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PubMed2006

V3A processes contour curvature as a trackable feature for the perception of rotational motion.

Contour curvature (CC) is a vital cue for the analysis of both form and motion. Using functional magnetic resonance imaging, we localized the neural correlates of CC for the processing and perception of rotational motion. We found that the blood oxygen level-dependent signal in retinotopic area V3A and possibly also lateral occipital cortex (LOC) varied parametrically with the degree of CC. Control experiments ruled out the possibility that these modulations resulted from either changes in the area of the stimuli, the velocity with which contour elements were actually translating, or perceived angular velocity. We conclude that neurons within V3A and perhaps also LOC process continuously moving CC as a trackable feature. These data are consistent with the hypothesis that V3A contains neural populations that process trackable form features such as CC, not to solve the "ventral problem" of determining object shape but in order to solve the "dorsal problem" of what is going where.

Adolescent↗
PubMed2004

An earlier component of face perception detected by seeing-as-face task.

To investigate the time sequence of the neural processes underlying face perception, magnetoencephalography was performed using a seeing-as-face task, in which visual inputs were identical across two conditions, but subject perceptions differed: one being a non-specific pattern of geographical shapes, the other being a percept of a face. Subtraction between the two conditions revealed a response occurring 120 ms after stimulus onset in right occipital, approximately 50 ms earlier than previously reported response at a latency of 170 ms at the right fusiform gyrus. As our novel task completely excluded differences in low-level properties of visual stimuli between control and face conditions, these two responses were considered specific to face perception. The result supported the two-stage theory of face processing.

Adult↗
PubMed2001

Equiluminant red-green and blue-yellow VEPs in multiple sclerosis.

The primate visual system is composed by two color-opponent pathways--red-green (R-G) and blue-yellow (B-Y)--subserved by the so-called parvo- and koniocellular streams respectively. The authors' aim was to compare the relative involvement of chromatic visual subsystems in multiple sclerosis (MS). In 30 MS patients with different forms of MS they recorded visual evoked potentials (VEPs) to onset (300 msec) and offset (700 msec) of equiluminant R-G and B-Y sinusoidal gratings of different contrast (90% and 25%). Equiluminance was established psychophysically by establishing the R-G and the B-Y color ratio at which chromatic gratings alternating at 15 and 10 Hz respectively had minimum visibility. The negative wave at stimulus onset with a peak latency of 120 to 160 msec was evaluated. Ordinary VEPs to luminance (LUM) contrast (black-white reversing checkerboards of 15' check size and 50% contrast) were also recorded for comparison. Latencies of R-G VEPs were abnormal in 53.3% and 58.3% of patients at 90% and 25% contrast respectively, whereas abnormal B-Y VEPs were 56.6% and 48.3%. Latencies of LUM VEPs were abnormal in 45% of patients. Interocular latency asymmetries were abnormal in 59.2% and 33.3% of patients for R-G, and 51.8% and 62.9% for B-Y. Latency asymmetries for LUM VEP were abnormal in 46.4% of patients. The higher rate of VEP abnormalities found with equiluminant chromatic stimuli compared with achromatic stimuli confirms the general vulnerability of color-opponent visual pathways in MS, even if the number of patients with abnormal findings was not significantly different when both test conditions were compared. VEPs to R-G and B-Y equiluminant stimuli appear to be involved approximately to the same extent.

Adolescent↗
PubMed1993

Clinicopathological correlations of visual depth perception in patients with cerebrovascular disease.

Visual depth perception in 100 patients with cerebrovascular disease was evaluated using the Titumus stereotest. Twelve patients showed depth perception impairment. CT scans revealed that the lesion was located on the right hemisphere in 6 patients and on the left hemisphere in 3 patients, and that the remaining 3 patients had multiple infarctions. 123I SPECT was performed in 7 patients with moderate to severe depth perception impairment, of whom 6 patients showed a reduced blood flow in the posterior half of both the right and left cerebral hemispheres. Moderate to severe impairment of depth perception was more frequently observed in patients with a lesion in the right hemisphere or in the posterior half of either hemisphere.

Aged↗
PubMed1993

Pattern-reversal visual evoked potentials in Down's syndrome.

We examined pattern-reversal visual evoked potentials (PRVEPs) in 36 adult patients with Down's syndrome, and analyzed the effects of the ophthalmological abnormalities on results of PRVEPs. The P100 latency was significantly delayed in 24 eyes of 16 patients. The P100 latency was significantly longer and its amplitude was significantly smaller (P < 0.001) in Down's syndrome patients than in age-matched normal controls. In 9 patients without any ophthalmological abnormalities, P100 latency showed no significant difference from that in normal controls, but three of them showed a significant delay of P100. Their P100 amplitudes were significantly smaller than those in normal controls. Therefore, we considered that the ophthalmological abnormalities are one of the main factors causing PRVEPs abnormalities in Down's syndrome patients, but some unknown factors should be also responsible.

Adult↗
PubMed1991

Senile changes of crystalline lens: effects on the delayed latency of pattern visually evoked potentials in phakic and pseudophakic eyes.

We recorded visually evoked cortical potentials to pattern stimuli (PVECPs) in 22 patients who received a posterior chamber intraocular lens implant. The mean latency of the P100 obtained from patients was not significantly different from that of age-matched normal phakic subjects. Furthermore, we found that both groups showed a similar increased delay of the P100 latency with age. The results of this study indicated that the senile opacity of the crystalline lens does not contribute to changes of PVECPs with age. These alterations may be due to senile changes of the neural pathway.

Aged↗
PubMed1984

Pattern-reversal electroretinograms and visual evoked cortical potentials in multiple sclerosis.

Pattern-reversal and flash electroretinograms (ERG) and visual evoked cortical potentials (VECP) were recorded from 15 patients with definite multiple sclerosis (MS). All patients had prolonged VECP latency, indicating demyelination of one or both optic nerves. The pattern-reversal ERG amplitude was reduced below the level of normal variation (mean -2 SD) in 11 of the 22 eyes with prolonged VECP latency and in one of the eight eyes with normal VECP latency. The mean pattern-reversal ERG amplitude from eyes with prolonged VECP latencies was significantly lower than the mean amplitude from the normal controls. No abnormalities were observed in the flash ERGs. Degeneration of retinal ganglion cell axons has been demonstrated in MS patients. The amplitude reduction in the pattern-reversal ERG, observed in some 50% of the eyes with prolonged VECP latencies, is supposed to reflect retinal ganglion cell dysfunction or degeneration secondary to demyelination of the optic nerve.

Adult↗
PubMed1986

Pattern electroretinograms become abnormal when background diabetic retinopathy deteriorates to a preproliferative stage: possible use as a screening test.

The pattern electroretinogram (PERG) and other tests were given to a selected group of patients with diabetes, ranging from those who had no retinopathy or funduscopic changes to those in the preproliferative state. None had visual symptoms. The PERG was found to be normal in patients with microaneurysms and a few blot haemorrhages. However, when cotton-wool spots and angiographic evidence of areas of capillary non-perfusion were present, the PERG was reduced below the normal value. Similar changes occurred with the oscillatory potentials of the ERG evoked by an intense flash, but the results were more variable. So in the individual patient the test is not a reliable indicator of the progress of the retinopathy. The value of the PERG in screening is discussed.

Adult↗
PubMed1983

Visual evoked responses in diabetes.

It is commonly believed that diabetic optic neuropathy is very rare and visual loss in diabetes usually is attributed to other causes. We studied the extent of optic nerve involvement in 16 diabetics with no retinopathy or ocular disease and having an almost visual acuity, using visual evoked responses produced by pattern reversal stimulation. Comparing the responses with a group of 35 healthy subjects, the latency was increased by more than one standard deviation in 13 diabetics (81%) and by more than three standard deviations in 10 diabetics (62.5%), often associated with marked reduction in amplitude. There was good correlation between conduction in the optic nerve and peripheral sensory nerve. No correlation was noted to occur with duration of diabetes or diabetic control except perhaps with juvenile onset diabetes. Normal visual acuity was noted in many cases with severely slowed conduction showing early subclinical affection of optic nerves in diabetes. The extent of central nervous system involvement in diabetes has only recently been realised because of lack of physiological techniques and study of optic nerves in diabetes has not been attempted so far. The high incidence of abnormality of visual evoked potentials in diabetes could invalidate the usefulness of this test in diagnosing multiple sclerosis.

Adolescent↗
PubMed1984

Pattern electroretinogram in multiple sclerosis.

The pattern electroretinogram obtained in patients affected by multiple sclerosis were compared with those in a normal population. The pattern electroretinogram amplitude in multiple sclerosis optic neuritis frequently appeared normal, but pattern electroretinogram amplitude abnormalities were found in patients suffering from recurrent multiple sclerosis optic neuritis. Pattern electroretinogram examination appears a useful method in the differential diagnosis between axonal and demyelinating optic nerve impairment.

Adult↗
PubMed1990

Simultaneous VEP and PERG investigations in early Parkinson's disease.

To evaluate whether visual evoked potential (VEP) and pattern electroretinogram (PERG) abnormalities may be detectable early in the course of Parkinson's disease (PD) and to assess a possible interdependence between retinal and cortical potentials, simultaneous VEP and PERG were carried out in nine patients with early PD. The mean (SD) duration of the disease was 10 (6) months. None of the patients had been previously treated with levodopa or other anti-parkinsonian drugs. The results show VEP and PERG abnormalities that are spatial stimulus dependent, with higher frequencies being more involved and also indicate that VEP changes are not entirely dependent on alterations at the retinal level.

Aged↗
PubMed1993

Analysis of object motion in the ventral part of the medial superior temporal area of the macaque visual cortex.

1. The medial superior temporal area (MST) is an extrastriate area of the macaque visual cortex. Cells in MST have large receptive fields and respond to moving stimuli with directional selectivity. We previously suggested that the dorsal part of MST is mainly involved in analysis of field motion caused by movements of the animal itself, because most cells in the dorsal part preferentially responded to movements of a wide textured field rather than to movements of a small stimulus. To determine whether the remaining ventral part of MST differs in function from the dorsal part, we examined properties of cells in the ventral part in comparison with those of cells in the dorsal part, using anesthetized and paralyzed preparation. 2. Most cells in the ventral part preferably responded to movements of a small stimulus rather than to movements of a wide textured field. 3. Although the cells in the ventral part did not respond to movements of a textured field over a large window, many of them began to respond when a small stationary object was introduced in front of the moving field. The direction to which the cells responded in this stimulus configuration was opposite to the direction in which they responded to movements of an object on a stationary background. Activities of these cells thus represented the direction of relative movement of an object on a background, irrespective of whether the image of the object or the background moved on the retina. 4. We conclude that the ventral part of MST is distinctive from the dorsal part of MST and is mainly involved in the analysis of object movements in external space.

Animals↗
PubMed1994

Neural activity in cortical area MST of alert monkey during ocular following responses.

1. We studied response properties of neurons in the superior temporal sulcus (STS) of behaving monkeys that discharged during brief, sudden movements of a large-field visual stimulus, eliciting ocular following. Most neurons responded to movements of a large-field visual stimulus with directional selectivity, preferring high stimulus speeds. Neurons were mostly recorded in the medial superior temporal area (MST) (187/250) and the middle temporal area (MT) (57/250). Further response properties were studied in the MST neurons. 2. Response latencies were measured when a large-field random dot pattern was moved in the preferred direction and preferred speed for each neuron. Eighty percent (120/150) of the neurons were activated < 50 ms after the onset of the stimulus motion. In most cases (89%, 134/150), increased firing rates started before the eye movements, with 59% (88/150) starting > 10 ms before the eye movements. 3. The relationship between the latency of neuronal responses and that of eye movements was studied in 59 neurons by changing the stimulus speed systematically (10-160 degrees/s). The latencies of both neuronal and ocular responses decreased as stimulus speed increased. As a result, the time difference between the response latencies for neuronal and ocular responses varied little with changes in stimulus speed. 4. Blurring of the random dot pattern, by interposing a sheet of ground glass, increased the latency of both neuronal responses and eye movements. 5. With the use of a check pattern instead of random dots, both neuronal and ocular responses began to decrease rapidly when the temporal frequency of the visual stimulus exceeded 20 Hz. At 40 Hz the neurons showed a distinctive burst-and-pause firing pattern, and the eye movements showed signs of oscillation. 6. The response properties of the MST neurons during ocular following were similar to those of the dorsolateral pontine nucleus (DLPN) neurons, reported previously. Our results indicate that the MST neurons may provide visual information to the DLPN neurons and may play a role in eliciting ocular following. 7. Responses during smooth-pursuit eye movement were studied in 55 MST neurons. Each of these neurons responded to the moving large-field visual stimulus, which elicited ocular following, and 40 of these neurons were activated during smooth pursuit in the dark. Response latencies during smooth pursuit were long in those neurons having different directional preferences during smooth pursuit and ocular following but were short for those having the same directional preferences during smooth pursuit and ocular following.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Temporal modulation transfer function of vision by pattern visual evoked potentials in patients with optic neuritis.

To reveal the impairment of the temporal modulation transfer function of vision in patients with optic neuritis, the pattern visual evoked potentials (P-VEPs) were recorded at reversal frequencies ranging from 4 to 24 per second, and the fast Fourier transform (FFT) of VEPs were investigated. In normal subjects, curves of the square root of the power of the FFTs of P-VEPs versus temporal frequency showed the maximum peak at 6 Hz (12 reversals/s). The specific distribution of the power spectrum could be found at each temporal frequency, and the amplitudes of higher harmonic components decreased while a single power spectrum peak became prominent as the temporal frequency increased. In patients with optic neuritis, an abnormality of the power spectrum of steady-state P-VEPs could by detected by estimating the 1st and 2nd harmonic components. The abnormality of the power spectrum of transient P-VEPs could be detected by estimating the higher harmonic components of the power spectrum.

Adult↗
PubMed2000

Fine discrimination of faces can be performed rapidly.

Here we measure the smallest change in a face that can be discriminated. A morphing algorithm mixed two faces in variable proportions to create a series of synthetic faces that each differed by a tiny amount. By selecting from this series, a test face could be chosen so as to reach a just noticeable difference from a sample face. Face-discrimination thresholds were about 7% of the average difference between two faces, as quantified by coefficients of a principal components decom position. This threshold remained constant as the duration of the test face was reduced from 1,000 to 100 msec, and rose quickly for shorter stimulus durations. The behavioral evidence presented here indicates that complex visual processing can be completed within the first 100 msec of the signal, suggesting involvement of feedforward neural mechanisms, and placing constraints on possible computational algorithms employed within the ventral visual pathways.

Algorithms↗