Frontal Eyes Research Articles

Independence and synergy of spatial attention in the two visual systems of jumping spiders.

By selectively focusing on a specific portion of the environment, animals can solve the problem of information overload, toning down irrelevant inputs and concentrating only on the relevant ones. This may be of particular relevance for animals such as the jumping spider, which possess a wide visual field of almost 360° and thus could benefit from a low-cost system for sharpening attention. Jumping spiders have a modular visual system composed of four pairs of eyes, of which only the two frontal eyes (i.e., AMEs) are motile, whereas the other secondary pairs remain immobile. We hypothesized that jumping spiders can exploit both principal and secondary eyes for stimulus detection and attentional shift, with the two systems working synergistically. In Experiment 1 we investigated AMEs' attentional responses following a spatial cue presented to the secondary eyes. In Experiment 2, we tested for enhanced attention in the secondary eyes' visual field congruent with the direction of the AMEs' focus. In both experiments, we observed that animals were faster and more accurate in detecting a target when it appeared in a direction opposite to that of the initial cue. In contrast with our initial hypothesis, these results would suggest that attention is segregated across eyes, with each system working on compensating the other by attending to different spatial locations.

Crossed–uncrossed projections from primate retina are adapted to disparities of natural scenes

In mammals with frontal eyes, optic-nerve fibers from nasal retina project to the contralateral hemisphere of the brain, and fibers from temporal retina project ipsilaterally. The division between crossed and uncrossed projections occurs at or near the vertical meridian. If the division was precise, a problem would arise. Small objects near midline, but nearer or farther than current fixation, would produce signals that travel to opposite hemispheres, making the binocular disparity of those objects difficult to compute. However, in species that have been studied, the division is not precise. Rather, there are overlapping crossed and uncrossed projections such that some fibers from nasal retina project ipsilaterally as well as contralaterally and some from temporal retina project contralaterally as well as ipsilaterally. This increases the probability that signals from an object near vertical midline travel to the same hemisphere, thereby aiding disparity estimation. We investigated whether there is a deficit in binocular vision near the vertical meridian in humans and found no evidence for one. We also investigated the effectiveness of the observed decussation pattern, quantified from anatomical data in monkeys and humans. We used measurements of naturally occurring disparities in humans to determine disparity distributions across the visual field. We then used those distributions to calculate the probability of natural disparities transmitting to the same hemisphere, thereby aiding disparity computation. We found that the pattern of overlapping projections is quite effective. Thus, crossed and uncrossed projections from the retinas are well designed for aiding disparity estimation and stereopsis.

From swimming towards sessility in two metamorphoses – the drastic changes in structure and function of the nervous system of the bay barnacle Amphibalanus improvisus (Crustacea, Thecostraca, Cirripedia) during development

Knowledge about the development of the nervous system in cirripeds is limited, particularly with regard to the changes that take place during the two metamorphoses their larvae undergo. This study delivers the first detailed description of the development of the nervous system in a cirriped species, Amphibalanus improvisus by using immunohistochemical labeling against acetylated alpha-tubulin, and confocal laser scanning microscopy. The development of the nervous system in the naupliar stages corresponds largely to that in other crustaceans. As development progresses, the protocerebral sensory organs differentiate and the intersegmental nerves forming the complex peripheral nervous system appear, innervating the sensory structures of the cephalic shield. During metamorphosis into a cypris the lateral sides of the cephalic shield fold down into a bilateral carapace, which leads to a reorganization of the peripheral nervous system. The syncerebrum of the cypris exhibits the highest degree of complexity of all developmental stages, innervating the frontal filaments, nauplius eye, compound eyes and the antennules. During settlement, when the second metamorphosis occur, the closely associated frontal filaments and compound eyes are shed together with the cuticle of the carapace and the antennules. In adults, the syncerebral structures are reduced while the ventral nerve cord and the peripheral nervous system increase in complexity. The peripheral nervous system plays an important role in processing sensory input and also in settlement. In summary, through the larval development we observed a structural and thus also functional increase of complexity in favor of the peripheral nervous system and the ventral nerve cord.

Crustacean Larvae-Vision in the Plankton.

We review the visual systems of crustacean larvae, concentrating on the compound eyes of decapod and stomatopod larvae as well as the functional and behavioral aspects of their vision. Larval compound eyes of these macrurans are all built on fundamentally the same optical plan, the transparent apposition eye, which is eminently suitable for modification into the abundantly diverse optical systems of the adults. Many of these eyes contain a layer of reflective structures overlying the retina that produces a counterilluminating eyeshine, so they are unique in being camouflaged both by their transparency and by their reflection of light spectrally similar to background light to conceal the opaque retina. Besides the pair of compound eyes, at least some crustacean larvae have a non-imaging photoreceptor system based on a naupliar eye and possibly other frontal eyes. Larval compound-eye photoreceptors send axons to a large and well-developed optic lobe consisting of a series of neuropils that are similar to those of adult crustaceans and insects, implying sophisticated analysis of visual stimuli. The visual system fosters a number of advanced and flexible behaviors that permit crustacean larvae to survive extended periods in the plankton and allows them to reach acceptable adult habitats, within which to metamorphose.

Speed discrimination in the far monocular periphery: A relative advantage for interocular comparisons consistent with self-motion.

Some animals with lateral eyes (such as bees) control their navigation through the 3D world using velocity differences between the two eyes. Other animals with frontal eyes (such as primates, including humans) can perceive 3D motion based on the different velocities that a moving object projects upon the two retinae. Although one type of 3D motion perception involves a comparison between velocities from vastly different (monocular) portions of the visual field, and the other involves a comparison within overlapping (binocular) portions of the visual field, both compare velocities across the two eyes. Here we asked whether human interocular velocity comparisons, typically studied in the context of binocularly overlapping vision, operate in the far lateral (and hence, monocular) periphery and, if so, whether these comparisons were accordant with conventional interocular motion processing. We found that speed discrimination was indeed better between the two eyes' monocular visual fields, as compared to within a single eye's (monocular) visual field, but only when the velocities were consistent with commonly encountered motion. This intriguing finding suggests that mechanisms sensitive to relative motion information on opposite sides of an animal may have been retained, or at some point independently achieved, as the eyes became frontal in some animals.

Binocular vision, the optic chiasm, and their associations with vertebrate motor behavior

Ipsilateral retinal projections (IRP) in the optic chiasm (OC) vary considerably. Most animal groups possess laterally situated eyes and no or few IRP, but, e.g. cats and primates have frontal eyes and high proportions of IRP. The traditional hypothesis that bifocal vision developed to enable predation or to increase perception in restricted light conditions applies mainly to mammals. The eye-forelimb (EF) hypothesis presented here suggests that the reception of visual feedback of limb movements in the limb steering cerebral hemisphere was the fundamental mechanism behind the OC evolution. In other words, that evolutionary change in the OC was necessary to preserve hemispheric autonomy. In the majority of vertebrates, motor processing, tactile, proprioceptive, and visual information involved in steering the hand (limb, paw, fin) is primarily received only in the contralateral hemisphere, while multisensory information from the ipsilateral limb is minimal. Since the involved motor nuclei, somatosensory areas, and vision neurons are situated in same hemisphere, the neuronal pathways involved will be relatively short, optimizing the size of the brain. That would not have been possible without, evolutionary modifications of IRP. Multiple axon-guidance genes, which determine whether axons will cross the midline or not, have shaped the OC anatomy. Evolutionary change in the OC seems to be key to preserving hemispheric autonomy when the body and eye evolve to fit new ecological niches. The EF hypothesis may explain the low proportion of IRP in birds, reptiles, and most fishes; the relatively high proportions of IRP in limbless vertebrates; high proportions of IRP in arboreal, in contrast to ground-dwelling, marsupials; the lack of IRP in dolphins; abundant IRP in primates and most predatory mammals, and why IRP emanate exclusively from the temporal retina. The EF hypothesis seams applicable to vertebrates in general and hence more parsimonious than traditional hypotheses.

A new Imogine species (Turbellaria: Polycladida: Stylochidae) associated with rock oysters (Saccostrea cucullata) from the Persian Gulf, with a review of the genus.

A new species of acotylean polyclad, Imogine qeshmensis sp. nov. is described from Qeshm Island, Persian Gulf, Iran. I. qeshmensis is characterized by the number and arrangement of the tentacular, cerebral and frontal eyes, a body margin with opaque white bands and eyespots and a male genital complex with an highly muscular seminal vesicle equal in size to the prostatic vesicle.

Tight skin and limited joint movements as early presentation of Hutchinson-Gilford progeria in a 7-week-old infant

We present a 7-week-old male infant with pseudoscleroderma as a primary manifestation of the Hutchinson-Gilford syndrome of premature aging. He had suffered intra-uterine growth retardation; micrognathism and a cleft palate were evident at birth. He presented with feeding difficulties and severe, diffuse scleroderma-like lesions, a faint peri-oral cyanosis and prominent scalp veins. With time, special facial features became more and more apparent: frontal bossing, prominent eyes, thin and fine nose and lips, microstomia, low-set ears and occipito-parietal alopecia. Histopathology of the skin showed an increased density and thickness of collagen in the dermis and hypodermis. Within the 1st year of life, typical skeletal characteristics were observed. The diagnosis of Hutchinson-Gilford syndrome was confirmed by analysis of the lamin A gene, revealing a heterozygous c.1824C > T (G608G) mutation. Hutchinson-Gilford syndrome is an extremely rare disorder of which the full clinical spectrum becomes evident with time. Sclerodermatous changes in the infant can be the first manifestation.

Mitochondrial DNA from Myotragus balearicus, an extinct bovid from the Balearic Islands.

DNA was extracted from teeth and bones of Myotragus balearicus, a bovid that evolved in isolation on the Balearic Islands (Western Mediterranean) from the end of the Miocene, becoming extinct 4,000 years BP, after the arrival of humans in the islands. The numerous morphological apomorphies of Myotragus, most strikingly its dwarfism, frontal eyes, and ever-growing incisors, obscure its phylogenetic relationships with extant bovids. Therefore, the recovery of genetic information from Myotragus is of significant interest to help clarify the taxonomic position of this species. In this study we amplified and sequenced a 95 bp (base pair) fragment of the mtDNA cytochrome b gene from 6,000-year-old specimens of Myotragus. Several experimental controls, such as amino acid analysis, independent reproduction in two different laboratories, and cloning of the PCR product, support the authenticity of the ancient DNA sequence recovered. Phylogenetic comparison with orthologous sequences from supposedly related extant genera (serow, goral, mountain goat, chamois, takin, sheep, goat, Himalayan tahr, arctic musk ox, barbary sheep, blue sheep, and saiga) from the Caprinae subfamily suggests that Myotragus is related to some of these species. However, the real phylogenetic position of Myotragus is difficult to assess, due to the lack of resolution of the present molecular study, which can be partially attributed to the short length of the genetic fragment recovered.

Aspects of the functional anatomy of the eyes of the whip-scorpionThelyphonus caudatus(Chelicerata: Arachnida) and a discussion of their putative performance as photoreceptors

Abstract T. caudatus reacts to light with a momentary locomotory arrest. Two frontal ( = median) eyes each 370 μam in diameter, and a cluster of three small lateral eyes on either side of the prosoma are present. Each frontal eye possesses a large biconvex lens that produces a clear image approx. 200 μm behind the inner surface of the lens. This is compatible with an optically homogeneous lens of 1.51 refractive index. The retina of the frontal eye is eversc, and groups of predominantly three retinula cells, held together by desmosomes, give rise to centrally fused rhabdoms up to 20 μm wide. A tapetum is not developed in the frontal eye, but screening pigment granules are present; these remain in a dark-adapted position even when the eyes are fixed in daylight between 0700 and 0800 hr. Lateral eyes strongly reflect light because of a well developed tapetum. Although distally, clusters of mostly three cells resemble similar groups found in the frontal eyes, the retina of the lateral eye is reticulated and ...

The cerebellotectal pathway in the grey squirrel

In the well laminated superior colliculus of the grey squirrel the cells of origin of the crossed descending pathway to the brainstem gaze centers are contained within the inner sublamina of the intermediate grey layer. The technique of anterograde transport of horseradish peroxidase was used to determine whether the pathway from the cerebellum to the superior colliculus terminates in this region. The technique of retrograde transport of horseradish peroxidase was used to localize the source of this pathway within the cerebellum and to determine the morphology of the cerebellotectal neurons. The grey squirrel cerebellotectal pathway provides two terminal fields to the superior colliculus: a diffuse projection into the deep grey layer and a more concentrated, interrupted projection into the inner sublamina of the intermediate grey layer. The more concentrated projection overlies precisely the tectal sublamina that contains the cells of origin of the predorsal bundle. In contrast to animals with frontal eyes, the cerebellotectal pathway in the grey squirrel was found to project almost entirely contralaterally and the vast majority of the cells of origin for the pathway were distributed ventrally, in the caudal pole of the posterior interpositus nucleus and the adjacent region of the dentate. The labelled cells in both cerebellar nuclei were large and displayed similar morphologies.

An ecological analysis of binocular vision.

Underlying the classic binocularity problems of singleness and three-dimensionality is a theory that the stimulus for binocular vision constitutes two two-dimensional images and metric differences between parts of those images. This characterization of the stimulus is criticized here and in its stead an ecologically-based characterization is presented wherein a binocular transformational invariant is shown to specify absolute (body-scaled) size, shape, and distance. The transformation is characterized as a rotation and its specificity to distance assumes a constant interocular distance and either homogeneously textured or extended surfaces. Four experiments demonstrate perceivers' abilities to detect this information and report (verbally or by reaching) the absolute distances of surfaces in stereograms. A fifth experiment revealed that accurate performance did not depend on oculomotor information. The assumptions of texture extent and distribution and constant interocular distance and their possible violations were discussed. A sixth experiment demonstrated that violations of interocular distance are absorbed by surface shapes. The existence and detection of a binocular rotation dissolves the putative problems of singleness and stereopsis, indicates that the importance of having two frontal eyes is for perception of absolute distance, and reformulates the problems for an algorithmic (physiological) theory of vision.

The “Paratactic” Image in Egyptian Art

One of the characteristic features of the Egyptian art style is the “paratactic” (sometimes called “non-functional,” “conceptual,” or “ideoplastic”) representation of the figure, a stereotype with frontal eyes and shoulders, and profiled face, arms, and legs. The importance of this stereotype is, of course, strengthened by the frequent demands of the iconography for confrontations between victor and vanquished, subject and emperor, and emperor or priest and the deity.