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PubMed2001

Systematic eye movements do not account for the perception of motion during attentive tracking.

It has been suggested that attention can disambiguate stimuli that have equal motion energy in opposite directions (e.g. a counterphasing grating), such that a clear motion direction is perceived. The direction of this movement is determined by the observer and can be changed at will. Assuming that the responses of front-end motion detectors are equal for the two opponent directions, it has been proposed that the unambiguous motion perceived with attentive tracking arises from an independent mechanism that monitors the shifts of attention directed to the moving feature of interest. However, while perceiving motion under attentive tracking conditions, observers often report a strong impression that they are making eye movements. In this study, we investigated whether systematic eye movements are present during attentive tracking and, as a result, could be responsible for the subjective experience of movement. We had observers track an object in smooth motion, apparent motion and ambiguous motion, either with eye movements or with attention. The results show that there are negligible eye movements during attentive tracking, which are neither systematic nor correlated with the stimulus. Given that neither eye movements nor retinal image motion can account for subjectively perceived motion, as well as the absence of any other plausible explanation, we find it tempting evidence for an earlier suggestion that the percept of movement must arise from a specialized mechanism.

Attention↗
PubMed2002

Chromatic input to motion processing in the absence of attention.

While several previous psychophysical and neurophysiological studies have demonstrated chromatic (red/green) input to motion processing, the nature of this input is still a matter of debate. In particular, recent controversy has developed regarding whether chromatic motion processing relies on lower-level processes [J. Neurosci. 14 (1994) 4854; 19 (1999) 6571] versus higher-level, attention- or salience-based mechanisms [Science 257 (1992) 1563; Proc. Natl. Acad. Sci. 96 (1999a) 8289; 96 (1999b) 15374]. In this study, we investigated the degree to which chromatic motion is influenced by attentional mechanisms by employing a dual-task paradigm, which allowed us to compare the strength of chromatic motion under conditions of poor versus full attention. Here, we found that for equiluminant red/green gratings, chromatic motion processing is as robust in poor, as in full, attention conditions. This lack of an attentional effect suggests that chromatic motion processing must rely, at least in part, on lower-level (i.e., pre-attentive) motion mechanisms. For non-equiluminant (e.g., red brighter than green) gratings, however, attention significantly modulates chromatic motion strength. Possible explanations for this latter result are discussed in the context of inherent salience differences between the bright-red and dim-green stripes of the heterochromatic grating.

Attention↗
PubMed1997

Peripheral stimulus localization by infants with eye and head movements during visual attention.

The effect of attention to a focal stimulus on 14, 20 and 26-week-old infant's peripheral stimulus localization with eye and head movements was examined in this study. Fixation was engaged on a stimulus in the central visual field and a stimulus was presented in the periphery immediately or after a delay. Peripheral stimulus localization occurred less frequently near the beginning of fixation and when a significant heart rate deceleration had occurred (sustained attention), compared with when no focal stimulus was present or after heart rate had returned to prestimulus level (attention termination). Localization was accompanied by head movements on more than two-thirds of the trials, and the likelihood of head movements was positively associated with stimulus eccentricity. The saccades to localize the peripheral stimulus had unusually high velocities in the attention conditions for the two older aged groups relative to their saccades in inattentive conditions. There were unusual "localizing head movements" in the attention conditions in the absence of localizing saccades or changes in fixation for the two older age groups. Infant attention modulates eye movement characteristics of infants. These data also support the hypothesis that eye and head movement systems are relatively independent in the infant, and that eye-head relations during infant attention may be different from during inattention.

Aging↗
PubMed2004

Neuroimaging studies of attention and the processing of emotion-laden stimuli.

Because the processing capacity of the visual system is limited, selective attention to one part of the visual field comes at the cost of neglecting other parts. In this paper, we review evidence from single-cell studies in monkeys and functional magnetic resonance imaging (fMRI) studies in humans for neural competition and how competition is biased by attention. We suggest that, at the neural level, an important consequence of attention is to enhance the influence of behaviorally relevant stimuli at the expense of irrelevant ones, providing a mechanism for the filtering of distracting information in cluttered visual scenes. Psychophysical evidence suggests that processing outside the focus of attention is attenuated and may be even eliminated under some conditions. A major exception to the critical role of attention may be in the neural processing of emotion-laden stimuli, which are reported to be processed automatically, namely, without attention. Contrary to this prevailing view, in a recent study we found that all brain regions responding differentially to faces with emotional content, including the amygdala, did so only when sufficient resources were available to process those faces. After reviewing our findings, we discuss their implications, in particular (1) how emotional stimuli can bias competition for processing resources; (2) the source of the biasing signal for emotional stimuli; (3) how visual information reaches the amygdala; and finally (4) the relationship between attention and awareness.

Amygdala↗
PubMed2003

Cortical abnormalities in children and adolescents with attention-deficit hyperactivity disorder.

BACKGROUND: Results of structural brain imaging studies of patients with attention-deficit hyperactivity disorder have shown subtle reductions in total brain volume and in volumes of the right frontal lobe and caudate nucleus. Although various conventional volumetric and voxel-based methods of image analysis have been used in these studies, regional brain size and grey-matter abnormalities have not yet been mapped over the entire cortical surface in patients with this disorder. We aimed to map these features in patients with attention-deficit hyperactivity disorder. METHODS: We used high-resolution MRI and surface-based, computational image analytic techniques to map regional brain size and grey-matter abnormalities at the cortical surface in a group of 27 children and adolescents with attention-deficit hyperactivity disorder and 46 controls, who were group-matched by age and sex. FINDINGS: Abnormal morphology was noted in the frontal cortices of patients with attention-deficit hyperactivity disorder, with reduced regional brain size localised mainly to inferior portions of dorsal prefrontal cortices bilaterally. Brain size was also reduced in anterior temporal cortices bilaterally. Prominent increases in grey matter were recorded in large portions of the posterior temporal and inferior parietal cortices bilaterally. INTERPRETATION: The frontal, temporal, and parietal regions are heteromodal association cortices that constitute a distributed neural system, which subserves attention and behavioural inhibition. We have identified region-specific anatomical abnormalities in cortical components of attentional systems, which may help better account for the symptoms of attention-deficit hyperactivity disorder.

Adolescent↗
PubMed2000

The cognitive-energetic model: an empirical approach to attention-deficit hyperactivity disorder.

Attention Deficit/Hyperactivity Disorder (ADHD) is a childhood psychiatric disorder which when carefully defined, affects around 1% of the childhood population [Swanson JM, Sergeant JA, Taylor E, Sonuga-Barke EJS, Jensen PS, Canwell DP. Attention-deficit hyperactivity disorder and hyperkinetic disorder. Lancet 1998;351:429-433]. The primary symptoms: distractibility, impulsivity and overactivity vary in degree and association in such children, which led DSM IV to propose three subgroups. Only one of these subgroups, the combined subtype: deficits in all three areas, meets the ICD-10 criteria. Since the other two subtypes are used extensively in North America (but not in Europe), widely different results between centres are to be expected and have been reported. Central to the ADHD syndrome is the idea of an attention deficit. In order to investigate attention, it is necessary to define what one means by this term and to operationalize it in such a manner that others can test and replicate findings. We have advocated the use of a cognitive-energetic model [Sanders, AF. Towards a model of stress and performance. Acta Psychologica 1983;53: 61-97]. The cognitive-energetic model of ADHD approaches the ADHD deficiency at three distinct levels. First, a lower set of cognitive processes: encoding, central processing and response organisation is postulated. Study of these processes has indicated that there are no deficits of processing at encoding or central processing but are present in motor organisation [Sergeant JA, van der Meere JJ. Convergence of approaches in localizing the hyperactivity deficit. In Lahey BB, Kazdin AE, editors. Advancements in clinical child psychology, vol. 13. New York: Plenum press, 1990. p. 207-45; Sergeant, JA, van der Meere JJ. Additive factor methodology applied to psychopathology with special reference to hyperactivity. Acta Psychologica 1990;74:277-295]. A second level of the cognitive-energetic model consists of the energetic pools: arousal, activation and effort. At this level, the primary deficits of ADHD are associated with the activation pool and (to some extent) effort. The third level of the model contains a management or executive function system. Barkley [Barkley RA, Behavioral inhibition, sustained attention, and executive functions: constructing a unifying theory of ADHD. Psychological Bulletin 1997;121:65-94] reviewed the literature and concluded that executive function deficiencies were primarily due to a failure of inhibition. Oosterlaan, Logan and Sergeant [Oosterlaan J, Logan GD, Sergeant JA. Response inhibition in ADHD, CD, comorbid ADHD + CD, anxious and normal children: a meta-analysis of studies with the stop task. Journal of Child Psychology and Psychiatry 1998;39:411-426] demonstrated that this explanation was not specific to ADHD but also applied to children with the associated disorders of oppositional defiant and conduct disorder. Other executive functions seem to be intact, while others, are deficient. It is argued here that the cognitive-energetic model is a useful guide for determining not only ADHD deficiencies and associated disorders but also linking human cognitive neuroscience studies with neurobiological models of ADHD using animals [Sadile AG. Multiple evidence of a segmental defect in the anterior forebrain of an animal model of hyperactivity and attention deficits. Neuroscience and Biobehavioral Reviews, in press; Sagvolden T, Sergeant JA. Attention-deficit hyperactivity disorder: from brain dysyfunctions to behaviour. Behavioural Brain Research 1998;94:1-10]. A plea for an integrated attack on this research problem is made and the suggestion that conceptual refinement between levels of analysis is essential for further fundamental work to succeed is offered here.

Animals↗
PubMed1997

Genetic and developmental factors in spontaneous selective attention: a study of normal twins.

The Spontaneous Selective Attention Task (SSAT) is a visual word identification task designed to measure the type of selective attention that occurs spontaneously when there are multiple stimuli, all potentially relevant, and insufficient time to process each of them fully. These are conditions which are common in everyday life. SSAT performance is measured by word identification accuracy, first under a baseline divided attention condition with no predictability, then under a selective attention condition with partial predictability introduced via word repetition. Accuracy to identify novel words in the upper location which becomes partially predictable (P words) vs. the lower location which remains non-predictable (N words) can be used to calculate a baseline performance index and a P/N ratio measure of selective attention. The SSAT has been shown to identify an attentional abnormality that may be useful in the development of an attentional endophenotype for family-genetic studies of schizophrenia. This study examined age and genetic effects on SSAT performance in normal children in order to evaluate whether the SSAT has the potential to qualify as a candidate endophenotype for schizophrenia in studies of at-risk children. A total of 59 monozygotic twin pairs and 33 same-sex dizygotic twin pairs ranging from 10 to 18 years of age were tested on the SSAT, a Continuous Performance Test. (CPT), a Span of Apprehension Test (SPAN) and a full-scale IQ test. Baseline performance on the SSAT, which was correlated with verbal IQ and SPAN performance, improved with age but showed no significant heritability. The P/N selectivity ratio was stable over the 10-18-year age range, was not significantly correlated with IQ, CPT, or SPAN performance, and its heritability was estimated to be 0.41. These findings suggest that the P/N selectivity ratio measured by the SSAT may be useful as a vulnerability marker in studies of children born into families segregating schizophrenia.

Adolescent↗
PubMed1998

Divided attention in major depression.

Depressive illness has been reported to interfere with effortful processing, which requires conscious attention. The aim of this study was to evaluate divided attention in depressed patients, as a function of the degree of difficulty of the task performed. Tasks designed to measure unimodal and bimodal reaction times were presented to 10 patients with major depression and 10 normal control subjects. Performance was evaluated both before treatment when the patients were depressed and after treatment when they had recovered. Unlike the unimodal trials, the bimodal reaction time tasks were designed to evaluate decision-making under conditions in which attention was divided between two perceptual channels. Reaction times were measured under two different conditions in order to assess the extent of the response delay induced by divided attention, modality shifting, and decision processing. During simple response tasks, the depressed patients displayed significantly greater lengthening of reaction times when their attention was divided between two perceptual channels. This cross-modal delay effect occurred both for stimuli of the same modality and when shifting between modalities. The cross-modal delay effect was evident only for the choice tests in both the depressed and the recovered patients, but only the recovered patients were as accurate as the control subjects. These results suggest that the need for decision processing in depressed patients results in a failure to allocate the mental resources required to complete interchannel shifting, when attention is divided between two perceptual channels. These data are consistent with the hypothesis that attentional regulation is impaired in major depression.

Adult↗
PubMed2000

A 5-arm maze enables parallel measures of sustained visuo-spatial attention and spatial working memory in mice.

A 5-arm maze has been developed to provide parallel tests of sustained visuo-spatial attention and spatial working memory in mice. C57Bl/6 mice were trained to select, either by immediate response (attention) or by delayed-matching response (working memory), one target arm among the five open arms. For attention testing, mice were first trained to acquire the basic task in which one randomly selected baited arm remained lit until a choice was made. Criterion of >80% correct with a response latency <5 s was attained in 52-56 trials. Following this, attention was tested by using trials wherein light signal durations of 2, 1 or 0.5 s were intermixed to vary attentional load. In the working memory test, mice were submitted to a forced visit to a randomly selected baited arm during a presentation phase. Following a variable retention interval (R.I.), mice were replaced into the maze and rewarded for choosing this arm. Criterion of >80% correct was attained in 35-40 trials and mice exhibited high levels of retention for R.I.s up to 4 h. Results validate the 5-arm maze for evaluation of both sustained visuo-spatial attention and spatial working memory in mice. Both the tasks are rapidly acquired and the 20% chance level provides high resolution for evaluating performance. This comparative strategy allows to dissociate attention and memory and to reveal deficits in these processes during ageing or in knockout strains. The high level of retention performance over R.I.s of 4 h enables studies using pharmacological treatments differentially affecting the acquisition, encoding, retention or retrieval phases of working memory. Furthermore, functional brain imaging studies may be used to identify neuronal networks which are differentially activated during these distinct phases.

Animals↗
PubMed2002

Multisensory attention and tactile information-processing.

Although a great deal is now known about the peripheral sensory mechanisms involved in tactile information processing [Ann Rev Psychol 1990;50:305], it is only more recently that we have started to gain a clearer understanding of the effects of selective attention on tactile perception [Front Biosci 2000;5:D894]. To date, the majority of this selective attention research has considered each modality in isolation. However, in order to deal with the multimodal selection problems of everyday life, we need to be able to coordinate our selective attention cross-modally [Philos Trans R Soc, Sec B 1998:353; Curr Biol 2000;10:R731]. In this review, I will highlight the results of behavioral studies demonstrating the existence of extensive cross-modal links in selective attention between touch, vision, audition, and even olfaction. In particular, the review is structured around two key research questions: First, "Can attention can be selectively directed to a particular sensory modality?", and second "Are there cross-modal links in spatial attention?". The results of recent neuroimaging studies that have started to elucidate some of the neural mechanisms underlying these cross-modal attentional effects are also discussed, and potential questions for future research outlined.

Attention↗
PubMed2003

Startle eyeblink modulation: detecting changes in directed attentional allocation during early preattentive processing.

Startle eyeblink modification was examined as a measure of allocation of attentional resources during active attention tasks in the early stage of information processing. Fifty-five participants were presented with a series of 250- and 40-ms tones of either high or low pitch which were followed by startle-eliciting stimuli at a lead interval of 120 ms. Attentional allocation was manipulated by instructing one group (Passive) to simply listen to the tones; the second group (Active 1) to count the number of low tones and the third group (Active 2) to count the long high-pitched tones and the short low-pitched tones. Startle eyeblink was significantly more inhibited for the Active 1 group than the Passive group (control) with no significant difference between the two directed attentional conditions (Active 1 and Active 2 groups). However, across the three attentional groups, the degree of startle eyeblink modulation appeared to reflect the degree of attention allocated to the task. The results support the utility of the startle probe in evaluating controlled attentional allocation during the early stages of information processing.

Acoustic Stimulation↗
PubMed2003

Local-global processing in early-onset schizophrenia: evidence for an impairment in shifting the spatial scale of attention.

In this study we report the results of two experiments on visual attention conducted with patients with early-onset schizophrenia. These experiments investigated the effect of irrelevant spatial-scale information upon the processing of relevant spatial-scale information, and the ability to shift the spatial scale of attention, across consecutive trials, between different levels of the hierarchical stimulus. Twelve patients with early-onset schizophrenia and matched controls performed local-global tasks under: (1) directed attention conditions with a consistency manipulation and (2) divided-attention conditions. In the directed-attention paradigm, the early-onset patients exhibited the normal patterns of global advantage and interference, and were not unduly affected by the consistency manipulation. Under divided-attention conditions, however, the early-onset patients exhibited a local-processing deficit. The source of this local processing deficit lay in the prolonged reaction time to local targets, when these had been preceded by a global target, but not when preceded by a local target. These findings suggest an impaired ability to shift the spatial scale of attention from a global to a local spatial scale in early-onset schizophrenia.

Adolescent↗
PubMed2001

Facilitation and inhibition mechanisms of human visuospatial attention in a non-search task.

This study investigated both facilitation and inhibition mechanisms of attentional orienting. Orienting consists in shifting the attentional focus in the visual field. To study the distribution of attentional resources, a two-choice-reaction time task with compatible and incompatible flankers was used. When an irrelevant flanker is presented adjacent to a target stimulus, interference is observed when the two stimuli are associated with conflicting responses (flanker effect). Orienting of attention, at cued and uncued flanker locations, was manipulated by an exogenous cueing paradigm (automatic capture following a peripheral visual transient). Results showed that orienting of attention at cued distractor location produces an increased flanker effect as compared to the no-cue condition. In contrast, the flanker effect was absent when the attentional focus shifted to the uncued distractor location. These effects were interpreted in terms of facilitation and inhibition processes of visuospatial selection by early attentional competition models.

Analysis of Variance↗
PubMed2002

Spatial direction of attention enhances right hemispheric event-related gamma-band synchronization in humans.

Gamma-band oscillations are related to sensory information processing and attention. To further illuminate the relationship of gamma-band activity and selective somatic attention, we have studied the effects of direction of attention on the stimuli of somatosensory evoked potentials. Responses during focused attention to stimulation of the right median nerve and ignored stimulation at the right tibial nerve were compared with responses of ignored stimulation of the right median nerve but focused attention to stimulation at the right tibial nerve. Subtraction of the data demonstrated a significant predominantly right hemispheric event-related synchronization in the gamma-band by attention to the right median nerve in the time period between 280 and 325 ms post-stimulus. This finding implicates the involvement of a right temporoparietal network in selective spatial attention.

Adult↗
PubMedDate not supplied

Behavioral assessments of learning and attention in rats exposed perinatally to 3,3',4,4',5-pentachlorobiphenyl (PCB 126)

Evidence from humans suggests that cognitive dysfunction may result from perinatal exposure to polychlorinated biphenyls (PCBs), and the results of some animal research with PCBs have been interpreted in terms of possible impairment of attention. Long-Evans rats were fed 3,3',4,4',5-pentachlorobiphenyl (PCB 126), a coplanar congener, at doses of 0.25 or 1 microgram/kg/day [corrected] throughout gestation and nursing. Male offspring of these rats were trained as adults to perform 2 tests of attention for food reward. First, a cued target-detection task, modeled after Posner's covert orienting method for humans, was used to assess visuospatial attention. In this task, a visual target stimulus was presented in 1 visual hemifield on each trial, preceded either by a valid cue, an invalid cue, or no cue. A valid cue appeared in the same hemifield as the target, and an invalid cue appeared in the opposite hemifield. As expected, valid cues increased accuracy and speed of target detection and invalid cues decreased accuracy and speed; moreover, these effects were systematically related to changes in cue intensity and target duration. However, perinatal exposure to PCB 126 did not affect acquisition or performance of this task. The second task assessed sustained attention by means of a signal detection method in which a brief, spatially-constant but temporally unpredictable, visual signal indicated which of 2 responses would yield food. Varying the intensity of the signal greatly affected the probability of correctly reporting the signal. Perinatal exposure to PCB 126 did not affect acquisition of the response rule or performance of the task. Finally, all rats were challenged with chlordiazepoxide (CDP) at doses of 0, 3, 5, 8, or 12 mg/kg SC, 20 min before testing in the sustained attention task. In control rats, low doses (3, 5, and 8 mg/kg) of CDP reduced accuracy at low signal intensities only, suggesting an increase in visual threshold. The high dose of CDP reduced accuracy at all signal intensities and increased the false-alarm rate as well, suggesting an impairment of attention. The rats exposed perinatally to PCB 126 at 0.25 micrograms/kg [corrected] were unaffected by CDP, and those exposed to PCB 126 at 1 microgram/kg [corrected] showed a smaller decrement in performance after CDP than did the controls. Taken together, these data provide little support for the possibility that perinatal exposure to PCB 126 causes deficits in attention, but suggest that PCB 126 may alter GABA-mediated pathways in the CNS during development.

Animals↗
PubMed1998

Attention and perceptual learning modulate contextual influences on visual perception.

Brightness discrimination thresholds and facilitation by lateral interaction were measured in five human observers and two monkeys. The subjects judged the brightness of one of four peripherally seen lines against a reference. This experiment was performed both when the observer was cued to the position of the test line (focused attention) and when there was no cue (distributed attention). Discrimination was better with focused than with distributed attention. When the test line had a collinear flank, its brightness was enhanced; this enhancement was four times more prominent with distributed than with focused attention. After training, thresholds improved and collinear facilitation decreased under distributed but not under focused attention. The findings show that there are fewer benefits from contextual interaction once attention is directed toward a visual location, and that the attentional effects are subject to training.

Adult↗
PubMed2004

Effects of cholinergic enhancement on visual stimulation, spatial attention, and spatial working memory.

We compared behavioral and neural effects of cholinergic enhancement between spatial attention, spatial working memory (WM), and visual control tasks, using fMRI and the anticholinesterase physostigmine. Physostigmine speeded responses nonselectively but increased accuracy selectively for attention. Physostigmine also decreased activations to visual stimulation across all tasks within primary visual cortex, increased extrastriate occipital cortex activation selectively during maintained attention and WM encoding, and decreased parietal activation selectively during maintained attention. Finally, lateralization of occipital activation as a function of the visual hemifield toward which attention or memory was directed was decreased under physostigmine. In the case of attention, this effect correlated strongly with a decrease in a behavioral measure of selective spatial processing. Our results suggest that, while cholinergic enhancement facilitates visual attention by increasing activity in extrastriate cortex generally, it accomplishes this in a manner that reduces expectation-driven selective biasing of extrastriate cortex.

Acetylcholine↗
PubMed2002

Tracking the time-course of attentional involvement in spatial working memory: an event-related potential investigation.

Spatial working memory is a cognitive brain mechanism that enables the temporary maintenance and manipulation of spatial information. Recent neuroimaging and behavioral studies have led to the proposal that directed spatial attention is the mechanism by which location information is maintained in spatial working memory. Yet it is unclear whether attentional involvement is required throughout the period of active maintenance or is only invoked during discrete task-phases such as mnemonic encoding. In the current study, we aimed to track the time-course of attentional involvement during spatial working memory by recording event-related brain potentials (ERPs) from healthy volunteers. In Experiment 1, subjects performed a delayed-recognition task. Each trial began with the presentation of a brief stimulus (S1) that indicated the relevant location that subjects were to maintain in working memory. A 4.8-5.3 sec delay interval followed during which a single task-irrelevant probe was presented. The delay interval concluded with a test item (S2) to which subjects made a response indicating whether the S2-location was the same as the S1-memory location. To determine if attention was differentially engaged during discrete phases of the trial, task-irrelevant probes were presented early (400-800 msec following S1-offset) or late (2600-3000 msec following S1-offset) during the delay interval. Sensory-evoked ERPs (P1 and N1) elicited by these irrelevant probes showed attention-like modulations with greater amplitude responses for probes occurring at the S1-memory locations in comparison to probes presented at other locations. This pattern was obtained for both early- and late-delay probes. Probe-evoked activity during delayed-recognition trials was similar to activity observed when spatial attention was explicitly focused on a location in visual space (Experiment 2). These results are consistent with a model of spatial working memory in which perceptual level selective attention is utilized throughout the entire period of active maintenance to keep relevant spatial information in mind.

Adolescent↗