Increment-threshold Spectral Sensitivity Functions Research Articles

Increment-threshold spectral sensitivity during saccadic eye movements in uniform visual field

We measured increment-threshold spectral sensitivity functions during saccades, immediately after saccades and during fixation. A uniform white background field which covered observer’s whole visual field prevented any retinal masking effects. Visual sensitivity was degraded during saccades or after saccades. The reduction in sensitivity depended upon the wavelength of the test stimulus. The spectral sensitivity function during fixation produced a broad smooth curve in the middle and long wavelength region, while saccades caused a prominent dip around 570 nm. This finding indicates that saccadic suppression, which cannot be attributed to retinal masking, has more effect on the achromatic channel than the chromatic channel. The role of central and retinal processes dealing with the perceptual clearness and stableness across saccades will be discussed.

Modelling sensitivity losses in ocular disorders: colour vision anomalies following intense blue-light exposure in monkeys.

The effects of prolonged exposure to intense, short-wavelength light were studied in monkeys through the measurement of increment-threshold spectral sensitivity (ITSS) and threshold-versus-intensity (TVI) functions using a behavioural method. The long-term effect of intense blue-light exposure was to induce a short-wavelength (SW) sensitivity loss which did not depend on the intensity or chromatic composition of the adapting field. The TVI curves for short wavelength stimuli revealed an increase in test threshold without changes in field sensitivity. Since this SW sensitivity loss may generalize to characteristic colour vision defects found in many outer retinal diseases, models of acquired alterations of colour vision mechanisms are considered. These models describe probable changes in ITSS functions and TVI curves in diseases affecting the inner or outer retina as well as changes in dark adaptation.

Colour vision anomalies following experimental glaucoma in monkeys

Spectral sensitivity defects, associated with chronic elevated intraocular pressure (IOP) produced by Argon laser trabeculoplasty, were studied in monkeys. Increment-threshold spectral sensitivity (ITSS) and threshold versus intensity (TVI) functions were measured using a behavioural model. Elevated IOP resulted in short wavelength (SW) sensitivity losses characteristic of many ocular diseases. The amount of SW sensitivity loss for ITSS functions depended upon the intensity level and chromatic composition of the background field. The optimum condition identifying the greatest SW sensitivity reduction was a yellow background of moderate intensity (100-1000 Td). In the early stages of experimental glaucoma, the cone mechanisms and the rod mechanism typically showed decreased test and field sensitivities. The SW cone pathway has slightly greater threshold elevation (approximately 0.3 log unit) compared to the rod and cone pathways. On the other hand, in the advanced stages of experimental glaucoma, the largest sensitivity losses were in the longer-wavelength, red-green opponent mechanisms, with the rod and SW cone pathways showing smaller losses. The similarities of the colour vision anomalies in this animal model with those of patients with glaucoma, provides support for its use as an experimental model for human glaucoma.

Effects of chromatic adaptation on opponent interactions in monkey increment-threshold spectral-sensitivity functions

The effects of chromatic adaptation on the opponent interactions of cone mechanisms were investigated by using increment-threshold spectral-sensitivity (ITSS) functions and threshold-versus-radiance (TVR) curves in rhesus monkey subjects. The TVR curves showed shape- and field-sensitivity invariance for both 580- and 500-nm adapting backgrounds and indicated that three cone mechanisms were mediating detection over moderate adapting-field intensity levels. Differential adaptation between the long-wavelength-sensitive (L) and the middle-wavelength-sensitive (M) opponent (L - M) and nonopponent (L + M) channels and the short-wavelength-sensitive (S) channel caused changes in the shape of the ITSS function as the adapting-field intensity was increased without changes in the level of cone interaction. Chromatic adaptation also resulted in significant changes in the shape of the ITSS functions, but it still exhibited characteristic L-M opponent interactions. Converting ITSS data to cone-contrast coordinates for R-G adapting fields indicated that the relative contribution of the L and M cones at the second site was approximately equal (detection contour slope approximately 1). Consequently, most of the changes in the shape of ITSS functions under chromatic adaptation are explained by the von Kries adaptation principle. ITSS functions on a green background also exhibited opponent interactions between S cones and longer-wavelength cones. The cone-contrast coordinates, when expressed for S cones, showed that the inhibitory interactions occur because the S-cone signal subtracts from both M and L cones.

Red-green interactions in the spectral sensitivity of primates as derived from ERG and behavioral data

Different techniques were used to manipulate the inhibitory interaction between the red and green photoreceptors (R and G cones) of rhesus and human primates. The response techniques that were used were the corneal electroretinogram (ERG) and psychophysical increment-threshold spectral sensitivity functions. Red-green opponency, as measured by the depth of the notch at 580 nm, is removed by intravitreal injection of bicuculline but not by strychnine. Therefore, red-green opponency is mediated by GABA and not glycine. The depth of the notch is dependent upon stimulus size. Between 30' and 15' test light diameters, this sign of red-green opponency disappears. Psychophysical increment thresholds are shown to produce the notch while decrements do not and intravitreal APB is shown to reduce the notch, evidence that red-green opponency is carried by the "ON" and not the "OFF" bipolar pathways of the retina. Red and green annuli are shown to selectively reduce red and green inhibition, as though there were selective reduction of the surround response in center-surround organized red-green receptive fields.

Induced color blindness in goldfish: A behavioral and electrophysiological study

To answer the question whether, like man, ethambutol treated fish would become color-blind, wavelength discrimination was measured behaviorally in goldfish, preceding, during and after ethambutol treatment. The results are that of the three high discrimination abilities at around 400, 500 and 600 nm, ethambutol affected the latter one. Red-green discrimination is lost reversibly leaving the discriminations in the blue-green and violet range unaffected. This red-green discrimination deficiency cannot be accounted for by a loss of long wavelength cones since the ERG and luminosity functions remain unaffected. Intracellular horizontal cell recordings in goldfish show that ethambutol hyperpolarizes all three types of cone driven horizontal cells and changes their color coding such that their spectral characteristics become cone-like as is the case in dark adapted retina. So, the initial effect induced by ethambutol seems to be an adaptation deficiency in color vision related tasks. Human wavelength discrimination and increment threshold spectral sensitivity functions obtained at low luminance levels are compared to behavioral functions in ethambutol treated goldfish. The high similarity between the ethambutol effects in man and goldfish, and the effects observed in the horizontal cell responses in goldfish are highly indicative that horizontal cells play a key role in color vision. So far their function has been puzzling.

Behavioral studies of the sensitive periods of development of visual functions in monkeys

The age-dependent effects of monocular form deprivation on psychophysically determined visual functions were investigated in rhesus monkeys. Monocular form deprivation was initiated at various ages from 1 to 25 months and maintained for 18 months. The effects of form deprivation varied across the visual functions evaluated. Absolute scotopic sensitivity was depressed by form deprivation initiated only at 1 or 2 months of age. Photopic, increment-threshold spectral sensitivity functions showed alterations in sensitivity levels for monkeys treated at 5 months of age or earlier, with no effect thereafter. Monocular form deprivation at 1 to 5 months of age resulted in profound deficits in spatial modulation sensitivity. The effects on spatial vision decreased systematically as the age of onset was delayed from age 6 to 18 months. Finally, binocular summation measures revealed an absence of binocular vision even for the monkey form-deprived at 25 months of age, i.e. the experimental treatment series failed to define the upper limit of the age-range for the effects of monocular form deprivation on binocular summation mechanisms. Comparisons of the age-dependent effects of monocular form deprivation across the various functions demonstrated that the sensitive period, i.e. the period of life during which a visual function may be altered by monocular form deprivation, was different for each of the psychophysical measures of visual function.

Spectral sensitivity and adaptation characteristics of cone mechanisms under white-light adaptation

Increment-threshold spectral-sensitivity (ITSS) functions and threshold-versus-intensity (tvi) curves were measured under white-light adaptation in rhesus monkeys. The tvi curves showed shape and test wavelength invariance, implying that three cone mechanisms were mediating detection. In general, the results were in agreement with the differential adaptation hypothesis proposed by Stiles that predicted spectral shape invariance of the cone mechanisms but overall changes in the shape of the spectral-sensitivity function with increases in the intensity of the adapting field. The principal changes occurring in the ITSS function as the level of adaptation increased involved a smaller loss in sensitivity of the short-wavelength and the long-wavelength peaks compared with the corresponding loss in sensitivity of the middle-wavelength peak. A three-channel model with an opponent L-M mechanism and a nonopponent L-M mechanism (both with S-cone input) and an independent S-cone mechanism described the ITSS data as well as other increment-threshold and suprathreshold data. The model values for the ITSS functions, along with parameters derived from the transformation of these data to cone-contrast coordinates, permitted the factoring out of first-site adaptation, second-site adaptation, and the relative strengths of contribution of the L and M cones within the opponent and nonopponent L-M channels.

Color vision in the dog

The color vision of three domestic dogs was examined in a series of behavioral discrimination experiments. Measurements of increment-threshold spectral sensitivity functions and direct tests of color matching indicate that the dog retina contains two classes of cone photopigment. These two pigments are computed to have spectral peaks of about 429 nm and 555 nm. The results of the color vision tests are all consistent with the conclusion that dogs have dichromatic color vision.

A comparison of the spectral sensitivities of monkeys with anisometropic and stimulus deprivation amblyopia

Psychophysical procedures were used to determine increment-threshold spectral sensitivity functions for monkeys with either stimulus deprivation amblyopia produced by monocular lid suture or anisometropic amblyopia produced by optical defocus. The spectral sensitivity functions obtained from all of the non-treated control eyes had 3 sensitivity maxima at approximately 445, 520 and 610 nm, and were typical of functions for humans and monkeys with normal trichromatic vision. Relative to their paired control eyes, the amblyopic eyes of all of the lid-sutured monkeys demonstrated reductions in absolute sensitivity. In addition, the amblyopic eyes of the monkeys form-deprived at 1 month of age exhibited alterations in the shapes of their spectral sensitivity functions. The pattern of spectral sensitivity deficits observed in the monkeys form-deprived at 1 month of age varied with the duration of deprivation and indicated that the spectral characteristics of the neural mechanisms mediating stimulus detection in these lid-sutured monkeys' amblyopic and control eyes were substantially different. In contrast, none of the anisometropic amblyopes demonstrated any alterations in the shapes of their spectral sensitivity functions and only one anisometropic subject exhibited a reduction in sensitivity. A comparison of the spectral sensitivity deficits observed in our lid-sutured and anisometropic monkeys reveals that when lid suture and optical defocus are initiated early in life for equivalent periods of time, lid suture produces abnormalities which are both qualitatively and quantitively different from the abnormalities produced by optical defocus. Therefore, in addition to factors such as the age of onset and the duration of deprivation, it is concluded that the degree of image degradation is important in determining which visual functions are affected and to what extent they are affected.

Reexamination of spectral mechanisms in the rat (Rattus norvegicus).

The spectral mechanisms of the rat were studied in electrophysiological and behavioral experiments. The photopic electroretinogram (ERG) was recorded (a) to rapidly flickering lights, (b) during the cone phase of dark adaptation, and (c) with a flicker photometric procedure. Each procedure indicated the presence of a single cone mechanism having a lambda max of about 510 nm. Increment-threshold spectral sensitivity functions measured in a behavioral test situation yielded the same conclusion. A behavioral experiment failed to produce any evidence for the presence of color vision in this rodent. The consistent conclusion from both behavioral and electrophysiological experiments is that the rat retina contains only a single photopic spectral mechanism.

Color vision is altered during the suppression phase of binocular rivalry.

Increment-threshold spectral sensitivity functions were determined during the dominance and suppression phases of binocular rivalry. The shapes of the functions obtained during the dominance phase exhibited three maxima at approximately 440, 530, and 610 nanometers and resembled functions obtained for nonrivalrous control conditions. However, the functions measured during suppression had a single broad peak near 555 nanometers and were adequately described by functions measured with flicker methods during nonrivalrous conditions. The results indicate that binocular rivalry differentially attenuates opponent-color information relative to achromatic information.

Spectral sensitivity of the peripheral retina to large and small stimuli

Increment-threshold spectral sensitivity functions were taken foveally and at four other retinal locations with different sized test stimuli. For the fovea and parafovea at 4°, a 1°, 250 msec stimulus of variable wavelength, flashed on a 1000 td white background yielded spectral sensitivity curves with three distinct maxima located near 455, 530–540 and 600 nm. As eccentricity increased so did the minimum spot size needed to produce spectral curves with three peaks. In particular, the 2°10′ spot at 20°, 4°10′ at 30° and 5.5° at 45° gave this result. Smaller stimuli in the periphery yielded curves with a minor peak at 455 nm, present under some conditions, and a major broad peak at 560 nm that resembled the CIE photopic luminosity function. Two different systems subserve detection : the three-peaked curves indicate mediation by the opponent-color system while the other type of function can be attributed to the non-opponent system.

Increment-threshold spectral sensitivity in the tawny owl ( Strix aluco)

Colour vision has previously been shown to be present in the tawny owl ( Strix aluco)—a totally nocturnal bird. Photopic increment-threshold spectral sensitivity functions were behaviourally determined in three tawny owls, using a two-choice simultaneous discrimination procedure. The functions obtained from the three birds showed very close agreement. All had maximum sensitivity at about 580 nm and in two of the birds a submaximum at about 525 nm was evident. A comparison is made between this function and that from two humans tested in the same apparatus. The possible effects of selective absorption by pre-retinal media on the owl's function are considered. The owl's function is compared with similar data available for other species of bird.