Reversed visual motion and self-sustaining eye oscillations

A random-dot field undergoing counterphase flicker paradoxically appears to move in the same direction as head and eye movements, i.e. opposite to the optic-flow field. The effect is robust and occurs over a wide range of flicker rates and pixel sizes. The phenomenon can be explained by reversed phi motion caused by apparent pixel movement between successive retinal images. The reversed motion provides a positive feedback control of the display, whereas under normal conditions retinal signals provide a negative feedback. This altered polarity invokes self-sustaining eye movements akin to involuntary optokinetic nystagmus.     

Delayed retinal feedback of eye movements: A dynamic basis of perceptual disabilities.

Investigated temporal factors in vision in relation to the delay of the retinal feedback of ocular movements in eye tracking. A hybrid real-time computer system and dynamic programing methods were used to calibrate photoelectric eye-movement transducers in viewing visual targets, to yoke these targets to eye motion, to introduce feedback delays in eye-movement-retinal interaction, and to measure error in eye tracking. Results indicate that feedback delay affected the accuracy of both the compensatory and the pursuit tracking in a significant way, with a somewhat greater effect being found for pursuit movements. Since delay reduced smooth pursuit motions to saccadic reactions that varied in size with the delay interval, it is suggested that ocular dynamics and guidance in space perception are governed by time-specific neuron mechanisms of the central visual system. Findings negate classical theory of ocular dynamics and perception of direction by proving that directional guidance of the eyes is determined by directional specificity and temporal specificity of the feedback processes of pursuit and saccadic movements of the eyes and is not caused primarily by learned temporal association between visual and tactual sensory processes. It is concluded that major disabilities and distortions in vision, which are not reducible to traditionally defined optometric and ophthalmologic factors, may be produced by built-in developmental perturbations of ocular feedback timing. Findings emphasize dynamic optometric measurements in understanding common and elusive distortions of visual perception. (19 ref.) (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)     

Emergent textural contours: a new technique for visual monitoring in nystagmus, oculomotor dysfunction, and accommodative disorders

Emergent textural contours, the perceptual effect seen during continuous rotation of symmetrical arrays of uniform pattern elements, provide a unique source of visual feedback for eye movements and resolutional states and have potential for use as a new clinical tool. The phenomenon is produced by a combination of factors including the effects of visual persistence and differential resolution. A total of 28 subjects including 17 normals, 4 nystagmus, 4 oculomotor dysfunction, and 3 accommodative facility cases were shown an emergent textural contour with an instrument (the Goldrich Contour Rotator) for its display. Subjects were enabled to monitor their own eye movements and accommodative training. Nystagmus subjects were provided with a continuous source of visual input reflecting their ocular oscillations and a determination of the null point of nystagmus was made with the instrument.     

Illusory concomitant motion in ambiguous stereograms: Evidence for nonstimulus contributions to perceptual organization.

Performed 3 experiments to test whether perceptual organization is cognitively or motivationally penetrable. In Exp I, 8 undergraduate and graduate students viewed a reversible stereogram while instructed to hold 1 depth organization. Responses about depth were recorded indirectly by recording responses about direction of the illusory concomitant motion that is perceptually coupled to depth in a stereogram. It is contended that, inasmuch as perceptually coupled variables covary without necessary stimulus covariation, a postperceptual locus for any intention effects they exhibit is unlikely. Results show that instruction influenced perceived depth to a degree influenced by stimulus bias. Exps II and III examined the possibility that instructed intention might influence perception indirectly by influencing eye movements. Eight graduate student viewers' vergence position was measured directly through responses about alignment of a vernier nonius fixation. Findings from Exp II indicate an interaction between hold instruction and stimulus bias. However, unlike Exp I, instructed responses were larger with the depth response than with the motion response. Results from Exp III reveal that differential instructions produced different responses about perceptual organization, but that they were not reliably accompanied by different vergence movements. Overall findings suggest that instructed intention may influence perceptual organization by influencing internal nonstimulus components to the perceptual process. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of eye and head movements in detecting information about fly balls.

The authors attempted to identify perceptual mechanisms that pick up information for initiating a run to catch fly balls and for judging their landing locations. Fly balls have been shown to be tracked with the eyes and head (R. R. D. Oudejans, C. F. Michaels, F. C. Bakker, & K. Davids, 1999). This raised the question of whether constraining eye and head movements of experienced baseball players by having them wear eye-movement-preventing goggles (eye movements would lead to losing sight of the ball) or a head-movement-preventing neck brace, or both, would limit their capacity (a) to start running in the correct direction and (b) to make correct judgments about the balls' landing locations. Restrictions had minimal effects on response accuracy, but response latency was affected. The goggles increased latency of both running and judging. Moreover, the neck brace decreased judgment time, particularly for difficult balls, suggesting that head stability is important for making judgments. High performance levels suggested that the perceptual system was flexible; that is, different parts of the system can perform the same function. The implications of these findings for perceptual mechanisms are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Head and eye movements in unrestrained pigeons (Columba livia).

Head and eye movements were simultaneously recorded during locomotory and pecking behavior of 4 pigeons, which were trained to traverse a conditioning chamber, with a pecking key and a food dispenser at each end. Each trial involved key pecking, walking, and feeding. Head movements were registered with a skull-mounted miniature accelerometer, and eye movements were recorded with implanted electrooculogram (EOG) electrodes. An almost perfect temporal coordination between head and eye movements was observed during both walking and feeding bouts. During walking, head movements primarily provide retinal image stability, and eye movements support visual scanning. During feeding, head movements mainly subserve the grasping of food items, and eye movements maintain visual fixation on them. Because the eyes are reflexively closed during the middle phase of pecks, the head and eye movements are then under ballistic control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The time course of plausibility effects on eye movements in reading: Evidence from noun-noun compounds.

Readers' eye movements were monitored as they read sentences containing noun-noun compounds that varied in frequency (e.g., elevator mechanic, mountain lion). The left constituent of the compound was either plausible or implausible as a head noun at the point at which it appeared, whereas the compound as a whole was always plausible. When the head noun analysis of the left constituent was implausible, reading times on this word were inflated, beginning with the first fixation. This finding is consistent with previous demonstrations of very rapid effects of plausibility on eye movements. Compound frequency did not modulate the plausibility effect, and all disruption was resolved by the time readers' eyes moved to the next word. These findings suggest (contra Kennison, 2005) that the parser initially analyzes a singular noun as a head instead of a modifier. In addition, the findings confirm that the very rapid effect of plausibility on eye movements is not due to strategic factors, because in the present experiment, unlike in previous demonstrations, this effect appeared in sentences that were globally plausible. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stabilization of the retinal image: A review of method, effects, and theory.

A summary is presented of 3 basic methods used in reducing or stopping involuntary eye movements in order to produce a stable retinal image. This stabilization produces some degree of fading or disappearance of the target being viewed. Additional effects on such factors as acuity and contrast thresholds are considered, as well as the effects of such variables as exposure time, flicker, attention, meaning, and target complexity on the nature and extent of target disappearance. Some explanations for the phenomenon are presented, and the theoretical implications of invariant stimulation on the perceptual process are discussed. (39 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental response to limb deficiency and limb replacement.

Discusses perceptual–motor and cognitive development in children with congenital upper-limb deficiency and the use of myoelectric (i.e., responsive to muscle contractions) arm prosthesis in treatment. Ss can be trained to control motor activity that activates artificial limb movement, using conditioning or auditory and visual feedback. Limb deficient Ss may be delayed in the acquisition of object permanence, eye–hand coordination, and normal bilateral skills. Research on cognitive abnormalities in these Ss is inconclusive but may be influenced by the degree of limb deficiency. A longitudinal case study of a 19-mo-old quadrimembral amputee fitted with a myoelectric prosthesis is presented. (French abstract) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Trust my face: Cognitive factors of head fakes in sports.

In many competitive sports, players try to deceive their opponents about their behavioral intentions by using specific body movements or postures called fakes. For example, fakes are performed in basketball when a player gazes in one direction but passes or shoots the ball in another direction to avert efficient defense actions. The present study aimed to identify the cognitive processes that underlie the effects of fakes. The paradigmatic situation studied was the head fake in basketball. Observers (basketball novices) had to decide as quickly as possible whether a basketball player would pass a ball to the left or to the right. The player's head and gaze were oriented in the direction of an intended pass or in the opposite direction (i.e., a head fake). Responding was delayed for incongruent compared to congruent directions of the player's gaze and the pass. This head fake effect was independent of response speed, the presence of a fake in the immediately preceding trial, and practice with the task. Five further experiments using additive-factors logic and locus-of-slack logic revealed a perceptual rather than motor-related origin of this effect: Turning the head in a direction opposite the pass direction appears to hamper the perceptual encoding of pass direction, although it does not induce a tendency to move in the direction of the head's orientation. The implications of these results for research on deception in sports and their relevance for sports practice are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Experimental systems analysis of simulated vehicle steering and safety training.

Made an experimental feedback analysis of the human factors in steering, driver training, and automobile safety relative to the theory that steering is a distinctive form of self-guided activity distinct from stimulus tracking, and that the automobile is a special kind of wheeled exoskeleton. Results of systems experiments with 9 male undergraduates on delayed simulated driving, eye-hand synchronism in delayed steering, comparison between eye-hand coordination in steering and stimulus tracking, effects of road speed on steering error, and on effects of space displacement of steering visual feedback supported the view that the operator projects steering action relative to the space, time, and force compliances between driving responses, and the actions of the exoskeleton machine in relation to the feedback received from the road display. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eye-head coordination in labyrinthine-defective humans

Eye-head coordination during saccadic gaze shifts normally relies on vestibular information. A vestibulo-saccadic reflex (VSR) is thought to reduce the eye-in-head saccade to account for current head movement, and the vestibulo-ocular reflex (VOR) stabilizes postsaccadic gaze while the head movement is still going on. Acute bilateral loss of vestibular function is known to cause overshoot of gaze saccades and postsaccadic instability. We asked how patients suffering from chronic vestibular loss adapt to this situation. Eye and head movements were recorded from six patients and six normal control subjects. Subjects tracked a random sequence of horizontal target steps, with their heads (1) fixed in primary position, (2) free to move, or (3) preadjusted to different head-to-target offsets (to provoke head movements of different amplitudes). Patients made later and smaller head movements than normals and accepted correspondingly larger eye eccentricities. Targeting accuracy, in terms of the mean of the signed gaze error, was better in patients than in normals. However, unlike in normals, the errors of patients exhibited a large scatter and included many overshoots. These overshoots cannot be attributed to the loss of VSR because they also occurred when the head was not moving and were diminished when large head movements were provoked. Patients' postsaccadic stability was, on average, almost as good as that of normals, but the individual responses again showed a large scatter. Also, there were many cases of inappropriate postsaccadic slow eye movements, e.g., in the absence of concurrent head movements, and correction saccades, e.g., although gaze was already on target. Performance in patients was affected only marginally when large head movements were provoked. Except for the larger lag of the head upon the eye, the temporal coupling of eye and head movements in patients was similar to that in normals. Our findings show that patients with chronic vestibular loss regain the ability to make functionally appropriate gaze saccades. We assume, in line with previous work, three main compensatory mechanisms: a head movement efference copy, an active cervico-ocular reflex (COR), and a preprogrammed backsliding of the eyes. However, the large trial-to-trial variability of targeting accuracy and postsaccadic stability indicates that the saccadic gaze system of patients does not regain the high precision that is observed in normals and which appears to require a vestibular head-in-space signal. Moreover, this variability also permeates their gaze performance in the absence of head movements.     

Self-motion path discrimination: effects of image stabilization

Path-deviation thresholds were measured as the effects of eye movements in the retinal flow were minimized through image stabilization. Thresholds obtained with image stabilization were compared to those obtained with unstabilized viewing to determine whether the elimination of eye movements from the retinal flow improves self-motion judgments. The results showed that, at slow forward speeds, eliminating the retinal effects of eye movements did not improve path-discrimination performance; subjects required more of an angular deviation to discriminate a circular from a straight motion path with image stabilization than with unstabilized viewing. In an effort to understand the results, eye movements were measured in unstabilized viewing conditions, and the measured eye velocities were used to estimate the retinal-image motion. The results showed that, for slow forward speeds, eye movements increased the average retinal speed, independent of the circular flow direction. At fast forward speeds, there was no significant increase in the average retinal-image speed due to eye movements. A parsimonious explanation for the decreased performance with image stabilization at the slow forward speed is that retinal-image motion was too slow to optimally stimulate the visual motion sensors.     

Seesaw nystagmus associated with involuntary torsional head oscillations

OBJECTIVE: To assess the diagnostic value of eye-head coupling in seesaw nystagmus (SSN). BACKGROUND: SSN is a rare binocular disorder characterized by alternating skew deviation and conjugate ocular torsion. METHODS: We examined a patient with a congenital nystagmus that switched to a pendular SSN on near viewing and was associated with involuntary torsional head oscillations. RESULTS: The binocular torsional eye movements were in phase with the clinically visible head oscillations (i.e., head movements were not compensatory for the torsional eye movements). CONCLUSION: This finding suggests that torsional eye-head coupling in pendular SSN has a common pathologic origin. We suggest that alternating vertical disparity of both eyes in pendular SSN is compatible with an oscillating signal acting on an intact vestibular system. The absence of brainstem lesions on high-resolution MRI supports this assumption.     

Comparison of continuous versus pulsed CO2 and Nd:YAG laser-induced pulmonary parenchymal lung injury in a rabbit model

Two studies investigated the effects of delayed visual feedback on manual tracking. In Experiment 1, individuals practiced with visual feedback provided either immediately (0 delay) or with a 333-ms delay. During acquisition, the 0 delay group performed with less error than the 333-ms delay group. A retention test with 0 delay feedback was performed with the least error by the 0 delay group. A transfer test using a different 0 delay tracking pattern, was performed with the least error by the 333-ms delay group. In Experiment 2, individuals practiced at six different delays. Error increased as training feedback delay increased. For retention there were no differences between the delay groups during the 0 delay retention. At a 417-ms retention, test error decreased as training feedback delay increased. Results indicate that error during acquisition does not necessarily impair learning and that feedback delays can be beneficial for learning.     

Human oculomotor system accounts for 3-D eye orientation in the visual-motor transformation for saccades

A recent theoretical investigation has demonstrated that three-dimensional (3-D) eye position dependencies in the geometry of retinal stimulation must be accounted for neurally (i.e., in a visuomotor reference frame transformation) if saccades are to be both accurate and obey Listing's law from all initial eye positions. Our goal was to determine whether the human saccade generator correctly implements this eye-to-head reference frame transformation (RFT), or if it approximates this function with a visuomotor look-up table (LT). Six head-fixed subjects participated in three experiments in complete darkness. We recorded 60 degrees horizontal saccades between five parallel pairs of lights, over a vertical range of +/-40 degrees (experiment 1), and 30 degrees radial saccades from a central target, with the head upright or tilted 45 degrees clockwise/counterclockwise to induce torsional ocular counterroll, under both binocular and monocular viewing conditions (experiments 2 and 3). 3-D eye orientation and oculocentric target direction (i.e., retinal error) were computed from search coil signals in the right eye. Experiment 1: as predicted, retinal error was a nontrivial function of both target displacement in space and 3-D eye orientation (e.g., horizontally displaced targets could induce horizontal or oblique retinal errors, depending on eye position). These data were input to a 3-D visuomotor LT model, which implemented Listing's law, but predicted position-dependent errors in final gaze direction of up to 19.8 degrees. Actual saccades obeyed Listing's law but did not show the predicted pattern of inaccuracies in final gaze direction, i.e., the slope of actual error, as a function of predicted error, was only -0. 01 +/- 0.14 (compared with 0 for RFT model and 1.0 for LT model), suggesting near-perfect compensation for eye position. Experiments 2 and 3: actual directional errors from initial torsional eye positions were only a fraction of those predicted by the LT model (e. g., 32% for clockwise and 33% for counterclockwise counterroll during binocular viewing). Furthermore, any residual errors were immediately reduced when visual feedback was provided during saccades. Thus, other than sporadic miscalibrations for torsion, saccades were accurate from all 3-D eye positions. We conclude that 1) the hypothesis of a visuomotor look-up table for saccades fails to account even for saccades made directly toward visual targets, but rather, 2) the oculomotor system takes 3-D eye orientation into account in a visuomotor reference frame transformation. This transformation is probably implemented physiologically between retinotopically organized saccade centers (in cortex and superior colliculus) and the brain stem burst generator.     

Attending to Eye Movements and Retinal Eccentricity: Evidence for the Activity Distribution Model of Attention Reconsidered.

When testing between spotlight and activity distribution models of visual attention, D. LaBerge, R. L. Carlson, J. K. Williams, and B. G. Bunney (1997) used an experimental paradigm in which targets are embedded in 3 brief displays. This paradigm, however, may be confounded by retinal eccentricity effects and saccadic eye movements. When the retinal eccentricities of the targets are equated and eye position is monitored, the pattern of results reported by LaBerge et al., which supported the activity distribution model, is not found. This result underscores the importance of considering targets' eccentricity and people's inclination to make saccadic eye movements in certain types of visual cognition tasks. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Perceptual Interactions Between Bilaterally Presented Words: What You Get Is Often Not What You See.

Bilateral presentations of words, 1 in the left visual hemifield (LVF) and 1 in the right (RVF), are used widely in studies of hemispheric asymmetry. However, although words shown centrally (i.e., nonlaterally) produce perceptual interactions in which 1 word alters the perceived identity of the other, perceptual interactions between bilaterally presented words have never been reported. To investigate this issue, the authors used brief, bilateral displays of words (e.g., romp-ramp) presented simultaneously. An eye tracker and forced-choice task ensured appropriate presentation and testing. Report accuracy was greatest for RVF words. However, this was accompanied by perceptual interactions that occurred almost exclusively in responses to LVF words, indicating that RVF words often altered the perceived identity of LVF words but not vice versa. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prediction of complex two-dimensional trajectories by a cerebellar model of smooth pursuit eye movement

A neural network model based on the anatomy and physiology of the cerebellum is presented that can generate both simple and complex predictive pursuit, while also responding in a feedback mode to visual perturbations from an ongoing trajectory. The model allows the prediction of complex movements by adding two features that are not present in other pursuit models: an array of inputs distributed over a range of physiologically justified delays, and a novel, biologically plausible learning rule that generated changes in synaptic strengths in response to retinal slip errors that arrive after long delays. To directly test the model, its output was compared with the behavior of monkeys tracking the same trajectories. There was a close correspondence between model and monkey performance. Complex target trajectories were created by summing two or three sinusoidal components of different frequencies along horizontal and/or vertical axes. Both the model and the monkeys were able to track these complex sum-of-sines trajectories with small phase delays that averaged 8 and 20 ms in magnitude, respectively. Both the model and the monkeys showed a consistent relationship between the high- and low-frequency components of pursuit: high-frequency components were tracked with small phase lags, whereas low-frequency components were tracked with phase leads. The model was also trained to track targets moving along a circular trajectory with infrequent right-angle perturbations that moved the target along a circle meridian. Before the perturbation, the model tracked the target with very small phase differences that averaged 5 ms. After the perturbation, the model overshot the target while continuing along the expected nonperturbed circular trajectory for 80 ms, before it moved toward the new perturbed trajectory. Monkeys showed similar behaviors with an average phase difference of 3 ms during circular pursuit, followed by a perturbation response after 90 ms. In both cases, the delays required to process visual information were much longer than delays associated with nonperturbed circular and sum-of-sines pursuit. This suggests that both the model and the eye make short-term predictions about future events to compensate for visual feedback delays in receiving information about the direction of a target moving along a changing trajectory. In addition, both the eye and the model can adjust to abrupt changes in target direction on the basis of visual feedback, but do so after significant processing delays.