A model of contrast discrimination performance in human observers is developed and then extended to cover effects on performance of anticholinergic drugs. It is shown that it is necessary to assume that neural noise increases at high spatial frequencies in order to provide a satisfactory model of variations in discrimination performance with spatial frequency. The model results are compared with the results of empirical studies in which the effects of the muscarinic antagonist scopolamine (hyoscine) on contrast discrimination performance in human observers are examined. The purpose of the pharmacological work is to test the hypothesis that the differential contrast gain found psychophysically at different spatial frequencies might reflect differential facilitation by extrinsic cholinergic neurons. Contrast discrimination and contrast increment detection are found to be impaired by scopolamine in a manner that depends on both spatial frequency and base contrast. By comparing the empirical data with the predictions of the model, it is concluded that contrast constancy may reflect differential cholinergic modulation.

Using a reduced-silver neurofibrillar method, we stained a population of bipolar cells in the capybara retina. These cells are distributed throughout the retina following the same topography of other retinal cell classes as the A-type horizontal cells and ganglion cells. The level of axonal stratification, mosaic regularity, and dendritic coverage factor suggest that these neurofibrillar bipolar cells comprise a population of sublamina a cone bipolar cells.

The reports of rod-dominated psychophysical spectral sensitivity from the deprived eye of monocularly lid-sutured (MD) monkeys are intriguing but difficult to reconcile with the absence of any reported deprivation effects in retina. As most studies of MD retina have been from cat, we have examined psychophysically the increment threshold spectral sensitivity of MD cats using both reaction time and simultaneous two-choice behavioral procedures. Although the deprived eyes exhibited an absolute increment threshold sensitivity deficit, both rod and cone spectral sensitivity functions were obtained on large white backgrounds. This normal transition from rod to cone vision, as background luminance increased, was also found in threshold vs. intensity functions. Using their deprived eye, some cats exhibited a rod spectral sensitivity function when a smaller, normally photopic, background was used providing some support for a hypothesis that the rod-dominated spectral sensitivity observed in monkey may represent detection of scattered stimulus light. Alternatively monocular deprivation may reveal a rod-dominated mechanism which exists in monkey but not in cat.

Temporally varying chromatic-inducing light was used to infer receptive-field organization. Time-varying shifts in color appearance within a test field were induced by a surrounding chromatic pattern; the shifts were then nulled by adding a time-varying stimulus to the test area so the observer perceived a steady test. This method measured chromatic induction without requiring an observer to judge the color appearance of the test. The induced color shifts were consistent with a +s/−s spatially antagonistic neural receptive field, which also accounts for color shifts induced by static chromatic patterns (Monnier & Shevell, 2003, Monnier & Shevell, 2004). The response of this type of receptive-field, which is found only in the visual cortex, increases with S-cone stimulation at its center and decreases with S-cone stimulation within its surround. The measurements also showed a negligible influence of temporal inducing frequency in the range 0.5–4 Hz.

Due to technical difficulties that have since been rectified, the photomicrographs in this article did not reproduce at the best resolution possible. Also, Figure 12 has been revised and a corrected version of the article is reproduced on pp. 1R–9R, which follows. Cambridge University Press regrets any inconvenience that this inadvertent error may have caused.

(Article appeared in Visual Neuroscience (2002), 19, 257–264.)

Due to a production error, we are reprinting the following article because the color images were printed in black and white. The color images are so very important to the understanding of this article, we are reprinting it here with the color images in place.

Inhibitory effects have been reported when a target is preceded by a cue of the same color and location. Color-based inhibition was found using red and blue nonisoluminant stimuli (Law et al., 1995). Here we investigate whether this phenomenon depends on the chromatic subsystem involved by employing isoluminant colors varying along either the violet-yellow or purple-turquoise cardinal axis. Experiment 1 replicated Law et al.'s study: After fixating magenta, either a red or blue cue was presented, followed by a magenta “neutral attractor,” and, finally, by a red or blue target. In Experiment 2, violet and yellow, cue or target, varied along a tritan confusion line in the CIE 1976 chromaticity diagram. In Experiment 3, purple and turquoise, cue or target, varied along a deutan confusion line in the CIE 1976 chromaticity diagram. Normal trichromats (n = 19) participated in all three experiments. In Experiment 1, color repetition indeed resulted in longer reaction times (RTs) (4.7 ms, P = 0.038). In Experiment 2, however, no significant color repetition effect was found; RTs to violet and yellow were not significantly different, though tending toward slower responses (2 ms) for violet repetition but faster (5 ms) for yellow. Experiment 3 also showed no color repetition effect (P = 0.58); notably, RTs were overall faster for purple than for turquoise (22 ms, P < 0.0001). Furthermore, responses tended to be slower for purple repetition (4 ms, P > 0.05), but faster for turquoise (7 ms, P > 0.05). These findings demonstrate that color repetition is not always inhibitory but may turn facilitatory depending on the colors employed. The results indicate that disengagement of attention is an unlikely mechanism to be the sole explanation of previously reported color-based inhibition of return. We suggest a complementary, perceptual explanation: response (dis)advantage depends on whether the stimuli are isoluminant and on the opponent chromatic subsystem involved. The choice of the colors employed and the cue-attractor-target constellation also may be of significance.

Paradoxical shifts in human color (spectral) sensitivity occur on deep-red (658 nm) background fields. As the radiance of the deep-red background is increased from low to moderate levels, the spectral sensitivity for detecting 15-Hz flicker shifts toward shorter wavelengths, although by more than is predicted by selective chromatic adaptation (e.g., Eisner & MacLeod, 1981; Stromeyer et al., 1987; Stockman et al., 1993). Remarkably, though, at higher background radiances, the spectral sensitivity then shifts precipitously back towards longer wavelengths. Here, we show that both effects are due in large part to destructive and constructive interference between signals generated by the same cone type. Contrary to the conventional model of the human visual system, the M- and L-cone types contribute not just the customary fast signals to the achromatic or luminance pathway, but also slower signals of the same or opposite sign. The predominant signs of the slow M- and L-cone signals change with background radiance, but always remain spectrally opposed (M-L or L-M). Consequently, when the slow and fast signals from one cone type destructively interfere, as they do near 15 Hz, those from the other cone type constructively interfere, causing the paradoxical shifts in spectral sensitivity. The shift in spectral sensitivity towards longer wavelengths is accentuated at higher temporal frequencies by a suppression of fast M-cone signals by deep-red fields.

Knowing neuronal types is essential for understanding the structural and functional organization of the nervous system. It has long been recognized that neuronal types should be discovered and not defined. This can be done using cluster analysis (CA). Despite there being many studies using CA to classify neurons, only a few of them meet its formal prerequisites. In the present study, we provide an example of using CA in combination with other multivariate techniques for examining neuronal diversity. A special emphasis is put on formal prerequisites to the data and procedure. The data under scrutiny are a sample of ganglion cells projecting to the basal optic nucleus [accessory optic system-projecting ganglion cells (AOS GCs)] in the common frog. There is physiological evidence that these cells comprise at least two functional types but their structural heterogeneity has not been addressed. Cells were labeled with horseradish peroxidase in vivo and examined in whole-mounted retinae using light microscopy. A sample of well-stained cells was obtained and used to estimate 18 structural parameters. A variety of clustering algorithms were used to classify the cells. The joint polar distribution of dendrite mass was monomodal. CA did not reveal a statistically reliable cluster structure in the sample. The clusters were not cohesive and well isolated. ANOVA-on-Ranks revealed no significant between-cluster differences. Our formal conclusion is that functionally distinct frog AOS GCs do not differ in morphology or dendritic arbor orientation. The advantages and limitations of the adopted approach are discussed.

Light responses of R/G chromaticity-type horizontal cells (R/G HCs) and luminosity-type horizontal cells (LHCs) were intracellularly recorded in isolated superfused carp retina, and the response dynamics analyzed. The results revealed that (1) No significant difference in delay was detected between R/G HC red and green responses; (2) The rising speed was quicker for R/G HC depolarizing red responses compared to that of its hyperpolarizing green responses; and (3) Dynamic characteristics of R/G HC red responses and its changes caused by green background illumination did not follow that of LHC red response. All these results suggest that the depolarizing response of the R/G HCs cannot be entirely mediated by the negative feedback pathway from LHCs onto cones. A direct inhibitory input from red cones to R/G HCs may exist.

Although single-channel and whole-cell patch-clamp recordings have demonstrated the presence of Na+ currents in retinal ganglion cell somata, it has not previously been reported that an anti-Na+-channel antiserum stains both retinal ganglion cell somata and proteins with molecular weights corresponding to complexes of α and β subunits. We probed adult goldfish retinas for Na+ channel-like immunoreactivity with a polyclonal antibody directed against the EOIII segment of vertebrate voltage-gated Na+ channels. In vertical sections and whole mounts, this antibody consistently stained the somata, axons, and proximal dendrites of retinal ganglion cells. Some somata in the proximal third of the inner nuclear layer were also stained. In Western blots, this antibody specifically stained multiple protein bands from retina and optic nerve, all with apparent molecular weights between 200 and 315 kDa. The largest of these molecular weights agrees with that reported previously for complexes of α and β subunits in mammalian neurons, including retinal ganglion cells. The intermediate and lowest molecular weights are consistent with the presence of multiple Na+ channel α subunits, either in individual proximal retinal neurons or in different morphological subtypes.

The rhabdomeral microvilli in the eyes of invertebrates have a cytoskeletal core (Saibil, 1982; Blest et al., 1982a, b, 1983) of actin (de Couet et al., 1984; Arikawa et al., 1990; Williams, 1991; Caiman & Chamberlain, 1992) which might be involved in phototransduction. Tsukita et al. (1988) suggested that light stimulation triggers the breakdown of the microvillar actin filament complex and that this may play a role in phototransduction. To test their suggestion, we pressure-injected phalloidin into Limulus ventral photoreceptors to prevent actin depolymerization (Cooper, J.A., 1987) and tested to see if this blocked phototransduction. We have previously shown that injected rho-damine-phalloidin brightly labels the microvillar actin filaments in living Limulus ventral photoreceptors for several hours (Feng et al., 1994). In the experiments reported here, phalloidin unconjugated with fluorophore was used, and the final concentration in the cell after many small injections from a pipette containing 10 mg/ml phalloidin was estimated to be 1 mg/ml (1.2 mM). This concentration is 100 times higher than that used in an extracted cellular preparation to stabilize actin (Biegel & Pachter, 1992). Fig. 1 shows that the responses to steps of light at different intensities are normal 1 h after phalloidin injection. Similar results were obtained in two other cells.

In the past two years the field of fish vision research has lost three central figures, Bill McFarland, Bill Muntz, and Joe Bilotta. This volume of Visual Neuroscience is dedicated to them. Since the inception of this volume, Henk Spekreijse and Adam Locket, who made significant contributions to fish vision, have also passed away; they are also remembered.

Selective labeling of intravitreal Procion yellow dye by presumed blue-sensitive cone photoreceptors has been demonstrated in primate retina. To determine whether Procion yellow is selective for this cone type in an unrelated vertebrate species, labeling by this dye was studied in goldfish retina, where cone pigment type can be directly inferred from photoreceptor morphology. At low vitreal concentrations of the dye (<0.4%), only cone outer segments were labeled. At vitreal concentrations of 0.4–0.5%, the inner segments of short-double cones and a subset of long single cones (presumed green-sensitive cones) were selectively stained. At still higher vitreal concentrations (0.6–0.7%), the inner segments of short-single cones and miniature short-single cones (presumed blue-sensitive cones) showed evidence of Procion label, but were not as heavily labeled. The inner segments of long-double cones and a subset of long-single cones (presumed red-sensitive cones) did not label at any of these concentrations. These results show that Procion yellow is not a selective marker for blue-sensitive cones in the goldfish retina. In addition, stained rod and cone nuclei were observed at each dye concentration, including those concentrations at which no inner segments were labeled.

This study was performed in order to establish whether selective depletion of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the pigeon optic tectum (TeO) induced by p-chloroamphetamine (p-CA) modified tectal evoked potentials (TEPs). TEPs in response to sinusoidal gratings of different contrast, spatial and temporal frequency were recorded in control pigeons and in pigeons intraperitoneally injected with p-CA (10 mg/kg; two administrations in consecutive days). TEPs of p-CA treated pigeons, as compared to those of control pigeons, were reduced in amplitude as a function of contrast, spatial and temporal frequency. In addition, TEPs of p-CA treated pigeons differed from those recorded in controls in their transfer characteristics of contrast and spatial frequency. In particular, TEPs of p-CA treated pigeons did not saturate at moderate contrast, unlike those of controls. Furthermore, the TEP spatial tuning in p-CA treated pigeons is broader than that in controls; it thus suggests a reduction of spatial-frequency selectivity. These findings indicate that a selective neurotoxin for serotonergic systems, such as p-CA, can serve as a useful denervation tool for the study of the serotonergic function in the pigeon TeO. In addition, selective changes of TEP properties suggest the possibility that serotonergic afferents play a modulatory role on the receptive-field characteristics of tectal neurons.

The aim of this study was to use non-invasive magneto-encephalographic techniques, together with visual stimulus paradigms that can psychophysically separate the M- and P-pathways, to examine the physiological relations of the pathways at the fovea with (1) the magneto-encephalography components M70 and M100 (in latency and amplitude), and (2) the cortical oscillatory activities (alpha, beta, and gamma), respectively. The checkerboard stimuli accompanied with different spatial frequencies (SFs) (0.5 or 4 cycles per degree) were presented (within 2° of the retinal center) to six healthy subjects by using steady-pedestal and pulse paradigms, which could activate distinct populations of M- and P-neurons. SF analyzed brain responses in each paradigm. The results show a consistent trend in M70 and M100 with increased latencies and amplitudes in response to the high SF. Mean while, the beta to gamma activities are apparently enhanced by the stimulus of high SF, especially under pulse paradigm (p = 0.03). In this study, we suggest that M70 can be a good clue to characterize the P-pathway. Moreover, in the frequency analysis, the beta oscillations may serve for more detailed visual information, while the gamma oscillations seem to reflect the signal processing in the P-pathway and with sensitivity to the fovea.

(article appeared in Visual Neuroscience (2004), 21, 945–952)

As a result of a production error, the footnote to this article was incorrect. It should have stated that “the authors are in alphabetical order” instead of stating that “all authors contributed equally to this paper.” Because of the nature of this error, the online version has been corrected.

Contextual influences shape our perception of local visual stimuli. Relative-motion stimuli represent an important contextual influence, yet the mechanism subserving relative-motion computation remains largely unknown. In the present work, we investigated the responses of an established model for simple and complex cells to relative-motion stimuli. A straightforward mathematical analysis showed that relative-motion computation is inherent in the nonlinear transformation of the complex-cell model. Tuning to relative velocity is achieved by applying a temporal filter to the complex-cell response. The mathematical inference is supported by simulations that quantitatively reproduce measured complex-cell responses in both cat and monkey to a variety of relative-motion stimuli. Importantly, the posited mechanism for cortical computation of relative motion does not require an intermediate neural representation of local velocities and does not require lateral or feedback interactions within a network.

We examined whether lateral spread of adaptation can be observed in the electroretinogram in humans. Specifically, we tested whether the luminance level of a surrounding, nonmodulated annulus affects the multifocal electroretinogram (ERG) response of a modulated central area. Multifocal electroretinograms were recorded in response to an array of 37 unscaled hexagons subtending a retinal area of 38 deg × 35 deg. Responses were recorded in six control subjects. In the first series of experiments, only the center hexagon was modulated, while the surrounding 36 hexagons were held constant at either 0.45, 172, or 340 cd/m2. In a subsequent series of control experiments, modulation depth of the center hexagon was varied and the proximity of the surrounding hexagon systematically altered. For the center-modulated condition, response amplitude and implicit time for the first-order kernel response significantly decreased as a function of increasing surround luminance. Control experiments demonstrated that the effect of the surround illumination was not due to scattered light but was influenced by the proximity of the surrounding annulus. These results demonstrate that lateral adaptation influences can be measured using the multifocal ERG.