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PubMed2001

Invariant object recognition in the visual system with error correction and temporal difference learning.

It has been proposed that invariant pattern recognition might be implemented using a learning rule that utilizes a trace of previous neural activity which, given the spatio-temporal continuity of the statistics of sensory input, is likely to be about the same object though with differing transforms in the short time scale. Recently, it has been demonstrated that a modified Hebbian rule which incorporates a trace of previous activity but no contribution from the current activity can offer substantially improved performance. In this paper we show how this rule can be related to error correction rules, and explore a number of error correction rules that can be applied to and can produce good invariant pattern recognition. An explicit relationship to temporal difference learning is then demonstrated, and from this further learning rules related to temporal difference learning are developed. This relationship to temporal difference learning allows us to begin to exploit established analyses of temporal difference learning to provide a theoretical framework for better understanding the operation and convergence properties of these learning rules, and more generally, of rules useful for learning invariant representations. The efficacy of these different rules for invariant object recognition is compared using VisNet, a hierarchical competitive network model of the operation of the visual system.

Learning↗
PubMed1990

Interference with visual short-term memory.

Working memory (Baddeley and Hitch 1974) incorporates the notion of a visuo-spatial sketch pad; a mechanism thought to be specialized for short-term storage of visuo-spatial material. However, the nature and characteristics of this hypothesized mechanism are as yet unclear. Two experiments are reported which examined selective interference in short-term visual memory. Experiment 1 contrasted recognition memory span for visual matrix patterns with that for visually presented letter sequences. These two span tasks were combined with concurrent arithmetic or a concurrent task which involved manipulation of visuo-spatial material. Results suggested that although there was a small, significant disruption by concurrent arithmetic of span for the matrix patterns, there was a substantially larger disruption of the letter span task. The converse was true for the secondary visuo-spatial task. Experiment 2 combined the span tasks with two established tasks developed by Brooks (1967). Span for matrix patterns was disrupted by a visuo-spatial task but not by a secondary verbal task. The converse was true for letter span. These results suggest that the impairment in short-term visual memory resulting from secondary arithmetic reflects a small general processing load, but that the selective interference due to mode of processing is by far the stronger effect. Results are interpreted as being entirely consistent with the notion of a specialized visuo-spatial mechanism in working memory.

Adult↗
PubMed1982

Hemispheric functionality patterns between dextrals and sinistrals in tactile-visual tasks at lower or higher level of mental processes.

Two different patterns of unilateral tactile-visual recognition tasks with random shapes were administered to 64 subjects, 32 right-handed (16 males, 16 females) and 32 left-handed (16 males, 16 females). The main effects were found in the over-all performance: dextral subjects performed better than sinistral subjects; males performed better than females. On the task at a lower level of mental process dextral subjects performed better over-all than the sinistral subjects; however, neither group showed superiority of one hand over the other. On the task at a higher level of mental process performance of sinistral subjects improved to a level equivalent to that of the dextral subjects. Dextral subjects tended to perform better with their left hands, whereas the sinistral subjects scored equally with both hands. The findings are discussed in terms of quantitative and qualitative differences in patterns of hemispheric functionality between dextral and sinistral subjects, and the more specific cerebral activation for tasks at a higher level of mental process is hypothesized.

Adolescent↗
PubMed1978

Visual short-term memory, age, and imaging ability.

Visual short-term memory of young and older adults was studied in relation to imaging ability. Both recall and recognition memory tasks were used and additional variables included stimulus complexity and response delay (recognition tasks) and stimulus complexity and visual masking (recall tasks). Young and older participants were matched on visual discrimination, verbal intelligence, and imaging ability. Stimuli consisted of abstract visual patterns. Age-related decrements in recognition and recall were observed but performance was related to imaging ability only with recall tasks and only for older adults. The results were discussed with reference to mediational strategies and locus of occurrence of age-related decrements in short-term memory.

Adolescent↗
PubMed1991

[Pattern-reversal visual evoked potentials and electroretinography in the early diagnosis of chronic simple glaucoma].

For differential, therapeutic, and prognostic reasons the recognition of early lesions in glaucoma chronicum simplex is very important. Besides sophisticated ophthalmological investigations optic nerve and retinal functions can be tested by flash and pattern-reversal evoked visual potentials and electroretinograms. 38 glaucomatous eyes were investigated by VEP and ERG applying single and flicker flashes as well as transient pattern-reversal stimuli of different check sizes. The results related to the degree of visual field disturbances show the damage of retinal and neuronal elements in a descending order affecting first of all the macular cones, then the rod system, and later on the elements of the second retinal neuron. The ganglion cells seems to be affected after all.

Chronic Disease↗
PubMedDate not supplied

Visual discrimination and short-term memory for random patterns in patients with a focal cortical lesion.

Visual discrimination and short-term recognition memory for computer-generated random patterns were explored in 23 patients with a postsurgical lesion in one of the cortical hemispheres. Their results are compared with those of 23 age-matched volunteers. In a same-different forced-choice discrimination task, d' and log beta (measures of sensitivity and bias), as well as reaction time (RT) were determined. All participants viewed patterns defined either by luminance contrast or isoluminant red-green color contrast, the amplitude of which was adjusted to be 10 times the respective detection threshold level. Block patterns consisting of a 6 x 6 matrix of light and dark (red and green) checks were randomly configured on each presentation. They were presented in pairs, randomly in two visual quadrants for a duration of 200 msec. Three presentation conditions were used: simultaneous presentation of reference and test stimulus, sequential presentation with a short delay (interstimulus interval, ISI = 3 s), and sequential presentation with a long delay (ISI = 6 s). The results indicate that patients with a lesion in the occipitotemporal cortex, the superior temporal cortex and the frontal cortex were significantly impaired on both luminance-contrast and color-contrast pattern discrimination. Patients with damage in the anterior inferotemporal cortex showed no overall impairment. The results suggest that performance in visual discrimination and recognition memory tasks rely on distributed neural processes with more than one neocortical location.

Adult↗
PubMed1988

Tracking multiple independent targets: evidence for a parallel tracking mechanism.

There is considerable evidence that visual attention is concentrated at a single locus in the visual field, and that this locus can be moved independent of eye movements. Two studies are reported which suggest that, while certain aspects of attention require that locations be scanned serially, at least one operation may be carried out in parallel across several independent loci in the visual field. That is the operation of indexing features and tracking their identity. The studies show that: (a) subjects are able to track a subset of up to 5 objects in a field of 10 identical randomly-moving objects in order to distinguish a change in a target from a change in a distractor; and (b) when the speed and distance parameters of the display are designed so that, on the basis of some very conservative assumptions about the speed of attention movement and encoding times, the predicted performance of a serial scanning and updating algorithm would not exceed about 40% accuracy, subjects still manage to do the task with 87% accuracy. These findings are discussed in relation to an earlier, and independently motivated model of feature-binding--called the FINST model--which posits a primitive identity maintenance mechanism that indexes and tracks a limited number of visual objects in parallel. These indexes are hypothesized to serve the function of binding visual features prior to subsequent pattern recognition.

Algorithms↗
PubMed1995

Comparisons of memory for nonverbal auditory and visual sequential stimuli.

Properties of auditory and visual sensory memory were compared by examining subjects' recognition performance of randomly generated binary auditory sequential frequency patterns and binary visual sequential color patterns within a forced-choice paradigm. Experiment 1 demonstrated serial-position effects in auditory and visual modalities consisting of both primacy and recency effects. Experiment 2 found that retention of auditory and visual information was remarkably similar when assessed across a 10s interval. Experiments 3 and 4, taken together, showed that the recency effect in sensory memory is affected more by the type of response required (recognition vs. reproduction) than by the sensory modality employed. These studies suggest that auditory and visual sensory memory stores for nonverbal stimuli share similar properties with respect to serial-position effects and persistence over time.

Adult↗
PubMed1988

[Distribution of spatial attention in position recognition].

Spatial limitation in visual information processing was examined with dot-in-matrix patterns by using a probe recognition procedure. The independent variables were the number (1-16 dots) and the position of target dots. Subjects were four undergraduate students. The data were analyzed and discussed from three points of view; span of attention, spatial limitation of recognition and visual attention. The following became clear: First, the span of position recognition was 4.8. Second, "spatial span of attention" was defined as the range of dot positions at which subjects can perceive target dots with 75% or more accuracy. It extended around the fixation point and shrinked with the increase of the number of target dots. Finally, the distribution of spatial attention was estimated for each target dot condition under the assumption that the hit RT at each probe position reflects the amount of attention allocated there. Distributions estimated were cone-shaped, and the height and extent changed with the number of target dots. It was suggested that spatial limitation (i.e. spatial span of attention) in the processing of spatial positions can be explained by the notion of distribution of spatial attention.

Attention↗
PubMed1996

Recognition of visual stimuli from multiple neuronal activity in monkey visual cortex.

Response patterns recorded with 30 microelectrodes from area 17 of anaesthetized monkeys are analysed. A proportion of the patterns are used to define prototype response patterns. These in turn are used to recognize the stimulus from further non-averaged response patterns. In comparison, recognition by a feedforward 'neural network' is much slower, and slightly inferior. The excitation time structure, with a resolution of about 20 ms, is found to contribute strongly to the recognition. There is some inter-ocular recognition for oriented moving bars, and for on and off phases of switched lights, but none for colours. Generalizations over some stimulus parameters (i.e. cases of confusion) are examined: If small jerking shapes are incorrectly recognized, in general the jerk direction often is the correct one. The onset of a response can most easily be found by determining the dissimilarity relative to spontaneous activity in a sliding window.

Animals↗
PubMed1988

'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↗
PubMed1983

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↗
PubMed1995

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↗
PubMed1988

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↗
PubMed1987

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↗
PubMed1994

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↗