Showing papers in "Philosophical Transactions of the Royal Society B in 1992"
TL;DR: A new framework for describing the acoustic structure of speech based purely on temporal aspects has been developed, which is said to be comprised of three main temporal features, based on dominant fluctuation rates: envelope, periodicity, and fine-structure.
Abstract: The temporal properties of speech appear to play a more important role in linguistic contrasts than has hitherto been appreciated. Therefore, a new framework for describing the acoustic structure of speech based purely on temporal aspects has been developed. From this point of view, speech can be said to be comprised of three main temporal features, based on dominant fluctuation rates: envelope, periodicity, and fine-structure. Each feature has distinct acoustic manifestations, auditory and perceptual correlates, and roles in linguistic contrasts. The applicability of this three-featured temporal system is discussed in relation to hearing-impaired and normal listeners.
1,090 citations
TL;DR: The selectivity for view suggests that the neural operations underlying face or head recognition rely on parallel analyses of different characteristic views of the head, the outputs of these view-specific analyses being subsequently combined to support view-independent (object-centred) recognition.
Abstract: Cells selectively responsive to the face have been found in several visual sub-areas of temporal cortex in the macaque brain. These include the lateral and ventral surfaces of inferior temporal cortex and the upper bank, lower bank and fundus of the superior temporal sulcus (STS). Cells in the different regions may contribute in different ways to the processing of the facial image. Within the upper bank of the STS different populations of cells are selective for different views of the face and head. These cells occur in functionally discrete patches (3-5 mm across) within the STS cortex. Studies of output connections from the STS also reveal a modular anatomical organization of repeating 3-5 mm patches connected to the parietal cortex, an area thought to be involved in spatial awareness and in the control of attention. The properties of some cells suggest a role in the discrimination of heads from other objects, and in the recognition of familiar individuals. The selectivity for view suggests that the neural operations underlying face or head recognition rely on parallel analyses of different characteristic views of the head, the outputs of these view-specific analyses being subsequently combined to support view-independent (object-centred) recognition. An alternative functional interpretation of the sensitivity to head view is that the cells enable an analysis of 'social attention', i.e. they signal where other individuals are directing their attention. A cell maximally responsive to the left profile thus provides a signal that the attention (of another individual) is directed to the observer's left. Such information is useful for analysing social interactions between other individuals.(ABSTRACT TRUNCATED AT 250 WORDS)
833 citations
TL;DR: The understanding of some invertebrate sensory-motor systems has now reached a level able to provide valuable design hints and this approach brings into prominence the mutual constraints in the designs of a sensory and a motor system, in both living and non-living ambulatory creatures.
Abstract: Airborne insects are miniature w ing-flapping aircraft the visually guided manoeuvres of which depend on analogue, ‘fly-by-wire’ controls. The front-end of their visuomotor system consists of a pair of com pound eyes which are masterpieces of integrated optics and neural design. They rely on an array of passive sensors driving an orderly analogue neural network. We explored in concrete terms how motion-detecting neurons might possibly be used to solve navigational tasks involving obstacle avoidance in a creature whose wings are exquisitely guided by eyes with a poor spatial resolution. We designed, simulated, and built a complete terrestrial creature which moves about and avoids obstacles solely by evaluating the relative motion between itself and the environment. The compound eye uses an array of elementary motion detectors (emds) as smart, passive ranging sensors. Like its physiological counterpart, the visuomotor system is based on analogue, continuous-time processing and does not make use of conventional computers. It uses hardly any memory to adjust the robot’s heading in real time via a local and intermittent visuomotor feedback loop. This paper shows that the understanding of some invertebrate sensory-motor systems has now reached a level able to provide valuable design hints. Our approach brings into prominence the mutual constraints in the designs of a sensory and a motor system, in both living and non-living ambulatory creatures.
501 citations
TL;DR: For instance, this article found that young children do not form representations of newly encountered faces as efficiently as do adults, and that a major source of the improvement is acquisition of knowledge of faces per se, as opposed to age-related changes in general pattern encoding or memorial skills.
Abstract: Young children do not form representations of newly encountered faces as efficiently as do adults. A first step in explaining this difference, like any age-related change, is locating its source. A major source of the improvement is acquisition of knowledge of faces per se, as opposed to age-related changes in general pattern encoding or memorial skills. Two consequences of expertise at individualizing members of classes that share a basic configuration are known: a large inversion effect and a caricature advantage. It is possible that both of these effects reflect increased reliance, with expertise, on configuration distinguishing features. Several phenomena that indicate that inversion interferes with the encoding of configural aspects of faces are reviewed. Finally, developmental data are presented that confirm the suspicion that there are at least two distinct sources of the vulnerability of face encoding to inversion, perhaps reflecting two distinct senses of `configural encoding' of faces, only one of which is implicated in adult expertise at face encoding.
422 citations
TL;DR: Progress in understanding the psychology of lipreading and audio-visual speech perception is reviewed and how are the sights and sounds of talking faces represented at their conflux is reviewed.
Abstract: This paper reviews progress in understanding the psychology of lipreading and audio-visual speech perception. It considers four questions. What distinguishes better from poorer lipreaders? What are the effects of introducing a delay between the acoustical and optical speech signals? What have attempts to produce computer animations of talking faces contributed to our understanding of the visual cues that distinguish consonants and vowels? Finally, how should the process of audio-visual integration in speech perception be described; that is, how are the sights and sounds of talking faces represented at their conflux?
380 citations
TL;DR: New work on the nature of smiling shows that it is possible to distinguish the smile when enjoyment is occurring from other types of smiling, and implications for the differences between voluntary and involuntary expression are considered.
Abstract: Evidence on universals in facial expression of emotion and renewed controversy about how to interpret that evidence is discussed. New findings on the capability of voluntary facial action to generate changes in both autonomic and central nervous system activity are presented, as well as a discussion of the possible mechanisms relevant to this phenomenon. Finally, new work on the nature of smiling is reviewed which shows that it is possible to distinguish the smile when enjoyment is occurring from other types of smiling. Implications for the differences between voluntary and involuntary expression are considered.
369 citations
TL;DR: It is shown that the representation that is built in temporal cortical areas shows considerable invariance for size, contrast, spatial frequency and translation, and is in a form which is particularly useful for storage and as an output from the visual system.
Abstract: The ways in which information about faces is represented and stored in the temporal lobe visual areas of primates, as shown by recordings from single neurons in macaques, are considered. Some neurons that respond primarily to faces are found in the cortex in the anterior part of the superior temporal sulcus (in which neurons are especially likely to be tuned to facial expression and to face movement involved in gesture), and in the TE areas more ventrally forming the inferior temporal gyrus (in which neurons are more likely to have responses related to the identity of faces). Quantitative studies of the responses of the neurons that respond differently to the faces of different individuals show that information about the identity of the individual is represented by the responses of a population of neurons, that is, ensemble encoding rather than ‘grandmother cell’ encoding is used. It is argued that this type of tuning is a delicate compromise between very fine tuning, which has the advantage of low interference in neuronal network operations but the disadvantage of losing the useful properties (such as generalization, completion and graceful degradation) of storage in neuronal networks, and broad tuning, which has the advantage of allowing these properties of neuronal networks to be realized but the disadvantage of leading to interference between the different memories stored in an associative network. There is evidence that the responses of some of these neurons are altered by experience so that new stimuli become incorporated in the network. It is shown that the representation that is built in temporal cortical areas shows considerable invariance for size, contrast, spatial frequency and translation. Thus the representation is in a form which is particularly useful for storage and as an output from the visual system. It is also shown that one of the representations that is built is object based, which is suitable for recognition and as an input to associative memory, and that another is viewer centred, which is appropriate for conveying information about gesture. Ways are considered in which such cortical representations might be built by competitive self-organization aided by backprojections in the multistage cortical porcessing hierarchy which has convergence from stage to stage.
359 citations
TL;DR: The analysis of the spatial and temporal details of these fixations suggests that the underlying decision process that moves the eyes leaves key decisions until just before they are required.
Abstract: The small angle subtended by the human fovea places a premium on the ability to quickly and accurately direct the gaze to targets of interest. Thus the resultant saccadic eye fixations are a very instructive behaviour, revealing much about the underlying cognitive mechanisms that guide them. Of particular interest are the eye fixations used in hand-eye coordination. Such coordination has been extensively studied for single movements from a source location to a target location. In contrast, we have studied multiple fixations where the sources and targets are a function of a task and chosen dynamically by the subject according to task requirements. The task chosen is a copying task: subjects must copy a figure made up of contiguous coloured blocks as fast as possible. The main observation is that although eye fixations are used for the terminal phase of hand movements, they are used for other tasks before and after that phase. The analysis of the spatial and temporal details of these fixations suggests that the underlying decision process that moves the eyes leaves key decisions until just before they are required.
295 citations
TL;DR: In this article, the authors present a summary account of the ecology of the Danum Valley Conservation Area in the Malaysian state of Sabah, which is the site of a field centre and a collaborative research programme devoted to comparative study of primary forest ecology and the impacts of selective logging.
Abstract: The Malaysian state of Sabah occupies an area of 73 371 km $^{2}$ which is about 10% of the island of Borneo. About 60% of the land area is forested and 48% is gazetted as Permanent Forest Reserve or State or National Parks. The largest agent of forest disturbance is the timber industry, which plays a leading role in the state economy. A statutory body, the Sabah Foundation, holds a 100-year timber concession of 973 000 ha (9730 km $^{2}$ ) in the southeast of the state. Of this concession 9.7% has been reserved for conservation, including 43 800 ha (438 km $^{2}$ ) of uninhabited, mostly lowland forest in an area called Danum Valley. Since 1986, this has been the site of a field centre and a collaborative research programme devoted to comparative study of primary forest ecology and the impacts of selective logging. The paper includes a summary account of the ecology of the Danum Valley Conservation Area.
269 citations
TL;DR: The present benthic marine fauna of the Southern Ocean is rich and diverse, consisting of a mixture of taxa with differing evolutionary histories and biogeographical affinities, suggesting that at no time in the Cenozoic did continental ice sheets extend sufficiently to eradicate all shallow-water faunas around Antarctica at the same time.
Abstract: Environmental change is the norm and it is likely that, particularly on the geological timescale, the temperature regime experienced by marine organisms has never been stable. These temperature changes vary in timescale from daily, through seasonal variations, to long-term environmental change over tens of millions of years. Whereas physiological work can give information on how individual organisms may react phenotypically to short-term change, the way benthic communities react to long-term change can only be studied from the fossil record. The present benthic marine fauna of the Southern Ocean is rich and diverse, consisting of a mixture of taxa with differing evolutionary histories and biogeographical affinities, suggesting that at no time in the Cenozoic did continental ice sheets extend sufficiently to eradicate all shallow-water faunas around Antarctica at the same time. Nevertheless, certain features do suggest the operation of vicariant processes, and climatic cycles affecting distributional ranges and ice-sheet extension may both have enhanced speciation processes. The overall cooling of southern high-latitude seas since the mid-Eocene has been neither smooth nor steady. Intermittent periods of global warming and the influence of Milankovitch cyclicity is likely to have led to regular pulses of migration in and out of Antarctica. The resultant diversity pump may explain in part the high species richness of some marine taxa in the Southern Ocean. It is difficult to suggest how the existing fauna will react to present global warming. Although it is certain the fauna will change, as all faunas have done throughout evolutionary time, we cannot predict with confidence how it will do so.
258 citations
TL;DR: The properties of IT neurons are reviewed and it is considered how these properties may underlie the perceptual and mnemonic functions of IT cortex.
Abstract: In primates, inferior temporal (IT) cortex is crucial for the processing and storage of visual information about form and colour. This article reviews the properties of IT neurons and considers how these properties may underlie the perceptual and mnemonic functions of IT cortex. The available evidence suggests that the processing of the facial image by IT cortex is similar to its processing of other visual patterns. Faces and other complex visual stimuli appear to be represented by the pattern of responses over a population of IT neurons rather than by the responses of specific \`feature detectors' or \`grandmother' cells. IT neurons with adult-like stimulus properties are present in monkeys as young as six weeks old.
TL;DR: A slow run with very brief foot contact becomes the optimum gait at low speeds, at which people would walk, unless severe energy dissipation occurs in the compliance.
Abstract: Simple mathematical models capable of walking or running are used to compare the merits of bipedal gaits. Stride length, duty factor (the fraction of the stride, for which the foot is on the ground) and the pattern of force on the ground are varied, and the optimum gait is deemed to be the one that minimizes the positive work that the muscles must perform, per unit distance travelled. Even the simplest model, whose legs have neither mass nor elastic compliance, predicts the changes of duty factor and force pattern that people make as they increase their speed of walking. It predicts a sudden change to running at a critical speed, but this is much faster than the speed at which people make the change. When elastic compliance is incorporated in the model, unnaturally fast walking becomes uncompetitive. However, a slow run with very brief foot contact becomes the optimum gait at low speeds, at which people would walk, unless severe energy dissipation occurs in the compliance. A model whose legs have mass as well as elastic compliance predicts well the relationship between speed and stride length in human walking.
TL;DR: In this article, the authors found that most primary forest bird species were present in areas selectively logged eight years previously, however, certain taxa, such as flycatchers, woodpeckers, trogons and wren-babblers, became comparatively rare.
Abstract: In lowland dipterocarp forest in Sabah, Malaysia, most primary forest bird species were present in areas selectively logged eight years previously. However, certain taxa, notably flycatchers, woodpeckers, trogons and wren-babblers, became comparatively rare. In contrast, nectarivorous and opportunistic frugivorous species were significantly more abundant. Few species appeared to change foraging height, but netting rates suggest that the activity of some species had increased, or that some birds ranged over larger areas after logging. Although there is still much to be learned about the survival of birds in logged forest, large areas of this habitat are important for bird conservation. However, the susceptibility of logged forest to fire, and our present incomplete understanding of bird behaviour and population dynamics in logged forests mean that they should not be considered by conservationists as alternatives to reserves of primary forest.
TL;DR: The results of phylogenetic and extrapolatory approaches to the reconstruction of the shoulder musculature of the ornithomimid Struthiomimus are compared and it is suggested that the phylogenetic inference should be overturned only when the functional or other extrapolatories evidence is compelling.
Abstract: A research programme is proposed for the inference of unpreserved attributes of fossil taxa. The programme includes: (i) phylogenetic inference of attributes based on the cladistic distribution of known features in related taxa; and (ii) extrapolatory analyses that infer unpreserved features from the known attributes of the fossil. Phylogenetic inferences regarding the fossil taxon are based on the attributes of both the sister group of the fossil taxon and more distantly related clades. Unlike phylogenetic inferences that are based on a single related taxon, this broader phylogenetic context avoids unjustified assumptions regarding the occurrence of unpreserved features in particular fossil taxa. Phylogenetic inference is conservative; only features in related taxa can be inferred in the fossil. Extrapolatory analyses, such as form-function correlation and biomechanical design analysis, provide a means for choosing among equivocal phylogenetic inferences, and, on occasion, can provide a basis for rejecting a phylogenetic inference. Extrapolatory approaches provide the only means of inferring or interpreting autapomorphies in fossils. The results of phylogenetic and extrapolatory approaches to the reconstruction of the shoulder musculature of the ornithomimid Struthiomimus are compared. Results are congruent in most instances; however, many of the extrapolatory inferences are implicitly phylogenetic. The phylogenetic inferences constitute a null hypothesis regarding fossil attributes, and place constraints on the inferences generated by extrapolatory analyses. The potential uncertainty and untestability of many extrapolatory analyses suggests that the phylogenetic inference should be overturned only when the functional or other extrapolatory evidence is compelling. This procedure should identify and reduce speculation in fossil reconstruction.
TL;DR: The parasitoid lifeway has arisen most commonly in the Diptera, where it has evolved independently in 21 families (probably over 100 times) and has arisen in 11 coleopteran families but probably only once in the Hymenoptera.
Abstract: This paper reviews the biology of insect parasitoids and cleptoparasitoids and places them in an evolutionary context. Available biological data are reviewed and tabulated (at the family level) with an emphasis on non-hymenopteran parasitoids. Existing cladistic or near-cladistic treatments of the parasitoid groups are used to make outgroup comparisons, and pathways to and from the parasitoid lifeway are estimated. Approximately 10% of all described insect species are parasitoids or cleptoparasitoids. Of these about three-quarters are Hymenoptera, and one-quarter are either Diptera or Coleoptera. The parasitoid lifeway has arisen most commonly in the Diptera, where it has evolved independently in 21 families (probably over 100 times). It has arisen in 11 coleopteran families but probably only once in the Hymenoptera. In most cases host searching is by the adult female parasitoid but in a significant minority of cases host-searching is by the first instar larva of the parasitoid, or (more rarely) by the host ingesting the parasitoid's egg. Dipteran parasitoids (as a whole) have a wider host range than hymenopteran or coleopteran parasitoids. The most common pathways to parasitoidism are from mycophagy, saprophagy and predation. In contrast, evolutionary shifts away from parasitoidism are relatively rare. Possible evolutionary explanations for these pathways are reviewed and others are suggested. A possible (evolutionary) explanation of the common evolutionary association of parasitoids with specialized egg predators is also discussed.
TL;DR: The animals were less able than before to discern the angle of regard in pictures of faces, suggesting that this area of the brain may be concerned with the perception of facial expression and bearing, which are important social signals in primates.
Abstract: Cortical neurons that are selectively sensitive to faces, parts of faces and particular facial expressions are concentrated in the banks and floor of the superior temporal sulcus in macaque monkeys. Their existence has prompted suggestions that it is damage to such a region in the human brain that leads to prosopagnosia: the inability to recognize faces or to discriminate between faces. This was tested by removing the face-cell area in a group of monkeys. The animals learned to discriminate between pictures of faces or inanimate objects, to select the odd face from a group, to inspect a face then select the matching face from a pair of faces after a variable delay, to discriminate between novel and familiar faces, and to identify specific faces. Removing the face-cell area produced no or little impairment which in the latter case was not specific for faces. In contrast, several prosopagnosic patients were impaired at several of these tasks. The animals were less able than before to discern the angle of regard in pictures of faces, suggesting that this area of the brain may be concerned with the perception of facial expression and bearing, which are important social signals in primates.
TL;DR: A combined magnetic resonance imaging (MRI) and positron emission tomography (PET) study of regional cerebral blood flow (rCBF) in normal subjects performing different tasks of face and object processing indicates different patterns of cerebral activation depending on the requirements of the tasks within the processing of faces, as well as a clear dissociation of the neural substrates underlying face and objects processing.
Abstract: Studies of brain-damaged patients have revealed the existence of a selective impairment of face processing, prosopagnosia, resulting from lesions at different loci in the occipital and temporal lobes. The lesions are often extensive, and it is unclear what functional aspects of face processing are normally served by the damaged areas, and whether they are uniquely devoted to the processing of faces. These issues are further addressed through a combined magnetic resonance imaging (MRI) and positron emission tomography (PET) study of regional cerebral blood flow (rCBF) in normal subjects performing different tasks of face and object processing. The results indicate different patterns of cerebral activation depending on the requirements of the tasks within the processing of faces, as well as a clear dissociation of the neural substrates underlying face and object processing. These results are compared with radiological data from prosopagnosic patients, and are put in relation with the patterns of deficits observed in the patients as a function of the location of their lesions. Together, the findings offer new evidence regarding the functional neuroanatomy of face and object processing.
TL;DR: The main changes in the distribution and abundance of marine top predators in the Antarctic in the last two centuries were caused by an over-exploitation and certain taxa are especially vulnerable to at least some of the likely environmental changes.
Abstract: The main changes in the distribution and abundance of marine top predators in the Antarctic in the last two centuries were caused by hum an over-exploitation. Hypotheses that increases in populations of krill-eating penguins and seals represent recovery from exploitation, accelerated by removal of krill-eating whales, are being re-evaluated in the light of correlations between population size and reproductive success of seabirds and seals and various features of the biological and physical environment. These correlations involve phocid and otariid seals, penguins and flying birds and sites ranging from the Antarctic continent to sub-Antarctic islands. Although the nature of, and balance between, physical and biological influences differ between sites, regions and different types of predator, processes (including potentially important links with the Southern Oscillation) involving sea-ice extent and distribution play a key role. Major uncertainties over the nature of the links between physical and biological processes and the responses of marine populations preclude any confident prediction of the potential effects of future environmental change. However, certain taxa, especially those of specialist ecology, extreme demography and restricted distribution (especially in high latitudes) are especially vulnerable to at least some of the likely environmental changes.
TL;DR: The forest is differentiated by its dominance by Euphorbiaceae, in terms of tree density, and the high contributions made by Lauraceae and Meliaceae, and may reflect special site conditions and/or a late stage in recovery from past disturbance.
Abstract: Trees greater than or equal to 10 cm gbh were enumerated, mapped and identified in two 4 hectare (ha) (40 000 m 2 ) plots in 1985-1987. The number of species recorded was 511 (in 164 genera and 59 families) in a total sample of 17 985 individuals. Plots 1 and 2 contain 388 and 387 species respectively, and for trees greater than or equal to 30 cm gbh there are 247 and 242 species. Relative abundance patterns were fitted to a logseries distribution. In each plot, 51% of species are rare ( f f = 1). Common species ( f ≥ 5 ) achieve a minimum area at 2 ha. The plots are close ‘replicates’ in many respects, and 8 ha gives an adequate sample. The mean density of trees greater than or equal to 10 cm gbh and 30 cm gbh is 2248 ha -1 and 470 ha -1 , with corresponding basal areas of 30.7 m 2 ha -1 and 26.6 m 2 ha -1 . The linear relation between In frequency and In gbh, the small (0.5% ) ground area of gaps, and the low contribution by pioneer species show little recent disturbance. Dominance by 2-4 understorey species is pronounced. For trees greater than or equal to 30 cm gbh, the Euphorbiaceae contribute the most to density at 21% , with Dipterocarpaeceae second at 16%: corresponding basal areas are 7% and 49% . For trees greater than or equal to 10 cm gbh, density of the Euphorbiaceae reaches 28% , Dipterocarpaceae 9% , followed by Annonaceae 8% , Lauraceae 7% and Meliaceae 6% . Lauraceae was the most species-rich family (83 species), then Euphorbiaceae (51 species) and Meliaceae (36 species). Compared with the means of nine other sites in this forest type, Danum has 84% of the density and 74% of the basal area for trees greater than or equal to 30 cm gbh; and 60% of the species richness for this size class on a 1-1.6 ha basis. The forest is differentiated by its dominance by Euphorbiaceae, in terms of tree density, and the high contributions made by Lauraceae and Meliaceae. These attributes may reflect special site conditions and/or a late stage in recovery from past disturbance.
TL;DR: A detailed explanation of MarR's theory based upon an analogy between Marr's cerebellar model and an abstract model called the associative net is presented and it is found that in general terms his conclusion that each Purkinje cell can learn to respond to a large number of different patterns of activity in the mossy fibres is substantially correct.
Abstract: Marr’s theory of the cerebellar cortex as an associative learning device is one of the best examples of a theory that directly relates the function of a neural system to its neural structure. However, although he assigned a precise function to each of the identified cell types of the cerebellar cortex, many of the crucial aspects of the implementation of his theory remained unspecified. We attempted to resolve these difficulties by constructing a computer simulation which contained a direct representation of the 13 000 mossy fibres and the 200 000 granule cells associated with a single Purkinje cell of the cerebellar cortex, together with the supporting Golgi, basket and stellate cells. In this paper we present a detailed explanation of Marr’s theory based upon an analogy between Marr’s cerebellar model and an abstract model called the associative net. Although some of Marr’s assumptions contravene neuroanatom ical findings, we found that in general terms his conclusion that each Purkinje cell can learn to respond to a large number of different patterns of activity in the mossy fibres is substantially correct. However, we found that this system has a lower capacity and acts more stochastically than he envisaged. The biologically realistic simulated structure that we designed can be used to assess the computational capabilities of other network theories of the cerebellum.
TL;DR: The responses of DCN principal cells to filtered noise stimuli that model the spectral sound localization cues produced by the pinna imply that the DCN plays a role in interpreting sound localization cue cues; supporting evidence for such a role is discussed.
Abstract: The dorsal division of the cochlear nucleus (DCN) is the most complex of its subdivisions in terms of both anatomical organization and physiological response types. Hypotheses about the functional role of the DCN in hearing are as yet primitive, in part because the organizational complexity of the DCN has made development of a comprehensive and predictive model of its input-output processing difficult. The responses of DCN cells to complex stimuli, especially filtered noise, are interesting because they demonstrate properties that cannot be predicted, without further assumptions, from responses to narrow band stimuli, such as tones. In this paper, we discuss the functional organization of the DCN, i.e. the morphological organization of synaptic connections within the nucleus and the nature of synaptic interactions between its cells. We then discuss the responses of DCN principal cells to filtered noise stimuli that model the spectral sound localization cues produced by the pinna. These data imply that the DCN plays a role in interpreting sound localization cues; supporting evidence for such a role is discussed.
TL;DR: Insects use terrestrial landmarks both for retrieving important places in their environment, like a nest, and for guiding their way along frequently travelled routes, which need not be defined so precisely and landmarks are then employed in less demanding ways.
Abstract: Insects use terrestrial landmarks both for retrieving important places in their environment, like a nest, and for guiding their way along frequently travelled routes. Places are pinpointed by a form of image matching: the insect moves to maximize the fit between the image on its retina and its memory of surrounding landmarks as viewed from close to the goal. In this case, the insect’s stored representation seems to be a filtered but relatively unprocessed replica of the image falling on the retina, which is parsed for features like the position and orientation of edges, their speed of motion and their colour. Routes need not be defined so precisely and landmarks are then employed in less demanding ways.
TL;DR: The ecological and behavioural correlates of within- song complexity differ from those of between-song complexity, suggesting that they are not alternative solutions to the same selective pressures.
Abstract: Several ecological and behavioural factors are correlated with interspecific differences in the complexity and temporal arrangement of passerine songs. For example, song repertoires are larger in species where males provide more parental care; syllable repertoire sizes are greater in polygynous species; migrants have larger song and syllable repertoires; and more vocalization during a song bout is associated with higher fecundities and lower metabolic rates. These associations often differ at different taxonomic levels, suggesting that the factors causing divergence in song characters within genera are different from those responsible for divergence among more distantly related taxa. In general, correlates of greater song complexity can be interpreted as those factors likely to produce more intense inter- or intra-sexual selection (polygyny, migration, paternal care). Measures of song output are correlated with factors likely to be associated with species differences in energetic requirements (metabolic rate) or reproductive effort (fecundity). The ecological and behavioural correlates of within-song complexity differ from those of between-song complexity, suggesting that they are not alternative solutions to the same selective pressures.
TL;DR: Temporal continuity can be shown in the geographical distribution of stylistic markers and this suggests participation in a shared cognitive system at a period when selection for a gracile morphology may have been pronounced.
Abstract: This paper argues that southern Africa was a remote part of the Old World in the late Pleistocene (125- 10 ka ago). Because of this isolated position there was continuity without significant replacement in the resident population. Isolation and the relatively recent spread of agriculture to the region has allowed a section of this population to survive into the present. They are the Bushmen (San). Studies of geographic patterning in conventional genetic markers and mitochrondrial DNA indicate that the Bushman clade has a long evolutionary history in southern Africa. Estimates of more than 100 ka for the continued presence of this population in the region are supported in archaeological investigations of sites with long sequences such as Klasies River main site and Border Cave. Human remains dating to the earlier part of the late Pleistocene have been recovered from these sites and the samples form a morphological series with the Klasies River remains possibly 20 ka older than those from Border Cave. There is no fossil record for the later Pleistocene, however, at a period when selection for a gracile morphology may have been pronounced. The cultural associations in the earlier late Pleistocene are with the Middle Stone Age. Expressions of cultural ‘style’ and the occurrence of similar artefact design types in the Middle and Eater Stone Ages can be interpreted with reference to the ethnographic present. Temporal continuity can be shown in the geographical distribution of stylistic markers and this suggests participation in a shared cognitive system. The inference is that the people in the earlier late Pleistocene had cognitive abilities that are comparable to those shown by their Holocene and modern descendants. The presence of the ancestors of a modern population in the earlier late Pleistocene in this region is perhaps expected if modern people had their origins in Africa.
TL;DR: In this article, the occurrence, systematics, palaeobiological and evolutionary significance of Mesozoic bird and bird-like tracks are reviewed in the light of recent new discoveries in East Asia, Africa and North America.
Abstract: The occurrence, systematics, palaeobiological and evolutionary significance of Mesozoic bird and birdlike tracks are reviewed in the light of recent new discoveries in East Asia, Africa and North America. The most abundant footprint evidence currently comes from Lower Cretaceous deposits of East Asia and North America, where there is now a substantial track record for shorebirds. However, there is also a significant record of pre-Cretaceous bird-like tracks. The Cretaceous Jindong Formation of South Korea has recently yielded over 30 localities and stratigraphic levels, tripling the previous record worldwide and providing evidence of hitherto unknown large waders: Jindongornipes kimi ichnogen. et ichnosp. nov. Like other previously named ichnotaxa, this bird track type probably represents a charadriiform species. It is included with Ignotornis and Koreanaornis in the new ichnofamily Ignotornidae. Lower Cretaceous bird tracks are abundant, typically show high densities (100-300 tracks m 2 ) and often occur in association with invertebrate traces, inferred to have been made by the organisms on which the birds were feeding. Such track evidence suggests that waterbird communities were well-established by the end of the Early Cretaceous. This is about 30 Ma before the purported waterbird radiation inferred from Upper Cretaceous avian skeletal remains, but is consistent with hypotheses that suggest an ancestral shorebird stock. Bird and bird-like tracks from the Jurassic and Late Cretaceous are variable in morphology, still poorly understood, and sometimes attributed to small coelurosaurian dinosaurs. However, current evidence suggests that the Jurassic aviform ichnogenus Trisauropodiscus may be of avian origin. It is sufficiently distinct from typical grallatorid (coelurosaurian) tracks to warrant recognition of a new ichnofamily (Trisauropodiscidae), which includes the newly described ichnospecies Trisauropodiscus moabensis from North America. Bird and bird-like tracks from both the Jurassic and Cretaceous are shown to be much more abundant and distinctive than previously supposed. Moreover, they add significantly to our understanding of early avian evolution and palaeoecology, and provide insights into the timing of events in avian evolution.
TL;DR: In gaps, the most important determinant of seedling survival and growth was seedling size at the time of gap creation, regardless of species, which suggests an ability to persist for long periods under closed forest and slowly accumulate growth may bestow an enormous size advantage on seedlings when gaps occur.
Abstract: The theory of gap regeneration dynamics proposes that different species of tree partition canopy gaps because they are preferentially adapted to a particular gap size class. A variety of gap sizes would therefore favour the regeneration of a range of species. The theory has been used to explain the extraordinarily high tree species diversity of tropical rain forests. A test was mounted in lowland evergreen dipterocarp rain forest in the Danum Valley, Sabah, East Malaysia by the creation of ten, artificial canopy gaps ranging in size from 10 m 2 to 1500 m 2 (6 to 30% canopy openness). The responses of established populations of seedlings of three dipterocarp species ( Hopea nervosa , Parashorea malaanonan and Shorea johorensis ) with contrasting silvicultural reputations were monitored for 40 months in these gaps and under closed forest. There were significant differences in survival and growth under closed forest between these three species. However, in gaps, the most important determinant of seedling survival and growth was seedling size at the time of gap creation, regardless of species. An ability to persist for long periods under closed forest and slowly accumulate growth may bestow an enormous size advantage on seedlings when gaps occur. Generalizations on the regeneration dynamics of dipterocarp rain forests need to be modified in the light of this result. Further observations for several years are important to see whether forest recovery eventually converges on predictions from the original paradigm.
TL;DR: Data and analyses from pilot studies in the Danum area of Sabah, East Malaysia, and elsewhere in the Indo-Australian tropics are used to measure the effects of logging and other human disturbance, such as conversion to plantation, on insect diversity.
Abstract: Data and analyses from pilot studies in the Danum area of Sabah, East Malaysia, and elsewhere in the Indo-Australian tropics are used to measure the effects of logging and other human disturbance, such as conversion to plantation, on insect diversity. The two insect groups studied have very different trophic requirements: moths, with floristically specific herbivory, and dung and carrion beetles, exploiting resources of much more uniform quality over different forest systems. Moths show significant loss of diversity and taxonomic quality with disturbance and conversion to plantation. The beetles show much less change in diversity and faunistic composition. The implications for conservation of biodiversity are discussed, and suggestions for further work are made.
TL;DR: In this paper, a simple analysis of ecological parameters may be used to quantify the extent to which logging affects the forest ecosystem and the extent of which it recovers over time in two tropical rain forests in South-east Asia.
Abstract: The adoption of tropical rain forest management systems that conserve both timber stocks and the environment is increasingly viewed as a necessary development to maintain both the tropical timber trade and the forests themselves. There are no theoretical reasons why such systems should not be achievable. Ecological studies of vertebrate animal populations, and of wider ecosystem processes, can assist foresters in designing more appropriate forestry systems and in their long-term monitoring. Data are presented from two Forest Reserves in South-east Asia, Tekam in Peninsular Malaysia and Ulu Segama in Sabah, to show how simple analysis of ecological parameters may be used to quantify the extent to which logging affects the forest ecosystem and the extent to which it recovers over time.
TL;DR: Overall, the results demonstrate, that for a full understanding of diatom population dynamics, it is important to quantify events over complete life cycles.
Abstract: The life cycle of Aulacoseira subarctica (O. Muller) Haworth in Lough Neagh, Northern Ireland, is described. Cell numbers can reach up to 17000 per millilitre in spring. Most cells sediment to the bottom after silica limitation and go into a resting state during summer. The inoculum in autumn partly comes from resuspension, with the surviving cells (0.5-5%) continuing to grow through the winter, doubling every one to two weeks. T he population goes through a size reduction and regeneration cycle linked to sexual reproduction. Gametes are only produced in narrower cells (3.8-7.4 um diameter), usually after interruptions in growth caused by low light conditions (surface irradiance 100-150 pE m -2 s-1), but availability of nutrients, especially silica and nitrogen, is also important. Even the highest densities of auxospores (20 m1 -1) represent only a small proportion of the total cells present (0.16%). Size regeneration results in initial cells with diameters (14.8 ± 2 pm) about three times those of the parent. Larger parent cells usually give rise to larger initial cells. Subsequently, cell division leads to a decrease in population diameter, because of the way new valves are laid down below the girdle bands. Reductions are largest in broader cells (0.32 um per division) and gradually decrease as cells get narrower. Occasionally large reductions, up to 1 um, follow periods of environmental stress. By combining these results with studies of changes in cell size (width, length and volume) in related individuals along filaments, it was possible to explain why there have been difficulties in applying the MacDonald-Pfitzer hypothesis to natural populations. Theoretically, the life cycle in L. Neagh might extend over 100 divisions or 15 years but, in practice, cells reach a sexually inducible size in 4-6 years. The discrepancy is because environmental factors (e.g. sedimentation, resuspension, parasitism, etc.) are also important in size selectivity. The interaction of these factors, when combined with intermittent sexual reproduction at low frequencies, results in a relatively stable population size distribution, where there are always some cells in the size range in which sexual differentiation can be induced. Overall, the results demonstrate, that for a full understanding of diatom population dynamics, it is important to quantify events over complete life cycles.
TL;DR: The experiments with machine vision raise questions about the part played by perceptual context for object recognition in natural vision, and the neural mechanisms which might serve such a role.
Abstract: Recent work on the visual interpretation of traffic scenes is described which relies heavily on a priori knowledge of the scene and position of the cam era, and expectations about the shapes of vehicles and their likely movements in the scene. Knowledge is represented in the computer as explicit three-dimensional geometrical models, dynamic filters, and descriptions of behaviour. Model-based vision, based on reasoning with analogue models, avoids many of the classical problems in visual perception: recognition is robust against changes in the image of shape, size, colour and illumination. The three-dimensional understanding of the scene which results also deals naturally with occlusion, and allows the behaviour of vehicles to be interpreted. The experiments with machine vision raise questions about the part played by perceptual context for object recognition in natural vision, and the neural mechanisms which might serve such a role.