Costs of learning: the dynamics of mixed-prey exploitation by silver perch, Bidyanus bidyanus (Mitchell, 1838)

Although generalist predators have been reported to forage less efficiently than specialists, there is little information on the extent to which learning can improve the efficiency of mixed-prey foraging. Repeated exposure of silver perch to mixed prey (pelagic Artemia and benthic Chironomus larvae) led to substantial fluctuations in reward rate over relatively long (20-day) timescales. When perch that were familiar with a single prey type were offered two prey types simultaneously, the rate at which they captured both familiar and unfamiliar prey dropped progressively over succeeding trials. This result was not predicted by simple learning paradigms, but could be explained in terms of an interaction between learning and attention. Between-trial patterns in overall intake were complex and differed between the two prey types, but were unaffected by previous prey specialization. However, patterns of prey priority (i.e. the prey type that was preferred at the start of a trial) did vary with previous prey training. All groups of fish converged on the most profitable prey type (chironomids), but this process took 15-20 trials. In contrast, fish offered a single prey type reached asymptotic intake rates within five trials and retained high capture abilities for at least 5 weeks. Learning and memory allow fish to maximize foraging efficiency on patches of a single prey type. However, when foragers are faced with mixed prey populations, cognitive constraints associated with divided attention may impair efficiency, and this impairment can be exacerbated by experience. (c) 2005 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Pattern and correlates of inpatient admission during the initial acute phase of first-episode psychosis

Objectives: The first aim of this study was to examine the rate, pattern and correlates of inpatient admission during the first 3 months of treatment for first-episode psychosis (FEP). The second aim was to determine whether the pattern of inpatient admission during this period was associated with remission of psychotic symptoms or inpatient service use at 15-month follow-up. Method: One hundred and four consecutive patients with FEP at a specialist treatment service were approached to participate in a follow-up study. Patients were grouped on the basis of the pattern of inpatient admission (none, one, or multiple) during the first 3 months of treatment. Clinical ratings at baseline and 3-month follow-up, and ratings of remission of psychotic symptoms at 3 and 15-month follow-up, were available for two-thirds of the patients. Inpatient data for the 15-month follow-up period were derived from an electronic database for most patients (n = 98). Results: Eighty (76.9%) of the 104 patients were admitted to an inpatient unit during the first 3 months of treatment. Fifty-nine (56.7%) patients had a single admission and 21 (20.2%) had multiple admissions. At baseline, inpatient admission was associated with a diagnosis of affective psychosis and more severe behavioural and functional disturbance but not positive psychotic symptoms. Multiple admissions were associated with risks to self or others at baseline and 3-month follow-up, and lack of remission of positive symptoms at 3 and 15-month follow-up. There was no association between the pattern of inpatient admission during the initial 3-month period and inpatient service use during the following 12-month period. Conclusions: The substantial proportion of young patients with FEP admitted to hospital emphasizes the need for youth-friendly treatment environments and practices. Although patients with multiple admissions during the initial treatment period are less likely to achieve remission, these patients are no more likely to establish a pattern of revolving-door hospitalizations compared with other patients.

A sociocultural analysis of learning to teach

This paper addresses the question of how teachers learn from experience during their pre-service course and early years of teaching. It outlines a theoretical framework that may help us better understand how teachers' professional identities emerge in practice. The framework adapts Vygotsky's Zone of Proximal Development, and Valsiner's Zone of Free Movement and Zone of Promoted Action, to the field of teacher education. The framework is used to analyse the pre-service and initial professional experiences of a novice secondary mathematics teacher in integrating computer and graphics calculator technologies into his classroom practice. (Contains 1 figure.) [For complete proceedings, see ED496848.]