Biomedical subjects

J Driver

Publications and source records attributed to J Driver.

At least 19 recordsLinked to original sources

PubMed1999

Does auditory attention shift in the direction of an upcoming saccade?

In a series of experiments, we examined whether auditory attention shifts in the direction of an upcoming saccade, as recently reported for visual attention. Normal listeners made speeded discriminations for the elevation (up versus down) of abrupt sounds, regardless of their laterality. Each sound was presented around the time that a lateral saccade was made. Auditory elevation discriminations were reliably faster when the saccade was made towards the side of the auditory probe rather than away. Furthermore, an auditory probe on one side speeded up centrally-cued saccades made in that direction, although sounds did not influence saccades to peripheral visual events. The latter visual events were insufficient to affect hearing unless a saccade was made towards them. A further study showed that fixating towards or away from sounds, rather than saccading, could also affect elevation judgements, with poorer performance when fixating away. However, the influence of an upcoming saccade upon hearing could not be reduced to this fixation effect, since the saccade influence was found even for sounds which terminated before any shift in fixation began. Taken together, our results imply that the direction of an upcoming saccade can affect hearing, as can eye-position.

Adolescent↗

PubMed1999

Contrast polarity and face recognition in the human fusiform gyrus.

Functional imaging has revealed face-responsive visual areas in the human fusiform gyrus, but their role in recognizing familiar individuals remains controversial. Face recognition is particularly impaired by reversing contrast polarity of the image, even though this preserves all edges and spatial frequencies. Here, combined influences of familiarity and priming on face processing were examined as contrast polarity was manipulated. Our fMRI results show that bilateral posterior areas in fusiform gyrus responded more strongly for faces with positive than with negative contrast polarity. An anterior, right-lateralized fusiform region is activated when a given face stimulus becomes recognizable as a well-known individual.

Adult↗

PubMed1999

The neural consequences of conflict between intention and the senses.

Normal sensorimotor states involve integration of intention, action and sensory feedback. An example is the congruence between motor intention and sensory experience (both proprioceptive and visual) when we move a limb through space. Such goal-directed action necessitates a mechanism that monitors sensorimotor inputs to ensure that motor outputs are congruent with current intentions. Monitoring in this sense is usually implicit and automatic but becomes conscious whenever there is a mismatch between expected and realized sensorimotor states. To investigate how the latter type of monitoring is achieved we conducted three fully factorial functional neuroimaging experiments using PET measures of relative regional cerebral blood flow with healthy volunteers. In the first experiment subjects were asked to perform Luria's bimanual co-ordination task which involves either in-phase (conditions 1 and 3) or out-of-phase (conditions 2 and 4) bimanual movements (factor one), while looking towards their left hand. In half of the conditions (conditions 3 and 4) a mirror was used that altered visual feedback (factor two) by replacing their left hand with the mirror image of their right hand. Hence (in the critical condition 4) subjects saw in-phase movements despite performing out-of-phase movements. This mismatch between intention, proprioception and visual feedback engendered cognitive conflict. The main effect of out-of-phase movements was associated with increased neural activity in posterior parietal cortex (PPC) bilaterally [Brodmann area (BA) 40, extending into BA 7] and dorsolateral prefrontal cortex (DLPFC) bilaterally (BA 9/46). The main effect of the mirror showed increased neural activity in right DLPFC (BA 9/ 46) and right superior PPC (BA 7) only. Analysis of the critical interaction revealed that the mismatch condition led to a specific activation in the right DLPFC alone (BA 9/46). Study 2, using an identical experimental set-up but manipulating visual feedback from the right hand (instead of the left), subsequently demonstrated that this right DLPFC activation was independent of the hand attended. Finally, study 3 removed the motor intentional component by moving the subjects' hand passively, thus engendering a mismatch between proprioception and vision only. Activation in the right lateral prefrontal cortex was now more ventral than in studies 1 or 2 (BA 44/45). A direct comparison of studies 1 and 3 (which both manipulated visual feedback from the left hand) confirmed that a ventral right lateral prefrontal region is primarily activated by discrepancies between signals from sensory systems, while a more dorsal area in right lateral prefrontal cortex is activated when actions must be maintained in the face of a conflict between intention and sensory outcome.

Adult↗

PubMed1998

Phasic alerting of neglect patients overcomes their spatial deficit in visual awareness.

Patients with extensive damage to the right hemisphere of their brain often exhibit unilateral neglect of the left side of space. The spatial attention of these patients is strongly biased towards the right, so their awareness of visual events on the left is impaired. Extensive right-hemisphere lesions also impair tonic alertness (the ability to maintain arousal). This nonspatial deficit in alertness is often considered to be a different problem from spatial neglect, but the two impairments may be linked. If so, then phasically increasing the patients' alertness should temporarily ameliorate their spatial bias in awareness. Here we provide evidence to support this theory. Right-hemisphere-neglect patients judged whether a visual event on the left preceded or followed a comparable event on the right. They became aware of left events half a second later than right events on average. This spatial imbalance in the time course of visual awareness was corrected when a warning sound alerted the patients phasically. Even a warning sound on the right accelerated the perception of left visual events in this way. Nonspatial phasic alerting can thus overcome disabling spatial biases in perceptual awareness after brain injury.

Acoustic Stimulation↗

PubMed1998

Cross-modal links in spatial attention.

A great deal is now known about the effects of spatial attention within individual sensory modalities, especially for vision and audition. However, there has been little previous study of possible cross-modal links in attention. Here, we review recent findings from our own experiments on this topic, which reveal extensive spatial links between the modalities. An irrelevant but salient event presented within touch, audition, or vision, can attract covert spatial attention in the other modalities (with the one exception that visual events do not attract auditory attention when saccades are prevented). By shifting receptors in one modality relative to another, the spatial coordinates of these cross-modal interactions can be examined. For instance, when a hand is placed in a new position, stimulation of it now draws visual attention to a correspondingly different location, although some aspects of attention do not spatially remap in this way. Cross-modal links are also evident in voluntary shifts of attention. When a person strongly expects a target in one modality (e.g. audition) to appear in a particular location, their judgements improve at that location not only for the expected modality but also for other modalities (e.g. vision), even if events in the latter modality are somewhat more likely elsewhere. Finally, some of our experiments suggest that information from different sensory modalities may be integrated preattentively, to produce the multimodal internal spatial representations in which attention can be directed. Such preattentive cross-modal integration can, in some cases, produce helpful illusions that increase the efficiency of selective attention in complex scenes.

Attention↗

PubMed1998

Motor role of human inferior parietal lobe revealed in unilateral neglect patients.

The exact role of the parietal lobe in spatial cognition is controversial. One influential hypothesis proposes that it subserves spatial perception, whereas other accounts suggest that its primary role is to direct spatial movement. For humans, it has been suggested that these functions may be divided between inferior and superior parietal lobes, respectively. In apparent support of a purely perceptual function for the inferior parietal lobe (IPL), patients with lesions to this structure, particularly in the right hemisphere, exhibit unilateral spatial neglect (deficient awareness for the side of space opposite to that of their lesion). Here we show that patients with right IPL lesions also have a specific difficulty in initiating leftward movements towards visual targets on the left side of space. This motor impairment was not found in neglect patients with frontal lesions, contrary to previous proposals that motor aspects of neglect are particularly associated with anterior damage. Our results suggest that the human IPL operates as a sensorimotor interface, rather than subserving only perceptual functions.

Cerebrovascular Disorders↗

PubMed1998

Inhibition of return following an auditory cue. The role of central reorienting events.

It is currently controversial whether auditory events produce inhibition of return (IOR). Although some authors argue that this can arise, others propose that peripheral auditory cues do not produce the characteristic IOR pattern of delayed detection latencies for ipsilaterally presented auditory or visual targets, unless a saccade is made to the cued location. We suggest that these previous discrepancies may depend on whether attention is reoriented centrally following the peripheral sound. We presented spatially uninformative peripheral auditory cues prior to visual targets requiring speeded detection responses. IOR was found in the absence of eye movements, provided an auditory reorienting event was presented at central fixation between onset of the peripheral cue and the subsequent target, but not when the central reorienting event was visual. A subsequent experiment demonstrated that auditory IOR between successive targets is similarly significantly reduced in the absence of an appropriate central reorienting event. These results imply that auditory stimuli can induce IOR directly. Previous failures to demonstrate IOR following auditory cues may have been due to an opposing influence of long-lasting attentional facilitation at the cued location, rather than to the putative inability of auditory stimuli to engage oculomotor processes generating IOR.

Acoustic Stimulation↗

PubMed1998

Crossmodal attention.

Most selective attention research has considered only a single sensory modality at a time, but in the real world, our attention must be coordinated crossmodally. Recent studies reveal extensive crossmodal links in attention across the various modalities (i.e. audition, vision, touch and proprioception). Attention typically shifts to a common location across the modalities, despite the vast differences in their initial coding of space. These spatial synergies in attention can be maintained even when receptors are realigned across the modalities by changes in posture. Some crossmodal integration can arise preattentively. The mechanisms underlying these crossmodal links can be examined in a convergent manner by integrating behavioural studies of normal subjects and brain-damaged patients with neuroimaging and neurophysiological studies.

Attention↗

PubMed1998

Parietal neglect and visual awareness.

The last decade has seen a resurgence of interest in the neural correlates of conscious vision, with most discussion focused on the 'blindsight' that can follow damage to primary visual cortex, in the occipital lobe. We suggest that new insights into the neural basis of visual awareness may be gleaned from a different neuropsychological phenomenon, namely visual 'neglect' after injury to regions in the parietal lobe. Neglect provides several revealing contrasts with occipital blindsight. Here we summarise four key findings. First, unlike the deficits caused by damage to primary visual cortex, the loss of awareness in parietal neglect is characteristically not strictly retinotopic. Second, visual segmentation processes are preserved in neglect, and can influence what will reach the patient's awareness. Third, extensive unconscious processing takes place for those stimuli on the neglected side which escape awareness, including some degree of object identification. Finally, parietal damage affects initial stages of motor planning as well as perception. These findings are consistent with recent data on single-cell activity in the monkey brain. They also suggest why areas in the inferior parietal lobe may play a prominent role in visual awareness.

Animals↗

PubMed1998

Covert visual attention modulates face-specific activity in the human fusiform gyrus: fMRI study.

Several lines of evidence demonstrate that faces undergo specialized processing within the primate visual system. It has been claimed that dedicated modules for such biologically significant stimuli operate in a mandatory fashion whenever their triggering input is presented. However, the possible role of covert attention to the activating stimulus has never been examined for such cases. We used functional magnetic resonance imaging to test whether face-specific activity in the human fusiform face area (FFA) is modulated by covert attention. The FFA was first identified individually in each subject as the ventral occipitotemporal region that responded more strongly to visually presented faces than to other visual objects under passive central viewing. This then served as the region of interest within which attentional modulation was tested independently, using active tasks and a very different stimulus set. Subjects viewed brief displays each comprising two peripheral faces and two peripheral houses (all presented simultaneously). They performed a matching task on either the two faces or the two houses, while maintaining central fixation to equate retinal stimulation across tasks. Signal intensity was reliably stronger during face-matching than house matching in both right- and left-hemisphere predefined FFAs. These results show that face-specific fusiform activity is reduced when stimuli appear outside (vs. inside) the focus of attention. Despite the modular nature of the FFA (i.e., its functional specificity and anatomic localization), face processing in this region nonetheless depends on voluntary attention.

Adolescent↗

PubMed1998

Cross-modal links in exogenous covert spatial orienting between touch, audition, and vision.

Three experiments investigated cross-modal links between touch, audition, and vision in the control of covert exogenous orienting. In the first two experiments, participants made speeded discrimination responses (continuous vs. pulsed) for tactile targets presented randomly to the index finger of either hand. Targets were preceded at a variable stimulus onset asynchrony (150, 200, or 300 msec) by a spatially uninformative cue that was either auditory (Experiment 1) or visual (Experiment 2) on the same or opposite side as the tactile target. Tactile discriminations were more rapid and accurate when cue and target occurred on the same side, revealing cross-modal covert orienting. In Experiment 3, spatially uninformative tactile cues were presented prior to randomly intermingled auditory and visual targets requiring an elevation discrimination response (up vs. down). Responses were significantly faster for targets in both modalities when presented ipsilateral to the tactile cue. These findings demonstrate that the peripheral presentation of spatially uninformative auditory and visual cues produces cross-modal orienting that affects touch, and that tactile cues can also produce cross-modal covert orienting that affects audition and vision.

Adolescent↗

PubMed1998

Auditory and audiovisual inhibition of return.

Two experiments examined any inhibition-of-return (IOR) effects from auditory cues and from preceding auditory targets upon reaction times (RTs) for detecting subsequent auditory targets. Auditory RT was delayed if the preceding auditory cue was on the same side as the target, but was unaffected by the location of the auditory target from the preceding trial, suggesting that response inhibition for the cue may have produced its effects. By contrast, visual detection RT was inhibited by the ipsilateral presentation of a visual target on the preceding trial. In a third experiment, targets could be unpredictably auditory or visual, and no peripheral cues intervened. Both auditory and visual detection RTs were now delayed following an ipsilateral versus contralateral target in either modality on the preceding trial, even when eye position was monitored to ensure central fixation throughout. These data suggest that auditory target-target IOR arises only when target modality is unpredictable. They also provide the first unequivocal evidence for cross-modal IOR, since, unlike other recent studies (e.g., Reuter-Lorenz, Jha, & Rosenquist, 1996; Tassinari & Berlucchi, 1995; Tassinari & Campara, 1996), the present cross-modal effects cannot be explained in terms of response inhibition for the cue. The results are discussed in relation to neurophysiological studies and audiovisual links in saccade programming.

Adolescent↗

PubMed1997

Preattentive filling-in of visual surfaces in parietal extinction.

Unilateral brain damage frequently produces "extinction," in which patients can detect brief single visual stimuli on either side but are unaware of a contralesional stimulus if presented concurrently with an ipsilesional stimulus. Explanations for extinction have invoked deficits in initial processes that operate before the focusing of visual attention or in later attentive stages of vision. Preattentive vision was preserved in a parietally damaged patient, whose extinction was less severe when bilateral stimuli formed a common surface, even if this required visual filling-in to yield illusory Kanizsa figures or completion of partially occluded figures. These results show that parietal extinction arises only after substantial processing has generated visual surfaces, supporting recent claims that visual attention is surface-based.

Aged↗

PubMed1997

Visual extinction and prior entry: impaired perception of temporal order with intact motion perception after unilateral parietal damage.

Two patients with left-sided visual extinction after right parietal damage were each given two 'prior entry' tasks that have recently been used to study attentional biases in normals. The first task presented two unconnected bars, one in each visual field, with the patients asked to judge which appeared sooner. Both patients reported that the right bar preceded the left unless the latter led by over 200 msec, suggesting a severe bias to the right affecting the time-course of visual awareness. The second task presented one continuous line in a scrolling format across the same spatial extent, with the patients asked to judge which direction the line moved in. The patients now performed normally. Thus, the perception of temporal order for separate events was impaired by the lesions, but without disrupting motion perception within single events. The implications are discussed for theories of normal and pathological attention, visual awareness, and motion perception.

Aged↗

PubMed1997

Attentional competition between modalities: extinction between touch and vision after right hemisphere damage.

The phenomenon of extinction, which occurs frequently after unilateral brain damage, involves a failure to detect the more contralesional of two simultaneously presented stimuli, but with preserved detection of single ipsilesional or contralesional stimuli. Current accounts suggest that the disorder reflects a bias of selective attention, in which ipsilesional stimuli have a competitive advantage. Extinction may be manifested within any one of the major sensory modalities (vision, audition, touch), or it may occur within several modalities in a given individual. Given recent evidence in normals for attentional links between separate sensory modalities, we examined whether extinction can also occur cross-modally, i.e. for double-simultaneous stimuli in separate sensory modalities. We tested whether an ipsilesional event sufficient to extinguish a contralesional stimulus within the same modality may also extinguish a contralesional stimulus in a different modality. Our three patients had right hemisphere damage, and reliable within-modality extinction for visual and tactile stimuli. They also showed significant cross-modal extinction, such that an ipsilesional tactile (or visual) event extinguished awareness of a simultaneous visual (or tactile) event on the contralesional side. These results, which provide the first quantitative evidence for cross-modal extinction, were replicated in a second experiment in which visual and tactile stimuli in the cross-modal conditions were presented at non-homologous elevations within each hemispace. We conclude that after unilateral damage, ipsilesional stimuli have a competitive advantage over contralesional stimuli, and that this affects competition between stimuli from different modalities as well as stimuli within the same modality. These findings are consistent with recent evidence for competitive interactions between tactile and visual events in the control of spatial attention in normals.

Adult↗

PubMed1997

A functional role for illusory colour spreading in the control of focused visual attention.

In cases of modal completion, illusory colour spreading fills in the surface of a subjectively completed shape. In amodal completion, shapes are likewise completed, but now behind a partial occluder, so that filling in of illusory colour to the completed region no longer arises. We consider the possible functional effects that illusory colour spreading may exert on later stages of vision, and argue that comparisons of modal with amodal completion may be particularly revealing in this regard. It is hypothesised that cueing the inducers of a modally completed object should attract attention to the entire object, including the completed region, owing to the colour spreading there. By contrast, changes to the inducers of a comparable amodally completed object should only attract attention to the inducing regions themselves. This prediction is supported by findings in two experiments with stereoscopic displays, with control conditions ruling out nonattentional accounts, or explanations in terms of stereo disparity alone rather than the presence versus absence of illusory colour. We argue that illusory colours get filled in at quite early stages during modal completion, precisely so that later stages of vision, such as focused attention, can then be driven by the completed regions in the same way as for uniform regions that are physically present in the image.

Color Perception↗

PubMed1997

Audiovisual links in exogenous covert spatial orienting.

Subjects judged the elevation (up vs. down, regardless of laterality) of peripheral auditory or visual targets, following uninformative cues on either side with an intermediate elevation. Judgements were better for targets on either modality when preceded by an uninformative auditory cue on the side of the target. Experiment 2 ruled out nonattentional accounts for these spatial cuing effects. Experiment 3 found that visual cues affected elevation judgments for visual but not auditory targets. Experiment 4 confirmed that the effect on visual targets was attentional. In Experiment 5, visual cues produced spatial cuing when targets were always auditory, but saccades toward the cue may have been responsible. No such visual-to-auditory cuing effects were found in Experiment 6 when saccades were prevented, though they were present when eye movements were not monitored. These results suggest a one-way cross-modal dependence in exogenous covert orienting whereby audition influences vision, but not vice versa. Possible reasons for this asymmetry are discussed in terms of the representation of space within the brain.

Adult↗

PubMed1997

On measuring selective attention to an expected sensory modality.

Perceptual judgments can be affected by expectancies regarding the likely target modality. This has been taken as evidence for selective attention to particular modalities, but alternative accounts remain possible in terms of response priming, criterion shifts, stimulus repetition, and spatial confounds. We examined whether attention to a sensory modality would still be apparent when these alternatives were ruled out. Subjects made a speeded detection response (Experiment 1), an intensity or color discrimination (Experiment 2), or a spatial discrimination response (Experiments 3 and 4) for auditory and visual targets presented in a random sequence. On each trial, a symbolic visual cue predicted the likely target modality. Responses were always more rapid and accurate for targets presented in the expected versus unexpected modality, implying that people can indeed selectively attend to the auditory or visual modalities. When subjects were cued to both the probable modality of a target and its likely spatial location (Experiment 4), separable modality-cuing and spatial-cuing effects were observed. These studies introduce appropriate methods for distinguishing attention to a modality from the confounding factors that have plagued previous normal and clinical research.

Adult↗