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PubMed1980

Pattern ERGs are abnormal in many amblyopes.

We have used a pattern-reversing chequerboard (1 degree squares, or smaller: 84 per cent contrast, or less: 2 to 16 reversals/sec: field size 22 degrees x 16 degrees: mean luminance 50 cd/m2) to evoke responses from the eyes of young adults and children. ERGs were recorded with gold foil electrodes, which did not interfere with the normal optics. All patients were affected accurately. The fixation point was adjusted so that squinters received the stimulus on corresponding areas of each retina. The normal ERG obtained is 1.5 to 3 mu V in amplitude, and in thirteen normal subjects right and left eyes gave equal responses. The extreme asymmetry detected was c. 10 per cent. In all amblyopes, including children of 6 years old and upwards, satisfactory recordings were obtained. In most amblyopes, the response from the affected eye was 50 per cent or less of the response from the fellow eye. In all cases of failure to respond to treatment, the asymmetry was highly significant. In adults, occluding the screen area corresponding to the area of amblyopic suppression, reduces the ERG in the fellow eye, but does not reduce the ERG in the amblyopic eye. We conclude that amblyopic retina produces very little electrical activity that we can record. The timing, response to frequency of stimulation, and other parameters in the pattern ERG are dissimilar from those in the ERG produced by small changes of luminance. We have little evidence about the class of cell generating the response we observe, but evidently there is peripheral abnormality in the visual system even of amblyopic children.

Adolescent↗
PubMedDate not supplied

[Neurophysiologic mechanisms of the change in visual perception in children between 3 and 7 years of age].

Analysis of evoked potentials (EP) to visual images (a homogenous square, a checker-board and a schematic image of a face) has revealed one and the same type EP configuration and reactivity in the projection and posterior associative areas in three to four year old children. Six to seven year old children have exhibited a specialization of cortical areas involvement in the analysis of visual stimuli of different complexity, as manifested in the predominant reactivity of the projection and anterocentral areas in response to presentiation of the checker-board and of the temporo-parieto-occipital zone in response to the face image. Characteristics of involvement of different areas in the analysis of visual stimuli are compared with reaction time and the "time of central processing" in the course of elaboration of a reaction of choice of images out of various number of alternatives. The dynamics of such characteristics in three to four and six to seven year old children is the same in the choice of easily recognizable checker-board and familiar (face) images and does not coincide at the presentation of probabilistic textures: their differentation is readily achieved only by children of senior age. It is assumed that the nature of involvement of different areas in the reaction to complex visual stimuli accounts for the characteristics of visual perception at different stages of individual development.

Age Factors↗
PubMed1994

[Effect of change in refraction by increasing intraocular pressure with the suction cup method on pattern reversal VECP].

When IOP is increased by the suction cup method, refraction changes will occur, depending on the shape of the cup and the height of the IOP increase. Similar refraction changes were simulated in six healthy volunteers by employing spherical and cylindrical glasses during pattern-reversal visual evoked cortical potential (VECP) with various check sizes and amount of contrast. While the pattern-reversal VECP latencies were not influenced, the amplitudes were reduced considerably. By using contact lenses and a suitably shaped suction cup, refraction changes could be compensated for. In 22 healthy volunteers pattern-reversal VECPs were derived with and without the application of contact lenses with artificially raised IOP. A comparison showed that the amplitudes differed significantly. Without contact lenses a negative pressure of more than 40 mmHg resulted in a drop in the amplitudes with a plateau formed between 80 and 120 mmHg. With compensation by contact lenses the amplitudes are found to be unaltered or even slightly increased until a negative pressure of 120 mmHg is reached in the suction cup, after which they drop. Plotting the pattern-reversal VECP amplitudes (obtained with refraction changes being compensated for by contact lenses) against ciliary perfusion pressure, one finds the characteristic curve described by Ulrich et al., suggesting an autoregulative capacity between 15 and 20 mmHg in healthy persons. The latencies, which remain uninfluenced by refraction changes, are also not altered within an IOP increase of 15-20 mmHg.

Adult↗
PubMed1993

Nerve growth factor promotes functional recovery of retinal ganglion cells after ischemia.

PURPOSE: To investigate the effect of a transient complete ischemia on the function of cat retina and to determine whether nerve growth factor (NGF), which was previously shown to enhance retinal ganglion cell (RGC) survival after optic nerve section in the adult rat, can promote recovery of retinal neurons after the ischemic insult. METHODS: Function of distal and proximal retina was assessed by recording the electroretinogram in response to both homogeneous flickering light (FERG) and contrast reversing gratings (PERG), respectively, 30 days after the induction of a 60-minute episode of ischemia. Visual evoked potentials in response to contrast reversing gratings were also recorded to evaluate visual acuity and contrast thresholds. Cell survival after ischemia was assessed in retinal whole-mounts stained with cresyl violet. Cats were intraocularly treated with NGF every other day, 3 times a week, for 30 days. Controls were treated with either phosphate buffered saline or cytochrome c. RESULTS: After ischemia, the FERG was not significantly affected. On the contrary, the PERG, visual acuity, and contrast thresholds were severely impaired. After NGF treatment, PERG response amplitudes were much less reduced compared to controls, and visual acuity and contrast thresholds were virtually normal. In addition, a larger number of presumed RGCs was present in the NGF-treated retinas compared to the cyt c-treated ones. CONCLUSIONS: The more proximally located retinal neurons, in particular RGCs, are highly vulnerable to ischemia. Intraocular NGF treatment was effective in enhancing the survival and functional recovery of these neurons. This suggests that NGF may represent a novel therapeutic agent for the treatment of ischemic ocular pathologies.

Animals↗
PubMed1993

[Blue-sensitive mechanisms in pattern ERG and VEP].

Pattern onset-offset ERGs and VEPs in response to square-wave stripe patterns of different wavelengths and spatial frequencies under chromatic yellow adaptation (two-channel Maxwellian view) were studied in three subjects. One channel provided a steady homogeneous adapting field of 570 nm, while the other channel, containing the patterns, was superimposed on the adapting field (33 degrees). The spectral sensitivity curve of the ERG had a prominent peak in the blue (460 nm) and a shoulder in the red and green (above 500 nm). For wavelengths below 500 nm the shape of the psychophysically determined sensitivity curve to the onset and offset of the pattern was in close agreement with the electroretinal sensitivity curves determined for a low-amplitude criterion. With almost all wavelengths there were two components in the same VEP response at the same time: a slow negative wave with maximum sensitivity at 460 nm and an earlier fast positive component with maximum sensitivity in the red-green region. When the spatial frequency of a 460 nm test pattern was varied under yellow adaptation the onset response in the ERG showed only very slight spatial tuning. In the onset response of the VEP, however, the slow component showed prominent spatial tuning (around 2 c/deg) under the same conditions.

Adult↗
PubMed1996

[Reliability of parameters of cognitive evoked P3 potentials].

Reliability of event-related P3 parameters. Various parameters of the P3 wave were tested for reliability and test-retest stability. To this end, event-related P3 waves were evoked in 21 subjects during visual and auditory oddball tasks. The protocol was repeated one to two weeks later. Amplitude, latency and area between P3 and baseline were estimated by different procedures. The stability within and between sessions was assessed with the split-half method and a measure of test-retest reliability, respectively. A literature review revealed that latency estimation is most commonly done by computer-aided peak measurement, but determining peak parameters visually after interpellating superimposed artifacts turned out to be significantly more reliable. Interrater reliability for this visual inspection was very high if preestablished rules were employed. Amplitude and area were measured reliably by both computer-aided procedures and visual inspection. The area was quite stable both within and between sessions. Area can serve as a measure of cerebral activation and should therefore be determined. Based on the results recommendations are made about analyzing components of event-related potentials. The need to control for error variance is emphasized. This is the only way to improve methods enough that they will be suitable for use in single case diagnosis.

Adult↗
PubMed2007

Interference with bottom-up feature detection by higher-level object recognition.

Drawing portraits upside down is a trick that allows novice artists to reproduce lower-level image features, e.g., contours, while reducing interference from higher-level face cognition. Limiting the available processing time to suffice for lower- but not higher-level operations is a more general way of reducing interference. We elucidate this interference in a novel visual-search task to find a target among distractors. The target had a unique lower-level orientation feature but was identical to distractors in its higher-level object shape. Through bottom-up processes, the unique feature attracted gaze to the target. Subsequently, recognizing the attended object as identically shaped as the distractors, viewpoint invariant object recognition interfered. Consequently, gaze often abandoned the target to search elsewhere. If the search stimulus was extinguished at time T after the gaze arrived at the target, reports of target location were more accurate for shorter (T<500 ms) presentations. This object-to-feature interference, though perhaps unexpected, could underlie common phenomena such as the visual-search asymmetry that finding a familiar letter N among its mirror images is more difficult than the converse. Our results should enable additional examination of known phenomena and interactions between different levels of visual processes.

Attention↗
PubMed1994

Responses of inferior temporal cortex and hippocampal neurons during delayed matching to sample in monkeys (Macaca fascicularis).

Single-unit activity was recorded from inferior temporal (IT) cortex and the hippocampus in 2 macaques trained on auditory-visual and visual-visual delayed matching-to-sample tasks. The main purpose of the study was to compare the response properties of delay neurons between the 2 areas. The authors noted that (a) IT cortex delay activity was usually selective to a particular stimulus, whereas hippocampal delay activity was usually nonselective; (b) the level of delay activity was generally larger in the hippocampus than in IT cortex; and (c) unlike IT cortex delay activity, hippocampal delay activity tended to increase in magnitude as the delay progressed. The authors also examined the functional significance of delay activity and noted a higher probability of encountering a delay neuron when the monkeys were performing 75%-100% correct as compared with 50%-75% correct. The significance of these findings for visual recognition memory is discussed.

Animals↗
PubMed1999

ERP recordings during a picture fragment completion task: effects of memory instructions.

Sequential implicit (picture fragment completion) and explicit (free recall and recognition) memory tasks were performed by two groups of young adults. Subjects assigned to the intentional condition were asked to memorize the stimuli presented during the picture fragment completion task, whereas subjects assigned to the incidental condition were not so instructed. In the picture fragment completion task, all subjects showed savings (priming), i.e., their identification thresholds for previously seen fragments were lower than those for fragments not previously seen, and no between-group performance difference was found. Free recall performance was better for the intentional than the incidental group, but recognition performance did not differ between the groups. Despite similar between-group performance, event-related brain potentials (ERPs) recorded during the picture fragment completion and recognition tasks revealed between-group differences in information processing. The ERP data suggest that similar behavioral performance during memory tasks may have been associated with distinct neuronal mechanisms subserving priming and recollection.

Adult↗
PubMed2001

Repetition effects for words and nonwords as indexed by event-related fMRI: a preliminary study.

We have previously shown differential effects of stimulus familiarity on the repetition-related responses in right fusiform cortex to both faces and symbols. Repetition of familiar stimuli produced a response decrease, whereas repetition of unfamiliar stimuli produced a response increase. In the present experiment, we used words and nonwords as the familiar and unfamiliar stimuli respectively. In this case, the only fusiform region showing the familiarity-by-repetition interaction was in anterior left fusiform. This left-lateralisation of the fusiform interaction is consistent with our hypothesis that these repetition-related effects occur in the same regions responsible for perceptual recognition of familiar stimuli.

Adult↗
PubMed2001

Orientation discrimination independent of retinal matching by blowflies.

Blowflies, Phaenicia sericata, can be trained to discriminate in a learning paradigm in which one of the two visual cues is positively rewarded. Retinotopic matching of a learned visual image to the same retinal location from viewing to viewing has been hypothesized to underlie visual pattern learning and memory in insects. To address the theory of retinotopic matching, a detailed analysis was made of the flies' body orientations during learned discriminations between +45 degrees and -45 degrees gratings. Initial approaches to the positive rewarded visual cue did not originate from the same spatial location within the behavioral arena with respect to the visual cues; thus, individual flies approached the positive cue from a different vantage point from trial to trial. During initial approaches to the rewarded visual cue, the distributions of body angles with respect to the cue were different from trial to trial for each individual. These data suggest that Phaenicia sericata can learn a visual pattern with one eye region and later recognize the same pattern with another eye region. Thus, retinotopic matching is not necessary for the recognition of pattern orientation in the experimental paradigm used here. The average amount of head turning in the yaw plane was too small to compensate for the changes in body orientation exhibited by the flies. Flies view the visual patterns with distinct retinal regions from trial to trial during orientation discrimination.

Animals↗
PubMed1993

The role of the lateral suprasylvian visual cortex of the cat in object-background interactions: permanent deficits following lesions.

The contribution of the lateral suprasylvian cortex to pattern recognition was studied by behavioural detection experiments in combination with bilateral lesions of different parts of the lateral suprasylvian areas (LSA) and area 7 in seven cats. In a two-alternatives forced choice task the cats had to discriminate simple outline patterns which were additively superimposed on a structured visual background made up of broadband Gaussian noise. For various stimulus conditions (moving or stationary patterns and/or background) the detection probability (PD) of the cats was measured as a function of the signal-to-noise ratio (S/N). Each cat was tested before and after the lesion. Four different types of lesion could be distinguished depending on their extent: (1) lesion of parts of the (LSA); (2) lesion of parts of the LSA with undercutting of areas 17, 18 and 19; (3) lesion of area 7; (4) lesion of area 7 and parts of the LSA. 1. We found that a large bilateral lesion of the LSA led to significant deficits in all test situations which were dependent on the existence of relative velocity of moving patterns against a structured background. The ability of the cats to discriminate simple outline patterns which were kept stationary was not reduced. On the contrary, when they were tested with stationary and moving patterns on unfocused (empty) backgrounds, we found, to our great surprise, that the performance of the lesioned cats was significantly improved compared with intact animals. As these lesioned cats had no deficits with moving patterns on a uniformly grey background, we conclude that the deficits with the moving patterns must have been caused by interactions between patterns and background, and not by movement of a pattern per se. 2. As soon as the lesion of the LSA was extended by a bilateral undercutting of areas 17, 18 and 19 we found very severe deficits in all test situations, regardless of whether the patterns were moving or kept stationary, or whether they were superimposed on a background or not. The most substantial deficits occurred when the patterns were moving on a stationary background. In these situations the cats were no longer able to reach the 84% correct criterion. Again, the cats were able to reach criterion with moving patterns on a uniformly grey background indicating that this deficit is probably caused by the interaction of patterns and background and not by motion of the patterns per se.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗