Biomedical subjects

Avishai Henik

Publications and source records attributed to Avishai Henik.

17 recordsLinked to original sources

PubMed2005

Are numbers special? The comparison systems of the human brain investigated by fMRI.

Many studies have suggested that the intraparietal sulcus (IPS), particularly in the dominant hemisphere, is crucially involved in numerical comparisons. However, this parietal structure has been found to be involved in other tasks that require spatial processing or visuospatial attention as well. fMRI was used to investigate three different magnitude comparisons in an event-related-block design: (a) Which digit is larger in numerical value (e.g., 2 or 5)? (b) Which digit is brighter (e.g., 3 or 3)? (c) Which digit is physically larger (e.g., 3 or 3)? Results indicate a widespread cortical network including a bilateral activation of the intraparietal sulci for all different comparisons. However, by computing contrasts of brain activation between the respective comparison conditions and applying a cortical distance effect as an additional criterion, number-specific activation was revealed in left IPS and right temporal regions. These results indicate that there are both commonalities and differences in the spatial layout of the brain systems for numerical and physical comparisons and that especially the left IPS, while involved in magnitude comparison in general, plays a special role in number comparison.

Adult↗

PubMed2005

Competition between endogenous and exogenous orienting of visual attention.

The relation between reflexive and voluntary orienting of visual attention was investigated with 4 experiments: a simple detection task, a localization task, a saccade toward the target task, and a target identification task in which discrimination difficulty was manipulated. Endogenous and exogenous orienting cues were presented in each trial and their validity was manipulated orthogonally to examine whether attention mechanisms are mediated by separate systems and whether they have additive and independent effects on visual detection and discrimination. The results showed that each orienting mechanism developed its typical and independent effect in every case except for the difficult identification task. A theoretical framework for understanding the relationship between endogenous and exogenous orienting of attention is proposed, tested, and confirmed.

Attention↗

PubMed2004

Differential processing of word and color in unilateral spatial neglect.

The aim of the present study was to investigate mechanisms underlying processing of contralesional visual stimuli in brain-damaged patients with unilateral spatial neglect (USN). Nine right-hemisphere-damaged stroke patients with left-sided neglect and nine controls performed a reaction-time task involving manual response to a central color patch (target stimulus) flanked to the left or right by a Stroop stimulus they had to ignore. While the word dimension of the flanker affected patients' responses considerably and equally when presented to either side, the color dimension of the flanker had no effect when presented to the left, but had a large effect when presented to the right. Four of the patients performed a control task requiring same/different judgments between either of the two flanker dimensions (color and word) and the central target. Their performance indicated that they were able to process color information from the contralesional field, despite their results in the first experiment. These findings demonstrate a dissociation between how the patients processed different dimensions of the same stimuli and imply that the extent of processing in the contralesional hemifield depends both on task requirements and on the exact features of the stimuli. The implications of these results on normal attentional mechanisms is also discussed.

Adult↗

PubMed2004

Role of disengagement failure and attentional gradient in unilateral spatial neglect - a longitudinal study.

PURPOSE: To assess the importance of 'disengagement failure' and 'attentional gradient' in unilateral spatial neglect (USN) and in recovery from neglect. METHOD: Eight right-hemisphere-damaged stroke patients performed the standardized Behavioural-Inattention-Test battery for visual neglect, line-bisection tests, and two computerized reaction-time (RT) tasks: a variant of Posner's 'Spatial-Cueing' paradigm (with special emphasis on the magnitude of leftward disengagement time) and a signal-detection task (marking the spatial gradient of attention by the distribution of RTs to target stimuli in different spatial locations). The correlation between the different measures was assessed at two points in time, before and after a period of rehabilitation treatment. RESULTS: A recovery pattern could be identified in both RT paradigms. However, the correlation between standard measures of neglect and performance on both, spatial-cueing and signal-detection tasks, was weak. CONCLUSION: Neither difficulty disengaging attention from an ipsilesional stimulus nor changes in the attentional gradient can fully explain the processes underlying USN and its recovery. A large interpersonal variance exists among USN patients in the expression of disengagement and other spatial-attention deficits. Hence, individual patients should be tested by measuring different factors known to play a role in USN. This information is crucial for assigning the appropriate treatment for each patient in accord with the specific deficit revealed.

Adult↗

PubMed2004

Parietal lobe lesions disrupt saccadic remapping of inhibitory location tagging.

Maintaining a coherent percept of the visual scene while eye position continuously changes requires that saccades be accompanied by remapping of the visual environment. We studied saccadic remapping in patients with unilateral lesions in the intraparietal sulcus and healthy controls, using inhibition of return (IOR)-an inhibitory tag that enables efficient visual search. In healthy controls, IOR was found at both retinal and environmental locations of the cue, indicating that the inhibitory tag had been remapped into environmental coordinates. In contrast, right parietal patients demonstrated IOR only at the retinal location of the cue, indicating that the intraparietal sulcus is involved in remapping of the environment after eye movements to afford a stable, environmentally based reference frame. Note that patients did not show environmental IOR in either visual field. These results also suggest that this region may be the neural substrate for encoding inhibitory spatial tags in an environmentally based reference frame.

Adult↗

PubMed2004

Schizophrenia and the stroop effect.

Conflict between irrelevant words and relevant colors in the Stroop task creates interference, long considered a measure of how well individuals focus attention. In the traditional card version of the Stroop task, schizophrenia patients exhibit increased interference, consistent with the distractibility they exhibit in everyday life. In contrast, on other versions of the Stroop task they show augmented facilitation (faster responding to congruent than to neutral trials). We suggest that schizophrenia patients possess adequate attentional resources to avoid interference when each letter string is presented individually but face difficulty when delays are imposed and multiple attentional demands appear. Although psychiatric symptomatology may contribute to different patterns of performance, there is no evidence that medication modulates this.

Affect↗

PubMed2003

Is there a "strength effect" in automatic semantic priming?

According to spreading activation models of automatic priming, highly related associates should yield stronger priming effects than weakly related associates. The strength of relations is usually based on word association norms. However, this strength effect has been found in some studies but not in others. The present study suggests that one factor that might be responsible for this inconsistency is whether the weak associate is the primary or nonprimary response in the word association norms This possibility was explored by comparing priming effects of weak nonprimary and primary associates with those of strong primary associates. Comparable priming effects were found for the strong and weak primary associates whereas the weak nonprimary associates did not yield any priming effects. These results were obtained both in paired (Experiment 1) and single (Experiment 2) presentation priming procedures. Thus, the rank of the associate is an important factor in predicting the magnitude of the priming effect.

Automatism↗

PubMed2003

Auditory imagery from musical notation in expert musicians.

Anecdotal evidence has suggested that musical notation can trigger auditory images. Expert musicians silently read scores containing well-known themes embedded into the notation of an embellished phrase and judged if a tune heard aloud thereafter was the original theme (i.e., melodic target) or not (i.e., melodic lure). Three experiments were conducted employing four score-reading conditions: normal nondistracted reading, concurrent rhythmic distraction, phonatory interference, and obstruction by auditory stimuli. The findings demonstrate that phonatory interference impaired recognition of original themes more than did the other conditions. We propose that notational audiation is the silent reading of musical notation resulting in auditory imagery. The research suggests that it also elicits kinesthetic-like phonatory processes.

Adolescent↗

PubMed2002

Electroencephalographic activity in a flanker interference task using Japanese orthography.

The neural activities for color word interference effects were investigated using event-related brain potentials (ERPs) recorded in a flanker-type interference task. Kanji words (Japanese morphograms) and kana words (Japanese phonograms) were used as the flanker stimuli to obtain insights about hemispheric specialization for processing two types of Japanese orthographies. Interference effects in reaction time were larger when kanji words were presented in the left visual field and when kana words were in the right visual field. ERPs were modulated by the incongruent flankers, which generated a negative ERP component with the different onset and offset depending on flanker attributes. Consistent with the behavioral data, the interference-related negativity was observed for kanji words presented in the left visual field and for kana words in the right visual field. The negativity distributed maximally over the fronto-central site. The early part of the negativity distributed strongly over the frontal midline area, whereas it extended bilaterally over the frontal area in the late phase. The present results support the view of preferential processing of kanji in the right hemisphere and that of kana in the left hemisphere. The temporal profile of scalp topographies for the interference-related neural activity suggests that the medial and dorsolateral prefrontal regions may be involved in maintaining attentional set and conflict resolution.

Adult↗

PubMed2002

Preliminary evidence of reduced cognitive inhibition in methamphetamine-dependent individuals.

Chronic methamphetamine abuse is associated with disruption of frontostriatal function involving serotonin and dopamine circuitry. Clinically, methamphetamine-dependent (MD) individuals are highly distractible and have difficulty focussing. Here, we used a computerized single-trial version of the Stroop Test to examine selective attention and priming in MD. Subject groups comprised eight MD men (31.7+/-7.2 years of age), who had used methamphetamine for 15.75+/-8.4 years but were currently abstinent for 2-4 months, and 12 controls (35.7+9.7 years of age). Compared with the control group, the MD group exhibited significantly greater interference (P<0.05) despite intact priming. Error rates did not differ between the groups. This preliminary finding of reduced cognitive inhibition in MD individuals is consistent with the distractibility they show clinically. Furthermore, the dissociation between explicit attentional performance and priming effects suggests that some attentional functions are not as affected by long-term methamphetamine use as others.

Adult↗

PubMed2002

Attentional control and word inhibition in schizophrenia.

Previous studies have suggested that schizophrenia patients do not utilize contextual information efficiently to modulate attentional performance. The goal of the current study was to compare the utilization of context in modulating responses to irrelevant information on the Stroop task between a group of schizophrenia outpatients and matched controls. A single-trial version of the Stroop task was used to investigate performance on the Stroop task under three expectancy conditions. Eleven schizophrenia outpatients (on and off antipsychotic medication) and sixteen matched controls were tested. The schizophrenia patients showed: (1) augmented facilitation; (2) interference comparable to normals; and (3) normal ability to reduce interference under certain experimental circumstances. Schizophrenia patients were able to utilize contextual information under certain conditions and could modulate the magnitude of irrelevant word interference, although they were not able to overcome the prepotent tendency to read the word during the Stroop task as effectively as normals, which was reflected in greater Stroop facilitation. This suggests that the integrity or impairment of cognitive control functions in schizophrenia is related to the complexity of the context representation required to support that function.

Adult↗

PubMed2002

Attending to the thalamus: inhibition of return and nasal-temporal asymmetry in the pulvinar.

Inhibition of return (IOR) is a mechanism whereby the attentional system favors novel locations by inhibiting already scanned ones. An important question is what the neural structures are involved. Recently, we studied a patient with damage to the superior colliculus (SC) and concluded that the SC generates IOR. However, it is possible that IOR is generated beyond the colliculus, for example, by the pulvinar. In this paper we tested three patients with unilateral damage to the pulvinar and demonstrated that the pulvinar is not necessary for IOR generation, providing additional support to the suggestion that the SC generates IOR. In addition, since we used monocular presentation, we were able to furnish behavioral evidence for nasal-temporal asymmetrical representation of visual input in the pulvinar.

Analysis of Variance↗

PubMed2002

Implicit learning of emotional information under anesthesia.

Surgical stress activates the amygdala and secretion of norepinephrine, both involved in memory and unconscious processing of emotionally negative information. This study examined surgically induced facilitation of implicit learning of emotionally negative information. Thirty patients undergoing laparoscopic cholecystectomy under general anesthesia were tested. Between 2 and 4 h after surgery, patients provided word-associates to cues previously presented (old) or not previously presented during anesthesia (new). Half the cues were emotionally negative and half neutral. Patients took less time to provide correct associates to old emotionally negative cues than to new emotionally negative cues (p < 0.05). Spectral edge frequency (SEF) of cerebral activity during surgery converged with this finding. Implicit learning during general anesthesia may be stronger for emotionally negative information and is detected by SE.

Adult↗

PubMed2002

The development of internal representations of magnitude and their association with Arabic numerals.

Developmental aspects of number concepts were evaluated using participants from the beginning and end of first grade (6-7 years old), third and fifth grades (7-11 years old), and university (22 years old). Participants evaluated the numerical value or physical size of stimuli varying along both dimensions. The numerical distance effect appeared in all groups. In contrast, the size congruity effect started to appear only at the end of first grade. Based on our results, a model of internal representation of magnitude claiming that there are two different representations was propose. At the beginning of first grade children can automatically access only one of these representations and only from the end of first grade can they access both of these representations.

Adult↗

PubMed2002

Is an ant larger than a lion?

In order to examine the influence exerted by an irrelevant semantic variable in a comparative judgment task, we employed a Stroop-like paradigm. The stimuli were pairs of animal names that were different in their physical and semantic sizes (e.g., ant lion). Participants were asked to judge which of the two words was larger either in physical or in semantic size. Size congruity effect (i.e., faster reaction times with congruent than with incongruent stimuli) appeared in both semantic and physical judgments. The semantic distance effect (i.e., large semantic distances are processed faster than smaller ones), appeared only when the semantic dimension was relevant to the task. The findings indicate that when a word (animal name) is presented, its meaning is accessed automatically. Part of this meaning (at least with our stimuli) relates to the size of the animal in real life. Processing of meaning of the size of the words is carried out in parallel with the extraction of the physical features of the presented stimuli.

Adult↗

PubMed2002

Immediate versus sustained processing in schizophrenia.

A Stroop negative priming (NP) task was used to assess immediate selective attention and priming in schizophrenia and schizoaffective disorder. Subject groups were comprised of 12 state hospital inpatients (41.8 +/- 7.5 years of age), 11 outpatients (39.8 +/- 7.5 years of age), and 16 controls (36.4 +/- 11.7 years of age). Compared with the control group and the outpatients, inpatients failed to exhibit NP [F(2,36) = 6.09, p < .01], despite exhibiting equivalent Stroop RT interference (p > .05). Error rates did not differ significantly between the 3 groups. Although medication types and dosages were similar between the 2 patient groups, length of illness was significantly longer in the inpatients (19.8 years) than in the outpatients (12.4 years; p < .05). Positive symptom ratings were also significantly higher in the inpatients. The finding of reduced NP in the state hospital patients appears to be related to severity of symptomatology and chronicity of illness.

Adult↗

PubMed2002

The importance of irrelevant-dimension variability in the stroop flanker task.

Two experiments in which the Stroop flanker task was used were conducted in order to examine the influence of irrelevant dimension invariance on congruency effects. Participants responded manually to a central color patch flanked by a Stroop stimulus. In Experiment 1, invariance in flanker location was found to have no influence on word and color congruency effects. In contrast, invariance of flanker identity led to the disappearance of congruency effects. Experiment 2 indicated that the elimination of a congruency effect was restricted to the dimension that remained constant and did not influence the congruency effect of the other dimension that was presented at the same location. Results suggest that variance is a prerequisite to congruity effects, determining the activation of irrelevant dimensions.

Attention↗