Visuomotor Transformation in the Fly Gaze Stabilization System

For sensory signals to control an animal's behavior, they must first be transformed into a format appropriate for use by its motor systems. This fundamental problem is faced by all animals, including humans. Beyond simple reflexes, little is known about how such sensorimotor transformations take place. Here we describe how the outputs of a well-characterized population of fly visual interneurons, lobula plate tangential cells (LPTCs), are used by the animal's gaze-stabilizing neck motor system. The LPTCs respond to visual input arising from both self-rotations and translations of the fly. The neck motor system however is involved in gaze stabilization and thus mainly controls compensatory head rotations. We investigated how the neck motor system is able to selectively extract rotation information from the mixed responses of the LPTCs. We recorded extracellularly from fly neck motor neurons (NMNs) and mapped the directional preferences across their extended visual receptive fields. Our results suggest that—like the tangential cells—NMNs are tuned to panoramic retinal image shifts, or optic flow fields, which occur when the fly rotates about particular body axes. In many cases, tangential cells and motor neurons appear to be tuned to similar axes of rotation, resulting in a correlation between the coordinate systems the two neural populations employ. However, in contrast to the primarily monocular receptive fields of the tangential cells, most NMNs are sensitive to visual motion presented to either eye. This results in the NMNs being more selective for rotation than the LPTCs. Thus, the neck motor system increases its rotation selectivity by a comparatively simple mechanism: the integration of binocular visual motion information

White-headed Vultures Trigonoceps occipitalis show visual field characteristics of hunting raptors

The visual fields of Aegypiinae vultures have been shown to be adapted primarily to meet two key perceptual challenges of their obligate carrion-feeding behaviour: scanning the ground and preventing the sun’s image falling upon the retina. However, field observations have shown that foraging White-headed Vultures (Trigonoceps occipitalis) are not exclusively carrion-feeders; they are also facultative predators of live prey. Such feeding is likely to present perceptual challenges that are additional to those posed by carrion-feeding. Binocularity is the key component of all visual fields and in birds it is thought to function primarily in the accurate placement and time of contact of the talons and bill, especially in the location and seizure of food items. We determined visual fields in White-headed Vultures and two species of carrion-eating Gyps vultures, and show that the visual field of White-headed Vultures have more similarities with those of predatory raptors (e.g. Accipitrid hawks), compared with the taxonomically more closely related Gyps vultures. We found that maximum binocular field width in White-headed vultures (30°) is significantly wider than Gyps vultures (20°). The broader binocular fields in White-headed Vultures probably facilitate accurate placement and timing of the talons when capturing evasive live prey

Rules for the Cortical Map of Ocular Dominance and Orientation Columns

Three computational rules are sufficient to generate model cortical maps that simulate the interrelated structure of cortical ocular dominance and orientation columns: a noise input, a spatial band pass filter, and competitive normalization across all feature dimensions. The data of Blasdel from optical imaging experiments reveal cortical map fractures, singularities, and linear zones that are fit by the model. In particular, singularities in orientation preference tend to occur in the centers of ocular dominance columns, and orientation contours tend to intersect ocular dominance columns at right angles. The model embodies a universal computational substrate that all models of cortical map development and adult function need to realize in some form.Air Force Office of Scientific Research (F49620-92-J- 0499, F49620-92-J-0334); Office of Naval Research (N00014-92-J-4015, N00014-91-J-4100); National Science Foundation (IRI-90-24877); British Petroleum (BP 89A-1204

Saccadic latency in amblyopia.

We measured saccadic latencies in a large sample (total n = 459) of individuals with amblyopia or risk factors for amblyopia, e.g., strabismus or anisometropia, and normal control subjects. We presented an easily visible target randomly to the left or right, 3.5° from fixation. The interocular difference in saccadic latency is highly correlated with the interocular difference in LogMAR (Snellen) acuity-as the acuity difference increases, so does the latency difference. Strabismic and strabismic-anisometropic amblyopes have, on average, a larger difference between their eyes in LogMAR acuity than anisometropic amblyopes and thus their interocular latency difference is, on average, significantly larger than anisometropic amblyopes. Despite its relation to LogMAR acuity, the longer latency in strabismic amblyopes cannot be attributed either to poor resolution or to reduced contrast sensitivity, because their interocular differences in grating acuity and in contrast sensitivity are roughly the same as for anisometropic amblyopes. The correlation between LogMAR acuity and saccadic latency arises because of the confluence of two separable effects in the strabismic amblyopic eye-poor letter recognition impairs LogMAR acuity while an intrinsic sluggishness delays reaction time. We speculate that the frequent microsaccades and the accompanying attentional shifts, made while strabismic amblyopes struggle to maintain fixation with their amblyopic eyes, result in all types of reactions being irreducibly delayed

Linking binocular vision neuroscience with clinical practice

yesBinocularity in the human visual system poses two interesting and extremely challenging questions. The first, and perhaps most obvious stems from the singularity of perception even though the neural images we see originate as two separate images in the right and left eyes. Mechanistically we can ask how and where do we convert two images into one? The second question is more of a “why” question. By converting lateral eyes with their inherent panoramic visual field into frontal eyes with overlapping binocular visual fields, primates have developed an extremely large blind region (the half of the world behind us). We generally accept that this sacrifice in visual field size was driven by the potential benefit of extracting information about the 3rd dimension from overlapping right and left eye visual fields. For some people, both of these core processes of binocularity fail: a single fused binocular image is not achieved (when diplopia or suppression is present), and the ability to accurately represent the 3rd dimension is lost (stereo-blindness). In addition to these failures in the core functions of the human binocular system, early imbalances in the quality of right and left eye neural images (e.g. due to anisometropia, monocular deprivation, and/or strabismus), can precipitate profound neurological changes at a cortical level which can lead to serious vision loss in one eye (amblyopia). Caring for patients with malfunctioning binocular visual systems is a core therapeutic responsibility of the eye care professions (optometry, ophthalmology and orthoptics) and significant advances in patient care and subsequent visual outcomes will be gained from a deeper understanding of how the human brain accomplishes full binocular integration. This feature issue on binocular vision brings together original articles and reviews from leading groups of neuroscientists, psychophysicists and clinical scientists from around the world who embrace the multidisciplinary nature of this topic. Our authors have taken on the big issues facing the research community tasked with understanding how binocular vision is meant to work, how it fails, and how to better treat those with compromised binocularity. These studies address deep issues about how the human brain functions and how it fails, as well as how it can be altered by therapy

Sparse representation based stereoscopic image quality assessment accounting for perceptual cognitive process

In this paper, we propose a sparse representation based Reduced-Reference Image Quality Assessment (RR-IQA) index for stereoscopic images from the following two perspectives: 1) Human visual system (HVS) always tries to infer the meaningful information and reduces uncertainty from the visual stimuli, and the entropy of primitive (EoP) can well describe this visual cognitive progress when perceiving natural images. 2) Ocular dominance (also known as binocularity) which represents the interaction between two eyes is quantified by the sparse representation coefficients. Inspired by previous research, the perception and understanding of an image is considered as an active inference process determined by the level of “surprise”, which can be described by EoP. Therefore, the primitives learnt from natural images can be utilized to evaluate the visual information by computing entropy. Meanwhile, considering the binocularity in stereo image quality assessment, a feasible way is proposed to characterize this binocular process according to the sparse representation coefficients of each view. Experimental results on LIVE 3D image databases and MCL database further demonstrate that the proposed algorithm achieves high consistency with subjective evaluation

A new apparatus for visual field testing with binocular fixation

A new instrument for visual field examination with binocular fixation is described. The binocular vision was dissociated with polarizing plates. Only the point of fixation was visible to both eyes while the testing chart (Amsler chart) was visible to one eye in the use of this apparatus. The examination was done with both the patient's eyes open. With the use of this apparatus, not only was the visual line fixed steadily in order to detect various changes of the central visual field due to maculopathy or optic neuropathy and these changes were detected accurately and quickly, but also suppression scotoma associated with amblyopia or squint could be detected quantitatively.</p

Unilateral Aphakia and Contact Lenses

The binocular functions of a group of 60 patients with unilateral aphakia were tested after fitting with a contact lens. Results showed a high degree of extramacular fusion in the group. However, only 50% of these patients obtained satisfactory stereoacuity levels. There was no relation between the time elapsed from cataract extraction to contact lens fitting and the amount of ultimate stereoacuity obtained. Some factors presenting common obstacles to successful fitting of aphakic contact lenses are discussed

Prehension of a flanked target in individuals with amblyopia.

yesPurpose: Reduced binocularity is a prominent feature of amblyopia and binocular cues are thought to be important for prehension. We examine prehension in individuals with amblyopia when the target-object was flanked, thus mimicking everyday prehension. Methods: amblyopes (n=20, 36.4±11.7 years; 6 anisometropic, 3 strabismic, 11 mixed) and visually-normal controls (n=20, 27.5±6.3 years) reached forward, grasped and lifted a cylindrical target-object that was flanked with objects on either (lateral) side of the target, or in front and behind it in depth. Only 6 amblyopes (30%) had measurable stereoacuity. Trials were completed in binocular and monocular viewing, using the better eye in amblyopic participants. Results: Compared to visual normals, amblyopes displayed a longer overall movement time (p=0.031), lower average reach velocity (p=0.021), smaller maximum aperture (p=0.007) and longer durations between object contact and lift (p=0.003). Differences between groups were more apparent when the flankers were in front and behind, compared to either side, as evidenced by significant group-by-flanker configuration interactions for reach duration (p<0.001), size and timing of maximum aperture (p≤0.009), end-of-reach to object-contact (p<0.001), and between object contact and lift (p=0.044), suggesting that deficits are greatest when binocular cues are richest. Both groups demonstrated a significant binocular advantage, in that in both groups performance was worse for monocular compared to binocular viewing, but interestingly, amblyopic deficits in binocular viewing largely persisted during monocular viewing with the better eye. Conclusions: These results suggest that amblyopes either display considerable residual binocularity or that they have adapted to make good use of their abnormal binocularity