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PubMed1995

Electrophysiological signs of sustained and transient attention to spatial locations.

Event-related potentials were elicited by bilateral and unilateral stimulus arrays flashed in rapid sequence in order to investigate both focused attention and attentional orienting. Subjects attended selectively to the stimuli on one side of the bilateral arrays and were required to discriminate infrequent target stimuli on either the attended side (no switch of attentional focus) or unattended side of the array (switch of attentional focus). The ERPs to the bilateral stimuli elicited an occipital P1 component that was larger in amplitude over scalp regions contralateral to the attended visual half-field. The ERPs to the unilateral stimuli on the attended side also showed an amplitude enhancement of early P1 components, followed by a positive shift that lasted until 200 msec latency over the contralateral occipital scalp. No enhancement of the N1 component was observed to attended-side stimuli. These patterns were not different for conditions requiring or not requiring a spatial switch of the attentional focus. In conjunction with ERP signs of focused spatial attention, significant differences in discrimination performance (d') were obtained for the attended vs unattended-side targets; no changes in measures of criterion (beta) were obtained. These data support the idea that the early occipital P1 attention effect represents a facilitation of visual inputs that occur at attended locations in the visual field.

Adolescent↗
PubMed1996

The effect of Huntington's disease and Gilles de la Tourette's syndrome on the ability to hold and shift attention.

Huntington's disease (HD) and Tourette's syndrome (TS) are two basal ganglia (BG) disorders, associated not simply with hyperkinetic movements but also with attentional impairments. The purpose of this experiment was to evaluate the attention deficits reported in HD and TS via the use of a vibrotactile choice reaction time (CRT) procedure involving biased probabilities of event occurrence. We attempted to ascertain whether HD and TS patients are impaired in their ability to shift their attention to an unexpected location, or when they have to hold attention to an expected location. The results demonstrate that HD patients, as compared to controls, experience difficulties in shifting their attention from expected to unexpected spatial locations; this effect was exacerbated with the adoption of a crossed arm configuration. On the other hand, TS patients' performance, although slower overall, was not qualitatively greatly different from that of the controls. We had previously found, with a similar paradigm, that Parkinson's disease patients instead manifest problems in holding or maintaining attention to an expected locus. We conclude that HD patients experience considerable difficulties in allocating attentional resources between expected and unexpected event occurrences. Perhaps due to pervasive subcortical damage and dysfunction in the circuits linking the frontal lobes with the BG. In TS, a similar if milder functional rather than structural deficit may be reflected in a pattern of responses which resembles a weaker version of the HD response pattern.

Adult↗
PubMed1987

Shared attentional control of smooth eye movement and perception.

Subjects performed a concurrent smooth pursuit and perceptual task to determine whether smooth pursuit eye movements and perception share the same attentional mechanism. Subjects pursued a pair of eccentric rows of moving characters while simultaneously attempting to identify and locate the single numeral in these target rows and the single numeral in a pair of untracked background rows, which moved at a different velocity. Average smooth pursuit gain (eye velocity/target velocity) was 0.7 to 1. Visual search was better for target rows (approximately 65% correct) than for background rows (approximately 22% correct). Superior search performance for the target was not due to its lower retinal speed: performance on the target was 2-3 times better than on the background when retinal speeds were the same. Superior performance for the pursuit target suggests that smooth eye movements and perception share the same selective attentional mechanism. A shared attentional mechanism was further supported by findings that subjects could not: (1) maintain a stable line of sight on a central stationary point while simultaneously attending to moving rows; and (2) pursue one pair of rows and attend the other, untracked rows. Attempts to attend untracked rows did, however, produce a partial improvement in search performance which was accompanied by only a very slight change in eye velocity. This demonstrates that the effects of decisions about how to apportion attention across the visual field depend on the task. Despite the common selective attentional mechanism, smooth eye movements do not provide accurate external indicators of attention unless the consequences of attentional decisions for performance are determined separately for oculomotor and for perceptual tasks.

Attention↗
PubMed1989

Effects of cocaine and d-amphetamine on sustained and selective attention in rats.

The effects of cocaine and d-amphetamine were compared in two attention-loading tasks. Cued by the position of a light, rats were food-reinforced for pressing one of two levers in a 2-choice, discrete-trial procedure. In the "sustained attention" task, the cue light was illuminated for a brief period (1.8 sec or less) at the beginning of each trial. In the "selective attention" task, the cue light remained on until a level press, while a blinking light over the incorrect lever served as a distractor. In the sustained attention task, low doses of d-amphetamine (0.25 mg/kg SC) and cocaine (2.5 mg/kg SC) enhanced accuracy; some doses of d-amphetamine (0.75 mg/kg SC) and cocaine (1.25 and 2.5 mg/kg SC) also reduced choice latencies. In the selective attention task, the lower doses of these drugs had no effect on accuracy, the highest dose of d-amphetamine (1.25 mg/kg SC) disrupted accuracy, and all doses of the drugs reduced choice latencies. The time to retrieve food was increased in a dose-dependent fashion by both drugs in both tasks. These results indicate that, other than differences in potency, cocaine and d-amphetamine induce similar behavioral effects in attention-loading tasks, with improvement or interference with performance dependent on the dose and the type of attention demanded of the task.

Animals↗
PubMedDate not supplied

Mapping study of somatosensory evoked potentials during selective spatial attention.

We have investigated the effects of selective spatial attention on early and middle-latency SEPs. Baseline control responses to electrical stimulation of 2 digits of the hand were recorded first in conditions of mental relaxation, in the absence of any cognitive task, to obtain truly 'neutral' responses uncontaminated by cognitive components. Then, during a 'task condition,' identical stimuli were applied to the same two fingers, but the subject's attention was driven towards the stimulated territory by the bias of mechanical taps delivered to the same digits. The earliest effect of directing attention towards the territory stimulated was a positive shift on contralateral somatosensory responses, with onset at 27.4 +/- 4 msec post stimulus. This SEP modification: (a) did not entail any change in the scalp distribution of components, as assessed by topographic mapping, and (b) was not present when attention was directed towards the hand contralateral to that receiving electrical stimuli. A second effect was represented by a parieto-central negativity in the 60-80 msec latency range; this feature could also be observed during contralaterally driven attention and was associated with topographical changes in SEP scalp distribution. Finally, a late centro-frontal negativity beginning at 90-100 msec (N140) appeared during ipsilateral attention, while P100 was not enhanced. Subcortical P14 and primary cortical N20 were not significantly affected by the tasks. We conclude that the 'early positive shift' is linked to the spatial aspects of selective attention and represents in part modulation of obligatory components (P25 through P45) existing in control SEPs; it probably corresponds with the deflections with similar polarity and time-course that have been described by others in response to somatosensory target stimuli. Conversely, 60-80 msec negative enhancement is less spatially selective and may represent non-specific arousal effects. The late negative component (N140) shares several features with the 'processing negativity' described in auditory paradigms and could represent the equivalent of this effect in the somatosensory system.

Adult↗
PubMed1989

Stimulus intensity, attentional instructions, and the ear advantage during dichotic listening.

The present experiment was designed to investigate the effects of the following two variables on the identification of dichotically presented CV syllables: (1) the relative difference in intensity levels of the stimuli presented to the two ears and (2) the instructions to attend to both ears or to focus attention on one ear. As expected for a verbal task, more CV's were identified from the right ear than from the left ear. Furthermore, identification of stimuli presented to one ear improved when (1) those stimuli were relatively higher in volume than the stimuli presented to the other ear and (2) when subjects were instructed to focus attention on only that ear rather than distribute attention across both ears. Of particular importance is the finding that the effects of relative stimulus intensity are the same under conditions of focused attention as under conditions of divided attention. This finding is inconsistent with an attention explantation of the relative intensity effects. Instead, the results are consistent with a model of dichotic listening in which ear of stimulus presentation and relative stimulus intensity influence a perceptual stage of information processing and attentional instructions influence a subsequent response selection stage.

Adult↗
PubMed1979

Event-related potentials and selective attention to auditory stimuli varying in pitch and localization.

Event-related potentials were recorded from subjects performing a discrimination task which required selective attention to one of (or divided attention to both of) two classes of tone pips imaged to arrive over two independent sound sources varying systematically in pitch and spatial localization. In selective attention N1 amplitude was larger and P2 amplitude was inversely smaller to the attended tones than to the unattended tones; P2 latency was prolonged to the attended tones; in divided attention, both N1 and P2 amplitudes and P2 latency were intermediate between selective attention and inattention. These attention effects upon both N1 and P2 components were interpreted to be due to a growth of a negative shift superimposed on those evoked components, rather than a modification of each component itself. This endogenous negativity was also considered to reflect the allocation of attentional capacity for discrimination processing whether tones coming from the attended source were 'signal' or not.

Adult↗
PubMedDate not supplied

Effects of information processing demands on slow negative shift latencies and N100 amplitude in selective and divided attention.

The influence of information processing demands on auditory event-related potentials (ERPs) in selective and divided attention was examined by varying the stimulation rate and target difficulty in a two-channel discrimination task. Subjects were required to detect targets in either one or both ears (channels) in a series of tones presented randomly to both ears. The amplitude of the N100 component (latency 80-140 msec) of the ERP to all stimuli in an attended channel was greater if attention was focused on that channel that if it was directed to the opposite channel. N100 amplitude was also reduced in divided attention compared to focused attention. In general, these effects were obtained only if the stimulation rate was high and/or targets were difficult to detect. However, these effects of attention modulated an underlying slow negative shift (SNS) rather than N100 directly. The onset and peak latencies of the SNS were strongly dependent on the processing demands of the task. The results show that the temporal relationship of the SNS to the N100 component is the principal factor responsible for variations in the effects of attention on the ERP with changes in information processing demands. The relationship between these ERP components and resource allocation theories of attention is discussed.

Adolescent↗
PubMed1995

Event related potentials during covert orientation of visual attention: effects of cue validity and directionality.

Covert orientation of attention was studied in 30 adults who fixated warning cues and pressed a button at target onset. Directional cues (arrows) indicated the most probable (p = 0.8) side of target occurrence. Subjects responded fastest when validly cued, slowest to invalidly cued targets, and at an intermediate rate when the cue (a cross) was not directional. Directional cues took longer to evaluate (increased N1 and P2 latencies) and produced more focussed attention and greater response preparation (enhanced CNV and P3 amplitude) than non-directional cues. These findings indicate that the expectancy of a target can be manipulated by a spatial cue at three levels, sensory, attention, and response preparation, and lead to changes in the sensory perceptual processing of the target. Validly cued targets produced an increase in P1 amplitude reflecting attention enhanced sensory processing whereas invalidly cued targets increased N1 and P3 amplitudes reflecting the re-orientation of attention, and further processing and updating of information required of low probability stimuli respectively. P3 latency to invalidly cued targets was also delayed reflecting the additional processes required to shift attention to a new location. The P3 latency validity effect was smaller than that found for response time suggesting response execution may also be affected by spatial attention.

Aged↗
PubMedDate not supplied

Vagal tone regulation during sustained attention in boys exposed to opiates in utero.

Attention and learning problems among children exposed to opiates in utero have been previously reported but are difficult to interpret due to imprecise measurement and inadequate control of postnatal factors. In this study, we used a behavior-based measure of attention (continuous-performance tasks) and a physiological index of sustained attention (cardiac vagal tone) to measure more precisely the process of sustained attention. Boys, aged 7 to 12, exposed to opiates in utero, were compared to boys whose mothers began using illicit substances after the child's birth (environmental controls), and boys whose mothers were non-drug users. This three-group design was intended to isolate in utero effects from postnatal environmental influences. Vagal tone, a measure of heart-rate variability sensitive to vagal influences on the heart, was measured pre- and postbaseline and during the three tasks of the Gordon Diagnostic System (Delay, Vigilance, and Distractibility). Vagal tone has been found to be sensitive to changes in environmental demand for sustained attention in infants, school-age children, and adults. Results indicated that when distractors were added to the vigilance task (Distractibility task), opiate-exposed boys failed to suppress vagal tone compared to both control groups. However, both the opiate-exposed boys and the environmental controls made fewer correct responses than non-drug-exposed controls on this task. These results indicate that normal physiological responses to increased attentional demand may be impaired in boys exposed in utero to opiates in this age range. However, the poor Distractibility scores of both the opiate-exposed and environmental controls suggests an important role of environmental influences on attentional performance.

Arousal↗
PubMed1996

Evoked otoacoustic emissions and auditory selective attention.

The auditory system has an extensive peripheral efferent innervation. The question addressed in this paper is whether the olivocochlear bundle (OCB) efferent system innervating the outer hair cells (OHC) of the cochlea plays a role in selective attention. As evoked otoacoustic emissions (EOAE) provide a measure of the active micromechanical properties of OHCs, they can be used to assess the role of the efferent system in attention. Six experiments using tone-pip EOAEs are reported. In each experiment, EOAEs generated by 1 or 2 kHz tone pips when they were attended were compared with EOAEs to the same stimuli when they were unattended. In three experiments (1-4), a non-linear stimulus difference method was used to record a pure cochlear component of EOAEs. In Exps. 1-5, 1 and 2 kHz tone pips were delivered to the same ear and the difficulty of the subjects' task was manipulated in order to produce a more focussed attentional state or contralateral noise was presented to determine whether attention effects are dependent upon having an already activated efferent system. In Exp.6, the 1 and 2 kHz stimuli were delivered to opposite ears. A total of 70 subjects participated in the six experiments. There were no effects of attention on EOAEs in any of the experiments in the direction of previously reported effects. The results of these first six experiments employing simple attention switches between fixed auditory objects do not support active cochlear involvement in selective attention.

Acoustic Stimulation↗
PubMed1996

Spatial selective attention in schizophrenic, affective disorder, and normal subjects.

Schizophrenic, affective disorder, and normal subjects performed tasks involving exogenous (automatic) and endogenous (voluntary) attention. In the exogenous attention task, schizophrenic subjects demonstrated a greater benefit in response time than did normal subjects. In the endogenous attention task, however, schizophrenic subjects showed a smaller benefit in response time than did normal subjects. These results are consistent with a model of schizophrenia that predicts a deficit in voluntary (endogenous) control, and a disinhibition and therefore enhancement of the automatic (exogenous) processes of spatial selective attention. Affective disorder subjects did not demonstrate a greater benefit in response time than normal subjects in the exogenous attention task, but did show a smaller benefit in response time than normal subjects in the endogenous attention task. The somewhat similar pattern of behavior of schizophrenic and affective disorder subjects suggests that abnormal spatial selective attentional processes may not be specific to schizophrenia.

Adult↗
PubMed1995

Luminance and spatial attention effects on early visual processing.

Event-related potentials (ERPs) were recorded from healthy subjects in response to unilaterally flashed high and low luminance bar stimuli presented randomly to left and right field locations. Their task was to covertly and selectively attend to either the left or right stimulus locations (separate blocks) in order to detect infrequent shorter target bars of either luminance. Independent of attention, higher stimulus luminance resulted in higher ERP amplitudes for the posterior N95 (80-110 ms), occipital P1 (110-140 ms), and parietal N1 (130-180 ms). Brighter stimuli also resulted in shorter peak latency for the occipital N1 component (135-220 ms); this effect was not observed for the N1 components over parietal, central or frontal regions. Significant attention-related amplitude modulations were obtained for the occipital P1, occipital, parietal and central N1, the occipital and parietal P2, and the parietal N2 components; these components were larger to stimuli at the attended location. In contrast to the relatively short latencies of both spatial attention and luminance effects, the first interaction between luminance and spatial attention effects was observed for the P3 component to the target stimuli (350-750 ms). This suggests that interactions of spatial attention and stimulus luminance previously reported for reaction time measures may not reflect the earliest stages of sensory/perceptual processing. Differences in the way in which luminance and attention affected the occipital P1, occipital N1 and parietal N1 components suggest dissociations among these ERPs in the mechanisms of visual and attentional processing they reflect.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed2005

D-Amphetamine remediates attentional performance in rats with dorsal prefrontal lesions.

Although amphetamine treatment has been shown to promote recovery of motor function in animals with cortical ablations, the potential therapeutic effect of amphetamine on processes other than motor control, such as attention and working memory, has been relatively unexplored. Accordingly, we investigated the beneficial effect of D-amphetamine treatment in animals with dorsal prefrontal cortex lesions (dPFC) compared with sham controls on a novel combined attention-memory task (CAM) that simultaneously measures attention to a visual stimulus and memory for that stimulus. The dPFC group was impaired in their ability to correctly detect the visual stimulus. Although this deficit occurred together with increased omissions and slow response latencies, these associated deficits largely recovered within the 10 post-operative baseline sessions revealing a selective attentional deficit in this group of animals. Nonetheless, the dPFC lesion did not substantially affect the working memory component of the task. The systemic administration of d-amphetamine served to ameliorate the attentional deficit in the dPFC group at the low dose only (0.2 mg/kg). By contrast, the dPFC group were less sensitive to the detrimental effects of the high dose (0.8 mg/kg) on any aspect of task performance. However, despite improving attention to the visual stimulus, D-amphetamine did not improve memory for that stimulus which instead appeared to deteriorate. The results provide apparently the first demonstration that low doses of D-amphetamine can ameliorate an attentional deficit in animals with selective dPFC lesions and may be a useful model of cognitive deficit in ADHD, schizophrenia or frontal brain injury.

Animals↗
PubMed2004

Differences in startle modulation during instructed threat and selective attention.

This study investigated whether attentional processes contribute to fear-potentiated startle. Ten subjects participated in a threat of shock experiment and an attentional control condition. In the threat of shock experiment, visual cues indicated whether or not an aversive shock might occur. In the attentional control, the shocks were replaced by faint vibrotactile stimuli that had to be counted. The P300 amplitudes of the ERP evoked by the visual cues did not differ under threat and counting, which suggested that both conditions engaged attention to the same extent. In contrast, startle potentiation in the threat condition was an order of magnitude larger than the marginally significant attentional startle facilitation in the counting condition. These results indicate that an attentional contribution to fear-potentiated startle under the present experimental conditions is small. In addition, contextual effects of threat of shock became manifest as baseline startle was facilitated relative to the attention condition. This may reflect a more sustained state of anxiety on which cue-specific fear responses are superimposed.

Acoustic Stimulation↗
PubMed2005

Lateralized irrelevant speech alters visuospatial selective attention mechanisms.

Recent studies indicate that the coordination of spatial attention across modalities may in part be mediated by a supramodal attentional system. We try to extend the concept of a supramodal system and hypothesized that involuntary modulations of auditory attentional processes by irrelevant speech signals influence visuospatial attention, suggesting crossmodal links between vision and speech. In order to test this we recorded event-related brain potentials (ERPs) of 12 healthy subjects in a visuospatial selective attention task. The task to identify target stimuli appearing at lateral visual field locations caused the expected enhancements of the early P1 and N1 ERP components to attended visual stimuli. Understandable and ununderstandable task irrelevant speech was presented either at the visually attended position or in the opposite visual field location. Speech contralateral to unattended visual stimuli led to a decreased N1 amplitude. This effect was stronger for understandable speech. Thus, speech influences the allocation of visual spatial attention if it is presented in the unattended location. The results suggest crossmodal links of speech and visuospatial attention mechanisms at a very early stage of human perception.

Adult↗
PubMed2006

Improved selective and divided spatial attention in early blind subjects.

Spatial attention paradigms using auditory or tactile stimulation were used to explore neural and behavioral reorganization in early blind subjects. Although it is commonly assumed that blind subjects outperform sighted subjects in such tasks, the empirical data to confirm this remain controversial. Moreover, previous studies have often confounded factors of sensory acuity with those of attention. In the present work, we compared the performance of individually matched early blind and sighted subjects during auditory and tactile tasks. These consisted of sensory acuity tests, simple reaction time task as well as selective and divided spatial attention tasks. Based on sensory measurements, we made sure that the reliability and salience of auditory and tactile information were identical between the two populations to estimate attentional performance independently of sensory influence. Results showed no difference between groups in either sensory sensitivity or simple reaction time task for both modalities. However, blind subjects displayed shorter reaction times than sighted subjects in both tactile and auditory selective spatial attention tasks and also in bimodal divided spatial attention tasks. The present study thus demonstrates an enhanced attentional performance in early blind subjects which is independent of sensory influence. These supra-normal abilities could be related to quantitative and qualitative changes in the way early visually deprived subjects process non-visual spatial information.

Acoustic Stimulation↗
PubMed2007

The neural circuitry underlying the executive control of auditory spatial attention.

Although a fronto-parietal network has consistently been implicated in the control of visual spatial attention, the network that guides spatial attention in the auditory domain is not yet clearly understood. To investigate this issue, we measured brain activity using functional magnetic resonance imaging while participants performed a cued auditory spatial attention task. We found that cued orienting of auditory spatial attention activated a medial-superior distributed fronto-parietal network. In addition, we found cue-triggered increases of activity in the auditory sensory cortex prior to the occurrence of an auditory target, suggesting that auditory attentional control operates in part by biasing processing in sensory cortex in favor of expected target stimuli. Finally, an exploratory cross-study comparison further indicated several common frontal and parietal regions as being involved in the control of both visual and auditory spatial attention. Thus, the present findings not only reveal the network of brain areas underlying endogenous spatial orienting in the auditory modality, but also suggest that the control of spatial attention in different sensory modalities is enabled in part by some common, supramodal neural mechanisms.

Acoustic Stimulation↗