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Biomedical subjects

Amir Raz

Publications and source records attributed to Amir Raz.

18 recordsLinked to original sources
PubMed2006

Suggestion overrides the Stroop effect in highly hypnotizable individuals.

Cognitive scientists distinguish between automatic and controlled mental processes. Automatic processes are either innately involuntary or become automatized through extensive practice. For example, reading words is a purportedly automatic process for proficient readers and the Stroop effect is consequently considered the "gold standard" of automated performance. Although the question of whether it is possible to regain control over an automatic process is mostly unasked, we provide compelling data showing that posthypnotic suggestion reduced and even removed Stroop interference in highly hypnotizable individuals. Drawing on a large sample of highly hypnotizable participants, we examined the effects of suggestion on Stroop performance both with and without a posthypnotic suggestion to perceive the input stream as meaningless symbols. We show that suggestion administered to highly hypnotizable persons significantly reduced Stroop interference and derailed a seemingly automatic process.

Adult↗
PubMed2006

Neuroimaging and genetic associations of attentional and hypnotic processes.

In the aftermath of the human genome project, genotyping is fast becoming an affordable and technologically viable complement to phenotyping. Whereas attempts to characterize hypnotic responsiveness have been largely phenomenological, data emanating from exploratory genetic data may offer supplementary insights into the genetic bases of hypnotizability. We outline our genetic and neuroimaging findings and discuss potential implications to top-down control systems. These results may explain individual differences in hypnotizability and propose new ideas for studying the influence of suggestion on neural systems.

Attention↗
PubMed2006

A statistical framework for the classification of tensor morphologies in diffusion tensor images.

Tractography algorithms for diffusion tensor (DT) images consecutively connect directions of maximal diffusion across neighboring DTs in order to reconstruct the 3-dimensional trajectories of white matter tracts in vivo in the human brain. The performance of these algorithms, however, is strongly influenced by the amount of noise in the images and by the presence of degenerate tensors-- i.e., tensors in which the direction of maximal diffusion is poorly defined. We propose a simple procedure for the classification of tensor morphologies that uses test statistics based on invariant measures of DTs, such as fractional anisotropy, while accounting for the effects of noise on tensor estimates. Examining DT images from seven human subjects, we demonstrate that this procedure validly classifies DTs at each voxel into standard types (nondegenerate DTs, as well as degenerate oblate, prolate or isotropic DTs), and we provide preliminary estimates for the prevalence and spatial distribution of degenerate tensors in these brains. We also show that the P values for test statistics are more sensitive tools for classifying tensor morphologies than are invariant measures of anisotropy alone.

Algorithms↗
PubMed2006

Typologies of attentional networks.

Attention is a central theme in cognitive science - it exemplifies the links between the brain and behaviour, and binds psychology to the techniques of neuroscience. A visionary model suggested by Michael Posner described attention as a set of independent control networks. This challenged the previously held view of attention as a uniform concept. The idea that disparate attentional networks correlate with discrete neural circuitry and can be influenced by focal brain injuries, mental state and specific drugs has since been supported by converging data from several modern methodologies. Given the recent explosion in empirical data, attentional typologies provide powerful conceptual tools with which to contextualize and integrate these findings.

Attention↗
PubMed2006

Suggestion reduces the stroop effect.

We examined the effects of suggestion on Stroop interference in highly suggestible individuals. Participants completed the Stroop task with and without a suggestion to perceive Stroop words as meaningless symbols. Half the participants were given this suggestion in hypnosis, and half were given the suggestion without the induction of hypnosis. Suggestion produced a significant reduction in Stroop inhibition, accounting for about 45% of the variance in Stroop responding, regardless of whether hypnosis had been induced. These findings indicate that suggestion can at least partially overcome the automaticity associated with the Stroop effect.

Adult↗
PubMed2005

Hypnotic suggestion reduces conflict in the human brain.

Many studies have suggested that conflict monitoring involves the anterior cingulate cortex (ACC). We previously showed that a specific hypnotic suggestion reduces involuntary conflict and alters information processing in highly hypnotizable individuals. Hypothesizing that such conflict reduction would be associated with decreased ACC activation, we combined neuroimaging methods to provide high temporal and spatial resolution and studied highly and less-hypnotizable participants both with and without a suggestion to interpret visual words as nonsense strings. Functional MRI data revealed that under posthypnotic suggestion, both ACC and visual areas presented reduced activity in highly hypnotizable persons compared with either no-suggestion or less-hypnotizable controls. Scalp electrode recordings in highly hypnotizable subjects also showed reductions in posterior activation under suggestion, indicating visual system alterations. Our findings illuminate how suggestion affects cognitive control by modulating activity in specific brain areas, including early visual modules, and provide a more scientific account relating the neural effects of suggestion to placebo.

Adult↗
PubMed2005

Ecological nuances in functional magnetic resonance imaging (fMRI): psychological stressors, posture, and hydrostatics.

Brain imaging techniques such as functional magnetic resonance imaging (fMRI) have forged an impressive link between psychology and neuroscience. Whereas most experiments in cognitive psychology require participants to perform while sitting upright in front of display devices, fMRI obliges participants to perform cognitive tasks while lying supine and motionless inside a narrow bore. In addition to introducing psychological and physical stressors, such as loud thumps and head restraints, fMRI procedures also alter brain hydrostatics. The ecological factors associated with current fMRI technology, such as supine posture, may skew cognitive processing and influence hemodynamic and electrophysiological measurements, especially in extreme age groups and pathological populations. Recognizing the central role of fMRI in unraveling the neural mechanisms of cognition, we outline ways to address these limitations.

Animals↗
PubMed2005

Attention and hypnosis: neural substrates and genetic associations of two converging processes.

Although attention is a central theme in psychological science, hypnosis researchers rarely incorporate attentional findings into their work. As with other biological systems, attention has a distinct anatomy that carries out basic psychological functions. Specific brain injuries, states, and drugs can all influence attentional networks. Investigation into these networks using modern neuroimaging techniques has revealed important mechanisms involved in attention. In this age of genomics, genetic approaches can supplement these neuroimaging techniques. As genotyping becomes an affordable and technologically viable complement to phenotyping, exploratory genetic assays offer insights into the genetic bases of both attention and hypnotizability. This paper discusses relevant aspects of attentional mechanisms and their underlying neuroanatomy as they relate to hypnosis. Underlining data from attentional networks, neuroimaging, and genetics, these findings should help to explain individual differences in hypnotizability and the neural systems subserving hypnosis.

Arousal↗
PubMed2004

Anatomy of attentional networks.

Attention is a central theme in psychological science. As with other biological systems, attention has a distinct anatomy that carries out basic psychological functions. Disparate attentional networks correlate with discrete neural circuitry and can be influenced by specific brain injuries, states, and drugs. Accordingly, thinking about attention as an organ system is advantageous for understanding the details of this complex cognitive process. In the context of an influential model of attention, this article introduces the broad notion of attention, then addresses its prominent characteristics, mechanisms, and theories. The presentation emphasizes the role of recent neuroimaging data in outlining the functional neuroanatomy subserving distinct attentional networks. A discussion of pertinent results connects attentional networks with self-regulation, development, and rehabilitation training.

Attention↗
PubMed2004

See clearly: suggestion, hypnosis, attention, and visual acuity.

Some reports claim that positive suggestion (e.g., using hypnosis) can significantly improve visual acuity (e.g., in myopes). Based on behavioral, neurocognitive, and ophthalmological findings, the authors provide a critical account to review and challenge some of these data. While acknowledging the relative merits of hypnosis for investigating visual phenomena, an array of arguments converges to propose caveats to the apparent influence suggestion can exert on visual acuity. The authors argue that neither suggestion nor hypnotic phenomena are likely to significantly improve myopic vision and contend that a responsible scientific attitude should carefully outline what hypnosis and suggestion cannot do in addition to what they can. It seems likely that the small apparent influence of suggestion on visual acuity is mediated by changes in attention. The authors outline how attention can affect visual acuity.

Attention↗
PubMed2004

Critique of claims of improved visual acuity after hypnotic suggestion.

Psychological approaches to improving vision present an enticing alternative to invasive procedures and corrective lenses; hypnotic suggestion is one such technique. During the past 60 years, multiple studies have documented improvements in the vision of myopic individuals after hypnotic interventions. Given the increasing interest in behavioral and alternative approaches, we have reviewed the pertinent studies to evaluate their validity. We delineate various shortcomings in these reports, including potential methodological caveats, problems with experimental controls, and controversial data interpretation. Overall, the data do not seem to support hypnosis as a viable option for significant long-term improvement of myopia. However, hypnosis can increase one's subjective feeling of enhanced visual acuity by affecting higher cognitive functions, such as attention, memorization, and perceptual learning, which could influence performance on visual tasks.

Attention↗
PubMed2004

Substrates of negative accommodation.

Negative accommodation refers to a unique phenomenon, sparsely documented in rare individuals, whereby evanescent increases in vision (described as "flashes" of clear vision) accompany a decrease in the overall plus power of the eye. Complementing less than a handful of dated studies, a few recent personal communications from eye care clinicians claim to have objectively assessed negative accommodation (e.g., by retinoscopy). Whereas negative accommodation may explain informal accounts claiming occasional improved visual acuity in uncorrected myopes, its mode of operation is not established. We sketch a potential mechanism by which negative accommodation may operate, if it exists.

Accommodation, Ocular↗
PubMed2003

Posthypnotic suggestion and the modulation of Stroop interference under cycloplegia.

Recent data indicate that under a specific posthypnotic suggestion to circumvent reading, highly suggestible subjects successfully eliminated the Stroop interference effect. The present study examined whether an optical explanation (e.g., visual blurring or looking away) could account for this finding. Using cyclopentolate hydrochloride eye drops to pharmacologically prevent visual accommodation in all subjects, behavioral Stroop data were collected from six highly hypnotizables and six less suggestibles using an optical setup that guaranteed either sharply focused or blurred vision. The highly suggestibles performed the Stroop task when naturally vigilant, under posthypnotic suggestion not to read, and while visually blurred; the less suggestibles ran naturally vigilant, while looking away, and while visually blurred. Although visual accommodation was precluded for all subjects, posthypnotic suggestion effectively eliminated Stroop interference and was comparable to looking away in controls. These data strengthen the view that Stroop interference is neither robust nor inevitable and support the hypothesis that posthypnotic suggestion may exert a top-down influence on neural processing.

Adult↗
PubMed2002

Testing the efficiency and independence of attentional networks.

In recent years, three attentional networks have been defined in anatomical and functional terms. These functions involve alerting, orienting, and executive attention. Reaction time measures can be used to quantify the processing efficiency within each of these three networks. The Attention Network Test (ANT) is designed to evaluate alerting, orienting, and executive attention within a single 30-min testing session that can be easily performed by children, patients, and monkeys. A study with 40 normal adult subjects indicates that the ANT produces reliable single subject estimates of alerting, orienting, and executive function, and further suggests that the efficiencies of these three networks are uncorrelated. There are, however, some interactions in which alerting and orienting can modulate the degree of interference from flankers. This procedure may prove to be convenient and useful in evaluating attentional abnormalities associated with cases of brain injury, stroke, schizophrenia, and attention-deficit disorder. The ANT may also serve as an activation task for neuroimaging studies and as a phenotype for the study of the influence of genes on attentional networks.

Adult↗
PubMed2002

Hypnosis and neuroscience: a cross talk between clinical and cognitive research.

Despite its long use in clinical settings, the checkered reputation of hypnosis has dimmed its promise as a research instrument. Whereas cognitive neuroscience has scantily fostered hypnosis as a manipulation, neuroimaging techniques offer new opportunities to use hypnosis and posthypnotic suggestion as probes into brain mechanisms and, reciprocally, provide a means of studying hypnosis itself. We outline how the hypnotic state can serve as a way to tap neurocognitive questions and how cognitive assays can in turn shed new light on the neural bases of hypnosis. This cross talk should enhance research and clinical applications.

Attention↗
PubMed2002

Hypnotic suggestion and the modulation of Stroop interference.

BACKGROUND: Hypnosis has been used clinically for hundreds of years and is primarily a phenomenon involving attentive receptive concentration. Cognitive science has not fully exploited hypnosis and hypnotic suggestion as experimental tools. This study was designed to determine whether a hypnotic suggestion to hinder lexical processing could modulate the Stroop effect. METHODS: Behavioral Stroop data were collected from 16 highly suggestible and 16 less suggestible subjects; both naturally vigilant and under posthypnotic suggestion. Subjects were urged to only attend to the ink color and to impede reading the stimuli under posthypnotic suggestion. RESULTS: Whereas posthypnotic suggestion eliminated Stroop interference for highly suggestible subjects, less suggestible control subjects showed no significant reduction in the interference effect. CONCLUSIONS: This outcome challenges the dominant view that word recognition is obligatory for proficient readers, and may provide insight into top-down influences of suggestion on cognition.

Adult↗