Biomedical subjects

Tony Ro

Publications and source records attributed to Tony Ro.

At least 19 recordsLinked to original sources

PubMed2006

Attention attenuates metacontrast masking.

The influence of attention on perceptual awareness was examined using metacontrast masking. Attention was manipulated with endogenous cues to assess the effects on the temporal and spatial parameters of target visibility. Experiment 1 examined the time course of effective masking when the target and mask set were presented at an attended vs. an unattended location. The valid allocation of attention decreased the magnitude of the masking effect (i.e. increased visibility) for approximately 80 ms. Furthermore, even with spatial displacements of the target and mask and center-to-center separations of 1.5 degrees or 2.7 degrees of visual angle (Experiment 2), target visibility was increased when attention was validly allocated. These results indicate that attention influences low-level visual processes to enhance visual awareness.

Adolescent↗

PubMed2006

Visually induced feelings of touch.

Recent studies have reported that vision can enhance tactile perception, even in patients with somatosensory deficits. However, it is unclear in these previous studies whether visual input truly enhances detection of tactile stimuli or induces a higher propensity for reporting touch by changing response criteria. In this study, we demonstrate in neurologically normal subjects that in addition to small increases in tactile sensitivity when a non-informative, suprathreshold visual stimulus is presented, there are highly consistent changes in response criteria for reporting touch with vision, even when no tactile stimulus is delivered. These results suggest that some of the previously reported enhancements of touch from vision may rather be a consequence of strategic sensory encoding processes that rely upon the typical correlations between multisensory events.

Emotions↗

PubMed2006

Assessing and inducing neuroplasticity with transcranial magnetic stimulation and robotics for motor function.

OBJECTIVES: To describe 2 new ways of assessing and inducing neuroplasticity in the human brain--transcranial magnetic stimulation (TMS) and robotics--and to investigate and promote the recovery of motor function after brain damage. DATA SOURCES: We identified recent articles and books directly bearing on TMS and robotics. Articles using these tools for purposes other than rehabilitation were excluded. From these studies, we emphasize the methodologic and technical details of these tools as applicable for assessing and inducing plasticity. STUDY SELECTION: Because both tools have only recently been used for rehabilitation, the majority of the articles selected for this review have been published only within the last 10 years. DATA EXTRACTION: We used the PubMed and Compendex databases to find relevant peer-reviewed studies for this review. The studies were required to be relevant to rehabilitation and to use TMS or robotics methodologies. Guidelines were applied via independent extraction by multiple observers. DATA SYNTHESIS: Despite the limited amount of research using these procedures for assessing and inducing neuroplasticity, there is growing evidence that both TMS and robotics can be very effective, inexpensive, and convenient ways for assessing and inducing rehabilitation. Although TMS has primarily been used as an assessment tool for motor function, an increasing number of studies are using TMS as a tool to directly induce plasticity and improve motor function. Similarly, robotic devices have been used for rehabilitation because of their suitability for delivery of highly repeatable training. New directions in robotics-assisted rehabilitation are taking advantage of novel measurements that can be acquired via the devices, enabling unique methods of assessment of motor recovery. CONCLUSIONS: As refinements in technology and advances in our knowledge continue, TMS and robotics should play an increasing role in assessing and promoting the recovery of function. Ongoing and future studies combining TMS and robotics within the same populations may prove fruitful for a more detailed and comprehensive assessment of the central and peripheral changes in the nervous system during precisely induced recovery.

Brain Mapping↗

PubMed2006

Visual restoration in cortical blindness: insights from natural and TMS-induced blindsight.

Unilateral damage to visual cortex of the parietal or occipital lobe can cause the patient to be unaware of contralesional visual information due to either hemispatial neglect or hemianopia. It is now known that both neglect and hemianopia result from the disruption of a dynamic interaction between cortical visual pathways and more phylogenetically primitive visual pathways to the midbrain. We consider the therapeutic implications of these cortical-subcortical interactions in the rehabilitation of hemianopia. We start with the pheonmenon of "blindsight", in which patients with hemianopia can be shown, by implicit measures of visual detection or discrimination, to process visual information without conscious awareness. Some variants of blindsight have been postulated to recruit subcortical processes, while others may reflect compensatory optimisation of processing of spared visual cortex. Both mechanisms may offer opportunities for innovative strategies for rehabilitation of visual field defects. We relate the neural mechanisms that have been proposed to underlie blindsight to those that have been suggested to underlie the recovery of visual function after rehabilitation. It is suggested that the similarity and overlap of the neural processes supporting blindsight and recovery of visual function might provide insights for effective rehabilitation strategies for restoring visual functions.

Animals↗

PubMed2006

Functional reorganization and recovery after constraint-induced movement therapy in subacute stroke: case reports.

Preliminary assessments of the feasibility, safety, and effects on neuronal reorganization measured with transcranial magnetic stimulation (TMS) from Constraint-Induced Movement Therapy (CIMT) of the upper extremity were made in eight cases of subacute stroke. Within fourteen days of their stroke, patients were randomly assigned to two weeks of CIMT or traditional therapy. Baseline motor performance and cortical/subcortical representation for movement with TMS were assessed before treatment. Post-treatment assessments were made at the end of treatment and at three months after the stroke. The TMS mapping showed a larger motor representation in the lesioned hemisphere of the CIMT patients as compared to the controls at the three-month follow-up assessment. The enlarged motor representation in the lesioned hemisphere for hand movement correlated with improved motor function of the affected hand, suggesting a link between movement representation size as measured with TMS and functionality. These results suggest that TMS can be safely and effectively used to assess brain function in subacute stroke and further suggest that CIMT may enhance cortical/subcortical motor reorganization and accelerate motor recovery when started within the first two weeks after stroke.

Aged↗

PubMed2005

Unconscious processing of orientation and color without primary visual cortex.

In humans, the primary visual cortex (V1) is essential for conscious vision. However, even without V1 and in the absence of awareness, some preserved ability to accurately respond to visual inputs has been demonstrated, a phenomenon referred to as blindsight. We used transcranial magnetic stimulation (TMS) to deactivate V1, producing transient blindness for visual targets presented in a foveal, TMS-induced scotoma. Despite unawareness of these targets, performance on forced choice discrimination tasks for orientation (experiment 1) and color (experiment 2) were both significantly above chance. In addition to demonstrating that TMS can be successfully used to induce blindsight within a normal population, these results suggest a functioning geniculoextrastriate visual pathway that bypasses V1 and can process orientation and color in the absence of conscious awareness.

Color Perception↗

PubMed2005

Modulation of antisaccades by transcranial magnetic stimulation of the human frontal eye field.

It has been suggested that the frontal eye field (FEF), which is involved with the inhibition and generation of saccades, is engaged to a different degree in pro- and antisaccades. Pro- and antisaccades are often assessed in separate experimental blocks. In such cases, saccade inhibition is required for antisaccades but not for prosaccades. To more directly assess the role of the FEF in saccade inhibition and generation, a new paradigm was used in which inhibition was necessary on pro- and antisaccade trials. Participants looked in the direction indicated by a target ('<' or '>') that appeared in the left or right visual field. When the pointing direction and the location were congruent, prosaccades were executed; otherwise antisaccades were required. Saccadic latencies were measured in blocks without and with single pulse transcranial magnetic stimulation (TMS) to the right FEF or a right posterior control site. Results showed that antisaccades generated into the hemifield ipsilateral to the TMS were significantly delayed after TMS over the FEF, but not the posterior control site. This result is interpreted in terms of a modulation of saccade inhibition to the contralateral visual field due to disruption of processing in the FEF.

Adaptation, Physiological↗

PubMed2004

Constraint-induced movement therapy.

Constraint-induced movement therapy improves outcome after chronic stroke, conforms experimental observations of neuronal plasticity, and proves the efficacy of intensive occupational therapy. More acutely instituted constraint-induced movement therapy has both practical and theoretic risks and benefits that deserve further careful evaluation.

Animals↗

PubMed2004

Extrageniculate mediation of unconscious vision in transcranial magnetic stimulation-induced blindsight.

The proposed neural mechanisms supporting blindsight, the above-chance performance of cortically blind patients on forced-choice visual discrimination tasks, are controversial. In this article, we show that although subjects were unable to perceive foveally presented visual stimuli when transcranial magnetic stimulation over the visual cortex induced a scotoma, responses nonetheless were delayed significantly by these unconscious distractors in a directed saccade but not in an indirect manual response task. These results suggest that the superior colliculus, which is involved with sensory encoding as well as with the generation of saccadic eye movements, is mediating the unconscious processing of the transcranial magnetic stimulation-suppressed distractors and implicate a role of the retinotectal pathway in many blindsight phenomena.

Adult↗

PubMed2004

A comparison of masking by visual and transcranial magnetic stimulation: implications for the study of conscious and unconscious visual processing.

Visual stimuli as well as transcranial magnetic stimulation (TMS) can be used: (1) to suppress the visibility of a target and (2) to recover the visibility of a target that has been suppressed by another mask. Both types of stimulation thus provide useful methods for studying the microgenesis of object perception. We first review evidence of similarities between the processes by which a TMS mask and a visual mask can either suppress the visibility of targets or recover such suppressed visibility. However, we then also point out a significant difference that has important implications for the study of the time course of unconscious and conscious visual information processing and for theoretical accounts of the processes involved. We present evidence and arguments showing: (a) that visual masking techniques, by revealing more detailed aspects of target masking and target recovery, support a theoretical approach to visual masking and visual perception that must take into account activities in two separate neural channels or processing streams and, as a corollary, (b) that at the current stage of methodological sophistication visual masks, by acting in more highly specifiable ways on these pathways, provide information about the microgenesis of form perception not available with TMS masks.

Consciousness↗

PubMed2004

Unconscious color priming occurs at stimulus- not percept-dependent levels of processing.

Although past studies have shown that visual information can be processed without awareness, the types and levels of this processing have yet to be determined. We used metacontrast masking to explore unconscious priming effects of white, blue, and green stimuli generated on a color video display. We found that a white prime tends to act more like a green than a blue one. Color confusions among unmasked and masked primes and calibrations of the display phosphors show that physical rather than perceptual properties of the stimuli best explain the white prime's effects. We conclude that unconscious color priming in normal observers occurs at early wavelength-dependent levels of processing prior to later color-percept-dependent levels.

Color Perception↗

PubMed2003

Feedback contributions to visual awareness in human occipital cortex.

It has traditionally been assumed that processing within the visual system proceeds in a bottom-up, feedforward manner from retina to higher cortical areas. In addition to feedforward processing, it is now clear that there are also important contributions to sensory encoding that rely upon top-down, feedback (reentrant) projections from higher visual areas to lower ones. By utilizing transcranial magnetic stimulation (TMS) in a metacontrast masking paradigm, we addressed whether feedback processes in early visual cortex play a role in visual awareness. We show that TMS of visual cortex, when timed to produce visual suppression of an annulus serving as a metacontrast mask, induces recovery of an otherwise imperceptible disk. In addition to producing disk recovery, TMS suppression of an annulus was greater when a disk preceded it than when an annulus was presented alone. This latter result suggests that there are effects of the disk on the perceptibility of the subsequent mask that are additive and are revealed with TMS of the visual cortex. These results demonstrate spatial and temporal interactions of conscious vision in visual cortex and suggest that a prior visual stimulus can influence subsequent perception at early stages of visual encoding via feedback projections.

Feedback, Physiological↗

PubMed2003

Inhibition of return and the human frontal eye fields.

Inhibition of return (IOR) is a bias against reorienting attention to a previously cued location. In this study, using single-pulse transcranial magnetic stimulation (TMS), we show that the human frontal eye fields (FEF) play a crucial role in the generation of IOR. When TMS was applied over the right FEF at a time interval after a visual cue but shortly before the target, IOR was modulated in the hemifield ipsilateral to the TMS such that responses to a previously cued target were no longer slower than responses to uncued targets. Control TMS over the superior parietal lobule, as well as TMS of the FEF shortly after the cue but well before the target, had no influence on IOR. We further show that the FEF is involved with visual selection as responses to targets appearing contralateral to the TMS of the FEF, but not the control site, were delayed. These results suggest that the FEF produces IOR by biasing attention and eye movements away from a previously attended location and facilitating target detection at novel locations.

Adolescent↗

PubMed2003

The role of perceptual load in processing distractor faces.

It has been established that successful ignoring of irrelevant distractors depends on the extent to which the current task loads attention. However, the previous load studies have typically employed neutral distractor stimuli (e.g., letters). In the experiments reported here, we examined whether the perception of irrelevant distractor faces would show the same effects. We manipulated attentional load in a relevant task of name search by varying the search set size and found that whereas congruency effects from meaningful nonface distractors were eliminated by higher search load, interference from distractor faces was entirely unaffected by search load. These results support the idea that face processing may be mandatory and generalize the load theory to the processing of meaningful and more complex nonface distractors.

Adult↗

PubMed2002

A temporal/nasal asymmetry for blindsight in a localisation task: evidence for extrageniculate mediation.

Some patients with hemianopia due to striate cortex lesions show above chance ability in reporting visual stimuli presented in the blind visual field, a phenomenon commonly known as blindsight. Here we report a patient with a dense right hemianopia whose blindsight shows a temporal/nasal asymmetry. MP was tested in a two-alternative forced-choice localisation task, with either the right eye or the left eye patched in separate blocks. When targets appeared in the contralesional temporal hemifield, MP's localisation performance was extremely accurate, whilst she performed at chance with targets in the contralesional nasal hemifield. This is the first demonstration of a temporal/nasal asymmetry for blindsight in a forced-choice paradigm, and is consistent with blindsight in MP's hemianopic field being mediated by a subcortical, extrageniculate route.

Blindness↗

PubMed2002

A left visual field advantage in perception of gaze direction.

Previous work has found a left visual field (LVF) advantage for various judgements on faces, including identity and emotional expression. This has been related to possible right-hemisphere specialisation for face processing, and it has been proposed that this might reflect configural processing. We sought to determine whether a similar LVF advantage may also exist for gaze perception. In two experiments, normal adult subjects made judgements for seen gaze direction (left, right or straight). To assess how visual field may influence perception of gaze direction, eye stimuli were briefly presented unilaterally or bilaterally. In the latter case, the gaze direction of the two seen eyes could be congruent or incongruent (i.e. the two eyes could gaze in the same or different directions). For unilateral displays, performance was more accurate for LVF stimuli than RVF. With bilateral incongruent gaze, the LVF eye influenced judgements more strongly than the RVF eye. No such LVF advantage was found in a control experiment, in which subjects judged pupil size for similar eye stimuli. Taken together, these results reveal a LVF advantage for perception of gaze direction. Since only the eye region was visible, our results cannot be due to a LVF bias in processing the entire face context. Instead they suggest lateralisation specifically in processing the direction of seen gaze.

Adult↗

PubMed2002

Locating the human frontal eye fields with transcranial magnetic stimulation.

The variability in the location and function of the human frontal eye fields (FEFs) was assessed using transcranial magnetic stimulation (TMS). Ten subjects performed a saccadic eye movement task previously shown to be influenced by TMS of the FEFs. A sequence of points over the prefrontal cortex was stimulated until an effective site of the TMS was found that induced contralateral saccade delays. In 7 out of the 10 subjects, we were able to localize a region in the prefrontal cortex that when stimulated produced delays in the execution of contralateral saccadic eye movements. The location of this functionally defined FEF region across these subjects was approximately 1.5 cm anterior to the motor hand area, although there was considerable variability in this measure. In the remaining 3 subjects, no site within our circumscribed probing was found that when disrupted with TMS produced delays in contralateral saccadic eye movements. The inter-individual differences in the location and function of the FEFs highlights the importance of using functional as well as anatomical landmarks when attempting to localize brain structures.

Adult↗

PubMed2002

Covert orienting to the locations of targets and distractors: effects on response channel activation in a flanker task.

The role of covert orienting of attention in response channel activation was examined using the flanker interference and precueing paradigms. Four experiments assessed the influence of distractors on the discrimination of a target colour patch undercueing conditions (three with noninformative, exogenous cues and one with informative, endogenous cues) that modulated attention at the flanker or target locations. Across all of the experiments, the amount of interference generated by the distractors was not modulated by the facilitation and inhibition of return induced by spatial attention precues. These results are consistent with previous reports of patients with neglect, which demonstrated that flanker interference proceeds at unattended locations (Audet, Bub, & Lecours, 1991; Cohen, Ivry, Rafal, & Kohn, 1995), and they suggest that response channel activation can occur independently from spatial attention.

Adolescent↗