Host selection in phytophagous insects: a new explanation for learning in adults

Insect learning can change the preferences an egg laying female displays towards different host plant species. Current hypotheses propose that learning may be advantageous in adult host selection behaviour through improved recognition, accuracy or selectivity in foraging. In this paper, we present a hypothesis for when learning can be advantageous without such improvements in adult host foraging. Specifically, that learning can be an advantageous strategy for egg laying females when larvae must feed on more than one plant in order to complete development, if the fitness of larvae is reduced when they switch to a different host species. Here, larvae benefit from developing on the most abundant host species, which is the most likely choice of host for an adult insect which increases its preference for a host species through learning. The hypothesis is formalised with a mathematical model and we provide evidence from studies on the behavioural ecology, of a number of insect species which demonstrate that the assumptions of this hypothesis may frequently be fulfilled in nature. We discuss how multiple mechanisms may convey advantages in insect learning and that benefits to larval development, which have so far been overlooked, should be considered in explanations for the widespread occurrence of learning.

Development of educational policy and early intervention for learning difficulties in Australia: In the case of Queensland

This paper aims to describe the historical outline and current development of the educational policy for students with learning difficulties in Australia, focusing especially on the state of Queensland. In order to develop educational policy of learning difficulities at the state level, the concept of learning difficulities had been discussed until the middle of the 1970's. Receiving the submissions which argued strongly against a diagnostically-oriented definition of learning disabilities, the Select Comittee concluded that there was much conceptual confusion regarding the definition and cause of learining difficulties that might take many years to resolve. Despite that it was recongnised that action was needed to assist children by looking at their "total learning environmerit", and recommended the development of an educational policy for students with learning difficulties. During 1980's, support teachers for students with learning difficulties were employed in many schools. Scince the early 1980's support teachers have been making their efforts in regular classrooms rather than in the resource rooms. Their roles have been to help students with learning difficulties using effective and specific skills, and to consult with the regular classroom teacher in solving the problems related to learning difficulties in regular classes. Currently, the support system for students with learning difficulties has been employed to organize a more systematic and broader approach in Queensland based on the accountability of schools. In the context of enphasizing literacy and numeracy, a systematic whole school approach and particular programs, such as the Year 2 Diagnostic Net and Reading Recovery, have been introduced into the educational system for early identification and early intervention.

Can long-distance dispersal be inferred from the New Zealand plant fossil record?

New Zealand is generally thought to have been physically isolated from the rest of the world for over 60 million years. But physical isolation may not mean biotic isolation, at least on the time scale of millions of years. Are New Zealand's present complement of plants the direct descendants of what originally rafted from Gondwana? Or has there been total extinction of this initial flora with replacement through long-distance dispersal (a complete biotic turnover)? These are two possible extremes which have come under recent discussion. Can the fossil record be used to decide the relative importance of the two endpoints, or is it simply too incomplete and too dependent on factors of chance? This paper suggests two approaches to the problem-the use of statistics to apply levels of confidence to first appearances in the fossil record and the analysis of trends based on the entire palynorecord. Statistics can suggest that the first appearance of a taxon was after New Zealand broke away from Gondwana-as long as the first appearance in the record was not due to an increase in biomass from an initially rare state. Two observations can be drawn from the overall palynorecord that are independent of changes in biomass: (1) The first appearance of palynotaxa common to both Australia and New Zealand is decidedly non-random. Most taxa occur first in Australia. This suggests a bias in air or water transport from west to east. (2) The percentage of endemic palynospecies in New Zealand shows no simple correlation with the time New Zealand drifted into isolation. The conifer macrorecord also hints at complete turnover since the Cretaceous.

Monocular and binocular distance cues: insights from visual form agnosia I (of III)

The human nervous system constructs a Euclidean representation of near (personal) space by combining multiple sources of information (cues). We investigated the cues used for the representation of personal space in a patient with visual form agnosia (DF). Our results indicated that DF relies predominantly on binocular vergence information when determining the distance of a target despite the presence of other (retinal) cues. Notably, DF was able to construct an Euclidean representation of personal space from vergence alone. This finding supports previous assertions that vergence provides the nervous system with veridical information for the construction of personal space. The results from the current study, together with those of others, suggest that: (i) the ventral stream is responsible for extracting depth and distance information from monocular retinal cues (i.e. from shading, texture, perspective) and (ii) the dorsal stream has access to binocular information (from horizontal image disparities and vergence). These results also indicate that DF was not able to use size information to gauge target distance, suggesting that intact temporal cortex is necessary for learned size to influence distance processing. Our findings further suggest that in neurologically intact humans, object information extracted in the ventral pathway is combined with the products of dorsal stream processing for guiding prehension. Finally, we studied the size-distance paradox in visual form agnosia in order to explore the cognitive use of size information. The results of this experiment were consistent with a previous suggestion that the paradox is a cognitive phenomenon.

Maximum Likelihood Estimation of Mixture Densities for Binned and Truncated Multivariate Data

Binning and truncation of data are common in data analysis and machine learning. This paper addresses the problem of fitting mixture densities to multivariate binned and truncated data. The EM approach proposed by McLachlan and Jones (Biometrics, 44: 2, 571-578, 1988) for the univariate case is generalized to multivariate measurements. The multivariate solution requires the evaluation of multidimensional integrals over each bin at each iteration of the EM procedure. Naive implementation of the procedure can lead to computationally inefficient results. To reduce the computational cost a number of straightforward numerical techniques are proposed. Results on simulated data indicate that the proposed methods can achieve significant computational gains with no loss in the accuracy of the final parameter estimates. Furthermore, experimental results suggest that with a sufficient number of bins and data points it is possible to estimate the true underlying density almost as well as if the data were not binned. The paper concludes with a brief description of an application of this approach to diagnosis of iron deficiency anemia, in the context of binned and truncated bivariate measurements of volume and hemoglobin concentration from an individual's red blood cells.

Early intervention: Narratives of learning, discipline and enculturation

Current understandings about literacy have moved away from the belief that literacy is simply a process that individuals do in their heads. These understandings do not negate the importance of the individual aspects of literacy learning, but they emphasize understandings of literacy as a social practice. In many cases, responses to early literacy intervention seem to be grounded in theories that appear out of step with current literacy research and consequent evidence that literacy is socially and culturally constructed. One such response is the Reading Recovery programme based on Clay’s theory of literacy acquisition. Clay (1992) describes the programme as a second chance to learn. However, others have suggested that programmes like Reading Recovery may in fact work toward the marginalization of particular groups, thereby helping to maintain the status quo along class, gender and ethnic lines. This article allows two professionals to bring their insider’s knowledge of Reading Recovery to an analysis of the construction of the programme. The article interweaves this analysis with the personal narratives of the researchers as they negotiated the borders between different understandings and beliefs about literacy and literacy pedagogy.