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Adult jumping spiders are known for their extraordinary eyesight and complex, visually guided behaviors, including elaborate communicatory displays, navigational abilities, and prey-specific predatory strategies. Juvenile spiders also exhibit many of these behaviors, yet their visual systems are many times smaller. How do juveniles retain high visually guided performance despite severe size constraints on their visual systems? We investigated developmental changes in eye morphology and visual function in the jumping spider Phidippus audax using morphology, histology, ophthalmoscopy, and optical measurements. We find that juvenile spiders have proportionally larger lenses in relation to their body size than adults. This should alleviate some of the costs of small body size on visual function. However, photoreceptor number in the anterior lateral eyes (ALE) remains constant from early development onward, consistent with a developmental constraint on photoreceptor differentiation. To accommodate these photoreceptors within the diminutive volume of the spiderling cephalothorax, ALE rhabdoms in early life stages are more tightly packed and significantly smaller in diameter and length, properties that expand across development. Lens focal lengths increase as eyes and retinas grow, resulting in a remarkable maintenance of ALE spatial acuity and field-of-view across life stages. However, this maintenance of acuity comes at a sensitivity cost given the small rhabdomal volumes required by space constraints early in life. Taken together, our results indicate that young jumping spiders have eyes already equipped for high acuity vision, but these young spiders may struggle to perform visually demanding behaviors in low-light environments, a notion that warrants further testing.

To further extent our understanding of aquatic vision, we introduce a complete optical model of a goldfish eye, which comprises all important optical parameters for the first time. Especially a spherical gradient index structure for the crystalline lens was included, thus allowing a detailed analysis of image quality, regarding spot size, and wavelength dependent aberration. The simulation results show, that our realistic eye model generates a sufficient image quality, with a spot radius of 4.9 mm which is below the inter cone distance of 5.5 mm. Furthermore, we optically simulate potential mechanical processes of accommodation and compare the results with contradictory findings of previous experimental studies. The quantitative simulation of the accommodation capacity shows that the depth of field is strongly dependent on the resting position and becomes significantly smaller when shorter resting positions are assumed. That means, to enable an extended depth perception with high acuity for the goldfish an adaptive, lens shifting mechanism would be required. In addition, our model allows a clear prediction of the expected axial lens-shift, which is necessary to ensure a sufficient resolution over a large object range.

In the presence of optical blur at the fovea, blur adaptation can improve visual acuity (VA) and perceived image quality over time. However, little is known regarding blur adaptation in the peripheral retina. Here, we examined neural adaptation to myopic defocus at the fovea and parafovea (10° temporal retina) in both emmetropes and myopes. During a 60-min adaptation period, subjects (3 emmetropes and 3 myopes) watched movies with +2 diopters of defocus blur through a 6-mm artificial pupil in two separate, counter-balanced sessions for each retinal location. VA was measured at 10-min intervals under full aberration-corrected viewing using an adaptive optics (AO) vision simulator. By correcting subjects' native optical aberrations with AO, we bypassed the influence of the individual subjects' optical aberrations on visual performance. Overall, exhibited a small but significant improvement after the 60-min of adaptation at both the fovea (mean±SE VA improvement: -0.06±0.04 logMAR) and parafovea (mean±SE VA improvement: -0.07±0.04 logMAR). Myopic subjects exhibited significantly greater improvement in parafoveal VA (mean±SE VA improvement: 0.10±0.02 logMAR), than that of emmetropic subjects (mean±SE VA improvement: 0.04±0.03 logMAR). In contrast, there was no significant difference in foveal VA between the two refractive-error groups. In conclusion, our results reveal differences in peripheral blur adaptation between refractive-error groups, with myopes displaying a greater degree of adaptation.

Polarized light detection has been documented in only a small number of fish species. The benefit of polarization vision for fish is not fully understood, nor is the transduction mechanism that underlies it. Past studies proposed that one possible advantage of polarization vision is that it enhances the contrast of zooplankton targets by breaking their transparency. Here, we used an optomotor apparatus to test the responses of the planktivorous Hardyhead silverside fish Atherinomorus forskalii (Atherinidae) to vertical unpolarized (intensity) and polarized gratings. We also tested and compared the spatial and temporal resolutions of A. forskalii in the intensity and polarization domains. A. forskalii responded to the polarization pattern, but only under illumination that included ultraviolet-blue (λ>380nm) wavelengths. The spatial resolution of A. forskalii was measured as a minimum separable angle of 0.57° (a 1-mm prey viewed from 100-mm distance). The temporal resolution to unpolarized vs. polarized gratings was constant, at 33 and 10Hz respectively at most of the stripe widths tested. At the smallest stripe width tested (1mm=the minimal separable angle), which correlates with the size of prey typically consumed by these fish, the temporal resolution to the polarized grating increased to 42Hz. We conclude that A. forskalii is polarization sensitive, may use polarization vision to improve detection of its planktonic prey, and that polarization may be perceived by the fish via a separate visual pathway than intensity.

Experiments involving the orientation of animals, especially birds, have shown that the visual system and geomagnetic field are linked. On the basis of these findings, we have addressed the question of whether there is an influence of the geomagnetic field on light-sensitivity of the visual system in man. Here we report on measurements of the photopic sensitivity of the human visual system for a 0.5s test-stimulus without magnetic field and with the full local field of 48μT rotated into the line of view. The experiments show that the geomagnetic field increases this sensitivity by 6–7%, depending on the stimulated area. Based on this increase the probable change in perception of the background luminance was calculated by the Weber-law.

PurposeThis study investigated changes in refraction, corneal curvature, axial components and weight of posterior sclera in guinea pig eyes during the normal development from birth.MethodsSixty-four guinea pigs were assigned to eight groups (n=8 each). Each group underwent a series of ocular measurements at one of the eight time-points (0, 1, 2, 3, 5, 7, 9 and 11 weeks), including refraction (streak retinoscopy), corneal radius of curvature (CRC; keratometry), anterior segment length (AS: corneal thickness and depth of the anterior chamber), thickness of the crystalline lens (CL), vitreous chamber length (VC; all A-scan ultrasonography) and dry weight of a circular 6mm diameter punch in the posterior sclera (electronic balance). Results of all the measurements were statistically compared between right eye and left eye, male and female and among different age groups. Artifacts of retinoscopy due to small eye artifact were also estimated at different ages.ResultsThe refraction in guinea pig eyes was +5.22±0.23D (Mean, SE) at birth. This value decreased rapidly during the first 3 weeks followed by a slow decline. The overall decrease in refraction was highly significant from birth to 11 weeks (p

The pattern electroretinogram (PERG) was used to measure the visual acuity and refractive state of nine American kestrels (Falco sparverius). Visual acuity was determined from psychometric functions of PERG amplitude vs. spatial frequency. Refractive state was measured by finding the trial lens that resulted in the highest acuity. All nine kestrels were found to be emmetropic. Their median visual acuity was 29 c/deg. The PERG, however, underestimates behaviorally determined visual acuity by approximately 37%. When adjusted for this underestimation, the median kestrel acuity was 46 c/deg. The visual acuity of American kestrels is compared to reports in the literature of 17 other species of birds.

The reported size of microsaccades is considerably larger today compared to the initial era of microsaccade studies during the 1950s and 1960s. We investigate whether this increase in size is related to the fact that the eye-trackers of today measure different ocular structures than the older techniques, and that the movements of these structures may differ during a microsaccade. In addition, we explore the impact such differences have on subsequent analyzes of the eye-tracker signals. In Experiment I, the movement of the pupil as well as the first and fourth Purkinje reflections were extracted from series of eye images recorded during a fixation task. Results show that the different ocular structures produce different microsaccade signatures. In Experiment II, we found that microsaccade amplitudes computed with a common detection algorithm were larger compared to those reported by two human experts. The main reason was that the overshoots were not systematically detected by the algorithm and therefore not accurately accounted for. We conclude that one reason to why the reported size of microsaccades has increased is due to the larger overshoots produced by the modern pupil-based eye-trackers compared to the systems used in the classical studies, in combination with the lack of a systematic algorithmic treatment of the overshoot. We hope that awareness of these discrepancies in microsaccade dynamics across eye structures will lead to more generally accepted definitions of microsaccades.

An imaging polarimeter using liquid-crystal variable retarders (Bueno, J. M., Artal, P. (1999). Double-pass imaging polarimetry in the human eye. Optics Letters, 24, 64–66) has been used to study the parameters of polarization in the living human eye. Retardation introduced by birefringent structures of the eye has been calculated by using a spatially resolved collection of Mueller matrices obtained from series of 16 double-pass retinal images. Results for images with a 2-mm pupil diameter show that although the retardation introduced by the eye in a double-pass varies among individuals, at the central cornea the slow axis is directed along the upper-temporal to lower-nasal line and the ellipticity is close to zero, which indicates the presence of linear birefringence. As pupil size increased, the measured retardation also increased, while ocular birefringence remained linear and azimuthal angle changed without a clear tendency.

We examined the 2D surface formed by 3D eye positions of normal subjects to determine whether the shape and thickness changed in tasks that differed in saccadic directions; random, horizontal, vertical, radial, clockwise and counter-clockwise. Eye positions during the random task did not lie precisely on Listing's plane but on a surface with a small twist. This twist was present before, during, and after saccades. The degree of twist changed with the task; becoming less twisted for horizontal tasks and more twisted in the vertical tasks. The surface thickness changed with the task becoming thicker for multidirectional tasks. This greater thickness may occur because surfaces obtained in multidirectional tasks are the composite of surfaces with slightly different shapes.

Available literature on the spectral transmittance of the eye media in the infrared (IR) is insufficiently accurate to estimate the deposited doses, e.g. in view of light damage risks. Analysis of the data of Boettner and Wolter [Investigative Ophthalmology and Visual Science, 1, 776-783 (1962)] for cornea, anterior chamber, lens and vitreous separately, shows that they can be explained on the basis of the pure water content. The transmittance spectrum of Geeraets et al. [Archives of Ophthalmology, 64, 606-615 (1960)] for all eye media combined is found to be impossible. It is concluded that in the near-IR, light losses in the eye media are best estimated with the absorption coefficient for pure water. A table is given from 700-2500 nm in steps of 10 nm.

Using an 8 mm pupil, 2AFC-method, and 2 × 2 deg 2 grating at 2 c/deg we measured contrast sensitivity as a function of integrated radiance for a series of interference filters with peak wavelengths at 400–700 nm. Irrespective of the radiance level, contrast sensitivity was highest when wavelengths was at and around 550 nm. It decreased towards longer and shorter wavelengths, reflecting the variation of the probability of quantal catch with light wavelength. When contrast sensitivity functions plotted in double logarithmic coordinates were shifted horizontally by multiplying the integrated radiances of each filter by an appropriate scaling factor, the functions superimposed onto a single curve. Contrast sensitivity at lower levels of relative radiance ( R ) increased in proportion to ∐ R , obeying DeVries-Rose law, but at higher levels contrast sensitivity was constant, obeying Weber's law. Scaling factors plotted as a function of wavelength provided an estimate of V (λ) quite similar to the standard 2 deg photopic spectral-luminosity function of CIE 1924. Copyright © 1996 Elsevier Science Ltd.

The image of a distant unresolved point (point image or PI) and modulation transfer function (MTF) of the eye and lens of the trout were recorded with high spatial (0.3 μm) and dynamic (4096 grey levels) resolution for various entrance aperture sizes and focal positions in monochromatic light, and in broadband light simulating sunlight absorbed by a retinal cone pigment. The PI is light, and in broadband light simulating sunlight absorbed by a retinal cone pigment. The PI is irregular, with streaks, wisps and speckle, as a result of lens structural irregularity and diffraction of light scattered within the lens and cornea. Maximum diameter of a diffraction-limited aperture area of the eye is about 0.3 mm. Axially spaced multiple foci are caused by irregular and discontinuous zonal spherical aberration. Lens substance dispersion causes strong longitudinal chromatic aberration, resulting in a broadband PI with concentric coloured haloes. Incident linearly polarized light is slightly depolarized in the PI. The nature of the image is discused relative to lens and cornea structure, optical modelling and vision. Human subjective entoptic phenomena analogous to those observed objectively in the trout are described. Copyright © 1996 Elsevier Science Ltd.

Among the oldest fossil crustaceans are those of the Late Cambrian (Furongian 499 ± 0.3-488.3 ± 1.7 Ma) of Vastergotland, central Sweden and the lower Ordovician (Tremadocian 488.3 and 478.6 Ma) of the island of Őland. These are three-dimensionally preserved in nodules from the so called 'stinkstone' ('Orsten') limestone. 'Orsten'-like fossils represent tiny, often meiobenthic organsisms (Haug, Maas, & Waloszek, 2009) smaller than 2mm, which mainly were arthropods, especially crustaceans close to the stemline. As a result of phosphatisation, hairs, bristles and even cellular structures up to 0.3 μm are preserved (Walossek, 1993), especially compound eyes, as typical for all visually orientated crustaceans (Schoenemann et al., 2011). We show a miniscule prototype of a compound eye (∼40 μm) in a small crustacean, which lived almost half a billion years ago. The eye is close to but comfortably established above being limited in its resolving power by diffraction, but it is too small to be an apposition eye, normally regarded as the basal form of all compound eyes, as is found in bees, dragonflies, crustaceans and many other arthropods still living today. The facets of this compound eye are ∼8 μm in size, the surface structure indicates the relicts of a tiny lens covering each facet. In order to work functionally and to ensure that that diffraction and waveguide problems were avoided, it seems reasonable to suppose that the compound eye consisted of visual units, each with a single photoreceptor cell directly below a weak lens for capturing and slightly focusing the light. The entire unit has a diameter similar to that of a normal sensory cell as found in compound eyes. Thus, the early compound eye analysed here may be interpreted as a prototype representing the earliest stages of the evolution of crustacean compound eyes.

The angle of pitch of a visual field consisting of only a single vertical, 64 degrees-long, eccentrically-located line in otherwise total darkness influences the elevation of a target set to appear at eye level (VPEL). The influence changes linearly with the magnitude of pitch over the range from -30 degrees to +20 degrees. The average slope of the VPEL-vs-pitch function is +0.53. The influence on VPEL of a pitched visual field consisting of two parallel vertical lines is slightly greater (slope = +0.56), and the influence of the pitch of a complexly-structured well-illuminated pitched room is slightly greater yet (slope = +0.63). The pitch of a frontoparallel plane containing one horizontal line has a small influence on VPEL (slope = +0.08); the influence with two horizontal lines is slightly greater (slope = +0.18). The slope of the VPEL-vs-pitch function differs among individual subjects but is linear for each of the eight subjects. A great deal of consistency is manifested by individual subjects across all of the visual fields: an individual with a steep slope with one visual field tends to have a steep slope with all visual fields. The individual's characteristic response in total darkness is strongly correlated with the response to an erect well-illuminated visual field. The significant aspect of the pitched-from-vertical line stimulus is the change in orientation of its retinal image. An additional experiment with a small pupil (pilocarpine) indicates that cues related to other retinal gradients or to accommodation play no role in the influence of the visual field on VPEL. The experiments provide support for treating the visual influence on VPEL by means of the Great Circle Model.

Optical quality in barn owl eyes is presented in terms of measuring the ocular wavefront aberrations with a standard Tscherning-type wavefront aberrometer under natural viewing conditions. While accommodative state was uncontrolled, all eyes were focused within 0.4D with respect to the plane of the aberrometer. Total RMS wavefront error was between 0.06 and 0.15 microm (mean: 0.10 microm, STD: 0.03 microm, defocus cancelled) for a 6 mm pupil. The results suggest that image quality in barn owl eyes is excellent.

Rhinoceroses have been supposed to be myopic; however, our examination of four specimens by retinoscopy, infrared photorefraction, and telescopic pointspread retinoscopy has shown them to be mildly hyperopic.

The notion of blindsight was recently challenged by evidence that patients with occipital damage and contralateral field defects show residual islands of vision which may be associated with spared neural tissue. However, this possibility could not explain why patients who underwent the resection or disconnection of an entire cerebral hemisphere exhibit some forms of blindsight. We present here a model for the detection of intraocular scatter, which can account for human sensitivity values obtained in the blind field of hemidecorticated patients. The model demonstrates that, under controlled experimental conditions i.e. where the extraocular scatter is eliminated, Lambertian intraocular scatter alone can account for the visual sensitivities reported in these patients. The model also shows that it is possible to obtain a sensitivity in the blind field almost equivalent to that in the good field using the appropriate parameters. Finally, we show with in-vivo spectroreflectometry measurements made in the eyes of our hemidecorticated patients, that the relative drop in middle wavelength sensitivity generally obtained in the blind field of these patients can be explained by selective intraocular spectral absorption.

The tachykinin-1 gene in mammals produces structurally-related regulatory peptides, substance P (SP), neurokinin A (NKA), neuropeptide K (NPK) and neuropeptide-gamma. The production of these peptides is regulated by both differential mRNA transcription and post-translational precursor processing. Such processes are known to be highly tissue- and species-specific. In this study, we have examined tachykinin-1 gene expression and precursor processing in porcine ocular tissues by employing specific tachykinin radioimmunoassays coupled with reverse phase HPLC characterization. Optic nerve, cornea, iris, ciliary body, retina, choroid and sclera were micro-dissected from freshly enucleated porcine eyes (n = 10). Following acidified ethanol extraction of tissues, dried extracts were reconstituted and subjected to two radioimmunoassays, one of which is highly specific for intact SP, the other for NKA, NKB, NPK and neuropeptide-gamma. In all tissue extracts except the retina, the molar concentration of SP immunoreactivity was significantly greater than that of NKA. These data would imply expression of both alpha- and beta-preprotachykinin-1 in these ocular tissues. Reverse phase HPLC analysis confirmed the presence of authentic SP and NKA in all tissue extracts. However, in extracts of the retina, NKA immunoreactivity co-eluted with synthetic NPK standard. These chromatographic data suggest differential processing of the beta-preprotachykinin-1 precursor in the retina compared with the other ocular tissues. Thus differential mRNA transcription of the tachykinin-1 gene coupled with differential precursor processing appears to occur in porcine ocular tissues and may be a process of functional significance in the regulation of visual physiology.

A bi-local detector array model was assumed to describe the functional performance of monocular motion perception. Distributions of model parameters were measured in human vision at several positions in the visual field. The stimulus paradigm was designed to measure directional motion perception thresholds for individual combinations of spatial displacement and temporal delay in random dot apparent motion stimuli. The resulting data support previous results on perceivable spatial displacement limits in human vision but also indicate that both minimum and maximum perceivable spatial displacement thresholds in human observers have a similar dependence on temporal delay. This dependence changes with eccentricity in the visual field in a qualitatively similar manner but by quantitatively different factors. A description of possible biological properties of the bi-local detector population is presented that may explain how detection of spatio-temporal pattern displacements can be performed by a single system. Such a system also predicts that minimum and maximum perceivable spatial displacement thresholds should scale with visual field eccentricity in a manner consistent with our results.

The practicality of recording visual evoked magnetic fields in 100 subjects 15-87 yr of age using a single channel d.c. SQUID second order gradiometer in an unshielded environment was investigated. The pattern reversal response showed a major positive component between 90 and 120 msec (P100M) while the response to flash produced a major positive component between 90 and 140 msec (P2M). Latency norms of the P100M were more variable than the corresponding P100 and P2 visual evoked potentials. The latency of the P100M may show a steep increase with age in most subjects after about 55 yr whereas only a small trend of latency with age was detected for the flash P2M.

We had the rare opportunity to examine a patient with a unilateral complete ophthalmoplegia in an eye with normal visual acuity. We recorded the movements of the covered, sound eye of the patient during full-field optokinetic stimulation of his seeing, immobile eye (open loop condition). The open loop gain for low velocity stimuli (less than 1 deg/sec) was high (greater than 50) but progressively fell with faster stimuli. This finding is inconsistent with the representation of the optokinetic system as a linear velocity servo. In a second experiment, the patient foveally fixated, with the immobile eye, a head-fixed target during sinusoidal, en block rotation. The vestibular movements of the sound eye were suppressed, even though no retinal image motion occurred in the seeing eye. This suggests that visual attention to a stable retinal image can be used to suppress the vestibulo-ocular reflex. Our results were from one patient only and any generalizations must be made cautiously. Nevertheless, our findings are comparable with previous "open loop" studies in normal human beings and patients.

The necessary data were measured for the computation of a schematic eye for a frog (Rana esculenta) in non-paralysed and paralysed conditions (Flaxedil). The consequences for the image forming on the retina with and without correction lenses is discussed (paralysed condition). A possible manner of accommodation is considered. The visual fields of one eye and both eyes were estimated. The situation of underwater vision is also considered in comparison to vision in air.

We employed stereograms having disparity and identical luminance and contrast, or disparate stereograms having binocular differences in luminance (luminance dichopticity) combined with either intermediate or extreme binocular differences in target-background contrast (contrast dichopticity). Stereoscopic depth was reported for the identical and dichoptic half-images with intermediate contrast dichopticity although attenuated depth estimates arose from the latter patterns. Binocular rivalry rather than depth was reported for the disparate patterns that carried luminance and extreme contrast dichopticities. The present results indicate that disparity information is. modified by accentuated dichoptic patterns.

Several entoptic phenomena are described, arising in a range of conditions from free-viewing with closed lids to deep pressure on the eyeballs. The resulting phosphenes provide some clues and some puzzles concerning the organisation of the visual system, from the retina to the cortex.

Thicknesses and curvatures of the optic components of enucleated eyes were determined in both transverse and sagittal planes. The cornea and lens surfaces are closer approximations to spheres than are the retina and choroid. Refractive indices of the cornea, aqueous and vitreous humours were obtained by two techniques at eight wavelengths across the visible spectrum. Photography of light beams passing through the crystalline lens immersed in albumin gave the "back vertex power", and thus (assuming homogeneity) the "equivalent" refractive index. With this assumption, which is supported by additional modelling, calculations for the eyes of six individual rats show chromatic aberration across the spectrum of 5.8 (5.5-6.0) diopter. Longitudinal chromatic aberration may make a significant contribution to image blur.

Binocular (dichoptic) summation was studied for identical wavelengths (monochromatic combinations) and dissimilar wavelengths (bichromatic combinations) presented to each eye. For comparison, monocular summation data were obtained from the same subjects. Dichoptic bichromatic additivity failures were found to be qualitatively similar to, but more pronounced than, corresponding bichromatic monoptic additivity failures. Also, for color normals, dichoptic monochromatic summation was greatest for saturated spectral hues and least for less saturated hues.

Using a binocular search coil technique, we measured oculomotor behavior during gentle pressing with a finger on the outer canthus of one eye. With a steadily pressed viewing eye, and the fellow eye occluded, the occluded eye deviates while the pressed eye does not. If the eye is rapidly pressed and released, the compensation of rotational force in the pressed eye becomes incomplete, so that both eyes move. At high frequencies of press (greater than 1 Hz) the pressed eye is deviated and the contralateral eye no longer moves. In darkness the pressed eye always rotates but the contralateral eye never does, demonstrating that any inflow from proprioceptors sensing rotation of the pressed eye does not affect oculomotor posture as measured in the fellow eye. With binocular viewing the results are more variable. On some trials neither eye moves, while on others both move. The results can be interpreted as a Hering's law controlled attempting to reconcile disparate inputs from the two eyes. The results confirm and extend, with objective measures, earlier conclusions from subjective experiments.

Two macaques and three humans fixated luminous targets in a dark field. All subjects had greater dispersion of eye position from trial-to-trial (between-trial variability) than would be predicted from sampling error and within-trial variability. Monkeys had greater between-trial dispersion on the vertical meridian than humans because of less precise control of saccades. Mean vertical eye position of the monkeys varied idiosyncratically with the fixation task (spot-dim or line-tilt). Between-trial fixation variability of both monkeys and humans was large enough to affect the interpretation of experiments relating visual performance to retinal anatomy or to neurophysiology.

Spectral sensitivity of the dark-adapted frog's eye, eye cup and isolated retina was studied by means of an electroretinogram between 280 and 580 nm. Spectral sensitivity curve of isolated retina shows three peaks corresponding to α-, β- and protein absorption bands of the rhodopsin. Quantum yield of retinal excitation in the protein band, at 280 nm, is 0.45. Ocular media of Rana temporaria are transparent down to 330 nm so that the whole eye shows an appreciable sensitivity in the near ultraviolet. This fact may be of some ecological importance.

Spectral sensitivities were measured by a procedure of flicker threshold. The shape of the spectral sensitivity curve depends systematically on both the frequency and percentage of temporal modulation. The variations in spectral sensitivity are consistent with two different sets of deLange characteristics, one set applicable to short and medium wavelengths, the second applicable to long wavelengths.

In four experiments we have shown that a McCollough color aftereffect (CAE) built up through one eye may or may not be influenced by simultaneous stimulation of the other eye depending on the kinds of similarity and dissimilarity between the two views. Binocular rivalry-produced suppression is not effective per se. However, there is a specifically binocular component that contributes strength to the CAE, and true interocular transfer takes place when facilitated by homochromatic stimulation of the two eyes. The establishment of CAE strength can also be impeded under certain conditions of dichoptic viewing.

The results of retinoscopic refraction measurements in rabbits are compared with the results of two alternative refraction methods. In one of these methods the response to moving gratings is measured in relation to the added lenspower; in the second method retinoscopy is executed with monochromatic lights. From the results of both methods it is concluded that rabbits are emmetropic within the wavelength range 470–530 nm. This emmetropy is of a biological significance in view of the spectral sensitivity of this animal and its lack of accommodative power. The apparent hypermetropy resulting from conventional retinoscopy is due to chromatic aberration.

1. The ERG's of five species of Insects were studied, the stimulus being a white flux modulated in sinusoidal function of time. 2. The amplitudes, phase shifts and Fourier coefficients of distortion were measured and Bode's diagrams were plotted. 3. Carbaryl intoxication resulted in an important decrease of the flicker fusion frequencies, a decrease of the phase shifts at high frequencies, and a decrease of the coefficients of distortion. 4. A model of the electrical response is propounded, consisting in three linked servo-systems. The order of the system depends on the species, and carbaryl intoxication results in a decrease of that order.

The magnitude of the receptor potential of Limulus lateral eye retinular cells elicited by the first light flash administered after dark adaptation (15 min or longer) in an environment 50 mM with respect to NaCl is almost as large as the first response elicited in an environment of 435 mM NaCl. This relative independence of the dark adapted receptor potential on [NaCl] out is called the dark adaptation effect (DAE). It is postulated that the DAE depends upon the extrusion of intracellular sodium during the period of dark adaptation in an environment low with respect to NaCl. thus establishing an approximately normal [Na] gradient. Exposure of the isolated photoreceptor preparations to ouabain (1 to 2 × 10 −5 M) or acetylstrophanthidin (0.5 to 5 × 10 −6 M ) abolished the DAE. The iontophoretic injection of Na + into retinular cells just prior to administration of the first light flash after a period of dark adaptation also suppressed the DAE. Incubation of lateral eye preparations in 50 mM NaCl environments deficient in KCl enhanced the DAE. It is concluded that: (1) the DAE is a sensitive measure of sodium pump activity in Limulus lateral eye retinular cells; (2) that the activity of the sodium pump varies among different photoreceptor preparations; and (3) that low [KCl] out in an environment low in NaCl stimulates active sodium transport.

Following an extensive single subject pilot study 12 Ss viewed a continuously cycling (3 Hz), two stimulus, apparent motion (AM) display. The "AM breakdown effect" was utilised to gather visual evoked potentials (VEPs) from sites O1, O2, T5, T6, P3, and P4 during periods in which the display elicited either: the percept of motion; or the percept of two discrete alternating stimuli. VEPs displayed components of larger amplitude during motion periods in all right (but no left) hemisphere sites during periods 60-82 msec post left field stimulus onset (positive component) and 100-126 msec post right field stimulus onset (negative component). Results were interpreted as indicating initial extraction of motion information within the occipital lobe, with further motion processing taking place in temporal and parietal lobes.

Measurements are made of the optomotor response of tethered, flying flies to stimuli that contain a signal component and a noise component, displayed on a computer-driven CRT. The signal consists of a moving grating; the noise consists of variations of optical intensity that are random in space and time. Threshold signal-to-noise ratio (S/N) for the optomotor response is about 1/8. Discrimination by the fly's visual system rivals and sometimes surpasses that of the human. Results are analyzed in terms of the Reichardt correlation model of movement detection to highlight two mechanisms that could contribute to noise rejection: (a) movement detection via multiplicative processing, (b) spatial summation of responses of small-field movement-detector units by a large-field optomotor neuron. Movement discrimination at low S/N could have adaptive value at low light levels, when quantum noise is appreciable.

The apparent motion of a fixated stimulus during head translation in the dark was found to depend on the magnitude of the vestibulo-ocular reflex (VOR). Absolute convergence level determines VOR magnitude and thereby influences apparent motion during head movement by determining the magnitude and direction of the pursuit effort required to maintain gaze stability. The results are discussed in terms of the biological utility of the coupling between convergence and the VOR in maintaining image stability, and the role of the pursuit eye movement system in illusory movement.

Interocular transfer of a spatial frequency shift was obtained with equiluminous color gratings. Gratings which combined both color and luminance contrast yielded small aftereffects and no interocular transfer. Recent electrophysiological work has uncovered color-sensitive binocularly driven cells in visual cortex. These cells are transient and often respond to color contrast in the absence of luminance contrast. The stimulus parameters associated with successful interocular transfer, equiluminous colors and brief test, matched the properties of these cells. Previous failure to induce interocular transfer of color effects may be explained by inappropriate stimulus parameters.

Ocular alignment on a stimulus with a vertical disparity of up to 20′ has been measured by the subjective nonius-line method and by objective recording of the position of the eyes. Both methods indicate that the vertical disparity is almost entirely eliminated by appropriate vergence eye-movements. The results strongly suggest that the subjective nonius-line method is valid for determination of the vertical alignment of the eyes, just as the results of previous studies suggest it to be valid for the determination of horizontal alignment and torsional alignment.

We develop formulas for calculating the approximate depth of focus of any eye. They show that the magnitude of depth of focus is inversely proportional to the size of the eye and to its visual acuity. One particular implication of these quantitative relations, which is supported by previous data from rats and human infants, is that small eyes with low acuity should have large depths of focus. We show that the observed relation between defocus and contrast sensitivity in rats in predicted by our formulas. We also analyze recent findings in human infants and show that they demonstrate a good correspondence between the improvement in accuracy of the accommodative response with age and the reduction in depth of focus (predicted from our formulas) as acuity and eye size increase over the same age range. Optical factors such as astigmatism, refractive error and chromatic and spherical aberration should have no effect on visual resolution unless they exceed the depth of focus of an eye. Thus, our arguments imply that these factors may be relatively unimportant in small eyes with low acuity.

The retardation of the optical system of the living human eye has been measured psychophysically as a function of the place of entry of the incident light in the pupil plane with the help of interference patterns projected on the retina. The retardation of the ocular media was found to increase more along the horizontal and vertical meridians than along the diagonal meridians. If the contribution of lens and vitreous to the measured retardation are neglected a corneal birefringence can be computed. The average value of this birefringence for two observers was found to be 0.0020. Finally we calculated the polarization of the light at the retina for a linearly polarized beam, entering the eye through a 6 mm pupil, making use of the measured retardation.