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Individual Stimuli (individual + stimulus)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Children use categories to maximize accuracy in estimation

DEVELOPMENTAL SCIENCE, Issue 6 2006
Sean Duffy
The present study tests a model of category effects upon stimulus estimation in children. Prior work with adults suggests that people inductively generalize distributional information about a category of stimuli and use this information to adjust their estimates of individual stimuli in a way that maximizes average accuracy in estimation (see Huttenlocher, Hedges & Vevea, 2000). However, little is known about the developmental origin of this cognitive process. In the present study, 5- and 7-year-old children viewed stimuli that varied in size and reproduced each from memory. Consistent with the predictions of a Bayesian model of category effects on estimation, responses were adjusted toward the central value of the stimulus distribution. Additionally, the dispersion of the stimulus distribution affected the pattern of bias and variability of responses in a way that is predicted by the model. The results suggest that, like adults, children use categories for increasing average accuracy in estimating inexact stimuli. [source]

Motor foundations of higher cognition: similarities and differences in processing regular and violated perceptual sequences of different specificity

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2009
Andreja Bubic
Abstract Processing perceptual sequences relies on the motor system, which is able to simulate the dynamics of the environment by developing internal representations of external events and using them to predict the incoming stimuli. Although it has previously been demonstrated that such models may incorporate predictions based on exact stimulus properties and single stimulus dimensions, it is not known whether they can also support abstract predictions pertaining to the level of stimulus categories. This issue was investigated within the present event-related functional magnetic resonance imaging study, which compared the processing of perceptual sequences of different specificity, namely those in which the sequential structure was based on the order of presentation of individual stimuli (token), and those in which such structure was defined by stimulus categories (type). The results obtained indicate a comparable engagement of the basic premotor,parietal network in processing both specific and categorical perceptual sequences. However, type sequences additionally elicited activations within the lateral prefrontal, occipital and posterior temporal regions that supported categorization in this task context. Introducing sequential deviants into token sequences activated parietotemporal and ventrolateral frontal cortices, whereas a less pronounced overall response, dominated by lateral prefrontal activation, was elicited by violations introduced into type sequences. Overall, the findings obtained suggest that, although forward models in perception may be able to incorporate expectations of lower specificity when compared to the motor domain, such processing is crucially dependent on additional contributions from lateral prefrontal as well as inferior occipital and temporal cortices that support categorization occurring in such a dynamic context. [source]

Rapid assessment of in vivo cholinergic transmission by amperometric detection of changes in extracellular choline levels

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2004
Vinay Parikh
Abstract Conventional microdialysis methods for measuring acetylcholine (ACh) efflux do not provide sufficient temporal resolution to relate cholinergic transmission to individual stimuli or behavioral responses, or sufficient spatial resolution to investigate heterogeneities in such regulation within a brain region. In an effort to overcome these constraints, we investigated a ceramic-based microelectrode array designed to measure amperometrically rapid changes in extracellular choline as a marker for cholinergic transmission in the frontoparietal cortex of anesthetized rats. These microelectrodes exhibited detection limits of 300 nm for choline and selectivity (> 100 : 1) of choline over interferents such as ascorbic acid. Intracortical pressure ejections of choline (20 mm, 66,400 nL) and ACh (10 and 100 mm, 200 nL) dose-dependently increased choline-related signals that were cleared to background levels within 10 s. ACh, but not choline-induced signals, were significantly attenuated by co-ejection of the acetylcholinesterase inhibitor neostigmine (Neo; 100 mm). Pressure ejections of drugs known to increase cortical ACh efflux, potassium (KCl; 70 mm, 66, 200 nL) and scopolamine (Scop; 10 mm, 200 nL), also markedly increased extracellular choline signals, which again were inhibited by Neo. Scop-induced choline signals were also found to be tetrodotoxin-sensitive. Collectively, these findings suggest that drug-induced increases in current measured with these microelectrode arrays reflect the oxidation of choline that is neuronally derived from the release and subsequent hydrolysis of ACh. Choline signals assessed using enzyme-selective microelectrode arrays may represent a rapid, sensitive and spatially discrete measure of cholinergic transmission. [source]

Transitivity, flexibility, conjunctive representations, and the hippocampus.

HIPPOCAMPUS, Issue 3 2003

Abstract After training on a set of four ordered, simultaneous, odor discrimination problems (A+B,, B+C,, C+D,, D+E), intact rats display transitivity: When tested on the novel combination BD, they choose B. Rats with damage to the hippocampus, however, do not show transitivity (Dusek and Eichenbaum, 1997. Proc Natl Acad Sci U S A 94:7109,7114). These results have been interpreted as support for the idea that the hippocampus is a relational memory storage system that enables the subject to make comparisons among representations of the individual problems and choose based on inferential logic. We provide evidence for a simpler explanation. Specifically, subjects make their choices based on the absolute excitatory value of the individual stimuli. This value determines the ability of that stimulus to attract a response. This conclusion emerged because after training on a five-problem set (A+B,, B+C,, C+D,, D+E,, E+F,) rats preferred B when tested with BE, but not when tested with BD. The implication of these results for how to conceptualize the role of the hippocampus in transitive-like phenomena is discussed. Hippocampus 2003;13:334,340. © 2003 Wiley-Liss, Inc. [source]