Organization of interneuronal interaction in the cerebral cortex of cats during training in the recognition of visual signals.
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Animals↗
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Results for “Pattern Recognition, Visual”
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'Real-motion' cells in visual area V2 of behaving macaque monkeys.
Extracellular recordings were made in area V2 of behaving macaque monkeys. Neurons were classified into three groups: non-oriented cells, oriented cells with antagonistic areas and oriented cells without antagonistic areas in their receptive field. All neurons were tested with standard visual stimulations in order to assess whether they gave different responses to the movement of a stimulus and to the movement of its retinal image alone, when the stimulus was motionless and the animal voluntarily moved its eyes. To do this, neuronal responses obtained when a moving stimulus swept a stationary receptive field (during steady fixation) and when a moving receptive field swept a stationary stimulus (during tracking eye movements), were compared. The receptive field stimulation at retinal level was physically the same in both cases, but only in the first was there actual movement of the visual stimulus. Control trials, where the monkeys performed tracking eye movements without any intentional receptive field stimulation, were also carried out. Out of a total of 263 neurons isolated in the central 10 deg representation of area V2, 101 were fully studied with the visual stimulation described above. Most of these (83/101; 82%) gave about the same response to the two situations. About 14% (14/101) gave a good response to stimulus movements during steady fixation and a very weak one to retinal image displacements of stationary stimuli during visual tracking. We have called neurons of this type "real-motion cells" (cf. Galletti et al. 1984). None of the non-oriented cells was a real-motion one, while about an equal percentage of real-motion cells was found among the oriented cells with and without antagonistic areas. Finally, we found only 4 neurons which showed behaviour opposite to that of real-motion cells, i.e. they showed a better response to displacement of the retinal image of stationary stimuli than to actual movement of stimuli. We suggest that real-motion cells might contribute to correctly evaluating movement in the visual field in spite of eye movements and that they might allow recognition of the movement of an object even if it moves across a non-patterned visual background. Present data on area V2, together with similar results observed in area V1 (Galletti et al. 1984; Battaglini et al. 1986), support the view that these two cortical areas analyse the movement in a parallel fashion along with many other characteristics of the visual stimulus.
Animals↗
Visual recognition impairment following medial thalamic lesions in monkeys.
Monkeys with surgical lesions which removed the medial portions of the medial and anterior thalamic nuclei were markedly impaired on a test of object recognition. The same animals were able to learn visual pattern discriminations and a spatial delayed response task at a normal rate. These findings indicate that lesions in the medial thalamus produce a selective impairment in visual recognition memory in monkeys and, consequently, may provide an experimental model for human "diencephalic amnesia".
Animals↗
Variability analysis of visual evoked potentials in humans by pattern recognition in phase domain.
A novel approach to single trial visually evoked potentials (VEP) variability analysis based on a new model of post-stimulus brain electrical activity is presented. The convolution model introduced by the author is experimentally verified by the analysis of flash stimulus effects on EEG amplitude and phase spectra. Pattern recognition in the signal phase domain is proposed for detection of any time locked transient signals. This is illustrated by an application of a clustering algorithm in two-dimensional unwrapped phase of EEG Fourier transform space for occipitally recorded VEPs in human subjects.
Adult↗
Patterns of visual-spatial performance and 'spatial ability': dissociation of ethnic and sex differences.
Is there a common basis for the ethnic and sex differences that are characteristically obtained on psychometric tests of spatial ability? Three experiments approached this question by observing subject differences in the recognition and reconstruction of visual-spatial displays. The pattern of performance on these experimental tasks was compared with that on a traditional spatial ability test. In the first experiment, two samples of 40 students, balanced for sex, from Zimbabwe and Scotland respectively, attempted a forced-choice recognition task for meaningful scenes. Both ethnic groups and both sexes showed equivalent performance. The same subjects then undertook a task involving the reproduction of an arrangement of blocks into two-dimensional plan and elevation views. On this task, involving spatial reorientation, the Zimbabweans made over three times as many errors as the Scots. In a third experiment the requirement for spatial reorientation was added to the original recognition task and this was performed by a further 40 subjects. A significant difference between ethnic groups now emerged and this effect covaried with spatial ability. Again, however, no sex difference was observed. The overall pattern of results points to spatial reorientation as a major factor in the cross-ethnic differences. The absence of a sex difference on the experimental tasks contrasts with its appearance in both samples on the spatial ability test and represents a puzzling obstacle to our current understanding. This dissociation of sex and ethnic differences provides evidence against the hypothesis that they stem from the same source.
Adult↗
Visual discrimination of simple geometrical patterns: II. Atypical responses in a subject suffering difficulties with pattern recognition.
We have applied the experimental methods described by Ike et al. (Spatial Vision, 1987, 2, 13-29) in the study of pattern discrimination by subjects who, during childhood, experienced severe difficulties with reading and spelling. Of the six subjects studied, one still suffers from such difficulties and we show that she performs atypically in certain of the discrimination tasks. In particular, her discrimination responses for elements such as delta are markedly different from those of all other subjects. We interpret these abnormal responses on the basis of the discrimination mechanisms for line orientation and rotation of the elements which were discussed by Ike et al. (1987).
Adult↗
The visual filter mediating letter identification.
We hear periodic sounds, or tones, by means of parallel auditory filters, each tuned to a band of temporal frequency, and we see periodic patterns, or gratings, by means of parallel visual filters, each tuned to a band of spatial frequency. Beyond helping us to see gratings, do these visual filters participate in everyday tasks such as reading and object recognition? After all, grafting visibility only requires the distinguishing of pattern from blank, whereas object recognition, for example letter identification, requires classification by the observer into one of many learned categories. Here we make use of results from hearing research, applying to vision a noise-masking paradigm that reveals the filter(s) mediating any threshold task. We find that letter-identification and grating-detection filters are identical, showing that the recognition of these objects at one size is mediated and constrained by a single visual filter, or 'channel'.
Humans↗
[Evoked potentials in the recognition of words].
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Electroencephalography↗
Event-related potentials of 4-7-week-old infants in a visual recognition memory task.
Event-related brain potentials were recorded from 4-7-week-old infants viewing a visual oddball task. During the task the duration of the infant's visual fixations of the stimuli was recorded. The latency of a frontally predominant negative component (Nc) and magnitude of an early slow wave (NSW) changed as a function of stimulus experience, thereby indicating a sensitivity to the infant's attention, stimulus discrimination and, perhaps, recognition memory. Nc latencies were faster and NSW magnitude was larger to the oddball stimulus than to the frequent stimulus. In addition, the latency of a component over occipital scalp. (N378) was faster to the oddball stimulus and may reflect the first perceptual registration of stimulus change. The latencies of the components allow an analysis of the infant's chronometry of processing. Analysis of looking behavior indicated that the infants also gave longer oddball looks than frequent looks. The relation of the ERP data to the infant's looking behavior suggests that fixation duration and the ERP components can be used as complementary measures of different aspects of the infant's attentional-cognitive processes.
Analysis of Variance↗
Face recognition as a function of social attention in non-human primates: an ERP study.
Epidural event related potentials (ERPs) were recorded from four squirrel monkeys (Saimiri sciureus) during the presentation of pictoral stimuli that comprised real human and monkey faces. Subjects viewed tachistoscopically presented stimuli belonging to four different categories: familiar and unfamiliar human faces, and familiar and unfamiliar monkey faces. Familiar faces were subcategorized into top, middle and bottom according to the perceived individual's dominance ranking in a social hierarchy, as rated by human judges observing the group's social behavior. Waveform peak components to monkey and human faces showed similarities in their spatial distribution. However, larger amplitude N1 and N2 components were elicited in response to monkey compared to human faces, particularly over lateral temporo-parietal sites. A similar trend was observed for the P3 component, with maximal differences along midline electrode site. Responses to familiar and unfamiliar monkey faces showed larger N1s to familiar monkey faces and larger P3s to unfamiliar monkey faces. N1 and P3 components elicited by human faces showed no significant differences between conditions. N2 amplitudes were larger over posterior sites for top-ranked monkeys and larger over frontal sites for middle- and bottom-ranked monkeys. Top-ranked human faces elicited the largest N2 components, middle-ranked faces the next largest, and bottom-ranked faces the smallest. N1, N2, and P3 latencies were similarly sensitive to the ranking of human but not monkey faces. These data suggest that non-human primates exhibit evoked potentials to conspecific and non-conspecific faces that are similar in morphology but different in function. Larger amplitude responses to monkey faces suggests increased processing for that category of stimuli. Additionally, monkey ERPs reflect familiarity with conspecifics but not with human faces. Finally, the social status of the perceived individual, or at least the perceived threat posed by an individual, affects the latencies and magnitudes of ERP components produced by the viewer. These data are consistent with social attention hypotheses which propose that higher status (i.e. more dominant or socially meaningful) members of a group receive more attention than lower status individuals.
Animals↗
Pattern reversal visual evoked potentials following early treatment of unilateral, congenital cataract.
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Aphakia, Postcataract↗
Relationship between cortical lamination and texture sensitivity in complex neurones of the striate cortex in cats.
The present study provides detailed anatomical evidence that the strongly texture-sensitive complex neurones of the cat's striate cortex constitute a discrete subset of all complex neurones, and lie in two bands, deep in lamina III and in lamina V. Physiological properties of simple and complex striate cortical neurones were characterized extracellularly in lightly anaesthetized cats by use of micropipettes filled with 12% Fast Green FCF dye in 2.0 M sodium chloride. Complex neurones were further subdivided on the basis of their length-summating properties for an optimally oriented bar into "standard," "special," or "intermediate" categories and on the basis of their tuning and degree of sensitivity to motion of random texture. Extracellular dye marks were made at strategic locations along each microelectrode track, especially at the site of recording from strongly texture-sensitive complex neurones. Tracks were reconstructed with the aid of the histologically recovered dye marks in sections counterstained with cresyl violet to reveal cortical lamination. The results confirm and refine the inference made by Hammond and MacKay (Exp. Brain Res. 22:427-430, '75; Exp. Brain Res. 30:275-296, '77) and the gross observations from 2-deoxyglucose uptake studies by Wagner, Hoffmann, and Zwerger (Brain Res. 224:31-43, '81) concerning the laminar distribution of texture-sensitive complex neurones in the cat's striate cortex.
Animals↗
Luminance-unbalanced pattern onset-offset electroretinogram and visual evoked cortical potential.
The effects of a luminance-unbalanced pattern onset-offset mode of stimulation on electroretinograms and visual evoked cortical potentials were investigated. With the use of originally devised software, only offset luminance was varied from 14.7 to 62.3 cd/m2. A vertical grating pattern (1.5 c/deg, 38.8 cd/m2 mean luminance, 0.95 contrast) was presented for 260 ms and was absent for 260 ms to normal subjects. With an increase in the luminance level of the offset pattern from the lowest level, the amplitude of the onset electroretinogram increased by degrees, while that of the offset electroretinogram gradually decreased. Conversely, onset visual evoked cortical potential responses decreased gradually, and offset visual evoked cortical potentials increased correspondingly. Furthermore, the spatial tuning of the onset pattern electroretinogram was already ambiguous, even when there was only a 4-cd/m2 difference between onset and offset pattern luminances. Thus, luminance control is indispensable for pattern onset-offset stimulation.
Adult↗
The application of Laplacian analysis in the recording of half-field pattern-onset evoked potentials.
The Laplacian operator in electroencephalographic measurements consists of a mathematical combination of the responses from a number of electrodes (e.g., five in a crosswise montage). It enhances activity from sources lying underneath the area covered, relative to activity from outside this area. Thus, by appropriate positioning, the contributions of extrastriate and striate sources can be recorded selectively. To quantify the contribution of each hemisphere to half-field onset evoked potentials, the responses in two Laplacian operators, one over each hemisphere, were analyzed and compared to monopolar derivations and a bipolar derivation between the two hemispheres. Both the Laplacian and bipolar analyses were helpful in interpretation of the responses.
Electrodes↗
Influence of a twofold voluntary hyperventilation on visually evoked cortical potentials and human pupillogram.
We studied the direct and aftereffects of twofold hyperventilation (HV) on pattern reversing VEPs and pupillograms (PGs) of 19 healthy volunteers. The VEP-N80 and P100 latencies increased during HV. Both peak times were maintained for a longer period, up to 20 minutes after HV-2 ended. In addition, the PG-latency time during HV and the PG-construction time during and after HV were increased. The results indicated a temporary delay of neural afferent transmission in the visual system during and after HV. A similar delay of the nervous transmission appeared in the efferent part of the system regulating the pupillary movements after HV ended. The observed changes of the VEP and PG parameters most probably resulted from the hypocapnia cased by HV and its effect on the brain vessels, although other explanations for the changes of the VEP- and PG-parameters may have been possible.
Adult↗
Spatial frequency characteristics of brisk and sluggish ganglion cells of the cat's retina.
Receptive fields of cat retinal ganglion cells were stimulated by a drifting sinusoidal luminance pattern of fixed (50%) contrast and the amplitude of the fundamental frequency component of response was determined as a function of spatial frequency. Frequency response functions for most cells were unimodal and skewed towards zero frequency when plotted on linear scales. At a fixed retinal location, cells of different classes had different frequency response functions. Heterogeneity within some of the classes could be largely removed by normalizing the axes, thus, revealing a common shape of function for the class. At a fixed retinal location, the maximum response obtained at each spatial frequency was always obtained from a cell of the brisk, rather than sluggish, classes. Spatial frequency resolution was highest for brisk-sustained cells and usually lowest for brisk transient cells.
Animals↗
Topographic mapping and source localization of the pattern reversal visual evoked magnetic response.
The topography of the visual evoked magnetic response (VEMR) to pattern reversal stimulation was studied in four normal subjects using a single channel BTI magnetometer. VEMRs were recorded from 20 locations over the occipital scalp and the topographic distribution of the most consistent component (P100M) studied. A single dipole in a sphere model was fitted to the data. Topographic maps were similar when recorded two months apart on the same subject to the same stimulus. Half field (HF) stimulation elicited responses from sources on the medial surface of the calcarine fissure mainly in the contralateral hemisphere as predicted by the cruciform model. The full field (FF) responses to large checks were approximately the sum of the HF responses. However, with small checks, FF stimulation appeared to activate a different combination of sources than the two HFs. In addition, HF topography was more consistent between subjects than FF for small check sizes. Topographic studies of the VEMR may help to explain the analogous visual evoked electrical response and will be essential to define optimal recording positions for clinical applications.
Adult↗
The pattern electroretinogram and visual-evoked potential in glaucoma.
The pattern electroretinogram (PERG) may reflect ganglion cell or inner retinal layer activity. The most sensitive spatial and temporal variables for testing patients with glaucoma have not yet been identified. Fifty-two glaucoma suspects, 51 glaucoma patients, and 28 normal subjects were studied with the PERG and VEP, using three repetition rates and three spatial frequencies. Fast Fourier transforms were calculated at each spatial frequency and reversal rate. An analysis of variance revealed that normals could be differentiated from ocular hypertension and glaucoma patients using the amplitude of the PERG (second and fourth harmonic). Abnormalities in phase of the PERG between groups were also detected. A discriminant analysis of all amplitude and phase data revealed that the phase shift of the response of the second harmonic at 11 alternations/s (15-min checks) and at 5.5 alternations/s (15-min checks) correctly identified 81% of the normal and 75% of the glaucoma patients. The phase shift determinations of the VEP revealed significant abnormalities using 2 and 1/2 standard deviation confidence limits. There was significant overlap in the pattern ERG amplitude and phase shift in all three groups.
Analysis of Variance↗