The latency of target elicited saccadic eye movements

In 1967 M.G. Saslow found that latencies of target elicited saccades were significantly reduced when the target onset was preceded shortly by the offset of a fixation point (Saslow, 1967). This result has subsequently been replicated by various authors, and has provided the basis for a number of investigations into the properties of the mechanisms of saccadic control. In 1983 B. Fischer and R. Boch reported the discovery of a second effect. Using the same basic experimental methods and using monkeys as subjects, they found a population of saccades with extremely short reaction times in addition to the general reduction in saccade latencies previously reported. They termed this population 'express saccades' (Fischer and Boch, 1983).Various models have been proposed to explain both the reduction in saccade latencies reported by Saslow, and the occurrence of 'express saccades’ reported by Fischer et al. This thesis provides an explicit, quantitative framework against which these models can be compared. Although the phenomenon of express saccades has been well established for monkeys, the evidence for their occurrence in humans appears less convincing. This thesis tests in a rigorous manner for a population of saccades in humans equivalent to the express saccades found for monkeys. Chapter One reviews the experimental factors that affect the latencies of target elicited saccades. The validity of the 'when/where' distinction in models of saccadic control is discussed in Chapter Two. In Chapter Three the reduction in saccade latencies found by Saslow, and express saccades, are discussed in greater detail together with models proposed in explanation. The fourth chapter gives the rationale for experiments designed to test these models, and in Chapter Five these experiments are described and their results and implications for models of saccadic latency are discussed. Conclusions to the thesis are given in Chapter Six

Stone tools and the linguistic capabilities of earlier hominids

The evolution of human manipulative abilities may be clearly linked to the evolution of speech motor control Both creativity and complexity in vocal and manipulative gestures may be closely linked to a single dimension of brain evolution — the evolution of absolute brain size. Inferring the linguistic capabilities of earlier hominids from their lithic artefacts, however, required us to take account of domain-specific constraints on manipulative skill In this article we report on a pilot flint-knapping experiment designed to identify such constraints ‘in action’

Food insecurity in urban Tanzania

The urban food security challenge in Tanzania is both distinct and pressing. With an urban population that is set to more than double by 2030, so will its food requirements. Many food security challenges exist, including weak rural-urban food supply linkages, an inadequate food import budget and production constraints on the smallholder farming sector. In light of this, Tanzanian policy is aiming to improve the capacity of rural areas to meet the growing urban food demand

Strengthening the contribution of cities to growth

Strengthening the role of Africa’s urban areas as engines of growth remains a major challenge; while research can make a contribution, the focus needs increasingly to be on appropriate policies and the mobilisation of resources in support of those policie

Economies of scale, distribution costs and density effects in urban water supply: a spatial analysis of the role of infrastructure in urban agglomeration

Economies of scale in infrastructure are a recognised factor in urban agglomeration. Less recognised is the effect of distribution or access costs. Infrastructure can be classified as: (a) Area-type (e.g. utilities); or (b) Point-type (e.g. hospitals). The former involves distribution costs, the latter access costs. Taking water supply as an example of Area-type infrastructure, the interaction between production costs and distribution costs at settlement level is investigated using data from England & Wales and the USA. Plant level economies of scale in water production are confirmed, and quantified. Water distribution costs are analysed using a new measure of water distribution output (which combines volume and distance), and modelling distribution areas as monocentric settlements. Unit distribution costs are shown to be characterised by scale economies with respect to volume but diseconomies with respect to average distance to properties. It follows that higher settlement densities reduce unit distribution costs, while lower densities raise them. The interaction with production costs then means that (a) higher urban density (“Densification”) is characterised by economies of scale in both production and distribution; (b) more spread out settlement (“Dispersion”) leads to diseconomies in distribution; (c) “Suburbanisation” (expansion into lower density peripheral areas) lies in between, with roughly constant returns to scale, taking production and distribution together; and (d) “Constant density” expansion leads to small economies of scale. Keeping (per capita) water supply costs low thus appears to depend as much on density as size. Tentative generalisation suggests similar effects with other Area-type infrastructure (sewerage, electricity supply, telecommunications); and with Point-type infrastructure (such as hospitals), viewing access costs as distribution costs in reverse. It follows that the presumption in urban economics that such services are always characterised by economies of scale and therefore conducive to agglomeration may not be correct

The essential elephant: northwest European hominin adaptations through the Middle–Late Pleistocene And Neanderthal extinction

This paper firstly presents the “Ebbsfleet elephant”, an instance of Middle Pleistocene elephant ex- ploitation from the southeast United Kingdom. The find is well-dated to fully interglacial condi- tions in the early temperate part of MIS 11. The as- sociation of hominin activity with the elephant re- mains is clear-cut. The elephant bones comprise the partial remains of an adult male, occurring in near- life position in one well-defined horizon. A scatter of refitting flint artifacts was found in close associa- tion, beside the rib area. Although there is no direct evidence as to how the beast died (and whether it was hunted), it seems inescapable that this find rep- resents hominin exploitation of the carcass. The find is then considered from a wider ecological perspec- tive: firstly, for the importance of elephants (and other megaherbivores) for hominin adaptations to more-seasonal environments of higher latitudes, and northward colonization during post-glacial cli- matic ameliorations as exemplified in MIS 11; and secondly for their importance for the persistence of more-northerly populations during pre-glacial climatic deterioration and cold glacial stages. It is suggested that elephant (and mammoth/rhino) exploitation may have been an important enabling factor for settlement of northern latitudes, and may have been a critical constraint upon hominin range during periods of climatic deterioration. This per- spective then leads to the conjecture that Neander- thal extinction in northwest Europe during the last ice age was fundamentally caused by the reliance by both modern humans and Neanderthals on a mammoth-niche, and by the unstainable over-ex- ploitation of this niche by the former leading to the demise of the latter.The symposium and the volume "Human-elephant interactions: from past to present" were funded by the Volkswagen Foundation

Inappropriate use of the title 'chiropractor' and term 'chiropractic manipulation' in the peer-reviewed biomedical literature

BACKGROUND: The misuse of the title 'chiropractor' and term 'chiropractic manipulation', in relation to injury associated with cervical spine manipulation, have previously been reported in the peer-reviewed literature. The objectives of this study were to - 1) Prospectively monitor the peer-reviewed literature for papers reporting an association between chiropractic, or chiropractic manipulation, and injury; 2) Contact lead authors of papers that report such an association in order to determine the basis upon which the title 'chiropractor' and/or term 'chiropractic manipulation' was used; 3) Document the outcome of submission of letters to the editors of journals wherein the title 'chiropractor', and/or term 'chiropractic manipulation', had been misused and resulted in the over-reporting of chiropractic induced injury. METHODS: One electronic database (PubMed) was monitored prospectively, via monthly PubMed searches, during a 12 month period (June 2003 to May 2004). Once relevant papers were located, they were reviewed. If the qualifications and/or profession of the care provider/s were not apparent, an attempt was made to confirm them via direct e-mail communication with the principal researcher of each respective paper. A letter was then sent to the editor of each involved journal. RESULTS: A total of twenty four different cases, spread across six separate publications, were located via the monthly PubMed searches. All twenty four cases took place in one of two European countries. The six publications consisted of four case reports, each containing one patient, one case series, involving twenty relevant cases, and a secondary report that pertained to one of the four case reports. In each of the six publications the authors suggest the care provider was a chiropractor and that each patient received chiropractic manipulation of the cervical spine prior to developing symptoms suggestive of traumatic injury. In two of the four case reports contact with the principal researcher revealed that the care provider was not a chiropractor, as defined by the World Federation of Chiropractic. The authors of the other two case reports did not respond to my communications. In the case series, which involved twenty relevant cases, the principal researcher conceded that the term chiropractor had been inappropriately used and that his case series did not relate to chiropractors who had undergone appropriate formal training. The author of the secondary report, a British Medical Journal editor, conceded that he had misused the title chiropractor. Letters to editors were accepted and published by all four journals to which they were sent. To date one of the four journals has published a correction. CONCLUSION: The results of this year-long prospective review suggests that the words 'chiropractor' and 'chiropractic manipulation' are often used inappropriately by European biomedical researchers when reporting apparent associations between cervical spine manipulation and symptoms suggestive of traumatic injury. Furthermore, in those cases reported here, the spurious use of terminology seems to have passed through the peer-review process without correction. Additionally, these findings provide further preliminary evidence, beyond that already provided by Terrett, that the inappropriate use of the title 'chiropractor' and term 'chiropractic manipulation' may be a significant source of over-reporting of the link between the care provided by chiropractors and injury. Finally, editors of peer-reviewed journals were amenable to publishing 'letters to editors', and to a lesser extent 'corrections', when authors had inappropriately used the title 'chiropractor' and/or term 'chiropractic manipulation'

Terrace reconstruction and long profile projection: a case study from the Solent river system near Southampton, England

River terrace sequences are important frameworks for archaeological evidence and as such it is important to produce robust correlations between what are often fragmentary remnants of ancient terraces. This paper examines both conceptual and practical issues related to such correlations, using a case study from the eastern part of the former Solent River system near Southampton, England. In this region two recent terrace schemes have been constructed using different data to describe the terrace deposits: one based mainly on terrace surfaces; the other on gravel thicknesses, often not recording the terrace surface itself. The utility of each of these types of data in terrace correlation is discussed in relation to the complexity of the record, the probability of post-depositional alteration of surface sediments and comparison of straight-line projections with modern river long profiles. Correlation using age estimates is also discussed, in relation to optically-stimulated luminescence dating of sand lenses within terrace gravels in this region during the PASHCC project. It is concluded that the need for replication at single sites means that this approach has limited use for correlative purposes, although dating of sediments is important for understanding wider landscape evolution and patterns of human occupation