Biomedical subjects

A Zangaladze

Publications and source records attributed to A Zangaladze.

11 recordsLinked to original sources

PubMed2002

Feeling with the mind's eye: contribution of visual cortex to tactile perception.

Visual imagery is implicated in the normal tactile perception of certain object properties. This is an example of cross-modal interactions that characterize normal perception. Here we review recent studies from our laboratory on cross-modal interactions between vision and touch in normally sighted humans. Positron emission tomography was used to demonstrate activation of a region of extrastriate visual cortex, near the parieto-occipital fissure, during tactile discrimination of grating orientation. Transcranial magnetic stimulation (TMS) over this region interfered with performance of this tactile task. In both studies, visual cortical involvement was found for tactile discrimination of orientation but not spatial frequency. Thus, this cortical region is not only active during but also necessary for optimal tactile sensing of orientation. Recent findings implicating visual cortex in Braille-reading in the blind should be evaluated from this perspective.

Animals↗

PubMed2001

Feeling with the mind's eye: the role of visual imagery in tactile perception.

Cross-modal interactions are characteristic of normal perception. In this article, we discuss our work on cross-modal interactions between touch and vision in normally sighted humans. A region of extrastriate visual cortex, near the parieto-occipital fissure, is not only active during but also necessary for tactile discrimination of grating orientation (but not spatial frequency). This is consistent with a role for visual imagery in certain aspects of tactile perception. These findings have implications for the interpretation of visual cortical involvement in Braille reading by the blind.

Humans↗

PubMed1999

Involvement of visual cortex in tactile discrimination of orientation.

The primary sense modalities (vision, touch and so on) are generally thought of as distinct. However, visual imagery is implicated in the normal tactile perception of some object properties, such as orientation, shape and size. Furthermore, certain tactile tasks, such as discrimination of grating orientation and object recognition, are associated with activity in areas of visual cortex. Here we show that disrupting function of the occipital cortex using focal transcranial magnetic stimulation (TMS) interferes with the tactile discrimination of grating orientation. The specificity of this effect is illustrated by its time course and spatial restriction over the scalp, and by the failure of occipital TMS to affect either detection of an electrical stimulus applied to the fingerpad or tactile discrimination of grating texture. In contrast, TMS over the somatosensory cortex blocked discrimination of grating texture as well as orientation. We also report that, during tactile discrimination of grating orientation, an evoked potential is recorded over posterior scalp regions with a latency corresponding to the peak of the TMS interference effect (about 180 ms). The findings indicate that visual cortex is closely involved in tactile discrimination of orientation. To our knowledge, this is the first demonstration that visual cortical processing is necessary for normal tactile perception.

Evoked Potentials↗

PubMed1999

Tactile perception in developmental dyslexia: a psychophysical study using gratings.

Multiple sensory abnormalities have been reported in individuals with developmental dyslexia, especially in the visual and auditory systems. We used gratings of alternating ridges and grooves to investigate tactile perception in this disorder using two tasks: spatial acuity-dependent discrimination of grating orientation and discrimination of gratings varying in ridge width. Compared to age-matched normal subjects, dyslexics were significantly impaired on grating orientation discrimination, with mean thresholds that were nearly twice normal. Unlike normal subjects, their performance on this task was slightly but significantly worse on the dominant hand than on the non-dominant hand. Dyslexics also showed a substantial but non-significant trend for impairment on grating ridge width discrimination. A group of subjects with attention deficit disorder did not differ significantly from normal on any of these measures. These findings expand the range of perceptual deficits reported in developmental dyslexia. Possible explanations for the results, including difficulties with temporal processing, abnormal lateral masking or parietal lobe dysfunction are discussed.

Adolescent↗

PubMed1998

Perceptual learning in tactile hyperacuity: complete intermanual transfer but limited retention.

We investigated intermanual transfer and long-term retention of practice-related perceptual learning in the domain of tactile hyperacuity. Subjects discriminated a row of three dots in which the central dot was offset laterally from a row without such offset. Performance at the right index fingerpad improved with practice. Practice effects transferred essentially completely to the left index fingerpad. When tested some months later at the right index fingerpad, long-term retention of learning was limited and further practice was required to stabilize discrimination thresholds. Intermanual transfer of tactile learning appears to be a general phenomenon, while long-term retention appears to be limited in hyperacuity tasks.

Adult↗

PubMed1997

Feeling with the mind's eye.

Mental imagery is thought to play a key role in certain aspects of visual perception and to depend on neural activity in visual cortex. We asked whether tactile discrimination of grating orientation, which appears to involve visual mental imagery, recruits visual cortical areas. H215O positron emission tomography was performed in humans during presentation of gratings to the right index fingerpad. Selective attention to grating orientation significantly increased regional cerebral blood flow, relative to a control task involving selective attention to grating dimensions, in a region located in left parieto-occipital cortex. We propose that this activation reflects the use of imagery-related visuo-spatial processes to enable the tactile discrimination of orientation.

Adult↗

PubMed1997

Tactile spatial acuity and roughness discrimination: impairments due to aging and Parkinson's disease.

We used gratings of alternating ridges and grooves in a quantitative psychophysical investigation of tactile perception in patients with Parkinson's disease (PD) and age-matched normal controls. The groove width required for threshold discrimination of grating orientation was 25% higher in the control subjects compared to younger individuals studied previously (p = 0.004), indicating a small but significant decline in tactile spatial acuity with age. Relative to age-matched controls, patients with PD showed a twofold increase in the tactile spatial threshold (p = 3.07 x 10(-8), with somewhat greater impairment on the side more affected clinically (p = 0.03). Testing with the forearm prone, as compared to supine, produced a small improvement in the acuity of patients (p = 0.01) but not controls (p = 0.26). PD patients were also impaired in tactually discriminating grating roughness: their difference limens were over three times higher than those of controls (p = 5.74 x 10(-5)) for gratings differing in groove width, and over twice as high (p = 0.0003) for gratings differing in ridge width. We conclude that PD significantly impairs performance on these tactile tasks.

Adult↗

PubMed1997

Tactile learning is task specific but transfers between fingers.

Practice-related improvement in visual perception is highly specific for properties of the stimulus used in training. We explored the specificity of such perceptual learning in the human tactile system, using gratings consisting of alternating ridges and groves. Practice effects on grating discrimination showed limited transfer between grating sets defined by spatial variation in either groove width or ridge width, consistent with partially overlapping neural representations of these two spatial parameters. In contrast, substantial interdigital transfer of practice effects occurred for discrimination of gratings varying in either spatial parameter and also for spatial acuity-dependent discrimination of grating orientation. We conclude that tactile learning, although quite as task specific as in other sensory systems, generalizes with considerable facility across fingers, unlike visual learning, which is highly location specific.

Adult↗

PubMed1996

Magnetic coil suppression of extrafoveal visual perception using disappearance targets.

We used magnetic brain stimulation with a butterfly coil over the occipital lobes to study extrafoveal visual field effects in six subjects. The visual test pattern was a grid of asterisks around a central fixation point, and the target was the disappearance of one asterisk for a single frame of the video monitor. Using single magnetic pulses at stimulator outputs of 55-95%, we noted robust interference effects at latencies < or = 100 ms, peaking at approximately 50-90 ms. Suppression of visual perception occurred with both transverse and sagittal alignments of the coil. When the coil was moved laterally over either occipital lobe, perception of target disappearance was consistently suppressed in the contralateral visual field. Movement of the coil rostrally produced consistent suppression in the lower and middle field, but preferential suppression of the upper field could not be obtained. This altitudinal asymmetry may be correlated with the anatomy of the occipital lobe in relation to the scalp surface.

Attention↗

PubMed1996

Magnetic coil suppression of visual perception at an extracalcarine site.

Perception of extrafoveal visual targets can be suppressed by magnetic stimulation over the occipital lobes, but the site of interference for this and similar phenomena has not been well defined. We modified a previously used technique to determine the locus of magnetic activation. Using butterfly stimulus coils of different sizes and electric field profiles, we determined a scalp position of minimum threshold and a level of stimulator output that produced 50% error rates for each coil. Intersection of the corresponding electric field profiles in air and in a saline model head was similar and identified superficial occipital cortex rather than the primary visual area as the site of perceptual suppression. Less direct analyses involving the distribution of induced electric fields produced the same conclusion. These results suggest specific hypotheses about the effects of magnetic stimulation on visual physiology.

Attention↗

PubMed1996

Tactile spatial acuity at the human fingertip and lip: bilateral symmetry and interdigit variability.

We used the spatial threshold for discrimination of grating orientation to assess tactile spatial acuity at the lower lip and each fingertip, bilaterally, in seven normal human subjects. We confirmed previous findings that: (1) this test is highly reliable, and (2) acuity at the lip is substantially higher than at the fingertips. In addition, we showed that: (1) acuity does not differ significantly between right and left sides, and (2) among fingertips, acuity is lowest at the fifth digit and comparable on the other digits.

Analysis of Variance↗