Bright Stimuli Research Articles

Evaluating the perceived brightness of chromatic stimuli with backgrounds of varying luminance

AbstractReproducing near‐gamut colors on an emissive display often causes them to appear brighter than an achromatic color of the same luminance. This phenomenon can be explained by the Helmholtz–Kohlrausch (H–K) effect, which describes an increase in perceived brightness when increasing the chroma of a stimulus. Although recent studies have attempted to incorporate the H–K effect into their modeling, none of these studies have directly explored how the perception of chromatic stimuli changes with background luminance. In this article, we present results from a psychophysical brightness‐matching experiment conducted across different levels of background luminance. The experimental results show the magnitude of the H–K effect upon simultaneous lightness contrast for high chroma colors. We, then, compare our results to CAM16 and other published models that propose modifications to CAM16 to account for the H–K effect. The findings reveal that CAM16 overestimates the perceived rate of lightness change by more than double for highly saturated, low luminance colors with increasing background luminance levels. Despite the progress made in incorporating the H–K effect into models, our study indicates the need for further data to establish a more accurate and robust modeling of this phenomenon.

Light-evoked deformations in rod photoreceptors, pigment epithelium and subretinal space revealed by prolonged and multilayered optoretinography

Phototransduction involves changes in concentration of ions and other solutes within photoreceptors and in subretinal space, which affect osmotic pressure and the associated water flow. Corresponding expansion and contraction of cellular layers can be imaged using optoretinography (ORG), based on phase-resolved optical coherence tomography (OCT). Until now, ORG could reliably detect only photoisomerization and phototransduction in photoreceptors, primarily in cones under bright stimuli. Here, by employing a phase-restoring subpixel motion correction algorithm, which enables imaging of the nanometer-scale tissue dynamics during minute-long recordings, and unsupervised learning of spatiotemporal patterns, we discover optical signatures of the other retinal structures’ response to visual stimuli. These include inner and outer segments of rod photoreceptors, retinal pigment epithelium, and subretinal space in general. The high sensitivity of our technique enables detection of the retinal responses to dim stimuli: down to 0.01% bleach level, corresponding to natural levels of scotopic illumination. We also demonstrate that with a single flash, the optoretinogram can map retinal responses across a 12° field of view, potentially replacing multifocal electroretinography. This technique expands the diagnostic capabilities and practical applicability of optoretinography, providing an alternative to electroretinography, while combining structural and functional retinal imaging in the same OCT machine.

Human perception of flicker-fused letters that are luminance balanced.

The Talbot-Plateau law specifies what combinations of flash frequency, duration, and intensity will yield a flicker-fused stimulus that matches the brightness of a steady stimulus. It has proven to be remarkably robust in its predictions, and here we provide additional support though the use of a contrast discrimination task. However, we also find that the visual system can register flicker-fused letters when the combination of frequency and duration is relatively low. The letters are recognized even though they have the same physical luminance as background. We hypothesize that the letters elicit synchronous oscillations that encode for stimulus attributes, which prevents the letter from blending into the background.

Brainwaves and Emotional Responses to Changes in Red Eye Shadow Brightness and Saturation

Purpose: Investigating how Munsell’s primary color (i.e., red eye shadow) influences human brain and emotional responses to establish foundational data for image formation. Methods: We analyzed the relative power differences in background brainwaves due to variations in five levels of brightness and saturation for each eye both in male and female individuals in their twenties. We used the coefficient of variation for brainwaves for our analysis. In addition, we assessed the preferences for altered red eye shadow and the emotional responses to determine the average preference index. We performed statistical analysis for brainwaves and emotional evaluations using repeated measure analysis of variance in SPSS, followed by post hoc testing with Tukey’s test at a 95% confidence level. Results: The brainwave and emotional responses obtained by presenting red eye shadow brightness and saturation modification-created stimuli revealed that both men and women exhibited beta and gamma wave activation and alpha wave inactivation upon low brightness and high saturation stimuli. Men were more sensitive to brightness stimuli, whereas women displayed higher-level variability in brainwave responses upon saturation changes. Both genders preferred red eye shadows with brightness and saturation levels of 8 and 2, respectively. The perceptual image responses indicated that stimuli with low or high brightness were perceived as modern and subtle or clear and cute, respectively. Medium or high saturation stimuli were perceived as clear and natural or associated with a modern image, respectively, by both genders. Conclusion: This study demonstrated the impact of various color stimuli on the human brain and emotions. We consider the obtained results as foundational data, which could be used in future image consulting or when crafting desired image presentations.

The brightness of chromatic stimuli

AbstractWe present the results of a series of three brightness‐matching experiments which include a key refinement in this established psychophysical method. Constraining the chroma difference between pairs of stimuli matched in brightness allows us to use a novel calculus‐based approach to building a model of the brightness of chromatic visual stimuli and the Helmholtz‐Kohlrausch effect. The proposed models, compatible with the CIECAM16 color appearance model and CIELAB color space, are compared to other models of the Helmholtz‐Kohlrausch effect on these data and other past brightness‐matching studies. The proposed CIECAM16‐based model demonstrates the overall best performance on predicting the Helmholtz‐Kohlrausch effect in four newer data sets but overpredicts the weaker effect reported in three older data sets. The potential experimental factors in this divide between new and old studies are also discussed.

Time-on-task effects on human pupillary and saccadic metrics after theta burst transcranial magnetic stimulation over the frontal eye field

Pupil size undergoes constant changes primarily influenced by ambient luminance. These changes are referred to as the pupillary light reflex (PLR), where the pupil transiently constricts in response to light. PLR kinematics provides valuable insights into autonomic nervous system function and have significant clinical applications. Recent research indicates that attention plays a role in modulating the PLR, and the circuit involving the frontal eye field (FEF) and superior colliculus is causally involved in controlling this pupillary modulation. However, there is limited research exploring the role of the human FEF in these pupillary responses, and its impact on PLR metrics remains unexplored. Additionally, although the protocol of continuous theta-burst stimulation (cTBS) is well-established, the period of disruption after cTBS is yet to be examined in pupillary responses. Our study aimed to investigate the effects of FEF cTBS on pupillary and saccadic metrics in relation to time spent performing a task (referred to as time-on-task). We presented a bright stimulus to induce the PLR in visual- and memory-delay saccade tasks following cTBS over the right FEF or vertex. FEF cTBS, compared to vertex cTBS, resulted in decreased baseline pupil size, peak constriction velocities, and amplitude. Furthermore, the time-on-task effects on baseline pupil size, peak amplitude, and peak time differed between the two stimulation conditions. In contrast, the time-on-task effects on saccadic metrics were less pronounced between the two conditions. In summary, our study provides the first evidence that FEF cTBS affects human PLR metrics and that these effects are modulated by time-on-task.

Modeling the critical fliker fusion frequency in the human visual system

The temporal resolving power of the visual system is essential for the perception of the objective world. The lowest sampling rate of a sequence of images at which perception becomes fused is called the critical flicker fusion frequency. The variety of experimental data on critical frequency thresholds can be explained from a point of view of a model of the contrast sensitivity of the visual system that based on the tremor modulation signal. The model describes the dependence of critical frequency on stimulus brightness, adaptation brightness, duration, and the angular size of the stimulus. This model demonstrates that for bright stimuli with short duration and a large angular size, critical frequency values lie in the range up to 1000 Hz; the frame rate of 300-500 Hz should be considered optimal for the visual system; for small-sized angular stimuli, the critical frequency lies in the low-frequency region. Differences in the rate of flicker fusion can be explained by temporal sensitivity of magno- and parvocellular neurons.

Features of perception of color stimuli in achromatopsia

Introduction. Understanding the peculiarities of perception of color images by patients with achromatopsia helps to identify and differentiate this pathology from diseases with similar clinical symptoms in time. This is becoming increasingly relevant due to ongoing developments in the field of virus vector therapy using an adeno-associated virus carrying the CNGB3 and CNGA3 genes.Purpose: to investigate the features of perception of color images by patients with achromatopsia, using in addition to the generally accepted developed proprietary tests to quantify the brightness of perceived images.Materials and methods. Five school-age patients (12–17 years) with complete achromatopsia were observed. The control group included 36 schoolchildren aged from 10 to 17 (av. 13.4 ± 0.5) with a normal state of visual functions. The ophthalmological examination included standard research methods. In children with achromatopsia, OСT data and ERG indicators were taken into account. To study color vision in all children, the following methods were used: E.B. Rabkin’s polychromatic tables, Neitz Test, Farnsworth–Munsell Dichotomodus D-15 Test, a study of the field of vision for white and colored stimuli (on the perimeter of PNR-03). In addition, in children with achromatopsia, the perception of color stimuli with achromatic stimuli was compared using special proprietary images.Results. Comparison of the results of the study of color vision in patients with achromatopsia in different ways demonstrates the greatest probability of diagnostic errors when using polychromatic tables, which may be due to the ability of these patients to distinguish test figures in some tables based on brightness contrast, rather than contrast of color tones. Increased sensitivity of photoreceptors to short-wave (blue part of the spectrum) radiation and significantly reduced sensitivity to short-wave (red part of the spectrum) in patients with achromatopsia may cause the expansion of the boundaries of the field of view to green and blue stimuli (while the boundaries of the field of view to the blue stimulus almost reach the values for the white stimulus), as well as a significant narrowing to red stimuli compared with the indicators in the control group (p < 0.001). The developed own test images made it possible to quantify the brightness of chromatic stimuli perceived by patients with achromatopsia in comparison with the brightness of achromatic stimuli. The brightest (90–100%) for them was the blue stimulus and practically merged with the white background of the screen. The red stimulus was perceived to be the darkest (minimum brightness). Based on the data obtained, an approximate model of the perception of color images in achromatopsia was created. Conclusion. The obtained data complement the existing ideas about the peculiarities of perception of color images by patients with achromatopsia and can be used to develop new and improve existing methods of diagnosing this disease, as well as to create recommendations for the design of illustrative, educational and advertising material.

Effects of Stimulus Luminance, Stimulus Color and Intra-Stimulus Color Contrast on Visual Field Mapping in Neurologically Impaired Adults Using Flicker Pupil Perimetry.

We improve pupillary responses and diagnostic performance of flicker pupil perimetry through alterations in global and local color contrast and luminance contrast in adult patients suffering from visual field defects due to cerebral visual impairment (CVI). Two experiments were conducted on patients with CVI (Experiment 1: 19 subjects, age M and SD 57.9 ± 14.0; Experiment 2: 16 subjects, age M and SD 57.3 ± 14.7) suffering from absolute homonymous visual field (VF) defects. We altered global color contrast (stimuli consisted of white, yellow, cyan and yellow-equiluminant-to-cyan colored wedges) in Experiment 1, and we manipulated luminance and local color contrast with bright and dark yellow and multicolor wedges in a 2-by-2 design in Experiment 2. Stimuli consecutively flickered across 44 stimulus locations within the inner 60 degrees of the VF and were offset to a contrasting (opponency colored) dark background. Pupil perimetry results were compared to standard automated perimetry (SAP) to assess diagnostic accuracy. A bright stimulus with global color contrast using yellow (p=0.009) or white (p=0.006) evoked strongest pupillary responses as opposed to stimuli containing local color contrast and lower brightness. Diagnostic accuracy, however, was similar across global color contrast conditions in Experiment 1 (p=0.27) and decreased when local color contrast and less luminance contrast was introduced in Experiment 2 (p=0.02). The bright yellow condition resulted in highest performance (AUC M =0.85±0.10, Mdn=0.85). Pupillary responses and pupil perimetry's diagnostic accuracy both benefit from high luminance contrast and global but not local color contrast.

An Advanced Color Model for Evaluating New Display Technologies

AbstractUnderstanding chromatic stimuli's brightness using experienced color range can help scientists and consumers predict the perceptual attributes of electronic displays.

SSVEP-based Brain-Computer Interface Controlled Robotic Platform with Velocity Modulation.

Steady-state visual evoked potential (SSVEP)-based brain-computer interfaces (BCIs) have been extensively studied due to many benefits, such as non-invasiveness, high information transfer rate, and ease of use. SSVEP-based BCI has been investigated in various applications by projecting brain signals to robot control commands. However, the movement direction and speed are generally fixed and prescribed, neglecting the user's requirement for velocity changes during practical implementations. In this study, we proposed a velocity modulation method based on stimulus brightness for controlling the robotic arm in the SSVEP-based BCI system. A stimulation interface was designed, incorporating flickers, target and a cursor workspace. The synchronization of the cursor and robotic arm does not require the subject's eye switch between the stimuli and the robot. The feature vector consists of the characteristics of the signal and the classification result. Subsequently, the Gaussian mixture model (GMM) and Bayesian inference were used to calculate the posterior probabilities that the signal came from a high or low brightness flicker. A brain-actuated speed function was designed by incorporating the posterior probability difference. Finally, the historical velocity was considered to determine the final velocity. To demonstrate the effectiveness of the proposed method, online experiments, including single- and multi-target reaching tasks, were conducted. The extensive experimental results validated the feasibility of the proposed method in reducing reaching time and achieving proximity to the target.

Investigating the role of human frontal eye field in the pupil light reflex modulation by saccade planning and working memory.

The pupil constricts in response to an increase in global luminance level, commonly referred to as the pupil light reflex. Recent research has shown that these reflex responses are modulated by high-level cognition. There is larger pupil constriction evoked by a bright stimulus when the stimulus location spatially overlaps with the locus of attention, and these effects have been extended to saccade planning and working memory (here referred to as pupil local-luminance modulation). Although research in monkeys has further elucidated a central role of the frontal eye field (FEF) and superior colliculus in the pupil local-luminance modulation, their roles remain to be established in humans. Through applying continuous theta-burst transcranial magnetic stimulation over the right FEF (and vertex) to inhibit its activity, we investigated the role of the FEF in human pupil local-luminance responses. Pupil light reflex responses were transiently evoked by a bright patch stimulus presented during the delay period in the visual- and memory-delay tasks. In the visual-delay task, larger pupil constriction was observed when the patch location was spatially aligned with the target location in both stimulation conditions. More interestingly, after FEF stimulation, larger pupil constriction was obtained when the patch was presented in the contralateral, compared to the ipsilateral visual field of the stimulation. In contrast, FEF stimulation effects were absence in the memory-delay task. Linear mixed model results further found that stimulation condition, patch location consistency, and visual field significantly modulated observed pupil constriction responses. Together, our results constitute the first evidence of FEF modulation in human pupil local-luminance responses.

Why Achromatic Response is not a Good Measure of Brightness

Luminance underestimates the brightness of chromatic visual stimuli. This phenomenon, known as the Helmholtz-Kohlrausch effect, is due to the different experimental methods—heterochromatic flicker photometry (luminance) and direct brightness matching (brightness)—from which these measures are derived. This paper probes the relationship between luminance and brightness through a psychophysical experiment that uses slowly oscillating visual stimuli and compares the results of such an experiment to the results of flicker photometry and direct brightness matching. The results show that the dimension of our internal color space corresponding with our achromatic response to stimuli is not a scale of brightness or lightness.

Faster Detection of "Darks" than "Brights" by Monkey Superior Colliculus Neurons.

Visual processing is segregated into ON and OFF channels as early as in the retina, and the superficial (output) layers of the primary visual cortex (V1) are dominated by neurons preferring dark stimuli. However, it is not clear how the timing of neural processing differs between "darks" and "brights" in general, especially in light of psychophysical evidence; it is also equally not clear how subcortical visual pathways that are critical for active orienting represent stimuli of positive (luminance increments) and negative (luminance decrements) contrast polarity. Here, we recorded from all visually-responsive neuron types in the superior colliculus (SC) of two male rhesus macaque monkeys. We presented a disk (0.51° radius) within the response fields (RFs) of neurons, and we varied, across trials, stimulus Weber contrast relative to a gray background. We also varied contrast polarity. There was a large diversity of preferences for darks and brights across the population. However, regardless of individual neural sensitivity, most neurons responded significantly earlier to dark than bright stimuli. This resulted in a dissociation between neural preference and visual response onset latency: a neuron could exhibit a weaker response to a dark stimulus than to a bright stimulus of the same contrast, but it would still have an earlier response to the dark stimulus. Our results highlight an additional candidate visual neural pathway for explaining behavioral differences between the processing of darks and brights, and they demonstrate the importance of temporal aspects in the visual neural code for orienting eye movements.SIGNIFICANCE STATEMENT Objects in our environment, such as birds flying across a bright sky, often project shadows (or images darker than the surround) on our retina. We studied how primate superior colliculus (SC) neurons visually process such dark stimuli. We found that the overall population of SC neurons represented both dark and bright stimuli equally well, as evidenced by a relatively equal distribution of neurons that were either more or less sensitive to darks. However, independent of sensitivity, the great majority of neurons detected dark stimuli earlier than bright stimuli, evidenced by a smaller response latency for the dark stimuli. Thus, SC neural response latency can be dissociated from response sensitivity, and it favors the faster detection of dark image contrasts.

Color appearance models CAM16, ZCAM and CAM20u for video applications

This work is devoted to the study of the possibility to use color perception models for processing streaming videos. The paper describes the principles of the control of image parameters which depend on the image adaptive properties. Methods for obtaining adaptive parameters such as brightness of adaptation, brightness of stimulus and brightness of background, as well as observation conditions are described. The CAM16 color perception model is accepted as the main one as well as the ZCAM and CAM20u models as the promising ones. The usability of color perception models is estimated, namely, the change of color rendering vector is assessed. It is shown that the chromaticity points that make up the color tone lines have a different nature of change – slope, shape. The estimates of the dependence of transmitted colors on lightness are provided. It is demonstrated that the lightness parameter is more non-linear character CAM20u as compared to the previous models.

Objective Measures of Immediate "Energizing" Effect of Light: Studies Review and Data Analysis.

While the energizing effect of light has been known since the early years of light therapy, its reliable detection using objective measures is still not well-established. This review aims to ascertain the immediate energizing effect of light and determine its best indicators. Sixty-four articles published before July 2022 were included in the review. The articles described 72 (sub-)studies performed in healthy individuals. Fourteen measures were analyzed. The analysis showed that light causes an energizing effect that can be best documented by measuring core (rectal) body temperature: the proportion of the studies revealing increasing, unchanging, and decreasing rectal temperature was 13/6/1. The second most suitable indicator was heart rate (10/22/1), which showed concordant changes with rectal temperature (a trend, seven mutual studies). There is no evidence from the reviewed articles that oxygen consumption, skin conductance, blood pressure, heart rate variability, non-rectal inner temperature (combined digestive, tympanic, and oral), skin temperature, or cortisol levels can provide light effect detection. Four other measures were found to be unsuitable as well but with less certainty due to the low number of studies (≤3): skin blood flow, noradrenaline, salivary alpha-amylase, and thyroid-stimulating hormone levels. On the other hand, light exposure had a noticeable effect on sympathetic nerve activity measured using microneurography; however, this measure can be accepted as a marker only tentatively as it was employed in a single study. The analysis took into account three factors—study limitation in design/analysis, use of light in day- or nighttime, and relative brightness of the light stimulus—that were found to significantly influence some of the analyzed variables. The review indicates that the energizing effect of light in humans can be reliably detected using rectal temperature and heart rate.

Cortical mechanisms of visual brightness.

SUMMARYThe primary visual cortex signals the onset of light and dark stimuli with ON and OFF cortical pathways. Here, we demonstrate that both pathways generate similar response increments to large homogeneous surfaces and their response average increases with surface brightness. We show that, in cat visual cortex, response dominance from ON or OFF pathways is bimodally distributed when stimuli are smaller than one receptive field center but unimodally distributed when they are larger. Moreover, whereas small bright stimuli drive opposite responses from ON and OFF pathways (increased versus suppressed activity), large bright surfaces drive similar response increments. We show that this size-brightness relation emerges because strong illumination increases the size of light surfaces in nature and both ON and OFF cortical neurons receive input from ON thalamic pathways. We conclude that visual scenes are perceived as brighter when the average response increments from ON and OFF cortical pathways become stronger.

Comparison of unifocal, flicker, and multifocal pupil perimetry methods in healthy adults.

To this day, the most popular method of choice for testing visual field defects (VFDs) is subjective standard automated perimetry. However, a need has arisen for an objective, and less time-consuming method. Pupil perimetry (PP), which uses pupil responses to onsets of bright stimuli as indications of visual sensitivity, fulfills these requirements. It is currently unclear which PP method most accurately detects VFDs. Hence, the purpose of this study is to compare three PP methods for measuring pupil responsiveness.Unifocal (UPP), flicker (FPP), and multifocal PP (MPP) were compared by monocularly testing the inner 60 degrees of vision at 44 wedge-shaped locations. The visual field (VF) sensitivity of 18 healthy adult participants (mean age and SD 23.7 ± 3.0 years) was assessed, each under three different artificially simulated scotomas for approximately 4.5 minutes each (i.e. stimulus was not or only partially present) conditions: quadrantanopia, a 20-, and 10-degree diameter scotoma.Stimuli that were fully present on the screen evoked strongest, partially present stimuli evoked weaker, and absent stimuli evoked the weakest pupil responses in all methods. However, the pupil responses in FPP showed stronger discriminative power for present versus absent trials (median d-prime = 6.26 ± 2.49, area under the curve [AUC] = 1.0 ± 0) and MPP performed better for fully present versus partially present trials (median d-prime = 1.19 ± 0.62, AUC = 0.80 ± 0.11).We conducted the first in-depth comparison of three PP methods. Gaze-contingent FPP had best discriminative power for large (absolute) scotomas, whereas MPP performed slightly better with small (relative) scotomas.

Visual Stimulation Induces Distinct Forms of Sensitization of On-Off Direction-Selective Ganglion Cell Responses in the Dorsal and Ventral Retina.

Experience-dependent modulation of neuronal responses is a key attribute in sensory processing. In the mammalian retina, the On-Off direction-selective ganglion cell (DSGC) is well known for its robust direction selectivity. However, how the On-Off DSGC light responsiveness dynamically adjusts to the changing visual environment is underexplored. Here, we report that On-Off DSGCs tuned to posterior motion direction [i.e. posterior DSGCs (pDSGCs)] in mice of both sexes can be transiently sensitized by prior stimuli. Notably, distinct sensitization patterns are found in dorsal and ventral pDSGCs. Although responses of both dorsal and ventral pDSGCs to dark stimuli (Off responses) are sensitized, only dorsal cells show the sensitization of responses to bright stimuli (On responses). Visual stimulation to the dorsal retina potentiates a sustained excitatory input from Off bipolar cells, leading to tonic depolarization of pDSGCs. Such tonic depolarization propagates from the Off to the On dendritic arbor of the pDSGC to sensitize its On response. We also identified a previously overlooked feature of DSGC dendritic architecture that can support dendritic integration between On and Off dendritic layers bypassing the soma. By contrast, ventral pDSGCs lack a sensitized tonic depolarization and thus do not exhibit sensitization of their On responses. Our results highlight a topographic difference in Off bipolar cell inputs underlying divergent sensitization patterns of dorsal and ventral pDSGCs. Moreover, substantial crossovers between dendritic layers of On-Off DSGCs suggest an interactive dendritic algorithm for processing On and Off signals before they reach the soma.SIGNIFICANCE STATEMENT Visual neuronal responses are dynamically influenced by the prior visual experience. This form of plasticity reflects the efficient coding of the naturalistic environment by the visual system. We found that a class of retinal output neurons, On-Off direction-selective ganglion cells, transiently increase their responsiveness after visual stimulation. Cells located in dorsal and ventral retinas exhibit distinct sensitization patterns because of different adaptive properties of Off bipolar cell signaling. A previously overlooked dendritic morphologic feature of the On-Off direction-selective ganglion cell is implicated in the cross talk between On and Off pathways during sensitization. Together, these findings uncover a topographic difference in the adaptive encoding of upper and lower visual fields and the underlying neural mechanism in the dorsal and ventral retinas.

밝기 척도를 위한 정신물리학 실험 방법 비교: 크기 추정법과 크기 생성법

The psychophysical experimental methods affect the observer’s evaluation because of the bias error. Therefore, it is necessary to design experiments properly. In this study, the experimental methods were compared for the brightness scale experiment, and the effect of stimuli setting was investigated. Magnitude estimation and magnitude production were used for comparison. There were three brightness scale experiments which have different stimuli settings. Each experiment had two phases. The magnitude estimation and magnitude production were conducted in each phase. The neutral patches were used for stimuli. In magnitude estimation, observers evaluated the brightness of test stimuli by number compared with reference. Magnitude production is the inverse of magnitude estimation. Observer was provided with a number representing the magnitude of a stimulus and adjusted the luminance of the stimulus to produce corresponding brightness with given number. As an overall result, there are large differences between magnitude estimation and magnitude production. As the luminance of test stimulus increases or decreases compared to reference stimulus, the difference between results of two methods is increased. The range of test stimuli and the number of stimuli also affect the result. As the range of test stimuli became wider and the number of test stimuli increased, the effect of the experimental method decreases in a mid-range. Therefore, to reduce the bias according to the psychophysical experimental method, it is necessary to set a wide stimulus range and the number of stimuli properly when conducting a brightness scale experiment.