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PubMed2005

Brain activations associated with probability matching.

Previously, in a simple probability-matching experiment with two split-brain patients that involved having the participant predict which of two events will happen on the next trial, we found that the left hemisphere tended to look for patterns and match the frequency of previous occurrences but not the right hemisphere [Wolford, G., Miller, M. B., & Gazzaniga, M. S. (2000). The left hemisphere's role in hypothesis formation. Journal of Neuroscience, 20(RC64), 1-4]. In this study, we examined those findings in normal subjects using fMRI. Subjects alternated between blocks of trials in which they predicted the location of a stimulus and those in which they detected the location of a stimulus. Previous investigators using similar paradigms reported mostly right hemisphere activations, including activations in the right dorsolateral and ventrolateral prefrontal cortex, the medial prefrontal cortex, and the right lateral parietal lobe. We also found mostly right hemisphere activations, but we found that some of the activations in the dorsolateral prefrontal and parietal cortices were sensitive to individual differences in the tendency to look for patterns in random sequences. Further, we found that, by controlling for the working memory component of the predicting task, all brain activations in the normal brain associated with looking for patterns were related to the task demands of working memory processes underlying probability matching and predicting.

Adult↗

PubMed2005

The involvement of the orbitofrontal cortex in learning under changing task contingencies.

Previous investigations examining the rat prefrontal cortex subregions in attentional-set shifting have commonly employed two-choice discriminations. To better understand how varying levels of difficulty influence the contribution of the prefrontal cortex to learning, the present studies examined the effects of orbitofrontal cortex inactivation in a two- or four-choice odor reversal learning test. Long-Evans rats were trained to dig in cups that contained distinct odors. In the two-choice odor discrimination, one odor cup was always associated with a cereal reinforcement in acquisition while the opposite odor cup was associated with a cereal reinforcement in reversal learning. In the four-choice odor discrimination, an additional two cups containing distinct odors were used that were never associated with reinforcement in acquisition or reversal learning. Bilateral infusions of the GABA-A agonist, muscimol (0.5 microg) into the orbitofrontal cortex did not impair acquisition of either the two- or four-choice discrimination task. However, muscimol infusions into the orbitofrontal cortex impaired two- and four-choice reversal learning. In the two-choice odor reversal, muscimol treatment selectively increased perseverative errors. In the four-choice odor reversal, muscimol treatment increased perseverative, regressive, as well as irrelevant errors. These findings suggest that the orbital prefrontal cortex not only enables task switching by supporting the initial inhibition of a previously relevant choice pattern, but under increasing task demands also enables the reliable execution of a new choice pattern and reduction of interference to irrelevant stimuli.

Animals↗

PubMed2006

Motor response selection in children with fetal alcohol spectrum disorders.

Previous work has reported timing delays in motor response selection in children with prenatal exposure to alcohol when the information load involved responding to two stimulus choices. The present study examined whether the delay in response selection extends to conditions in which the information load is increased to four and eight stimulus choices. Twenty children aged between 12 and 17 years with fetal alcohol spectrum disorders (FASD) were compared to 17 non-alcohol-exposed controls (NC) on a reaction time (RT) task involving 1, 2, 4 or 8 visual stimulus choices. The task demands required the participant to release a response key as fast as possible when the stimulus light electronically paired with the response key was activated. With the number of stimulus choices expressed on a logarithmic scale, there was a significant and linear increase in RT for the FASD children as predicted by information processing theory. Additionally, the increase in RT for the FASD group was comparable to that observed for the NC children at each level of stimulus choice examined. It was concluded that FASD adolescents require additional time to process increasing amount of information, but that the time required for motor response selection is not delayed relative to control group performance.

Adolescent↗

PubMed2004

Cognitive modulation of pain-related brain responses depends on behavioral strategy.

Interactions of pain and cognition have been studied in humans and animals previously, but the relationship between such behavioral interactions and brain activity is unknown. We aimed to show using functional MRI (fMRI) how a cognitively demanding task (Stroop) modulates pain-related brain activations and conversely, how pain modulates attention-related activity. Reaction time data indicated two types of pain responders: subjects in the A group had a faster Stroop reaction time when pain was concomitant to the attention task, while those in the P group had a slower Stroop performance during painful stimulation. fMRI data obtained during Stroop performance with and without noxious stimulation were subjected to region of interest analyses. We first tested whether brain activity during painful median nerve stimulation was modulated by cognitive load. We next tested whether brain activity during the high conflict cognitive task was modulated by pain. Pain-related activity in three regions, primary (S1), and secondary (S2) somatosensory cortices, and anterior insula, was attenuated by cognitive engagement, but this effect was specific to the A group. Pain-related activations in the caudal and rostral anterior cingulate cortex (ACC) and ventroposterior thalamus were not modulated by cognitive load. None of the areas showing attention-related responses, including bilateral dorsolateral prefrontal and posterior parietal cortices, were modulated by pain. These findings suggest that cortical regions associated with pain can be modulated by cognitive strategies. Furthermore, the distinction of behavioral subgroups may relate to cognitive coping strategies taken by patients with chronic pain.

Adult↗

PubMed2006

Interaction of psychosocial risk factors explain increased neck problems among female office workers.

This study investigated the relationship between psychosocial risk factors and (1) neck symptoms and (2) neck pain and disability as measured by the neck disability index (NDI). Female office workers employed in local private and public organizations were invited to participate, with 333 completing a questionnaire. Data were collected on various risk factors including age, negative affectivity, history of previous neck trauma, physical work environment, and task demands. Sixty-one percent of the sample reported neck symptoms lasting greater than 8 days in the last 12 months. The mean NDI of the sample was 15.5 out of 100, indicating mild neck pain and disability. In a hierarchical multivariate logistic regression, low supervisor support was the only psychosocial risk factor identified with the presence of neck symptoms. Similarly, low supervisor support was the only factor associated with the score on the NDI. These associations remained after adjustment for potential confounders of age, negative affectivity, and physical risk factors. The interaction of job demands, decision authority, and supervisor support was significantly associated with the NDI in the final model and this association increased when those with previous trauma were excluded. Interestingly, and somewhat contrary to initial expectations, as job demands increased, high decision authority had an increasing effect on the NDI when supervisor support was low.

Adolescent↗

PubMedDate not supplied

Behavioral function effects on intervention acceptability and effectiveness for self-injurious behavior.

A variety of variables have been found to augment perceived social validity of behavioral interventions. In the present study, potential effects of behavioral function were evaluated. Sixty students inexperienced in work with people with mental retardation, and 60 experienced staff watched one of two carefully matched acted videos depicting self-injury maintained by attention or escape from task demands. Participants were also told whether the self-injury depicted typically led to mild or severe consequences for the person filmed. Participants rated six interventions in terms of their acceptability and effectiveness for the behavior depicted. A hierarchy of acceptability was replicated: reinforcement-based procedures were rated as more acceptable and effective. There were also effects of behavior severity and rater experience. However, few effects of behavioral function were found. Potential implications of staff undifferentiated attitudes towards functional treatments are discussed.

Adolescent↗

PubMed2006

Beyond faces and modularity: the power of an expertise framework.

Studies of perceptual expertise typically ask whether the mechanisms underlying face recognition are domain specific or domain general. This debate has so dominated the literature that it has masked the more general usefulness of the expertise framework for studying the phenomenon of category specialization. Here we argue that the value of an expertise framework is not solely dependent on its relevance to face recognition. Beyond offering an alternative to domain-specific accounts of face specialization in terms of interactions between experience, task demands, and neural biases, expertise studies reveal principles of perceptual learning that apply to many different domains and forms of expertise. As such the expertise framework provides a unique window onto the functional plasticity of the mind and brain.

Animals↗

PubMed2005

Serial visual search from a parallel model.

We tested a parallel neural network model of visual search, and found that it located targets more quickly when allowed to take several fast guesses. We suggest that this serially iterated parallel search may be the mode used by the visual system, in accord with theories such as the Guided Search model. Furthermore, in our model the most efficient mode of processing varied with the type of search. If the nature of visual search varies with task demands, seemingly contradictory findings can be reconciled.

Discrimination, Psychological↗

PubMed2006

Initial visual information determines endpoint precision for rapid pointing.

We investigated how visual noise in the initial estimate of target location affects precision for rapid pointing. Visual localization thresholds (an error measure) rise systematically with eccentricity, doubling at eccentricities of a degree or less. Previous work, which we confirmed, has shown that the precision of pointing, measured by the standard deviation, to a single isolated target is relatively constant over small lateral extents near the midline, and that pointing error is substantially larger than visual error. We used target uncertainty (randomly chosen locations) to greatly increase visual noise so that we could explore the influence of visual noise on pointing error. We compared precision for comparable visual and pointing tasks as a function of target eccentricity. The target was presented for 110 ms at one of eight isoeccentric locations, chosen at random. Under these conditions, pointing error increased significantly with increasing target eccentricity. Beyond 4 degrees eccentricity, visual thresholds and pointing error were identical. Even when the target remained visible until the movement was completed, initial target eccentricity affected pointing error. The quality of visual information varies with task demands, and therefore so does its influence on endpoint precision. Our results demonstrate that the initial visual information about target location can limit endpoint precision, even over as small a range as 12 degrees in the central visual field (a lateral extent of +/-8.5 cm at the midline).

Fingers↗

PubMed1997

Visual search strategy and perceptual organization covary with individual preference and structural complexity.

The pattern of interactions between visual search profile (serial versus nonserial) and perceptual organization type (functionally local versus global) was investigated in three experiments. The task was a matching judgment performed on two separate figures that fit in a jigsaw-puzzle fashion. Reaction times and errors showed that serial search preferably goes together with local organization and nonserial search with global organization. Choice of search profile and organization type depend on task and individual preference. Structural complexity in the target area reinforces the combination of local organization and serial search. This combination was also chosen by subjects preferring accuracy. The combination of global organization and nonserial search was chosen with simpler targets or by subjects preferring speed. The results support an interactive notion of perceptual organization and search. Perceptual organization type is determined by individual preferences in combination with visual search task demands; visual search is guided by the specific organization of the stimulus pattern.

Humans↗

PubMed2003

Wavelet analysis of nonstationary fluctuations of Monte Carlo-simulated excitatory postsynaptic currents.

Tracking spectral changes of rapidly varying signals is a demanding task. In this study, we explore on Monte Carlo-simulated glutamate-activated AMPA patch and synaptic currents whether a wavelet analysis offers such a possibility. Unlike Fourier methods that determine only the frequency content of a signal, the wavelet analysis determines both the frequency and the time. This is owing to the nature of the basis functions, which are infinite for Fourier transforms (sines and cosines are infinite), but are finite for wavelet analysis (wavelets are localized waves). In agreement with previous reports, the frequency of the stationary patch current fluctuations is higher for larger currents, whereas the mean-variance plots are parabolic. The spectra of the current fluctuations and mean-variance plots are close to the theoretically predicted values. The median frequency of the synaptic and nonstationary patch currents is, however, time dependent, though at the peak of synaptic currents, the median frequency is insensitive to the number of glutamate molecules released. Such time dependence demonstrates that the "composite spectra" of the current fluctuations gathered over the whole duration of synaptic currents cannot be used to assess the mean open time or effective mean open time of AMPA channels. The current (patch or synaptic) versus median frequency plots show hysteresis. The median frequency is thus not a simple reflection of the overall receptor saturation levels and is greater during the rise phase for the same saturation level. The hysteresis is due to the higher occupancy of the doubly bound state during the rise phase and not due to the spatial spread of the saturation disk, which remains remarkably constant. Albeit time dependent, the variance of the synaptic and nonstationary patch currents can be accurately determined. Nevertheless the evaluation of the number of AMPA channels and their single current from the mean-variance plots of patch or synaptic currents is not highly accurate owing to the varying number of the activatable AMPA channels caused by desensitization. The spatial nonuniformity of open, bound, and desensitized AMPA channels, and the time dependence and spatial nonuniformity of the glutamate concentration in the synaptic cleft, further reduce the accuracy of estimates of the number of AMPA channels from synaptic currents. In conclusion, wavelet analysis of nonstationary fluctuations of patch and synaptic currents expands our ability to determine accurately the variance and frequency of current fluctuations, demonstrates the limits of applicability of techniques currently used to evaluate the single channel current and number of AMPA channels, and offers new insights into the mechanisms involved in the generation of unitary quantal events at excitatory central synapses.

Algorithms↗

PubMed2004

The number space and neglect.

Recent cognitive models of numerical abilities have postulated that number processing may in part rely on a representation of quantities where magnitude is organized by spatial proximity, along a "mental number line" extending from left to right. We describe four experiments that examined whether such a spatial representation of number would be affected by the presence of unilateral neglect after right hemisphere damage. When asked to judge whether a single number shown at fixation was smaller or larger than "5", patients with neglect were selectively slower to respond to "4", but when asked to compare numbers to "7" they were selectively slower to respond to "6". This is consistent with a representational deficit for numbers located to the left of a reference point along the mental number line and was not found in other right brain-damage patients without neglect. No effect of represented number position was found in a non-numerical task requiring judgements of the physical size of single digit characters. Finally, when asked to classify numbers as indicating hours earlier or later than six o'clock, neglect patients showed a reverse pattern with slower responses to numbers larger than "6', consistent with a representational deficit for hour numbers located on the left side of an imagined clock-face. Our findings demonstrate that unilateral spatial neglect may produce specific representational deficits in number processing that implicate different spatial representations according to the task demands.

Aged↗

PubMed1998

Prosopagnosia and alexia without object agnosia.

Following a trauma causing bilateral posterior brain damage, a patient complained of dyslexia and prosopagnosia, but not object agnosia. On testing she showed intact recognition of object drawings, even when it was assessed with perceptually demanding tasks such as Ghent's overlapping figures and Street completion test. This pattern of deficit is inconsistent with Farah's (1990) prediction that the simultaneous occurrence of alexia and prosopagnosia is invariably associated with object agnosia. The patient's reading performance had the features typically found in letter-by-letter readers. On face tests, she showed a discrepancy between the impairment exhibited in familiarity recognition and famous face naming and the correct (though slow) performance in matching the names of famous persons with their photographs. This apparent contradiction was clarified by showing that the patient had maintained the ability to generate the mental images of famous faces in response to the presentation of their names. We assume that face recognition units were intact, but partially disconnected from the output of perceptual processing.

Adult↗

PubMed1980

Hemispheric superiority for recognizing faces depends upon how they are learned.

To investigate whether the type of information available influences encoding strategy, and subsequent hemispheric advantage, for face recognition, Experiment I presented photographs of faces for initial viewing centrally, under two conditions: verbal presentation of (a) molar personality or (b) physical feature information about each target face. The recognition task presented targets and distractors tachistoscopically to each visual field. Recognition accuracy scores displayed a highly significant pattern of contrasting hemispheric superiorities under the two informational conditions, but the direction of this contrast was not consistent for all subjects. The first part of Experiment II replicated the procedures of Experiment I, except that all verbal encoding information was omitted. Under these control conditions, the "crossover" pattern of hemispheric superiorities did not emerge, and subjects instead displayed consistent LH or RH superiorities. A second experimental session demonstrated the reliability and generality of the crossover phenomenon: When the same subjects were recalled and the original encoding manipulation applied to a new set of faces, the pattern of contrasting hemispheric superiorities again emerged. No aspect of subjects' performance in the control condition was found to predict the direction of crossover in the subsequent experimental session. We infer that intra-subject contrasts in hemispheric superiority reflect the use of alternative encoding or processing strategies under the two informational conditions, but the relation of such strategies to specific hemispheric advantages remains unclear. A general statement of the relation of cognitive processing, task demand characteristics, and observed hemispheric advantage is proposed.

Adolescent↗

PubMed1983

An unexpected interactive pattern of visual field asymmetries revealed by faster/slower response partitioning.

Subjects were presented with unilaterally-exposed schematic, outline faces in one condition, and three-letter single-syllable first names in another. In either case there was an ensemble of four items which were to be partitioned, by the subjects making a manual choice-reaction-time response, into two subsets. No easy rule permitted the partitioning either of the faces or of the names (DEN, LES versus LEN, DES). While no clear pattern of asymmetries emerged from an overall analysis, or from a simple comparison of the two types of response, when the subjects' individual responses were instead partitioned into faster and slower, a striking pattern of interactive asymmetries emerged which was consistent for both sexes and both tasks. Thus the slower of the two responses was associated with a left field superiority, and the faster with a right. These findings were discussed in the context of perceived or covert task demands, which are not always immediately recognizable from a superficial or conventional analysis of response data, and the effect of positive (target) and negative (nontarget) processing upon behavioral asymmetries.

Discrimination Learning↗

PubMed1996

Semantic processing without conscious understanding in a global aphasic: evidence from auditory event-related brain potentials.

We report a global aphasic who showed evidence of implicit semantic processing of spoken words. Auditory event-related brain potentials (ERPs) to semantically congruous and incongruous final words in spoken sentences were recorded. 17 elderly adults served as control subjects. Their ERPs were more negative to incongruous than to congruous final words between 300 and 800 ms after stimulus onset (N400), and more positive between 800 and 1500 ms (Late Positivity). The aphasic showed an exactly similar pattern of ERP components as the controls did, but his performance in a task demanding explicit differentiation between semantically congruous and incongruous sentences was at the chance level. During follow-up, his explicit understanding recovered over the chance level but the ERPs remained fairly similar. We conclude that implicit semantic activation at the conceptual level can take place even in the absence of conscious (explicit) comprehension of the meaningfulness of linguistic stimuli.

Acoustic Stimulation↗

PubMed2002

Chromatographic enrichment and enantiomer separation of axially chiral polybrominated biphenyls in a technical mixture.

The separation properties of different chromatographic methods regarding the enantioselective separation of axially chiral (atropisomeric) polybrominated biphenyls (PBB) were studied. For this purpose, the technical hexabromobiphenyl product Firemaster BP-6 was characterised by gas-chromatography coupled to electron capture detection (GC/ECD) and electron-capture negative ion mass spectrometry (GC/ECNI-MS) as well as by liquid chromatographic fractionating on active carbon and celite. Twelve individual PBBs including potential atropisomeric PBBs were isolated from Firemaster BP-6 by reversed-phase high-performance liquid chromatography (HPLC) on three serially coupled octadecylsilane columns. Six of the 12 isolated PBBs (three tri-ortho and di-ortho substituted PBBs, respectively) were separated into atropisomers on a HPLC column containing permethylated beta-cyclodextrin on silica. Moreover, the temperature dependency of the enantiomer separations is discussed. Gas chromatographic enantiomer separation of PBBs is a very demanding task due to high elution temperatures. However, the atropisomers of one tri-ortho substituted PBB congener (PBB 149) could be resolved on a column coated with randomly modified heptakis(6-O-tert.-butyldimethylsilyl-2,3-di-O-methyl)-beta-cyclodextrin in OV 1701.

Chromatography, Gas↗

PubMed2001

Brain activation during automatic and controlled processing of semantic relations: a priming experiment using lexical-decision.

Semantic relations may be studied using the experimental technique known as semantic priming, in which a word 'primes' the processing of a related target (e.g. lion-tiger), following a short delay. Priming may be automatic or, with longer delays, under more controlled processing. This study used functional magnetic resonance imaging (fMRI) to examine the cerebral activation during two lexical-decision semantic priming experiments, with a short and long delay, representing automatic and controlled processing, respectively. A further two un-primed lexical-decision tasks were performed to distinguish cerebral activation specific to semantic priming itself from those utilised during lexical-decision processes. Distinct regions of anterior cingulate cortex (ACC) were critical to automatic and controlled semantic priming, whilst the putamen and hippocampal complex responded differently to unrelated and semantically related prime-target pairs. Lexical-decision alone revealed activation in posterior temporal cortex especially on the left, in agreement with previous neuroimaging studies. The results provide a plausible neural substrate for common semantic relations independent of task demands and further emphasise the regional functional specialisation of the ACC.

Adult↗