Perception of dynamic Glass patterns

AbstractIn the mammalian brain, form and motion are processed through two distinct pathways at early stages of visual processing. However, recent evidence suggests that these two pathways may interact. Here we used dynamic Glass patterns, which have been previously shown to create the perception of coherent motion in humans, despite containing no motion coherence. Glass patterns are static stimuli that consist of randomly positioned dot pairs that are integrated spatially to create the perception of a global form, whereas dynamic Glass patterns consist of several independently generated static Glass patterns presented sequentially. In the current study, we measured the detection threshold of five types of dynamic Glass patterns and compared the rank order of the detection thresholds with those found for static Glass patterns and real motion patterns (using random dot stimuli). With both the static Glass patterns and dynamic Glass patterns, detection thresholds were lowest for concentric and radial patterns and highest for horizontal patterns. We also found that vertical patterns were better detected than horizontal patterns, consistent with prior evidence of a “horizontal effect” in the perception of natural scene images. With real motion, detection thresholds were equivalent across all patterns, with the exception of higher thresholds for spiral patterns. Our results suggest that dynamic Glass patterns are processed primarily as form prior to input into the motion system

Temporal summation of global form signals in dynamic Glass patterns

AbstractThe ability to perceive complex objects in the environment requires that the visual system integrate local form information into global shapes. Glass patterns (GPs) are stimuli that are commonly used to study this integration process. GPs consist of randomly positioned dot-pairs oriented in a coherent way to create a global form. When multiple GPs are presented sequentially, observers report a percept of illusory coherent motion and have lower detection thresholds relative to a single presentation GPs. The percept of illusory motion has been attributed to the visual system interpreting the dot-pairs in GPs as motion streaks. However, it remains unclear why dynamic GPs are detected at lower thresholds than static GPs. Two main differences exist between static and dynamic GPs: (a) dynamic GPs contain multiple presentations of global form signals compared to a single presentation in static GPs and (b) dynamic GPs have a greater temporal frequency than static GPs. Here we investigated which of these two factors contributed to the heightened sensitivities for dynamic GPs. We systematically varied the number of unique GPs and the rate at which each unique frame is presented (i.e., temporal frequency). The results show that, within the range of temporal frequency used, the primary influence on detection thresholds was the number of unique frames. These results suggest that the improved detection sensitivities can be driven by a mechanism of temporal summation of global form

The contribution of nonrigid motion and shape information to object perception in pigeons and humans

The ability to perceive and recognize objects is essential to many animals, including humans. Until recently, models of object recognition have primarily focused on static cues, such as shape, but more recent research is beginning to show that motion plays an important role in object perception. Most studies have focused on rigid motion, a type of motion most often associated with inanimate objects. In contrast, nonrigid motion is often associated with biological motion and is therefore ecologically important to visually dependent animals. In this study, we examined the relative contribution of nonrigid motion and shape to object perception in humans and pigeons, two species that rely extensively on vision. Using a parametric morphing technique to systematically vary nonrigid motion and three-dimensional shape information, we found that both humans and pigeons were able to rely solely on either shape or nonrigid motion information to identify complex objects when one of the two cues was degraded. Humans and pigeons also showed similar 80% accuracy thresholds when the information from both shape and motion cues were degraded. We argue that the use of nonrigid motion for object perception is evolutionarily important and should be considered in general theories of vision at least with respect to visually sophisticated animals

Integrating brain, behavior, and phylogeny to understand the evolution of sensory systems in birds

Sherpa Romeo green journal: open accessThe comparative anatomy of sensory systems has played a major role in developing theories and principles central to evolutionary neuroscience. This includes the central tenet of many comparativestudies, the principle of proper mass, which states that the size of a neural structure reflects its processing capacity. The size of structures within the sensory system is not, however, the only salient variable in sensory evolution. Further, the evolution of the brain and behavior are intimately tied to phylgenetic history, requiring studies to integrate neuroanatomy with behavior and phylogeny to gain a more holistic view of brain evolution. Birds have proven to be a useful group for theses tudies because of widespread interest in their phylogenetic relationships and a wealth of information on the functional organization of most of their sensory pathways. In this review, we examine the principle of proper mass in relation differences in the sensory capabilities among birds. We discuss how neuroanatomy, behavior, and phylogeny can be integrated to understand the evolution of sensory systems in birds providing evidence from visual, auditory, and somatosensory systems. We also consider the concept of a “trade-off,” where by one sensory system (or subpathway within a sensory system), may be expanded in size, at the expense of others, which are reduced in size.Ye

Zebrin II / Aldolase C expression in the cerebellum of the western diamondback rattlesnake (Crotalus atrox)

Sherpa Romeo green journal: open accessAldolase C, also known as Zebrin II (ZII), is a glycolytic enzyme that is expressed in cerebellar Purkinje cells of the vertebrate cerebellum. In both mammals and birds, ZII is expressed heterogeneously, such that there are sagittal stripes of Purkinje cells with high ZII expression (ZII+), alternating with stripes of Purkinje cells with little or no expression (ZII-). The patterns of ZII+ and ZII- stripes in the cerebellum of birds and mammals are strikingly similar, suggesting that it may have first evolved in the stem reptiles. In this study, we examined the expression of ZII in the cerebellum of the western diamondback rattlesnake (Crotalus atrox). In contrast to birds and mammals, the cerebellum of the rattlesnake is much smaller and simpler, consisting of a small, unfoliated dome of cells. A pattern of alternating ZII+ and ZII- sagittal stripes cells was not observed: rather all Purkinje cells were ZII+. This suggests that ZII stripes have either been lost in snakes or that they evolved convergently in birds and mammals.Ye

Explicating ways of consensus-making in science and society: distinguishing the academic, the interface and the meta-consensus

In this chapter, we shed new light on the epistemic struggle between establishing consensus and acknowledging plurality, by explicating different ways of consensus-making in science and society and examining the impact hereof on their field of intersection, i.e. consensus conferences (in particular those organized by the National Institute of Health). We draw a distinction between, what we call, academic and interface consensus, to capture the wide appeal to consensus in existing literature. We investigate such accounts - i.e. from Miriam Solomon, John Beatty and Alfred Moore, and Boaz Miller - as to put forth a new understanding of consensus-making, focusing on the meta-consensus. We further defend how (NIH) consensus conferences enable epistemic work, through demands of epistemic adequacy and contestability, contrary to the claim that consensus conferences miss a window for epistemic opportunity (Solomon M, The social epistemology of NIH consensus conferences. In: Kincaid H, McKitrick J (ed) Establishing medical reality: methodological and metaphysical issues in philosophy of medicine. Springer, Dordrecht, 2007). Paying attention to the dynamics surrounding consensus, moreover, allows us to illustrate how the public understanding of science and the public use of the ideal of consensus could be well modified

The objectivity of local knowledge. Lessons from ethnobiology

This article develops an account of local epistemic practices on the basis of case studies from ethnobiology. I argue that current debates about objectivity often stand in the way of a more adequate understanding of local knowledge and ethnobiological practices in general. While local knowledge about the biological world often meets criteria for objectivity in philosophy of science, general debates about the objectivity of local knowledge can also obscure their unique epistemic features. In modification of Ian Hacking’s suggestion to discuss “ground level questions” instead of objectivity, I propose an account that focuses on both epistemic virtues and vices of local epistemic practices

Diversity in olfactory bulb size in birds reflects allometry, ecology, and phylogeny

The relative size of olfactory bulbs (OBs) is correlated with olfactory capabilities across vertebrates and is widely used to assess the relative importance of olfaction to a species’ ecology. In birds, variations in the relative size of OBs are correlated with some behaviors; however, the factors that have led to the high level of diversity seen in OB sizes across birds are still not well understood. In this study, we use the relative size of OBs as a neuroanatomical proxy for olfactory capabilities in 135 species of birds, representing 21 orders. We examine the scaling of OBs with brain size across avian orders, determine likely ancestral states and test for correlations between OB sizes and habitat, ecology, and behavior. The size of avian OBs varied with the size of the brain and this allometric relationship was for the most part isometric, although species did deviate from this trend. Large OBs were characteristic of more basal species and in more recently derived species the OBs were small. Living and foraging in a semiaquatic environment was the strongest variable driving the evolution of large OBs in birds; olfaction may provide cues for navigation and foraging in this otherwise featureless environment. Some of the diversity in OB sizes was also undoubtedly due to differences in migratory behavior, foraging strategies and social structure. In summary, relative OB size in birds reflect allometry, phylogeny and behavior in ways that parallel that of other vertebrate classes. This provides comparative evidence that supports recent experimental studies into avian olfaction and suggests that olfaction is an important sensory modality for all avian species