Effects of alcohol ingestion on tracking performance during angular acceleration.

Gave practice and base-line tests of tracking performance in both static (stationary) and dynamic (whole body angular acceleration) conditions to 20 male undergraduates. 10 ss then drank orange juice that contained 2 ml. Of 100-proof vodka/kg of s weight, while the others drank a control beverage. Tests, conducted 1-10 hr. After drinking, were in total darkness with the exception of the illuminated visual display. Static tracking errors for alcohol ss were significantly higher than those of controls only at the 4-hr session. However, alcohol ss made significantly more dynamic tracking errors during the 1-, 2-, and 4-hr sessions and, concomitantly, had significantly more nystagmic eye movements and higher rates of slow phase eye velocity than did controls. Results indicate that, although eye-hand coordination may show little or no impairment following alcohol ingestion in static situations, it may be seriously degraded during motion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Photoelectric methods of recording eye movements.

Presents 2 photoelectric methods of recording eye movements to investigate the oculomotor system of hospitalized patients with local brain lesions. The general appearance, operation, and advantages of (a) recording horizontal eye movements with direct ink-writing registration, and (b) simultaneous recording of horizontal and vertical eye movements are described. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Patterns of eye movements during parallel and serial visual search tasks.

In 2 experiments with a total of 24 undergraduates, eye movements were monitored while Ss performed parallel and serial search tasks. In Exp 1a, Ss searched for an "O" among "X"s (parallel condition) and for a "T" among "L"s (serial condition). In the parallel condition of Exp 1b, "Q" was the target and "O"s were distractors; in the serial condition, these stimuli switched roles. Displays contained 1, 12, or 24 stimuli, with both target-present and target-absent trials. RT and eye-movement measures (number of fixations, saccadic error, and latency to move) indicated that search efficiency was greatest in the parallel conditions, followed by the serial condition of Exp 1a and, finally, by the serial condition of Exp 1b. This suggests that eye movements are correlated with the attentional processes underlying visual search. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Infrared television recording and measurement of ocular behavior in the human infant.

Considers the variables of eye position, eye movements, pupillary dilation, and extent of eyelid opening in the method of closed circuit television (CCTV). New and relatively inexpensive devices are described for making CCTV more feasible for recording behavioral activity. The recording, displaying, and measuring of the images are described and exemplified. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Directional organization of eye movement and visual signals in the floccular lobe of the monkey cerebellum

The floccular lobe of the monkey is critical for the generation of visually-guided smooth eye movements. The present experiments reveal physiological correlates of the directional organization in the primate floccular lobe by examining the selectivity for direction of eye motion and visual stimulation in the firing of individual Purkinje cells (PCs) and mossy fibers. During tracking of sinusoidal target motion along different axes in the frontoparallel plane, PCs fell into two classes based on the axis that caused the largest modulation of simple-spike firing rate. For "horizontal" PCs, the response was maximal during horizontal eye movements, with increases in firing rate during pursuit toward the side of recording (ipsiversive). For "vertical" PCs, the response was maximal during eye movement along an axis just off pure vertical, with increases in firing rate during pursuit directed downward and slightly contraversive. During pursuit of target motion at constant velocity, PCs again fell into horizontal and vertical classes that matched the results from sinusoidal tracking. In addition, the directional tuning of the sustained "eye velocity" and transient "visual" components of the neural responses obtained during constant velocity tracking were very similar. PCs displayed very broad tuning approximating a cosine tuning curve; the mean half-maximum bandwidth of their tuning curves was 170-180 degrees. Other cerebellar elements, related purely to eye movement and presumed to be mossy fibers, exhibited tuning approximately 40 degrees narrower than PCs and had best directions that clustered around the four cardinal directions. Our data indicate that the motion signals encoded by PCs in the monkey floccular lobe are segregated into channels that are consistent with a coordinate system defined by the vestibular apparatus and eye muscles. The differences between the tuning properties exhibited by PCs compared with mossy fibers indicate that a spatial transformation occurs within the floccular lobe.     

Contrast letter thresholds in the non-affected eye of strabismic and unilateral eye enucleated subjects

To investigate the effects of visual disruption on contrast letter thresholds of the non-affected eye, subjects with one eye enucleated, strabismic subjects using the non-deviating eye and normal control subjects were asked to identify letters on eye charts and single letter cards which varied in contrast (between 4 and 96%) and size. At all contrast, contrast letter acuity of eye enucleated subjects was superior to both normal control subjects and strabismic subjects. Early onset strabismic subjects (onset < 24 months) showed inferior performance to normal control subjects at all contrasts of 25% and above. Late onset strabismic subjects showed normal performance at all contrasts, except for high contrast single letters, where performance was inferior to normal control subjects. Further, for all subjects groups, performance on letter charts was similar to performance on single letter cards. We conclude that disruption to the visual system caused by eye enucleation or strabismus is not equivalent. These differences may be due to intrinsic differences between the visual systems of eye enucleated subjects and strabismic subjects and/or to the profound differences in deprivation caused by the two conditions.     

Properties of memory-guided saccades toward targets flashed during smooth pursuit in human subjects

PURPOSE: This study in human subjects investigated whether or not the saccade system can monitor smooth changes of the eye position in total darkness. METHODS: The authors studied the properties of memory-guided saccades toward targets flashed during pursuit eye movements (target velocities of 15 degrees/s, 30 degrees/s, and 45 degrees/s) in four normal human subjects. Subjects were instructed to execute memory-guided saccades toward the position of the flashed target in total darkness when the pursuit target was extinguished. RESULTS: The vector of the saccade was more highly correlated with the vector of "spatial error" (the vector from the position of the eye at the time of the saccade to the position of the flashed target in space) than with the vector of "retinal error" (the vector from the position of the eye at the time of the presentation of the flashed target to the position of the flashed target). The amplitude and direction errors of memory-guided saccades were correlated with the amplitude of the retinal error but not with amplitude of eye deviation after the presentation of the flashed target. Pursuit velocity did not affect the error of the saccade. CONCLUSIONS: These findings suggest that the saccade system can monitor smooth changes of the eye position in total darkness, regardless of the velocity of pursuit, and that the accuracy of memory-guided saccades is dependent only on the amplitude of the retinal error.     

Lateral eye movements and hemispheric asymmetry: A critical review.

Eye movements to the left or right have been hypothesized to reflect activation of the cerebral hemisphere contralateral to the direction of gaze. This hypothesis was tested by comparing the direction of lateral eye movements (LEMs) following questions designed to engage the left or right hemisphere. The evidence from such studies was equivocal. Fewer than half found the predicted pattern of more right LEMs for left-hemisphere questions, and conceptual and methodological ambiguities in the questions, scoring, and experimental situation made interpretation of these studies difficult. In addition, findings showing more upward eye movements and more stares for right-hemisphere questions cannot be incorporated into the hemispheric asymmetry model of LEMs. Studies on individual differences in LEM patterns indicated a fair degree of stability and some consistency in their correlates. However, since "right" and "left movers" do not differ in verbal or spatial abilities, there is little justification for linking LEM patterns with "hemisphericity." It is concluded that further research on the relationship between directional ocular events and cognitive-affective processes is required before inferences about hemispheric function can be drawn from studies of lateral eye movements. (2? p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Oculocentric coding of inhibited eye movements to recently attended locations.

Results are reported for experiments that examined eye movements directed toward recently cued objects. In 1 experiment participants were slower to initiate saccades toward the earlier location of an object that had been cued, even though the cued object had subsequently moved away from that location. Other experiments involved exploring the reference frame within which the inhibited eye movements are encoded. These experiments revealed that the eye movement that is inhibited is encoded in an oculocentric—rather than an environmental—reference frame. However, simple detection as indexed by manual keypress responses is encoded in an environmental reference frame. The results have implications for inhibition of return, for the link between eye movements and attention, and for the nature of the spatial reference frames in which both covert and overt movements of attention are encoded. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Checking groups of letters.

Reports 2 experiments designed to find the optimum size of groups for letter checking, to study the effects of increasing the spatial separation between horizontal paired groups, and to examine S's scanning patterns by recording eye movements during search. Data from 35 undergraduates indicate that (a) the time spent looking at group increased with the number of letters/group; (b) during error checking, the 2nd member of a pair of groups was looked at longer than the 1st; and (c) with small groups, more than 1 group was processed at a time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Three-dimensional organization of otolith-ocular reflexes in rhesus monkeys. I. Linear acceleration responses during off-vertical axis rotation

1. The dynamic properties of otolith-ocular reflexes elicited by sinusoidal linear acceleration along the three cardinal head axes were studied during off-vertical axis rotations in rhesus monkeys. As the head rotates in space at constant velocity about an off-vertical axis, otolith-ocular reflexes are elicited in response to the sinusoidally varying linear acceleration (gravity) components along the interaural, nasooccipital, or vertical head axis. Because the frequency of these sinusoidal stimuli is proportional to the velocity of rotation, rotation at low and moderately fast speeds allows the study of the mid-and low-frequency dynamics of these otolith-ocular reflexes. 2. Animals were rotated in complete darkness in the yaw, pitch, and roll planes at velocities ranging between 7.4 and 184 degrees/s. Accordingly, otolith-ocular reflexes (manifested as sinusoidal modulations in eye position and/or slow-phase eye velocity) were quantitatively studied for stimulus frequencies ranging between 0.02 and 0.51 Hz. During yaw and roll rotation, torsional, vertical, and horizontal slow-phase eye velocity was sinusoidally modulated as a function of head position. The amplitudes of these responses were symmetric for rotations in opposite directions. In contrast, mainly vertical slow-phase eye velocity was modulated during pitch rotation. This modulation was asymmetric for rotations in opposite direction. 3. Each of these response components in a given rotation plane could be associated with an otolith-ocular response vector whose sensitivity, temporal phase, and spatial orientation were estimated on the basis of the amplitude and phase of sinusoidal modulations during both directions of rotation. Based on this analysis, which was performed either for slow-phase eye velocity alone or for total eye excursion (including both slow and fast eye movements), two distinct response patterns were observed: 1) response vectors with pronounced dynamics and spatial/temporal properties that could be characterized as the low-frequency range of "translational" otolith-ocular reflexes; and 2) response vectors associated with an eye position modulation in phase with head position ("tilt" otolith-ocular reflexes). 4. The responses associated with two otolith-ocular vectors with pronounced dynamics consisted of horizontal eye movements evoked as a function of gravity along the interaural axis and vertical eye movements elicited as a function of gravity along the vertical head axis. Both responses were characterized by a slow-phase eye velocity sensitivity that increased three- to five-fold and large phase changes of approximately 100-180 degrees between 0.02 and 0.51 Hz. These dynamic properties could suggest nontraditional temporal processing in utriculoocular and sacculoocular pathways, possibly involving spatiotemporal otolith-ocular interactions. 5. The two otolith-ocular vectors associated with eye position responses in phase with head position (tilt otolith-ocular reflexes) consisted of torsional eye movements in response to gravity along the interaural axis, and vertical eye movements in response to gravity along the nasooccipital head axis. These otolith-ocular responses did not result from an otolithic effect on slow eye movements alone. Particularly at high frequencies (i.e., high speed rotations), saccades were responsible for most of the modulation of torsional and vertical eye position, which was relatively large (on average +/- 8-10 degrees/g) and remained independent of frequency. Such reflex dynamics can be simulated by a direct coupling of primary otolith afferent inputs to the oculomotor plant. (ABSTRACT TRUNCATED)     

Attentional and ocular movements.

The relationship between eye movements and movements of attention was examined in a series of 6 experiments. A temporal order judgment technique was used to index attentional allocation. The results showed that endogenous movements of attention were slower than movements of the eyes and that the participants were able to hold attention at one location while executing an eye movement to another location. Under conditions of exogenous cueing, attention moved rapidly to the cued location, in advance of the eyes. These findings challenge the prevailing view that ocular movements must necessarily be preceded by a movement of attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Left hemisphere dysfunction and left hemisphere overactivation in schizophrenia.

Reports 2 experiments relating schizophrenia to functional brain asymmetry. In Exp I, 24 schizophrenics (mean age, 30.8 yrs) were compared to 24 matched controls (mean age, 37.3 yrs) on 2 tachistoscopic tasks (Syllable Test and Dot Location Test) designed to measure verbal and spatial information processing in the 2 hemispheres. Unlike the controls, the schizophrenics showed a right hemisphere superiority both on the verbal and on the spatial tests, indicating left hemisphere dysfunction in the initial processing of verbal information. In Exp II, lateral eye movements, as an index of contralateral hemispheric activation, were measured in a group of 24 paranoid schizophrenics (mean age, 28.9 yrs), 24 nonparanoid schizophrenics (mean age, 32.7 yrs), and 24 matched controls (mean age, 31.2 yrs). The eye movements were elicited by presenting the Ss with verbal neutral, verbal emotional, spatial neutral, and spatial emotional questions. The schizophrenics had significantly more rightward eye movement, compared to controls, regardless of question type, indicating left hemisphere overactivation. Results suggest that schizophrenia is associated with a pattern consisting of both left hemisphere dysfunction and overactivation. (63 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Respiratory changes associated with rapid eye movements in normo- and hypercapnia during sleep

Rapid eye movements during rapid-eye-movement (REM) sleep are associated with rapid, shallow breathing. We wanted to know whether this effect persisted during increased respiratory drive by CO2. In eight healthy subjects, we recorded electroencephalographic, electrooculographic, and electromyographic signals, ventilation, and end-tidal PCO2 during the night. Inspiratory PCO2 was changed to increase end-tidal PCO2 by 3 and 6 Torr. During normocapnia, rapid eye movements were associated with a decrease in total breath time by -0.71 +/- 0.19 (SE) s (P < 0.05) because of shortened expiratory time (-0.52 +/- 0.08 s, P < 0.001) and with a reduced tidal volume (-89 +/- 27 ml, P < 0.05) because of decreased rib cage contribution (-75 +/- 18 ml, P < 0.05). Abdominal (-11 +/- 16 ml, P = 0.52) and minute ventilation (-0.09 +/- 0.21 ml/min, P = 0.66) did not change. In hypercapnia, however, rapid eye movements were associated with a further shortening of total breath time. Abdominal breathing was also inhibited (-79 +/- 23 ml, P < 0.05), leading to a stronger inhibition of tidal volume and minute ventilation (-1.84 +/- 0.54 l/min, P < 0.05). We conclude that REM-associated respiratory changes are even more pronounced during hypercapnia because of additional inhibition of abdominal breathing. This may contribute to the reduction of the hypercapnic ventilatory response during REM sleep.     

Quantitative evaluation of saccadic and smooth pursuit eye movements. Is it reliable?

PURPOSE: The authors evaluated the reliability of the coefficients of the (1) amplitude/duration and (2) amplitude/peak velocity relationships of the mean precision values and the mean latency values (saccadic eye movements) and the coefficients of the target velocity/gain relationship (smooth pursuit eye movements). They computed test-retest maximum variability limits for these parameters. METHODS: After a 1-week interval, saccadic and smooth pursuit eye movements were recorded twice from 20 healthy subjects; 12 of these subjects underwent a third recording session. The estimate of the intraclass coefficient of reliability, R, was adopted to evaluate the reliability of eye movement quantitative analysis. RESULTS: The data demonstrated that the reliability was fairly good for the amplitude/peak velocity relationship, was good for the precision, and was excellent for the amplitude/duration, the target velocity/gain relationships, and the latency. CONCLUSIONS: Quantitative analysis of both saccadic and smooth pursuit eye movements is reliable. One statistic used to estimate reliability, ie, the within-subjects mean square value, also enables the determination of test-retest normal variability values for both the variances and the differences of measurements.     

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.     

Modeling vestibulo-ocular reflexes in everyday activities

Fundamental data for the establishment of a new clinical testing procedure for patients suffering from equilibrium disorders were developed. A mathematical model that predicts vestibulo-ocular reflex responses (eye velocities) to three-dimensional head movements was investigated. An experimental set-up permitting the simultaneous recording of the head and eye movements was developed to investigate the vestibulo-ocular reflex (VOR) during everyday activities. The test results show that computer simulation of the VOR occurring during complex movements is indeed possible. The model was able to predict the trend of the experimentally determined eye velocities. It was ascertained that for the further development of the model, the influence of the cervico-ocular reflex (COR) on the resulting eye velocities also has to be taken into account. The proposed method for investigating patients with equilibrium disorders appears suitable enough to make further development to the clinical stage worthwhile. An adaptation of the feedback amplification parameters of the model to take account of the nature of the stimulus and the influence of COR is needed to improve the agreement between the amplitudes of measured and predicted eye velocities. To reliably quantify the feedback amplification parameters, tests need to be carried out in a large number of subjects.     

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)     

Infant color vision: moving tritan stimuli do not elicit directionally appropriate eye movements in 2- and 4-month-olds

The purpose of the present study was to investigate the capacity of infants to code the direction of motion of moving tritan-modulated gratings. Infant and adult subjects were tested with 0.2 c/d sinusoidal gratings moving at a speed of 20 deg/sec. Three conditions were tested: luminance-modulated gratings, tritan-modulated gratings, and luminance- vs tritan-modulated gratings superimposed and moving in opposite directions in a chromatic motion nulling paradigm. Two-month-old infants were tested in all three conditions, while 4-month-olds were tested in only the first two conditions. For infant subjects, an adult observer reported the direction of the slow phase of the infant's eye movements; adult subjects judged the perceived direction of motion of the stimuli. Luminance-modulated gratings produced directionally appropriate eye movements (DEM) in all age groups. Tritan gratings presented alone did not produce DEM in either 2- or 4-month-olds, but did so in adults. Mean equivalent luminance contrasts were near zero in 2-month-olds, and small but reliably above zero in adults. In sum, the present study provides no evidence that infants can code the direction of motion of moving tritan gratings.     

Lateral inhibitory interactions in the intermediate layers of the monkey superior colliculus

The intermediate layers of the monkey superior colliculus (SC) contain neurons the discharges of which are modulated by visual fixation and saccadic eye movements. Fixation neurons, located in the rostral pole of the SC, discharge action potentials tonically during visual fixation and pause for most saccades. Saccade neurons, located throughout the remainder of the intermediate layers of the SC, discharge action potentials for saccades to a restricted region of the visual field. We defined the fixation zone as that region of the rostral SC containing fixation neurons and the saccade zone as the remainder of the SC. It recently has been hypothesized that a network of local inhibitory interneurons may help shape the reciprocal discharge pattern of fixation and saccade neurons. To test this hypothesis, we combined extracellular recording and microstimulation techniques in awake monkeys trained to perform oculomotor paradigms that enabled us to classify collicular fixation and saccade neurons. Microstimulation was used to electrically activate the fixation and saccade zones of the ipsilateral and contralateral SC to test for inhibitory and excitatory inputs onto fixation and saccade neurons. Saccade neurons were inhibited at short latencies following electrical stimulation of either the ipsilateral (1-5 ms) or contralateral (2-7 ms) fixation or saccade zones. Fixation neurons were inhibited 1-4 ms after electrical stimulation of the ipsilateral saccade zone. Stimulation of the contralateral saccade zone led to much weaker inhibition of fixation neurons. Stimulation of the contralateral fixation zone led to short-latency (1-2 ms) excitation of fixation neurons. Only a small percentage of saccade and fixation neurons were activated by the electrical stimulation (latency: 0.5-2.0 ms). These responses were confirmed as either orthodromic or antidromic responses using collision testing. The results suggest that a local network of inhibitory interneurons may help shape not only the reciprocal discharge pattern of fixation and saccade neurons but also permit lateral interactions between all regions of the ipsilateral and contralateral SC. These interactions therefore may be critical for maintaining stable visual fixation, suppressing unwanted saccades, and initiating saccadic eye movements to targets of interest.