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At least 109 records · Page 6Linked to original sources
PubMed1987

A versatile programmable pattern generator.

A versatile visual pattern generator is described that can be programmed by a microcomputer and is developed as a part of a portable visual evoked potential analysis system. The hardware is contained on one printed circuit board (3" X 10", 7.5 X 25.5 cm) residing in an interface connector of a microcomputer (Apple II). The generator produces signals for commercial 50 Hz video monitors; a calibration procedure based on a photocell measurement corrects for the non-linear voltage intensity characteristic of the phosphor of the video monitor.

Computer Graphics↗
PubMed1991

Visual evoked potential responses of the anesthetized cat to contrast modulation of grating patterns.

Contrast modulation affords independent control of static contrast (C) and changes in contrast (delta C). We found that in anesthetized, paralyzed cats, the visual evoked potential (VEP) was dependent only on magnitude of delta C at each pattern transition, and was independent of the starting or ending contrast level. Increasing modulation frequency to above 2 Hz reduced the VEP monotonically, implying that the time constant for differentiation by the VEP is of the order of 250 msec. The essentially perfect a.c. coupling suppresses standing contrast completely, permitting the full dynamic range of the VEP response system to be used for detection of contrast increments (which results in a decreasing Weber fraction). The difference between our results and those of behavioral studies using contrast modulation can be explained by eye movements present in the behavioral studies which refresh the retinal image of the static contrast in a way uncorrelated to temporal modulation of the stimulus, thus introducing a masking effect.

Anesthesia, General↗
PubMed1992

Analysis of striate activity underlying the pattern onset EP of children.

The checkerboard onset Evoked Potential (EP) does not obtain its adult form before puberty. To determine the site of origin of these processes we studied the origin of the checkerboard onset EP in a group of 10 children between the ages of 6 and 16 years. Since the development of the waveform of the pattern onset EP varies with check size we also studied the dependence of these EPs on check size. The child checkerboard onset EPs described in this paper are dominated by a single source. Following an equivalent dipole source localization approach, the position, orientation and variation in strength of the equivalent dipole is estimated. The position and orientation of this dipole indicates an origin in the primary visual cortex (area 17). The variation in strength of the dipole changes from a single positive deflection, specific for children of 8 years and younger, into a negative-positive complex for the children studied between the age of 9 and 16 years. These changes in waveform must be due to changes in the activity pattern of the striate cortex.

Adolescent↗
PubMed1993

Interactions of spectral, spatial, and temporal mechanisms in the human pattern visual evoked potential.

The human pattern onset-offset visual evoked potential (VEP) was studied with different colours and spatial frequencies presented on a steady homogeneous intensive yellow background. Under this condition a broad, late negative wave (N2) dominated by the blue-sensitive mechanism and a sharper earlier positive wave (P1) dominated by the red-green-sensitive mechanism can be observed. With a 460 nm pattern N2 shows a strong amplitude tuning at low-medium spatial frequencies. With 550 nm an early negative component (N1) is added showing an amplitude tuning at high spatial frequencies. Different spatial resolutions of the two colour mechanisms are thus indicated. With pattern-reversal stimuli the 550 nm stimulus shows a higher temporal resolution than the 460 nm stimulus.

Color Perception↗
PubMed1994

Visual evoked potentials in three-dimensional color space: correlates of spatio-chromatic processing.

Visual evoked potentials (VEPs) were measured for sinusoidal gratings with spatio-chromatic modulation defined in a three-dimensional color space. The spatio-chromatic modulation of the gratings can be decomposed into contributions from an achromatic luminance varying component, an isoluminant component which modulates only the activities of L cones and M cones, and an isoluminant component corresponding to modulation of only S-cone activity. The emphasis of this report is the nature of VEPs resulting from isoluminant spatio-chromatic modulation. The VEP response was characterized along a number of spatial, temporal, and chromatic stimulus dimensions: contrast, spatial frequency, chromaticity in the isoluminant plane, chrominance/luminance ratio, orientation, and temporal frequency. Isoluminant VEPs resulting from stimuli modulating L and M cones are compared with those from S-cone modulation. When appropriate spatiotemporal conditions are employed, both types produce robust VEPs; however, the S-pathway VEPs show considerably longer latencies than do those from LM-pathway activation. The VEP results are compared to psychophysical and single unit electrophysiological observations. VEP latencies exhibit the lowpass character of psychophysical chromatic contrast sensitivity functions but VEP amplitudes show bandpass tuning along both the S and LM axes. An oblique effect, i.e. shorter latencies for horizontal and vertical gratings than for diagonal, is observed in the isoluminant VEP. S-pathway VEPs are used to demonstrate an electophysiological correlate of transient tritanopia. Normative amplitude and latency data for VEPs from selectivity stimulated chromatic mechanisms provide a baseline for clinical electrodiagnostic applications.

Adaptation, Ocular↗
PubMed1996

Specificity and selectivity of chromatic visual evoked potentials.

A paper by Rabin et al. (1994) Vision Research, 34, 2657-2671, claimed that spatially extensive grating stimuli could be used to generate chromatic-specific visual evoked potentials from subjects assumed to have standard spectral sensitivity and tritanopic confusion lines. Here we demonstrate that such spatially extensive stimuli may generate responses which are contaminated by luminance-contrast intrusions. Such intrusions are mainly due to chromatic aberrations and are compounded by the abovementioned assumptions. Claims regarding the chromatic selectivity of VEPs must, therefore, be substantiated by establishing correlations with the known properties of the chromatic system.

Color Perception↗
PubMed1993

Acute effects of ethanol on pattern reversal and flash-evoked potentials in rats and the relationship to body temperature.

The effects of acute ethanol treatment on flash and pattern reversal visual evoked potentials (FEPs and PREPs, respectively) were examined in three experiments using Long-Evans rats. The relationships of evoked potential parameters with blood ethanol concentration and body temperature were examined. In Experiment 1, rats were treated i.p. with vehicle or 0.5, 1.0 or 2.0 g ethanol/kg body weight, and tested 30 min later. The 2.0 g/kg group had prolonged latencies of PREP peaks, no changes in PREP peak-to-peak amplitudes, and lower body temperatures than saline-treated controls. The peak latency shifts were significantly correlated with both blood ethanol concentration and body temperature, and were of a magnitude to be expected from similar changes in body temperature alone. Experiment 2 measured both PREPs and paired-flash FEPs in rats 30 min after injection of either 0, 0.5 or 2.0 g/kg ethanol. PREP changes were found following treatment with the high dose which were similar to those of Experiment 1. Some FEP peak latencies were prolonged and peak-to-peak amplitudes were reduced by both doses of ethanol, despite the fact that body temperatures were reduced at only the high dose. At 2.0 g/kg ethanol, the FEP changes in latency, but not amplitude, were in accordance with what would be expected from body temperature changes alone. The third study attempted to investigate the role of reduced body temperature in producing the visual evoked potential changes by testing at room temperatures of 22 or 30 degrees C. Contrary to expectations, the rats receiving 2 g/kg ethanol were approx. 1 degree C cooler than controls at both room temperatures. Evoked potential latencies were greater in ethanol-treated rats than controls at both room temperatures. There were no significant effects of ethanol on FEP amplitudes. Overall, the effects of low doses of ethanol were independent of temperature changes, but the effects of higher doses of ethanol (2.0 g/kg) could not be distinguished from those produced by differences in body temperature alone.

Analysis of Variance↗
PubMed1984

Spatio-temporal mapping of evoked cerebral activity.

A technique is described for the colour-coded display of averaged scalp electrical activity at 40 instants in time. An application of this technique to the pattern reversal visual evoked potential is discussed, showing the value of spatio-temporal mapping in the interpretation of multichannel evoked potential recordings.

Brain↗
PubMed1986

Methods for the identification of evoked response components in the frequency and combined time/frequency domains.

Two prominent frequency components designated f1 and f2 have been identified in the visual evoked response to the transient presentation of sinusoidal luminance gratings in the range of 0.5-8 c/deg. The components occur at temporal frequencies below the alpha band, with the f1 frequency being roughly half that of the f2 frequency. The f1 component is largest at low spatial frequencies with f2 becoming progressively dominant as spatial frequency is increased. The frequency and amplitude of f1 and f2 change substantially over the time course of the response. This has been studied by calculating the temporal frequency spectrum of the transient evoked potential over successive short-time epochs running through the response. Using this technique, the response is shown to consist of narrow-band frequency peaks or 'formants' emerging at different times after stimulus onset. These formants occur at frequencies other than those of the spontaneous EEG and undergo changes in frequency and amplitude over the time course of the response. Two spectrum analysis techniques were employed: the Discrete Fourier Transform and Linear Predictive Coding. Frequency components were successfully identified in single-trial responses using the LPC technique.

Electroencephalography↗
PubMedDate not supplied

Neuronal generators of the visual evoked potentials: intracerebral recording in awake humans.

Flash and pattern reversal visual evoked potentials were recorded in awake patients undergoing stereotactic procedures for severe dyskinetic disorders resistant to medical treatment. The nucleus ventralis lateralis thalami was reached via an occipital approach. VEPs were recorded on the scalp at the entrance of the intracerebral electrode, and serially from sites at different depths. A polarity reversal of the surface recorded wave form took place as the intracerebral electrode was advanced beneath the surface cortical layers. As concerns F-VEPs, most of the scalp activity mirrored the potentials recorded down to the depth of 70-65 mm from the thalamus. The largest amplitude of intracerebral F-VEPs was obtained from recording sites at 50-70 mm from the thalamus, i.e., in the depth of the calcarine fissure. A negative wave, peaking around 47-50 msec, became evident in recording sites at 30-40 mm from the thalamus but vanished as the electrode was advanced farther. In only one patient could we record a small negative wave, peaking at 33 msec, in the vicinity of the corpus geniculatum externum. Furthermore, the oscillatory activity recorded from the scalp appeared to be generated in the cortical layers. PR-VEPs also underwent polarity reversal as the electrode traversed the cortex. PR-VEPs disappeared more superficially than F-VEPs. No PR-evoked activity could be recorded in the vicinity of the corpus geniculatum externum. We conclude that slow and fast components of VEPs recorded from the scalp are entirely generated in cortical layers.

Brain Mapping↗
PubMedDate not supplied

The influence of pattern size on amplitude, latency and wave form of retinal and cortical potentials elicited by checkerboard pattern reversal and stimulus onset-offset.

Transient pattern electroretinograms (PERGs) and visual evoked potentials (VEPs) were recorded with checkerboard pattern reversal and equiluminance stimulus onset-offset, elicited by a high quality moving mirror stimulator. Different sized checkerboard patterns (0.35-4.2 c/deg) were used as stimulus patterns. The wave forms of the equiluminance stimulus onset responses were similar to ERGs evoked with luminance decrease and the stimulus offset PERGs were like ERGs elicited by luminance increase. The PERG c wave and the VEP showed spatial frequency tuning with pattern reversal and stimulus offset. Spatial frequency tuning was not detectable with PERG a and b waves. Pattern reversal and stimulus onset evoked PERGs had no major spectral components above 40 Hz; stimulus offset evoked PERGs contained components up to 55.3 Hz. Retino-cortical time--measured as a latency difference of the PERG b wave to VEP P100--was identical with pattern reversal and stimulus onset and about 12 msec longer with stimulus offset. Our results suggest that the 3 stimulation modes, reversal, onset and offset induce different types of processing at the retinal and cortical levels. PERG a and b waves to our high luminance/contrast stimuli contain no pattern specific information and the c waves are the sum of luminance and pattern specific responses.

Cerebral Cortex↗
PubMed1992

Alterations in rat flash and pattern reversal evoked potentials after acute or repeated administration of carbon disulfide (CS2).

Because solvents may selectively alter portions of visual evoked potentials, we examined the effects of carbon disulfide (CS2) on flash (FEPs) and pattern reversal (PREPs) evoked potentials. Long-Evans rats were administered ip carbon disulfide either acutely or for 30 days. FEPs or PREPs were recorded prior to and 1, 2, 4, 8, or 24 hr after a single dose of CS2 (0, 100, 200, 400, or 500 mg/kg). Flash evoked potentials were also recorded 1, 2, 6, and 24 hr after the last of 30 doses of 200 mg CS2/kg/day. Acute exposure to CS2 consistently decreased the amplitude of FEP peak N160 at 1 hr, depressed peak N30 amplitude over 2-4 hr, and increased the latency of peaks P21, N30, P46, N56, and N160 for up to 4 hr after treatment. Carbon disulfide decreased the amplitude of PREP peaks P65, N83, P88, and N122 4 hr after treatment. Colonic temperature was depressed up to 8 hr after treatment. Administration of 200 mg CS2/kg/day decreased the amplitude of FEP peak N30 and increased the latencies of peaks P21, N30, P46, N56, and N160 up to 24 hr after the last dose. The differential effects of CS2 on portions of FEPs indicate that FEP peaks can be independently modulated. Changes in PREPs were temporally correlated with alterations in early FEP peaks, but FEP peak N160 was depressed at an earlier time point. Repeated CS2 exposure affected FEPs at lower doses and for a longer time than an acute exposure, similar to the reported greater severity of neurological disturbances following repeated CS2 exposures in humans.

Animals↗
PubMed1981

[Determination of visual acuity by the visually evoked cortical potential (author's transl)].

Monocularly evoked cortical potentials were recorded monopolarly (3 cm above Prot. occ. ext. sup.) to steady-state checkerboard stimuli (check sizes 1.4 to 26 min, rev. freq. 7/s, mean luminance 10.8 cd/m2, field diameter 4.5 deg., centr. fix.). For a number of visual acuities (obtained by inserting plus lenses up to 3.0 dpt) the smallest check size evoking reliable VECPs was related to the visual acuities obtained at a visual test chart. The use of 20 instead of 100 per cent contrast stimuli provided a significant decrease of slope of threshold check size versus visual acuity, resulting in a three-fold increase in the resolution of data. The method permits the evaluation of visual acuities between 0.1 and 1.0 in normals and patients within limits of +/- log 0.1 (1 sigma) and +/- log 0.2 visual acuity (2 sigma).

Adult↗
PubMed1994

Brain potentials and the availability of semantic and phonological codes over time.

ERPs were recorded from subjects performing semantic and rhyme matching tasks using either spoken words, printed words or pictures as stimuli. Mismatches enhanced N400 (in the semantic task) and N450 (in the rhyme task). Onset and peak latencies were shorter for N450 than for N400 with spoken words; this relationship was inverted for pictures. Thus these latencies could index availability of semantic and phonological codes. For printed words, the latencies were shorter for N400 than N450, a result that supports direct-access modes of reading with late phonological code activation. The longer latencies found for N400 and N450 to pictures could suggest longer initial decoding for pictures with respect to words.

Adolescent↗
PubMed1992

A developmental event-related potential study of picture matching in children, adolescents, and young adults: a replication and extension.

Event-related potentials were recorded in a developmental study of picture matching using an adaptation of Posner's (1978) letter-matching tasks. Subjects ranging in age from 6-39 were asked to decide whether two line drawings, presented sequentially, were the same or different on the basis of physical (physical identity), nominal (name identity), or categorical (category identity) criteria. The amplitude of a negativity at 400 ms (Neg400) increased as the number of dimensions on which the two line drawings differed increased. This effect held for all age groups, and was interpreted as reflecting the degree of semantic and/or physical relationship between the two pictures. However, one finding for Neg400 did suggest a qualitative difference in processing mode between the younger and older subjects. Both Neg400 and P3b latencies showed highly significant linear age trends, decreasing with increasing age. These age-related changes were interpreted as demonstrating quantitative speed of processing differences among age groups. The latencies of both Neg400 and P3b increased as the matching criteria became more complex. Moreover, P3b latency increased as the number of dimensions on which the two pictures differed increased, and this did not interact with age. Although both Neg400 and P3b showed age-related changes in scalp distribution, the fact that each was related to the experimental variables in similar fashion in all age groups suggested that they were homologous components across the age range studied. Taken as a whole, the data support continuity of information processing during these tasks across a wide age range.

Adolescent↗