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PubMed2001

Attention, consciousness, and electrical wave activity within the cortical column.

The triangular circuit theory of attention is extended to activity of pyramidal neurons in cortical columns. The expanded theory accounts for both the brief attention of locating and identifying objects and the sustained attention of preparation for and maintenance of attention to objects, attributes, and locations. It is proposed that sustained attention is expressed in a cortical column by repeated surges of current in the long apical dendrites of pyramidal neurons, which form a wave. When the wave is sufficiently intense in a cluster of these neurons, it can be measured at the scalp as EEG oscillations. The wave of attention may or may not produce output pulses from the neuron. Selective attention may be expressed as enhanced processing of pulses arriving at the basal dendrites and leaving at the soma of these pyramidal neurons. It is also proposed that wave activity in the apical dendrites of cortical pyramidal neurons generates subjective experience. When wave activity is produced by the attention circuit in a cortical area beyond the primary sensory areas, it generates our foreground experience of an object. When wave activity is produced in the primary sensory areas by signals from sensory receptors, it generates our background experience, or consciousness.

Attention↗
PubMed2000

Modulation of attentional inhibition by norepinephrine and cortisol after psychological stress.

Two of the most salient physiological responses to stress are increased norepinephrine (NE) and cortisol (CORT) activities. However, it is unclear how these neurochemical events affect cognition, especially attention. We examined the effects of mild psychological stress on selective attention, as assessed by the negative priming (NP) paradigm. Salivary measures of the stress hormone CORT and alpha-amylase (a correlate of NE) were assayed to probe the relationship between the stress response and attentional inhibition. Healthy subjects (N = 20) engaged in the attention task, which was then followed by 15 min of a stressful video game before a return to the attentional task. Baseline saliva samples were obtained before the experiment began, 1 min after the video-game stressor, and 20 min post-stress. Subjects showed a significant reduction in NP and a decrease in reaction time (RT) after the video game. Moreover, alpha-amylase levels increased significantly after the stressor, indicating the role of NE in the acute stress response. While CORT levels remained unchanged after stress, CORT correlated significantly with both NP scores and RT after the stressor. These results imply that mild psychological stress can significantly alter attentional processes. Given the increase in alpha-amylase and the correlation between attention and CORT after stress, it seems likely that attentional processes are under tight control by brain systems which mediate the fight-or-flight response.

Adolescent↗
PubMed2003

Attentional deployment in visual half-field tasks: the effect of cue position on word naming latency.

Divided visual-field research suggests that attentional factors may contribute to the left hemisphere's (LH) superiority for language processing. The LH's parallel recognition strategy, specialised for whole word encoding, is largely unaffected by the distribution of spatial attention. In contrast, the right hemisphere's (RH) serial, letter-by-letter strategy places far greater demands on attentional resources. By manipulating spatial attention, the present study gauged the effect of cueing the beginning vs. the end of the word on LH and RH naming latency. Results indicated no effect of cue position on LH performance, consistent with research indicating that the LH enjoys an attentional advantage, deploying attention in parallel across the stimulus. As anticipated, the RH showed a facilitatory effect of beginning cue, which draws spatial attention to the initial letter cluster, enabling efficient implementation of the RH's sequential strategy. These findings suggest that differences in attentional deployment contribute to hemispheric asymmetries for word recognition.

Attention↗
PubMedDate not supplied

Longitudinal investigation of task persistence and sustained attention in children with prenatal cocaine exposure.

The present study estimates the longitudinal effects of prenatal cocaine exposure on indicators of sustained attention processing at 3, 5 and 7 years of age in an urban sample of full-term African-American children (235 cocaine-exposed, 207 noncocaine-exposed). The sample was enrolled prospectively at birth, with documentation of prenatal drug exposure status through maternal interview, urine and meconium toxicology assays. Sustained attention was measured at age 3 years using a standardized measure of task persistence during a challenging task [G.A. Morgan, N.A. Busch-Rossnagel, C.A. Maslin-Cole and R.J. Harmon, Individualized Assessment of Mastery Motivation: Manual for 15-36 Month Old Children, 1992.], and at ages 5 and 7 years using omission error scores from computerized continuous performance tasks (CPT) [L. Greenberg, R. Leark, T. Dupuy, C. Corman, C. Kindschi, M. Cenedela, Test of Variables of Attention (T.O.V.A. and T.O.V.A.-A.), 22, Universal Attention Disorders, Los Alamitos, CA, 1996; C.K. Conners, Conners' Continuous Performance Test (CPT), second ed., Multi-Health Systems, Canada, 1995.]. Findings from longitudinal GLM/GEE analyses of the three measured time points support a stable influence of prenatal cocaine exposure on indicators of sustained attention, after controlling for prenatal exposure to alcohol, marijuana, tobacco and over 20 additional medical and social-demographic covariates drawn from potentially confounding influences assessed at birth and later assessment visits (D=0.21; 95% CI=0.04, 0.38; P=.017). This effect was not mediated by fetal growth or gestational age and remained highly stable with increasing levels of covariate control. Separately, using the age 7 data, a structural equations model (SEM) was constructed combining all available self-report and bioassay data to measure magnitude of cocaine exposure in relationship to attention task performance. Results indicated a gradient of influence, with each standard deviation increase in the level of prenatal cocaine exposure relating to a 16% standard deviation increase in omission error scores at age 7. Overall findings support a stable cocaine-specific effect on indicators of sustained attention processing during the early childhood years. Results are discussed within the context of neurobiological and behavioral research linking prenatal cocaine exposure to long-lasting disruption of the brain systems subserving arousal and attention.

Black or African American↗
PubMed1996

Reality monitoring failure in schizophrenia: the role of selective attention.

Reality monitoring and selective attention have been repeatedly shown to be impaired in schizophrenia. Positive symptomatology has been found to be associated with deficits in both reality monitoring and selective attention. Therefore, a direct link between reality monitoring and selective attention was hypothesized. Thirty-two schizophrenic patients and 32 normal controls were administered the Stroop test as a measure of selective attention along with a test of three indices of reality monitoring, involving discrimination of: events vs. non-events, self- vs. externally-generated events, and oral vs. pictorial sources. A global memory test was administered for comparison. Results showed that schizophrenic patients were impaired in both reality monitoring and selective attention, and that these two were significantly correlated with each other in the schizophrenic sample. On the contrary, selective attention was not significantly correlated with memory efficiency in either group. Further, multiple regression analyses in schizophrenic patients showed that only selective attention contributed significantly to the variance in reality monitoring measures. Therefore, the results argue in favor of a specific role of a selective attention deficit in reality monitoring failure in schizophrenia.

Adult↗
PubMed2002

The temporal dynamics of the effects in occipital cortex of visual-spatial selective attention.

The temporal dynamics of the effects of lateralized visual selective attention within the lower visual field were studied with the combined application of event-related potentials (ERPs) and positron emission tomography (15O PET). Bilateral stimuli were rapidly presented to the lower visual field while subjects either passively viewed them or covertly attended to a designated side to detect occasional targets. Lateralized attention resulted in strongly enhanced PET activity in contralateral dorsal occipital cortex, while ERPs showed an enhanced positivity (P1 effect, 80-160 ms) for all stimuli (both non-targets and targets) over contralateral occipital scalp. Dipole modeling seeded by the dorsal occipital PET foci yielded an excellent fit for the peak P1 attention effect. However, more detailed ERP modeling throughout the P1 latency window (90-160 ms) suggested a spatial-temporal movement of the attention-related enhancement that roughly paralleled the shape of the dorsal occipital PET attention-related activations-likely reflecting the sequential attention-related enhancement of early visual cortical areas. Lateralized spatial attention also resulted in a longer-latency contralateral enhanced negativity (N2 effect, 230-280 ms) with a highly similar distribution to the earlier P1 effect. Dipole modeling seeded by the same dorsal occipital PET foci also yielded an excellent fit. This pattern of results provides evidence for re-entrance of attention-enhanced activation to the same retinotopically organized region of dorsal extrastriate cortex. Finally, target stimuli in the attended location elicited an additional prolonged enhancement of the longer-latency negativity over contralateral occipital cortex. The combination of PET activation and dipole modeling suggested contribution from a ventral-occipital generator to this target-related activity.

Adolescent↗
PubMed2003

Event-related potential correlates of the attentional blink phenomenon.

The attentional blink phenomenon results from a transitory impairment of attention that can occur during rapid serial stimulus presentation. A previous study on the physiological correlates of the attentional blink employing event-related potentials (ERPs) suggested that the P3 ERP component for target items presented during this impairment is completely suppressed. This has been taken to indicate that the target-related information does not reach working memory. To reevaluate this hypothesis, we compared ERPs evoked by detected and missed targets in the attentional blink paradigm. Eighteen subjects performed a rapid serial visual presentation (RSVP) task in which either one target (control condition) or two targets had to be detected. ERPs elicited by the second target were analyzed separately for trials in which the target had been detected and missed, respectively. As predicted, detected targets did elicit a P3 during and after the attentional blink period. No clear P3 was found for detected targets presented before the attentional blink, that is, at lag 1. In contrast, missed targets generally did not evoke a P3. Our results provide evidence that targets presented during the attentional blink period can reach working memory. Thus, these findings contribute to evaluating theories of the attentional blink phenomenon.

Adult↗
PubMed2002

Color and luminance contrasts attract independent attention.

Paying attention can improve vision in many ways, including some very basic functions such as contrast discrimination, a task that probably reflects very early levels of visual processing. Electrophysiological, psychophysical, and imaging studies on humans as well as single recordings in monkey show that attention can modulate the neuronal response at an early stage of visual processing, probably by acting on the response gain. Here, we measure incremental contrast thresholds for luminance and color stimuli to derive the contrast response of early neural mechanisms and their modulation by attention. We show that, for both cases, attention improves contrast discrimination, probably by multiplicatively increasing the gain of the neuronal response to contrast. However, the effects of attention are highly specific to the visual modality: concurrent attention to a competing luminance, but not chromatic pattern, greatly impedes luminance contrast discrimination; and attending to a competing chromatic, but not luminance, task impedes color contrast discrimination. Thus, the effects of attention are highly modality specific, implying separate attentional resources for different fundamental visual attributes at early stages of visual processing.

Attention↗
PubMed2003

Attentional inhibition of visual processing in human striate and extrastriate cortex.

Allocating attention to a spatial location in the visual field is associated with an increase in the cortical response evoked by a stimulus at that location, compared to when the same stimulus is unattended. We used event-related functional magnetic resonance imaging to investigate attentional modulation of the cortical response to a stimulus probe at an attended location and to multiple probes at unattended locations. A localizer task and retinotopic mapping were used to precisely identify the cortical representations of each probe within striate (V1) and extrastriate cortex (V2, VP, V3, V4v, and V3A). The magnitude and polarity of attentional modulation were assessed through analysis of event-related activity time-locked to shifts in spatial attention. Attentional facilitation at the attended location was observed in striate and extrastriate cortex, corroborating earlier findings. Attentional inhibition of visual stimuli near the attended location was observed in striate cortex, and attentional inhibition of more distant stimuli occurred in both striate and extrastriate cortex. These findings indicate that visual attention operates both through facilitation of visual processing at the attended location and through inhibition of unattended stimulus representations in striate and extrastriate cortex.

Adult↗
PubMed2003

Adolescent immaturity in attention-related brain engagement to emotional facial expressions.

Selective attention, particularly during the processing of emotionally evocative events, is a crucial component of adolescent development. We used functional magnetic resonance imagining (fMRI) with adolescents and adults to examine developmental differences in activation in a paradigm that involved selective attention during the viewing of emotionally engaging face stimuli. We evaluated developmental differences in neural activation for three comparisons: (1) directing attention to subjective responses to fearful facial expressions relative to directing attention to a nonemotional aspect (nose width) of fearful faces, (2) viewing fearful relative to neutral faces while attending to a nonemotional aspect of the face, and (3) viewing fearful relative to neutral faces while attention was unconstrained (passive viewing). The comparison of activation across attention tasks revealed greater activation in the orbital frontal cortex in adults than in adolescents. Conversely, when subjects attended to a nonemotional feature, fearful relative to neutral faces influenced activation in the anterior cingulate more in adolescents than in adults. When attention was unconstrained, adolescents relative to adults showed greater activation in the anterior cingulate, bilateral orbitofrontal cortex, and right amygdala in response to the fearful relative to neutral faces. These findings suggest that adults show greater modulation of activity in relevant brain structures based on attentional demands, whereas adolescents exhibit greater modulation based on emotional content.

Adolescent↗
PubMed2001

Alpha activity as an index of cortical inhibition during sustained internally controlled attention in infants.

OBJECTIVES: The study examined the suggestion that infant ability to maintain attention in anticipatory task and to sustain interference is related to the active inhibitory processes in cortical neural networks. METHODS: The extent of selective EEG synchronization in the alpha range has been taken as a measure of cortical inhibition. EEG was registered in 60 infants aged 8-11 months during: (1) attention to an object in the visual field (externally controlled attention); (2) anticipation of the person in the peek-a-boo game (internally controlled attention). RESULTS: The infants who demonstrated longer periods of anticipatory attention had higher absolute spectral amplitude in the broad frequency range under both experimental conditions. It was suggested that the effect of 'overall' EEG synchronization is related to some stable individual differences in psychophysiological traits. To control for the effect of overall EEG synchronization the relation between relative alpha amplitudes in 6.4-10 Hz range and the duration of internally controlled attention was analyzed. The infants with longer compared to shorter anticipatory attention spans had relatively higher 6.8 Hz alpha synchronization at posterior parietal sites under this experimental condition. CONCLUSIONS: It was suggested that alpha synchronization over posterior parietal cortex reflects an active inhibition of certain parietal networks involved in maintaining attention to peripheral visual field rather than merely an 'idle' state of this cortical area. Such an inhibition appears to allow infants to avoid interference of concurrent visual stimulation at the periphery of the visual field.

Aging↗
PubMed2002

Selective attention to spatial frequency: an ERP and source localization analysis.

OBJECTIVES: Physiological correlates of visual selective attention have been observed by recording ERPs to attended versus ignored target stimuli. Over many such studies, spatial attention has been observed to modulate early sensory components beginning 70 ms after stimulus onset, while effects of selection based on other stimulus features such as color and spatial frequency occur at longer latencies. Together, these findings argue for a primacy of location in early attentional selection. However, there have been some reports suggesting attention effects on short latency sensory-evoked potentials during selection of spatial frequency. The prime objective of the present study was to assess whether or not spatial frequency-dependent potentials are modulated by attention at a latency as early as 70-100 ms. METHODS: Checkerboard patterns were flashed to the subject, one being the target requiring a response. We investigated attentional effects using high-density scalp mapping and inverse dipole modeling. RESULTS: The earliest robust signs of selective attention to spatial frequencies consisted of an occipital selection negativity (OSN) and a frontal selection positivity (FSP). The OSN started at a latency of 140 ms, the FSP somewhat earlier at 120 ms. These attention effects were readily modeled by sources in cortical areas ventrally and laterally to the more primary areas generating the shorter-latency sensory components. CONCLUSIONS: This pattern of results has been found for non-spatial stimulus features in several studies, and is clearly different from the ERP correlates of spatial selection.

Adolescent↗
PubMed1999

Can attention be directed to opposite locations in different modalities? An ERP study.

OBJECTIVES: An event-related brain potential (ERP) study investigated whether spatially selective processing in vision and audition is controlled by a single supramodal system or by independent modality-specific systems. METHODS: Event-related brain potentials were recorded in response to visual and auditory stimuli at attended and unattended locations. In the 'Attend Same' condition, attention was directed to a single location in both modalities, while in the 'Attend Opposite' condition, visual and auditory attention had to be directed into opposite directions. RESULTS: Sensory-specific effects of attention on visual and auditory ERPs reflecting attentional modulations of perceptual processing were obtained in the 'Attend Same' condition, but not the 'Attend Opposite' condition. Beyond 200 ms post-stimulus, attentional ERP effects were also found in the 'Attend Opposite' condition. CONCLUSION: Results are inconsistent with the view that spatially selective processing is controlled by independent modality-specific systems. Effects of spatial attention on visual and auditory perceptual processing are closely linked, suggesting the existence of a supramodal attentional control system. At post-perceptual levels, attentional control may be more flexible.

Adult↗
PubMed2001

Attention problems in adolescents with congenital hypothyroidism: a multicomponential analysis.

Even though early treatment of congenital hypothyroidism (CH) with newborn screening prevents the mental retardation previously seen in cretinism, affected children still exhibit subtle persisting neurocognitive deficits. One of their commonest problems is poor attention, which reflects both early disease severity and later (high) circulating thyroid hormone levels. While attention is currently regarded as multicomponential in nature, with different processing components supported by different brain regions, the specific components of attention affected by CH have not been identified. In light of animal evidence showing that neonatal thyroid hormone deficiencies impede the neurodevelopment of structures important for selective aspects of attention, we proposed a multicomponential approach to study attention in children with CH. This was accomplished via retrospective analysis of existing data on adolescents with CH whose attention was previously evaluated using multiple tests. Results showed significantly poorer overall attention in CH than controls with differences occurring mainly on focus and inhibit indices. However, performance on various indices was associated with different disease parameters. Poor encode and focus were correlated with more severe hypothyroidism and a longer period of thyroid hormone insufficiency and poor select and shift with higher thyroid hormone levels at testing. These results signify that thyroid hormone is important for the development and later regulation of brain structures supporting distinct aspects of attention.

Adolescent↗
PubMed2005

Prefrontal lesions and attentional skills in childhood.

Despite the potential impact on development, few studies have examined the influence of prefrontal lesions occurring prior to maturation of the central nervous system. This study investigates the effect of prefrontal lesions in general, as well as the impact of lesion laterality, with respect to attentional abilities. The sample comprised 36 children with prefrontal lesions and 40 healthy controls. Attentional function was assessed across four domains: selective, shifting and divided attention, and processing speed. Group mean performances for children with prefrontal lesions indicated global attentional deficits, with greatest difficulties for "higher-order" skills including shifting and divided attention. Children with left prefrontal lesions performed similarly to controls, with a specific deficit characterized by difficulties with on-line processing of auditory-verbal information. Right prefrontaj lesions were primarily associated with impairments in day-to-day executive functions, including reduced monitoring, poor shifting attention and disinhibition. Children with bilateral prefrontal lesions performed worse than controls on tasks requiring greater cognitive resources. These results provide evidence of the important role played by prefrontal cortex in the development of attentional skills, and the particular role of the right prefrontal cortex. The pattern of attention deficits observed following early prefrontal lesions suggests some lateralization of function within the frontal lobes, even during childhood.

Adolescent↗
PubMed2006

Comparing attentional skills in children with acquired and developmental central nervous system disorders.

Attentional impairments in children occur in the context of both developmental and acquired disorders involving the central nervous system (CNS) and may have implications for ongoing development, potentially impeding cognitive, educational, and behavioral functions. Using a continuous performance paradigm (CPT), this study compared attentional profiles of children with developmental and acquired conditions impacting on the CNS: (i) attention deficit-hyperactivity disorder (ADHD: n=27); (ii) moderate traumatic brain injury (TBI: n=41); (iii) acute lymphoblastic leukemia (n=31); and (iv) insulin-dependent diabetes mellitus (n=39). A healthy control group (n=46) was also examined. Groups were compared on measures of sustained attention, selective attention, and response inhibition. In addition, measures of performance variability and deterioration and processing speed were examined. Results showed that children with ADHD exhibited global and severe attentional impairments in contrast to all other groups. Children with moderate TBI displayed mild attentional difficulties, restricted to selective and sustained attention domains. In conclusion, although CPT parameters differentiated the ADHD group from all others, a disorder-specific profile was not observed.

Adolescent↗
PubMed2004

Self-organization of an artificial neural network subjected to attention shift impairments and familiarity preference, characteristics studied in autism.

Autism is a developmental disorder with possibly multiple pathophysiologies. It has been theorized that cortical feature maps in individuals with autism are inadequate for forming abstract codes and representations. Cortical feature maps make it possible to classify stimuli, such as phonemes of speech, disregarding incidental detail. Hierarchies of such maps are instrumental in creating abstract codes and representations of objects and events. Self-Organizing Maps (SOMs) are artificial neural networks that offer insights into the development of cortical feature maps. Attentional impairment is prevalent in autism, but whether it is caused by attention-shift impairment or strong familiarity preference or negative response to novelty is a matter of debate. We model attention shift during self-organization by presenting a SOM with stimuli from two sources in four different modes, namely, novelty seeking (regarded as normal learning), attention-shift impairment (shifts are made with a low probability), familiarity preference (shifts made with a lower probability to the source that is the less familiar to the SOM of the two sources), and familiarity preference in conjunction with attention-shift impairment. The resulting feature maps from learning with novelty seeking and with attention-shift impairment are much the same except that learning with attention-shift impairment often yields maps with a somewhat better discrimination capacity than learning with novelty seeking. In contrast, the resulting maps from learning with strong familiarity preference are adapted to one of the sources at the expense of the other, and if one of the sources has a set of stimuli with smaller variability, the resulting maps are adapted to stimuli from that source. When familiarity preference is less pronounced, the resulting maps may become normal or fully restricted to one of the sources, and in that case, always the source with smaller variability if such a source is present. Such learning, in a system with many different maps, will result in very uneven capacities. Learning with familiarity preference in conjunction with attention-shift impairment surprisingly has higher probability for the development of normal maps than learning with familiarity preference alone.

Attention↗
PubMed2005

Components of attentional set-switching.

A series of distinct event-related potentials (ERPs) have been recorded from the scalp of human subjects as they switch from one task to another. It is possible that task switching may depend on different mechanisms depending on whether the switch requires a change in attentional set, in other words the redirecting of attention to different aspects of a sensory stimulus, or whether it requires a change in intentional set, in others words a change in the way that responses are selected. To address this issue, the current study recorded ERPs while subjects switched between attentional sets and the results were compared with those of a previous investigation in which subjects switched between intentional sets. Subjects selected stimuli according to two conflicting attentional sets, each emphasizing one visual stimulus dimension (colour, shape). Pairs of stimuli, only one of which was to be attended, were presented for between eight and seventeen trials then either a switch or a stay cue was shown. The switch cue instructed subjects to switch from the current attentional set to the other set, while the stay cue instructed subjects to maintain the current set. Comparing ERPs time-locked to the switch and stay cues revealed neural correlates of the initiation of a task switch. Comparing the ERPs time locked to the first stimuli after either stay or switch cues identified neural correlates of the implementation of a task switch. A similar modulation over parietal electrodes was seen when subjects were switching between either attentional or intentional sets. While an intentional set switch began with a medial frontal modulation, attentional set switching began with a lateral frontal modulation. Implementing a new attentional set was associated with modulation of relatively early visual potentials, while implementing a new intentional set was associated with modulation of later response-related potentials. The results confirm that task switching consists of a number of constituent processes which may be taxed to different degrees depending on whether a task-switch paradigm requires subjects to change the way in which they select stimuli or responses.

Attention↗