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PubMed1995

Binocular alignment and vergence in early infancy.

Vergence to static targets presented at five distances between 25 and 200 cm from the subject was measured in 631 infants aged between 17 and 120 days. Photographic images of the eyes were magnified and measured to yield information on the monocular and binocular eye positions for each target. Vergence data were fit by a linear function and compared to the vergence calculated from target distance and each infant's measured interpupillary distance. Differences in vergence across targets were also evaluated for each subject by calculating the change in angle of rotation for each eye. Many of even the youngest infants showed good ocular alignment both monocularly and binocularly, although the youngest infants showed the greatest variability in vergence. However, the median difference in vergence angle between the eyes for even the youngest group was < 4 deg (6.8 prism D), and some of this difference is attributed to versional eye movements and to slightly off-axis head position across trials. The average infant of 1-2 months showed substantially better vergence than has been reported in some recent studies. Apparently, oculomotor constraints are not a significant barrier to the development of the higher forms of binocularity that begin to emerge in the months immediately following the interval studied here, and may form the substrate for later developments in binocular vision.

Child Development↗
PubMed1995

Initiation of disjunctive smooth pursuit in monkeys: evidence that Hering's law of equal innervation is not obeyed by the smooth pursuit system.

Monkeys generated disjunctive smooth pursuit eye movements when they tracked visual targets that moved toward or away from them. Eye acceleration was computed during the initial 100 msec of pursuit (the open-loop interval) for various target trajectories. The initial acceleration of either eye was a function of the target's motion with respect to that eye, regardless of whether or not the pursuit was conjugate or disjunctive, or performed with one eye occluded. Eye movements produced by fusional vergence could be separated temporally from eye movements produced by smooth pursuit using step-ramp paradigms. The separation of the two responses demonstrates that the fusional vergence system operates in parallel with the smooth pursuit system, presumably to minimize disparity, but not to generate disjunctive components of smooth pursuit eye movements.

Animals↗
PubMed1996

Motion sharpening: evidence for the addition of high spatial frequencies to the effective neural image.

The perceived blur of drifting sinusoidal gratings was compared to that of static, blurred "square wave" gratings before and after adaptation to a missing fundamental (MF) pattern. The results indicate that the perceived blur of a drifting sine grating is inversely related to its drift speed. However, after adaptation to a MF pattern, this effect is reduced. The adaptation effect is most profound for low contrast gratings. The results provide tentative evidence for a non-linear stage in motion processing which serves to introduce higher frequencies into the neural image which are not present in the original signal.

Adaptation, Ocular↗
PubMed2006

Individual differences in the asymmetry of binocular saccades, analysed with mixed-effects models.

We analysed the reliability of individual differences in parameters of binocular saccadic eye movements. During saccades between isovergent targets, the movement of the right and left eye are not exactly symmetrical (conjugate). Typically, the abducting eye has a shorter latency and reaches a higher velocity, so that a transient divergence occurs during the saccade. For the asymmetry in latency and for the maximum of transient divergence, we applied statistical mixed-effects models in a repeated-measures design with 39 subjects and found that the variability between subjects was much larger than the variability from Sessions 1 to 2 (about 8 days later). The retest correlations were 0.54 for the latency difference, and 0.82 for the transient divergence maximum. We conclude that significant individual differences exist in the asymmetry of binocular saccades and that these can be observed with about 20 saccadic trials per subject.

Attention↗
PubMed2004

The contribution of spatial remapping impairments to unilateral visual neglect.

Left visual neglect following right hemisphere damage is a heterogeneous phenomenon, in which several underlying impairments have been identified. Despite recent advances in understanding the neural and cognitive bases of these impairments, current theories of neglect, particularly those that emphasise attentional deficits, do not explain a number of phenomena, including: 'Ipsilesional' neglect after left orienting. Positive or 'productive' manifestations. Spatial transposition errors. Mislocalisations. Revisiting behaviour during visual search. Lack of awareness for objects toward the contralesional side of space. We propose that these manifestations of neglect can be accounted for by an additional underlying disorder of spatial remapping due to parietal dysfunction. In primary visual areas, retinotopic maps are renewed and thus overwritten at each new ocular fixation. Remapping processes operating in higher-level oculocentric visual maps of the parietal cortex ensure visual integration of these successive retinal images over time and space, by creating a constantly updated representation of stimulus locations in terms of distance and direction from the fovea. They consist in the storage, refreshment and re-localization of the different components of the visual scene that are successively attended during its exploration, and provide spatial constancy of visual perception and a spatial buffer for working memory [Cereb Cortex 5 (1995) 470; Visual Cogn 7 (2000) 17]. We begin this article by reviewing theoretical and experimental arguments that have highlighted the importance of parietal remapping processes in maintaining an accurate representation of space across saccadic shifts. We then focus on findings from the double-step saccade task, [Ann Neurol 38 (1995) 739] as a basis for our model of the role of remapping impairments in many of the symptoms of neglect. From these results, remapping impairments would be demonstrated when a saccade has to be guided across the midline after having fixated an object in either the left or right visual field for patients with either left- or right-side parietal lesions. In addition, patients with right-side lesions will have remapping impairments within the left visual field following a saccade to a left-side target (see Fig. 5). In a large part of the article, we seek to build our hypothesis based on this basic model and more speculative assumptions supported with extensive evidence from the literature.

Attention↗
PubMed2006

The global processing deficit in amblyopia involves noise segregation.

Some studies have reported deficits in amblyopia for global form and motion integration, whereas other studies have shown global integration of form and motion information to be normal in amblyopia. Here, we attempt to resolve this discrepancy by showing that amblyopes only exhibit selective performance deficits on global tasks that contain noise as well as signal. We hypothesized that signal integration is normal, but noise segregation is not. We used comparable global orientation and motion direction discrimination tasks to measure integration performance in the presence of controlled amounts of pedestal noise (i.e., elements whose orientations or directions were randomly selected). We modelled the performance using an equivalent noise model, which has the parameters of internal noise and number of samples. Our results show that amblyopic eyes can integrate form (i.e., orientation) and motion information (i.e., motion direction) similarly to normals when all the information is signal (i.e., no pedestal noise). However, introducing pedestal noise perturbs the performance of the amblyopic eyes significantly more than that of the normal eyes.

Amblyopia↗
PubMed2000

Divided visuo-spatial attention systems with total and anterior callosotomy.

The role of the corpus callosum in the inter-hemispheric integration of the visuo-spatial attention system, was investigated in patients with a total callosotomy or with an anterior callosal section. Subjects produced simple reaction times (RTs) to visual targets shown to the left or right visual hemifield. Preceding the target by an interval of 500 ms, arrow cues predicting the target location were shown left and right of the point of ocular fixation. For a majority of total and anterior callosotomy patients, results with valid focused cues (both arrows pointing to the target location) and with divided-attention cues (arrows pointing away from fixation) did not differ and both conditions produced shorter RTs than with neutral cues (equal signs). In contrast, neurologically intact subjects showed equal RTs with divided-attention and neutral cues, whereas valid focused cues produced reduced RTs relative to neutral cues. These results indicate that most split-brains, in contrast to normal observers, are capable of directing their attention to left and right visual field locations simultaneously, and therefore that each cerebral hemisphere controls its own visuo-spatial attention mechanism.

Adult↗
PubMed1998

The effect of photon noise on the detection of white flashes.

Thresholds for detecting brief, white, foveal test flashes drop abruptly within 0.2 sec of the offset of a white adapting field. The magnitude of the abrupt drop is proportional to the square root of field intensity (square root of I) correct for bleaching and dark light. Thresholds are then stable out to 1.6 sec for 200 msec tests, or recover only slightly for 20 msec tests. These results exclude some simple deterministic models in which Weber-like gain controls in the luminance pathway are assumed to recover exponentially in the dark, but can be explained parsimoniously if turning off the field abolishes photon-driven noise, improving the S/N ratio while leaving visual responsivity virtually unaltered. This theory was first put forward by Krauskopf and Reeves [(1980) Vision Research, 20, 193-196] for S-cone thresholds; it implies that the Weber law for increment thresholds is not due to a single gain control, but rather expresses the product of two distinct square root of I factors, adjustment of responsivity and photon-driven noise. Removal of the noise, not recovery of gain, permits thresholds to fall in early dark adaptation.

Adaptation, Ocular↗
PubMed1998

Visual test of Listing's law during vergence.

A simple visual test was used to measure how much Listing's plane rotates as a function of the vergence angle. This test measured the elevation-dependent torsional disparity of horizontal and vertical lines during three tasks: vergence on a near target, vergence through prisms that remained fixed, and through prisms that rotated with eye elevation. Consistent with our previous search-coil measurements, the results here suggest that the angle between the Listing's planes of the two eyes is somewhat less than the vergence angle.

Convergence, Ocular↗
PubMed1999

Wondering about the wandering cyclopean eye.

Arguments against recent claims (Erkelens, Muijs & van Ee (1996). Vision Research, 36, 2141-2147; Mansfield & Legge (1996). Vision Research, 36, 27-41. (1997), Vision Research, 37, 1610-1613) that the position of the cyclopean eye is stimulus specific are presented. Critical to these arguments are the differences between relative and absolute visual direction tasks (Howard (1982). Human visual orientation. Wiley, New York; Ono & Mapp (1995). A restatement and modification of Wells-Hering's laws of visual direction. Perception, 24, 237-252), and between physical and perceptual descriptions of visual direction (Ono, Ohtsuka & Lillakas (1998). Proceedings of the international workshop on advances in research on visual cognition, Tsukuba, Japan (pp. 125-136); Ono & Lillakas (1997). Proceedings of the fourth international display workshop, Nagoya, Japan (pp. 831-834)).

Convergence, Ocular↗
PubMed1989

Head kinematic during various motor tasks in humans.

Head kinematic during various motor tasks was studied in ten subjects. The movement of the body was recorded with a video system (E.L.I.T.E.) which allows a computer reconstruction of three-dimensional motion of selected points on the body. Analysis is focused on head rotation in the horizontal and vertical planes. The results demonstrate that the amplitude and the maximum velocity do not exceed respectively 38 deg/s and 185 deg/s. However the head is intermittently stabilized and the angle of this stabilization is dependent upon the task and related to the direction of gaze. Darkness had no significant effect on head rotational velocity during walking but caused a decrease in velocity during running and hopping. The results suggest that head stabilization (1) is related to an ocular fixation point in the direction of gaze in space and (2) is probably regulated on the basis of a predictive mode of sensory motor control.

Adult↗
PubMed1996

Visual-auditory integration in cat superior colliculus: implications for neuronal control of the orienting response.

Previous physiological studies have demonstrated that inputs from different sensory modalities converge on individual neurons in the superior colliculus. Moreover, in anesthetized, paralyzed animals, those tectal neurons which are most directly connected to brain stem circuits mediating orienting eye and head movements are highly likely to exhibit significant integration of sensory inputs from multiple modalities. The purpose of the present study was to examine the responses of tectal neurons in the alert cat when visual and auditory stimuli were presented as targets for ocular fixation and orienting responses. For comparison to previous work in anesthetized, paralyzed animals, we also examined the responses of tectal neurons to the presentation of these stimuli during periods when the cats voluntarily maintained their eyes near primary position in the absence of a fixation target. Under these conditions, there were significant differences between the strength of the response to the simultaneous presentation of visual and auditory targets and the strength of response to the most effective unimodal stimulus in about 40% of the cells tested. Many tectal neurons also responded tonically during fixation of visual, auditory and bimodal targets, and some of these also exhibited significant bimodal interactions. However, among individual neurons which responded phasically to stimulus onset or offset and tonically during fixation, there was only a weak correlation between the extent of bimodal interaction under the two conditions. Finally, among saccade-related neurons, the magnitude of saccade-related activity was only slightly affected when a biomodal target was used to elicit a saccade, and the extent of bimodal interactions was generally less than was found for the onset and offset of sensory targets. Such multisensory interactions can be significant for behavior. Indeed, simply using a multisensory target has been shown to influence the probability and latency of overt orienting responses, although the extent of such effects will probably vary across both tasks and stimulus conditions. Strong multi-sensory interactions are most likely to occur when low intensity stimuli are used. Our use of moderately intense sensory stimuli probably accounts for our finding of a relatively small percentage of cells in which bimodal responses were greater than the sum of their unimodal responses.

Animals↗
PubMed1992

[Automatic analysis by computer of the visual suppression test of pendular rotatory vestibular nystagmus].

This study presents an automatic computerized analysis of the visual suppression test of vestibular nystagmus. Visual suppression is measured during rotatory nystagmus examination. The amplitude variations and the frequency of the nystagmus are computed in the dark and in the light. This allows the computer to furnish with the help of an algorithm the percentage of nystagmus suppressed by ocular fixation. The results of the computerized analysis are compared to a qualitative evaluation. A percentage of 70% and more indicates a normal suppression reflex and corresponds qualitatively to a total or subtotal visual suppression. A percentage smaller than 70% indicates a pathological reflex corresponding qualitatively to a partial, weak or absent visual suppression. The study is based on 149 examinations realised in 12 healthy subjects and 137 patients. The patients are classified into 4 groups: a) 59 patients with peripheral vestibular lesions (Ménière's diseases 21, vestibular neuronitis 15, cupulolithiasis 16, ototoxicity 7), b) 67 patients with central lesions of the cerebellum and the brainstem (multiple sclerosis 23, infratentorial tumors 14, vascular brainstem lesions 14, degenerative diseases of the central nervous system 16), c) 6 patients with supratentorial central lesions (hemispheric vascular lesions 4, supratentorial tumors 2), d) 5 patients with congenital nystagmus. All healthy subjects and all patients with peripheral vestibular lesions have a total or subtotal visual suppression corresponding to computed rates greater than 70% (mean: 86.7% and 83.1%). In cerebellar and brainstem lesions about half the patients (56.8%) present a partial, weak or absent visual suppression corresponding to computed rates inferior to 70% (mean: 52.7%). In supratentorial disorders the visual suppression is total or subtotal with computed rates superior to 70% (mean: 79.2%). By patients with congenital nystagmus the visual suppression is uniformly pathological with computed rates inferior to 70% (mean: 19.2%). The results of the visual suppression test are concordant with those of smooth pursuit in 92.6% of cases and with those of optokinetic nystagmus in 89.3% of cases. This study confirms that the visual suppression test is a useful examination to detect disorders of the cerebellum and brainstem.

Adolescent↗
PubMed1982

Adaptation to incomplete flow patterns: no evidence for 'filling-in' the perception of flow patterns.

Inspecting a radial flow pattern reduced visual sensitivity to changes in the size of a test square of 0.5 deg side length when the square was accurately located at the point previously occupied by the focus of the adapting flow pattern. The effect was reduced by a third when there was a 1.0 deg diameter hole at the centre of the flow pattern, and abolished when the hole was 1.5 or 2.0 deg in diameter. These findings support the idea that any depression of sensitivity in the hole is entirely due to spread of adaptation from the stimulated region, and provide no evidence for 'filling-in' or 'visual-phantom' phenomena in flow patterns.

Adaptation, Ocular↗