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Stimulus Presentation (stimulus + presentation)
Selected AbstractsEnhanced mismatch negativity brain response after binaural word presentationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2004Tanja Endrass Abstract An oddball paradigm was used to investigate brain processes elicited by spoken words and pseudowords played monaurally, to the left or right ear, or simultaneously to both ears of human subjects instructed to ignore acoustic stimuli but watch a silent video film. The mismatch negativity (MMN), a neurophysiological index of the automatic activation of cortical memory traces, was calculated as the difference between the event-related potential elicited by an infrequent deviant stimulus and the event-related potential to the same item presented as a frequent standard stimulus. Consistent with earlier reports, the MMN to words was larger than that to pseudowords, possibly reflecting the existence of memory traces for spoken words. Bilateral redundant stimulus presentation led to a further increase of the MMN to words relative to both unilateral stimulation modes. This bilateral redundancy gain was absent for pseudowords. We interpret the neurophysiological manifestation of a word-specific bilateral redundancy gain as evidence for interhemispheric cooperation in the automatic access to memory traces for spoken words. Accordingly, word-related cortical networks distributed over both hemispheres allow summation of neural activity between and within hemispheres, thereby potentiating the word-related MMN. [source] Biphasic hemodynamic responses influence deactivation and may mask activation in block-design fMRI paradigmsHUMAN BRAIN MAPPING, Issue 4 2008Jed A. Meltzer Abstract A previous block-design fMRI study revealed deactivation in the hippocampus in the transverse patterning task, specifically designed, on the basis of lesion literature, to engage hippocampal information processing. In the current study, a mixed block/event-related design was used to determine the temporal nature of the signal change leading to the seemingly paradoxical deactivation. All positive activations in the hippocampal-dependent condition, relative to a closely matched control task, were seen to result from positive BOLD transients in the typical 4,7 s poststimulus time range. However, most deactivations, including in the hippocampus and in other "default mode" regions commonly deactivated in cognitive tasks, were attributable to enhanced negative transient signals in a later time range, 10,12 s. This late hemodynamic transient was most pronounced in medial prefrontal cortex. In some regions, the hippocampal-dependent condition enhanced both the early positive and late negative transients to approximately the same degree, resulting in no significant signal change when block analysis is used, despite very different event-related responses. These results imply that delayed negative transients can play a role in determining the presence and sign of brain activation in block-design studies, in which case an event-related analysis can be more sensitive than a block analysis, even if the different conditions occur within blocks. In this case, default mode deactivations are timelocked to stimulus presentation as much as positive activations are, but in a later time range, suggesting a specific role of negative transient signals in task performance. Hum Brain Mapp, 2008. © 2007 Wiley-Liss, Inc. [source] Functional source separation applied to induced visual gamma activityHUMAN BRAIN MAPPING, Issue 2 2008Giulia Barbati Abstract Objective of this work was to explore the performance of a recently introduced source extraction method, FSS (Functional Source Separation), in recovering induced oscillatory change responses from extra-cephalic magnetoencephalographic (MEG) signals. Unlike algorithms used to solve the inverse problem, FSS does not make any assumption about the underlying biophysical source model; instead, it makes use of task-related features (functional constraints) to estimate source/s of interest. FSS was compared with blind source separation (BSS) approaches such as Principal and Independent Component Analysis, PCA and ICA, which are not subject to any explicit forward solution or functional constraint, but require source uncorrelatedness (PCA), or independence (ICA). A visual MEG experiment with signals recorded from six subjects viewing a set of static horizontal black/white square-wave grating patterns at different spatial frequencies was analyzed. The beamforming technique Synthetic Aperture Magnetometry (SAM) was applied to localize task-related sources; obtained spatial filters were used to automatically select BSS and FSS components in the spatial area of interest. Source spectral properties were investigated by using Morlet-wavelet time-frequency representations and significant task-induced changes were evaluated by means of a resampling technique; the resulting spectral behaviours in the gamma frequency band of interest (20,70 Hz), as well as the spatial frequency-dependent gamma reactivity, were quantified and compared among methods. Among the tested approaches, only FSS was able to estimate the expected sustained gamma activity enhancement in primary visual cortex, throughout the whole duration of the stimulus presentation for all subjects, and to obtain sources comparable to invasively recorded data. Hum Brain Mapp 29:131,141, 2008. © 2007 Wiley-Liss, Inc. [source] Differential activity in left inferior frontal gyrus for pseudowords and real words: An event-related fMRI study on auditory lexical decisionHUMAN BRAIN MAPPING, Issue 2 2005Zhuangwei Xiao Abstract After Newman and Twieg ([2001]: Hum Brain Mapp 14:39,47) and others, we used a fast event-related functional magnetic resonance imaging (fMRI) design and contrasted the lexical processing of pseudowords and real words. Participants carried out an auditory lexical decision task on a list of randomly intermixed real and pseudo Chinese two-character (or two-syllable) words. The pseudowords were constructed by recombining constituent characters of the real words to control for sublexical code properties. Processing of pseudowords and real words activated a highly comparable network of brain regions, including bilateral inferior frontal gyrus, superior, middle temporal gyrus, calcarine and lingual gyrus, and left supramarginal gyrus. Mirroring a behavioral lexical effect, left inferior frontal gyrus (IFG) was significantly more activated for pseudowords than for real words. This result disconfirms a popular view that this area plays a role in grapheme-to-phoneme conversion, as such a conversion process was unnecessary in our task with auditory stimulus presentation. An alternative view was supported that attributes increased activity in left IFG for pseudowords to general processes in decision making, specifically in making positive versus negative responses. Activation in left supramarginal gyrus was of a much larger volume for real words than for pseudowords, suggesting a role of this region in the representation of phonological or semantic information for two-character Chinese words at the lexical level. Hum Brain Mapp 25:212,221, 2005. © 2005 Wiley-Liss, Inc. [source] Feature uncertainty activates anterior cingulate cortex,HUMAN BRAIN MAPPING, Issue 1 2004Szabolcs Kéri Abstract In visual discrimination tasks, the relevant feature to discriminate is defined before stimulus presentation. In feature uncertainty tasks, a cue about the relevant feature is provided after stimulus offset. We used 15O-butanol positron emission tomography (PET) in order to investigate brain activation during a feature uncertainty task. There was greater activity during the feature uncertainty task, compared with stimulus detection and discrimination of orientation and spatial frequency, in the lateral and medial prefrontal cortex, the cuneus, superior temporal and inferior parietal cortex, cortical motor areas, and the cerebellum. The most robust and consistent activation was observed in the dorsal anterior cingulate cortex (Brodmann area 32; x = 0 y = 16, z = 40). The insula, located near the claustrum (x = ,38, y = 8, z = 4), was activated during the discrimination tasks compared with the feature uncertainty condition. These results suggest that the dorsal anterior cingulate cortex is important in feature uncertainty conditions, which include divided attention, expectancy under uncertainty, and cognitive monitoring. Hum. Brain Mapp. 21:26,33, 2004. © 2003 Wiley-Liss, Inc. [source] Differential Frontal Cortex Activation Before Anticipatory and Reactive Saccades in InfantsINFANCY, Issue 2 2001Gergely Csibra Neural correlates of anticipatory and reactive saccades were studied in 4-month-old infants by recording high-density event-related potentials. Infants were presented with a fixed sequence of stimulus presentation to which they rapidly showed anticipatory saccades, as well as continuing with some reactive (stimulus-driven) saccades. As in a previous study, no clear evidence was found for adultlike, saccade-related potentials, although some presaccadic differences between reactive and anticipatory saccades were observed. Infants also showed different stimulus offset-related effects preceding the 2 types of trials with a right-frontal positivity when an anticipatory look follows, but only left-frontal positivity when a reactive saccade follows. [source] Language dominance assessment by means of fMRI: Contributions from task design, performance, and stimulus modalityJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2001Margret Hund-Georgiadis MD Abstract We investigated the influence of different task demands, task designs, and presentation modalities on the functional MRI activation patterns during a language lateralization task in a group of 14 right-handed control subjects. A word classification task was presented as target task appropriate to evoke language-related activation in the inferior frontal gyrus (IFG). The choice of the contrasting baseline task was demonstrated to have a major impact on the functional outcome: While a fixation baseline elicited activations in the inferior frontal gyrus of both hemispheres, a nonsemantic perceptual control task helped to isolate the relevant target task of word classification. The modality of stimulus presentation did not influence the functional data: Auditory and visual presentation modes broadly evoked activations in similar brain regions during word classification. Minor differences in task performance and the side of the responding hand did not interfere with the functional activation patterns of the target task. On the basis of our results, a protocol of functional lateralization in the inferior frontal gyrus is suggested. J. Magn. Reson. Imaging 2001;13:668,675. © 2001 Wiley-Liss, Inc. [source] Long-Term Behavioral Changes in Response to Early Developmental Exposure to Ethanol in ZebrafishALCOHOLISM, Issue 4 2009Yohaan Fernandes Background:, Zebrafish is becoming an important research tool for the analysis of brain function and behavior. It has been proposed to model human alcoholism as well as fetal alcohol syndrome. Previous studies investigating the consequences of exposure to ethanol during early development of zebrafish employed robust dosing regimens (high ethanol concentration and long exposure) that may model a rare situation in the human clinic. These studies found major structural abnormalities developing in the exposed fish. Methods: Here we hope to avoid such gross changes and administer only low doses of ethanol (0.00, 0.25, 0.50, 0.75, 1.00 vol/vol %) at 24-hour postfertilization and for only a short period of time (for 2 hours). We analyze the behavior of exposed fish at adult stage using computerized stimulus presentation and automated videotracking response quantification. Results: Despite the short ethanol exposure period and the modest concentrations, significant behavioral alterations were found: fish exposed to higher doses of ethanol swam at an increased distance from a computer-animated zebrafish shoal while their activity levels did not change. Conclusions: Although the interpretation of and the mechanisms underlying this finding will require further investigation, the results suggest that zebrafish will be an appropriate model organism for the analysis of the effects of moderate to mild prenatal ethanol exposure. [source] A COMPUTERIZED SYSTEM FOR CONTROLLING AND MEASURING GUSTATORY REACTION TIMESJOURNAL OF SENSORY STUDIES, Issue 4 2000MIGUELINA GUIRAO ABSTRACT Reaction Time (RT) procedures are widely used in cognitive and behavioral experiments. In the sensory realm RT has been traditionally applied to measure visual, auditory or motor responses. The application of the RT method to gustatory stimuli has proved to be difficult. Attempts to develop automatic control techniques have been restrained by difficulties related to the control of variables, e.g. physiochemical characteristics of chemical solutions and the procedure for stimulus presentation. In this report we describe a computer based system that was designed to measure the reaction time to taste solutions dropped on the tongue. The equipment consists of a pumping system, an interface between the computer and the pumping system, the software required to control the interface and to measure reaction time, and a push button to detect the subject's response. The system can be used as a tool for both research and evaluation tests. [source] Signaling stimulus presentation during treatment with noncontingent reinforcement: Visual versus vocal signalsBEHAVIORAL INTERVENTIONS, Issue 2 2009John J. Schadler Jr. The independent effects of two signals implemented during treatment with noncontingent reinforcement (NCR) were examined. First, functional analyses showed that problem behavior exhibited by two individuals with developmental disabilities was sensitive to social positive reinforcement. A reversal design was then used to compare the effectiveness of a timer (NCR-visual) to a vocal statement (NCR-vocal) indicating when the stimulus would be returned in the context of a NCR procedure. Results showed that NCR reduced problem behavior for both participants. In addition, for one participant, the NCR-visual condition reduced problem behavior to a greater degree than the NCR-vocal condition. Copyright © 2009 John Wiley & Sons, Ltd. [source] Reaction time during semi-automated kinetic perimetry (SKP) in patients with advanced visual field lossACTA OPHTHALMOLOGICA, Issue 1 2010Katarzyna Nowomiejska Abstract. Purpose:, This study aimed to evaluate reaction time (RT) in patients with advanced visual field (VF) loss using semi-automated kinetic perimetry (SKP). Methods:, Seventy-eight patients with advanced VF loss caused by glaucoma (31) or retinitis pigmentosa (19), homonymous VF loss caused by post-chiasmal lesions (18) and unilateral anterior ischaemic optic neuropathy (AION) (10) were examined with SKP (Octopus 101 perimeter). One eye in each patient was enrolled. Additionally, VFs in the 10 healthy fellow eyes of the patients with AION were compared with those in the 10 affected eyes. Reaction time was assessed during the SKP session by presenting kinetic stimuli (III4e) with constant angular velocities of 3 °/second moving linearly along so-called ,RT vectors' at four different locations inside the III4e isoptre. Each stimulus presentation was repeated four times in randomized order. Results:, The geometric mean RT was 794 ms (95% reference interval [RI] 391,1615 ms) in patients with glaucoma, 702 ms (95% RI 306,1608 ms) in patients with retinitis pigmentosa and 675 ms (95% RI 312,1460 ms) in patients with hemianopia. Increases in RT for every 1 ° of eccentricity were 1%, 0.9% and 0.4%, respectively. The geometric mean RT in the 10 patients with unilateral optic neuropathy was 644 ms in affected eyes and 435 ms in unaffected eyes, reflecting an increase of 51% (95% confidence interval 42,62%). Conclusions:, We found substantial inter-subject variability in RT in patients with advanced VF loss. It is possible to correct the position of the isoptres by assessing individual RT. There were no relevant differences in RT between the disease groups. Reaction time increases with eccentricity. In monocular disease (AION), RT is prolonged, compared with in healthy fellow eyes. However, in clinical routine the RT-related displacement of isoptres is negligible in the vast majority of cases. [source] Development of Tactile Responses in Human Preterm and Full-Term Infants From 30 to 40 Weeks Postconceptional AgeINFANCY, Issue 1 2002Isabel Fearon Maturation of tactile sensitivity prior to term was examined in 36 preterm and 13 full-term infants using a fixed-trial, habituation procedure. Each infant was presented with a series of 8 habituation (arm stroke), 2 novel (arm lift), and 2 recovery (arm stroke) stimulus trials while heart rate and body movements were recorded. Maturation was observed with a gradual increase in the magnitude of the stimulus-elicited cardiac acceleration and cardiac-movement coupling from 30 to 40 weeks postconceptional age. The majority of infants displayed habituation,an excitatory response (heart rate acceleration and body movement),to the initial presentation of a tactile stimulus, response decline with repeated stimulations, and renewed response to a novel stimulus. A substantial number of infants (40%) failed to respond initially to the tactile stimulus, increased responding over several stimulus presentations, and failed to discriminate the presentation of a novel stimulus. We speculate that these differences in response patterns observed over all ages represent individual difference in the perception of stimulus intensity. [source] Persistent Deficits in Heart Rate Response Habituation Following Neonatal Binge Ethanol ExposureALCOHOLISM, Issue 9 2009Katherine C. Morasch Background:, We have previously shown that the rate of habituation of the heart rate orienting response to a novel odor in rats is negatively affected by neonatal ethanol exposure. Thus far, however, only young rats (16 days of age) have been tested. Given the persistence of attention and memory problems evident in humans exposed to ethanol in utero, the purpose of this experiment was to examine the longer-term consequences of ethanol exposure on response habituation. Methods:, Ethanol (5.25 g/kg/d) was administered intragastrically to male and female Sprague-Dawley rats on postnatal days (PD) 4 to 9, and controls were given sham intubations. Animals were tested for heart rate orienting and response habituation to a novel olfactory stimulus (amyl acetate) on PD 16, 23, or 30. Results:, Animals tested on PD 16 or 23 showed normal heart rate deceleration to the novel odor, a measure of the orienting response. However, ethanol-treated subjects showed impaired response habituation compared with sham controls. While controls exhibited complete habituation within 4 to 5 trials, ethanol-treated animals continued to respond throughout the testing session, with little decrement in heart rate response magnitude across 10 stimulus presentations. A different pattern of responding was observed in animals tested during adolescence (PD 30). Control animals failed to show the typical heart rate decrease indicative of orienting, and instead showed a tendency toward tachycardia. In contrast, ethanol-treated animals tested on PD 30 showed orienting bradycardia that persisted for several trials. Conclusions:, These data suggest that there are relatively long-term consequences of neonatal ethanol exposure on nonassociative memory. This impairment in habituation may be relevant to the distractibility and poor focused attention that is pervasive among humans diagnosed with fetal alcohol spectrum disorders. 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