Angels on a Pin: Dimensions of the Crisis in Invertebrate Conservation

Problems of measuring invertebrate diversity in natural communitiesare discussed, together with the rationale of setting prioritiesfor effective conservation of invertebrates. The "Crisis" ininvertebrate conservation has scientific, logistic, and ethicaldimensions. There is need to estimate these in conjunction witha range of values and educational imperatives to overcome publicprejudice against invertebrates and to increase conservationfunding for invertebrates. Values for selecting priority groupsare discussed, and a suite of priority taxa defined to maximisethe conservation value of the limited resources available.     

Vision without Frames: A Semiotic Paradigm of Event Based Computer Vision

Conventional imagers and almost all vision processes use and rely on theories that are based on the principle of static image-frames. A frame is a 2D matrix that represents the spatial locations of intensities of a scene projected on the imager. The notion of a frame itself is so embedded in machine vision, that it is usually taken for granted that this is how biological systems store light information. This paper presents a biosinpired event-based image formation principle, which output data rely on an asynchronous acquisition process. The generated information is stored in temporal volumes, which size and information depend only on the dynamic content of observed scenes. Practical analysis of such information will shows that the processing of visual information can only be based on a semiotic process. The paper also provides a general definition of the notion of visual features as the interpretation of signs according to different possible readings of the codified visual signal.     

Vision: in the brain of the beholder

It is commonly thought that neural activity in the visual cortex reflects retinal input. Recent studies, however, suggest that patterns of cortical activity are mostly intrinsically generated, and that visual input exerts but a modulatory influence.     

Vision: in the blink of an eye

Although we blink every 4 to 6 seconds, we notice neither the act of blinking nor the mini-blackouts they cause. A new study using imaging techniques identifies the neural structures in humans involved in suppressing vision processing and visual awareness during blinking.     

Vision: the when of perception

A visual image can be described by its temporal as well as spatial properties. A recent study of the asynchronous colour and motion perception has led to a new view of perceptual synchronisation, in which the temporal structures of events in the external world provide a general explanation of how events are bound or misbound in time.     

Vision: attending the invisible

In everyday vision, attention and awareness are hand in glove and almost impossible to tell apart. Recent work has exploited more contrived situations that allow these psychologically defined processes to be dissociated, providing insights into their respective neurophysiological correlates.     

Vision: stimulating your attention

Attentional selection biases the processing of higher visual areas to particular parts of a scene. Recent experiments show how stimulation of neurons in the frontal eye fields can mimic this process.     

Vision in microalgae

Flagellate green algae such as Chlamydomonas and related genera are guided by their eyes to places where light conditions are optimal for photosynthetic growth. These eyes constitute the simplest and most common visual system found in nature. The eyes contain optics, photoreceptors and the elementary components of a signal-transduction chain. Rhodopsin serves as the photoreceptor, as it does in animal vision. Upon light stimulation, its all-trans-retinal chromophore isomerizes into 13-cis and activates a photoreceptor channel which leads to a rapid Ca²⁺ influx into the eyespot region. At low light levels, the depolarization activates small flagellar currents which induce in both flagella small but slightly different beating changes resulting in distinct directional changes. In continuous light, Ca²⁺ fluxes serve as the molecular basis for phototaxis. In response to flashes of higher energy the larger photoreceptor currents trigger a massive Ca²⁺ influx into the flagella which causes the well-known phobic response. The identification of proteins contributing to this signalling system has just begun with the isolation and cloning of the opsins from Chlamydomonas and Volvox. These plant opsins are highly charged, are not typical seven-helix receptors, and are believed to form a protein complex with the photoreceptor channel. In Spermatozopsis, a G-protein has been found which interacts either directly with the rhodopsin or with the rhodopsin-ion channel complex. By using insertional mutagenesis, genes coding for proteins that are involved in signalling have been tagged. One of them is connected to the flagellar channel and crucial for the flagellar action potential. Elucidation of photoreception in flagellated algae will provide deeper insight into the development of visual systems, starting from single-celled organisms and moving up through higher animals. Received: 10 March 1997 / Accepted: 18 April 1997     

Bio Vision: microscopy in three dimensions.

Conventional electron microscopy is inadequate for visualizing the three-dimensional networks supporting cell architecture: the cytoskeleton and nuclear matrix. Consequently, we have not appreciated the extent to which the cell, its biochemistry, and its molecular biology are structured. A new technology combining in situ cell fractionation and resinless section electron microscopy allows the visualization of cell structure in three dimensions and permits the localization of individual components. These techniques reveal a far richer cell architecture than had been assumed and will allow important problems of biology, which have not surrendered their secrets to a purely biochemical approach, to be addressed.     

Vision in Flies: Measuring the Attention Span

A visual stimulus at a particular location of the visual field may elicit a behavior while at the same time equally salient stimuli in other parts do not. This property of visual systems is known as selective visual attention (SVA). The animal is said to have a focus of attention (FoA) which it has shifted to a particular location. Visual attention normally involves an attention span at the location to which the FoA has been shifted. Here the attention span is measured in Drosophila. The fly is tethered and hence has its eyes fixed in space. It can shift its FoA internally. This shift is revealed using two simultaneous test stimuli with characteristic responses at their particular locations. In tethered flight a wild type fly keeps its FoA at a certain location for up to 4s. Flies with a mutation in the radish gene, that has been suggested to be involved in attention-like mechanisms, display a reduced attention span of only 1s.