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.

Does physical pain augment anxious attachment?

This study tested the hypothesis derived from social pain theory (MacDonald & Leary, 2005) that pain affect serves as a signal of perceived social exclusion. Participants ranging in experience of persistent physical pain completed measures of pain affect, anxious and avoidant attachment, anxiety, and depression. Higher levels of pain affect were found to relate to higher levels of anxious, but not avoidant, attachment. Further, anxious attachment partially mediated the relation between pain affect and emotional distress. These data support the conclusion that one reason individuals with persistent pain experience anxiety and depression is because of heightened concerns over rejection. The data also support the conclusion that anxious attachment is more strongly related to the fight-flight-freezing system than avoidant attachment.

Effects of acoustic startle stimuli on interceptive action

In reaction time (RT) tasks, presentation of a startling acoustic stimulus (SAS) together with a visual imperative stimulus can dramatically reduce RT while leaving response execution unchanged. It has been suggested that a prepared motor response program is triggered early by the SAS but is not otherwise affected. Movements aimed at intercepting moving targets are usually considered to be similarly governed by a prepared program. This program is triggered when visual stimulus information about the time to arrival of the moving target reaches a specific criterion. We investigated whether a SAS could also trigger such a movement. Human experimental participants were trained to hit moving targets with movements of a specific duration. This permitted an estimate of when movement would begin (expected onset time). Startling and sub-startle threshold acoustic probe stimuli were delivered unexpectedly among control trials: 65, 85, 115 and 135 ms prior to expected onset (10:1 ratio of control to probe trials). Results showed that startling probe stimuli at 85 and 115 ms produced early response onsets but not those at 65 or 135 ms. Sub-threshold stimuli at 115 and 135 ms also produced early onsets. Startle probes led to an increased vigor in the response, but sub-threshold probes had no detectable effects. These data can be explained by a simple model in which preparatory, response-related activation builds up in the circuits responsible for generating motor commands in anticipation of the GO command. If early triggering by the acoustic probes is the mechanism underlying the findings, then the data support the hypothesis that rapid interceptions are governed by a motor program. © 2006 Published by Elsevier Ltd on behalf of IBRO.

Effects of psychological contract breach on performance of IT employees: The mediating role of affective commitment

In this study, we investigated the relationships between psychological contract breach, affective commitment, and two types of employee performance (i.e. civic virtue behaviour and in-role performance). It was predicted that an experience of contract breach can severely hurt the affective commitment of the employees and this, in turn, results in poor in-role performance and less civic virtue behaviours. Results revealed that affective commitment had differential mediating effects on the two types of employee performance. That is, affective commitment mediated the relationship between breach and self-reported and supervisor-rated civic virtue, but not the relationship between breach and in-role performance.

Enlisting the influence of others: Alternative strategies for persuasive media campaigns

This study investigated an Australian antidrug campaign that targeted adolescents directly and indirectly via recruiting parents into drug prevention. Eighty-six parent-child dyads completed surveys measuring campaign evaluations, discussions about drugs, and beliefs about risks to self (own child) and to the average young Australian. Adolescents were optimistic about risks, and media impact was evident only in perceptions of risk to others. Parents were less optimistic, and perceptions of campaign quality predicted perceived risk to own child and discussion about drugs. However, this was moderated by negative affect associated with the campaign. There was some evidence that discussions influenced adolescents' perceptions of personal risk. This demonstrates the importance of individual responses and communication processes in determining the impact of persuasive media messages.

Evaluation of unsupervised semantic mapping of natural language with Leximancer concept mapping

The Leximancer system is a relatively new method for transforming lexical co-occurrence information from natural language into semantic patterns in an unsupervised manner. It employs two stages of co-occurrence information extraction-semantic and relational-using a different algorithm for each stage. The algorithms used are statistical, but they employ nonlinear dynamics and machine learning. This article is an attempt to validate the output of Leximancer, using a set of evaluation criteria taken from content analysis that are appropriate for knowledge discovery tasks.

Evidence for retarded extinction of aversive learning in anxious children

The habituation to intense acoustic stimuli and the acquisition of differentially conditioned fear were assessed in 53 clinically anxious and 30 non-anxious control children and young adolescents. Anxious children tended to show larger electrodermal responses during habituation, but did not differ in blink startle latency or magnitude. After acquisition training, non-anxious children rated the CS + as more fear provoking and arousing than the CS- whereas the ratings of anxious children did not differ. However, anxious children rated the CS + as more fear provoking after extinction, a difference that was absent in non-anxious children. During extinction training, anxious children displayed larger blink magnitude facilitation during CS + and a trend towards larger electrodermal responses, a tendency not seen in nonanxious children. These data suggest that extinction of fear learning is retarded in anxious children. (c) 2005 Elsevier Ltd. All rights reserved.

Need for systematic synthetic phonics teaching within the early reading curriculum

Both the New Zealand Ministry of Education's Literacy Experts Group and the Australian National Inquiry into the Teaching of Literacy have recently acknowledged the centrality of systematic instruction in synthetic phonics to early reading instruction, but this conclusion remains contentious in some circles. This paper briefly summarises empirical research in basic psychology and evidence-based evaluation studies supporting the inclusion of systematic synthetic phonics instruction within the early reading curriculum, allowing practising psychologists to develop an informed opinion on this issue.

Neuromuscular-skeletal constraints on the acquisition of skill in a discrete torque production task

The organisation of the human neuromuscular-skeletal system allows an extremely wide variety of actions to be performed, often with great dexterity. Adaptations associated with skill acquisition occur at all levels of the neuromuscular-skeletal system although all neural adaptations are inevitably constrained by the organisation of the actuating apparatus (muscles and bones). We quantified the extent to which skill acquisition in an isometric task set is influenced by the mechanical properties of the muscles used to produce the required actions. Initial performance was greatly dependent upon the specific combination of torques required in each variant of the experimental task. Five consecutive days of practice improved the performance to a similar degree across eight actions despite differences in the torques required about the elbow and forearm. The proportional improvement in performance was also similar when the actions were performed at either 20 or 40% of participants' maximum voluntary torque capacity. The skill acquired during practice was successfully extrapolated to variants of the task requiring more torque than that required during practice. We conclude that while the extent to which skill can be acquired in isometric actions is independent of the specific combination of joint torques required for target acquisition, the nature of the kinetic adaptations leading to the performance improvement in isometric actions is influenced by the neural and mechanical properties of the actuating muscles.

Position information but not force information is used in adapting to changes in environmental dynamics

This study investigated how movement error is evaluated and used to change feedforward commands following a change in the environmental dynamics. In particular, we addressed the question of whether only position-error information is used or whether information about the force-field direction can also be used for rapid adaptation to changes in the environmental dynamics. Subjects learned to move in a position-dependent force field (PF) with a parabolic profile and the dynamics of a negative spring, which produced lateral force to the left of the target hand path. They adapted very rapidly, dramatically reducing lateral error after a single trial. Several times during training, the strength of the PF was unexpectedly doubled (PF2) for two trials. This again created a large leftward deviation, which was greatly reduced on the second PF2 trial, and an aftereffect when the force field subsequently returned to its original strength. The aftereffect was abolished if the second PF2 trial was replaced by an oppositely directed velocity-dependent force field (VF). During subsequent training in the VF, immediately after having adapted to the PF, subjects applied a force that assisted the force field for similar to 15 trials, indicating that they did not use information about the force-field direction. We concluded that the CNS uses only the position error for updating the internal model of the environmental dynamics and modifying feedforward commands. Although this strategy is not necessarily optimal, it may be the most reliable strategy for iterative improvement in performance.

Toddler subtraction with large sets: further evidence for an analog-magnitude representation of number

Two experiments were conducted to test the hypothesis that toddlers have access to an analog-magnitude number representation that supports numerical reasoning about relatively large numbers. Three-year-olds were presented with subtraction problems in which initial set size and proportions subtracted were systematically varied. Two sets of cookies were presented and then covered The experimenter visibly subtracted cookies from the hidden sets, and the children were asked to choose which of the resulting sets had more. In Experiment 1, performance was above chance when high proportions of objects (3 versus 6) were subtracted from large sets (of 9) and for the subset of older participants (older than 3 years, 5 months; n = 15), performance was also above chance when high proportions (10 versus 20) were subtracted from the very large sets (of 30). In Experiment 2, which was conducted exclusively with older 3-year-olds and incorporated an important methodological control, the pattern of results for the subtraction tasks was replicated In both experiments, success on the tasks was not related to counting ability. The results of these experiments support the hypothesis that young children have access to an analog-magnitude system for representing large approximate quantities, as performance on these subtraction tasks showed a Webers Law signature, and was independent of conventional number knowledge.

Understanding the multidimensionality of group development

This article presents a three-dimensional definition space of the group development literature that differentiates group development models on three dimensions: content, population, and path dependency. The multidimensional conceptualization structures and integrates the vast group development literature, enabling direct comparison of competing theories. The utility of this definition space is demonstrated by using the relative positioning of two seemingly competing group development models-the punctuated equilibrium model and the integrative model-to demonstrate their complementarity. The authors also show how organizational researchers and practitioners can use the three-dimensional definition space to select an appropriate theoretical model for the group or group process with which they are working.

Virtual reality exposure therapy: 150-degree screen to desktop PC

Virtual reality exposure therapy (VRET) developed using immersive or semi-immersive virtual environments present a usability problem for practitioners. To meet practitioner requirements for lower cost and portability VRET programs must often be ported onto desktop environments such as the personal computer (PC). However, success of VRET has been shown to be linked to presence, and the environment's ability to evoke the same reactions and emotions as a real experience. It is generally accepted that high-end virtual environments ( VEs) are more immersive than desktop PCs, but level of immersion does not always predict level of presence. This paper reports on the impact on presence of porting a therapeutic VR application for Schizophrenia from the initial research environment of a semi-immersive curved screen to PC. Presence in these two environments is measured both introspectively and across a number of causal factors thought to underlie the experience of presence. Results show that the VR exposure program successfully made users feel they were present in both platforms. While the desktop PC achieved higher scores on presence across causal factors participants reported they felt more present in the curved screen environment. While comparison of the two groups was statistically significant for the PQ but not for the IPQ, subjective reports of experiences in the environments should be considered in future research as the success of VRET relies heavily on the emotional response of patients to the therapeutic program.

When group members admit to being conformist: The role of relative intragroup status in conformity self-reports

Five studies examined the hypothesis that people will strategically portray the self as being more g-roup influenced the more junior they feel within the group. Among social psychologists (Study 1), ratings of self-conformity by g-roup members were greater when the status of the participant was low than when it was high. These effects were replicated in Studies 2, 3, and 4 in which relative intragroup status was manipulated. In Study 3, the authors found junior group members described themselves as more conformist than senior members when they were addressing an ingroup audience, but when they were addressing an outgroup audience the effect disappeared. Furthermore, junior members (but not senior members) rated themselves as more conformist when they were led to believe their responses were public than when responses were private (Study 5). The discussion focuses on the strategic processes underlying low-status group members' self-reports of group influence and the functional role of conformity in groups.