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PubMed2001

Dissociating top-down attentional control from selective perception and action.

Research into the neural mechanisms of attention has revealed a complex network of brain regions that are involved in the execution of attention-demanding tasks. Recent advances in human neuroimaging now permit investigation of the elementary processes of attention being subserved by specific components of the brain's attention system. Here we describe recent studies of spatial selective attention that made use of positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and event-related brain potentials (ERPs) to investigate the spatio-temporal dynamics of the attention-related neural activity. We first review the results from an event-related fMRI study that examined the neural mechanisms underlying top-down attentional control versus selective sensory perception. These results defined a fronto-temporal-parietal network involved in the control of spatial attention. Activity in these areas biased the neural activity in sensory brain structures coding the spatial locations of upcoming target stimuli, preceding a modulation of subsequent target processing in visual cortex. We then present preliminary evidence from a fast-rate event-related fMRI study of spatial attention that demonstrates how to disentangle the potentially overlapping hemodynamic responses elicited by temporally adjacent stimuli in studies of attentional control. Finally, we present new analyses from combined neuroimaging (PET) and event-related brain potential (ERP) studies that together reveal the timecourse of activation of brain regions implicated in attentional control and selective perception.

Attention↗

PubMed2002

Replication of a premenstrual decrease in right-ear advantage on language-related dichotic listening tests of cerebral laterality.

Five fused dichotic word tasks measured perceptual asymmetry in 30 women at 4 weekly intervals. The five tasks varied according to whether the stimuli presented were word-word pairs or nonsense word-pairs, or whether they consisted of neutral words paired with positive emotion-evoking words (e.g. hug-tug), neutral words paired with negative emotion-evoking words (e.g. till-kill), or neutral words paired with neutral words (e.g. bean-dean). Overall right-ear advantage (REA) decreased in the premenstrual week relative to the postmenstrual week, replicating previous results using identical measures. In addition, REA scores were similar at menstrual, postmenstrual and midcycle weeks. Additional data from 12 men suggests sex differences in task performance were small or non-existent. In both women and men, there were no effects of repeated testing on REA, but emotional proclivity indices, defined as the tendency to recall words of positive or negative affective tone, increased across the four test sessions. As found previously, there was a trend for women to hear fewer positive words during the premenstrual week. These data are consistent with other research suggesting that a progesterone-mediated decrease in functional asymmetry occurs in the luteal phase. Future research manipulating task demands (e.g. memory load) or the affective valence of the stimuli may be useful in understanding the observed changes in hemispheric advantage.

Adolescent↗

PubMed2002

Naturalistic action impairments in dementia.

Naturalistic actions are everyday tasks (e.g. cooking) that require one to use multiple objects and sequence steps to achieve a goal. Naturalistic action impairment has been attributed to executive dysfunction [Higher cortical functions in man. New York: Basic Books, 1966], semantic knowledge degradation [Brain 111 (1988) 1173], and, more recently, general limitations in cognitive resources [Neuropsychology 12 (1998) 13]. Action impairments were explored in 51 dementia participants with the short form of the multi-level action test (MLAT-S). A clinical neuropsychological test protocol was also administered. Regression analyses including measures of executive functioning, semantic knowledge, and global cognitive functioning showed that global cognitive functioning was the best predictor of MLAT-S errors. Furthermore, task demands significantly influenced the type and frequency of errors, and dementia participants showed a pattern of errors similar to that reported in other clinical populations [Cognitive Neuropsychology 15 (1998) 617; Neuropsychologia 37 (1999) 51; Neuropsychology 12 (1998) 13]. Taken together, the present findings are inconsistent with semantic and executive accounts, but support the limited-capacity resource theory of naturalistic action impairment.

Activities of Daily Living↗

PubMed2002

Inter-hemispheric interaction facilitates face processing.

Many recent studies have revealed that interaction between the left and right cerebral hemispheres can aid in task performance, but these studies have tended to examine perception of simple stimuli such as letters, digits or simple shapes, which may have limited naturalistic validity. The present study extends these prior findings to a more naturalistic face perception task. Matching tasks required subjects to indicate when a target face matched one of two probe faces. Matches could be either across-field, requiring inter-hemispheric interaction, or within-field, not requiring inter-hemispheric interaction. Subjects indicated when faces matched in emotional expression (Experiment 1; n=32) or in character identity (Experiment 2; n=32). In both experiments, across-field performance was significantly better than within-field performance, supporting the primary hypothesis. Further, this advantage was greater for the more difficult character identity task. Results offer qualified support for the hypothesis that inter-hemispheric interaction is especially advantageous as task demands increase.

Brain↗

PubMed2002

Expectation-based attentional modulation of visual extinction in spatial neglect.

Visual extinction, the failure of patients with unilateral focal brain damage to report the contralesional of two simultaneously presented stimuli, may be modulated by characteristics of the display such as similarity, collinearity, or connectedness. Since these factors affect the perceptual configuration of stimuli, the modulation of extinction is believed to reflect low-level perceptual grouping. In the present study, patient AG did not show any modulation of contralesional detection when the ipsilesional and contralesional stimulus grouped by colour, by form, or both (Experiment 1). In contrast, identification of the contralesional stimulus was facilitated when the stimuli grouped (Experiment 2), suggesting a modulation of extinction by specific task demands. Experiment 3 used a cueing procedure to demonstrate modulation of extinction by expectation biases. Prior to stimulus presentation, AG was cued to attend to a particular feature (e.g. colour). After stimulus exposure he was prompted to identify the expected feature on valid trials and the unexpected feature on invalid trials. AG showed a significant validity effect for contralesional stimuli i.e. he identified the expected feature (e.g. colour) significantly better than the unexpected feature (e.g. form). These results suggest that competition for selection between visual stimuli may not only be influenced by perceptual characteristics of the display, but also by high-level factors such as the response criterion or expectation biases.

Attention↗

PubMed1997

Auditory inattention in right-hemisphere-damaged patients with and without visual neglect.

Fifteen right-hemisphere-damaged patients, eight with- and seven without visual neglect (N+ and N-, respectively), were assessed for the presence of auditory neglect using free-field bilateral simultaneous stimulation (BSS) and pseudorandom unilateral stimulation. Eight healthy subjects served as controls. Both N+ and N- groups extinguished left-sided sound stimuli in the BSS condition. N+ (but not N-) patients showed a right-side advantage in sound localization and were inferior, compared to normal individuals, in their ability to localize unilaterally administered sounds on the left side. Blindfolding significantly improved the localization performance. In a task demanding stimulus identification, both N+ and N- groups performed abnormally when auditory stimuli came from the left. Free-field stimulation is thus an adequate technique for the detection of auditory neglect. The results are consistent with the notion that left-sided neglect reflects a pathologically exaggerated attentional bias towards the right in normal individuals.

Adult↗

PubMed1998

Unilateral medial temporal lobe memory impairment: type deficit, function deficit, or both?

Previous research has characterized memory deficits resulting from unilateral hippocampal system damage as 'material specific', suggesting that left damage results in verbal memory impairment with preservation of visuospatial function and the converse with right damage. Implicit within this hypothesis are the assumptions that the systems are independent and memory is lateralized for each type of material. To test the verbal component of this hypothesis, unilateral hippocampal lesion and commissurotomy patients were compared with controls on a multiple-list free-recall task. The material specific hypothesis predicts severe impairment only with left lesions; right lesions and commissurotomy patients should be only minimally impaired. However, secondary memory was compromised at immediate recall for all patient groups, with both unilateral groups showing comparable and severe verbal episodic memory deficits. Final testing across all lists also revealed severe impairment in commissurotomy patients. Finding both unilateral groups to be similarly impaired for verbal material is taken as evidence against a material specific deficit during this verbal episodic memory task. Although previous data suggest that left patients are considerably more impaired during some verbal tasks, this may not be specific to the material, but rather the combination of material and task demands. Implications for the material specific hypothesis are discussed.

Adult↗

PubMed1999

Naturalistic action production following right hemisphere stroke.

An unselected group of right hemisphere, semi-acute stroke patients (n = 30) was run on a laboratory test of naturalistic action production and was found to commit errors of action at a higher rate than what was previously reported for recovering head injury patients [Schwartz et al., Naturalistic action impairment in closed head injury. Neuropsychology, 1997, 8, 59-72]. There were strong similarities in how these two patient groups responded to variations in task demands and in the pattern of errors they produced. Hemispatial biases were evident in the errors of right hemisphere patients with neglect but not those without neglect; and neglect patients also many errors that were unrelated to the spatial layout. We argue that a non-specific resource limitation--which might translate as reduced arousal or effort--is central to the breakdown of naturalistic action production after brain damage, and right hemisphere patients are especially vulnerable to this resource limitation and its behavioral consequences.

Adult↗

PubMed2001

Responding to feature or location: a re-examination of inhibition of return and facilitation of return.

It was found [Vision Res. 36 (1996) 2125] that reaction times for repeated targets were longer in detection and location discrimination tasks (inhibition of return; IOR) and shorter in color and orientation discrimination tasks (facilitation of return; FOR). The present experiment, using a more detailed analysis, shows that both IOR and FOR can be found in the discrimination tasks. Overall, the results are inconsistent with the notion that IOR and FOR effects reside in separate visual pathways. Rather, the results are accounted for by repetition priming and IOR that occur with specific combinations of target features and task demands.

Analysis of Variance↗

PubMed1980

The medical problem solving process.

Understanding the medical problem solving process has implications for medical education and the effectiveness of medical services. Through adaptation to the task at hand the human problem solver is able to ameliorate the effects of inherent limitations. In adapting to the medical problem solving task demands related to diagnosis and therapy, the physician uses the hypotheticodeductive process. The process draws upon the problem solver's disease centered and data centered knowledge and can be made more effective through the use of various heuristic rules and strategies that the physician develops with increasing expertise. Additional and more refined modes of laboratory support for the medical problem solver can evolve through further understanding of the problem solving process.

Clinical Laboratory Techniques↗

PubMed1985

Effects of the knowledge base on children's memory strategies.

In this article, the importance of examining the linkage between knowledge and strategic factors in children's memory has been suggested. Indeed, it has been argued that a more complete analysis of the development of remembering in children requires a consideration of the operation of memory strategies in the context of the growing knowledge base. The effects of the knowledge base were analyzed in terms of concurrent influences on the use of strategies and long-term consequences for the development of increasingly skilled memory processing. The available evidence suggests that age-related changes in the contents of the knowledge system, as well as increases in the ease with which information can be accessed, contribute to the strategies that are used by children of different ages, and influence the development of efficient modes of processing. Continued research on the concurrent effects of the knowledge base should provide a more complete account of children's memory than that currently available, taking into consideration knowledge of the materials, understanding of the task demands, as well as overall strategic abilities. Similarly, research on the long-term developmental effects of the knowledge base on memory strategies should facilitate an understanding of the mechanisms by which memory processing becomes more efficient and less effortful. Ideally, studies that examine these issues should be longitudinal in scope (Ornstein et al., 1985a), but even cross-sectional research that explores the interrelationships between strategies and knowledge will facilitate an understanding of the development of memory in children.

Adolescent↗

PubMed2002

A brain adaptation view of plasticity: is synaptic plasticity an overly limited concept?

A view that is emerging is that the brain has multiple forms of plasticity that must be governed, at least in part, by independent mechanisms. This view is illustrated by: (1) the apparent separate governance of some non-neural changes by activity, in contrast to synaptic changes driven by learning; (2) the apparent independence of different kinds of synaptic changes that occur in response to the learning aspects of training; (3) the occurrence of separate patterns of synaptic plasticity in the same system in response to different task demands; and (4) apparent dissociations between behaviorally induced synaptogenesis and LTP. The historical focus of research and theory in areas ranging from learning and memory to experiential modulation of brain development has been heavily upon synaptic plasticity since shortly after the discovery of the synapse. Based upon available data, it could be argued that: (1) synaptic, and even neuronal, plasticity is but a small fraction of the range of changes that occur in response to experience; and (2) we are just beginning to understand the importance of these other forms of brain plasticity. Appreciation of this aspect of the brain's adaptive process may allow us to better understand the capacity of the brain to tailor a particular set of changes to the demands of the specific experiences that generated them.

Adaptation, Physiological↗

PubMed2006

Event-related potential studies of language and emotion: words, phrases, and task effects.

This chapter reviews research that focuses on the effects of emotionality of single words, and of simple phrases, on event-related brain potentials when these are presented visually in various tasks. In these studies, presentation of emotionally evocative language material has consistently elicited a late (c. 300-600 ms post-onset) positive-going, largely frontal-central shift in the event-related potentials (ERPs), relative to neutral materials. Overall, affectively pleasant and unpleasant words or phrases are quite similar in their neuroelectric profiles and rarely differ substantively. This emotionality effect is enhanced in both amplitude and latency when emotional content is task relevant, but is also reliably observed when the task involves other semantically engaging tasks. On the other hand, it can be attenuated or eliminated when the task does not involve semantic evaluation (e.g., lexical decisions to words or orthographic judgments to the spelling patterns) or when comprehension of phrases requires integration of the connotative meaning of several words (e.g., compare dead puppy and dead tyrant). Taken together, these studies suggest that the emotionality of written language has a rapid and robust impact on ERPs, which can be modulated by specific task demands as well as the linguistic context in which the affective stimulus occurs.

Brain↗

PubMed2006

Affective and linguistic processing of speech prosody: DC potential studies.

Speech melody or prosody subserves linguistic, emotional, and pragmatic functions in speech communication. Prosodic perception is based on the decoding of acoustic cues with a predominant function of frequency-related information perceived as speaker's pitch. Evaluation of prosodic meaning is a cognitive function implemented in cortical and subcortical networks that generate continuously updated affective or linguistic speaker impressions. Various brain-imaging methods allow delineation of neural structures involved in prosody processing. In contrast to functional magnetic resonance imaging techniques, DC (direct current, slow) components of the EEG directly measure cortical activation without temporal delay. Activation patterns obtained with this method are highly task specific and intraindividually reproducible. Studies presented here investigated the topography of prosodic stimulus processing in dependence on acoustic stimulus structure and linguistic or affective task demands, respectively. Data obtained from measuring DC potentials demonstrated that the right hemisphere has a predominant role in processing emotions from the tone of voice, irrespective of emotional valence. However, right hemisphere involvement is modulated by diverse speech and language-related conditions that are associated with a left hemisphere participation in prosody processing. The degree of left hemisphere involvement depends on several factors such as (i) articulatory demands on the perceiver of prosody (possibly, also the poser), (ii) a relative left hemisphere specialization in processing temporal cues mediating prosodic meaning, and (iii) the propensity of prosody to act on the segment level in order to modulate word or sentence meaning. The specific role of top-down effects in terms of either linguistically or affectively oriented attention on lateralization of stimulus processing is not clear and requires further investigations.

Brain↗

PubMed2003

Attentional resource and processing speed limitations during sentence processing in Parkinson's disease.

Several studies have suggested that patients with Parkinson's disease (PD) have sentence comprehension difficulty in part because of their limited executive resources. However, these assessments confound the executive resources contributing to sentence comprehension with the resources needed for task performance. In the present study, we used a word detection technique that minimizes task demands in order to evaluate attentional and processing speed resources during the comprehension of simple sentences without subordinate clauses and sentences containing subject-relative and object-relative center-embedded subordinate clauses. We found that PD patients have poor sensitivity to phonetic errors embedded in unbound grammatical morphemes, regardless of the clausal structure of the sentence, suggesting difficulty attending to grammatical morphemes. We also found that PD patients are significantly slowed in their sensitivity to phonetic errors in content words embedded in object-relative center-embedded sentences. Slowed sensitivity to content words in object-relative sentences was correlated with timed executive measures of planning. On a traditional measure of comprehension, these PD patients were impaired for sentences containing object-relative center-embedded clauses compared to sentences with subject-relative center-embedded clauses, and comprehension of object-relative sentences was correlated with executive measures. Our findings are consistent with the claim that limited executive resources for strategic attention and processing speed contribute to the sentence comprehension difficulties of PD patients.

Aged↗

PubMed2001

Laparoscopic surgery for pheochromocytoma.

Because of the excessive production of catecholamines, surgery for pheochromocytoma carries a certain risk that can be reduced by accurate preoperative evaluation and by pretreatment with alpha-blockers. The authors' experience and that of other groups suggests that this inherent risk is not enhanced by the laparoscopic approach, and that, following successful surgery, patients benefit from the minimal invasiveness of this technique. Most surgeons recommend the transperitoneal approach that allows direct access to the adrenal vein, facilitating early ligation. This recommendation does not apply to other pathologies of the adrenal gland. Bilateral adrenal tumors are only seen in patients with familial pheochromocytomas. In this setting, adrenal-sparing surgery should be considered, which can also be performed laparoscopically. Previous adrenal surgery is not a contraindication but will render the procedure more difficult. Laparoscopic excision of paragangliomas is also technically feasible. Laparoscopic adrenal surgery for pheochromocytoma is a difficult and demanding task that must be performed by an experienced surgeon in cooperation with a team of specialists including an internist, endocrinologist, and anesthesiologist.

Adolescent↗

PubMed2002

Carbohydrate ingestion, blood glucose and mood.

A series of studies have reported that a high carbohydrate meal, or diets high in carbohydrate, were associated with feeling less energetic. However, after a drink containing pure sugar most studies report no effect. Meals almost exclusively carbohydrate increase the availability of tryptophan and hence serotonin synthesis in the brain, however, a small amount of protein blocks this mechanism making it an uncommon response. In many individuals, poor mood stimulates the eating of palatable high carbohydrate/high fat foods that stimulate the release of endorphins. There is a tendency for those with lower blood glucose, when performing cognitively demanding tasks, to report poorer mood. In a range of situations an association between a tendency for blood glucose levels to fall rapidly, and irritability, has been found. Differences in the ability to control blood glucose levels influence the association between carbohydrate intake and mood. There is a need in future research to contrast the impact of carbohydrate on mood in those distinguished because of their pre-existing psychological and physiological functioning.

Affect↗

PubMed2002

Depression and grief reactions in hospice caregivers: from pre-death to 1 year afterwards.

BACKGROUND: As the US population ages, more and more individuals will find themselves facing the demanding task of caring for terminally ill family members. Yet strikingly little is known about the emotional toll such caregiving exacts from caregivers, or how the stresses and strains of caregiving affect later grief reactions. This study examines the emotional adjustment and grief intensity of bereaved caregivers from their prebereavement (caregiving) baseline through the first year after the death and compares the effects of caregiving and subsequent bereavement on spouses and adult children. METHODS: Forty-eight adult children and spousal caregivers of hospice patients and 36 controls were evaluated shortly before the deaths of their loved ones and again at 2, 7, and 13 months after their deaths. All subjects were administered the Hamilton Rating Scale for Depression, Brief Symptom Inventory, and the Texas Revised Instrument of Grief. RESULTS: Depression and other indices of psychological distress are highest during the caregiving period and during the first few months after the death, before decreasing over the duration of the first year. Many symptoms of grief remain prominent as long as 13 months after the death of a parent or a spouse. There were no differences in intensity of grief, depression or other indices of distress between bereaved children and bereaved spouses. CONCLUSIONS: The magnitude of the stress of caregiving may be underestimated. Depression is at least as likely to emerge in the context of caregiving as it is in the postbereavement period. Therapeutic interventions may need to take into consideration the expected distress associated with caregiving and the chronicity of grief reactions. LIMITATIONS: The large dropout rate, reliance on self-report ratings and demographically homogeneous sample may limit generalizability of findings.

Bereavement↗