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At least 163 records · Page 9Linked to original sources
PubMed1989

Forebrain norepinephrine involvement in selective attention and neophobia.

It has been reported that depletion of forebrain norepinephrine via 6-hydroxydopamine infusion into the dorsal bundle decreases the rat's ability to selectively attend to relevant stimuli and thus increases the rat's responsiveness to novelty. In this study we measured 6-hydroxydopamine lesion effects on 1) selective attention via the nonreversal shift task and extinction of continuous reinforcement bar pressing and on 2) neophobia via consumption of a novel solution in a familiar environment; exploratory behaviors and consumption of a familiar food in a novel environment; and consumption of familiar and novel foods in a novel environment. Our data do not support a role for the dorsal bundle in selective attention. Our data do support a role for forebrain norepinephrine in neophobia and suggest that the lesion effects on neophobia result from an interaction between novelty of environment and novelty of food.

Animals↗
PubMed2005

Latencies of stimulus-driven eye movements are shorter in dyslexic subjects.

Eye movements latencies toward peripherally presented stimuli were measured in 10-year-old dyslexic and control children. Dyslexic subjects, previously found to be oversensitive to stimulation of the magnocellular channel, showed reduced latencies as compared to normally reading controls. An attention shifting task was also used which showed no group differences in latencies of eye movements. The data are discussed in terms of the hypothesis of magnocellular system alteration and attention dysfunction in dyslexia. Additionally, sex differences in eye movement latencies were found and are discussed.

Attention↗
PubMed2006

Imaging human EEG dynamics using independent component analysis.

This review discusses the theory and practical application of independent component analysis (ICA) to multi-channel EEG data. We use examples from an audiovisual attention-shifting task performed by young and old subjects to illustrate the power of ICA to resolve subtle differences between evoked responses in the two age groups. Preliminary analysis of these data using ICA suggests a loss of task specificity in independent component (IC) processes in frontal and somatomotor cortex during post-response periods in older as compared to younger subjects, trends not detected during examination of scalp-channel event-related potential (ERP) averages. We discuss possible approaches to component clustering across subjects and new ways to visualize mean and trial-by-trial variations in the data, including ERP-image plots of dynamics within and across trials as well as plots of event-related spectral perturbations in component power, phase locking, and coherence. We believe that widespread application of these and related analysis methods should bring EEG once again to the forefront of brain imaging, merging its high time and frequency resolution with enhanced cm-scale spatial resolution of its cortical sources.

Brain↗
PubMed2005

Transient BOLD responses at block transitions.

Block-design fMRI responses include sustained components present for the duration of each task block as well as transient components at the beginning and end of each block. Almost all prior block-design fMRI studies have focused on the sustained response components while the transient responses at block transitions have been largely ignored. These transients, therefore, remain poorly characterized. We here present a systematic study of block-transition transient responses obtained using four widely divergent tasks. We characterize transient response topography and examine the extent to which these responses vary across different tasks and between block onset and offset. Our analysis reveals that certain regions show transient responses regardless of task or transition type. However, our analysis also shows that specific task state transitions give rise to transient responses with unique spatial profiles. Relevance of the current findings to studies of exogenous attention, task shifting, and the BOLD overshoot is discussed.

Adult↗
PubMed2006

Metallothionein expression and neurocognitive function in mice.

Transition metals have been associated with impaired neurological development, and neurobehavioral activity. Metallothioneins are central components in the metabolism and detoxification of a variety of metals, however, little is known concerning their role in cognitive function. To determine the role of metallothionein in learning and memory, mice with deletions of two metallothionein genes (MT-1 and MT-2) were trained on a win-shift task in an 8-arm radial maze. The parental strain of mice learned the maze at a normal rate over an 18-session acquisition period. In contrast, the MT-1/MT-2-null mice, which had a similar choice accuracy level at the beginning of training, showed a poorer rate of learning during the training period. In addition, the MT-1/MT-2-null mice showed significantly less choice accuracy than the parental strain. The MT-1/MT-2-null mice also showed a significant hypoactivity during the early and middle parts of acquisition training, but they were not different from the wildtype controls during the final phase of training. Nicotine treatment, which can improve working memory, eliminated the impairment associated with the deletion of the MT-1 and MT-2 genes in a dose-related fashion after acquisition training in the aging adult mice. These results suggest that metallothioneins, through there roles in metal physiology or cellular protection, are involved in spatial learning and memory function.

Animals↗
PubMed2005

Edges and bars: where do people see features in 1-D images?

There have been two main approaches to feature detection in human and computer vision--based either on the luminance distribution and its spatial derivatives, or on the spatial distribution of local contrast energy. Thus, bars and edges might arise from peaks of luminance and luminance gradient respectively, or bars and edges might be found at peaks of local energy, where local phases are aligned across spatial frequency. This basic issue of definition is important because it guides more detailed models and interpretations of early vision. Which approach better describes the perceived positions of features in images? We used the class of 1-D images defined by Morrone and Burr in which the amplitude spectrum is that of a (partially blurred) square-wave and all Fourier components have a common phase. Observers used a cursor to mark where bars and edges were seen for different test phases (Experiment 1) or judged the spatial alignment of contours that had different phases (e.g. 0 degrees and 45 degrees ; Experiment 2). The feature positions defined by both tasks shifted systematically to the left or right according to the sign of the phase offset, increasing with the degree of blur. These shifts were well predicted by the location of luminance peaks (bars) and gradient peaks (edges), but not by energy peaks which (by design) predicted no shift at all. These results encourage models based on a Gaussian-derivative framework, but do not support the idea that human vision uses points of phase alignment to find local, first-order features. Nevertheless, we argue that both approaches are presently incomplete and a better understanding of early vision may combine insights from both.

Contrast Sensitivity↗
PubMed2001

Attention shifts and anticipatory mechanisms in hyperactive children: an ERP study using the Posner paradigm.

BACKGROUND: The aim of this study was to assess attentional, decisional, and motor processing stages during the performance of an attention shifting paradigm, both in normal children and children with attention-deficit/hyperactivity disorder (ADHD). METHODS: We recorded event-related potentials (ERPs) and performance measures during a variant of the Posner paradigm in 13 control subjects and 24 ADHD children. Subjects responded with a spatially concordant motor response to left or right visual targets, which could be either preceded by a spatial cue ("valid" = same side; "invalid" = opposite side) or presented uncued. RESULTS: Patients made significantly more errors than control subjects, with predominance of the anticipatory type. As compared to control subjects, ADHD children had faster reaction times, as well as a shortened interval between the N2 and P3 ERPs and the motor response. Patients also showed a decreased attentional priming effect on early sensory responses (P1). Finally, the slow negativity (contingent negative variation/readiness potential) that preceded the target in the "no cue" condition was absent in ADHD patients. CONCLUSIONS: The combined analysis of electrophysiological and behavioral data suggest a characteristic mode of response of ADHD in attention shifting tasks, characterized by "motor impulsivity" with release of motor responses before stimulus processing is adequately completed, as well as a lack of strategic planning/anticipatory mechanisms in the absence of warning stimulus. These deficits may be partly attributed to dysmaturation of executive frontal functions. In addition, a minor deficit in early attentional priming was also observed in ERPs, with no apparent behavioral counterparts.

Attention Deficit Disorder with Hyperactivity↗
PubMed1998

Water version of the radial-arm maze: learning in three inbred strains of mice.

The conventional land radial-arm maze has several disadvantages, including requiring a complicated automated apparatus, the elimination of odors as cues, and the use of food deprivation. We have created a water version of the maze, based on the principles of the land version, which maintains the advantages and excludes some of the disadvantages. In our maze, BXSB and C57BL/6 mice significantly reduced the number of working and reference memory errors committed over sessions, while NZB mice did not. For each strain, as the working memory 'load' increased during a session, the number of errors increased. However, with practice the BXSB and C57BL/6 strains were able to handle this memory load more effectively. Mice were able to learn the maze without extensive adaptation, training, or testing and they did not exhibit 'chaining'. This maze can also be considered to be an example of a water win-shift task that mice can easily learn. Therefore, the water version of the radial-arm maze can be a simple and useful tool for studying rodent learning and memory.

Animals↗
PubMed1997

Eye-position effects in directional hearing.

The influence of gaze direction on azimuthal sound localization was investigated by presenting free-field acoustical stimuli in combination with a visual fixation task. In Experiment 1, a two-alternative forced-choice method was employed. While fixating visual targets, subjects judged whether noise bursts, presented from various directions, were perceived as being on the left or right of either a visual reference indicating straight ahead or the subjective straight-ahead direction. The psychometric functions measured with the first task shifted consistently opposite to the direction of eccentric gaze, i.e., the location of the auditory stimulus was perceived as shifted toward the direction of gaze. The mean magnitude of the shift was 4.7 degrees over a range of fixation angles up to 45 degrees on either side. Without an external reference indicating straight ahead, shifts of sound localization were inconsistent, either opposite or toward the direction of fixation in individual subjects. In Experiment 2, subjects orientated their head toward sound stimuli while fixating visual targets in various directions. As in Experiment 1, head position as a measure of sound localization shifted significantly toward the direction of eccentric gaze when a visual reference of the head median plane was present, and the results were inconsistent across subjects when it was absent. The results indicate a significant effect of gaze direction on the spatial agreement of auditory and visual perception which may be based on the superposition of distinct auditory and visual eye-position effects. The effect is in agreement with previous neurophysiological results that have suggested an incomplete neural transformation of auditory spatial coordinates from a craniocentric into an oculocentric frame of reference.

Acoustic Stimulation↗
PubMed2002

Effects of acute tryptophan depletion on cognitive function in euthymic bipolar patients.

Decreasing brain 5-HT levels by acute tryptophan depletion has been shown to selectively impair cognition in healthy volunteers. In bipolar disorder, ATD causes measurable neurophysiological effects without altering mood. The purpose of this study was to examine the effects of ATD on neuropsychological performance in 14 euthymic bipolar patients. Cognitive function was evaluated 4-6 h after ingestion of a control or depleting amino-acid drink. Plasma tryptophan levels fell significantly following the depleting drink, however there were no main effects on the ID/ED set-shift task, Paired Associates Learning or Vigil. A trend towards a decrease in the proportion of perfect solutions on the Tower of London task was observed when depleted. While ATD reduces 5-HT levels in the brain, it does not appear to alter neuropsychological performance on tests of sustained attention or associative learning. Effects on specific 'executive' functions are less clear, and should be the focus for future research.

Adult↗
PubMed1998

The impact of participation in a study abroad programme on students' conceptual understanding of community health nursing in a developing country.

A pilot study was undertaken to ascertain the changes in conceptual understanding that resulted from participation in a study abroad programme in Chiang Mai in Thailand of a small group of Australian final year nursing students. Students' conceptual understandings were measured by means of open-ended interviews based on a case study scenario describing health conditions in a hypothetical Thai village. Students were asked to imagine that they had been appointed to work as a community health nurse in the village and describe how they would undertake the task. Shifts in understanding were detected by interviewing the participants before, during and after their participation in the programme and comparing their responses. The results of this limited study indicated that the impact of participation in the programme was less than expected. Furthermore, the factors of which students tended to show greatest awareness were those about which they had been briefed prior to departure. Nevertheless participants reported they had learnt much from their experiences. It is suggested that the discrepancy between the evidence provided by interview data and students' self-reports may be explained by participation having resulted primarily in the acquisition of the tacit rather than conceptual knowledge.

Adult↗
PubMed2002

Effect of beta-adrenoceptor antagonists on autonomic control of ciliary smooth muscle.

PURPOSE: Pharmacological intervention with peripheral sympathetic transmission at ciliary smooth muscle neuro-receptor junctions has been used against a background of controlled parasympathetic activity to investigate the characteristics of autonomic control of ocular accommodation. METHODS: A continuously recording infra-red optometer was used to measure accommodation on a group of five visually normal emmetropic subjects under open- and closed-loop conditions. A double-blind protocol between saline, timolol and betaxolol was used to differentiate between the localised action on ciliary smooth muscle and effects induced by changes in stimulus conditions. Data were collected before and 45 min following the instillation of saline, timolol or betaxolol. Open-loop post-task decay was investigated following 3 min sustained near fixation of a stimulus placed 3 D above the subject's pre-task tonic accommodation level. Closed-loop dynamic responses were recorded for each treatment condition while subjects viewed sinusoidally (0.05-0.6 Hz) or stepwise vergence-modulated targets over a 2 D range (2-4 D). RESULTS: Open-loop data demonstrate a rapid post-task regression to pre-task tonic accommodation levels for saline and betaxolol control conditions. A slow positive post-task shift was induced by timolol indicating that sympathetic inhibition contributes to accommodative adaptation during sustained near vision. Closed-loop accommodation responses to temporally modulated sinusoidal stimuli showed characteristic features for both saline and betaxolol control conditions. Timolol induced a reduced gain for low- and mid-temporal frequencies (< 0.3 Hz) but did not affect the response at higher temporal frequencies. Response times to stepwise stimuli increased following the instillation of timolol for the near-to-far fixation condition compared with the controls and was related to the period of sustained prior fixation. CONCLUSIONS: Modulation of accommodation under open- and closed-loop conditions by a non-selective beta-blocker is consistent with the temporal and inhibitory features of sympathetic innervation to ciliary smooth muscle. Although parasympathetic innervation predominates there is evidence to support a role for sympathetic innervation in the control of ocular accommodation.

Accommodation, Ocular↗
PubMed2005

Attentional flexibility and perseveration: developmental aspects in young children.

Whereas a growing interest in the development of attentional flexibility (AF) and in perseverative behavior, being one marker of this component, exists in neuropsychological studies and in the domain of developmental psychopathology (e.g., PKU, infantile schizophrenia, autism and Parkinson's disease) (Pennington & Ozonoff, 1996; Stahl & Pry, 2002), only a few studies have concerned themselves with this subject in normal children. It is thus of interest to add more empirical data to the existing literature in this domain. Therefore, the aim of our study was to explore the development of AF and of perseverative errors in young preschool children with normal development, aged 1.5 to 6 years. Using set-shifting tasks of increasing difficulty level, three age groups were compared with respect to their AF skills. Results show a developmental factor underlying AF, with different levels of this form becoming more and more complex with age, ranging from a rudimentary visual form to a complex representational form of flexibility. Overall, few perseverative errors occurred and they decreased with age. Results are discussed from a developmental and neuropsychological perspective.

Age Factors↗
PubMed2004

Differential effects of methylphenidate on attentional functions in children with attention-deficit/hyperactivity disorder.

OBJECTIVE: To examine the effects of methylphenidate on different attentional functions and behavior in children with attention-deficit/hyperactivity disorder (ADHD). METHOD: A total of 60 ADHD children aged between 8 and 12 years completed a randomized, double-blind, placebo-controlled, within-subject crossover trial with two doses of methylphenidate (0.25 and 0.5 mg/kg body weight) and placebo. A comprehensive neuropsychological test battery was applied, including tests of alertness and sustained, focused, and divided attention as well as two executive tests, the stop-signal paradigm and a visual set-shifting task. RESULTS: A linear improvement was identified for both medication conditions in the alertness and focused and sustained attention task, but no significant improvement was found for divided attention. Quadratic trends were found for both executive tasks. Responders defined by behavior ratings did not differ from nonresponders. CONCLUSIONS: Results indicate that attentional functions are influenced differentially by methylphenidate: intensity-dimension functions are best influenced by higher doses, executive functions by moderate doses, and selectivity-dimension functions by variable doses. In addition, divergent results from behavior rating scales and from attentional paradigms emphasize that clinicians have to decide what constitutes an appropriate clinical response. A more comprehensive assessment of attention may help to find an individually optimal dose for the treatment of attentional dysfunctions.

Attention↗
PubMed1992

Factors influencing accommodative adaptation.

Previous studies have ascertained that a broad range of parameters have the facility to induce or modify accommodative adaptation, i.e., the post-task shift in dark accommodation (DA) which may be observed after a period of sustained fixation. This paper reviews the optical (i.e., related to a change in the form of the retinal image) and nonoptical (i.e., independent of the composition of the retinal image) stimuli which can influence the degree of adaptation. It is concluded that DA probably represents an aggregate response resulting from multiple inputs whose interactions may be too complex to allow the isolation and measurement of any single nonoptical component. Accordingly, the exact mechanism of accommodative adaptation remains unclear at the present time.

Accommodation, Ocular↗
PubMed1992

Pharmacological effects on accommodative adaptation.

We review the research which has attempted to determine whether the characteristics of autonomic innervation of ciliary smooth muscle are relevant to the process of accommodative adaptation. The effect of various topical autonomic drugs on the three phases of adaptation were analyzed: pre-task tonic accommodation (open-loop); within-task accommodative response (closed-loop); and post-task regression of accommodation to pre-task tonic levels. Although it is clear that parasympathetic innervation predominates, there is evidence that some individuals utilize supplementary inhibitory sympathetic innervation. When sympathetic innervation is augmented by substantial levels of concurrent parasympathetic accommodative activity, it may serve to attenuate the magnitude and duration of post-task shifts in tonic accommodation. It is proposed that individuals with a deficit in sympathetic inhibition may therefore be predisposed to anomalies of accommodative adaptation. However, the mechanism by which the oculomotor system responds to such predisposition is at present obscure.

Accommodation, Ocular↗
PubMed2005

Selected executive skills in adolescents with recent first episode major depression.

BACKGROUND: To investigate whether recent first episode major depression in adolescence is characterised by selected executive difficulties in attentional flexibility, behavioural inhibition and decision-making. METHODS: Selected executive functions were compared in adolescents with recent (past year) first episode major depression (n = 30) and community controls (n = 49). Three computerised tests within the CANTAB battery were completed by all subjects (the Intra-Dimensional, Extra-Dimensional Set-Shifting task, the Affective Go, No-Go task, and the Decision-Making task). RESULTS: Compared with controls, recently depressed cases displayed a bias towards negative stimuli with fewer errors on sad words as well as being more accurate in their responses to sad targets on the Affective Go, No-Go task. Cases also made faster decisions in the context of betting more of their available points compared to controls, as indexed by the Decision-Making task. These results were not influenced by age, gender, IQ, recent mood, severity of depression, medication or comorbidity. CONCLUSIONS: Adolescents with recent first episode major depression show greater attention towards sad stimuli and more impulsive behaviour when making decisions. They were able to switch attentional set to neutral stimuli. This study demonstrates that computerised tests for measuring executive functions can be successfully deployed in adolescents, and suggests that specific patterns of neuropsychological functions may be relatively compromised in first episode major depression. These, together with their underlying neural substrates, deserve further investigation within this age range.

Adolescent↗
PubMed1989

The measurement of adaptation of tonic accommodation under two open-loop conditions.

Pre- and post-task tonic accommodation (TA) was measured using an objective infra-red optometer under two open-loop conditions: a darkroom and a bright empty-field (60 cd m-2). The task was of 10 minutes' duration and was located at -1, -3 and -5 D. Post-task TA was measured immediately after the task and over a period of 90 s. Mean data for the group of 10 young men subjects showed that the open-loop condition adopted had no significant influence on the post-task regression patterns of TA towards pre-task values. Three subjects did, however, show significantly more sustained increases in post-task TA for the bright-field condition; one markedly so. Conversely, two subjects showed more pronounced post-task shifts for the darkroom condition.

Accommodation, Ocular↗