Panum's Area Research Articles

Update zur Fixationsdisparität

Purpose. The aim of the paper is to summarise and discuss the current state of knowledge on the overall topic of fixation disparity (FD). Material and Methods. A systematised PubMed literature search based on the term “fixation disparity” was conducted; in addition, the publication relies on the reference book on “Perceiving in Depth” written by I. P. Howard. Results. Until the 1990s, the understanding regarding subjective FD was quite uniform. Studies with high-resolution, objective examination methods and simultaneous measurement of subjective and objective FD have since shown that the vergence error (= objective FD) is usually not very well correlated with the vernier error (= subjective FD). It can therefore be assumed that the two types of FD are two different phenomena. The objective vergence error can indicate how large the shift of the image position on the retina is within the central panum area. Subjective FD, on the other hand, must be seen as the result of multiple processing events in the brain. Conclusion. There is a difference between subjective and objective FD. This finding does not contradict the clinical rel- evance of subjective FD. Aligning prisms to correct subjective FD are effective in reducing visual complaints in certain cases. It is possible that aligning prisms reduce a relevant proportion of heterophoria. Keywords binocular vision, fixation disparity, vergence error, vernier error

The upper disparity limit increases gradually with eccentricity.

Stereopsis is important for tasks of daily living such as eye-hand coordination. It is best in central vision but is also mediated by the periphery. Previously we have shown that individuals with central-field loss who have residual stereopsis in the periphery perform better at an eye-hand-coordination task when they perform the task binocularly rather than monocularly. Here we seek to determine what sets the limit of stereopsis, defined as the largest disparity that supports the sustained appearance of depth, in the near periphery in healthy individuals. While stereoacuity thresholds increase sharply with eccentricity, Panum's area increases much more slowly. We used a rigorous method to determine the uppermost limit of disparity. At long durations, the two half-images that define a large disparity appear as two isolated targets in the same flat plane; small incremental changes in disparity produce changes in the separation between the half-images, and disparity magnitude can be judged on the basis of separation, like a monocular width judgment. The disparity limit is the point at which the threshold for judging dichoptic separation between the half-images is equal to the monocular width-discrimination threshold. The disparity limit at 10° was a factor of 2–4 times larger than the fovea, regardless of the meridian tested. The increase in the disparity limit with eccentricity was shallow, similar to that of Panum's area. Within this disparity limit, disparity increment thresholds were comparable for foveal and peripheral targets, illustrating the significance and utility of peripheral stereopsis, especially in the absence of foveal stereopsis.

Abnormal stereopsis and reduced retinal sensitivity in patients with retinitis pigmentosa

The aim of the study was to evaluate retinal sensitivity and stereoacuity (SA) in retinitis pigmentosa (RP) patients. Twenty-six patients with RP were examined, mean age 36.4 ± 7.21 (SD)years old and best corrected visual acuity better than 0.15 logMAR. The control group (CG) included 25 healthy subjects matching the RP group by age and sex. Every patient and healthy control underwent a complete ophthalmologic examination: Titmus, Lang, TNO stereotests and microperimetry (MP-1) (Nidek Technologies). Results were subjected to factor analysis using Varimax rotation, and p values < 0.05 were considered statistically significant. With the Titmus stereotest, the mean SA was 136.52 ± 26.5(SD)arcsec in the RP group and 67.2 ± 11.5(SD) in CG; Lang SA was 391.39 ± 53.72(SD) in RP group and 1150 ± 33.4(SD) in CG; and TNO SA was 69.3 ± 14.39(SD) in the RP group and 15.97 ± 3.7(SD) in CG. Factor analysis showed significant correlation between visual acuity and SA (p = 0.0001) in RP group. MP-1 demonstrated that in RP patients, inter-ocular difference in retinal sensitivity and fixation stability was related to anomalous stereopsis (p values < 0.05). Progressive RP degeneration in the cone system could determine a significant impairment in the binocular vision due to anomalous inter-ocular retinal sensitivity and incomplete Panum's area utilization, causing an incongruent retinal localization. These findings suggest a possible reason why RP patients with a central retinal involvement, even if minimal, perceive a damaged stereoscopic perception that produces a severe disability.

Vector model for mapping of visual space to subjective 4-D sphere

Here we present a mathematical model of binocular vision that maps a visible physical world to a subjective perception of it. The subjective space is a set of 4-D vectors whose components are outputs of four monocular neurons from each of the two eyes. Monocular neurons have one of the four types of concentric receptive fields with Gabor-like weighting coefficients. Next this vector representation of binocular vision is implemented as a pool of neurons where each of them is selective to the object's particular location in a 3-D visual space. Formally each point of the visual space is being projected onto a 4-D sphere. Proposed model allows determination of subjective distances in depth and direction, provides computational means for determination of Panum's area and explains diplopia and allelotropia.

Fisiologia da visão binocular

A visão binocular de seres humanos resulta da superposição quase completa dos campos visuais de cada olho, o que suscita discriminação perceptual de localizações espaciais de objetos relativamente ao observador (localização egocêntrica) bem mais fina (estereopsia), mas isso ocorre em, apenas, uma faixa muito estreita (o horóptero). Aquém e além dela, acham-se presentes diplopia e confusão, sendo necessária supressão fisiológica (cortical) para evitá-las. Analisa-se a geometria do horóptero e suas implicações fisiológicas (o desvio de Hillebrand, a partição de Kundt, a área de Panum), assim como aspectos clínicos da visão binocular normal (percepção simultânea, fusão, visão estereoscópica) e de adaptações a seus estados afetados (supressão patológica, ambliopia, correspondência visual anômala).

Ibn al-Haytham on binocular vision: a precursor of physiological optics

The modern physiological optics introduces the notions related to the conditions of fusion of binocular images by the concept of correspondence, due to Christiaan Huygens (1704), and by an experiment attributed to Christoph Scheiner (1619). The conceptualization of this experiment dates, in fact, back to Ptolemy (90-168) and Ibn al-Haytham (d. after 1040). The present paper surveys Ibn al-Haytham's knowledge about the mechanisms of binocular vision. The article subsequently explains why Ibn al-Haytham, a mathematician, but here an experimenter, did not give the circular figure of the theoretical horopter, construction due to Gerhard Vieth (1818) and Johannes Müller (1826). But, on the other hand, it is clear that Ibn al-Haytham's experimental study puts in place the notion of corresponding points, the cases of homonymous and cross diplopia, and even prepares the discovery of Panum area.

Disconjugate oculomotor learning caused by feeble image-size inequality: differences between secondary and tertiary positions

In order to examine the minimum value of image-size inequality capable of inducing lasting disconjugacy of the amplitude of saccades, six normal emmetropic subjects were exposed for 16 min to 2% image size inequality. Subjects were seated at 1 m in front of a screen where a random-dot pattern was projected and made saccades of 7.5 and 15 deg along the horizontal and vertical principal meridians and to tertiary positions in the upper and lower field. During the training period, compensatory disconjugacy of the amplitude of the saccades occurred for the principal horizontal and vertical meridians; such increased disconjugacy persisted after training, suggesting learning. In contrast, for horizontal saccades to or from tertiary positions made in the upper and lower field, no consistent changes in the disconjugacy occurred, either during training or after the training condition. In an additional experiment, three subjects read sequences of words with the 2% magnifier in front of their dominant eye: in such a task, horizontal saccades to or from tertiary positions at the upper or lower field showed appropriate and lasting disconjugacy for two of the three subjects. We conclude that even a 2% image size inequality stimulates oculomotor learning, leading to persistent disconjugacy of saccades. The small disparity created by the image-size inequality is thus compensated by the oculomotor system rather than tolerated by the sensory system (e.g. by enlarging the Panum's area).

Cortical hypercolumn size determines stereo fusion limits.

The size of a pair of cortical ocular dominance columns determines a basic anatomical module of V-1 which Hubel and Wiesel have termed the hypercolumn. Does this correspond to a basic functional, or psychophysically measurable, module as well? This is the basic question addressed in the present paper. Since the ocular dominance column architecture is presumed to be related to stereo vision, it is natural to assume that hypercolumn size should provide a modular basis for basic phenomena of stereopsis. In previous work, we have suggested that local nonlinear filtering via the cepstral transform, operating on a local window of cortical tissue scaled by hypercolumn size, provides such a modular model of stereopsis. In the present paper, we review this model and then discuss a number of issues related to the biological plausibility and implementation of this algorithm. Then, we present the main result of this paper: we have analyzed a number of experiments related to stereo fusion limits (Panum's area) and to disparity gradient and disparity scaling, and demonstrate that there is a simple unifying explanation for these phenomena in terms of a constant cortical module whose size is determined by a pair of ocular dominance columns. As a corollary, Panum's area must increase according to (inverse) cortical magnification factor. We show that this is supported by all existing experimental data.

Comparison of fixation disparities obtained by objective and subjective methods.

Fixation disparities (FD) were measured as a function of forced vergence using binocular scleral search coils and simultaneously with nonius lines. The slope of the objective FD curve was significantly greater than the subjective FD curve for three of five subjects. This indicates an alteration in retinal correspondence of up to one degree, that shifts Panum's area to avoid the diplopia normally present with large disparities. This process allows for fusion in the presence of large objective fixation disparities which would normally cause diplopia. The shift in correspondence enhances the range of forced vergence, since the larger objective FDs serve as more effective stimuli to fusional vergence. The remaining subjects who lacked this effect had "flat" FD curves indicative of high vergence adaptation.

Fixation Disparity as a Function of Viewing Distance and Prism Load

In binocular vision, fixation disparity is present when a fixation point falls within Panum's area, but not on corresponding retinal points. To investigate the effect of vergence load, fixation disparity was measured at viewing distances of 20, 30, 40, 60, and 100 cm (while the test subtended a constant angular size) by the psychophysical method of dichoptically presented nonius lines with a central fusion stimulus. As the viewing distance was shortened from 100 to 20 cm, mean fixation disparity changed monotonically from 1 min arc esophoria (ie the eyes converged in front of the target) to 3 min arc exophoria. The average standard deviation of the psychometric function, which is a measure of the temporal variability of vergence, was smallest at 100 cm (when fixation disparity was esophoric) and increased at shorter distances. Fixation disparity was also measured at a constant distance of 40 cm, but with prisms in front of the eyes that induced the same vergence angles as would be induced by viewing distances between 20 and 100 cm. The slope of these conventional ‘fixation disparity curves’ as a function of prism load correlated with the slope of fixation disparity as a function of viewing distance ( r=0.39, p=0.02, n=25). However, testing at different distances, as introduced here, has the advantage of preserving the natural interaction between vergence and accommodation. Since the change of fixation disparity with distance differed reliably among subjects (with a test — retest correlation of 0.65 in 34 subjects with good binocular vision) this measure may be useful for identifying subjects who are prone to near-vision complaints.

3D reconstruction and interpretation in human binocular vision by processing of disparity information

After a review of fundamental definitions in binocular vision-binocular convergence, retinal disparity and their perceptual correlates (fusion, diplopia, suppression and stereoscopic depth)-psychophysical data on Panum's area and their spatial and temporal characteristics are presented. Specific features of stereopsis as the visual perception of three-dimensional space based on binocular disparities are described: horizontal disparity processing for depth perception, global stereopsis according to Julesz, and the disparity gradient limit for binocular matching. A discussion of stereoscopic acuity and of the neurophysiological basis of stereopsis is also included.

Physiologic Diplopia in Binocular Vision (Normal and Anomalous)

The study of physiologic diplopia and Panum's area was done on an apparatus using only the central straight ahead area instead of the entire visual space. In normal subjects, Panum's area measured ...

The extent of Panum's area and the human cortical magnification factor.

The horizontal extent of Panum's fusional area was measured by means of a single-vertical-line stimulus placed at thirty-two locations throughout the peripheral visual field. These results were transformed by using known values of the human cortical magnification factor (CMF), and the hypothesis that variations in the magnitude of Panum's area may be accounted for by variations in the CMF was tested. It was found that the increase in Panum's area with increasing stimulus eccentricity correlates well with the CMF, but that variations in the extent of Panum's area as a function of angular position around the line of sight do not correspond well with the CMF.

Relationship of Heterophoria to Stereopsis

Eighty patients with 6/7.5 (20/25) or better visual acuity in each eye noted differences in stereoacuity with crossed and uncrossed disparity. Esophoric patients who perceived a difference were more likely to have greater stereoacuity with uncrossed disparity, and exophoric patients who perceived a difference were more likely to have greater stereoacuity with crossed disparity. Asymmetry of Panum's area may be a factor in this phenomenon.

Binocularity in comitant strabismus: binocular visual fields studies.

A critical review is made of the literature on binocular perimetry in strabismus. A broad range of results was obtained by various authors, because different testing techniques were used. The concept of sensory testing of strabismic patients in casual seeing condition should be introduced also into binocular perimetry. Therefore a series of experiments is presented in which patients with small-angle comitant strabismus were tested. It was shown that: a) in small-angle esotropia the areas of single vision previously thought to be due to suppression are, instead, areas of binocular vision sustained by anomalous retinal correspondence (ARC); b) this can be seen only when using fusable stimuli as test targets; c) no suppression scotomas were found in patients with small-angle strabismus in the whole visual field; d) appropriate control-marks for binocularity are necessary, i.e. monocularly presented items. They influence the results, as well e) the area of binocular single vision in strabismus (called pseudo-Panum's area) is wider than the Panum's area of normals. Moreover it is easier to disrupt binocular cooperation sustained by ARC causing diplopia than binocular cooperation in normals; f) ARC seems to be more deeply rooted in the center than in the periphery of the visual field; g) superimposable findings were obtained in small-angle constant exotropia; h) in large-angle exotropia wide suppression scotomas were found, which often override the midline. Hemianopic suppression scotomas in exotropia can be found only when 'dissociating' testing techniques are used; i) the same group of patients with small-angle esotropia was examined with the author's technique and with the classical method proposed by Harms. The results were strongly dependent on the method used and the same patient responded differently to the two tests. It is concluded that in small-angle strabismus there is an anomalous type of binocular single vision, which can be tested with binocular visual field techniques. This binocularity can only be found when non-artificial testing conditions are used. The usefulness of this anomalous binocular vision in the every day seeing condition of the patient is discussed.

The Effect of Fixation Disparity on the Size of Panum ‘s Fusional Area

Factors affecting the size of Panum's fusional area are reviewed. One of these factors, prolonged fixation disparity, is investigated. The results show that this does not appear to significantly alter the size of Panum's area within the limitations of the tests used in detecting subjects with prolonged fixation disparity.

Columnar architecture and computational anatomy in primate visual cortex: segmentation and feature extraction via spatial frequency coded difference mapping.

Columnar architecture is a well established organizational principle for a variety of cortical systems. If two topographically mapped receptor systems, which receive slightly different "views" of the same physical stimulus, are interlaced as "columns", then the difference map of the afferent inputs is coded within a spatial frequency channel of the resultant map. The difference map of the left and right retinal views of a three dimensensional scene contains cues for the binocular disparity of the objects in the scene. Physical objects which are located at a common distance from the observer will be represented by area's of difference mapping which possesss common cortical textural values. Thus, segmentation of the cortical representation of the visual scene by values of positional disparity may be accomplished by conventional monocular segmentation techniques, applied to the cortical representation. The difference map is carried by a spatial frequency modulation determined by the period of the columnar interlacing. Ocular dominance columns in human striate cortex suggest a spatial frequency carrier which is roughly equal to the inverse of Panum's area. Since the difference mapping is a global attribute of the cortical representation, and is not contingent on the existence of labeled single cell feature extractors, the difference mapping algorithm represents a distinct alternative to conventional single cell approaches to feature extraction. The difference mapping algorithm is briefly discussed in relation to other difference channels, such as color opponent segmentation and binocular orientation disparity. It is suggested that difference mapping may reflect a general synergistic mechanism relating topographic mapping and columnar architecture, which reduces the problem of feature extraction and segmentation for depth and color opponent channels to a single "textural" mechanism.

A neurophysiological model for anomalous correspondence based on mechanisms of sensory fusion.

Normal retinal correspondence is not stable. The arguments for the plasticity of correspondence in normal binocular vision have been given into previous papers (Nelson, 1975, 1977). In this paper, both laboratory research and the clinical strabismus literature are reviewed to show similarities between normal and abnormal binocular vision. In particular, it is argued that sensory fusion (Panum's areas) and anomalous retinal correspondence (AC) obey similar principles, and so a sensory fusional model of AC may be developed. Recent advances in the neurophysiology of binocular vision are reviewed, but current laboratory knowledge cannot account for many phenomena known clinically unless certain postulates are made. Two hypothesized intracortical interactions among binocular disparity detectors, termed disparity domain inhibition and spatial domain facilitation, play key roles in extending the neurophysiology of binocular vision to an account of both normally - and clinically - observed plasticities of correspondence. The fusional model of retinal correspondence developed here from postulated domain interactions contrasts with the older concept of fixed corresponding points, an approach which has failed to provide a unified foundation for the treatment of normal and abnormal binocular vision.

Stereoscopic vision with central scotomata (author's transl)

Thirty-nine patients with convergent microstrabismus and 24 patients with central organic scotoma underwent measurements of stereo acuity. Stereopsis at distance was measured by means of a polarization haploscope using "plane-tests" and random dot tests respectively. For near stereopsis were used commercially available tests (Titmus Test, TNO-Test). Organic scotomata can be divided into "circumscribed central scotomata" and "sievelike scotomata", the latter leading to poorer performance in random dot tests. Large plane tests yielded better results than small ones. In microstrabism we found stereo acuities similar to those of patients with "sievelike scotoma". The results support the theory of displacement of fusion within Panum's area in microstrabismus leading to decreased local stereopsis due to decreased concentration of stereo units at the border of Panum's area.

Spatio-temporal properties of Panum's fusional area

Horizontal and vertical disparity limits of binocular fusion were examined with temporal or with spatio-temporal modulation of binocular disparity for two lines at 0.5 deg retinal eccentricity. For both horizontal and vertical disparity, Panum's fusional areas became extended by low spatial frequency variation in disparity. The horizontal extent of Panum's area also varied with temporal frequency of disparity variation. Under low spatial frequency conditions, Panum's area increased horizontally by as much as a factor of 10 (but vertically by less than a factor of 2) when temporal frequency decreased from 5.0 Hz to 0.1 Hz. At high spatial frequencies the horizontal and vertical extents of Panum's area remained almost constant (within a factor of 1.5) over the entire range of temporal frequencies. These results illustrated that Panum's area is the combination of a constant minimum area with an extended area that responds to low frequency time-varying disparities.