Biomedical subjects

Jon Driver

Publications and source records attributed to Jon Driver.

At least 37 records · Page 2Linked to original sources

PubMed2005

To look or not to look? Typical and atypical development of oculomotor control.

The ability to inhibit saccades toward suddenly appearing peripheral stimuli (prosaccades) and direct them to contralateral locations instead (antisaccades) is a crucial marker of eye movement control. Typically developing infants as young as 4-month-olds can learn to inhibit reflexive saccades to peripheral stimuli, but they do not produce antisaccades, whose development later in infancy and its underlying neural computations remain unexplored. Here we tested oculomotor control in typically developing toddlers and toddlers with fragile X syndrome (FXS), a disorder of known genetic origin that allows the investigation of the neuro-computational properties contributing to the development of saccadic control. Typically developing toddlers decreased looking toward peripheral cues that predicted contralateral rewards, whose appearance they anticipated. Furthermore, this correlated with age, indicating a gradual development of saccadic control. In contrast with the typical case, toddlers with FXS did not decrease their looks to peripheral onsets that predicted contralateral events. Importantly, the atypical pattern of performance was also evident in the elimination of the correlation with mental or chronological age found in controls. Taken together, the findings suggest that control of saccades and its developmental trajectory is atypical in toddlers with FXS, consistent with inhibitory deficits previously shown at later ages in this condition. Potential implications for the neural mechanisms underlying the typical and atypical development of oculomotor control are discussed.

Age Factors↗

PubMed2005

Priming of color and position during visual search in unilateral spatial neglect.

We examined priming of visual search by repeated target location or color in two patients with left visual neglect and extinction, following strokes centered on the right inferior parietal lobe. Both patients, like the healthy controls we tested, showed intact priming, with performance speeded when either the location or color of a singleton target was repeated over successive trials in a standard search condition (Experiment 1). This was observed both from and to targets on the contralesional (left) side. Moreover, priming of search was still observed even when a return of fixation back to display-center was required between successive trials (Experiment 2). When briefer displays were used (Experiment 3), the patients often failed to detect left targets. This situation revealed an important dissociation: Whereas location priming only arose from preceding left targets that had been consciously detected, color priming (possibly arising within the intact ventral stream) did not depend on awareness of the preceding target. There was considerable color priming from missed targets. These findings demonstrate relatively intact priming of visual search by color and location in patients with right parietal damage, and also reveal that location priming may differ from color priming in requiring awareness.

Aged↗

PubMed2005

Selective attention modulates neural substrates of repetition priming and "implicit" visual memory: suppressions and enhancements revealed by FMRI.

Attention can enhance processing for relevant information and suppress this for ignored stimuli. However, some residual processing may still arise without attention. Here we presented overlapping outline objects at study, with subjects attending to those in one color but not the other. Attended objects were subsequently recognized on a surprise memory test, whereas there was complete amnesia for ignored items on such direct explicit testing; yet reliable behavioral priming effects were found on indirect testing. Event-related fMRI examined neural responses to previously attended or ignored objects, now shown alone in the same or mirror-reversed orientation as before, intermixed with new items. Repetition-related decreases in fMRI responses for objects previously attended and repeated in the same orientation were found in the right posterior fusiform, lateral occipital, and left inferior frontal cortex. More anterior fusiform regions also showed some repetition decreases for ignored objects, irrespective of orientation. View-specific repetition decreases were found in the striate cortex, particularly for previously attended items. In addition, previously ignored objects produced some fMRI response increases in the bilateral lingual gyri, relative to new objects. Selective attention at exposure can thus produce several distinct long-term effects on processing of stimuli repeated later, with neural response suppression stronger for previously attended objects, and some response enhancement for previously ignored objects, with these effects arising in different brain areas. Although repetition decreases may relate to positive priming phenomena, the repetition increases for ignored objects shown here for the first time might relate to processes that can produce "negative priming" in some behavioral studies. These results reveal quantitative and qualitative differences between neural substrates of long-term repetition effects for attended versus unattended objects.

Adult↗

PubMed2005

New indirect measures of "inattentive" visual grouping in a change-detection task.

It has often been suggested that Gestalt-like visual grouping processes may operate preattentively, but Mack and Rock (1998) suggested that no visual grouping takes place under "inattention." We introduced a new method to assess this. While participants performed a demanding change-detection task on a small matrix at fixation, task-irrelevant background elements were arranged by color sinilarity into columns, rows, or pseudorandomly. Independent of any change in the target matrix, background grouping could also change or remain the same on each trial. This influenced accuracy of change judgments for the central task, even though background grouping or its change usually could not be explicitly reported when probed with surprise questions as in Mack and Rock. This suggests that visual grouping may arise implicitly under inattention and provides a new method for testing the boundaries of this processing. Here we extended the initial result to changes in background grouping remote from the target and to those occurring across an intervening saccade.

Adolescent↗

PubMed2005

Task-dependent modulation of target-flanker lateral interactions in vision.

Visibility of a central target Gabor element often improves in the presence of collinear flankers. Such lateral interactions may reflect fundamental mechanisms underlying the perceptual integration of contours in early vision. We recently reported (Freeman, Sagi, & Driver, 2001) attentional modulation of these interactions. Here, we test whether this modulation is task dependent. Subjects had to detect a near-threshold central target while performing a secondary discrimination task on one pair of flankers that could appear with another distractor pair (one pair collinear with the target, the other orthogonal). Central target thresholds were lowered when collinear flankers were judged for the secondary task, but only when this task concerned the global spatial relationship between these flankers (discrimination of their Vernier offset or global orientation). Other secondary tasks involving discriminating the local orientations, contrasts, or colors of the relevant flanker pair produced no such attentional modulation. However, this task-dependent modulation was observed only when two flanker pairs were present, not for displays with only a single flanker pair. Top-down modulation of lateral interactions may function to select between overlapping potential contours whenever the global spatial properties of one are task relevant.

Adult↗

PubMed2005

Recognition memory for distractor faces depends on attentional load at exposure.

Incidental recognition memory for faces previously exposed as task-irrelevant distractors was assessed as a function of the attentional load of an unrelated task performed on superimposed letter strings at exposure. In Experiment 1, subjects were told to ignore the faces and either to judge the color of the letters (low load) or to search for an angular target letter among other angular letters (high load). A surprise recognition memory test revealed that despite the irrelevance of all faces at exposure, those exposed under low-load conditions were later recognized, but those exposed under high-load conditions were not. Experiment 2 found a similar pattern when both the high- and low-load tasks required shape judgments for the letters but made differing attentional demands. Finally, Experiment 3 showed that high load in a nonface task can significantly reduce even immediate recognition of a fixated face from the preceding trial. These results demonstrate that load in a nonface domain (e.g., letter shape) can reduce face recognition, in accord with Lavie's load theory. In addition to their theoretical impact, these results may have practical implications for eyewitness testimony.

Attention↗

PubMed2004

Morphing Marilyn into Maggie dissociates physical and identity face representations in the brain.

How the brain represents different aspects of faces remains controversial. Here we presented subjects with stimuli drawn from morph continua between pairs of famous faces. In the paired presentations, a second face could be identical to the first, could share perceived identity but differ physically (30% along the morph continuum), or could differ physically by the same distance along the continuum (30%) but in the other direction. We show that, behaviorally, subjects are more likely to classify face pairs in the third paired presentation as different and that this effect is more pronounced for subjects who are more familiar with the faces. In functional magnetic resonance imaging (fMRI), inferior occipital gyrus (IOG) shows sensitivity to physical rather than to identity changes, whereas right fusiform gyrus (FFG) shows sensitivity to identity rather than to physical changes. Bilateral anterior temporal regions show sensitivity to identity change that varies with the subjects' pre-experimental familiarity with the faces. These findings provide neurobiological support for a hierarchical model of face perception.

Adult↗

PubMed2004

Distant influences of amygdala lesion on visual cortical activation during emotional face processing.

Emotional visual stimuli evoke enhanced responses in the visual cortex. To test whether this reflects modulatory influences from the amygdala on sensory processing, we used event-related functional magnetic resonance imaging (fMRI) in human patients with medial temporal lobe sclerosis. Twenty-six patients with lesions in the amygdala, the hippocampus or both, plus 13 matched healthy controls, were shown pictures of fearful or neutral faces in task-releant or task-irrelevant positions on the display. All subjects showed increased fusiform cortex activation when the faces were in task-relevant positions. Both healthy individuals and those with hippocampal damage showed increased activation in the fusiform and occipital cortex when they were shown fearful faces, but this was not the case for individuals with damage to the amygdala, even though visual areas were structurally intact. The distant influence of the amygdala was also evidenced by the parametric relationship between amygdala damage and the level of emotional activation in the fusiform cortex. Our data show that combining the fMRI and lesion approaches can help reveal the source of functional modulatory influences between distant but interconnected brain regions.

Adult↗

PubMed2004

Attentional load and sensory competition in human vision: modulation of fMRI responses by load at fixation during task-irrelevant stimulation in the peripheral visual field.

Perceptual suppression of distractors may depend on both endogenous and exogenous factors, such as attentional load of the current task and sensory competition among simultaneous stimuli, respectively. We used functional magnetic resonance imaging (fMRI) to compare these two types of attentional effects and examine how they may interact in the human brain. We varied the attentional load of a visual monitoring task performed on a rapid stream at central fixation without altering the central stimuli themselves, while measuring the impact on fMRI responses to task-irrelevant peripheral checkerboards presented either unilaterally or bilaterally. Activations in visual cortex for irrelevant peripheral stimulation decreased with increasing attentional load at fixation. This relative decrease was present even in V1, but became larger for successive visual areas through to V4. Decreases in activation for contralateral peripheral checkerboards due to higher central load were more pronounced within retinotopic cortex corresponding to 'inner' peripheral locations relatively near the central targets than for more eccentric 'outer' locations, demonstrating a predominant suppression of nearby surround rather than strict 'tunnel vision' during higher task load at central fixation. Contralateral activations for peripheral stimulation in one hemifield were reduced by competition with concurrent stimulation in the other hemifield only in inferior parietal cortex, not in retinotopic areas of occipital visual cortex. In addition, central attentional load interacted with competition due to bilateral versus unilateral peripheral stimuli specifically in posterior parietal and fusiform regions. These results reveal that task-dependent attentional load, and interhemifield stimulus-competition, can produce distinct influences on the neural responses to peripheral visual stimuli within the human visual system. These distinct mechanisms in selective visual processing may be integrated within posterior parietal areas, rather than earlier occipital cortex.

Adult↗

PubMed2004

Auditory deficits in visuospatial neglect patients.

Since the pioneering experimental work of Bisiach et al. (1984) on deficits in sound localisation associated with unilateral brain lesions and visual neglect, a number of systematic investigations have examined auditory processing in visuospatial neglect patients. Evidence from a variety of experimental paradigms has revealed some auditory deficits in detection and identification tasks, during bilateral stimulation; plus localisation deficits for single sounds. These deficits emerge predominantly for contra-lesional sounds, although some auditory disturbances applying to both contra- and ipsilesional sounds have also been documented. Here we review evidence suggesting that some of these auditory deficits arise in relatively high-level stages of spatial processing. In addition, we present new analyses showing that auditory deficits in identification and localisation tasks often correlate with clinical measures of visual neglect, across a variety of different studies and tasks. This empirical relation suggests that a disturbance of multisensory spatial processing may often account for the joint auditory and visual spatial deficits in neglect patients, although rarer dissociations between the modalities should also be considered.

Auditory Perception↗

PubMed2004

Configuration-specific attentional modulation of flanker- -target lateral interactions.

Elements of a contour are often easier to detect when they possess collinearity, with their local orientations matching the global orientation of the contour. We recently reported attentional modulation of such lateral interactions between a central near-threshold target Gabor patch and flanking high-contrast patches (Freeman et al, 2001 Nature Neuroscience 4 1032-1036). Here, we examined whether such attentional effects reflect specific modulation of mechanisms sensitive to collinear configurations, or instead more general modulation of sensitivity to either the global or local orientation-components of the stimulus. Thresholds for detecting a central Gabor target were measured, while observers also judged the Vernier alignment between one pair of flankers and ignored a second flanker pair (when present). Target contrast-thresholds were facilitated only when attending collinear flankers. There was no facilitation when attending flankers that shared only local orientation with the target, or flankers that fell on a global axis aligned with target orientation but having orthogonal local orientation. Ignored collinear flankers had no effect on target thresholds. These results demonstrate strong and specific attentional modulation of contour-integration mechanisms in early vision sensitive to collinear configurations.

Attention↗

PubMed2004

Visual search in typically developing toddlers and toddlers with Fragile X or Williams syndrome.

Visual selective attention is the ability to attend to relevant visual information and ignore irrelevant stimuli. Little is known about its typical and atypical development in early childhood Experiment 1 investigates typically developing toddlers' visual search for multiple targets on a touch-screen. Time to hit a target, distance between successively touched items, accuracy and error types revealed changes in 2- and 3-year-olds' vulnerability to manipulations of the search display. Experiment 2 examined search performance by toddlers with Fragile X syndrome (FXS) or Williams syndrome (WS). Both of these groups produced equivalent mean time and distance per touch as typically developing toddlers matched by chronological or mental age; but both produced a larger number of errors. Toddlers with WS confused distractors with targets more than the other groups; while toddlers with FXS perseverated on previously found targets. These findings provide information on how visual search typically develops in toddlers, and reveal distinct search deficits for atypically developing toddlers.

Attention↗

PubMed2004

ERP evidence for cross-modal audiovisual effects of endogenous spatial attention within hemifields.

Previous ERP studies have uncovered cross-modal interactions in endogenous spatial attention. Directing attention to one side to judge stimuli from one particular modality can modulate early modality-specific ERP components not only for that modality, but also for other currently irrelevant modalities. However, past studies could not determine whether the spatial focus of attention in the task-irrelevant secondary modality was similar to the primary modality, or was instead diffuse across one hemifield. Here, auditory or visual stimuli could appear at any one of four locations (two on each side). In different blocks, subjects judged stimuli at only one of these four locations, for an auditory (Experiment 1) or visual (Experiment 2) task. Early attentional modulations of visual and auditory ERPs were found for stimuli at the currently relevant location, compared with those at the irrelevant location within the same hemifield, thus demonstrating within-hemifield tuning of spatial attention. Crucially, this was found not only for the currently relevant modality, but also for the currently irrelevant modality. Moreover, these within-hemifield attention effects were statistically equivalent regardless of the task relevance of the modality, for both the auditory and visual ERP data. These results demonstrate that within-hemifield spatial attention for one task-relevant modality can transfer cross-modally to a task-irrelevant modality, consistent with spatial selection at a multimodal level of representation.

Acoustic Stimulation↗

PubMed2004

Spatial constraints on visual-tactile cross-modal distractor congruency effects.

Across three experiments, participants made speeded elevation discrimination responses to vibrotactile targets presented to the thumb (held in a lower position) or the index finger (upper position) of either hand, while simultaneously trying to ignore visual distractors presented independently from either the same or a different elevation. Performance on the vibrotactile elevation discrimination task was slower and less accurate when the visual distractor was incongruent with the elevation of the vibrotactile target (e.g., a lower light during the presentation of an upper vibrotactile target to the index finger) than when they were congruent, showing that people cannot completely ignore vision when selectively attending to vibrotactile information. We investigated the attentional, temporal, and spatial modulation of these cross-modal congruency effects by manipulating the direction of endogenous tactile spatial attention, the stimulus onset asynchrony between target and distractor, and the spatial separation between the vibrotactile target, any visual distractors, and the participant's two hands within and across hemifields. Our results provide new insights into the spatiotemporal modulation of cross-modal congruency effects and highlight the utility of this paradigm for investigating the contributions of visual, tactile, and proprioceptive inputs to the multisensory representation of peripersonal space.

Adult↗

PubMed2003

When pros become cons for anti- versus prosaccades: factors with opposite or common effects on different saccade types.

In five experiments we compared prosaccade and antisaccade performance in normal human observers. This was first examined for visual stimulation in temporal or nasal hemifields, under monocular viewing. Prosaccades were faster following temporal than nasal stimulation, in accordance with previous results. The novel finding was that the opposite pattern was observed for antisaccades, consistent with a difficulty in overcoming a stronger prosaccade tendency after temporal-hemifield stimulation. A second experiment showed that these results were not simply due to antisaccades following nasal stimulation benefitting from being made towards a temporal place-holder. Prosaccades and antisaccades were then compared for visual versus somatosensory stimulation. The substantial latency difference between prosaccades and antisaccades for visual stimuli was eliminated for somatosensory stimuli. Antisaccades can thus benefit in relative terms when the competing prosaccadic tendency is weakened; but two further experiments revealed that not all manipulations induce opposing outcomes for the two types of saccade. Although reducing the contrast of visual targets can slow prosaccades and conversely speed antisaccades, this was not the case at the lowest contrast level used, where both types of saccade were slowed, thus indicating some common limiting source. Moreover, warning sounds presented shortly before a visual target speeded both prosaccades and antisaccades. These results illustrate that several factors which slow prosaccades can speed antisaccades (consistent with competition between different pathways); but also reveal some notable exceptions, where both types of saccade are slowed or speeded together, suggesting some common pathways that may precede competition over the direction of the saccade.

Acoustic Stimulation↗

PubMed2003

Multisensory integration and the body schema: close to hand and within reach.

There has been a recent and dramatic growth of interest in the psychological and neural mechanisms of multisensory integration between different sensory modalities. Much of this recent research has focused specifically on how multisensory representations of body parts and of the 'peripersonal' space immediately around them, are constructed. Research has also focused on how this may lead to multisensorially determined perceptions of body parts, to action execution, and even to attributions of agency and self-ownership for the body parts in question. Converging evidence from animal and human studies suggests that the primate brain constructs various body-part-centred representations of space, based on the integration of visual, tactile and proprioceptive information. These representations can plastically change following active tool-use that extends reachable space and also modifies the representation of peripersonal space. These new results indicate that a modern cognitive neuroscience approach to the classical concept of the 'body schema' may now be within reach.

Animals↗

PubMed2003

Multimodal spatial representations engaged in human parietal cortex during both saccadic and manual spatial orienting.

BACKGROUND: Recent neuroimaging studies have found that several areas of the human brain, including parietal regions, can respond multimodally. But given single-cell evidence that responses in primate parietal cortex can be motor-related, some of the human multimodal activations might reflect convergent activation of potentially motor-related areas, rather than multimodal representations of space independent of motor factors. Here we crossed sensory stimulation of different modalities (vision or touch, in left or right hemifield) with spatially directed responses to such stimulation by different effector-systems (saccadic or manual). RESULTS: The fMRI results revealed representations of contralateral space in both the posterior part of the superior parietal gyrus and the anterior intraparietal sulcus that activated independently of both sensory modality and motor response. Multimodal saccade-related or manual-related activations were found, by contrast, in different regions of parietal cortex. CONCLUSIONS: Whereas some parietal regions have specific motor functions, others are engaged during the execution of movements to the contralateral hemifield irrespective of both input modality and the type of motor effector.

Adult↗

PubMed2003

Top-down modulation of lateral interactions in early vision: does attention affect integration of the whole or just perception of the parts?

Attention can modulate sensitivity to local stimuli in early vision. But, can attention also modulate integration of local stimuli into global visual patterns? We recently measured effects of attention on the phenomenon of lateral interactions between collinear elements, commonly thought to reflect long-range mechanisms in early visual cortex underlying contour integration. We showed improved detection of low-contrast central Gabor targets in the context of collinear flankers, but only when the collinear flankers were attended for a secondary task rather than ignored in favor of an orthogonal flanker pair. Here, we contrast two hypotheses for how attention might modulate flanker influences on the target: by changing just local sensitivity to the flankers themselves (flanker-modulation-only hypothesis), or by weighting integrative connections between flanker and target (connection-weighting hypothesis). Modeled on the known nonlinear dependence of target visibility on collinear flanker contrast, the first hypothesis predicts that an increase in physical flanker contrast should readily offset any reduction in their effective contrast when ignored, thus eliminating attentional modulation. Conversely, the second hypothesis predicts that attentional modulation should persist even for the highest flanker contrasts. Our results showed the latter outcome and indicated that attention modulates flanker-target integration, rather than just processing of local flanker elements.

Attention↗