A Diffusion Model Analysis of the Effects of Aging in the Lexical-Decision Task.

The effects of aging on response time (RT) are examined in 2 lexical-decision experiments with young and older subjects (age 60-75). The results show that the older subjects were slower than the young subjects, but more accurate. R. Ratcliff s (1978) diffusion model provided a good account of RTs, their distributions, and response accuracy. The fits show an 80-100-ms slowing of the nondecision components of RT for older subjects relative to young subjects and more conservative decision criterion settings for older subjects than for young subjects. The rates of accumulation of evidence were not significantly different for older compared with young subjects (less than 2% and 5% higher for older subjects relative to young subjects in the 2 experiments). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Remote sensing of wetlands in South America: status and challenges

South America has a large proportion of wetlands compared with other continents. While most of these wetlands were conserved in a relatively good condition until a few decades ago, pressures brought about by land use and climate change have threaten their integrity in recent years. The aim of this article is to provide a bibliometric analysis of the available scientific literature relating to the remote sensing of wetlands in South America. From 1960 to 2015, 153 articles were published in 63 different journals, with the number of articles published per year increasing progressively since 1990. This rise is also paralleled by an increase in the contribution of local authors. The most intensively studied regions are the wetland macrosystems of South American mega-rivers: the Amazon and Paraná Rivers, along with the Pantanal at the headwaters of Paraguay River. Few studies spanned more than two countries. The most frequent objectives were mapping, covering all types of wetlands with optical data, and hydrology, focusing on floodplain wetlands with microwave data as the preferred data source. The last decade substantial growth reflects an increase in technological and scientific capacities. Nevertheless, the state of the art regarding the remote sensing of wetlands in South America remains enigmatic. Fundamental questions and guidelines which may contribute to the understanding of the functioning of these ecosystems are yet to be fully defined and there is considerable dispersion in the use of data and remote-sensing approaches.     

A simple and effective heuristic for the resource constrained project scheduling problem

This paper investigates the development and application of a simple heuristic to the resource constrained project scheduling problem (RCPSP). This computer heuristic, which is based on the COMSOAL heuristic, constructs a feasible solution at each iteration and chooses the best solution of several iterations. Although COMSOAL was originally a solution approach for the assembly-line balancing problem, it can be extended to provide solutions to the resource allocation problem. The Modified COMSOAL technique presented in this paper uses priority schemes intermittently with a random selection technique. This hybrid of randomness and priority scheme allows a good solution to be found quickly while not being forced into the same solution at each iteration. Several different priority schemes are examined within this research. The COMSOAL heuristic modified with the priority schemes heuristic was tested on several established test sets and the solution values are compared with both known optimal values and the results of several other resource allocation heuristics. In the vast majority of cases, the Modified COMSOAL heuristic outperformed the other heuristics in terms of both average and maximum percentage difference from optimal. The Modified COMSOAL heuristic seems to have several advantages over other RCPSP heuristics in that it is easy to understand, easy to implement, and achieves good results.     

Redistribution of synaptic efficacy supports stable pattern learning in neural networks

Markram and Tsodyks, by showing that the elevated synaptic efficacy observed with single-pulse long-term potentiation (LTP) measurements disappears with higher-frequency test pulses, have critically challenged the conventional assumption that LTP reflects a general gain increase. This observed change in frequency dependence during synaptic potentiation is called redistribution of synaptic efficacy (RSE). RSE is here seen as the local realization of a global design principle in a neural network for pattern coding. The underlying computational model posits an adaptive threshold rather than a multiplicative weight as the elementary unit of long-term memory. A distributed instar learning law allows thresholds to increase only monotonically, but adaptation has a bidirectional effect on the model postsynaptic potential. At each synapse, threshold increases implement pattern selectivity via a frequency-dependent signal component, while a complementary frequency-independent component nonspecifically strengthens the path. This synaptic balance produces changes in frequency dependence that are robustly similar to those observed by Markram and Tsodyks. The network design therefore suggests a functional purpose for RSE, which, by helping to bound total memory change, supports a distributed coding scheme that is stable with fast as well as slow learning. Multiplicative weights have served as a cornerstone for models of physiological data and neural systems for decades. Although the model discussed here does not implement detailed physiology of synaptic transmission, its new learning laws operate in a network architecture that suggests how recently discovered synaptic computations such as RSE may help produce new network capabilities such as learning that is fast, stable, and distributed.     

Aging, practice, and perceptual tasks: A diffusion model analysis.

Practice effects were examined in a masked letter discrimination task and a masked brightness discrimination task for college-age and 60- to 75-year-old subjects. The diffusion model (Ratcliff, 1978) was fit to the response time and accuracy data and used to extract estimates of components of processing from the data. Relative to young subjects, the older subjects began the experiments with slower and less accurate performance; however, across sessions their accuracy improved because the quality of the information on which their decisions were based improved, and this, along with reduced decision criteria, led to shorter response times. For the brightness, but not the letter, discrimination task, the older subjects' performance matched that of the younger group by the end of 4 sessions, except that their nondecision components of processing were slightly slower. These analyses illustrate how a well-specified model can provide a unified view of multiple aspects of data that are often interpreted separately. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role conflict and role ambiguity: Do the scales measure these two constructs?

Confirmatory factor analysis was applied to the conflict and ambiguity scales developed by J. R. Rizzo et al (see record 1971-01407-001). Alternative models were contrasted to evaluate the possibilities that (a) the 14 items comprising the scales do measure the two purported constructs, (b) the 14 items measure only one construct, or (c) the 14 items load complexly on a second-order factor model. The second-order factor model was superior across three independent subject samples (total n?=?913), indicating that these measures do not establish role conflict and role ambiguity as two factorially independent constructs. The authors conclude that alternative scales are needed; suggestions for scale development are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ingestion of a novel flavor before exposure to pups injected with lithium chloride produces a taste aversion in mother rats (Rattus norvegicus).

A series of experiments investigated the ability of Sprague-Dawley mother rats to learn aversions to novel flavors ingested prior to the illness of their pups. In Exp I, 24 mothers learned to avoid a novel flavored solution ingested prior to the illness of their nursing litters. Exp II was designed to investigate the extent to which any adult rat is capable of such learning: 16 nonlactating multiparous females learned aversions to novel flavors ingested prior to exposure to pups injected with LiCl, whereas 16 nonlactating nulliparous females and 16 males did not learn these aversions. Several possible reasons for differences in this learning ability are discussed. In Exps III and IV, the nature of the UCS for these aversions was investigated. Visual, auditory, and taste cues associated with the lithium-injected pups did not mediate the aversions. Evidence suggests that olfactory characteristics of the lithium-injected pups mediated the flavor aversions in the present experiments. These olfactory cues did not appear to be general stress signals but instead were likely specific cues for gastrointestinal discomfort. Results are discussed in terms of classical conditioning and also of their adaptive significance for both mother and offspring. (63 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bias effects in implicit memory tasks.

A major focus of recent research in memory has been performance on implicit tasks. The phenomenon of most interest has been repetition priming, the effect that prior exposure to a stimulus has on later perception of the stimulus or on a later decision about the stimulus. Picture naming, word identification, and word production in stem- and fragment-completion tasks all show repetition priming effects. The separation of implicit from explicit memory systems provides 1 account of this data, but a different theoretical view is proposed here: Repetition-priming effects come about because the processes that perform a task are biased by prior exposure to a stimulus. The processing of the prior stimulus leaves behind byproducts, temporary modifications of the processes, which influence later processing. The aim of this article is to demonstrate the potential of this view for developing new theories and for prompting new empirical questions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)