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PubMed1986

Spin glass model of learning by selection.

A model of learning by selection is described at the level of neuronal networks. It is formally related to statistical mechanics with the aim to describe memory storage during development and in the adult. Networks with symmetric interactions have been shown to function as content-addressable memories, but the present approach differs from previous instructive models. Four biologically relevant aspects are treated--initial state before learning, synaptic sign changes, hierarchical categorization of stored patterns, and synaptic learning rule. Several of the hypotheses are tested numerically. Starting from the limit case of random connections (spin glass), selection is viewed as pruning of a complex tree of states generated with maximal parsimony of genetic information.

Learning↗
PubMedDate not supplied

Listening to spoken text: adult age differences as revealed by self-paced listening.

An experiment is reported in which young and older adults heard spoken narratives presented in a segment-by-segment fashion using the auditory moving window (AMW) technique. Participants were instructed to initiate the presentation of each segment at their own pace, their goal being to insure good comprehension of the main ideas of the narratives. The pattern of pause times across passages was compared for passages being heard for the first time (novel condition) or after the participants had heard the passages several times before (familiar condition). The analysis of participants' pause durations in pacing through the passages suggests that although young and older adults respond similarly at the textbase level of processing, older adults do not allocate additional resources at the start of a passage in order to develop a mental model of the narrative. This pattern differs from that typically found in reading time studies.

Aged↗
PubMed2001

Human cortical networks for new and familiar sequences of saccades.

Visual exploration is organized in sequences of saccadic eye movements that depend on both perceptual and cognitive context. Using functional magnetic resonance imaging, we studied the neural basis of sequential oculomotor behavior and its dependence on different types of memory by analyzing cerebral activity during performance of newly learned and familiar sequences of eye movements. Compared to a resting condition, both types of sequences activated a common fronto-parietal network, including frontal and supplementary eye fields, and several parietal areas. Within this network, newly learned sequences induced stronger activation than familiar sequences, probably reflecting higher attentional demands. In addition, specific regions were recruited for the performance of new sequences, including pre-supplementary eye fields, the precuneus and the caudate nucleus. This indicates that in addition to attentional modulation, novelty of saccadic sequences requires specific cortical resources, probably related to effortful sequence preparation and coordination as well as to spatial working memory. For familiar sequences, recalled from long-term memory, we observed specific right medial temporo-occipital activation in the vicinity of the boundary between the parahippocampal and lingual gyri, as well as an activation site in the parieto-occipital fissure. We conclude that neuronal resources recruited by the gaze system can change with the familiarity of the scanpath to be executed. This study is important to better understand how the brain implements memorized scanpaths for visual exploration and orienting.

Adult↗
PubMed1982

Aging and metamemory: the roles of relatedness and imagery.

The hypothesis that age deficits in long-term episodic memory tasks are due to imparied metamemorial skills was investigated in a paired-associate task that required participants to predict the likelihood of recalling individual items. Both young and old adults were able to predict their ability to recall, and both age groups were equally sensitive to the effects of differences in the degree of relatedness between word-pair members on subsequent recall. However, both old and young adults were insensitive to the beneficial effects of using interactive imagery at encoding. It was concluded that differences in metamemorial skills are not responsible for age differences in memory.

Adolescent↗
PubMed2001

Drug-induced amnesia is a separate phenomenon from sedation: electrophysiologic evidence.

BACKGROUND: Sedative-hypnotic drugs not only increase sedation, but also impair memory as serum concentration increases. These drugs also produce profound changes in the auditory event-related potential (ERP). The ability of various ERP components to predict changes in sedation and memory produced by various drugs was tested. METHODS: Sixty-five healthy volunteers randomly received intravenous placebo, midazolam, propofol, thiopental, fentanyl with ondansetron, or ondansetron alone at five different stable target concentrations (three increasing, two decreasing) using a computer-controlled infusion pump to produce varying degrees of sedation without loss of consciousness. ERPs were recorded while volunteer participants detected a deviant auditory stimulus and made a button-press response to a target tone (standard oddball paradigm, 80:20 ratio, to elicit a P3 response). At each target concentration, volunteers learned a list of 16 words. The predictive probabilities (Pk) of various ERP components were determined for word recognition at the end of the day (memory) and log reaction time to the deviant stimulus (sedation). RESULTS: The N2 latency of the ERP consistently predicted log reaction time in all groups (Pk +/- SE from 0.58 +/- 0.04 to 0.71 +/- 0.04). The N2P3 amplitude of the ERP was the best predictor of memory performance for midazolam (Pk, 0.63 +/- 0.04), propofol (Pk, 0.62 +/- 0.05), and thiopental (Pk, 0.66 +/- 0.04). There was a differential ability to predict memory performance from sedation for midazolam and propofol. CONCLUSIONS: Midazolam and propofol affect memory differentially from their sedative effects, and these are indexed by specific components of the auditory ERP. These components of the ERP are associated with specific, but not necessarily unique, neuroanatomic structures. Thus, these drugs act by additional mechanisms beyond general central nervous system depression to produce the effects of sedation and memory impairment.

Adult↗
PubMed2006

Model-based hand tracking using a hierarchical Bayesian filter.

This paper sets out a tracking framework, which is applied to the recovery of three-dimensional hand motion from an image sequence. The method handles the issues of initialization, tracking, and recovery in a unified way. In a single input image with no prior information of the hand pose, the algorithm is equivalent to a hierarchical detection scheme, where unlikely pose candidates are rapidly discarded. In image sequences, a dynamic model is used to guide the search and approximate the optimal filtering equations. A dynamic model is given by transition probabilities between regions in parameter space and is learned from training data obtained by capturing articulated motion. The algorithm is evaluated on a number of image sequences, which include hand motion with self-occlusion in front of a cluttered background.

Algorithms↗
PubMed1988

The changes in fetal habituation patterns due to a decrease in inspired maternal oxygen.

Habituation is widely regarded as a basic form of learning. A fully functioning central nervous system is probably required for a normal habituation pattern. Habituation of the behavioural response to vibroacoustic stimulation was studied in 23 normal human fetuses whose gestational age was 36 or more weeks. Eighteen were tested whilst their mothers breathed either air or a 12% oxygen in nitrogen mixture. The test was repeated the following day with the order of the gases reversed. In addition five fetuses were tested while their mothers breathed air on both occasions. Of the 18 fetuses 17 had a normal habituation pattern when tested in air but only two had a normal pattern when their mothers breathed 12% O2. Four of the five fetuses tested both days in air had normal patterns on the second day. Altering the amount of inspired maternal O2 alters the fetal habituation pattern.

Female↗
PubMed1995

Models of delayed recovery.

After a biologic insult has impaired function of the developing central nervous system, recovery may not become apparent for years. Probability models adopted from the carcinogenesis, developmental neurobiology, learning decay, and stochastic process literatures are presented so that assumptions about apparent delays in the recovery process can be tested with data from longitudinal studies after a temporally circumscribed adverse event/exposure. This process of evaluating multiple models is exemplified with one data set. Nonlinear models of recovery are important because some children with early deficits first show improvement months to years later.

Brain↗
PubMed1987

Reading fields of magnifying loupes.

For the purpose of understanding the influence of the use of magnifying loupes on the reading process, the reading field is a relevant concept. Three possible reading fields are distinguished: the monocular reading field, the binocular reading field, and the composite reading field. Theoretical expressions for the widths of reading fields are derived as a function of the physical parameters of the loupe and the geometry of the reading situation. Variation of reading-field width as a function of magnification is illustrated. For verification, experimentally determined reading-field widths were compared with the theoretical ones. There were small systematic deviations, probably caused by achromatic aberrations. In order to learn about the strategies that subjects use when reading with the aid of a loupe, loupe displacement was measured while subjects read text under conditions that provided a variety of reading-field widths. It was found that individual subjects use different strategies (i.e., they use different reading-field widths).

Fovea Centralis↗
PubMed2004

Learning to make decisions in dynamic environments: effects of time constraints and cognitive abilities.

This study investigated the effects of time constraints and cognitive abilities on dynamic decision making (DDM). The learning and performance of individuals trained in a DDM task with time constraints were compared with those who were trained without time constraints. Although all participants received the same total amount of time to perform the task, individuals under more stringent time constraints were given 3 times more practice trials on the first 2 days of the study than were people under less stringent time constraints. Despite the additional practice runs, participants under high time constraints performed worse than did participants under low time constraints on the 3rd day of the study. A subsequent analysis of cognitive abilities and decision heuristics revealed that individuals' actions corresponded with simple heuristic predictions more closely with minimal practice than with extended practice, under high rather than low time constraints, and in individuals with low rather than high cognitive abilities. These findings suggest that mere repetition of a task with less time within a trial is counterproductive to learning and that learning depends on cognitive abilities. Potential applications of this research include the design of training procedures for dynamic tasks.

Adaptation, Psychological↗
PubMed1988

A test of symmetry and transitivity in the conditional discrimination performances of pigeons.

In a matching-to-sample context, pigeons were taught two conditional discriminations according to one of three equivalence paradigms: train if A, then select B and if B, then select C; train if B, then A and if B, then C; or train if A, then B and if C, then B. Test trials without reinforcement revealed that the conditional relations did not satisfy the symmetrical and transitive properties of an equivalence relation. Apparently, only specific if... then relations were learned. Contrary to Kendall's (1983) findings, and probably as a consequence of procedural differences, none of the pigeons in the present experiment were observed to emit mediating behavior during the transitivity probe trials. The absence of symmetry and transitivity may be related to the individual stimuli not being reflexive. Behavioral techniques other than the commonly used matching-to-sample technique might better succeed in avoiding unintended stimulus control in the study of the formation of stimulus classes.

Journal Article↗
PubMed1976

Some aspects of normal behavior: their use in understanding problems encountered by document examiners.

The premise that progress in document examination will depend on employing techniques useful in the more formal branches of science is not exactly logical. The correlation between the work of the document examiner and the behavioral sciences has been discussed by presenting some random thoughts which have occurred to the author over a period of years. The suggestion is made, by illustration and implication, that the unfortunate connotation of the word "behavior" with the word "graphology" has tended to direct the attention of document examiners away from a study of the behavioral sciences, a branch of science from which much can be learned. The fact that the subjective concepts of probability formed by the mature document examiner will approach mathematical expectation has been noted.

Behavior↗
PubMedDate not supplied

[Glutamate-related excitotoxicity neuroprotection with memantine, an uncompetitive antagonist of NMDA-glutamate receptor, in Alzheimer's disease and vascular dementia].

AIM: To review the therapeutic efficacy of memantine, an uncompetitive antagonist of N-methyl-D-aspartate (NMDA)-glutamate receptor. DEVELOPMENT: Alzheimer's disease (AD) is the most common neurodegenerative disorder and cause of dementia with ageing worldwide. The main AD symptoms are a gradual loss of cognitive function and a functional impairment. Glutamatergic excitatory neurotransmission, an important process in learning and memory, is severely disrupted in AD, probably due to the oxidative stress associated with the beta-amyloid peptide (1-42) increase. The glutamate-related excitotoxicity, mainly mediated by NMDA subtype of the glutamate receptors, is a common clue of pathogenesis for neurodegenerative disorders. CONCLUSIONS: Memantine, a moderate-affinity, voltage-dependent, uncompetitive antagonist of NMDA receptor, shows neuroprotective effects in patients with moderate-to-severe AD. Memantine is a drug with neuroprotective and cognition-enhanced properties, which can be combined with other treatments for AD. Thus, memantine does not stop or reverse AD, but its moderating effect in protecting the brain from the toxic levels of calcium, allows normal signaling among brain neurons. The efficacy and safety profile of memantine have been reported in several clinical trials for treatment of AD and vascular dementia.

Alzheimer Disease↗