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Radonjic A, Ding X, Krieger A, Aston S, Hurlbert AC, Brainard DH. Illumination discrimination in the absence of a fixed surface-reflectance layout. J Vis 2018; 18:11. [PMID: 29904786 PMCID: PMC5962298 DOI: 10.1167/18.5.11] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2017] [Accepted: 03/08/2018] [Indexed: 11/24/2022] Open
Abstract
Previous studies have shown that humans can discriminate spectral changes in illumination and that this sensitivity depends both on the chromatic direction of the illumination change and on the ensemble of surfaces in the scene. These studies, however, always used stimulus scenes with a fixed surface-reflectance layout. Here we compared illumination discrimination for scenes in which the surface reflectance layout remains fixed (fixed-surfaces condition) to those in which surface reflectances were shuffled randomly across scenes, but with the mean scene reflectance held approximately constant (shuffled-surfaces condition). Illumination discrimination thresholds in the fixed-surfaces condition were commensurate with previous reports. Thresholds in the shuffled-surfaces condition, however, were considerably elevated. Nonetheless, performance in the shuffled-surfaces condition exceeded that attainable through random guessing. Analysis of eye fixations revealed that in the fixed-surfaces condition, low illumination discrimination thresholds (across observers) were predicted by low overall fixation spread and high consistency of fixation location and fixated surface reflectances across trial intervals. Performance in the shuffled-surfaces condition was not systematically related to any of the eye-fixation characteristics we examined for that condition, but was correlated with performance in the fixed-surfaces condition.
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Affiliation(s)
- Ana Radonjic
- Department of Psychology, University of Pennsylvania, Philadelphia, PA, USA
| | - Xiaomao Ding
- Department of Psychology & Neuroscience Graduate Group, University of Pennsylvania, Philadelphia, PA, USA
| | - Avery Krieger
- Department of Psychology, University of Pennsylvania, Philadelphia, PA, USA
- Neurosciences Graduate Program, Stanford University, Stanford, CA, USA
| | - Stacey Aston
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
- Department of Psychology, Durham University, Durham, UK
| | - Anya C Hurlbert
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK
| | - David H Brainard
- Department of Psychology, University of Pennsylvania, Philadelphia, PA, USA
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Radonjic A, Pearce B, Aston S, Krieger A, Dubin H, Cottaris NP, Brainard DH, Hurlbert AC. Illumination discrimination in real and simulated scenes. J Vis 2016; 16:2. [PMID: 28558392 PMCID: PMC5024666 DOI: 10.1167/16.11.2] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2016] [Indexed: 11/24/2022] Open
Abstract
Characterizing humans' ability to discriminate changes in illumination provides information about the visual system's representation of the distal stimulus. We have previously shown that humans are able to discriminate illumination changes and that sensitivity to such changes depends on their chromatic direction. Probing illumination discrimination further would be facilitated by the use of computer-graphics simulations, which would, in practice, enable a wider range of stimulus manipulations. There is no a priori guarantee, however, that results obtained with simulated scenes generalize to real illuminated scenes. To investigate this question, we measured illumination discrimination in real and simulated scenes that were well-matched in mean chromaticity and scene geometry. Illumination discrimination thresholds were essentially identical for the two stimulus types. As in our previous work, these thresholds varied with illumination change direction. We exploited the flexibility offered by the use of graphics simulations to investigate whether the differences across direction are preserved when the surfaces in the scene are varied. We show that varying the scene's surface ensemble in a manner that also changes mean scene chromaticity modulates the relative sensitivity to illumination changes along different chromatic directions. Thus, any characterization of sensitivity to changes in illumination must be defined relative to the set of surfaces in the scene.
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Affiliation(s)
- Ana Radonjic
- Department of Psychology, University of Pennsylvania, Philadelphia, PA, ://www.sas.upenn.edu/~radonjic/
| | - Bradley Pearce
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne,
| | - Stacey Aston
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, ://staceyaston.com/
| | - Avery Krieger
- Department of Psychology, University of Pennsylvania, Philadelphia, PA,
| | - Hilary Dubin
- Department of Psychology, University of Pennsylvania, Philadelphia, PA,
| | - Nicolas P Cottaris
- Department of Psychology, University of Pennsylvania, Philadelphia, PA, ://color.psych.upenn.edu/people/nicolas-p-cottaris
| | - David H Brainard
- Department of Psychology, University of Pennsylvania, Philadelphia, PA, ://color.psych.upenn.edu/people/brainard
| | - Anya C Hurlbert
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, ://www.ncl.ac.uk/ion/staff/profile/anyahurlbert.html
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Radonjić A, Brainard DH. The nature of instructional effects in color constancy. J Exp Psychol Hum Percept Perform 2016; 42:847-65. [PMID: 26727021 DOI: 10.1037/xhp0000184] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The instructions subjects receive can have a large effect on experimentally measured color constancy, but the nature of these effects and how their existence should inform our understanding of color perception remains unclear. We used a factorial design to measure how instructional effects on constancy vary with experimental task and stimulus set. In each of 2 experiments, we employed both a classic adjustment-based asymmetric matching task and a novel color selection task. Four groups of naive subjects were instructed to make adjustments/selections based on (a) color (neutral instructions); (b) the light reaching the eye (physical spectrum instructions); (c) the actual surface reflectance of an object (objective reflectance instructions); or (d) the apparent surface reflectance of an object (apparent reflectance instructions). Across the 2 experiments we varied the naturalness of the stimuli. We find clear interactions between instructions, task, and stimuli. With simplified stimuli (Experiment 1), instructional effects were large and the data revealed 2 instruction-dependent patterns. In 1 (neutral and physical spectrum instructions) constancy was low, intersubject variability was also low, and adjustment-based and selection-based constancy were in agreement. In the other (reflectance instructions) constancy was high, intersubject variability was large, adjustment-based constancy deviated from selection-based constancy and for some subjects selection-based constancy increased across sessions. Similar patterns held for naturalistic stimuli (Experiment 2), although instructional effects were smaller. We interpret these 2 patterns as signatures of distinct task strategies-1 is perceptual, with judgments based primarily on the perceptual representation of color; the other involves explicit instruction-driven reasoning. (PsycINFO Database Record
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Affiliation(s)
- Ana Radonjić
- Department of Psychology, University of Pennsylvania
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Radonjić A, Cottaris NP, Brainard DH. Color constancy supports cross-illumination color selection. J Vis 2015; 15:13. [PMID: 26024460 DOI: 10.1167/15.6.13] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
We rely on color to select objects as the targets of our actions (e.g., the freshest fish, the ripest fruit). To be useful for selection, color must provide accurate guidance about object identity across changes in illumination. Although the visual system partially stabilizes object color appearance across illumination changes, how such color constancy supports object selection is not understood. To study how constancy operates in real-life tasks, we developed a novel paradigm in which subjects selected which of two test objects presented under a test illumination appeared closer in color to a target object presented under a standard illumination. From subjects' choices, we inferred a selection-based match for the target via a variant of maximum likelihood difference scaling, and used it to quantify constancy. Selection-based constancy was good when measured using naturalistic stimuli, but was dramatically reduced when the stimuli were simplified, indicating that a naturalistic stimulus context is critical for good constancy. Overall, our results suggest that color supports accurate object selection across illumination changes when both stimuli and task match how color is used in real life. We compared our selection-based constancy results with data obtained using a classic asymmetric matching task and found that the adjustment-based matches predicted selection well for our stimuli and instructions, indicating that the appearance literature provides useful guidance for the emerging study of constancy in natural tasks.
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Foster DH, Amano K, Nascimento SMC. Time-lapse ratios of cone excitations in natural scenes. Vision Res 2015; 120:45-60. [PMID: 25847405 DOI: 10.1016/j.visres.2015.03.012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Revised: 03/23/2015] [Accepted: 03/27/2015] [Indexed: 10/23/2022]
Abstract
The illumination in natural environments varies through the day. Stable inferences about surface color might be supported by spatial ratios of cone excitations from the reflected light, but their invariance has been quantified only for global changes in illuminant spectrum. The aim here was to test their invariance under natural changes in both illumination spectrum and geometry, especially in the distribution of shadows. Time-lapse hyperspectral radiance images were acquired from five outdoor vegetated and nonvegetated scenes. From each scene, 10,000 pairs of points were sampled randomly and ratios measured across time. Mean relative deviations in ratios were generally large, but when sampling was limited to short distances or moderate time intervals, they fell below the level for detecting violations in ratio invariance. When illumination changes with uneven geometry were excluded, they fell further, to levels obtained with global changes in illuminant spectrum alone. Within sampling constraints, ratios of cone excitations, and also of opponent-color combinations, provide an approximately invariant signal for stable surface-color inferences, despite spectral and geometric variations in scene illumination.
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Affiliation(s)
- David H Foster
- School of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL, UK.
| | - Kinjiro Amano
- School of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL, UK.
| | - Sérgio M C Nascimento
- Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal.
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Morgenstern Y, Geisler WS, Murray RF. Human vision is attuned to the diffuseness of natural light. J Vis 2014; 14:14.9.15. [PMID: 25139864 DOI: 10.1167/14.9.15] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
All images are highly ambiguous, and to perceive 3-D scenes, the human visual system relies on assumptions about what lighting conditions are most probable. Here we show that human observers' assumptions about lighting diffuseness are well matched to the diffuseness of lighting in real-world scenes. We use a novel multidirectional photometer to measure lighting in hundreds of environments, and we find that the diffuseness of natural lighting falls in the same range as previous psychophysical estimates of the visual system's assumptions about diffuseness. We also find that natural lighting is typically directional enough to override human observers' assumption that light comes from above. Furthermore, we find that, although human performance on some tasks is worse in diffuse light, this can be largely accounted for by intrinsic task difficulty. These findings suggest that human vision is attuned to the diffuseness levels of natural lighting conditions.
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Affiliation(s)
- Yaniv Morgenstern
- Department of Psychology, University of Minnesota, Minneapolis, MN, USA
| | - Wilson S Geisler
- Department of Psychology and Center for Perceptual Systems, University of Texas at Austin, Austin, TX, USA
| | - Richard F Murray
- Department of Psychology and Centre for Vision Research, York University, Toronto, ON, Canada
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Maniatis LM. A theory divided: current representations of the anchoring theory of lightness contradict the original's core claims. Vision Res 2014; 102:89-92. [PMID: 24796510 DOI: 10.1016/j.visres.2014.04.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2014] [Revised: 03/30/2014] [Accepted: 04/14/2014] [Indexed: 11/29/2022]
Abstract
The anchoring theory of lightness perception (Gilchrist et al., Psychological Review 106 (1999) 795-834) has been described as one of the most successful approaches to lightness perception. Yet, not only does the original proposal contain serious gaps and inconsistencies, later expressions of the theory, which was never formally revised, seem to contradict the original claims while leaving the gaps unresolved. These problems call into question the theory's viability.
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Madigan SC, Brainard DH. Scaling measurements of the effect of surface slant on perceived lightness. Iperception 2014; 5:53-72. [PMID: 25165517 PMCID: PMC4130508 DOI: 10.1068/i0608] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Revised: 01/13/2014] [Indexed: 11/27/2022] Open
Abstract
The light reflected from an object depends on its reflectance, the illumination, and the pose of the object within the scene. An observer is called lightness constant if the perceived reflectance (lightness) of achromatic objects stays the same despite variation in object-extrinsic factors such as illumination and pose. Here, we used a dissimilarity scaling task to measure lightness constancy as the intensity of the illuminant and the slant of test surfaces were varied. Across two experiments, we had observers rate the dissimilarity of flat grayscale test stimulus pairs. The test stimuli were real illuminated surfaces, not computer simulations. Each test stimulus was seen in its own illuminated chamber, with the two chambers viewed side by side. We varied test surface reflectance, chamber illumination intensity, and the slant of the test in relation to the single light source in each chamber. Data were analyzed using nonmetric multidimensional scaling. The data were well-described by a one-dimensional perceptual representation. This representation was consistent across observers, revealed partial lightness constancy with respect to a change in illumination intensity, and no lightness constancy with respect to changes in surface slant. An additional experiment using a matching procedure and the same stimulus set, however, revealed moderate constancy with respect to changes in surface slant. The difference in results between the two methods is interesting, but not understood.
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Affiliation(s)
- Sean C Madigan
- Department of Psychology, University of Pennsylvania, 3401 Walnut Street, Philadelphia, PA; e-mail:
| | - David H Brainard
- Department of Psychology, University of Pennsylvania, 3401 Walnut Street, Philadelphia, PA; e-mail:
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