Biomedical subjects

Laurence T Maloney

Publications and source records attributed to Laurence T Maloney.

At least 19 recordsLinked to original sources

PubMed2006

Where are kin recognition signals in the human face?

We report two experiments that aimed to determine where in the face the cues that signal kinship fall. In both experiments, participants were shown 30 pairs of photographs of children's faces. Half of the pairs portrayed siblings and half did not. The 220 participants were asked to judge whether each pair of photographs portrayed siblings. We measured the effect on kin recognition performance of masks that covered the upper half or the lower half of the face (Experiment 1) and the eye region or the mouth region (Experiment 2). In Experiment 1, we found that the signal detection estimate of performance d' decreased only 5.3% (ns) when the lower face was masked but by more than 65% when the upper face was masked. We tested whether the combination of kinship information from the two halves of the face can be treated as optimal combination of independent cues and found that it could be. In Experiment 2, we found that masking the eye region led to only a 20% reduction (ns) in performance whereas masking the mouth region led to a nonsignificant increase in performance. We also found that the eye region contains only slightly more information about kinship than the upper half of the face outside of the eye region.

Adult↗

PubMed2006

Color constancy and hue scaling.

In this study, we used a hue scaling technique to examine human color constancy performance in simulated three-dimensional scenes. These scenes contained objects of various shapes and materials and a matte test patch at the center of the scene. Hue scaling settings were made for test patches under five different illuminations. Results show that subjects had nearly stable hue scalings for a given test surface across different illuminants. In a control experiment, only the test surfaces that belonged to one illumination condition were presented, blocked in front of a black background. Surprisingly, the hue scalings of the subjects in the blocked control experiment were not simply determined by the color codes of the test surface. Rather, they depended on the sequence of previously presented test stimuli. In contrast, subjects' hue scalings in a second control experiment (with order of presentations randomized) were completely determined by the color codes of the test surface. Our results show that hue scaling is a useful technique to investigate color constancy in a more phenomenological sense. Furthermore, the results from the blocked control experiment underline the important role of slow chromatic adaptation for color constancy.

Color↗

PubMed2006

Kin recognition and the perceived facial similarity of children.

We examine the connection between a hypothetical kin recognition signal available in visual perception and the perceived facial similarity of children. One group of observers rated the facial similarity of pairs of children portrayed in photographs. Half of the pairs were siblings but the observers were not told this. A second group classified the pairs as siblings or nonsiblings. An optimal Bayesian classifier, given the similarity ratings of the first group, was as accurate in judging siblings as the second group. Mean rated similarity was also an accurate linear predictor (R2 = .96) of the log-odds that the rated pair portrayed were, in fact, siblings. Surprisingly, mean rated similarity did not vary with the age difference or gender difference of the pairs, both of which were counterbalanced across the stimuli. We conclude that the perceived facial similarity of children is little more than a graded kin recognition signal and that this kin recognition signal is effectively an estimate of the probability that two children are close genetic relatives.

Adult↗

PubMed2006

Combining achromatic and chromatic cues to transparency.

We investigated how achromatic and chromatic cues interact to produce transparency. Observers were shown six-region stimulus displays similar to those used by R. Kasrai and F. A. A. Kingdom (2001) and made adjustments of the color and luminance attributes of one of the filter regions to achieve the best percept of transparency. The dependent measure of primary interest was setting reliability, the reciprocal of setting variance. We wished to determine whether the combination of chromatic and achromatic information leads to enhanced reliability of perceived transparency. In Experiment 1, we measured reliability for achromatic, L, superimposed luminance with color, L + C, and superimposed luminance with polarity-reversing color, L + iC. We found that observers' reliability was highest for the L + C condition, consistent with effective cue combination. In a second experiment, we compared setting reliability for L, L + C, and a new chromatic-only condition C. In the L + C condition, observers were asked to make separate and iterative settings of luminance and color to achieve the best percept of transparency. We compared their settings in L with the luminance settings in L + C and their settings in C with their color settings in L + C. Color adjustments were more reliable when accompanied by luminance information but not vice versa. In Experiment 3, we manipulated the transmittance of the achromatic and chromatic filters separately and investigated how this influences the settings made for each attribute. No systematic influence of filter transmittance on the settings made for perceived transparency was found.

Color↗

PubMed2006

Limits to human movement planning with delayed and unpredictable onset of needed information.

In motor tasks with explicit rewards and penalties, humans choose movement strategies that nearly maximize expected gain (Trommershäuser et al. in J Opt Soc Am A 20:1419-1433, 2003). Here, we examine whether performance is still close to optimal when information about payoffs is not available prior to movement onset. Subjects rapidly touched a target region while trying to avoid hitting an overlapping penalty region placed randomly to the left or right of the target. Subjects received rewards and incurred penalties for hitting the corresponding regions. Late responses (>700 ms) were heavily penalized. The penalty region was displayed 0, 200 or 400 ms after the reward region and the subject could not know where it would be until then. Reaction times to begin the movement after stimulus appearance were constant across conditions. Median reaction times were approximately 200 ms, i.e., the time the penalty was first displayed in the 200 ms delay condition. Performance was compared to that of an optimal movement planner that chooses mean end points to maximize expected gain despite movement variability. In the 0 and 200 ms delay conditions, subjects selected strategies that did not differ significantly from optimal, indicating that humans are able to plan their movements well despite delayed and unpredictable onset of information. Performance dropped below optimal in the 400 ms delay condition, with mean movement end points closer to the penalty region than predicted by the optimal strategy (in the high-penalty condition). We conclude that relevant information concerning the reward structure is required between 200 and 400 ms prior to the end of the movement, but can still be integrated into the movement plan after movement initiation.

Adult↗

PubMed2006

How direction of illumination affects visually perceived surface roughness.

We examined visual estimation of surface roughness using random, computer-generated, three-dimensional (3D) surfaces rendered under a mixture of diffuse lighting and a punctate source. The angle between the tangent to the plane containing the surface texture and the direction to the punctate source was varied from 50 to 70 deg across lighting conditions. Observers were presented with pairs of surfaces under different lighting conditions and indicated which 3D surface appeared rougher. Surfaces were viewed either in isolation or in scenes with added objects whose shading, cast shadows, and specular highlights provided information about the spatial distribution of illumination. All observers perceived surfaces to be markedly rougher with decreasing illuminant angle. Performance in scenes with added objects was no closer to constant than that in scenes without added objects. We identified four novel cues that are valid cues to roughness under any single lighting condition but that are not invariant under changes in lighting condition. We modeled observers' deviations from roughness constancy as a weighted linear combination of these "pseudocues" and found that they account for a substantial amount of observers' systematic deviations from roughness constancy with changes in lighting condition.

Computer Graphics↗

PubMed2006

Cues to an equivalent lighting model.

We investigate how human observers make use of three candidate cues in their lightness judgments. Each cue potentially provides information about the spatial distribution of light sources in complex, rendered 3D scenes. The illumination (lighting model) of each scene consisted of a punctate light source combined with a diffuse light source. The cues were (1) cast shadows, (2) surface shading, and (3) specular highlights. Observers were asked to judge the albedo of a matte grayscale test patch that varied in orientation with respect to the punctate light source. We tested their performance in scenes containing only one type of cue and in scenes where all three cue types were present. From the results, we deduced how accurately they had estimated the spatial distribution of light sources in each scene given the cues available. In Experiment 1, we established that all of the individual cues were used in isolation. We showed that the highlight and cast shadow cues in isolation were used by more than half of the observers. We could reject the hypothesis that the observers did not make use of the shading cue for only one observer. In Experiment 2, we showed that the observers combined information from multiple cues when all three cues were presented together.

Cues↗

PubMed2006

Limits to human movement planning in tasks with asymmetric gain landscapes.

We studied human movement planning in a task with predefined costs and benefits to movement outcome. Participants pointed rapidly at stimulus configurations consisting of a target region and up to two penalty regions. Hits on the target and penalty regions resulted in monetary gains and losses. In previous studies involving single penalty regions or other symmetric target-penalty configurations, performance was optimal in the sense of maximizing expected gain. In this study, more complex, asymmetric configurations were used in which the two penalty regions carried different penalties. With these configurations, the landscape of expected gain as a function of mean end point (MEP) was spatially asymmetric. Further, the optimal movement plan with these configurations was sometimes counterintuitive (e.g., one should aim slightly inside the lesser penalty region). In one asymmetric condition, four out of six naïve participants' performed suboptimally, indicating that there are limits to human movement planning. Further, the suboptimal performance was inconsistent with a model in which participants misestimate motor variability but otherwise optimally plan their movement.

Adult↗

PubMed2006

Humans rapidly estimate expected gain in movement planning.

We studied human movement planning in tasks in which subjects selected one of two goals that differed in expected gain. Each goal configuration consisted of a target circle and a partially overlapping penalty circle. Rapid hits into the target region led to a monetary bonus; accidental hits into the penalty region incurred a penalty. The outcomes assigned to target and penalty regions and the spatial arrangement of those regions were varied. Subjects preferred configurations with higher expected gain whether selection involved a rapid pointing movement or a choice by key press. Movements executed to select one of two goal configurations exhibited the same movement dynamics as pointing movements directed at a single configuration, and were executed with the same high efficiency. Our results suggest that humans choose near-optimal strategies when planning their movement, and can base their selection of strategy on a rapid judgment about the expected gain associated with possible movement goals.

Adult↗

PubMed2006

The proximity structure of achromatic surface colors and the impossibility of asymmetric lightness matching.

In asymmetric lightness matching tasks, observers sometimes report that they cannot achieve satisfactory matches between achromatic surfaces under different neutral illuminants. The surfaces appear different, yet no further adjustment of either surface improves the match. There are evident difficulties in interpreting data from a task that the observer cannot always do, and these difficulties likely affect the interpretation of a large number of previous studies. We investigated, as an alternative to asymmetric matching, the direct use of proximity judgments in the study of surface lightness perception. We asked observers to rate the perceived dissimilarity of pairs of achromatic surfaces that were placed in identical scenes and viewed under different neutral illuminants. We develop a parametric model that accurately predicts perceived dissimilarity in terms of physical light intensities and surface albedos. The parameters of this model are readily interpretable. In particular, the ratio of the influence of changes in illuminant intensity and changes in surface albedo is a measure of the extent to which the observer discounts the illuminant. Asymmetric lightness matching can be interpreted as an unachievable limiting case of proximity judgment.

Color Perception↗

PubMed2005

Illumination estimation in three-dimensional scenes with and without specular cues.

We report the results of three experiments in which observers judged the albedo of surfaces at different locations in rendered, three-dimensional scenes consisting of two rooms connected by a doorway. All surfaces composing the rooms were achromatic and Lambertian, and a gradient of illumination increased with depth. Observers made asymmetric albedo matches between a standard surface placed in the rooms at different depths along the line of sight and an adjustable surface at a fixed location. In Experiment 1, gradients of intensity on the walls, floor, and ceiling of the scene, as well as its three-dimensional structure, provided information about variations in the intensity of illumination across depth (the illumination profile). In Experiment 2, specular spheres provided an additional veridical cue to the illumination profile. We sought to determine whether observers would make use of this additional cue. They did: all observers exhibited a greater degree of lightness constancy in Experiment 2 than in Experiment 1. In Experiment 3, the specular spheres reflected an illumination profile in conflict with that signaled by the other cues in the scene. We found that observers chose albedo matches consistent with an illumination profile that was a mixture of the illumination profiles signaled by the specular spheres and by the remaining cues.

Cues↗

PubMed2005

Explicit estimation of visual uncertainty in human motion processing.

We examine whether human observers have explicit access to an estimate of their own uncertainty in extrapolating the motion trajectories of moving objects. Objects moved across a display area at constant speed changing direction at short time intervals. Each new direction was obtained by adding a random perturbation to the previous direction. The perturbation distribution was always symmetric with mean zero (no change in direction) but could differ in variability: objects with low directional variability tended to travel in straight lines while objects with high directional variability moved more erratically. Objects eventually disappeared behind the near edge of an occluder. Observers marked a 'capture region' along the far edge of the occluder that they estimated would contain the object when it re-emerged. We varied both occluder width and directional variability across trials and found that observers correctly compensated for these changes. We present a two-stage model of observer performance in which the visual system first estimates the directional variability of the object and then uses this estimate to set a capture region.

Cues↗

PubMed2005

Optimal compensation for changes in task-relevant movement variability.

Effective movement planning should take into account the consequences of possible errors in executing a planned movement. These errors can result from either sensory uncertainty or variability in movement planning and production. We examined the ability of humans to compensate for variability in sensory estimation and movement production under conditions in which variability is increased artificially by the experimenter. Subjects rapidly pointed at a target region that had an adjacent penalty region. Target and penalty hits yielded monetary rewards and losses. We manipulated the task-relevant variability by perturbing visual feedback of finger position during the movement. The feedback was shifted in a random direction with a random amplitude in each trial, causing an increase in the task-relevant variability. Subjects were unable to counteract this form of perturbation. Rewards and penalties were based on the perturbed, visually specified finger position. Subjects rapidly acquired an estimate of their new variability in <120 trials and adjusted their aim points accordingly. We compared subjects' performance to the performance of an optimal movement planner maximizing expected gain. Their performance was consistent with that expected from an optimal movement planner that perfectly compensated for externally imposed changes in task-relevant variability. When exposed to novel stimulus configurations, aim points shifted in the first trial without showing any detectable trend across trials. These results indicate that subjects are capable of changing their pointing strategy in the presence of externally imposed noise. Furthermore, they manage to update their estimate of task-relevant variability and to transfer this estimate to novel stimulus configurations.

Adaptation, Physiological↗

PubMed2005

Distortions of perceived length in the frontoparallel plane: tests of perspective theories.

The perceived length of a line segment in a frontoparallel plane is sometimes affected by the presence of other line segments in the visual field. Perspective theories attribute such interactions to size-constancy scaling: The configuration of line segments present in the visual field includes depth cues that trigger size scaling of each line segment. In three experiments, we test this claim for a range of simple configurations composed of two line segments joined at a point. These configurations include the inverted T configuration of the bisection illusion, as well as the L configuration of the horizontal-vertical illusion. We conclude that the available depth cues, even when supplemented by known biases in perspective interpretations, do not account for observed distortions in judgments of relative length.

Adult↗

PubMed2004

Perceived surface color in binocularly viewed scenes with two light sources differing in chromaticity.

We examined the effect of perceived orientation on the perceived color of matte surfaces in rendered three-dimensional scenes illuminated by a blue diffuse light and a yellow punctate light. On each trial, observers first adjusted the color of a matte test patch, placed near the center of the scene, until it appeared achromatic, and then estimated its orientation by adjusting a monocular gradient probe. The orientation of the test patch was varied from trial to trial by the experimental program, effectively varying the chromaticity of the light mixture from the two light sources that would be absorbed and reemitted by a neutral test patch. We found that observers' achromatic settings varied with perceived orientation but that observers only partially discounted orientation in making achromatic settings. We developed an equivalent illuminant model for our task in which we assumed that observers discount orientation using possibly erroneous estimates of the chromaticities of the light sources and/or their spatial distribution. We found that the observers' failures could be explained by two factors: errors in estimating the direction to the punctate light source and errors in estimating the chromaticities of the two light sources. We discuss the pattern of errors in estimating these factors across observers.

Color Perception↗

PubMed2004

Perception of color and material properties in complex scenes.

How do human observers estimate the location, form, and color of objects? Accurate estimation is challenging because the light arriving at the eyes depends not only on object properties, but also on the spectra and spatial layout of the light sources (Nassau, 1983; Foley et al., 1990). How well the visual system separates illuminant and object properties to achieve a stable representation has traditionally been studied under the rubric of color and lightness constancy. Most previous work used very simple stimuli, typically a few diffusely illuminated surfaces arranged perpendicular to the line of sight. Over the past several years, however, there has been an evident increase of interest in expanding the conceptualization of this area to incorporate effects that emerge only for complex, typically three-dimensional, scenes. The current issue features papers that represent various manifestations of this interest. One line of research investigates how the three-dimensional layout of a scene affects the perception of lightness and color. Although the current work has long-standing antecedents (e.g. Mach, 1886/1959; Hochberg and Beck, 1954; Gilchrist, 1980), methodological advances in i) experimentation with real illuminated objects (e.g. Brainard et. al, 1987; Rutherford and Brainard, 2002; Ripamonti et al., 2004; Robilotto and Zaidi, 2004), ii) the use of sophisticated graphics simulations (e.g. Yang and Maloney, 1999; Fleming, Dror, & Adelson, 2003; Boyaci, Maloney, & Hersh, 2003; Delahunt and Brainard, 2004), iii) the design of hybrid systems that combine real objects with image-based graphics and video projection (Ling and Hurlbert, 2004), and iv) psychophysical procedures (Maloney and Yang, 2003; Obein, Knoblauch, & Vienot, 2004) have opened the door for systematic exploration of a wider range of phenomena. Recent papers include work on how well vision compensates for changes in surface orientation (Boyaci et al., 2003; Ripamonti et al., 2004), how effectively it discounts inter-reflections among nearby surfaces (Bloj, Kersten, & Hurlbert, 1999; Doerschner, Boyaci, & Maloney, 2004; Delahunt and Brainard, 2004), and how the visual system effectively estimates the spectral properties and spatial layout of the illuminant in three-dimensional scenes (Kraft & Brainard, 1999; Yang & Maloney, 1999; Boyaci, Maloney, & Hersh, 2003; Bloj et al., 2004; Boyaci, Doerschner, & Maloney, 2004; Khang and Zaidi, 2004). The second thread that leads to papers in the current issue is a focus on the functional utility of color and lightness perception -- the idea that these percepts inform us about the properties of objects rather than those of light spectra. This focus resulted in a renaissance of research in color constancy over the past two decades, with particular progress being made in the development of computational models that explore how, in principle, object surface properties can be estimated from image data. As with the experimental lines, early work focused on simple scene geometries (for reviews see Hurlbert, 1998; Maloney, 1999) but consideration has recently expanded to three-dimensional configurations (Adelson and Pentland, 1996; Yang and Maloney, 1999; Bell and Freeman, 2001; Dror, Willsky, & Adelson, 2004) Of particular interest has been the elaboration of purely computational formulations into parametric models of human performance (e.g. Brainard Brunt, & Speigle, 1997; Brainard Kraft, & Longere, 2003; Boyaci et al., 2003; Doerschner et al., 2004; Boyaci et al., 2004; Bloj et al., 2004), tests of how well the visual system exploits image information identified in computational studies (Yang and Maloney, 2001; Delahunt and Brainard, 2004; Smithson and Zaidi, 2004), investigations of how well the visual system recovers perceptual correlates of material properties other than diffuse surface reflectance, such as gloss and translucency (Lu, Koenderink, & Kappers, 2000; Fleming et al., 2003; Pont & Koenderink, 2003; Obein et al., 2004), as well as how geometric aspects of surface reflectance interact with the perception of shape (Fleming et al., 2003).

Color Perception↗

PubMed2004

Human observers compensate for secondary illumination originating in nearby chromatic surfaces.

In complex scenes, the light absorbed and re-emitted by one surface can serve as a source of illumination for a second. We examine whether observers systematically discount this secondary illumination when estimating surface color. We asked six naïve observers to make achromatic settings of a small test patch adjacent to a brightly colored orange cube in rendered scenes. The orientation of the test patch with respect to the cube was varied from trial to trial, altering the amount of secondary illumination reaching the test patch. Observers systematically took orientation into account in making their settings, discounting the added secondary illumination more at orientations where it was more intense. Overall, they tended to under-compensate for the added secondary illumination.

Absorption↗

PubMed2004

Interpolating sampled contours in 3D: perturbation analyses.

In four experiments, observers interpolated parabolic sampled contours confined to planes in three-dimensional space. Each sampled contour consisted of eight visible points, placed irregularly along the otherwise invisible parabolic contour. Observers adjusted an additional point until it fell on the contour. We sought to determine how each visible point influenced interpolation by measuring the effect of slightly perturbing its location. Influence fell rapidly to zero as distance from the interpolated point increased, indicating that human visual interpolation of parabolic contours is local. We compare the measured influence for human observers to that predicted by three standard interpolation algorithms. The results were inconsistent with a fit of a quadratic to the points, but were reasonably consistent with a cubic spline and most consistent with an algorithm that minimizes the variance of angles between neighboring line segments defined by the sampled points.

Algorithms↗