Assessing perceptual chromatic equiluminance using a reflexive pupillary response (original) (raw)
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Chromatic Contrast Sensitivity Functions Measured Using Optokinetic Nystagmus and Psychophysics
Optokinetic nystagmus (OKN) is a sequence of involuntary eye movements comprising slow phases of tracking a moving stimulus followed by fast saccades to reset the eye position. Although previous studies have studied the relationship between human OKN and functional vision via measurement of the contrast-sensitivity function (CSF), it has not been investigated using colour-varying, red-green, equiluminant patterns. In human vision, spatiotemporal changes in luminance convey a stronger sense of motion than do equiluminant patterns; yet, motion can nevertheless be perceived without luminance cues. The present study used spatial-frequency, band-pass luminance and red-green equiluminant noise patterns to measure OKN, and thus characterise the chromatic input to the mechanisms that drive the optokinetic response. The CSFs of 21 observers with normal vision were recorded using OKN and perceptual report. The results of the study demonstrate that an equiluminant red green stimulus can evoke a robust OKN response. There was a high correlation between OKN and perceptual report, for both luminance and colour stimuli, an indication of a common neural mechanism for defining stimulus direction. In all stimulus conditions tested, OKN can deliver a valid alternate technique for measuring the CSF.
Pupillary responses to stimulus structure, colour and movement
Ophthalmic and Physiological Optics, 2007
Pupillary responses to stimuli which favour the preferential stimulation of neural mechanisms involved in the detection of visual attributes such as colour, spatial structure, movement and light flux changes on the retina have been measured and compared. Pupil responses to a decrement in stimulus luminance (i.e., a flash of darkness), suggest that at least three components are involved in this response, their relative contribution being determined largely by stimulus size, contrast and presentation time. A comparison of pupil responses to gratings of equal and lower space-averaged luminance shows that the amplitude of pupillary constriction at grating onset for the equal luminance condition is about twice that measured with similar gratings in the lower luminance condition. Pupillary responses to chromatic isoluminant gratings are in general of longer latency when compared to responses of similar amplitude elicited by achromatic gratings. Small pupillary constrictions elicited by the onset of coherent movement in dynamic, random dot patterns are also demonstrated under stimulus conditions which eliminate pupillary responses to sudden light flux changes on the retina. The results support an earlier hypothesis which suggests that the onset of sudden changes in neural activity in the visual cortex when a visual stimulus is presented to the eye causes an overall perturbation which weakens transiently the regulatory inhibitory input to the pupillomotor nucleus. This, in turn, results in a transient increase in the efferent parasympathetic innervation of the iris sphincter muscle and hence the observed constriction of the pupil. The characteristics of the pupillary response reflect the properties of the mechanisms and the number of neurones which participate in the detection of each simulus attribute.
A linear chromatic mechanism drives the pupillary response
Proceedings of the Royal Society B: Biological Sciences, 2001
Previous studies have shown that a chromatic mechanism can drive pupil responses. The aim of this research was to clarify whether a linear or nonlinear chromatic mechanism drives pupillary responses by using test stimuli of various colours that are de¢ned in cone contrast space. The pupil and accommodation responses evoked by these test stimuli were continuously and simultaneously objectively measured by photorefraction. The results with isochromatic and isoluminant stimuli showed that the accommodative level remained approximately constant (5 0.25 D change in mean level) even when the concurrent pupillary response was large (ca. 0.30 mm). The pupillary response to an isoluminant grating was sustained, delayed (by ca. 60 ms) and larger in amplitude than that for a isochromatic uniform stimulus, which supports previous work suggesting that the chromatic mechanism contributes to the pupillary response. In a second experiment, selected chromatic test gratings were used and isoresponse contours in cone contrast space were obtained. The results showed that the isoresponse contour in cone contrast space is well described (r 2 0.99) by a straight line with a positive slope. The results indicate that a jL7Mj linear chromatic mechanism, whereby a signal from the long wavelength cone is subtracted from that of the middle wavelength cone and vice versa, drives pupillary responses.
Modeling Chromatic Pupillary Responses in Healthy People
2007 4th International Conference on Electrical and Electronics Engineering, 2007
We propose a model to determinate pupillary changes due to chromatic stimulus. The pupillary diameters (PD) from 44 subjects with normal vision of colors were measured. These PD were elicited by 26 different chromatic stimuli (from 400 to 650 nm). The proposed model establishes the pupillary behavior for different colors. To determinate this model, we consider the characteristics of the subject (age and gender), stimulus (luminance and wavelength) as the diameter of their pupil (for white stimulus). With our approach the maximum coefficient of correlation obtained was of 1.0 in 90% of the cases analyzed (PD measured and calculated). This proposed model is the first all over the world.
Pupillary response to chromatic flicker
Experimental Brain Research, 2001
There is significant evidence for higher-level cortical control of pupillary responses to visual stimuli, suggesting that factors other than luminance changes may induce a pupillary response. In the present study, the pupillary responses to equiluminant flickering stimuli in a range of 3-13 Hz were examined. Flicker stimuli included color-black (luminance-modulated) and color-color (huemodulated) flicker. Equiluminance was determined both by objective luminance measures as well as by subjective, perceptual equiluminance for each subject. For both objectively and subjectively equiluminant flicker, significant, sustained pupillary constrictions were recorded. The magnitude of these responses was sensitive to both color and frequency parameters; Red-Blue color-paired flicker consistently produced the strongest constrictions. These responses occurred even when the flicker was of a lower luminance, both physically and perceptually, than a preceding nonflickering color, indicating that chromatic rather than luminance-sensitive mechanisms are involved in this response. Interestingly, the color-and frequency-sensitivity of constriction parallels those of flickers which maximally stimulate photosensitive epileptic patients, raising the possibility that chromatic response may be a factor in photosensitivity.
Role of eye movements in chromatic induction
There exist large interindividual differences in the amount of chromatic induction [Vis. Res. 49, 2261 (2009)]. One possible reason for these differences between subjects could be differences in subjects' eye movements. In experiment 1, subjects either had to look exclusively at the background or at the adjustable disk while they set the disk to a neutral gray as their eye position was being recorded. We found a significant difference in the amount of induction between the two viewing conditions. In a second experiment, subjects were freely looking at the display. We found no correlation between subjects' eye movements and the amount of induction. We conclude that eye movements only play a role under artificial (forced looking) viewing conditions and that eye movements do not seem to play a large role for chromatic induction under natural viewing conditions.
Graefe's Archive for Clinical and Experimental Ophthalmology
Purpose To examine systematically how prechiasmal, chiasmal, and postchiasmal lesions along the visual pathway affect the respective pupillary responses to specific local monochromatic stimuli. Methods Chromatic pupil campimetry (CPC) was performed in three patient groups (10 subjects with status after anterior ischemic optic neuropathy, 6 with chiasmal lesions, and 12 with optic tract or occipital lobe lesions (tumor, ischemia)) using red, low-intensity red, and blue local stimuli within the central 30° visual field. Affected areas - as determined by visual field defects revealed using conventional static perimetry - were compared with non-affected areas. Outcome parameters were the relative maximal constriction amplitude (relMCA) and the latency to constriction onset of the pupillary responses. Results A statistically significant relMCA reduction was observed in the affected areas of postchiasmal lesions with red (p = 0.004) and low-intensity red stimulation (p = 0.001). RelMCA re...
Effect of Single and Combined Monochromatic Light on the Human Pupillary Light Response
Frontiers in Neurology, 2018
The pupillary light reflex (PLR) is a neurological reflex driven by rods, cones, and melanopsin-containing retinal ganglion cells. Our aim was to achieve a more precise picture of the effects of 5-min duration monochromatic light stimuli, alone or in combination, on the human PLR, to determine its spectral sensitivity and to assess the importance of photon flux. Using pupillometry, the PLR was assessed in 13 participants (6 women) aged 27.2 ± 5.41 years (mean ± SD) during 5-min light stimuli of purple (437 nm), blue (479 nm), red (627 nm), and combinations of red+purple or red+blue light. In addition, nine 5-min, photon-matched light stimuli, ranging in 10 nm increments peaking between 420 and 500 nm were tested in 15 participants (8 women) aged 25.7 ± 8.90 years. Maximum pupil constriction, time to achieve this, constriction velocity, area under the curve (AUC) at short (0-60 s), and longer duration (240-300 s) light exposures, and 6-s post-illumination pupillary response (6-s PIPR) were assessed. Photoreceptor activation was estimated by mathematical modeling. The velocity of constriction was significantly faster with blue monochromatic light than with red or purple light. Within the blue light spectrum (between 420 and 500 nm), the velocity of constriction was significantly faster with the 480 nm light stimulus, while the slowest pupil constriction was observed with 430 nm light. Maximum pupil constriction was achieved with 470 nm light, and the greatest AUC 0−60 and AUC 240−300 was observed with 490 and 460 nm light, respectively. The 6-s PIPR was maximum after 490 nm light stimulus. Both the transient (AUC 0−60) and sustained (AUC 240−300) response was significantly correlated with melanopic activation. Higher photon fluxes for both purple and blue light produced greater amplitude sustained pupillary constriction. The findings confirm human PLR dependence on wavelength, monochromatic or bichromatic light and photon flux under 5-min duration light stimuli. Since the most rapid and high amplitude PLR occurred within the 460-490 nm light range (alone or combined), our results suggest that color Bonmati-Carrion et al. Wavelength and Intensity on PLR discrimination should be studied under total or partial substitution of this blue light range (460-490 nm) by shorter wavelengths (∼440 nm). Thus for nocturnal lighting, replacement of blue light with purple light might be a plausible solution to preserve color discrimination while minimizing melanopic activation.
Detection of between-eye differences in color: Interactions with luminance
Between-eye differences in color or luminance result in the appearance of luster, which provides a cue for detecting between-eye differences. We measured thresholds for detecting between-eye differences in both hue and chromatic contrast (saturation) in dichoptically superimposed color patches. Sensitivity was found to be highest at isoluminance and decreased with the addition of task-irrelevant, spatially coextensive, binocular (i.e., same in both eyes) luminance contrast. However, when the members of each dichoptic pair were presented side by side on the screen and viewed with the same eye, the added luminance contrast had no effect on the detection of their differences. If the effect of the luminance contrast was simply to dilute or desaturate the chromatic signals, we would expect thresholds to increase for the within-eye and not just the between-eye (dichoptic) conditions. We suggest that the presence of binocular luminance contrast reduces the interocular suppression between the dichoptic colors, causing the dichoptic color pairs to blend, thus rendering their differences harder to detect.