Traditionally, it has been thought that the processing of binocular disparity for the perception of stereoscopic depth is accomplished via three types of disparity-selective channels – “near,” “far,” and “tuned.” More recent evidence challenges this notion. We have derived disparity-tuning functions psychophysically using a subthreshold summation (i.e. low-level masking) technique. We measured correlation-detection thresholds for dynamic random-element stereograms containing either one or two surfaces in depth. The resulting disparity-tuning functions show an opponent-type profile, indicating the presence of inhibition between disparity-tuned units in the visual system. Moreover, there is clear inhibition between disparities of the same sign, obviating a strict adherence to near-far opponency. These results compare favorably with tuning functions derived psychophysically using an adaptation technique, and with the tuning profiles from published single-unit recordings. Our results suggests a continuum of overlapping disparity-tuned channels, which is consistent with recent physiological evidence as well as models based on other psychophysical data.

Isolated photoreceptors are desirable for whole-cell and patch-clamp studies of functional properties of visual processes that cannot be clearly analyzed when the photoreceptors are coupled. The retina of the compound lateral eye of the horseshoe crab, Limulus polyphemus, was dissociated into individual retinular cells using an enzyme pretreatment consisting of collagenase, papain, and trypsin, and a two-stage mechanical dissociation. These photoreceptors are functionally viable in an organ culture medium for up to 1 week and possess naked arhabdomeral and rhabdomeral segment membranes which are easily accessible for whole-cell recordings. A dissection technique was also developed whereby the retinal epidermis and neural plexus, as well as the second-order eccentric cells, could be separated from the ommatidia of the compound lateral eye in one simple step, providing viable isolated ommatidia attached to the cornea. The enzyme pretreatment used for dissociating the retina was then used to remove the individual ommatidia from the corneal cones.

Hoffman modulation contrast microscopy was used to develop a reliable method for sorting and collecting viable isolated retinular cells for morphological and electrophysiological studies. Morphological analysis using light microscopy and scanning and transmission electron microscopy revealed that isolated retinular cells are morphologically nearly identical to retinular cells in situ. Isolated retinular cells possess a normal rhabdomere with no apparent loss of microvillar membrane as a result of the isolation process. Ommatidia can presently be isolated with up to six retinular cells possessing essentially normal structure and ultrastructure including thick rays of rhabdom. Isolated ommatidia possess naked A-segment membranes which are also well suited for whole-cell recording techniques.

A combination of enzymatic digestions and mechanical disruption was used to isolate photoreceptor cells from the compound lateral eye of the horseshoe crab, Limulus polyphemus. The cells were maintained in a culture medium and tested for function using whole-cell and cell-attached patch configurations of the gigaseal technique. The cells dissociated from the eye generated spontaneous voltage and current bumps in the dark, and depolarized in a graded fashion to increasing intensities of light over several decades, producing responses similar to those of cells in vivo. Currents evoked during voltage clamp were similar to those in ventral photoreceptor cells of Limulus, although transient currents in the dark- and light-activated currents were smaller in isolated lateral eye cells, perhaps because of the slow speed and spatial nonuniformity of the clamp in these large cells. In addition to isolated cells, dissociation of the compound eye produced small clusters of cells and isolated ommatidia which were also tested for function. Comparison of the electrical characteristics of isolated cells with those of cells in small clusters and in their ommatidial matrix suggests that the electrical junctions normally connecting photoreceptor cells within an ommatidium are functional in the latter groups, but not in isolated cells. Cell-attached patches of rhabdomeral membrane of isolated cells contained light-activated channels, resembling those observed in ventral photoreceptor cells, but no voltage-activated channels. Similar patches of arhabdomeral membrane contained voltage-activated channels, but no light-activated channels. We conclude that this preparation is suitable for studies of processes involved in generating the light response in invertebrate photoreceptor cells.

Melatonin biosynthesis in chick retina occurs as a circadian rhythm. Biosynthesis of the neurohormone is highest at night in darkness, and is suppressed by light. The role of gamma-aminobutyric acid (GABA) in the nocturnal regulation of melatonin synthesis was examined. Systemic or intravitreal administration of muscimol, a GABA-A receptor agonist, to light-exposed chicks at the beginning of the dark phase of the light/dark cycle increased retinal melatonin levels and the activity of serotonin N-acetyltransferase (NAT), a key regulatory enzyme of the melatonin biosynthetic pathway. Baclofen, a GABA-B receptor agonist, also increased NAT activity of light-exposed retinas, but muscimol was approximately 40-fold more potent than baclofen. Effects of both muscimol and baclofen on NAT activity were inhibited by GABA-A antagonists, bicuculline and picrotoxin, and the effect of baclofen was unaffected by the GABA-B selective antagonist, CGP 35348. Thus, activation of GABA-A receptors appears to be associated with increased melatonin biosynthesis. The GABA-uptake inhibitor, nipecotic acid, and the GABA-transaminase inhibitor, aminooxyacetic acid, also increased NAT activity of light-exposed retinas. The high levels of NAT activity associated with exposure to darkness were unaffected by either muscimol or baclofen, but picrotoxin and bicuculline significantly inhibited retinal NAT activity in darkness.

The rate of dopamine synthesis, estimated from in situ tyrosine hydroxylase activity, was higher in light-exposed retinas than in darkness. Muscimol inhibited dopamine synthesis in light, and picrotoxin stimulated dopamine synthesis in darkness. The stimulation of melatonin synthesis by muscimol in light-exposed retinas appears to be related to inhibition of retinal dopamine neurons. The increase of NAT activity elicited by muscimol in light-exposed retinas was inhibited by administration of the dopamine receptor agonists apomorphine and quinpirole. Blocking dopamine receptors with spiperone or inhibiting dopamine biosynthesis with α-methyl-ρ tyrosine also increased NAT activity in light, and the effects of the dopamine antagonists and muscimol were not additive. The decrease of NAT activity elicited by GABA antagonists in darkness was inhibited by spiperone. Thus, GABA may indirectly regulate retinal melatonin biosynthesis, by inhibiting dopaminergic activity in retina.

We recorded the responses of neurons from the cat’s lateral geniculate nucleus to drifting sine-wave grating stimuli both before and during electrical stimulation of the parabrachial region of the midbrain. The parabrachial region provides a mostly cholinergic input to the lateral geniculate nucleus, and our goal was to study its effect on responses of geniculate cells to visual stimulation. Geniculate neurons respond to visual stimuli in one of two modes. At relatively hyperpolarized membrane potentials, low threshold (LT) Ca2+ spikes are activated, leading to high-frequency burst discharges (burst mode). At more depolarized levels, the low threshold Ca2+ spike is inactivated, permitting a more tonic response (relay or tonic mode). During our intracellular recordings of geniculate cells, we found that, at initially hyperpolarized membrane potentials, LT spiking in response to visual stimulation was pronounced, but that parabrachial activation abolished this LT spiking and associated burst discharges. Coupled with the elimination of LT spiking, parabrachial activation also led to a progressive increase in tonic responsiveness. Parabrachial activation thus effectively switched the responses to visual stimulation of geniculate neurons from the burst to relay mode. Accompanying this switch was a gradual depolarization of resting membrane potential by about 5–10 mV and a reduction in the hyperpolarization that normally occurs in response to the inhibitory phase of the visual stimulus. Presumably, the membrane depolarization was sufficient to inactivate the LT spikes. We were able to extend and confirm our intracellular observations on the effects of parabrachial activation to a sample of cells recorded extracellularly. This was made possible by adopting empirically determined criteria to distinguish LT bursts from tonic responses solely on the basis of the temporal pattern of action potentials. During parabrachial activation, every cell responded only in the relay mode, an effect that corresponds to our intracellular observations. We quantified the effects of parabrachial activation on various response measures. The fundamental Fourier response amplitude (Fl) was calculated separately for the total response, the tonic response component, and the LT burst component. Parabrachial activation resulted in an increased Fl amplitude for the total response. This increase was due to an increase in the tonic response component. For a subset of cells showing epochs of LT bursting, parabrachial activation concurrently reduced LT bursting and increased the amplitude of the tonic response. Parabrachial activation, by eliminating LT bursting, also caused cells to respond with more linearity. By keeping geniculate cells in the relay mode, the parabrachial region serves to maintain a more linear retinogeniculate transfer of information to cortex, and this may be important for detailed analysis of visual targets. However, when a geniculate neuron becomes hyperpolarized, as may occur during states of visual inattention, it would not respond well to visual stimuli without the sort of nonlinear amplification provided by the LT spike. Thus, the LT spike may permit hyperpolarized cells to relay to cortex the presence of a potentially salient or dangerous stimulus, but this is done at the expense of linearity. This may serve as a sort of “wake-up call” that redirects attention to a particular stimulus and eventually enhances activity of appropriate parabrachial inputs to switch the critical geniculate neurons into the relay mode.

Walking crabs move their eyes to compensate for retinal image motion only during rotation and not during translation, even when both components are superimposed. We tested in the rock crab, Pachygrapsus marmoratus, whether this ability to decompose optic flow may arise from topographical interactions of local movement detectors. We recorded the optokinetic eye movements of the rock crab in a sinusoidally oscillating drum which carried two 10-deg wide black vertical stripes. Their azimuthal separation varied from 20 to 180 deg, and each two-stripe configuration was presented at different azimuthal positions around the crab. In general, the responses are the stronger the more widely the stripes are separated. Furthermore, the response amplitude depends also strongly on the azimuthal positions of the stripes. We propose a model with excitatory interactions between pairs of movement detectors that quantitatively accounts for the enhanced optokinetic responses to widely separated textured patches in the visual field that move in phase. The interactions take place both within one eye and, predominantly, between both eyes. We conclude that these interactions aid in the detection of rotation.

We investigated the attributes of transduction and light-adaptation in rods, single cones, and twin cones isolated from the retina of striped bass (Morone saxatilis). Outer-segment membrane currents were measured with suction electrodes under voltage clamp provided by tight-seal electrodes applied to the cell’s inner segment. Brief flashes of light transiently reduced the outer-segment current with kinetics and sensitivity characteristic of each receptor type. In all cells, the responses to dim lights increased linearly with light intensity. The amplitude-intensity relation for rods and single cones were well described by an exponential saturation function, while for twin cones it was best described by a Michaelis-Menten function. At the wavelength of maximum absorbance, the average intensity necessary to half-saturate the peak photocurrent in dark-adapted rods was 28 photons/μm2 and in single cones it was 238 photons/μm2. Among twin cones, the common type (88% of all twins recorded) half-saturated at an average of 1454 photons/μm2, while the fast type reached half-saturation at an average of 9402 photons/μm2. The action spectrum of the photocurrent in the three receptor types was well fit by a nomogram that describes the absorption spectrum of a vitamin A2-based photopigment. The wavelength of maximum absorbance for rods was 528 nm, for single cones it was 542 nm and for twin cones it was 605 nm. Both members of the twin pair contained the same photopigment and they were electrically coupled. Under voltage clamp, the response to dim flashes of light in both single and twin cones was biphasic. The initial peak was followed by a smaller amplitude undershoot. Single cones reached peak in 86 ms and common twins in 50 ms. Background light desensitized the flash sensitivity in all photoreceptor types, but was most effective in rods and least effective in fast twins. In the steady state, the desensitizing effect of a background intensity, Ib, at the respective optimum wavelength for each cell was well described by the Weber-Fechner law (1/(1 + Ib/Ibo)), where Ibo was, on average (in units of photons/μm2/s), 1.45 for rods, 1.81 x 103 for single cones, 4.56 x 103 for common twins, and 6.79 x 104 for fast twins.

Tethered adult female praying mantises, Sphodromantis lineola (Burr.), were presented with various computer-generated visual stimuli that moved against patterned or homogeneous white backgrounds in predetermined patterns and at predetermined speeds. The degrees to which the stimulus configurations elicited appetitive behaviors (attempting to approach and/or striking) indicated the relative degrees to which the stimuli were classified as prey. Mantises readily struck at cartoon “crickets” that subtended visual angles as great as 24.5 deg x 62.5 deg, but response rate was suppressed if the stimuli were superimposed on horizontally moving patterned backgrounds. Mantises also displayed appetitive behaviors to moving black squares (edge lengths = 10–47 deg) that moved in predetermined “erratic” paths; however, their response rates were affected by several factors: (1) response rate declined as edge length increased over 10 deg; (2) striking was emitted to stimuli viewed from 23 mm (but not farther) away; and (3) both stimulus displacement rate (distance moved between video frames) and apparent speed (video frame rate) dramatically affected the releasing strength of the stimuli. Finally, mantises responded appetitively to random dot patterns moving synchronously against identically patterned backgrounds and to pairs of black squares moving synchronously against a white background. However, in the latter case, response rate declined as the squares were moved farther apart horizontally or vertically. These and previous results from our laboratory on mantises are congruent with behavioral results obtained from other insects such as flies (Diptera) and dragon flies (Odonata) and suggest that there are neuroanatomical similarities between these groups.

During optic nerve regeneration in the frog, axons transiently grow along the opposite optic nerve forming a retino-retinal projection. In the present study, we crushed the left optic nerve in the frog Litoria (Hyla) moorei and later applied horseradish peroxidase (HRP) or diamidino yellow (DY) to the right optic nerve. In one series, retinae were examined 3 days after application of the tracer. The retino-retinal projection was found to be maximal at 5 weeks, fell significantly by 7 weeks, and returned to close-to-normal levels by 24 weeks. In a second series, we applied DY at 5 weeks as before but did not sacrifice the frogs until 7 weeks. Numbers of labeled ganglion cells were not significantly different from those frogs in the first series labeled and examined at 5 weeks. We conclude that ganglion cells giving rise to the retino-retinal projection had not died in appreciable numbers, presumably being sustained by collateral axons in the brain.

We have developed an optical method to monitor the activity of the ON and OFF channels in the anuran retina. The change in the fraction of near infrared that is transmitted transversely through the retina in an eyecup slice is monitored during stimulation by visible, green light. Near-infrared transmission increases both at the onset and at the termination of a step stimulus. This “ON/OFF” response is maximal in the neural retina. Sodium L-aspartate, which blocks the light-evoked activity of post-photoreceptor neurons, abolishes the “ON/OFF” response. L-AP4, used as a selective blocker of the ON channel, reduces the “ON” component and has little or no effect on the “OFF” component. The “ON” and “OFF” processes observed optically are distinct from those that generate the b– and d–waves of the electroretinogram, and the “ON” and “OFF” components may be superior to the b– and d–waves as indicators of ON and OFF channel activity. The optical method is almost as simple as electroretinography and has the advantage that responses can be spatially localized with ease.

Neurons likely to utilize glycine (GLY) as a neurotransmitter were identified immunocytochemically in the “all-cone” lizard retina and the basic anatomical organization of the retinal GLY and gamma-aminobutyric acid (GABA) systems was compared. Four types of GLY-immunoreactive (GLY-IR) neurons were identified. Most GLY-IR cells were amacrine cells, which comprised at least two types. GLY-IR interplexiform cells and ganglion cells also were identified. The first GLY-IR amacrine cell type was characterized by a small pyriform soma, located distal to the border of the inner plexiform layer (IPL), and fine dendrites. Most GLY-IR amacrine cells were of this type and several subtypes may exist within this group. The second amacrine cell type was characterized by a large, distally located soma and a large descending process. This amacrine cell type showed colocalization of GLY-IR and GABA-IR and comprised about 4% of the total GLY-IR amacrine cell population.

Comparison of GLY-IR and GABA-IR on serial sections showed that GLY and GABA were present in largely separate neuronal populations. Generally, GLY-IR amacrine cells were smaller, more distally located in the inner nuclear layer and had finer dendrites than GABA-IR amacrine cells. Distribution of GLY-IR and GABA-IR in the outer plexiform layer and the inner plexiform layer differed considerably.

Based on the segregated distribution of GLY-IR and GABA-IR in the synaptic layers of the lizard retina, GLY and GABA may have fundamentally different roles in retinal processing.

Previous research suggests that plaid-induced motion aftereffects (MAEs) involve extrastriate mechanisms (Wenderoth et al., 1988). There is evidence also that binocular rivalry occurs beyond VI and that it disrupts the processing of MAEs which are believed to be based upon extrastriate mechanisms (e.g. the spiral MAE) but not MAEs, such as linear MAE induced by a drifting grating, which are thought to arise in striate cortex (Wiesenfelder & Blake, 1990). The logical inference is that binocular rivalry during drifting plaid-induced adaptation should reduce the MAEs which result. We report experiments which confirm this prediction.

We present microspectrophotometric evidence for the existence of two distinct visual pigments residing in two different morphological types of photoreceptor of the sea lamprey. In the upstream migrant Petromyzon marinus, the pigment found in short receptors has a wavelength of peak absorbance (λmax) of 525 nm, whereas the pigment located in long receptors has a λmax of 600 nm. Although the former appears to be pure porphyropsin, the latter is akin to visual pigments found in the red-absorbing cones of amphibian and teleost retinae. The kinship is more than superficial pertaining to λmax of the a–band absorbance to its native maximum value. The presence of an anion-sensitive and an anion-insensitive pigment in a retina implies the expression of two distinct opsin genes. We infer this from several examples of correlation between anion sensitivity and opsin sequence groupings. Moreover, the presence of two distinct opsin genes expressed throughout six vertebrate classes implies their existence in a common ancestor to all.

The effects of V4, MT, and combined V4+MT lesions were assessed on a broad range of visual capacities that included measures of contrast sensitivity, wavelength and brightness discrimination, form vision, pattern vision, motion and flicker perception, stereopsis, and the selection of stimuli that were less prominent than those with which they appeared in stimulus arrays. The major deficit observed was a loss in the ability, after V4 lesions, to select such less prominent stimuli; this was the case irrespective of the manner in which the stimulus arrays were made visible, using either luminance, chrominance, motion, or stereoscopic depth as surface media. In addition, V4 lesions yielded mild deficits in color, brightness, and form vision whereas MT lesions yielded mild to moderate deficits in motion and flicker perception. Both lesions produced mild deficits in contrast sensitivity, shape-from-motion perception, and yielded increased reaction times on many of the tasks. The impairment resulting from combined V4 and MT lesions was not greater than the sum of the deficits of either lesion. None of the lesions produced significant deficits in stereopsis. The findings suggest that (1) area V4 is part of a neural system that is involved in extracting stimuli from the visual scene that elicit less neural activity early in the visual system than do other stimuli with which they appear and (2) several other extrastriate regions and more than just two major cortical processing streams contribute to the processing of basic visual functions in the extrastriate cortex.

Ablation of visual cortical areas 17 and 18 in neonatal and young adult cats induces novel retinal projections to terminate bilaterally in the lateral posterior nucleus (LP) at a position ventromedial from the medial interlaminar nucleus. Comparison with the visual-field maps of LP indicate that the terminations are focussed on the representation of the visual-field center.

The primary goal of this study was to expand the description of the filtering properties of the Y-cell receptive field, byquantitatively characterizing the spatial filtering properties of the receptive field’s center-and-surround components as a function of adapting light level. A range of more than five orders of magnitude in retinal illuminance were covered, including the vast majority of the cat’s functional range of vision.

Recordings were taken from optic tract fibers of Y cells in cats under general anesthesia. Sinusoidal gratings and a stimulus designed to selectively probe the properties of the surround mechanism were used. The cells’ responses to these stimuli were fit to a Gaussian center-surround receptive-field model, in which six parameters define the properties of the center and surround. Fits were made independently to data collected at each light level and changes in the values of the model’s parameters with illuminance are reported. A set of equations that summarize the changes in parameter values is given. From these summary equations, reasonable estimates of the parameters’ values can be determined across a wide range of illuminances. Hence, a quantitative model of the spatial properties of the center and surround of the Y-cell receptive field can now be derived from these equations for most of the levels of retinal illuminance experienced by a Y cell. The consistency between the description provided by our equations and results from earlier work is considered.

We have used frequency-domain methods to characterize the spatial receptive-field structure of cat retinal W cells. For most ON- and OFF-center tonic and phasic W cells, measurements of responsivity to drifting gratings at various spatial frequencies could be adequately described by a difference-of-Gaussians (DOG) function, consistent with the presence of center and surround mechanisms that are approximately Gaussian in shape and whose signals are combined additively. Estimates of the responsivity of the center mechanisms of tonic and phasic W cells were similar, but both were significantly lower than the corresponding values for X or Y cells. The width of the center mechanisms of tonic W cells, phasic W cells, and Y cells did not differ significantly from each other, but all were significantly larger than the width of X-cell centers. Surround parameters did not vary significantly among the four groups of ganglion cells. Measurements of contrast gain in both tonic and phasic W cells gave values that were significantly lower than in X or Y cells.

Virtually all of the phasic W cells in our sample displayed evidence of spatial non-linearities in their receptive fields, in the form of either d.c. responses to drifting sine-wave gratings or second harmonic responses to counterphased gratings. The spatial resolution of the mechanism underlying these nonlinearities was typically higher than that of the center mechanism of these cells. Most tonic W cells exhibited linear spatial summation, although a subset gave strong second harmonic responses to counterphased gratings.

Spatial-responsivity measurements for most ON-OFF and directionally selective W cells were not adequately described by DOG functions. These cells did, however, show evidence of spatial nonlinearities similar to those seen in phasic W cells. Suppressed-by-contrast cells gave both modulated and unmodulated responses to drifting gratings which both appeared to involved rectification, but which differed from each other in both spatial resolution and contrast gain.

These data confirm earlier reports that the receptive fields of tonic and most ON- or OFF-center phasic W cells appear to include classical center and surround mechanisms. However, the receptive fields of some phasic cells, as well as ON-OFF and directionally selective W cells may have quite different structures. Our results also suggest that phasic, ON-OFF, directionally selective, suppressed-by-contrast, and a subset of tonic W cells may all receive nonlinear inputs with characteristics similar to those described in the receptive fields of retinal Y cells. If so, this has important implications for identifying and understanding the presynaptic circuitry of W cells, as well as the nature of their output to both telencephalic and midbrain visual targets.