VSS, May 13-18

Color, Light and Materials: Mechanisms and models of visual processing

Talk Session: Monday, May 16, 2022, 10:45 am – 12:15 pm EDT, Talk Room 2
Moderator: David Brainard, U Penn

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Talk 1, 10:45 am, 42.21

Color appearance match can be performed among custom-made five-dimensional metamers

Akari Kagimoto1 (), Katsunori Okajima1; 1Yokohama National University, JAPAN

 We previously reported that color appearance between different devices can be perfectly matched when the spectral distributions are equal whereas metameric color matching mostly failed. In this study, we prepared custom-made 5D metamers whose stimulus values of three-types of cones, rod, and melanopsin cells were the same as those of reference stimuli for individuals, and we tested whether color appearances of the test and reference stimuli are matched or not. To derive spectral sensitivity functions considering individual optical characteristics, we developed an equipment consisting of an integrated sphere and 10 types of LED elements, and measured several parameters determining spectral sensitivity of each participant under a “2-degree visual angle” condition for estimating individual cone spectral sensitivities, and a “2-degree visual angle with a circular mask of 1.25-degree visual angle” condition for estimating individual melanopsin and rod spectral sensitivities. Next, we set up an equipment with a multi spectral light source, and conducted an experiment in which the color appearance of nine kinds of metamer stimulus pairs were compared. Results show that the color appearance of 5D metamers including rod and melanopsin based on CIE spectral sensitivity functions could not be matched. However, color appearances of custom-made 5D metamers were the same as the reference stimuli even if the spectral distributions were different. These results indicate that individual calibration of spectral sensitivities is essential for precise color appearance evaluation. In addition, the results show that color appearances of custom-made 3D metamers for cones with different rod or melanopsin response were not identical, suggesting that rod and melanopsin cells contribute to color appearance at the central two degrees.

Acknowledgements: JSPS KAKENHI JP19J15530 and JP18H04111

Talk 2, 11:00 am, 42.22

Perceptual scaling of suprathreshold chromatic increments and decrements using Maximum Likelihood Difference Scaling

Yangyi Shi1 (), Rhea T. Eskew, Jr.1; 1Psychology Department, Northeastern University

Color contrast provides rich information about the world. In the present study, we produce perceptual scales for suprathreshold color contrasts of different major directions in cone contrast space. In particular, we compared cone isolating increments and decrements (L±, M±, S±), as well as achromatic increments and decrements (A±), equiluminant R and G, and increments and decrements along the color direction that modulates L and M cones equally with S cones unmodulated (L=M±). The method we used is Maximum Likelihood Difference Scaling (MLDS; Knoblauch & Maloney, 2008), a fast way of producing interval perceptual scales. For each color direction, seven contrast values were linearly sampled between the observer’s threshold and maximum contrast of the monitor. In each trial, four practiced observers compared two pairs of 1.5°x1.5° squares. The squares were flashed for 0.33 seconds. All four squares were of the same color direction but with four different contrasts. Observers chose the pair in which the two squares looked more different, or in other words, the pair that had a larger perceptual interval. To traverse all interval pairs generated by 7 contrast values, 35 trials were measured for each color direction in a given session, and repeated three times over sessions. The MLDS results are nicely fit with a Michaelis-Menten function, producing a decelerating curve shape for each tested color direction; this function is an estimate of the contrast transducer that may underlie contrast discrimination (Foley & Legge, 1981). The general pattern was slightly more curvature for increments than decrements in most color directions. Achromatic increment scales are the most nonlinear of all directions we examined, consistent with processing by a mechanism summing cone signals that are processed less linearly for increments than decrements. Our results indicate that MLDS is a good method for perceptual scaling of suprathreshold chromatic increments and decrements.

Acknowledgements: NSF BCS-1921771

Talk 3, 11:15 am, 42.23

Do identical percepts from multiple ambiguous neural representations depend on the suppressed competing representations?

Emily Slezak1 (), Steven K Shevell2; 1University of Washington, 2University of Chicago

Perceptual resolution for multiple identical dichoptic stimuli will result at any given moment in some neural representations being dominant, so perceived by the observer, and others being suppressed. Often, a suppressed representation will become dominant (and the prior dominant representation will become suppressed) simultaneously for all the dichoptic stimuli so the observer perceives all stimuli as identical (Kovács et al., 1996), a phenomenon referred to as ‘grouping’. It is unclear, however, if the dominant and the suppressed neural representations must both be identical for every stimulus in view for grouping to occur; experiments here tested whether grouping is dependent on both representations. METHODS Stimuli were two dichoptic chromatic discs presented using interocular-switch rivalry to isolate a binocular level of neural competition (Slezak & Shevell, 2018). The possible percepts at each retinotopic location differed among conditions, though a grouped percept of both discs appearing the same color always was possible. A control condition had matched competing chromatic representations at both locations (e.g., both discs dichoptic red/green); a ‘mismatch condition’ had one matching and one different competing chromatic representation in the two locations (e.g., one disc dichoptic red/green and one dichoptic red/purple), so that only one possible percept could be grouped (e.g., red/red). RESULTS/CONCLUSIONS All five observers showed significant grouping when both dichoptic discs had identical possible percepts (control condition) while only one observer showed significant grouping when the discs had different alternative percepts and thus different neural competition at each location (mismatch condition). Further, four of five observers perceived grouped colors significantly more often when there was identical competition in both locations (control condition) than when it was not identical (mismatch condition). This indicates that grouping occurred significantly more often when the dominant and the suppressed representations were each identical, supporting the theory that fully identical competing neural representations drive grouping.

Acknowledgements: Funding: NIH grant EY-026618

Talk 4, 11:30 am, 42.24

Optimal sensitivity to a combination of color and luminance contrast between background and stimulus assessed with pupil orienting responses

Marnix Naber1 (), Saskia Imhof2, Giorgio Porro3, Brendan Portengen4; 1Experimental Psychology, Helmholtz Institute, Utrecht University, The Netherlands, 2Ophthalmology Department, University Medical Center Utrecht, The Netherlands

The visual system contains biases in sensitivity for selective features such as spatial frequencies around 3 cycles per degree and patterns with cardinal orientations. We hypothesized that a similar bias in perceptual sensitivity should exist for a selective combination of luminance- and color-contrast between a stimulus and its surrounding background. To find an optimal trade-off, we measured pupil orienting responses using gaze-contingent flicker pupil perimetry (gcFPP). We presented observers a sequence of stimuli, each flickering at 2 Hz for 5 seconds at a different angle and eccentricity across the visual field. To alter color contrast at the expense of luminance contrast with a stimulus, we systematically varied the color (dark blue or yellow) and luminance (0-45%) of the background. The stimulus-on color was complementary to the background (bright yellow or blue) and fixed at 100% luminance. To test local effects of luminance and color contrast changes, we also varied the stimulus-off color, being either black or displaying the background’s color. The amplitude of constrictions and dilations in response to stimulus on- and off-sets served as a proxy of visual sensitivity. We found an optimal pupil response amplitude for both yellow and blue stimuli presented on a background with 25-35% luminance. The amplitude decreased by 25% when displaying a colorless, black background. Furthermore, a black stimulus-off region amid a colored background evoked 23% stronger responses than a colored stimulus-off region. Modelling pupillary amplitudes as a reflection of the Euclidian distance between background and stimulus color in CIE LAB space suggested a sensitivity ratio of 0.8 for color- versus luminance-contrast. These findings imply (1) that a preferred trade-off between luminance- and color-contrast exists, (2) that global (not local) color contrast almost equally adds to visual sensitivity as luminance contrast does, and (3) that gcFPP efficiently measures color sensitivities.

Acknowledgements: This work was supported by a grant from UitZicht (#2017-18; ODAS foundation #2017-03; the Rotterdamse Stichting Blindenbelangen #B20170004 and #2018-10; the F.P. Fischer Foundation #170511), and a grant from the Janivo Foundation (#2017170).

Talk 5, 11:45 am, 42.25

Reconstructing attended and unattended colors from human scalp electroencephalography

Angus Chapman1, Viola Störmer2; 1University of California San Diego, 2Dartmouth College

Human electroencephalography (EEG) studies have shown that attention enhances relevant over irrelevant visual features (e.g., Andersen et al., 2013). Such amplitude modulations have been a major focus of feature-based attention research, alongside recent studies showing that the spatial pattern of scalp-recorded EEG activity conveys critical information about different stimuli. To date, the majority of these studies have focused on decoding visual-spatial features (location, orientation). Here, we test whether color—a non-spatial feature—can be reconstructed from the scalp activity pattern using steady-state visual evoked potentials (SSVEPs) and inverted encoding modeling (IEM). Furthermore, we test how these color reconstructions vary across different types of feature-based attention tasks. Participants (N=17) performed two color-based attention tasks: 1) a non-competitive task, in which they monitored a single array of colored dots to detect a brief interval of coherent motion; 2) a selective attention task in which participants focused on target-colored dots among distractors to detect a brief luminance decrease. In the selective task, the target and distractor colors were either distinct (180° away on a CIELab colorwheel) or similar (63° away). Stimuli flickered at different frequencies to elicit separable SSVEPs that we used to generate color-selective response profiles based on their spatially distributed patterns. Across both tasks, we found that information about the target and distractor colors was reliably recovered from single trials with IEMs, confirming the usefulness of this technique for investigating feature representations. Model-based reconstructions in the selective attention task were stronger for more distinct colors, suggesting that perceptually similar features might elicit less informative SSVEP signals due to greater overlap in the neural populations that encode them. Broadly, our results demonstrate that SSVEPs along with IEMs can be used to investigate non-spatial visual features that may not be as well represented as spatial information in event-related potentials or alpha-band signals.

Talk 6, 12:00 pm, 42.26

Isolating Saturation and Hue for Equally Bright Colors

Hao Xie1 (), Mark D. Fairchild1; 1Rochester Institute of Technology

The three fundamental attributes of color, i.e., brightness, hue, and saturation, have not found their singly corresponding physical correlates. Changes along one physical dimension also interfere with other color attributes. One example is the Helmholtz–Kohlrausch (H-K) effect, where an increase in saturation with constant hue and luminance also increases brightness as one manifestation of the luminance versus brightness discrepancy. Our recent work has collected Ralph Evans’s zero-grayness luminance to equalize brightness and thus incorporate the H-K effect. Furthermore, MacAdam’s optimal colors (as an interpolation handle) were found to be highly correlated with those equally bright colors. In this work, by navigating along the optimal color surface, the interaction between saturation and hue was further investigated. The stimulus set included five Munsell principal hues R (red) / Y (yellow) / G (green) / B (blue) / P (purple), which had dominant wavelength of 629, 576, 512, 485, 560 nm (the complementary), respectively, at different excitation purities. Observers (N = 14) were asked to first perform partition scaling for saturation given the neutral and one max-saturation hue as anchors. 50% midpoints and further 25% & 75% levels of saturation were collected. In the second part, the saturation scales across max-saturation hues were normalized relative to the max-saturation red via magnitude estimation by the same observers. The results suggest that 1) saturation is approximately linearly related to excitation purity with increasing slopes for Y < R/P < B < G; 2) when saturation is equated, the hue contribution in the H-K effect, quantified by B/L ratio, is ordered as Y/G < B < P/R; 3) the CIECAM02 and CIELAB saturation metrics either did not correlate with the saturation scales linearly or was not isotropic in hue. This work provides more solid scaffolds to develop independent color scales for each attribute.