920 research outputs found

    PROPUESTA PARA EL DESARROLLO DE CONTENIDOS EN TELEVISIÓN DIGITAL PARA PERSONAS CON LIMITACIÓN AUDITIVA

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    Eneste artículo se ha realizado una caracterización de la población con este tipo de limitación, concluyendo que existen diferentes desarrollos tecnológicos en donde se podrían observar de una forma más interactiva este tipo de contenidos aportando al desarrollo social, y educativo de esta población

    A `bright zone' in male hoverfly (Eristalis tenax) eyes and associated faster motion detection and increased contrast sensitivity

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    Eyes of the hoverfly Eristalis tenax are sexually dimorphic such that males have a fronto-dorsal region of large facets. In contrast to other large flies in which large facets are associated with a decreased interommatidial angle to form a dorsal `acute zone' of increased spatial resolution, we show that a dorsal region of large facets in males appears to form a `bright zone' of increased light capture without substantially increased spatial resolution. Theoretically, more light allows for increased performance in tasks such as motion detection. To determine the effect of the bright zone on motion detection, local properties of wide field motion detecting neurons were investigated using localized sinusoidal gratings. The pattern of local preferred directions of one class of these cells, the HS cells, in Eristalis is similar to that reported for the blowfly Calliphora. The bright zone seems to contribute to local contrast sensitivity; high contrast sensitivity exists in portions of the receptive field served by large diameter facet lenses of males and is not observed in females. Finally, temporal frequency tuning is also significantly faster in this frontal portion of the world, particularly in males, where it overcompensates for the higher spatial-frequency tuning and shifts the predicted local velocity optimum to higher speeds. These results indicate that increased retinal illuminance due to the bright zone of males is used to enhance contrast sensitivity and speed motion detector responses. Additionally, local neural properties vary across the visual world in a way not expected if HS cells serve purely as matched filters to measure yaw-induced visual motion

    Differences in the escape response of a grapsid crab in the field and in the laboratory

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    Escape behaviours of prey animals are frequently used to study the neural control of behaviour. Escape responses are robust, fast, and can be reliably evoked under both field and laboratory conditions. Many escape responses are not as simple as previously suggested, however, and are often modulated by a range of contextual factors. To date it has been unclear to what extent behaviours studied in controlled laboratory experiments are actually representative of the behaviours that occur under more natural conditions. Here we have used the model species, Neohelice granulata, a grapsid crab, to show that there are significant differences between the crabs' escape responses in the field compared to those previously documented in laboratory experiments. These differences are consistent with contextual adjustments such as the availability of a refuge and have clear consequences for understanding the crabs' neural control of behaviour. Furthermore, the methodology used in this study mirrors the methodology previously used in fiddler crab research, allowing us to show that the previously documented differences in escape responses between these grapsid species are real and substantial. Neohelice's responses are delayed and more controlled. Overall, the results highlight the adaptability and flexibility of escape behaviours and provide further evidence that the neural control of behaviour needs to be address in both the laboratory and field context.Fil: Hemmi, J. M.. University of Western Australia; AustraliaFil: Tomsic, Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentin

    Design principles of hair-like structures as biological machines

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    Hair-like structures are prevalent throughout biology and frequently act to sense or alter interactions with an organism's environment. The overall shape of a hair is simple: a long, filamentous object that protrudes from the surface of an organism. This basic design, however, can confer a wide range of functions, owing largely to the flexibility and large surface area that it usually possesses. From this simple structural basis, small changes in geometry, such as diameter, curvature and inter-hair spacing, can have considerable effects on mechanical properties, allowing functions such as mechanosensing, attachment, movement and protection. Here, we explore how passive features of hair-like structures, both individually and within arrays, enable diverse functions across biology. Understanding the relationships between form and function can provide biologists with an appreciation for the constraints and possibilities on hair-like structures. Additionally, such structures have already been used in biomimetic engineering with applications in sensing, water capture and adhesion. By examining hairs as a functional mechanical unit, geometry and arrangement can be rationally designed to generate new engineering devices and ideas

    Why do axons differ in caliber?

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    CNS axons differ in diameter (d) by nearly 100-fold (∼0.1-10 μm); therefore, they differ in cross-sectional area (d(2)) and volume by nearly 10,000-fold. If, as found for optic nerve, mitochondrial volume fraction is constant with axon diameter, energy capacity would rise with axon volume, also as d(2). We asked, given constraints on space and energy, what functional requirements set an axon's diameter? Surveying 16 fiber groups spanning nearly the full range of diameters in five species (guinea pig, rat, monkey, locust, octopus), we found the following: (1) thin axons are most numerous; (2) mean firing frequencies, estimated for nine of the identified axon classes, are low for thin fibers and high for thick ones, ranging from ∼1 to >100 Hz; (3) a tract's distribution of fiber diameters, whether narrow or broad, and whether symmetric or skewed, reflects heterogeneity of information rates conveyed by its individual fibers; and (4) mitochondrial volume/axon length rises ≥d(2). To explain the pressure toward thin diameters, we note an established law of diminishing returns: an axon, to double its information rate, must more than double its firing rate. Since diameter is apparently linear with firing rate, doubling information rate would more than quadruple an axon's volume and energy use. Thicker axons may be needed to encode features that cannot be efficiently decoded if their information is spread over several low-rate channels. Thus, information rate may be the main variable that sets axon caliber, with axons constrained to deliver information at the lowest acceptable rate

    Aerodynamic imaging by mosquitoes inspires a surface detector for autonomous flying vehicles

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    Some flying animals use active sensing to perceive and avoid obstacles. Nocturnal mosquitoes exhibit a behavioral response to divert away from surfaces when vision is unavailable, indicating a short-range, mechanosensory collision-avoidance mechanism. We suggest that this behavior is mediated by perceiving modulations of their self-induced airflow patterns as they enter a ground or wall effect. We used computational fluid dynamics simulations of low-altitude and near-wall flights based on in vivo high-speed kinematic measurements to quantify changes in the self-generated pressure and velocity cues at the sensitive mechanosensory antennae. We validated the principle that encoding aerodynamic information can enable collision avoidance by developing a quadcopter with a sensory system inspired by the mosquito. Such low-power sensing systems have major potential for future use in safer rotorcraft control systems

    The visual ecology of bees - Tales of diverse eyes and behaviours

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    The buzzing flight of bees is a popular summer hit. Yet, outside of a few familiar species of honeybees and bumblebees, these fantastic little creatures are still mostly unknown. With about twenty-five thousand species, bees are a very diverse group. They can be found in drastically different habitats. For example, some kinds of bumblebees endure the freezing temperatures and windswept tundra of Greenland, while others only thrive in the heat and humidity of the Amazonian forest. Some bees live in huge colonies with tens of thousands of members, while others live solitary lives. Some are narrower than a sesame seed, while others can reach the size of a human thumb. Despite these differences, bees all have in common the urge to visit flowers where they find their food. This habit makes them very important for the pollination of plants across the world. To go about their laborious life, bees make extensive use of their vision. They possess two types of eyes – ocelli and compound eyes – that they use to control their flight, find their way through the world, discover flowers and spot possible mates. To understand how bees interact with the environment, we thus need to explore the diversity of their eyes and of how they use them.The first chapter of my thesis is about landing, which is a fundamental behaviour in flying insects. However, in bees it is poorly known whether different species land in different ways. During an expedition to Brazil, I came across a species of bee with the most peculiar landing style. Rather than slowing down to land, as most animals do, these bees accelerate just before touchdown on the entrance to their hive. Why do these bees speed up when they land? Using a computer simulation, I found that this weird strategy may help the bees to avoid mid-air collisions with nestmates and reduce bee ‘traffic jams’ in front of the hive. In turn, this would make food collection more efficient for the colony and it would be easier for hive members to defend against intruders. With this chapter, I showed that the lifestyle of bees – where they live, how many there are and if they are exposed to intruders – can strongly influence their behaviour.In chapter two, I then asked if and how the bees from chapter one use vision to control their peculiar landing. I found that they did indeed rely on vision to control their landing and that they did so in a simple manner. Essentially, when the image of the entrance of the hive reaches a given size on their eyes, these bees start to speed up. When the image of the entrance reaches a second set size on the eyes of landing bees, they extend their landing gear – which is, for bees, their legs – in preparation for touchdown. This chapter reveals that bees can use simple rules to achieve complex behaviours such as landing safely.To explore the diversity of eyes in a large number of bees, we use X-ray images taken from a sample as it rotates (an approach known as computed tomography or CT, commonly used in a medical setting) to produce 3D images of the eyes. However, powerful tools are needed to analyse the large amounts of data that this approach generates. As I want to better understand how bee eyes work, I needed an efficient method for analysing 3D eye images created by CT, so I developed an automatic tool for distinguishing essential optical structures in the eyes of insects and other arthropods. In chapter three, I describe this method, provide a guide to use it, and give examples of its application to a few insect eyes.In the last chapter, I used CT to look into the diversity of the eyes across a range of bumblebees from different habitats around the world. Even though different species are genetically close to each other, I found that their eyes were far from ‘all the same’. For example, bumblebees that live in forests have eyes that may enable them to see less sharp but better in dim light than bumblebees living in open landscapes. I also found that cuckoo bumblebees – bees that lay their eggs in another bumblebee hive like cuckoo birds do – had peculiar eyes in comparison to other bumblebees. This indicates that the eyes of each species of bumblebees may be specialised for a specific combination of lifestyle and habitat. These results are important for the conservation of bumblebees because they suggest that the eyes of some species may make them more sensitive than others to changes in the environment. For example, farming practices that create large open fields may particularly disadvantage bumblebees with eyes adapted to forests.These four chapters only scratch the surface of the tight links between the eyes of bees, the ways they behave, and the worlds they live in. I hope that efforts to look into their diverse eyes will continue and will help to protect these crucial but endangered animals
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