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PubMed1985

Functional visual field of patients with visual field loss.

To assess the capability of perceiving forms in patients with visual field loss, a concept of functional visual field was introduced based on determinations of the time required for pattern recognition. Two series of stimulus patterns were made of Japanese syllabic hiragana characters drawn with black dots in the background of open circles of various sizes: the clear stimulus had only open circles in the background and the noisy stimulus had black dots scattered in the background. The stimuli were presented for various durations to 15 normal subjects and 25 patients with narrowed visual field; a correlation of the percentages of correct pattern recognition with the stimulus durations permitted calculations of the 50% recognition time. The recognition time was longer with the noisy than with the clear stimuli. The recognition time with a given stimulus size was longer in patients than in normal subjects. In 3 normal subjects the visual field was artificially narrowed and the recognition time was determined. The recognition time could be expressed by a power function of the ratio of the effective visual field diameter to the diameter of the stimulus pattern. On this basis the functional visual field size of a patient was defined as the size of the artificially narrowed visual field of the normal subject that required the same recognition time as that of the patient. The functional visual field of patients could be correlated with the area of the perimetric field with the V/4 target of Goldmann's projection perimeter. The concept of the functional visual field was found to be useful to express the patients' capability for pattern perception.

Adult↗
PubMed1982

Sensory and non-sensory visual disorders in man and monkey.

The posterior third of the cerebral cortex in monkeys consists of a patchwork of visual areas in each of which there is a 'map' of the retina. The details of the 'map' vary considerably from one area to another and one notable variation concerns the optimal visual feature to which the cells respond. Orientation, disparity, colour and movement are emphasized in separate areas that appear to be concerned with sensory analysis. Their existence and the possibility that brain damage is occasionally restricted chiefly to one such area may explain the rare highly selective visual sensory impairments that can follow posterior cerebral damage in man. Other areas are notable for having little or no retinotopic representation. Here the cells may have huge receptive fields and complex trigger features. When such regions are removed, the animal's visual sensory abilities are intact but its recognition of patterns and objects is not. This condition resembles human visual agnosia.

Agnosia↗
PubMed1992

The topographic distribution of the magnetic P100M to full- and half-field stimulation.

Visual evoked magnetic responses were recorded to full-field and left and right half-field stimulation with three check sizes (70', 34' and 22') in five normal subjects. Recordings were made sequentially on a 20-position grid (4 x 5) based on the inion, by means of a single-channel direct current-Superconducting Quantum Interference Device second-order gradiometer. The topographic maps were consistent on the same subjects recorded 2 months apart. The half-field responses produced the strongest signals in the contralateral hemisphere and were consistent with the cruciform model of the calcarine fissure. Right half fields produced upper-left-quadrant outgoing fields and lower-left-quadrant ingoing fields, while the left half field produced the opposite response. The topographic maps also varied with check size, with the larger checks producing positive or negative maximum position more anteriorly than small checks. In addition, with large checks the full-field responses could be explained as the summation of the two half fields, whereas full-field responses to smaller checks were more unpredictable and may be due to sources located at the occipital pole or lateral surface. In addition, dipole sources were located as appropriate with the use of inverse problem solutions. Topographic data will be vital to the clinical use of the visual evoked field but, in addition, provides complementary information to visual evoked potentials, allowing detailed studies of the visual cortex.

Adult↗
PubMed1991

Spatial frequency of the human short-wavelength-sensitive (blue) cone mechanism. Psychophysical studies and pattern-reversal visual evoked potentials.

The interactions of spatial and chromatic processing of the short-wavelength-sensitive cone mechanism were studied in humans with patterned (checkerboard) stimuli of various spatial frequency (10, 22, 44, and 85 min of are respectively), under steady exposure to yellow light (575 nm, 390 cd/m2). Psychophysical studies and pattern-reversal visual evoked potentials were employed. Parameters of the transient pattern-reversal visual evoked potentials (pattern reversal rate of 2.4 s-1) especially observed were the latencies of P2 (P100) and N3 and the amplitude of P2-N3. It was only with the largest applicable check size (85 min of arc) that both the psychophysical studies and visual evoked potentials could succeed in satisfactorily isolating the short-wavelength-sensitive cone mechanism. Pattern-reversal visual evoked potential latencies are recommended in the evaluation of this cone mechanism because of their smaller variance and higher selectivity in isolating the short-wavelength-sensitive cone mechanism than the amplitude. The peak sensitivity of this cone mechanism was shown to be about 449 nm at the corneal level. The short-wavelength sensitive cone mechanism represented the characteristics of low spatial resolution and long latencies of the pattern-reversal visual evoked potentials.

Adult↗
PubMed1986

Effect of contrast on spatial frequency tuning of neurones in area 17 of cat's visual cortex.

Previous investigations have revealed that perceived spatial frequency of gratings rises as contrast is lowered. In order to account for this finding it has been postulated that the spatial frequency which produces the maximum response from cortical neurones decreases with contrast. We have examined this hypothesis by determining optimal spatial frequency at 3-5 different contrast levels for 37 neurones in the cat striate cortex. For the complete sample no systematic changes in optimal spatial frequency was observed. However, a shift in the predicted direction was found for cells tuned to high spatial frequencies.

Animals↗
PubMed1986

Pattern-reversal visual-evoked potentials in the diagnosis of amblyopia in children.

We assessed the potential clinical usefulness of pattern-reversal visual-evoked potentials in the diagnosis of amblyopia. Twenty-seven children with anisometropic amblyopia and four children without amblyopia participated. Estimates of visual acuity for each eye (Snellen visual acuity) were obtained by conventional psychometric methods. Visual-evoked potentials to reversing checks subtending 15 minutes of visual arc were also obtained. Visual-evoked potential testing and interpretation were done in a masked fashion. Ten of the 31 children were retested seven to 21 days after the first test to estimate reliability of the procedures. Of the 27 amblyopic children, 22 were correctly identified by the visual-evoked potential test alone. In four patients initial visual-evoked potential tests failed to identify the disparity in visual acuity between the eyes and retests in two of the four again had false-negative results. In one child initial visual-evoked potential testing incorrectly identified the amblyopic eye but repeat testing did identify it. Of the four children with symmetrically good vision, three were correctly identified as normal by the initial visual-evoked potential test. The other normal child was incorrectly identified by the visual-evoked potential test as having amblyopia.

Adolescent↗
PubMed1987

Focal lesions of visual cortex--effects on visual evoked potentials in rats.

Focal lesions were placed in the visual cortex of Long-Evans hooded rats, immediately below skull screw recording electrodes. Lesions were produced by heat, and extended an average depth of about 0.9 mm below the cortical surface. Evoked potentials recorded from the electrode overlying the cortical lesion were compared with simultaneously recorded potentials from a contralateral homotopic site. The effects of the lesion were selective. Flash-evoked potential peaks P1, P2, and N2 were depressed by the lesion, and peaks N1 and P3 were augmented; peak N3 was unaffected. Pattern reversal evoked potential peak N3 was depressed by the lesion, and peaks N1 and P2 were made more distinct. The results emphasized that different peaks have different generators, and suggest in particular that flash-evoked potential peaks P1 and N2, and peak N3 of the pattern reversal-evoked potential require the superficial layers of the cortex.

Animals↗
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↗
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↗
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↗
PubMed1983

Abnormal evoked potential latencies in amblyopia.

The latency of the first (P1) and second (P2) major positive waves of the pattern reversal visual evoked potential (VEP) for small checks (15 minutes of arc) was measured in 68 visually normal children and 32 amblyopic children with mild to moderate visual acuity losses. In the normal children there were no P1 and P2 interocular latency differences. The amblyopic children showed longer P1 latencies and shorter P2 latencies in their amblyopic eye than their normal fellow eye. These findings can be accounted for by a selective loss of the contrast-specific evoked potential mechanisms in amblyopia. The 'shorter' P2 latency obtained from amblyopic eyes for small checks is a reflection of the luminance responses that are normally elicited by larger (60 minute) checks.

Amblyopia↗