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PubMed2002

Human cortical responses to coherent and incoherent motion as measured by magnetoencephalography.

To investigate the detail response properties for the incoherent motion of the human visual system, we measured the magnetoencephalographic neural responses to both coherent and incoherent motions at various speeds (from 0.65 to 20.6 degrees /s). The peak latency of the first component of the response from the extrastriate area was inversely related to the speed of motion (from 228 to 155 ms in mean) and there was no significant difference in the latency change between the two types of motion. There were significant differences in the peak amplitude change with the motion speed and a difference in the distribution of the magnetic fields of the responses was seen in six of the seven subjects. The results show that the speed of the incoherently moving dots is represented in the human visual system in the same manner as that of coherently moving dots. The differences in the magnetic fields between the two responses indicate that the same speed-related response changes can occur with different neural populations responsible for both motions.

Adult↗
PubMed2001

Age-related changes in brain neuromagnetic responses to face perception in humans.

In order to investigate the effects of ageing on face perception, we studied the magnetic responses to face images in 15 young (19-38 years) and 10 elderly (51-81 years) subjects. Face-specific responses (160mF), which originate in the inferior occipitotemporal cortices, and face non-specific responses (100m), which originate in the primary visual cortices, were evoked in all subjects. Averaged peak latency of the 160mF in the elderly group (174.0+/-9.1 ms) was significantly longer (P<0.0005) than that in the young group (161.5+/-5.1 ms), while no inter-group difference was found in the 100m latency. There was a significant correlation between age and 160mF latency (+0.35 ms/year, R=0.747) suggesting age-related decline of face perception.

Adult↗
PubMed1985

[Flash-pattern visual evoked potentials and limited lesions of the occipital lobe].

Four patients with restricted lobe lesions and one patient with large occipital lesions were selected for VEP studies to full-field and half-field flash pattern stimuli. The abnormalities of the responses were more important with full-field stimuli. In three patients with inner side occipital lobe damage, the P100 component disappeared ipsilaterally to the lesion, but N140 remained normal on bilateral occipital leads. In one patient with outer side occipital lobe damage, P100 was normal on bilateral occipital leads, but N140 disappeared ipsilaterally to the lesion. In one patient with large occipital lesion, P100 and N140 both disappeared ipsilaterally to the lesion. It appears that the P100 component is related to the inner and that N140 is related to the outer area of the occipital lobe.

Adult↗
PubMed2004

Influence of the state of alertness on the pattern visual evoked potentials (PVEP) in very young infant.

The aim of the study was to evaluate the pattern visual evoked potentials (PVEP) combined with an optimal state of vigilance, called liberated state (LS), in order to improve testing in very young infants. Transient PVEP were recorded in response to a checkerboard pattern of 120, 60 and 30 min of arc. in 56 fullterm newborns and 79 preterm infants from birth to 4 months of age. In the fullterms, 28 infants in each group were tested in LS or spontaneous alertness (SA) while in the preterms, 48 infants in each group were tested in LS or SA. No significant difference was found in the amplitude and/or peak time of the PVEP responses between subjects tested in LS compared to SA groups. However, the LS condition improved by approximately 25% the feasibility of prolonged PVEP testing in preterms aged less than 2 months (corrected age). This suggest that the LS condition enhances the clinical feasibility of PVEP testing in very young infants and should be used to optimize the evaluation of visual development in high risk infants in this age group.

Adult↗
PubMed2000

Comparative studies on pattern VECP between patients with ischemic optic neuropathy and optic neuritis.

PURPOSE: To evaluate whether and how VECPs are useful in differentiating ION from ON. METHODS: We retrospectively studied 27 patients with non-arteritic ION and 69 patients with ON using pattern visually evoked cortical potentials (PVECPs) to 3 rev/sec stimulation (transient) and 12 rev/sec stimulation (steady-state). RESULTS: In patients with ION, non-recordable responses were found in 25% of those with transient VECP and in 74% of those with steady-state VECP. In ON patients, non-recordable responses were found in 34% of those with transient VECP and in 64% of those with steady-state VECP. The average peak latency of P100 component in those with ION was significantly shorter than in those with ON. The amplitude ratio (affected eye/fellow eye) of steady-state VECP was significantly higher in those with ION than in those with ON. The amplitude ratio of P100 showed no significant differences between groups. CONCLUSION: The P100 peak latency of transient VECPs and the amplitude of steady-state VECPs have the potential to differentiate between ION and ON.

Adolescent↗
PubMed1999

Age-related changes in processing auditory stimuli during visual attention: evidence for deficits in inhibitory control and sensory memory.

Age-related declines in attention and cognition have been associated with a difficulty in inhibiting the processing of task-irrelevant information (i.e., the inhibitory deficit hypothesis). However, evidence supporting the inhibitory deficit hypothesis remains equivocal, in part because of complexities in examining the processing of irrelevant stimuli using purely behavioral techniques. The effects of age on the processing of task-irrelevant stimuli were examined using scalp-recorded event-related brain potentials. Participants performed a visual discrimination task while standard and deviant auditory stimuli were presented in the background. Deviant auditory stimuli generated a mismatch negativity (MMN) wave that decreased with age, in part because of an age-related enhancement in sensory-evoked responses. The age-related changes in processing task-irrelevant auditory stimuli are consistent with the inhibitory deficit hypothesis and suggest that impaired inhibitory control of sensory input may play a role in the age-related declines in performance during selective attention tasks.

Adult↗
PubMed1987

Adult age differences in the speed and capacity of information processing: 2. An electrophysiological approach.

A total of 60 subjects performed different variants of the Sternberg memory search task in an experiment designed to evaluate aging differences in the speed of the human information-processing system. The present study examined the nature of the age-related slowing using convergent methodologies of Sternberg's additive factors logic, the speed-accuracy trade-off, and the P300 component of the event-related brain potential. These methodologies revealed that a substantial component of slowing was manifest in perceptual encoding, response criterion adjustment, and response execution, with a lesser component related to memory search speed.

Adult↗
PubMed2006

Attending to affect: appraisal strategies modulate the electrocortical response to arousing pictures.

Arousing (unpleasant and pleasant) pictures elicit increased neurophysiological measures of perceptual processing. In particular, the electrocortical late positive potential (LPP) is enhanced for arousing, compared with neutral, pictures. To determine whether the magnitude of the LPP is sensitive to the way stimuli are appraised, 16 participants viewed both pleasant and unpleasant pictures and categorized them along an affective or nonaffective dimension. Results indicate that the LPP was reduced for both pleasant and unpleasant pictures when participants made nonaffective, compared with affective, judgments. These results are consistent with previous studies that have used functional neuroimaging to investigate the role of appraisal on emotional processing. The results are further discussed in terms of the utility of using the LPP to study emotion regulation.

Adult↗
PubMed1994

Flash and pattern visual evoked potentials in the diagnosis and monitoring of dysthyroid optic neuropathy.

Flash and pattern visual evoked potentials were recorded in 8 patients (13 eyes) with dysthyroid optic neuropathy (DON), diagnosed using the American Thyroid Association classification. All were treated with systemic steroids, but 4 patients (6 eyes) also required orbital decompression. Flash VEP (P2) and pattern VEP (P100) were recorded prior to and 2 weeks after commencing steroid treatment or decompression. Fifteen patients with Graves orbitopathy but without DON, and 20 healthy subjects, acted as controls. Before treatment visual acuity was reduced in 10 eyes and visual fields were abnormal in 5, but the VEP was abnormal in all 13, with the group mean amplitude of P2 and P100 significantly less than controls, and the group mean P100 latency significantly greater than controls. After treatment with high-dose steroids or surgical decompression there were significant improvements in the group mean amplitude of P2 and P100, and significant reductions in P2 and P100 latency; however, individually, improvements in amplitude were more significant than improvements in latency. We conclude that the VEP to flash and pattern stimuli provides a useful diagnostic and monitoring tool in patients with DON, combining objectivity with quantitative analysis.

Adult↗
PubMed2004

Parietal somatosensory association cortex mediates affective blindsight.

To investigate the neural substrates underlying emotional feelings in the absence of a conscious stimulus percept, we presented a visual stimulus in the blind field of partially cortically blind patients and measured cortical activity (by functional magnetic resonance imaging, fMRI) before and after the stimulus had been paired with an aversive event. After pairing, self-reported negative emotional valence and blood oxygen level-dependent (BOLD) responses in somatosensory association areas were enhanced, whereby somatosensory activity predicted highly corresponding reported feelings and startle reflex amplitudes across subjects. Our data provide direct evidence that cortical activity representing physical emotional states governs emotional feelings.

Affective Symptoms↗
PubMed2002

Spatial coding of position and orientation in primary visual cortex.

We examined the spatial distribution of population activity in primary visual cortex (V1) of tree shrews with optical imaging and electrophysiology. A line stimulus, thinner than the average V1 receptive field, evoked a broad strip of neural activity of nearly constant size for all stimulus locations tested within the central 10 degrees of visual space. Stimuli in adjacent positions activated highly overlapping populations of neurons; nevertheless, small changes in stimulus position produced orderly changes in the location of the peak of the population response. Statistically significant shifts in the population response were found for stimulus displacements an order of magnitude smaller than receptive field width, down to the limit of optical imaging resolution. Based on the pattern of population activity, we conclude that the map of visual space in V1 is orderly at a fine scale and has uniform coverage of position and orientation without local relationships in the mapping of these features.

Action Potentials↗
PubMed1996

[Measuring vernier acuity and motion perception with the parameter sweep VEP].

BACKGROUND: The visual abilities of infants and small children, who are unable to communicate verbally, can be determined with "objective" visual acuity tests as, e.g., preferential looking (PL) or visual evoked potentials (VEP). Both methods provide an estimate of grating visual acuity, but are unable to determine optotype visual acuity. Grating acuity, however, is not an optimum indicator for visual performance, as it is less affected than optotype acuity by pathological changes. The diagnostic relevance of objective methods may be improved by testing visual functions that are more strongly degraded by a malfunction of the fovea than is grating acuity. Visual functions such as vernier acuity and relative motion sensitivity are potential candidates. METHODS: Characteristic properties of vernier- and motion-VEP have been determined on adult subjects with a rapid-sweep-technique at various eccentricities. RESULTS: Both vernier and motion stimuli elicited VEP-responses at the 2nd harmonic (F2) of the stimulus frequency. A VEP-response at the fundamental frequency (F1) could be recorded with the vernier stimulus only. Foveal VEP-thresholds were very similar to psychophysical thresholds lying in the range from 11 to 25 arcsecs. The eccentricity dependence of the VEP-threshold recorded with vernier- and motion stimuli shows different cortical magnifications and supports the notion that the F1 response is related to the detection of the vernier offset, whereas the F2 response is generated by motion components of the stimuli. CONCLUSIONS: Vernier and relative motion-related VEP thresholds can be recorded with the steady-state VEP. They may provide more sensitive tests of foveal vision loss than grating visual acuity tests.

Attention↗
PubMed2000

Unconscious activation of visual cortex in the damaged right hemisphere of a parietal patient with extinction.

Visual extinction is a sign classically associated with right parietal damage. The patient can see a single stimulus presented in the ipsilesional or contralesional visual field, but is characteristically unaware of the same contralesional stimulus during simultaneous stimulation of both fields. The ipsilesional stimulus is said to 'extinguish' the contralesional stimulus from awareness during bilateral stimulation, perhaps due to a pathological bias in attention towards the ipsilesional side. Recent psychophysical evidence suggests that, although extinguished stimuli are not consciously seen, they may undergo residual processing and exert implicit effects on performance. However, the neural structures mediating such residual processing for extinguished stimuli remain unknown. Here we studied the neural activity evoked by an extinguished visual stimulus, using event-related functional MRI (fMRI), in a patient with circumscribed right inferior parietal damage and profound left-sided extinction. Monochrome objects (faces or houses) were presented in the left or right field, either unilaterally or bilaterally on each trial, with the patient indicating by button press whether he saw an object on the left, the right or on both sides. He usually saw only the right object on bilateral trials, yet the fMRI data showed activation of visual cortex contralateral to the extinguished left stimulus on these trials (compared with right-only stimulation), in both striate and early extrastriate areas of the right hemisphere. This activity had a similar location and time-course to that resulting from a single stimulus in the left versus right visual field. Cortical pathways involved in the normal processing of a single seen stimulus can thus still be activated by an unseen, extinguished stimulus after right parietal damage. Comparison of fMRI responses for faces versus houses revealed some category-specific activation for extinguished stimuli in right fusiform regions, but only at low statistical threshold. These results are discussed in terms of theoretical accounts for parietal extinction and, more generally, for the neural substrates of visual awareness.

Aged↗
PubMed2005

The rise and fall of priming: how visual exposure shapes cortical representations of objects.

How does the amount of time for which we see an object influence the nature and content of its cortical representation? To address this question, we varied the duration of initial exposure to visual objects and then measured functional magnetic resonance imaging (fMRI) signal and behavioral performance during a subsequent repeated presentation of these objects. We report a novel 'rise-and-fall' pattern relating exposure duration and the corresponding magnitude of fMRI cortical signal. Compared with novel objects, repeated objects elicited maximal cortical response reduction when initially presented for 250 ms. Counter-intuitively, initially seeing an object for a longer duration significantly reduced the magnitude of this effect. This 'rise-and-fall' pattern was also evident for the corresponding behavioral priming. To account for these findings, we propose that the earlier interval of an exposure to a visual stimulus results in a fine-tuning of the cortical response, while additional exposure promotes selection of a subset of key features for continued representation. These two independent mechanisms complement each other in shaping object representations with experience.

Adaptation, Physiological↗
PubMed2001

Pattern visual evoked potentials in malingering.

OBJECTIVES: We previously developed a new method for estimating objective visual acuity by means of pattern visual evoked potentials (PVEP). In this study, this method was applied to the diagnosis of malingering. MATERIALS AND METHODS: Six patients ranging in age from 40 to 54 years (mean 47 years) with suspected malingering were evaluated by means of the visual evoked potential test, optokinetic nystagmus (OKN) inhibition test, and the visual field test. In the PVEP study, the stimulus consisted of black and white checkerboards (39', 26', 15', and 9') with a visual angle of 8 degrees, contrast level of 15%, and a frequency of 0.7 Hz. One hundred PVEP responses were averaged per session. RESULTS: Routine ophthalmic examinations were normal in all patients. Five patients had a tubularly constricted visual field, and the remaining patient had a normal visual field. The objective visual acuities of the six patients estimated from PVEP were better than their subjective visual acuities estimated with Landolt rings. CONCLUSIONS: Among a variety of psychophysical and electrophysiologic ancillary tests, we consider our PVEP method a useful method for objectively determining visual acuity in a patient with signs of ocular malingering.

Adult↗
PubMed2002

Can the spotlight of attention be shaped like a doughnut? Evidence from steady-state visual evoked potentials.

Visual attention enables observers to extract and process high-priority information in the visualfield. Controversy remains as to whether or not observers can ignore information that falls within the spatial beam of attention. We used an objective physiological measure, the steady-state visual evoked potential (SSVEP), to investigate this question. A stream of flickering small, uppercase letters was embedded in the center of a stream of large, uppercase letters. A unitary beam would result in no difference of the SSVEP amplitude elicited by the small letter stream when it was attended versus ignored (i.e., when subjects attended the large letter stream). Contrary to this prediction, SSVEP amplitude increased by almost 100% when the small letter stream was attended compared with when it was ignored. The results support the notion that the attentional spotlight can be formed like a doughnut, processing central information differentially depending on whether it is attended or ignored.

Adult↗