Biomedical subjects

J Driver

Publications and source records attributed to J Driver.

At least 19 recordsLinked to original sources

PubMed2001

Tactile-visual links in exogenous spatial attention under different postures: convergent evidence from psychophysics and ERPs.

Tactile-visual links in spatial attention were examined by presenting spatially nonpredictive tactile cues to the left or right hand, shortly prior to visual targets in the left or right hemifield. To examine the spatial coordinates of any crossmodal links, different postures were examined. The hands were either uncrossed, or crossed so that the left hand lay in the right visual field and vice versa. Visual judgments were better on the side where the stimulated hand lay, though this effect was somewhat smaller with longer intervals between cue and target, and with crossed hands. Event-related brain potentials (ERPs) showed a similar pattern. Larger amplitude occipital N1 components were obtained for visual events on the same side as the preceding tactile cue, at ipsilateral electrode sites. Negativities in the Nd2 interval at midline and lateral central sites, and in the Nd1 interval at electrode Pz, were also enhanced for the cued side. As in the psychophysical results, ERP cueing effects during the crossed posture were determined by the side of space in which the stimulated hand lay, not by the anatomical side of the initial hemispheric projection for the tactile cue. These results demonstrate that crossmodal links in spatial attention can influence sensory brain responses as early as the N1, and that these links operate in a spatial frame-of-reference that can remap between the modalities across changes in posture.

Adult↗

PubMed2001

Seen gaze-direction modulates fusiform activity and its coupling with other brain areas during face processing.

Gaze-contact is often a preliminary to social interaction and so constitutes a signal for the allocation of processing resources to the gazing face. We investigated how gaze direction influences face processing in an fMRI study, where seen gaze and head direction could independently be direct or deviated. Direct relative to averted gaze elicited stronger activation for faces in ventral occipitotemporal cortices around the fusiform gyrus, regardless of head orientation. Moreover, direct gaze led to greater correlation between activity in the fusiform and the amygdala, a region associated with emotional responses and stimulus saliency. By contrast, faces with averted gaze (again, regardless of head orientation) yielded increased correlation between activity in the fusiform and the intraparietal sulcus, a region associated with shifting attention to the periphery.

Adult↗

PubMed2001

Functional magnetic resonance imaging and evoked potential correlates of conscious and unconscious vision in parietal extinction patients.

We describe recent functional magnetic resonance imaging (fMRI) and event-related potential (ERP) studies of visual extinction in patients with right parietal damage who can detect isolated visual stimuli on either side, yet often miss contralesional (left) stimuli during bilateral stimulation. We consider the neural fate of such extinguished visual stimuli and how neural responses differ for consciously detected versus extinguished stimuli. fMRI findings indicate that extinguished stimuli evoke activity in striate and ventral extrastriate visual cortex, despite escaping awareness. Activations for extinguished stimuli can be found even in category-specific (face-responsive) areas of the fusiform gyrus. On the other hand, activations in visual cortex are stronger for consciously detected versus extinguished stimuli, with parietal and frontal areas of the intact left hemisphere also implicated in this comparison. Recent ERP data likewise suggest differential neural responses for consciously detected versus extinguished stimuli. We discuss these findings in relation to current speculations about the neural basis of conscious and unconscious perception.

Attention↗

PubMed2001

Multimodal mechanisms of attention related to rates of spatial shifting in vision and touch.

Covert attention can be directed spatially in several different sensory modalities (e.g. vision and touch). Recent psychological experiments indicate the existence of crossmodal links in spatial attention, but their neural basis in humans remains underspecified. We used positron emission tomography (PET) to assess the role of stimulus modality in the activity of brain regions involved in different rates of spatial attention shifting. A 2 x 2 factorial design manipulated the rate (high versus low) of spatial attention shifts between left and right hemifields, plus the sensory modality (vision versus touch) of stimulation. Two brain regions showed activations related to attentional shift-rate, independent of the stimulated modality: these were the right frontopolar gyrus, and the right posterior superior temporal sulcus (STS). The anterior area showed higher blood flow with the high rate of shifts in spatial attention, while the posterior area showed higher flow during the low rate conditions, where attention was sustained for longer on one side. No area showed a significant rate effect in one modality without an effect in the second modality. These results demonstrate multimodal roles for the activated brain regions in relation to the rate of spatial attention shifting, plus right-hemisphere dominance for this. They also suggest that anterior and posterior regions of the spatial-attention network play different roles in attention shifting.

Adult↗

PubMed2001

Spatial deployment of attention within and across hemifields in an auditory task.

Research on visual attention has demonstrated that covert attention can be focused on particular locations within one hemifield, but that a specific "meridian" cost may also be found for shifting attention between hemifields. These issues have received less consideration for audition, even though reliable behavioral measures for the effects of spatial attention on hearing are now available. We examined the spatial distribution of covert attention in an auditory task following spatially non-predictive peripheral auditory cues (which should induce exogenous attention shifts), or following symbolic central cues that predicted the likely location for the auditory target (to induce endogenous attention shifts). In both cases, we found that attention can be focused not only on one hemifield versus another, but also within one hemifield in an auditory task. However, there was no unequivocal evidence for a meridian effect in audition.

Adult↗

PubMed2001

Cross-modal links in endogenous spatial attention are mediated by common external locations: evidence from event-related brain potentials.

Recent behavioural and event-related potential (ERP) studies reported cross-modal links in spatial attention between vision, audition and touch. Such links could reflect differences in hemispheric-activation levels associated with spatial attention to one side, or more abstract spatial reference-frames mediating selectivity across modalities. To distinguish these hypotheses, ERPs were recorded to lateral tactile stimuli, plus visual (experiment 1) or auditory stimuli (experiment 2), while participants attended to the left or right hand to detect infrequent tactile targets, and ignored other modalities. In separate blocks, hands were either in a crossed or uncrossed posture. With uncrossed hands, visual stimuli on the tactually attended side elicited enhanced N1 and P2 components at occipital sites, and an enhanced negativity at midline electrodes, reflecting cross-modal links in spatial attention from touch to vision. Auditory stimuli at tactually attended locations elicited an enhanced negativity overlapping with the N1 component, reflecting cross-modal links from touch to audition. An analogous pattern of results arose for crossed hands, with tactile attention enhancing auditory or visual responses on the side where the attended hand now lay (i.e. in the opposite visual or auditory hemifield to that enhanced by attending the same hand when uncrossed). This suggests that cross-modal attentional links are not determined by hemispheric projections, but by common external locations. Unexpectedly, somatosensory ERPs were strongly affected by hand posture in both experiments, with attentional effects delayed and smaller for crossed hands. This may reflect the combined influence of anatomical and external spatial codes within the tactile modality, while cross-modal links depend only on the latter codes.

Acoustic Stimulation↗

PubMed2001

Perceptual awareness and its loss in unilateral neglect and extinction.

We review recent evidence from studies of patients with unilateral neglect and/or extinction, who suffer from a loss of awareness for stimuli towards the affected side of space. We contrast their deficit with the effects of damage to primary sensory areas, noting that such areas can remain structurally intact in neglect, with lesions typically centred on the right inferior parietal lobe. In keeping with preservation of initial sensory pathways, many recent studies have shown that considerable residual processing can still take place for neglected or extinguished stimuli, yet without reaching the patient's awareness. This ranges from preserved visual grouping processes through to activation of identity, semantics and emotional significance. Similarly to 'preattentive' processing in normals, such residual processing can modulate what will enter the patient's awareness. Recent studies have used measures such as ERPs and fMRI to determine the neural correlates of conscious versus unconscious perception in the patients, which in turn can be related to the anatomy of their lesions. We relate the patient findings to neurophysiological data from areas in the monkey parietal lobe, which indicate that these serve as cross-modal and sensorimotor interfaces highlighting currently relevant locations as targets for intentional action. We speculate on the special role such brain regions may play in perceptual awareness, seeking to explain how damage to a system which appears primarily to code space could eliminate awareness even for non-spatial stimulus properties at affected locations. This may relate to the extreme nature of 'winner-takes-all' functions within the parietal lobe, and their correspondingly strong influence on other brain areas.

Awareness↗

PubMed2001

Segmentation, attention and phenomenal visual objects.

Issues concerning selective attention provoke new questions about visual segmentation, and vice-versa. We illustrate this by describing our recent work on grouping under conditions of inattention, on change blindness for background events and the residual processing of undetected background changes, on modal versus amodal completion in visual search, and the differential effects of these two forms of completion on attentional processes, and on attentional modulation of lateral interactions thought to arise in early visual cortex. Many of these results indicate that segmentation processes substantially constrain attentional processes, but the reverse influence is also apparent, suggesting an interactive architecture. We discuss how the 'proto-objects' revealed by studies of segmentation and attention (i.e. the segmented perceptual units which constrain selectivity) may relate to other object-based notions in cognitive science, and we wrestle with their relation to phenomenal visual awareness.

Attention↗

PubMed2001

Do neck-proprioceptive and caloric-vestibular stimulation influence covert visual attention in normals, as they influence visual neglect?

Neck-proprioceptive and caloric-vestibular stimulation have been shown to ameliorate the spatial bias exhibited by patients suffering from unilateral visual neglect. These interventions might in principle have their effect by biasing covert attention towards the neglected side. If so, the same interventions should also modulate covert attention in neurologically-intact subjects. However, we demonstrate here that neither neck-proprioception (vibration of left neck muscles) nor caloric-vestibular stimulation (injection of iced water into the left ear) affect covert visual attention in healthy individuals. These results from normals may distinguish between different accounts for unilateral neglect in patients. In particular, they argue against explanations of neglect solely in terms of a pathological misperception of body orientation within an otherwise normal neural representation of space.

Adult↗

PubMed2001

Spatial working memory deficit in unilateral neglect.

Based on the similarity of brain areas lesioned in neglect and those activated by spatial working memory (WM) tasks in normals, we hypothesized that neglect may involve spatial WM impairments. A left neglect patient with right inferior frontal and basal ganglia damage performed cancellation tasks, making either highly visible marks (to provide a reminder of visited items), or invisible marks (so only spatial WM could represent cancelled items). Invisible marks led to repeated cancellations for targets that differed only in location, but not for targets with memorable unique identities, suggesting a deficit of spatial WM, with non-spatial WM spared. Neglect was greater for cancellation with invisible marks, consistent with a role for deficient spatial WM in cancellation deficits, but contrary to account solely in terms of attention capture by salient visible marks made in ipsilesional space.

Attention↗

PubMed2001

Reaching with a tool extends visual-tactile interactions into far space: evidence from cross-modal extinction.

Several recent studies have shown cross-modal visual-tactile extinction in patients with right hemisphere lesions. In the present case, patient BV, a visual stimulus close to the right hand extinguished awareness of a touch on the left hand that would otherwise have been felt. Such extinction was reduced if the right visual stimulus was placed more distant from the patient's hand in the radial plane. However, when the patient held sticks in both hands, so that a far right visual stimulus was now at the end of the "tool" in his right hand, cross-modal extinction from this far stimulus increased. This effect depended on the patient holding a stick that reached to the position of the far visual stimulus; a similar large stick, but not connected with the patient's hand and laying passively on the right, had no effect. Wielding the stick induced a re-mapping of space, so that the far light became treated as near (and reachable by) the hand, thus modifying the spatial nature of cross-modal extinction. This may relate to the properties of multimodal neurons as found in the monkey intraparietal sulcus.

Aged↗

PubMed2001

Effects of attention and emotion on face processing in the human brain: an event-related fMRI study.

We used event-related fMRI to assess whether brain responses to fearful versus neutral faces are modulated by spatial attention. Subjects performed a demanding matching task for pairs of stimuli at prespecified locations, in the presence of task-irrelevant stimuli at other locations. Faces or houses unpredictably appeared at the relevant or irrelevant locations, while the faces had either fearful or neutral expressions. Activation of fusiform gyri by faces was strongly affected by attentional condition, but the left amygdala response to fearful faces was not. Right fusiform activity was greater for fearful than neutral faces, independently of the attention effect on this region. These results reveal differential influences on face processing from attention and emotion, with the amygdala response to threat-related expressions unaffected by a manipulation of attention that strongly modulates the fusiform response to faces.

Adult↗

PubMed2001

Superior visual search in autism.

Children with a diagnosis of autism and normally developing children, matched for age and general ability, were tested on a series of visual search tasks in 2 separate experiments. The children with autism performed better than the normally developing children on difficult visual search tasks. This result occurred regardless of whether the target was uniquely defined by a single feature or a conjunction of features, as long as ceiling effects did not mask the difference. Superior visual search performance in autism can be seen as analogous to other reports of enhanced unique item detection in autism. Unique item detection in autism is discussed in the light of mechanisms proposed to be involved in normal visual search performance.

Aptitude↗

PubMed2001

Shape-coding in IT cells generalizes over contrast and mirror reversal, but not figure-ground reversal.

We assessed how the visual shape preferences of neurons in the inferior temporal cortex of awake, behaving monkeys generalized across three different stimulus transformations. Stimulus-preferences of particular cells among different polygon displays were correlated across reversed contrast polarity or mirror reversal, but not across figure-ground reversal. This corresponds with psychological findings on human shape judgments. Our results imply that neurons in inferior temporal cortex respond to components of visual shape derived only after figure-ground assignment of contours, not to the contours themselves.

Animals↗

PubMed2001

Impaired spatial working memory across saccades contributes to abnormal search in parietal neglect.

Visual neglect of left space following right parietal damage in humans involves a lateral bias in attention, apparent in many search tasks. We hypothesized that parietal neglect may also involve a failure to remember which locations have already been examined during visual search: an impairment in retaining searched locations across saccades. Using a new paradigm, we monitored gaze during search, while simultaneously probing whether observers judged they had found a new target, or judged instead that they were re-fixating a previously examined target. A patient with left neglect following focal right parietal infarction repeatedly re-fixated right locations. Critically, he often failed to remember that these locations had already been searched, treating old targets as new discoveries at an abnormal rate. In comparison, healthy age-matched control subjects rarely re-fixated targets, and mistook old targets as new targets even more rarely. The frequency of such mistakes in the parietal patient, for different conditions, correlated with the severity of his neglect. Control experiments indicated no perceptual localization deficit in non-search tasks. These results suggest a deficit in retaining searched locations across saccades in parietal neglect, in addition to the lateral spatial bias. Moreover, the former deficit exacerbates the latter, such that patients do not realize that the rightward locations favoured by their bias have already been examined during previous fixations and, for this reason, they saccade back to them repeatedly. The combination of the two deficits (a lateral bias plus a deficit in retaining locations already searched) may thus explain the pathological pattern of search that characterizes parietal neglect: why stimuli on the right are re-examined recursively, as if being searched for the first time, and hence why stimuli on the left continue to be ignored even with unlimited viewing time. These proposals accord with recent electrophysiological and functional imaging data, demonstrating posterior parietal involvement in the retention of target locations across saccades.

Aged↗

PubMed2001

The cost of expecting events in the wrong sensory modality.

We examined the effects of modality expectancy on human performance. Participants judged azimuth (left vs. right location) for an unpredictable sequence of auditory, visual, and tactile targets. In some blocks, equal numbers of targets were presented in each modality. In others, the majority (75%) of the targets were presented in just one expected modality. Reaction times (RTs) for targets in an unexpected modality were slower than when that modality was expected or when no expectancy applied. RT costs associated with shifting attention from the tactile modality were greater than those for shifts from either audition or vision. Any RT benefits for the most likely modality were due to priming from an event in the same modality on the previous trial, not to the expectancy per se. These results show that stimulus-driven and expectancy-driven effects must be distinguished in studies of attending to different sensory modalities.

Adult↗

PubMed2001

A selective review of selective attention research from the past century.

Research on attention is concerned with selective processing of incoming sensory information. To some extent, our awareness of the world depends on what we choose to attend, not merely on the stimulation entering our senses. British psychologists have made substantial contributions to this topic in the past century. Celebrated examples include Donald Broadbent's filter theory of attention, which set the agenda for most subsequent work; and Anne Treisman's revisions of this account, and her later feature-integration theory. More recent contributions include Alan Allport's prescient emphasis on the relevance of neuroscience data, and John Duncan's integration of such data with psychological theory. An idiosyncratic but roughly chronological review of developments is presented, some practical and clinical implications are briefly sketched, and future directions suggested. One of the biggest changes in the field has been the increasing interplay between psychology and neuroscience, which promises much for the future. A related change has been the realization that selection attention is best thought of as a broad topic, encompassing a range of selective issues, rather than as a single explanatory process.

Attention↗

PubMed2000

Vision and touch through the looking glass in a case of crossmodal extinction.

When observing ourselves in a mirror, we see our body and adjacent objects (e.g. a comb or razor) projecting the image of distant objects. Are these recoded by the brain as reflecting stimuli in peripersonal space? To address this, we exploited the neuropsychological phenomenon of crossmodal, visual-tactile extinction, as shown by patient BV following right-hemisphere stroke. In such crossmodal extinction, a right visual event impairs the perception of a simultaneous left tactile event. In BV, the right visual stimulus (an LED flash) induced more extinction of touch on the contralesional left hand when presented near the ipsilesional right hand, than when distant from it. This agrees with previous data in patients and monkeys showing that visual-tactile interactions are strongest within peripersonal space. Crucially, we also found that an ipsilesional flash produced more extinction when observed as the distant mirror-reflection of an LED that lay close to the ipsilesional hand, rather than as a distant LED flash projecting an equivalent visual image directly. This suggests that in BV, seeing his own hand via a mirror activates a representation of peripersonal space around that hand, not of the extrapersonal space suggested by the distant visual image in the mirror. We discuss the possible neural basis of interpreting mirror reflections.

Aged↗