retinal cues. Finally, the classically described illusory visual effects of ocular paralysis were limited to a feeling of instability during self-motion.     

Predictive eye movements do not discriminate between dyslexic and control children

Pavlidis has suggested that predictive saccadic tracking eye movements distinguish between reading disabled and normal children. We have examined saccadic eye movement tracking in 34 dyslexic and 33 control subjects, between 10 and 12 yr old. The subjects were equivalent in performance IQ (WISC-R), with differences between verbal and performance IQ of less than 30 points. Children with neurological, visual or auditory deficits or histories of emotional problems and hyperactivity were excluded. There were no differences between the groups on the eye movement tracking task when scored objectively by computerized analysis of the eye movement records, or by ranking of the records by an experienced observer. Our results (and those of other recent studies) fail to support Pavlidis' contention that eye movements hold the key to dyslexia.     

Eye-hand interactions during goal-directed pointing movements

Saccadic eye and hand movements made to step displacements in target position were measured under conditions designed to dissociate the output of the ocular and manual motor systems. This was accomplished by having subjects look and point, either with or without vision of the hand (closed or open loop, respectively) at peripheral targets starting from independent initial positions. The results showed that the amplitude of open loop pointing responses increased in size when accompanied by saccades that were larger than the required hand movement. Providing the subject with visual feedback of the hand during the response or asking them to visually fixate caused this effect to disappear. Taken together, this pattern of results suggests that when vision of the hand is unavailable the programming of saccade metrics influences the control of simultaneously produced pointing movements in an on-line manner.     

Carbamazepine and lamotrigine in healthy volunteers: relevance to early tolerance and clinical trial dosage

This study was conducted to examine the effects of acute doses of lamotrigine (LTG) and carbamazepine (CBZ) in healthy subjects and determine whether the low tendency to impairment with LTG observed in animals applied to humans. Twelve healthy men participated in a placebo-controlled, balanced, double-blind comparison of the drugs on a series of psychomotor, autonomic, sensory, and subjective variables. Variables were analyzed by analysis of variance, and p < 0.05 was considered significant. Adaptive tracking and body sway were impaired by CBZ 600 mg. CBZ 400 and 600 mg impaired smooth pursuit eye movements and also reduced mean peak saccadic velocity. No differences from placebo occurred after LTG. CBZ 600 mg increased heart rate (HR), but no drug-related changes were noted in pupil size, salivary secretion, visual near point, or subjective effects. During the controlled study, mean plasma CBZ concentrations at 2 and 6.5 h after the 600-mg dose were 5.28 and 5.36 micrograms/ml; after LTG 300 mg, they were 3.16 and 3.00 micrograms/ml. Increased CBZ saliva concentrations were significantly associated (p < 0.01) with impaired adaptive tracking, smooth and saccadic eye movements and increased HR, and plasma concentrations were associated with impaired eye movements and body sway.     

The effect of the gap paradigm on the latency of human smooth pursuit of eye movement

When a temporal gap is introduced between the extinction of a central fixation target and the illumination of an eccentric target (the gap paradigm), normal human subjects initiate saccadic eye movements towards the eccentric target at lower latency than when there is no gap. The aim of this study was to examine the latency of human smooth pursuit eye movements using a modified gap paradigm. Smooth pursuit latency was reduced in gap tasks, and the magnitude of reduction was related to the duration of the gap. The distribution of smooth pursuit latencies was also altered. It thus appears that human smooth pursuit latency is modulated in a similar manner to saccade latency in gap tasks.     

Eye-head coordination toward auditory and visual targets in humans

Eye-head coordination during gaze orientation toward auditory targets in total darkness has been examined in human subjects. The findings have been compared, for the same subjects, with those obtained by using visual targets. The use of auditory targets when investigating eye-head coordination has some advantages with respect to the more common use of visual targets: (i) more eccentric target positions can be presented to the subject; (ii) visual feedback is excluded during the execution of gaze displacement; (iii) complex patterns of saccadic responses can be elicited. This last aspect is particularly interesting for examining the coupling between the eyes and the head displacements. The experimental findings indicate that during gaze orientation toward a visual or an auditory target the central nervous system adopts the same strategy of using both the saccadic mechanism and the head motor plant. In spite of a common strategy, qualitative and quantitative parameters of the resulting eye-head coordination are slightly different, depending on the nature of the target. The findings relating to patterns of eye-head coordination seem to indicate a dissociation between the eyes and the head, which receive different motor commands independently generated from the gaze error signal. The experimental findings reported in this paper have been summarized in a model of the gaze control system that makes use of a gaze feedback hypothesis through the central reconstruction of the eye and head positions.     

Dissociation of saccade-related and pursuit-related activation in human frontal eye fields as revealed by fMRI

The location of the human frontal eye fields (FEFs) underlying horizontal visually guided saccadic and pursuit eye movements was investigated with the use of functional magnetic resonance imaging in five healthy humans. Execution of both saccadic and pursuit eye movements induced bilateral FEF activation located medially at the junction of the precentral sulcus and the superior frontal sulcus and extending laterally to the precentral gyrus. These findings extend previous functional imaging studies by providing the first functional imaging evidence of a specific activation in the FEF during smooth pursuit eye movements in healthy humans. FEF activation during smooth pursuit performance was smaller than during saccades. This finding, which may reflect the presence of a smaller pursuit-related region area in human FEF than the saccade-related region, is consistent with their relative size observed in the monkey. The mean location of the pursuit-related FEF was more inferior and lateral than the location of the saccade-related FEF. These results provide the first evidence that there are different subregions in the human FEF that are involved in the execution of two different types of eye movements, namely saccadic and pursuit eye movements. Moreover, this study provides additional evidence that the human FEF is located in Brodmann's area 6, unlike the monkey FEF which is located in the posterior part of Brodmann's area 8.