Asymmetric Matching Research Articles

Color constancy supports cross-illumination color selection.

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.

On asymmetric matching between sets

A comparison of two objects may be viewed as an attempt to determine the degree to which they are similar or different in a given sense. Defining a good measure of proximity, or else similarity or dissimilarity between objects is very important in practical tasks as well as theoretical achievements. Each object is usually represented as a point in Cartesian coordinates, and therefore the distance between points reflects similarities between respective objects. In general, the space is assumed to be Euclidean, and a distance between points assigns a nonnegative number. From another point of view the concept of symmetry underlies essentially all theoretical treatments of similarity. Tversky (1977) provided empirical evidence of asymmetric similarities and argued that similarity should not be treated as a symmetric relation. According to Tversky’s consideration, an object is described by sets of features instead of geometric points in a metric space. In this paper we propose a new measure of remoteness between sets of nominal values. Instead of considering distance between two sets, we introduce the measures of perturbation type 1 of one set by another. The consideration is based on set-theoretic operations and the proposed measure describes changes of the second set after adding the first set to it, or vice versa. The measure of sets’ perturbation returns a value from [0,1], and it must be emphasized that this measure is not symmetric in general. The difference between 1 and the sum of these two measures of perturbation of a pair of sets can be understood as Jaccard’s extended similarity measure. In this paper several mathematical properties of the measure of sets’ perturbation are studied, and interpretation of proximity is explained by the comparison of selected measures.

An Asymmetric Matching Method for a Robust Binary Audio Fingerprinting

Audio fingerprinting has been successfully applied for the problems associated with the protection of intellectual property, management of large database and indexation of content. For a reliable fingerprinting system, improving fingerprint matching accuracy is crucial. In this letter, we try to improve a binary audio fingerprint matching performance by utilizing auxiliary information which is discarded while extracting fingerprint bits. Since it is not feasible to store all the auxiliary information in the fingerprint DB, we only utilize the auxiliary information obtained while extracting fingerprints from the input unknown audio. We call the proposed method an asymmetric fingerprint matching, since the auxiliary information is available only in one side. Experimental results show that the proposed asymmetric matching method is effective in improving fingerprint matching performance over the conventional Hamming distance.

Asymmetric group loans, non-assortative matching and adverse selection

This paper shows that an asymmetric group debt contract, where one borrower co-signs for another, but not vice versa, leads to heterogeneous matching. The analysis suggests that micro finance organizations can achieve the first best by offering asymmetric group contracts.

Lightness constancy and its link with cone contrast

The link between chromatic constancy (compensation for hue and saturation shifts) and lightness constancy (compensation for a change in surface reflectance) was tested theoretically by computing cone contrasts and by asymmetric matching experiments. The effect of a thin achromatic line (a frame) around the test sample was tested empirically. When the samples were outlined by the frame, lightness constancy was increased and chromatic constancy reduced (p<0.001). Changes in luminance are more likely to be compensated when the luminance contrast edge around the test stimulus is disturbed as with the addition of an achromatic frame.

A Spatial Division Clustering Method and Low Dimensional Feature Extraction Technique Based Indoor Positioning System

Indoor positioning systems based on the fingerprint method are widely used due to the large number of existing devices with a wide range of coverage. However, extensive positioning regions with a massive fingerprint database may cause high computational complexity and error margins, therefore clustering methods are widely applied as a solution. However, traditional clustering methods in positioning systems can only measure the similarity of the Received Signal Strength without being concerned with the continuity of physical coordinates. Besides, outage of access points could result in asymmetric matching problems which severely affect the fine positioning procedure. To solve these issues, in this paper we propose a positioning system based on the Spatial Division Clustering (SDC) method for clustering the fingerprint dataset subject to physical distance constraints. With the Genetic Algorithm and Support Vector Machine techniques, SDC can achieve higher coarse positioning accuracy than traditional clustering algorithms. In terms of fine localization, based on the Kernel Principal Component Analysis method, the proposed positioning system outperforms its counterparts based on other feature extraction methods in low dimensionality. Apart from balancing online matching computational burden, the new positioning system exhibits advantageous performance on radio map clustering, and also shows better robustness and adaptability in the asymmetric matching problem aspect.

Do asymmetric color matches predict cross-illumination color selection?

Do asymmetric color matches predict cross-illumination color selection?

Chromatic settings and the structural color constancy index

Color constancy is usually measured by achromatic setting, asymmetric matching, or color naming paradigms, whose results are interpreted in terms of indexes and models that arguably do not capture the full complexity of the phenomenon. Here we propose a new paradigm, chromatic setting, which allows a more comprehensive characterization of color constancy through the measurement of multiple points in color space under immersive adaptation. We demonstrated its feasibility by assessing the consistency of subjects' responses over time. The paradigm was applied to two-dimensional (2-D) Mondrian stimuli under three different illuminants, and the results were used to fit a set of linear color constancy models. The use of multiple colors improved the precision of more complex linear models compared to the popular diagonal model computed from gray. Our results show that a diagonal plus translation matrix that models mechanisms other than cone gain might be best suited to explain the phenomenon. Additionally, we calculated a number of color constancy indices for several points in color space, and our results suggest that interrelations among colors are not as uniform as previously believed. To account for this variability, we developed a new structural color constancy index that takes into account the magnitude and orientation of the chromatic shift in addition to the interrelations among colors and memory effects.

Systematic violations of von Kries rule reveal its limitations for explaining color and lightness constancy

Cone contrast remains constant, when the same object/background is seen under different illuminations-the von Kries rule [Shevell, Vis. Res. 18, 1649 (1978)]. Here we explore this idea using asymmetric color matching. We find that von Kries adaptation holds, regardless of whether chromatic constancy index is low or high. When illumination changes the stimulus luminance (reflectance), lightness constancy is weak and matching is dictated by object/background luminance contrast. When this contrast is masked or disrupted, lightness constancy mechanisms are more prominent. Thus von Kries adaptation is incompatible with lightness constancy, suggesting that cortical mechanisms must underlie color constancy, as expected from neurophysiological studies [Zeki, Nature 284, 412 (1980); Wild, Nature 313, 133 (1985)].

Kirschmann’s Fourth Law

Kirschmann’s Fourth Law states that the magnitude of simultaneous color contrast increases with the saturation of the inducing surround, but that the rate of increase reduces as saturation increases. Others since Kirschmann have agreed and disagreed. Here we show that the form of the relationship between simultaneous color contrast and inducer saturation depends on the method of measurement. Functions were measured by four methods: (i) asymmetric matching with a black surround, (ii) asymmetric matching with a surround metameric to equal energy white, (iii) dichoptic matching, and (iv) nulling an induced sinusoidal modulation. Results from the asymmetric matching conditions agreed with Kirschmann, whereas results from nulling and from dichoptic matching showed a more linear increase in simultaneous contrast with the saturation of the inducer. We conclude that the method certainly affects the conclusions reached, and that there may not be any “fair” way of measuring simultaneous contrast.

Naming versus matching and the stability of unique hues

It is known that there is a distortion of hue and saturation in the peripheral visual field. In a previous study, when an asymmetric matching paradigm was used, four hues in the blue, red, yellow and green regions of colour space were unchanged and these were referred to as peripherally invariant (Parry et al., J Opt Soc Am A, 23, 2006, 1586). Three of these invariant hues were similar to unique blue, red and yellow. However, for most observers there was a marked difference between unique and invariant green. To investigate this apparent paradox, we have measured unique hues using a range of eccentricities and colourimetric purities. An asymmetric matching and a 4-AFC paradigm were used to establish peripherally invariant and unique hues, respectively. In the asymmetric matching task the observer matched a peripheral spot with a para-foveal spot, for 24 different hues at 18° eccentricity. In the 4-AFC paradigm, 41 hues were presented 20 times at three purities (0.5, 0.75 and 1.0) and three eccentricities (18°, 10° and 1°). The observer had to name the hues as red, blue, green or yellow. Unique hues were found to be constant with eccentricity and purity. The unique green, established with 4-AFC, was found to differ from the invariant green, determined using the matching task. However, red, blue and yellow invariant hues correspond well with unique hues. The data suggest that different mechanisms mediate the matching of green compared with the identification of unique hues. This is similar to the difference between detection and discrimination of spectral stimuli: the detection process is dominated by the cone opponent mechanisms and is most sensitive, whereas more central processes, serving unique hues, influence discrimination.

Colour constancy as measured by least dissimilar matching

Although asymmetric colour matching has been widely used in experiments on colour constancy, an exact colour match between objects lit by different chromatic lights is impossible to achieve. We used a modification of this technique, instructing our observers to establish the least dissimilar pair of differently illuminated coloured papers. The stimulus display consisted of two identical sets of 22 Munsell papers illuminated independently by neutral, yellow, blue, green and red lights. The lights produced approximately the same illuminance. Four trichromatic observers participated in the experiment. The proportion of exact matches was evaluated. When both sets of papers were lit by the same light, the exact match rate was 0.92, 0.93, 0.84, 0.78 and 0.76 for the neutral, yellow, blue, green and red lights, respectively. When one illumination was neutral and the other chromatic, the exact match rate was 0.80, 0.40, 0.56 and 0.32 for the yellow, blue, green and red lights, respectively. When both lights were chromatic, the exact match rate was found to be even poorer (0.30 on average). Yet, least dissimilar matching was found to be rather systematic. Particularly, a statistical test showed it was symmetric and transitive. The exact match rate was found to be different for different papers, varying from 0.99 (black paper) to 0.12 (purple paper). Such a variation can hardly be expected if observers' judgements were based on an illuminant estimate. We argue that colour constancy cannot be achieved for all the reflecting objects because of mismatching of metamers. We conjecture that the visual system might have evolved to have colour constant perception for some ecologically valid objects at a cost of colour inconstancy for other types of objects.

Variability in symmetric and asymmetric colour matching

Variability in symmetric and asymmetric colour matching

Categorical color constancy for simulated surfaces

Color constancy is the ability to perceive constant surface colors under varying lighting conditions. Color constancy has traditionally been investigated with asymmetric matching, where stimuli are matched over two different contexts, or with achromatic settings, where a stimulus is made to appear gray. These methods deliver accurate information on the transformations of single points of color space under illuminant changes, but can be cumbersome and unintuitive for observers. Color naming is a fast and intuitive alternative to matching, allowing data collection from a large portion of color space. We asked observers to name the colors of 469 Munsell surfaces with known reflectance spectra simulated under five different illuminants. Observers were generally as consistent in naming the colors of surfaces under different illuminants as they were naming the colors of the same surfaces over time. The transformations in category boundaries caused by illuminant changes were generally small and could be explained well with simple linear models. Finally, an analysis of the pattern of naming consistency across color space revealed that largely the same hues were named consistently across illuminants and across observers even after correcting for category size effects. This indicates a possible relationship between perceptual color constancy and the ability to consistently communicate colors.

Stated beliefs versus inferred beliefs: A methodological inquiry and experimental test

Belief elicitation in game experiments may be problematic if it changes game play. We experimentally verify that belief elicitation can alter paths of play in a two-player repeated asymmetric matching pennies game. Importantly, this effect occurs only during early periods and only for players with strongly asymmetric payoffs, consistent with a cognitive/affective effect on priors that may serve as a substitute for experience. These effects occur with a common scoring rule elicitation procedure, but not with simpler (unmotivated) statements of expected choices of opponents. Scoring rule belief elicitation improves the goodness of fit of structural models of belief learning, and prior beliefs implied by such models are both stronger and more realistic when beliefs are elicited than when they are not. We also find that “inferred beliefs” (beliefs estimated from past observed actions of opponents) can predict observed actions better than the “stated beliefs” from scoring rule belief elicitation.

"Symmetric and asymmetric matching of joint presentations": Correction to Luce (2004).

"Symmetric and asymmetric matching of joint presentations": Correction to Luce (2004).

Distinct Mechanisms Mediate Visual Detection and Identification

A core organizing principle for studies of the brain is that distinct neural pathways mediate distinct behavioral tasks [1, 2]. When two related tasks are mediated by a common pathway, studies of one are likely to generalize to the other. Here, we test whether performance on two laboratory tasks that model object detection and identification are mediated by common mechanisms of visual adaptation. Although both tasks rely on the luminance pattern in images, their demands on visual processing are quite different. Object detection requires discriminating image luminance differences associated with the light reflected from adjacent objects. To encode these differences reliably, neurons adapt their limited dynamic range to prevailing viewing conditions [3-6]. Object identification, on the other hand, demands a fixed response to light reflected from an object independent of illumination [7]. We compared performance in discrimination and identification tasks for simulated surfaces. In striking contrast to studies with less structured contexts, we found clear evidence that distinct processes mediate judgments in the two tasks. These results challenge models that account for perceived lightness entirely through the action of image-encoding mechanisms.

Kirschmann's fourth law

Kirschmann's Fourth Law states that the magnitude of simultaneous color contrast increases with the saturation of the inducing surround, but that the rate of increase reduces as saturation increases. Others since Kirschmann have agreed and disagreed. Here we show that the form of the relationship between simultaneous color contrast and inducer saturation depends on the method of measurement. Functions were measured by four methods: (i) asymmetric matching with a black surround, (ii) asymmetric matching with a surround metameric to equal energy white, (iii) dichoptic matching, and (iv) nulling an induced sinusoidal modulation. Results from the asymmetric matching conditions agreed with Kirschmann, whereas results from nulling and from dichoptic matching showed a more linear increase in simultaneous contrast with the saturation of the inducer. We conclude that the method certainly affects the conclusions reached, and that there may not be any fair way of measuring simultaneous contrast.

Factors of colour perception constancy: Contrast and background adaptation

Colour constancy is the ability of the human visual system to comprehend the constant colour of an object with no regard to changes in the illumination spectrum. Each year witnesses the appearance of new scientific works in various countries. The works touch upon different aspects of the phenomenon. Although scientific research has been conducted for many years, there is no recognised theory explaining the mechanisms that are decisive for colour constancy. The aim of the present work was to establish the influence of contrast, adaptation and background structure upon colour constancy.All experiments were performed with the application of asymmetric matching. Five subjects took part in the experiments. Colour constancy was examined by performing experiments in three cycles. The test illuminants were two Planckian illuminants, standard illuminant A (u’= 0.2559, v’ = 0.5243), illuminant S (u’= 0.1744, v’= 0.3923) and illuminants r (u’/v’ = 0.2618/0.4533), g (u’/v’ = 0.1517/0.4667), v (u’/v’ = 0.2116/0.3766), y (u’/v’ = 0.1939/0.5180. The first set of 7/4 (value – 7/, chroma – /4) of 10 Munsell samples served as test stimuli in the experiments of the second cycle. Being 2° in size, they were generated in the centre of the monitor. The samples were surrounded by a neutral background, sized N7 20° (N meaning the colour being neutral, with the value of 7). Around the neutral background, subject of the experiment saw the non-radiating part of the screen, which we called the „black surround“ (Fig. 1). In the second set of the experiment, the subjects observed the stimuli througha cardboard tube (Fig. 2). Neutral N7 Munsell samples and a set of 7/4 (value – 7/, chroma – /4) of 10 Munsell samples served as test stimuli in the experiments of the third cycle.Colour constancy is quantitively evaluated on the basis of the Brunswik Ratio (BR) (Troost and de Weert, 1991). Higher values of BR were associated with longer adaptation periods, but only when a larger background was used (second cycle of experiments (Fig. 7)). Supplementary experiments showed that the changes in colour appearance were related to a slight shift in the perceived colour of the background. The timing of the colour shifts was modelled in terms of cone opponent responses.Our conclusions are:1. When stimuli are exposed for a short period of time (1 s), partial colour constancy takes place. It does not change (or changes insignificantly) when the stimulus is observed for a longer time (5 and 30 s). Such colour constancy is determined by fast processes which confirm the influence of simultaneous contrast on colour constancy.2. When the background is small, the influence of adaptation on colour constancy is little, even it the observation time is long (5 or 30 s).3. When the background fills the entire field of vision, adaptation results in a high colour constancy perception.

Effect of a yellow filter on brightness evaluated by asymmetric matching: measurements and predictions

We found that yellow filters reduce the mean brightness of a set of coloured samples significantly less with blue surrounds than with black, achromatic or yellow ones, in comparison with the naked eye and less than a yellow surround in comparison with a luminance-matched grey filter. The predictions of Hunt's model and Guth's ATD95 agree with these results. The yellow filter is actually capable of significantly increasing the brightness with the blue surround both in comparison with the naked eye (although only for our younger observer) and with the neutral filter. We show that in some samples the yellow filter causes global response increments in the chromatic mechanisms that compensate the response reduction in the achromatic mechanism, resulting in increased brightness. Although global chromatic response increments may arise from any chromatic mechanism, the blue–yellow mechanism determines in most cases the final result, even when the response of the red–green mechanism decreases.