RESUMEN
Humans show a natural tendency to discount bad news while incorporating good news into beliefs (the "good news-bad news effect"), an effect that may help explain seemingly irrational risk taking. Understanding how this bias develops with age is important because adolescents are prone to engage in risky behavior; thus, educating them about danger is crucial. We reveal a striking valence-dependent asymmetry in how belief updating develops with age. In the ages tested (9-26 y), younger age was associated with inaccurate updating of beliefs in response to undesirable information regarding vulnerability. In contrast, the ability to update beliefs accurately in response to desirable information remained relatively stable with age. This asymmetry was mediated by adequate computational use of positive but not negative estimation errors to alter beliefs. The results are important for understanding how belief formation develops and might help explain why adolescents do not respond adequately to warnings.
Asunto(s)
Toma de Decisiones/fisiología , Aprendizaje/fisiología , Asunción de Riesgos , Adolescente , Adulto , Factores de Edad , Niño , HumanosRESUMEN
Sensitivity to visual numerosity has previously been shown to predict human mathematical performance. However, it is not clear whether it is discrimination of numerosity per se that is predictive of mathematical ability, or whether the association is driven by more general task demands. To test this notion we had over 300 participants (ranging in age from 6 to 73 years) perform a symbolic mathematics test and 4 different visuospatial matching tasks. The visual tasks involved matching 2 clusters of Gabor elements for their numerosity, density, size or orientation by a method of adjustment. Partial correlation and regression analyses showed that sensitivity to visual numerosity, sensitivity to visual orientation and mathematical education level predict a significant proportion of shared as well as unique variance in mathematics scores. These findings suggest that sensitivity to visual numerosity is not a unique visual psychophysical predictor of mathematical ability. Instead, the data are consistent with mathematics representing a multi-factorial process that shares resources with a number of visuospatial tasks.
Asunto(s)
Conceptos Matemáticos , Percepción Visual/fisiología , Adolescente , Adulto , Factores de Edad , Anciano , Niño , Discriminación en Psicología/fisiología , Femenino , Humanos , Masculino , Persona de Mediana Edad , Estimulación Luminosa/métodos , Psicofísica , Análisis de Regresión , Umbral Sensorial/fisiología , Factores Sexuales , Adulto JovenRESUMEN
This article considers visual perception, the nature of the information on which perceptions seem to be based, and the implications of a wholly empirical concept of perception and sensory processing for vision science. Evidence from studies of lightness, brightness, color, form, and motion all indicate that, because the visual system cannot access the physical world by means of retinal light patterns as such, what we see cannot and does not represent the actual properties of objects or images. The phenomenology of visual perceptions can be explained, however, in terms of empirical associations that link images whose meanings are inherently undetermined to their behavioral significance. Vision in these terms requires fundamentally different concepts of what we see, why, and how the visual system operates.
Asunto(s)
Visión Ocular/fisiología , Percepción Visual/fisiología , Animales , Humanos , Luz , Modelos Biológicos , Movimiento (Física) , Estimulación LuminosaRESUMEN
BACKGROUND: The perception of brightness depends on spatial context: the same stimulus can appear light or dark depending on what surrounds it. A less well-known but equally important contextual phenomenon is that the colour of a stimulus can also alter its brightness. Specifically, stimuli that are more saturated (i.e. purer in colour) appear brighter than stimuli that are less saturated at the same luminance. Similarly, stimuli that are red or blue appear brighter than equiluminant yellow and green stimuli. This non-linear relationship between stimulus intensity and brightness, called the Helmholtz-Kohlrausch (HK) effect, was first described in the nineteenth century but has never been explained. Here, we take advantage of the relative simplicity of this 'illusion' to explain it and contextual effects more generally, by using a simple Bayesian ideal observer model of the human visual ecology. We also use fMRI brain scans to identify the neural correlates of brightness without changing the spatial context of the stimulus, which has complicated the interpretation of related fMRI studies. RESULTS: Rather than modelling human vision directly, we use a Bayesian ideal observer to model human visual ecology. We show that the HK effect is a result of encoding the non-linear statistical relationship between retinal images and natural scenes that would have been experienced by the human visual system in the past. We further show that the complexity of this relationship is due to the response functions of the cone photoreceptors, which themselves are thought to represent an efficient solution to encoding the statistics of images. Finally, we show that the locus of the response to the relationship between images and scenes lies in the primary visual cortex (V1), if not earlier in the visual system, since the brightness of colours (as opposed to their luminance) accords with activity in V1 as measured with fMRI. CONCLUSIONS: The data suggest that perceptions of brightness represent a robust visual response to the likely sources of stimuli, as determined, in this instance, by the known statistical relationship between scenes and their retinal responses. While the responses of the early visual system (receptors in this case) may represent specifically the statistics of images, post receptor responses are more likely represent the statistical relationship between images and scenes. A corollary of this suggestion is that the visual cortex is adapted to relate the retinal image to behaviour given the statistics of its past interactions with the sources of retinal images: the visual cortex is adapted to the signals it receives from the eyes, and not directly to the world beyond.
Asunto(s)
Percepción de Color/fisiología , Sensibilidad de Contraste/fisiología , Mapeo Encefálico , Humanos , Iluminación , Imagen por Resonancia Magnética , Modelos BiológicosRESUMEN
Determining the statistical relationships of images that facilitate robust visual behaviour is nontrivial. Here we ask if some spatial relationships are more easily learned by the visual brain than others. Visually naïve bumblebees were trained to recognise coloured artificial flowers in scenes of equal spatial complexity but differing patterns of stimulus intensity. When flowers of similar intensity were grouped into extended regions across the array (coincident with natural patterns of light), the accuracy of the bees' foraging behaviour was dependent on spatial context, even though this information was redundant to the task. When the same intensity information was organised into a pattern that was less consistent with natural patterns of illumination but of equal order, their behaviour was independent of spatial context and they required double the training time to solve the same conditional task. These observations suggest the brain is biased to more efficiently encode/learn ecologically 'meaningful' image correlations.
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Abejas/fisiología , Percepción de Color/fisiología , Reconocimiento Visual de Modelos/fisiología , Animales , Señales (Psicología) , Aprendizaje Discriminativo/fisiología , Ecosistema , Flores , Estimulación Luminosa/métodos , PsicofísicaRESUMEN
In contrast to the classical view of development as a preprogrammed and deterministic process, recent studies have demonstrated that stochastic perturbations of highly non-linear systems may underlie the emergence and stability of biological patterns. Herein, we address the question of whether noise contributes to the generation of the stereotypical temporal pattern in gene expression during flower development. We modeled the regulatory network of organ identity genes in the Arabidopsis thaliana flower as a stochastic system. This network has previously been shown to converge to ten fixed-point attractors, each with gene expression arrays that characterize inflorescence cells and primordial cells of sepals, petals, stamens, and carpels. The network used is binary, and the logical rules that govern its dynamics are grounded in experimental evidence. We introduced different levels of uncertainty in the updating rules of the network. Interestingly, for a level of noise of around 0.5-10%, the system exhibited a sequence of transitions among attractors that mimics the sequence of gene activation configurations observed in real flowers. We also implemented the gene regulatory network as a continuous system using the Glass model of differential equations, that can be considered as a first approximation of kinetic-reaction equations, but which are not necessarily equivalent to the Boolean model. Interestingly, the Glass dynamics recover a temporal sequence of attractors, that is qualitatively similar, although not identical, to that obtained using the Boolean model. Thus, time ordering in the emergence of cell-fate patterns is not an artifact of synchronous updating in the Boolean model. Therefore, our model provides a novel explanation for the emergence and robustness of the ubiquitous temporal pattern of floral organ specification. It also constitutes a new approach to understanding morphogenesis, providing predictions on the population dynamics of cells with different genetic configurations during development.
Asunto(s)
Epigénesis Genética/fisiología , Flores/crecimiento & desarrollo , Flores/genética , Redes Reguladoras de Genes/fisiología , Morfogénesis/genética , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Diferenciación Celular/genética , Análisis por Conglomerados , Simulación por Computador , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Modelos Biológicos , Modelos GenéticosRESUMEN
Lightness illusions are fundamental to human perception, and yet why we see them is still the focus of much research. Here we address the question by modelling not human physiology or perception directly as is typically the case but our natural visual world and the need for robust behaviour. Artificial neural networks were trained to predict the reflectance of surfaces in a synthetic ecology consisting of 3-D "dead-leaves" scenes under non-uniform illumination. The networks learned to solve this task accurately and robustly given only ambiguous sense data. In addition--and as a direct consequence of their experience--the networks also made systematic "errors" in their behaviour commensurate with human illusions, which includes brightness contrast and assimilation--although assimilation (specifically White's illusion) only emerged when the virtual ecology included 3-D, as opposed to 2-D scenes. Subtle variations in these illusions, also found in human perception, were observed, such as the asymmetry of brightness contrast. These data suggest that "illusions" arise in humans because (i) natural stimuli are ambiguous, and (ii) this ambiguity is resolved empirically by encoding the statistical relationship between images and scenes in past visual experience. Since resolving stimulus ambiguity is a challenge faced by all visual systems, a corollary of these findings is that human illusions must be experienced by all visual animals regardless of their particular neural machinery. The data also provide a more formal definition of illusion: the condition in which the true source of a stimulus differs from what is its most likely (and thus perceived) source. As such, illusions are not fundamentally different from non-illusory percepts, all being direct manifestations of the statistical relationship between images and scenes.
Asunto(s)
Inteligencia Artificial , Biomimética/métodos , Interpretación de Imagen Asistida por Computador/métodos , Red Nerviosa/fisiología , Ilusiones Ópticas/fisiología , Fotometría/métodos , Percepción Visual/fisiología , HumanosRESUMEN
Bees, like humans, can continue to see a surface from its color even when the scene's global illuminant changes (which is a phenomenon called color constancy). It is not known, however, whether they can also generate color-constant behavior in more natural complex scenes that are lit by multiple lights simultaneously, conditions in which most computational models of color constancy fail. To test whether they can indeed solve this more complex problem, bumblebees were raised in a highly controlled, yet ecological relevant environment consisting of a matrix of 64 artificial flowers under four spatially distinct lights. As in nature, the bees had no direct access to spectral information about the illuminants or flowers. Furthermore, the background of all of the flowers in the matrix was black, independent of illumination. The stimulus information presented to the bee was, therefore, far more constrained than that normally experienced in nature. And yet, bees learned to identify the rewarded flowers in each differently illuminated region of the matrix, even when the illumination of one of the regions was switched with one the bees had not previously experienced. These results suggest that bees can generate color-constant behavior by encoding empirically significant contrast relationships between statistically dependent, but visually distinct, stimulus elements of scenes.
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Abejas/fisiología , Percepción de Color , Visión Ocular , AnimalesRESUMEN
The principal challenge faced by any color vision system is to contend with the inherent ambiguity of stimulus information, which represents the interaction between multiple attributes of the world (e.g., object reflectance and illumination). How natural systems deal with this problem is not known, although traditional hypotheses are predicated on the idea that vision represents object reflectance accurately by discounting early in processing the conflating effects of illumination. Here, we test the merits of this general supposition by confronting bumblebees (Bombus terrestris) with a color discrimination task that can be solved only if information about the illuminant is not discounted but maintained in processing and thus available to higher-order learned behavior. We show that bees correctly use the intensity and chromaticity of illumination as a contextual cue to guide them to different target colors. In fact, we trained bees to choose opposite, rather than most similar, target colors after an illumination change. This performance cannot be explained with a simple color-constancy mechanism that discounts illumination. Further tests show that bees do not use a simple assessment of the overhead illumination, but that they assess the spectral relationships between a floral target and its background. These results demonstrate that bees can be color-constant without discounting the illuminant; that, in fact, they can use information about the illuminant itself as a salient source of information.
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Abejas/fisiología , Percepción de Color/fisiología , Señales (Psicología) , Animales , Color , Luz , Estimulación LuminosaRESUMEN
Surface perception is fundamental to human vision, yet most studies of visual cortex have focused on the processing of borders. We therefore investigated the responses of human visual cortex to parametric changes in the luminance of uniform surfaces by using functional MRI. Early visual areas V1 and V2/V3 showed strong and reliable increases in signal for both increments and decrements in surface luminance. Responses were significantly larger for decrements than for increments, which was fully accounted for by differences in retinal illumination arising from asymmetric pupil dynamics. Responses to both sustained and transient changes of illumination were transient. Signals in early visual cortex scaled linearly with the magnitude of change in retinal illumination, as did subjects' subjective ratings of the perceived brightness of the stimuli. Our findings show that early visual cortex responds strongly to surfaces and that perception of surface brightness is compatible with brain responses at the earliest cortical stages of processing.
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Mediciones Luminiscentes , Corteza Visual/metabolismo , Humanos , Factores de TiempoRESUMEN
We view the world with two eyes and yet are typically only aware of a single, coherent image. Arguably the simplest explanation for this is that the visual system unites the two monocular stimuli into a common stream that eventually leads to a single coherent sensation. However, this notion is inconsistent with the well-known phenomenon of rivalry; when physically different stimuli project to the same retinal location, the ensuing perception alternates between the two monocular views in space and time. Although fundamental for understanding the principles of binocular vision and visual awareness, the mechanisms under-lying binocular rivalry remain controversial. Specifically, there is uncertainty about what determines whether monocular images undergo fusion or rivalry. By taking advantage of the perceptual phenomenon of color contrast, we show that physically identical monocular stimuli tend to rival-not fuse-when they signify different objects at the same location in visual space. Conversely, when physically different monocular stimuli are likely to represent the same object at the same location in space, fusion is more likely to result. The data suggest that what competes for visual awareness in the two eyes is not the physical similarity between images but the similarity in their perceptual/empirical meaning.
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Percepción de Color/fisiología , Disparidad Visual/fisiología , Percepción Visual/fisiología , Humanos , Estimulación LuminosaRESUMEN
The relationship between luminance (i.e., the photometric intensity of light) and its perception (i.e., sensations of lightness or brightness) has long been a puzzle. In addition to the mystery of why these perceptual qualities do not scale with luminance in any simple way, "illusions" such as simultaneous brightness contrast, Mach bands, Craik-O'Brien-Cornsweet edge effects, and the Chubb-Sperling-Solomon illusion have all generated much interest but no generally accepted explanation. The authors review evidence that the full range of this perceptual phenomenology can be rationalized in terms of an empirical theory of vision. The implication of these observations is that perceptions of lightness and brightness are generated according to the probability distributions of the possible sources of luminance values in stimuli that are inevitably ambiguous.
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Sensibilidad de Contraste/fisiología , Luz , Atención/fisiología , Aprendizaje Discriminativo/fisiología , Humanos , Ilusiones Ópticas/fisiología , Reconocimiento Visual de Modelos/fisiología , Aprendizaje por Probabilidad , Psicofisiología , Células Ganglionares de la Retina/fisiología , Corteza Visual/fisiología , Vías Visuales/fisiologíaRESUMEN
Rationalizing the perceptual effects of spectral stimuli has been a major challenge in vision science for at least the last 200 years. Here we review evidence that this otherwise puzzling body of phenomenology is generated by an empirical strategy of perception in which the color an observer sees is entirely determined by the probability distribution of the possible sources of the stimulus. The rationale for this strategy in color vision, as in other visual perceptual domains, is the inherent ambiguity of the real-world origins of any spectral stimulus.
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Percepción de Color/fisiología , Probabilidad , Humanos , Luz , Estimulación LuminosaRESUMEN
The colors perceived by humans in response to light stimuli are generally described in terms of four color categories (reds, greens, blues and yellows), the members of which are systematically arrayed around gray. This broadly accepted description of color sensation differs fundamentally from the light that induces it, which is neither 'circular' nor categorical. What, then, accounts for these discrepancies between the structure of color experience and the physical reality that underlies it? We suggest that these differences are based on two related requirements for successful color vision: (1) that spectra be ordered according to their physical similarities and differences; and (2) that this ordering be constrained by the four-color map problem.