Detection and discrimination of simple and complex patterns at low spatial frequencies.
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Discrimination, Psychological↗
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Emotional memory systems in the brain.
The neural mechanisms of emotion and memory have long been thought to reside side by side, if not in overlapping structures, of the limbic system. However, the limbic system concept is no longer acceptable as an account of the neural basis of memory or emotion and is being replaced with specific circuit accounts of specific emotional and memory processes. Emotional memory, a special category of memory involving the implicit (probably unconscious) learning and storage of information about the emotional significance of events, is modeled in rodent experiments using aversive classical conditioning techniques. The neural system underlying emotional memory critically involves the amygdala and structures with which it is connected. Afferent inputs from sensory processing areas of the thalamus and cortex mediate emotional learning in situations involving specific sensory cues, whereas learning about the emotional significance of more general, contextual cues involves projections to the amygdala from the hippocampal formation. Within the amygdala, the lateral nucleus (AL) is the sensory interface and the central nucleus the linkage with motor systems involved in the control of species-typical emotional behaviors and autonomic responses. Studies of cellular mechanisms in these pathways have focused on the direct relay to the lateral amygdala from the auditory thalamus. These studies show that single cells in AL respond to both conditioned stimulus and unconditioned stimulus inputs, leading to the notion that AL might be a critical site of sensory-sensory integration in emotional learning. The thalamo-amygdala pathway also exhibits long-term potentiation, a form of synaptic plasticity that might underlie the emotional learning functions of the circuit. The thalamo-amygdala pathway contains and uses the amino acid glutamate in synaptic transmission, suggesting the possibility that an amino-acid mediated form of synaptic plasticity is involved in the emotional learning functions of the pathway. We are thus well on the way to a systems level and a cellular understanding of at least one form of emotional learning and memory.
Animals↗
Amplitude variations in P300 component due to unpredictable stepwise change of stimulus probability.
The present study investigates whether the amplitude of the P300 in 'normal' subjects adapts to unexpected changes in global stimulus probability. The adaptation level (AL) metrics (in terms of Helson's [1964] theory) was applied to explain the variations in the P300 amplitude. In an oddball paradigm the probability of the deviant tone (target 1000 Hz, 80 dB, 50 ms) occurring randomly in a train of standard ones (non-target 1100 Hz, 80 dB, 50 ms) was changed in a stepwise way from 0.5 to 0.3 and then to 0.1 in 3 blocks without interruption of the stimulus presentation. Two experiments were performed. In the first one the subjects did not receive any prior information about the changes in the stimulus probability, whereas in the second experiment they were aware of such changes. The task always required the subject to silently count the deviants. EEG was recorded monopolarly from Fz, Cz and Pz in a total of 15 subjects. The block averaged P300 increased monotonically with probability, the increase being larger in Expt. II. In contrast to the block averaged P300, the variations in the P300 amplitude following the abrupt change in probability showed a non-linear dependency. On the basis of the AL a simulation of the time course of the P300 variations with probability was performed and a clear similarity between the simulated P300 and the experimental data was found. Some properties of the AL model are discussed.
Acoustic Stimulation↗
Dissociation of intake adjustments to sustained and day-to-day changes in food caloric density.
Rats were subjected to day-to-day changes in food caloric density superimposed on a sustained (average) change above or below the basal value. This was done by giving them a different diet every day, so that caloric density gradually increased from a basal value. By repeating this procedure the caloric density varied in a sinusoidal pattern above or below the basal value. Short-term compensatory changes in food intake followed a reversed and delayed sinusoidal pattern (compared to that of caloric density), and achieved only an incomplete compensation of caloric intake. On the other hand, long-term changes in the average food intake led to a complete compensation of the average caloric intake for the high-calorie diets. The low-calorie diets produced a marked body weight loss, although these rats maintained the partly compensatory responses to the day-to-day changes in caloric density; that is, food intake decreased when the caloric density of the diet increased to the basal value, overriding any effect of body weight loss. It is concluded that short-term and long-term controls of food intake are relatively independent of each other and that the short-term control determines the daily caloric intake, with a delay that probably indicates learning processes, while the long-term control is determining the average caloric intake over a period of several days, accounting for a more or less complete compensation of caloric density changes.
Analysis of Variance↗
Differential conditioning of electrodermal responses: effects of performing a masking task during the interstimulus and intertrial intervals.
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Adolescent↗
Channel probability and Nd: an event-related potential sign of attention strategies.
Event-related potentials were recorded in a two-channel selective attention paradigm designed to assess the effects of channel probability on processing negativity. For channel probabilities of 70% or greater, the subtraction Nd for standard tones was greatly reduced or absent. This change was due to apparent processing negativity in the waveform of the irrelevant standards at high channel probabilities. Deviant long tones showed similar early Nds to standard tones, and also developed late attention-related negativity commencing at about 500 ms from stimulus onset. It was concluded that there was no evidence that processing negativity to the relevant tones, defined as a negative component associated with selective attention, is affected by channel probability. Changes in Nd amplitude as the channel probabilities became more unequal were attributed to changes in strategies used by subjects, which primarily altered ERPs associated with the irrelevant tones.
Adult↗
Stimulus probability and motor response in young and old adults: an ERP study.
The effects of responding hand and stimulus probability were investigated in young and old subjects in an RT task in which both rare and frequent stimuli required a response. It was found that the effect of stimulus probability was less pronounced in old subjects than in young, and that the latency of P3 was longer in the elderly, although their RTs were not different from young subjects. ERPs for right hand responses were larger than for left hand responses; this difference was discernible already in the P2 and N2 peaks of the ERP. A tentative explanation is offered for these large and unexpected hand differences. An interpretation in terms of an age-related decrease in resources is proposed for the increased P3 latency and the decreased probability effect on P3 amplitude in old subjects.
Adolescent↗
Time effects on event-related brain potentials and vigilance performance.
A review of the literature showed that in vigilance or oddball tasks, changes over time in event-related potentials (ERPs) and performance measures often seem to be unrelated, but a number of studies had some shortcomings. In the present study a visual vigilance experiment was carried out, in which single-trial ERPs and performance data of 40 males were obtained. A relationship between time trends in behavioral and ERP measures was found: an early P3 amplitude and response latency (RT) showed an inversely varying relation over time. Analysis of covariance showed that the two linear trends tap the same aspect of processing: both trends became insignificant when adjusted for common variance. A negative correlation between mean values of P3 amplitude and RT rather than for change scores has been observed in previous studies, but has been ignored in the literature. However, correlations with RT have also been reported for other ERP deflections. Although there were several correlations between mean scores, most time-induced changes in ERP parameters appeared to be unrelated to worsening performance, for which several explanations are advanced. The ERP results do not support the hypothesis that a decrement in performance is caused by increasing difficulty discriminating targets from nontargets. A gradual decline in effort or resources allocated to the task might be an alternative explanation of performance deterioration. However, an effort-hypothesis cannot easily be tested. Effort is often invoked post hoc, and has previously been associated with many ERP components. The relationship between ERPs and the signal detection measures "sensitivity" d' and "response bias" beta is discussed.
Adolescent↗
Cognitive load as a determinant of the dimensionality of the electroencephalogram: a replication study.
A sequel study to that reported by Gregson, Britton, Campbell and Gates (1990), partially replicating and extending findings which relate estimates of the dimensionality of the EEG to the complexity of task load in a visual scanning task, is described. The correlation dimensionality D2 of the attractor was computed using a variant of the Grassberger-Procaccia algorithm, and was shown to change in the expected direction, increasing as the task became more complicated. The effects are slight but consistent, and may be attenuated by nonstationarity over time, and by idiosyncratic factors. The results are numerically and qualitatively compatible with other recent reported studies, and support an interpretation linking brain dynamics to implied cognitive processes.
Adult↗
On the relationship between background EEG and the P300 event-related potential.
Background EEG was recorded from 24 subjects under eyes open/closed conditions for 5 min. The P3(00) event-related brain potential (ERP) was elicited with auditory stimuli when eyes were open/closed in the same subjects. Target stimulus probability was manipulated (0.20, 0.40, 0.60, 0.80) in different blocks under each eyes open/closed condition. Spectral analysis indicated that EEG power between 8 and 12 Hz demonstrated a similar scalp distribution as the P3 component of the ERP for the electrode sites employed. Spectral power and mean frequency were modestly correlated with P3 amplitude and peak latency primarily in the slower EEG bands, with associations observed across probability conditions and often strongest when target stimulus probability was .20. The results suggest that differences between individuals for EEG variation may contribute to P3 component variability, especially at the parietal recording site and under low target stimulus probability conditions when the P3 is largest and most stable.
Adolescent↗
Pathological gambling treated with cognitive behavior therapy: a case report.
A novel approach to the cognitive behavioral treatment of pathological gambling is described. The approach is based on the hypothesis that biased information may form the basis of the rules governing gambling behavior. The treatment focused on modifying assumptions and beliefs underlying the gambling behavior of a 47-year-old male with a 26-year gambling history. Based on a 6-month follow-up, the intervention successfully reduced the frequency of the client's gambling behavior from 10 times per month in the 3 years prior to treatment to three total times in the 6-month follow-up period.
Alcoholism↗
Objectives to direct the training of emergency medicine residents in off-service rotations: plastic surgery.
This is the fourth article in a continuing series on objectives for emergency medicine training; plastic surgery objectives will be presented. Plastic surgery topics overlap many in emergency medicine. Specific behaviorally based objectives for mastery of skills in plastic surgery are outlined. Specific references are provided for additional information and reinforcement in skill mastery. The basic concepts of plastic surgery are probably best learned by observation and supervised performance. Specific objectives provide guidance and direction for the didactic as well as the supervised experiences in skill mastery. These objectives provide a structure for systematically learning and mastering the content presented on a plastic surgical rotation or experience in emergency medicine training.
Education↗
Deficit of preparatory attention in frontotemporal dementia.
We studied preparatory attention in patients suffering from frontotemporal dementia in the beginning stages of the disease, using an experimental test developed by LaBerge, Auclair, and Siéroff (2000). In this experimental test, a distracter can appear while subjects have to prepare to respond to a simple target. The probability that a distracter can appear in a trial is varied across three blocks. Normal controls show an increase of response times to targets (slope) as a function of the distracter probability, preparatory attention to the target is reduced by the increase of the distracter probability. Patients suffering from frontotemporal dementia show a slope of response times which is more than twice as large as the slope obtained by their matched controls. Such an abnormal increase of response times to targets is interpreted as a deficit in preparatory attention. Patients also show more omissions than controls. We suggest that this deficit in preparatory attention is related to the frontal lesion presented by the patients and can result in higher distractibility, a symptom frequently encountered in these patients.
Aged↗
Et tu, Grotthuss! and other unfinished stories.
This review article is divided into three sections. In Section 1, a short biographical note on Freiherr von Grotthuss is followed by a detailed summary of the main findings and ideas present in his 1806 paper. Attempts to place Grotthuss contribution in the context of the science done at his time were also made. In Section 2, the modern version of the Grotthuss mechanism is reviewed. The classical Grotthuss model has been recently questioned and new mechanisms and ideas regarding proton transfer are briefly discussed. The last section discusses the significance of a classical Grotthuss mechanism for proton transfer in water chains inside protein cavities. This has been an interesting new twist in the ongoing history of the Grotthuss mechanism. A summary and discussion of what was learned from probably the simplest currently available experimental models of proton transfer in water wires in semi-synthetic ion channels are critically presented. This review ends discussing some of the questions that need to be addressed in the near future.
Electrochemistry↗
Economic context and pigeons' risk-taking: an integrative approach.
The present work tested pigeons' (Columba livia) risk sensitivity to changes in resource availability in the concurrent-chains choice procedure. Subjects were provided choices, generally between variable-ratio (VR) and fixed-ratio (FR) outcome schedules with equal or different mean values. Predictions from ecology's risk sensitivity, behavioral economic's rate maximization, and psychology's delay-reduction theory were contrasted under settings where budget was adversely affected by one of three manipulations in seven experiments: (1) session length was dramatically reduced; (2) choice-phase duration was substantially increased by increasing the response requirements in the choice phase, or (3) outcome duration was significantly increased by increasing the response requirements in the outcome phase while holding session length constant. Although preference measures were sensitive to every budget manipulation, the nature of the changes observed were dependent upon the manner in which resource availability was manipulated and the choice alternatives offered. For example, choice was affected in an opposite manner when budget was adversely altered by lengthening choice duration ("search time") as opposed to lengthening outcome duration ("handling time"). Findings revealed partial support for pigeons' sensitivity both to changes in budget and to changes in conditioned reinforcer value. The overall pattern of results thus favors an integrative approach to describing the effect of economic context on general risk sensitivity.
Animals↗
The present values of delayed rewards are approximately additive.
In two experiments, human subjects were asked to estimate their present values of single delayed rewards and their present values of temporal sequences of three rewards. Present values were solicited by asking subjects to indicate an amount of money v for which they would be indifferent between receiving v at the end of the session and receiving the delayed reward(s). A procedure was used for which responding the true value of v was the optimal strategy, and the actual payoff that each subject received was determined by one randomly selected trial. In Experiment 1 (n=29) each delayed reward was 9.90 dollars in cash. In Experiment 2 (n=19) the delayed rewards were dated 15 dollars gift certificates to a local restaurant. In both experiments, the present values of the sequences were approximately equal to the sums of the present values of their component rewards. The presence of outliers suggests that a few subjects may have valued sequences less than the sums of their single rewards. Effects of a preference for uniform sequences, if any, were too small to be detected. Discounting of sequences was well fit by a parallel hyperbolic discounting equation, consistent with Mazur's [Mazur, J.E., 1986. Choice between single and multiple delayed reinforcers. J. Exp. Anal. Behav. 46 (1), 67-77] results using multiple reinforcers.
Adult↗
The combined effects of delay and probability in discounting.
Human discounting studies have frequently observed hyperbolic discounting of rewards that are delayed or probabilistic. However, no studies have systematically combined delay and probability in a single discounting procedure. Indifference points of hypothetical money rewards that are both delayed and probabilistic were determined. Probabilities were converted into comparable delays according to the h/k constant of proportionality determined by , and discounting rates were calculated. These data provided a very good fit to the hyperbolic model of discounting, suggesting that delay and probability can be combined into a single metric in studies of discounting. The inclusion of a magnitude condition found the Magnitude Effect commonly found in studies of temporal discounting. A temporal resolution of uncertainty condition found no effect. The present paper offers a novel statistical method, within an established framework, for the analysis of data from studies of discounting that combine delay and probability.
Adolescent↗
An empirical test of signal detection theory as it applies to Batesian mimicry.
Signal detection theory (SDT) has been repeatedly invoked to understand how palatable prey might gain an advantage by resembling unpalatable prey. Here we developed an experimental test of the theory in which we sequentially presented computer-generated Mimics (profitable to attack) and Models (unprofitable to attack) to human volunteers, and asked them to forage in a way that maximized their personal scores. Both the Mimics and Models exhibited normally distributed variation in a single stimulus dimension. When we varied the mean similarity of Mimics to Models, and the proportion of all prey items that were Mimics, our human predators made foraging decisions that were close to those predicted by SDT, including the adoption of a threshold in appearance beyond which prey items were unlikely to be attacked. The fit of predictions to observations was marginally closer when including the time taken to handle the two types of prey. When Mimics and Models were allowed to evolve in appearance subject to selection, the evolutionary trajectory fitted the predictions of SDT closely. While our system was not appropriate to test all predictions of recent SDT theory, it provides strong support for the SDT framework as it applies to Batesian mimicry.
Adaptation, Biological↗