The role of signaled periods of nonreinforcement in responding on a random schedule in autoshaping

Little responding develops to a conditioned stimulus (CS) that is placed in a random relation to an unconditioned stimulus (US). However, if the USs not preceded by that CS are themselves signaled by another stimulus, then the CS does come to elicit responding. This result has been attributed (e.g., by Durlach, 1983) to the signal’s blocking of conditioning to background cues that otherwise would prevent conditioning of the CS. However, Goddard and Jenkins (1987) have suggested the alternative that signaling the USs promotes responding due to the adventitious creation of periods of signaled nonreinforcement. Two experiments were conducted to assess this alternative, involving an autoshaping preparation in pigeons. In Experiment 1, little responding to a keylight CS presented in a random relation to a food US occurred, despite the explicit presentation of a discrete noise signaling periods of no food in the intertrial interval (ITI). Experiment 2 was designed to replicate the procedure of Goddard and Jenkins, in which an auditory stimulus extended throughout the ITI of a random schedule, terminating only prior to extra USs and during the CS. Contrary to their findings, little responding developed to the target CS. However, responding did develop when the sound-free period occurred only prior to the extra USs. These results offer little support for the hypothesis that signaled periods of nonreinforcement promote responding on random schedules. However, they are consistent with the view that signaling of ITI USs acts by preventing conditioning of potentially competitive background cues.     

Age-related Asynchrony of Knowledge and Action

Children's ability to act in accordance with rules was assessed in 2 experiments. Experiment I included 66 children, aged 31, 33.5, or 36 months, who performed 2 tasks. In a forced-choice, deductive sorting task, children were told 2 rules (if-then statements) and then required to use the rules to sort items. A knowledge task tested children's knowledge about which rule's antecedent condition held true for each item. Rules were either based on natural categories (e.g., vehicles vs. musical instruments) or ad hoc categories (e.g., things found inside the house vs. things found outside). Children in the 2 younger age groups performed better on the knowledge task than on the sorting task. The 36-month-olds performed equally well on both tasks. In Experiment 2, groups of 12 32.25-month-olds received either the knowledge task, the sorting task, or a mnemonically supported version of the sorting task. The group that received the knowledge task performed better than the other groups, which did not differ. This result undermines the possibility that differential performance on the knowledge and sorting tasks is due to a difference in memory demand. Taken together, the results of Experiments 1 and 2 imply a relatively rapid, age-related change culminating in the ability to execute systematically rules that require access to extant knowledge.     

Relating Narrative, Inquiry, and Inscriptions: Supporting Consequential Play

In this paper we describe our research using a multi-user virtual environment, Quest Atlantis, to embed fourth grade students in an aquatic habitat simulation. Specifically targeted towards engaging students in a rich inquiry investigation, we layered a socio-scientific narrative and an interactive rule set into a multi-user virtual environment gaming engine to establish a virtual world through which students learned about science inquiry, water quality concepts, and the challenges in balancing scientific and socio-economic factors. Overall, students were clearly engaged, participated in rich scientific discourse, submitted quality work, and learned science content. Further, through participation in this narrative, students developed a rich perceptual, conceptual, and ethical understanding of science. This study suggests that multi-user virtual worlds can be effectively leveraged to support academic content learning.     

Auditory perceptual processing in reading disabled children

One hundred and three children attending Learning Assistance Centres due to reading difficulties and one hundred and three matched, average readers were administered a battery of auditory perceptual processing tasks. The battery was composed of auditory analysis and synthesis, auditory sequential memory, auditory discrimination, and phonemic segmentation tasks. A principal components analysis yielded four factors. These were determined to be advanced phonological awareness, sequential memory, discrimination, and simple phonological awareness. Discriminant analyses, using the factor scores, indicated that three of the four factors were able to discriminate between the able and disabled readers. Most notable among these was advanced phonological awareness. Auditory discrimination could not discriminate between the groups. The results suggest that there may not be one underlying phonological ability implicated in successful reading acquisition. Furthermore, it is clear that two levels of phonological awareness exist and that screening and diagnostic instruments should address both in order to have predictive validity.     

Performance of Montessori and traditionally schooled nursery children on tasks of seriation, classification, and conservation

It was hypothesized that the Montessori curriculum accelerates the acquisition of a number of concrete operational skills. To test this, eighty 4-year-old children were given three Piagetian problems—seriation, classification, and conservation. Half of the subjects were from Montessori schools, and the other half were from more traditional nursery settings. Within each type of school, half of the children were first year and the other half were second year enrollees. Results showed that significantly more Montessori than traditional children seriated and classified objects like concrete thinkers but that there were no differences on the conservation problem. Year of enrollment did not influence performance on any of the tasks. It was concluded that the hypothesis was confirmed and that the failure to find acceleration of conservation performance was due to its advanced nature relative to the other problems and/or the tangential manner in which Montessori exercises deal with the critical concepts that underly it.     

A Physical Interpretation of Factorization and Factor Modification in Structural Analysis

The physical interpretation of LDL^t factorization and Bennett's method for matrix factor modification applied to structural analysis are studied. The sparsity of the matrix factors and their effect on matrix modification are examined.     

下一代GPS系统

目前,经常使用全球定位系统(GPS)的人数已达2000万,24颗"导航之星"(NavStar)组成的地球同步轨道卫星群(轨道高度为2万千米)随时为这些用户提供信号.阿富汗战争和伊拉克战争都证明了GPS系统不可或缺.     

现代炼钛金术

踏破铁鞋无觅处，得来全不费工夫。发现之神将高科技材料的低成本生产工艺传授给我们。