Visual accommodation and active pursuit of prey underwater in a plunge-diving bird: the Australasian gannet

Australasian gannets (Morus serrator), like many other seabird species, locate pelagic prey from the air and perform rapid plunge dives for their capture. Prey are captured underwater either in the momentum (M) phase of the dive while descending through the water column, or the wing flapping (WF) phase while moving, using the wings for propulsion. Detection of prey from the air is clearly visually guided, but it remains unknown whether plunge diving birds also use vision in the underwater phase of the dive. Here we address the question of whether gannets are capable of visually accommodating in the transition from aerial to aquatic vision, and analyse underwater video footage for evidence that gannets use vision in the aquatic phases of hunting. Photokeratometry and infrared video photorefraction revealed that, immediately upon submergence of the head, gannet eyes accommodate and overcome the loss of greater than 45 D (dioptres) of corneal refractive power which occurs in the transition between air and water. Analyses of underwater video showed the highest prey capture rates during WF phase when gannets actively pursue individual fish, a behaviour that very likely involves visual guidance, following the transition after the plunge dive's M phase. This is to our knowledge the first demonstration of the capacity for visual accommodation underwater in a plunge diving bird while capturing submerged prey detected from the air.     

Lateralized visual behavior in bottlenose dolphins (Tursiops truncatus) performing audio-visual tasks: the right visual field advantage

Analyzing cerebral asymmetries in various species helps in understanding brain organization. The left and right sides of the brain (lateralization) are involved in different cognitive and sensory functions. This study focuses on dolphin visual lateralization as expressed by spontaneous eye preference when performing a complex cognitive task; we examine lateralization when processing different visual stimuli displayed on an underwater touch-screen (two-dimensional figures, three-dimensional figures and dolphin/human video sequences). Three female bottlenose dolphins (Tursiops truncatus) were submitted to a 2-, 3- or 4-, choice visual/auditory discrimination problem, without any food reward: the subjects had to correctly match visual and acoustic stimuli together. In order to visualize and to touch the underwater target, the dolphins had to come close to the touch-screen and to position themselves using monocular vision (left or right eye) and/or binocular naso-ventral vision. The results showed an ability to associate simple visual forms and auditory information using an underwater touch-screen. Moreover, the subjects showed a spontaneous tendency to use monocular vision. Contrary to previous findings, our results did not clearly demonstrate right eye preference in spontaneous choice. However, the individuals' scores of correct answers were correlated with right eye vision, demonstrating the advantage of this visual field in visual information processing and suggesting a left hemispheric dominance. We also demonstrated that the nature of the presented visual stimulus does not seem to have any influence on the animals' monocular vision choice.     

DARK ADAPTATION AND VISUAL SENSITIVITY IN SHALLOW AND DEEP-DIVING PINNIPEDS1

Pinnipeds forage almost exclusively underwater. Consequently, observing them is difficult and relatively little is known of how they use their senses to locate prey, avoid predators, and navigate while diving. Vision has been presumed to be of primary importance, although previous measurements of visual functioning in pinnipeds have been restricted to just a few shallow-diving species. As diving pinnipeds experience rapid changes in light levels during descent/ascent and low light levels at depth, it has not been clear whether they possess visual capabilities adequate for use while diving, particularly in the case of deep-diving species. To examine this issue, behavioral psychophysics have been used to assess and compare the dark adaptation rates and relative light sensitivities of a deep-diving pinniped (northern elephant seal, Mirounga angustirostris), two shallow-diving species (California sea lion, Zalophus californianus, and harbor seal, Phoca vitulina), and a human subject. In comparison to the human subject, both the California sea lion and the harbor seal dark-adapted relatively quickly and were more light sensitive. These findings suggest that both of these species are well suited for vision in the moderately dim shallow-water environments in which they dive to forage. In contrast, the elephant seal reached complete dark adaptation in less than half the time taken by the other pinnipeds, and it was significantly more light sensitive. Unlike the shallower-diving species, the visual abilities of the elephant seal are commensurate with the extreme conditions experienced while deep diving. Thus, we conclude that elephant seals are sufficiently adapted to rely on vision underwater, even while diving to depths in excess of 1000 meters where bioluminescence may be the sole source of ambient light.     

Stimulation of functional vision in children with perinatal brain damage

Cerebral visual impairment (CVI) is one of the most common causes of bilateral visual loss, which frequently occurs due to perinatal brain injury. Vision in early life has great impact on acquisition of basic comprehensions which are fundamental for further development. Therefore, early detection of visual problems and early intervention is necessary. The aim of the present study is to determine specific visual functioning of children with perinatal brain damage and the influence of visual stimulation on development of functional vision at early age of life. We initially assessed 30 children with perinatal brain damage up to 3 years of age, who were reffered to our pediatric low vision cabinet in "Little house" from child neurologists, ophthalmologists Type and degree of visual impairment was determined according to functional vision assessment of each child. On the bases of those assessments different kind of visual stimulations were carried out with children who have been identified to have a certain visual impairment. Through visual stimulation program some of the children were stimulated with light stimulus, some with different materials under the ultraviolet (UV) light, and some with bright color and high contrast materials. Children were also involved in program of early stimulation of overall sensory motor development. Goals and methods of therapy were determined individually, based on observation of child's possibilities and need. After one year of program, reassessment was done. Results for visual functions and functional vision were compared to evaluate the improvement of the vision development. These results have shown that there was significant improvement in functional vision, especially in visual attention and visual communication.     

The visual fields of Common Guillemots Uria aalge and Atlantic Puffins Fratercula arctica: foraging,vigilance and collision vulnerability

Significant differences in avian visual fields are found between closely related species that differ in their foraging technique. We report marked differences in the visual fields of two auk species. In air, Common Guillemots Uria aalge have relatively narrow binocular fields typical of those found in non‐passerine predatory birds. Atlantic Puffins Fratercula arctica have much broader binocular fields similar to those that have hitherto been recorded in passerines and in a penguin. In water, visual fields narrow considerably and binocularity in the direction of the bill is probably abolished in both auk species. Although perceptual challenges associated with foraging are similar in both species during the breeding season, when they are piscivorous, Puffins (but not Guillemots) face more exacting perceptual challenges when foraging at other times, when they take a high proportion of small invertebrate prey. Capturing this prey probably requires more accurate, visually guided bill placement and we argue that this is met by the Puffin's broader binocular field, which is retained upon immersion; its upward orientation may enable prey to be seen in silhouette. These visual field configurations have potentially important consequences that render these birds vulnerable to collision with human artefacts underwater, but not in air. They also have consequences for vigilance behaviour.     

Aerial and aquatic visual acuity of the grey bichir Polypterus senegalus,as estimated by optokinetic response

The present study assessed the aerial and aquatic visual abilities of juvenile grey bichir Polypterus senegalus, fish capable of terrestrial locomotion, by measuring the optokinetic response to stimuli of varying speed and spatial frequency. In water, fish tracked slow-moving (2° s⁻¹) stimuli moderately well and fast-moving stimuli very poorly. Spatial acuity was very low compared with many other species, with maximum response observed at 0.05–0.075 stimulus cycles per degree of visual arc; however, it should be noted that adult fish, with their larger eyes, are likely to have somewhat improved spatial acuity. Low spatial acuity and limited stimulus tracking ability might be expected in a nocturnal ambush predator such as P. senegalus, where gaze stabilization may be less crucial and other sensory inputs may have greater importance in perception of the environment. In air, spatial and temporal acuity were both poorer by every measure, but some visual ability persisted. As the eye shows no anatomical specialization for aerial vision, poor vision was expected; however, the large decrease in saccade velocity observed in air trials was unexpected. Stimulus parameters typically have little effect on the characteristics of the saccade, so this finding may suggest that the function of the reflex system itself could be compromised in the aerial vision of some fishes capable of terrestrial locomotion.     

Crocodiles don't focus underwater

Summary Crocodilians are amphibious reptiles which hunt prey both on land and in water. Previous refractive and anatomical studies have suggested that their eyes can focus objects in air and that their ability to refocus the eye underwater may be limited. Examination of the plane of focus of six species of crocodilians both in air and underwater has revealed that they are generally well focused in air for distant targets and severely defocused underwater. These results suggest that sensory systems other than vision must play an important role in prey capture underwater.Abbreviation D diopter     

Project Prakash: Challenging the critical period: Association of Research in Vision and Ophthalmology National Meeting

Project Prakash is an organization that reverses congenital blindness in children and adolescents in rural India with the hypothesis that these children will be able to recover some of their vision even though their visual system did not develop normally. This hypothesis challenges the scientific dogma established by the Nobel-prize winning research of Hubel and Wiesel that the brain cannot adapt to visual input after being completely deprived of vision during the critical first few months and years of life. Dr. Pawan Sinha presented his work at the largest and most respected ophthalmological research meeting, the Association for Research in Vision and Ophthalmology (ARVO), in Fort Lauderdale, Florida, on May 4, 2011.     

Observations on the use of grottos by Mediterranean Monk seals (Monachus monachus)

A group of six Monk seals ( Monachus monachus ) was discovered to lie up inside a grotto on the shores of a lake reached via an underwater passage. Nearly 1200 hours of observation on the movement of the seals showed that the greatest use of the grotto was made during the winter months and when the wind was towards the grotto entrance. Entry and exit times were not significantly affected by sea state, dark or light, nor were they significantly correlated with sunrise and sunset times or sea and air temperature. These variables did not significantly affect the length of stay in the grotto. Entry occurred most frequently in the early morning and exist at night.
Discussion is given of the possible reasons why grottos are used by Monk seals. This appears to be a recent adaptation which may be related to the effects of human disturbance.     

The sensitive period in the development of the human visual system

The human visual system is the most sensitive to the deprivation of the object vision up to the age of 7, when the amblyopia produced by congenital or traumatic cataract develops in all cases and is "relatively" sensitive during the period from 7 to 15 years, when probability of amblyopia development and its degree are determined by the age of cataract appearance and duration of its existence. Visual deprivation taking place after 15 years does not lead to ambliopy. The data on visual evoked potentials (VEP) obtained during stimulation of the ambyopic and the second, intact eye are used in discussion of the neurophysiological mechanisms of the unilateral visual deprivation and of informative importance of VEP.     

Patterns and properties of polarized light in air and water

Natural sources of light are at best weakly polarized, but polarization of light is common in natural scenes in the atmosphere, on the surface of the Earth, and underwater. We review the current state of knowledge concerning how polarization and polarization patterns are formed in nature, emphasizing linearly polarized light. Scattering of sunlight or moonlight in the sky often forms a strongly polarized, stable and predictable pattern used by many animals for orientation and navigation throughout the day, at twilight, and on moonlit nights. By contrast, polarization of light in water, while visible in most directions of view, is generally much weaker. In air, the surfaces of natural objects often reflect partially polarized light, but such reflections are rarer underwater, and multiple-path scattering degrades such polarization within metres. Because polarization in both air and water is produced by scattering, visibility through such media can be enhanced using straightforward polarization-based methods of image recovery, and some living visual systems may use similar methods to improve vision in haze or underwater. Although circularly polarized light is rare in nature, it is produced by the surfaces of some animals, where it may be used in specialized systems of communication.     

Designing a chamber for studies involving manipulation of light:dark cycles

The authors designed and built a device that can house mice or rats and allow researchers to control the light:dark cycles inside. They developed this chamber for neuroscientists who are studying the condition-dependent plasticity of the mouse visual cortex. The chamber, which (when closed) completely blocks outside light, consists of two units. Each unit can hold eight small mouse cages or six rat cages. Each unit contains an optical sensor that triggers an audible and visual alarm when light is detected. Researchers can monitor the environmental conditions inside each unit using a control panel located outside the unit. Researchers have reported that this chamber is ideal for use in their work involving manipulations of light:dark cycles.     

Retinal topography of ganglion cells in immature ocean sunfish, <Emphasis Type="Italic">Mola mola</Emphasis>

The ocean sunfish, Mola mola, is the largest known bony fish. Based on prior studies of diet composition, it is considered to be a pelagic zooplanktivore. However, a recent study using acoustic telemetry revealed that they repeatedly dive to depths of >50 m during the day. We examined the distribution of cells within the retinal ganglion cell layer in the immature ocean sunfish (c.a. 50 cm total length) and estimated their visual acuity with respect to the main visual axis and visual fields. Visual acuity was between 3.37 and 4.41 cycles/degree. The region of highest cell density was located in the dorso-temporal retina, indicating that the main visual axis of ocean sunfish is directed towards the lower frontal portion of the visual field. This axis is considered beneficial for detecting prey items when the sunfish are migrating vertically through the water column, and in foraging behavior near the sea bottom.     

Eye structure and amphibious foraging in albatrosses

Anterior eye structure and retinal visual fields were determined in grey-headed and black-browed albatrosses, Diomedea melanophris and D. chrysostoma (Procellariiformes, Diomedeidae), using keratometry and an ophthalmoscopic reflex technique. Results for the two species were very similar and indicate that the eyes are of an amphibious optical design suggesting that albatross vision is well suited to the visual pursuit of active prey both on and below the ocean surface. The corneas are relatively flat (radius ca. 14.5 mm) and hence of low absolute refractive power (ca. 23 dioptres). In air the binocular fields are relatively long (vertical extent ca. 70 degrees) and narrow (maximum width in the plane of the optic axes 26–32 degrees), a topography found in a range of bird species that employ visual guidance of bill position when foraging. The cyclopean fields measure approximately 270 degrees in the horizontal plane, but there is a 60 degrees blind sector above the head owing to the positioning of the eyes below the protruding supraorbital ridges. Upon immersion the monocular fields decrease in width such that the binocular fields are abolished. Anterior eye structure, and visual field topography in both air and water, show marked similarity with those of the Humboldt penguin.     

Touch Influences Visual Perception with a Tight Orientation-Tuning

Stimuli from different sensory modalities are thought to be processed initially in distinct unisensory brain areas prior to convergence in multisensory areas. However, signals in one modality can influence the processing of signals from other modalities and recent studies suggest this cross-modal influence may occur early on, even in ‘unisensory’ areas. Some recent psychophysical studies have shown specific cross-modal effects between touch and vision during binocular rivalry, but these cannot completely rule out a response bias. To test for genuine cross-modal integration of haptic and visual signals, we investigated whether congruent haptic input could influence visual contrast sensitivity compared to incongruent haptic input in three psychophysical experiments using a two-interval, two-alternative forced-choice method to eliminate response bias. The initial experiment demonstrated that contrast thresholds for a visual grating were lower when exploring a haptic grating that shared the same orientation compared to an orthogonal orientation. Two subsequent experiments mapped the orientation and spatial frequency tunings for the congruent haptic facilitation of vision, finding a clear orientation tuning effect but not a spatial frequency tuning. In addition to an increased contrast sensitivity for iso-oriented visual-haptic gratings, we found a significant loss of sensitivity for orthogonally oriented visual-haptic gratings. We conclude that the tactile influence on vision is a result of a tactile input to orientation-tuned visual areas.     

Eye-Head Coordination for Visual Cognitive Processing

We investigated coordinated movements between the eyes and head (“eye-head coordination”) in relation to vision for action. Several studies have measured eye and head movements during a single gaze shift, focusing on the mechanisms of motor control during eye-head coordination. However, in everyday life, gaze shifts occur sequentially and are accompanied by movements of the head and body. Under such conditions, visual cognitive processing influences eye movements and might also influence eye-head coordination because sequential gaze shifts include cycles of visual processing (fixation) and data acquisition (gaze shifts). In the present study, we examined how the eyes and head move in coordination during visual search in a large visual field. Subjects moved their eyes, head, and body without restriction inside a 360° visual display system. We found patterns of eye-head coordination that differed those observed in single gaze-shift studies. First, we frequently observed multiple saccades during one continuous head movement, and the contribution of head movement to gaze shifts increased as the number of saccades increased. This relationship between head movements and sequential gaze shifts suggests eye-head coordination over several saccade-fixation sequences; this could be related to cognitive processing because saccade-fixation cycles are the result of visual cognitive processing. Second, distribution bias of eye position during gaze fixation was highly correlated with head orientation. The distribution peak of eye position was biased in the same direction as head orientation. This influence of head orientation suggests that eye-head coordination is involved in gaze fixation, when the visual system processes retinal information. This further supports the role of eye-head coordination in visual cognitive processing.     

The human visual system is optimised for processing the spatial information in natural visual images

A fundamental tenet of visual science is that the detailed properties of visual systems are not capricious accidents, but are closely matched by evolution and neonatal experience to the environments and lifestyles in which those visual systems must work. This has been shown most convincingly for fish and insects. For mammalian vision, however, this tenet is based more upon theoretical arguments than upon direct observations. Here, we describe experiments that require human observers to discriminate between pictures of slightly different faces or objects. These are produced by a morphing technique that allows small, quantifiable changes to be made in the stimulus images. The independent variable is designed to give increasing deviation from natural visual scenes, and is a measure of the Fourier composition of the image (its second-order statistics). Performance in these tests was best when the pictures had natural second-order spatial statistics, and degraded when the images were made less natural. Furthermore, performance can be explained with a simple model of contrast coding, based upon the properties of simple cells in the mammalian visual cortex. The findings thus provide direct empirical support for the notion that human spatial vision is optimised to the second-order statistics of the optical environment.     

Adaptation to left-right reversed vision rapidly activates ipsilateral visual cortex in humans.

The brain mechanisms of adaptation to visual transposition are of increasing interest, not only for research on sensory-motor coordination, but also for neuropsychological rehabilitation. Sugita [Nature 380 (1996) 523] found that after adaptation to left-right reversed vision for one and a half months, monkey V1 neurons responded to stimuli presented not only in the contralateral visual field, but also in the ipsilateral visual field. To identify the underlying neuronal mechanisms of adaptation to visual transposition, we conducted fMRI and behavioral experiments for which four adult human subjects wore left-right reversing goggles for 35/39 days, and investigated: (1) whether ipsilateral V1 activation can be induced in human adult subjects; (2) if yes, when the ipsilateral activity starts, and what kind of behavioral/psychological changes occur accompanying the ipsilateral activity; (3) whether other visual cortices also show an ipsilateral activity change. The results of behavioral experiments showed that visuomotor coordinative function and internal representation of peripersonal space rapidly adapted to the left-right reversed vision within the first or second week. Accompanying these behavioral changes, we found that both primary (V1) and extrastriate (MT/MST) visual cortex in human adults responded to visual stimuli presented in the ipsilateral visual field. In addition, the ipsilateral activity started much sooner than the one and a half months, which had been expected from the monkey neurophysiological study. The results of the present study serve as physiological evidence of large-scale, cross-hemisphere, cerebral plasticity that exists even in adult human brain.     

Transcaruncular orbital decompression for management of compressive optic neuropathy in thyroid-related orbitopathy

This study was conducted to assess the outcome of transcaruncular orbital decompression to treat compressive optic neuropathy in thyroid-related orbitopathy. It involved a retrospective, noncomparative case series of 18 eyes of 10 consecutive patients with documented vision loss secondary to thyroid-related orbitopathy. Bony decompression of the orbital apex was performed via a transcaruncular approach. Main outcome measures were visual acuity, color vision, presence of diplopia, and reduction of exophthalmos. Of 18 eyes, 16 (89 percent) had improved visual acuity after the operation. One eye had no improvement and one had worsening of vision in the setting of diabetic retinopathy. Color vision was improved in 12 eyes (67 percent). Five of the patients did not have diplopia before the operation; none of these patients developed double vision after intervention. Exophthalmos was decreased by an average of 2.6 mm. The authors conclude that transcaruncular orbital decompression for compressive optic neuropathy in thyroid-related orbitopathy is successful in restoring visual function. Compared with other approaches used for decompression surgery, the transcaruncular approach offers direct access to the medial wall and orbital apex without a cutaneous incision or disruption of the medial canthus. In addition, this approach allows a controlled, graded removal of the ethmoidal air cells and reduced recovery time.     

Eye structure and foraging in King Penguins Aptenodytes patagonicus

Anterior eye structure and retinal visual fields were determined in King Penguins Aptenodytes patagonicus using keratometry and an ophthalmoscopic reflex technique. The cornea is relatively flat (radius 32.9 mm) and hence of low refractive power (10.2 dioptres in air) and this may be correlated with the amphibious nature of penguin vision. The large size of the eye and of the fully dilated pupil may be correlated with activity at low light levels. In air, the binocular field is long (vertical extent 180̀) and narrow (maximum width 29̀), with the bill placed approximately centrally—a topography found in a range of bird species which employ visual guidance of bill position when foraging. Upon immersion in water, the optical power of the cornea is abolished, with the effect that the monocular fields decrease and binocularity is lost. King Penguins have a pupil type which has not hitherto been recorded in birds. In daylight it contracts to a square-shaped pinhole but dilates to a large circular aperture in darkness. This change alters retinal illumination by 300-fold (2.5 log₁₀ units). When diving, this permits the retina to be pre-adapted to the low ambient light levels that the birds encounter upon reaching mesopelagic depths. These penguins also forage at depths where ambient light levels, even during the day, can fall below the equivalent of terrestrial starlight. Under these conditions, the birds must rely upon the detection of light from the photophores of their prey. In this they are aided by their absolutely large pupil size and broad cyclopean visual field.