Detection of changes in luminance distributions

How well can observers detect the presence of a change in luminance distributions? Performance was measured in three experiments. Observers viewed pairs of grayscale images on a calibrated CRT display. Each image was a checkerboard. All luminances in one image of each pair consisted of random draws from a single probability distribution. For the other image, some patch luminances consisted of random draws from that same distribution, while the rest of the patch luminances (test patches) consisted of random draws from a second distribution. The observers' task was to pick the image with luminances drawn from two distributions. The parameters of the second distribution that led to 75% correct performance were determined across manipulations of (1) the number of test patches, (2) the observers' certainty about test patch location, and (3) the geometric structure of the images. Performance improved with number of test patches and location certainty. The geometric manipulations did not affect performance. An ideal observer model with high efficiency fit the data well and a classification image analysis showed a similar use of information by the ideal and human observers, indicating that observers can make effective use of photometric information in our distribution discrimination task

Hunter-Gatherer Color Naming Provides New Insight into the Evolution of Color Terms

SummaryMost people name the myriad colors in the environment using between two and about a dozen color terms [1], with great variation within and between languages [2]. Investigators generally agree that color lexicons evolve from fewer terms to more terms, as technology advances and color communication becomes increasingly important [3]. However, little is understood about the color naming systems at the least technologically advanced end of the continuum. The Hadza people of Tanzania are nomadic hunter-gatherers who live a subsistence lifestyle that was common before the advent of agriculture (see Supplemental Experimental Procedures, section I; [4]), suggesting that the Hadzane language should be at an early stage of color lexicon evolution. When Hadza, Somali, and US informants named 23 color samples, Hadza informants named only the black, white, and red samples with perfect consensus. Otherwise, they used low-consensus terms or responded “don’t know.” However, even low-consensus color terms grouped test colors into lexical categories that aligned with those found in other world languages [5]. Furthermore, information-theoretic analysis showed that color communication efficiency within the Hadza, Somali, and US language communities falls on the same continuum as other world languages. Thus, the structure of color categories is in place in Hadzane, even though words for many of the categories are not in general use. These results suggest that even very simple color lexicons include precursors of many color categories but that these categories are initially represented in a diverse and distributed fashion

Color and material perception: Achievements and challenges

There is a large literature characterizing human perception of the lightness and color of matte surfaces arranged in coplanar arrays. In the past ten years researchers have begun to examine perception of lightness and color using wider ranges of stimuli intended to better approximate the conditions of everyday viewing. One emerging line of research concerns perception of lightness and color in scenes that approximate the three-dimensional environment we live in, with objects that need not be matte or coplanar and with geometrically complex illumination. A second concerns the perception of material surface properties other than color and lightness, such as gloss or roughness. This special issue features papers that address the rich set of questions and approaches that have emerged from these new research directions. Here, we briefly describe the articles in the issue and their relation to previous work. Keywords: color perception, material perception Citation: Maloney, L. T., & Brainard, D. H. (2010). Color and material perception: Achievements and challenges. Journal of Vision, 10(9):19, 1-6, http://www.journalofvision.org/content/10/9/19, doi:10.1167/10.9.19. Introduction The classic perceptual correlates of object surface properties are lightness and color. Although there are notable exceptions (e.g., Over the past decade, research has increasingly begun to focus on two rich generalizations of the classic "flatmatte" paradigm (for reviews, see In 2004, we edited a special issue in the Journal of Vision entitled "Perception of color and material properties in complex scenes" Characterizing, estimating, and discriminating the light field One of the most important themes in color and material perception is the role of scene illumination. In flat-matte scenes, the placement and directionality of light sources was little emphasized Journal of Vision Complex light fields and surface color/lightness perception In parallel with direct assessment of the perception of the light field, the past decade has seen a slew of papers that study how the visual system achieves color and lightness constancy in the context of spatially complex light fields (e.g., Along these lines in the current issue, Radonjić, Todorović, and Gilchrist (2010) examine surface lightness perception in three-dimensional scenes with directional lighting and show how grouping principles such as adjacency and surroundedness can help organize the empirical phenomena. Olkkonen, Witzel, Hansen, and Gegenfurtner (2010) study color categorization for real surfaces and daylight illuminants. An entire room with controlled illumination served as the laboratory. They find that color categorization was little changed by marked changes in daylight illumination. Surface material perception: Gloss, roughness A very active area of research is the assessment of lighting and environmental conditions that affect the perception of material properties such as gloss and roughness, and how these properties interact with the perception of color and lightness. Important early work includes Surface material perception is represented by a number of papers in this issue; Kim and Anderson Interactions There are several studies that examined interactions among different material properties. In this issue, Giesel and Gegenfurtner (2010) systematically investigate color perception for real objects made of different materials varying in roughness and gloss from smooth and glossy to matte and corrugated. They show that hue is quite stable across their manipulations, but that other attributes interact. Olkkonen and Brainard (2010) study how changes in real-world illumination affect perceived glossiness and lightness with emphasis on testing independence principles. They show, for example, that the effect of geometric changes in the light field on perceived glossiness is independent of the diffuse reflectance component of the surfaces. Novel themes A number of papers in the current issue introduce novel themes. Wolfe and Myers (2010) examine visual search performance when targets and distractors are characterized by surface material. They find that, although it may be easy to discriminate "fur" or "stone," searching for a patch of fur among the stones is difficult and time-consuming. Visual search based on material differences is inefficient. Motoyoshi (2010) examines how the relationship between highlights and shading triggers perception of translucency and transparency. Goddard, Solomon, and Colin (2010) study the adaptable neural mechanisms responsible for surface color constancy. Boyaci, Fang, Murray, and Kersten (2010) also consider mechanism. They report behavioral results showing how lightness across occlusion depends on spatially distant image features and show (using brain imaging) that human early visual cortex responds strongly to occlusion-dependent lightness variations. They conclude that early cortical processing of lightness is affected by three-dimensional scene interpretation

Detection of chromoluminance patterns on chromoluminance pedestals I: threshold measurements

AbstractMeasurement of the detection thresholds of patterns on pedestals of various kinds has the potential of providing insight into the mechanisms that mediate pattern vision. This study is concerned with chromoluminance patterns, that is, patterns that vary over space in luminance, chromaticity, or both. Contrast thresholds for 1 c/deg Gabor patterns (targets) were measured as a function of the contrast of Gabor pedestal patterns (TvC functions), where the pedestals paired with each target were modulated in a wide range of directions in color space. For most target-pedestal pairs, the TvC function decreased (facilitation) and then increased as pedestal contrast increased. The increase went above the absolute contrast threshold (masking) for all target-pedestal pairs except in cases where facilitation occurred at the upper end of the pedestal contrast range. The specific form of the TvC function varied greatly with the target and pedestal, consistent with a general model of pedestal effects proposed by Foley [Journal of the Optical Society of America A, 1994, 11(6)]. There were two sets of target-pedestal pairs for which facilitation did not occur, but masking did occur: pairs in which the target was a luminance modulation and the pedestals were individually isoluminant and pairs in which the pedestal was blue/yellow and the target was in any of our directions except blue/yellow

Melanopic stimulation does not alter psychophysical threshold sensitivity for luminance flicker

In addition to the rod and cone photoreceptors the retina contains intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells express the photopigment melanopsin and are known to be involved in reflexive visual functions such as pupil response and photo-entrainment of the circadian rhythm. It is possible that the ipRGCs contribute to conscious visual perception, either by providing an independent signal to the geniculo-striate pathway, or by interacting with and thus modifying signals arising from “classical” retinal ganglion cells that combine and contrast cone input. Here, we tested for the existence of an interaction by asking if a 350% change in melanopsin stimulation alters psychophysical sensitivity for the detection of luminance flicker. In Experiment 1, we tested for a change in the threshold for detecting luminance flicker in three participants after they adapted to backgrounds with different degrees of tonic melanopsin stimulation. In Experiments 2 and 3, this test was repeated, but now for luminance flicker presented on a transient pedestal of melanopsin stimulation. Across the three experiments, no effect of melanopsin stimulation upon threshold flicker sensitivity was found. Our results suggest that even large changes in melanopsin stimulation do not affect near-threshold, cone-mediated visual perception.TU Berlin, Open-Access-Mittel – 202

'A Nation of Poets and Thinkers' - Less So with Eastern Enlargement? Austria and Germany

Many people in the European Union fear that Eastern Enlargement will lead to major job losses. More recently, these fears about job losses have extended to high skill labor and IT jobs. The paper examines with new firm level data whether these fears are justified for the two neighboring countries of Eastern Enlargement Austria and Germany. We find that Eastern Enlargement leads to surprising small job losses, because jobs in Eastern Europe do not compete with jobs in Austria and Germany. Low cost jobs of affiliates in Eastern Europe help Austrian and German firms to stay competitive in an increasingly competitive environment. However, we also find that multinational firms in Austria and Germany are outsourcing the most skill intensive activities to Eastern Europe taking advantage of cheap abundant skilled labor in Eastern Europe. We find that the firms' outsourcing activities to Eastern Europe are a response to a human capital scarcity in Austria and Germany which has become particularly severe in the 1990s. Corporations' outsourcing of skill intensive firm activity to Eastern Europe has helped to ease the human capital crisis in both countries. We find that high skilled jobs transferred to Eastern Europe account for 10 percent of Germany's and 48 percent of Austria's supply of university graduates in the 1990s. We then discuss what can be done to address the skill exodus to Eastern Europe. We show that R&D subsidies do not work in economies with a skill crisis and we suggest to liberalize the movement of high skill labor with Eastern Enlargement

Natural images from the birthplace of the human eye

Here we introduce a database of calibrated natural images publicly available through an easy-to-use web interface. Using a Nikon D70 digital SLR camera, we acquired about 5000 six-megapixel images of Okavango Delta of Botswana, a tropical savanna habitat similar to where the human eye is thought to have evolved. Some sequences of images were captured unsystematically while following a baboon troop, while others were designed to vary a single parameter such as aperture, object distance, time of day or position on the horizon. Images are available in the raw RGB format and in grayscale. Images are also available in units relevant to the physiology of human cone photoreceptors, where pixel values represent the expected number of photoisomerizations per second for cones sensitive to long (L), medium (M) and short (S) wavelengths. This database is distributed under a Creative Commons Attribution-Noncommercial Unported license to facilitate research in computer vision, psychophysics of perception, and visual neuroscience.Comment: Submitted to PLoS ON

Temporal perception deficits in schizophrenia: integration is the problem, not deployment of attentions

Patients with schizophrenia are known to have impairments in sensory processing. In order to understand the specific temporal perception deficits of schizophrenia, we investigated and determined to what extent impairments in temporal integration can be dissociated from attention deployment using Attentional Blink (AB). Our findings showed that there was no evident deficit in the deployment of attention in patients with schizophrenia. However, patients showed an increased temporal integration deficit within a hundred-millisecond timescale. The degree of such integration dysfunction was correlated with the clinical manifestations of schizophrenia. There was no difference between individuals with/without schizotypal personality disorder in temporal integration. Differently from previous studies using the AB, we did not find a significant impairment in deployment of attention in schizophrenia. Instead, we used both theoretical and empirical approaches to show that previous findings (using the suppression ratio to correct for the baseline difference) produced a systematic exaggeration of the attention deficits. Instead, we modulated the perceptual difficulty of the task to bring the baseline levels of target detection between the groups into closer alignment. We found that the integration dysfunction rather than deployment of attention is clinically relevant, and thus should be an additional focus of research in schizophrenia

Canine and Human Visual Cortex Intact and Responsive Despite Early Retinal Blindness from \u3cem\u3eRPE65\u3c/em\u3e Mutation

Background RPE65 is an essential molecule in the retinoid-visual cycle, and RPE65 gene mutations cause the congenital human blindness known as Leber congenital amaurosis (LCA). Somatic gene therapy delivered to the retina of blind dogs with an RPE65 mutation dramatically restores retinal physiology and has sparked international interest in human treatment trials for this incurable disease. An unanswered question is how the visual cortex responds after prolonged sensory deprivation from retinal dysfunction. We therefore studied the cortex of RPE65-mutant dogs before and after retinal gene therapy. Then, we inquired whether there is visual pathway integrity and responsivity in adult humans with LCA due to RPE65 mutations (RPE65-LCA). Methods and Findings RPE65-mutant dogs were studied with fMRI. Prior to therapy, retinal and subcortical responses to light were markedly diminished, and there were minimal cortical responses within the primary visual areas of the lateral gyrus (activation amplitude mean ± standard deviation [SD] = 0.07% ± 0.06% and volume = 1.3 ± 0.6 cm3). Following therapy, retinal and subcortical response restoration was accompanied by increased amplitude (0.18% ± 0.06%) and volume (8.2 ± 0.8 cm3) of activation within the lateral gyrus (p \u3c 0.005 for both). Cortical recovery occurred rapidly (within a month of treatment) and was persistent (as long as 2.5 y after treatment). Recovery was present even when treatment was provided as late as 1–4 y of age. Human RPE65-LCA patients (ages 18–23 y) were studied with structural magnetic resonance imaging. Optic nerve diameter (3.2 ± 0.5 mm) was within the normal range (3.2 ± 0.3 mm), and occipital cortical white matter density as judged by voxel-based morphometry was slightly but significantly altered (1.3 SD below control average, p = 0.005). Functional magnetic resonance imaging in human RPE65-LCA patients revealed cortical responses with a markedly diminished activation volume (8.8 ± 1.2 cm3) compared to controls (29.7 ± 8.3 cm3, p \u3c 0.001) when stimulated with lower intensity light. Unexpectedly, cortical response volume (41.2 ± 11.1 cm3) was comparable to normal (48.8 ± 3.1 cm3, p = 0.2) with higher intensity light stimulation. Conclusions Visual cortical responses dramatically improve after retinal gene therapy in the canine model of RPE65-LCA. Human RPE65-LCA patients have preserved visual pathway anatomy and detectable cortical activation despite limited visual experience. Taken together, the results support the potential for human visual benefit from retinal therapies currently being aimed at restoring vision to the congenitally blind with genetic retinal disease