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PubMedDate not supplied

Pattern-onset visual evoked potentials: more useful than reversal for patients with nystagmus.

PURPOSE: The visual evoked potential is often used to assess visual function in neurologically impaired patients, a group in whom nystagmus is a common feature. Pattern-reversal stimuli are commonly used to produce visual evoked potentials in clinical practice. Previous reports have shown that this stimulus is not optimal when subjects have nystagmus. The present study aimed to compare the efficacy of pattern-onset and reversal stimuli when used to measure visual evoked potentials from subjects with idiopathic nystagmus. METHODS: In five adults with congenital nystagmus and 10 visually normal adults, VEPs were recorded and reproduced for checkerboard stimuli of two sizes (120' and 60'). Each size was presented as both pattern-onset and reversal check. RESULTS: Visually normal adults demonstrated similar visual evoked potential amplitudes and quality in response to pattern-reversal and pattern-onset. However, in the presence of nystagmus, visual evoked potentials recorded to pattern-reversal stimuli were significantly smaller and of poorer quality than those obtained to pattern-onset stimuli (analysis of variance p<0.05; Kendall's tau, p<0.05). CONCLUSIONS: Pattern-onset stimuli produce larger and clearer visual evoked potentials in patients with nystagmus compared with those produced to pattern-reversal stimuli.

Adult↗
PubMed2001

Detection of coloured patterns by honeybees through chromatic and achromatic cues.

We asked whether the detection range of two-coloured centre-surround patterns differs from that of single-coloured targets. Honeybees Apis mellifera were trained to distinguish between the presence and absence of a single-coloured disc or a coloured pattern at different visual angles. The patterns presented colours which were either different in chromatic and L-receptor contrasts to the background, equal in chromatic but different in L-receptor contrasts, or vice-versa. Patterns with colours presenting only chromatic contrast were also tested. Patterns with higher L-receptor contrast in its outer than in its inner element were better detected than patterns with a reversed L-contrast distribution. However, both were detected worse than single-coloured discs of the respective colours. When the L-receptor contrast was the same for both elements, the detection range of the two-coloured and single-coloured targets was the same. Patterns whose colours lacked L-receptor contrast were detected just as single-coloured targets of the same colours. These results demonstrate that both chromatic and L-receptor contrasts mediate the detection of coloured patterns and that particular distributions of L-receptor contrast within a target are better detected than others. This finding is consistent with the intervention of neurons with centre-surround receptive fields in the detection of coloured patterns.

Animals↗
PubMed1986

Pattern perception in infants: effects of structure and transformation.

Four experiments on pattern perception in 4-month-old infants are reported. The first two experiments examined the perception of pattern structure as defined by Garner (1974). Although the infants did not show an immediate preference for well-structured patterns (Experiment 1), during habituation they showed a reliable decrement in looking only to well-structured patterns (Experiment 2). On recovery trials in Experiment 2 infants were presented with two types of pattern change: a new configuration of the habituation pattern and a change in the orientation of the habituation pattern. The infants recovered looking to the orientation change, but generally not to the changes in configuration. It is argued that the results of Experiment 2 highlight the role of symmetry, especially vertical symmetry, in infant pattern perception. Recovery of looking to changes in the orientation, size, and position of the habituation pattern was examined in Experiments 3 and 4 where it was demonstrated that such changes are salient to the infant, arguably because of the presence of a surrounding, external frame.

Attention↗
PubMed2006

Gli2 and Gli3 play distinct roles in the dorsoventral patterning of the mouse hindbrain.

Sonic Hedgehog (Shh) signaling plays a critical role during dorsoventral (DV) patterning of the developing neural tube by modulating the expression of neural patterning genes. Overlapping activator functions of Gli2 and Gli3 have been shown to be required for motoneuron development and correct neural patterning in the ventral spinal cord. However, the role of Gli2 and Gli3 in ventral hindbrain development is unclear. In this paper, we have examined DV patterning of the hindbrain of Shh(-/-), Gli2(-/-) and Gli3(-/-) embryos, and found that the respective role of Gli2 and Gli3 is not only different between the hindbrain and spinal cord, but also at distinct rostrocaudal levels of the hindbrain. Remarkably, the anterior hindbrain of Gli2(-/-) embryos displays ventral patterning defects as severe as those observed in Shh(-/-) embryos suggesting that, unlike in the spinal cord and posterior hindbrain, Gli3 cannot compensate for the loss of Gli2 activator function in Shh-dependent ventral patterning of the anterior hindbrain. Loss of Gli3 also results in a distinct patterning defect in the anterior hindbrain, including dorsal expansion of Nkx6.1 expression. Furthermore, we demonstrate that ventral patterning of rhombomere 4 is less affected by loss of Gli2 function revealing a different requirement for Gli proteins in this rhombomere. Taken together, these observations indicate that Gli2 and Gli3 perform rhombomere-specific function during DV patterning of the hindbrain.

Animals↗
PubMed2002

Altered whisker patterns induced by ectopic expression of Shh are topographically represented by barrels.

Barrels in the somatosensory cortex are segregated columns, which somatotopically relate to facial whiskers. The barrel pattern is assumed to be determined by an extrinsic mechanism (the domino theory). This theory is based on whisker lesion experiments and developmental observations regarding the serial establishment of the somatotopic pattern in which pattern formations are relayed from the periphery to the central nervous system. However, the barrel pattern is possibly determined by an intrinsic mechanism, especially in its primitive form. In order to investigate the definitive mechanism, we established an experimental system in which the cortical barrel pattern can be altered, not by using a lesion paradigm, but by epigenetically changing the whisker pattern. Sonic hedgehog (Shh) plays a pivotal role in whisker development. We transfected an adenovirus harboring chicken Shh (Ad-cShh) to mouse embryos (E9.5-E11.5) using an in utero surgical technique. When Ad-cShh was expressed in the epidermis, Bmp4, Ptch, Ptch2 and Gli1 were induced ectopically in the interfollicular region. In contrast, the expression of Bmp2 and Shh itself was unaltered. At a suitable dose of Ad-cShh, some pups displayed supernumerary whiskers or a disordered whisker pattern. The barrel patterns of these mice after the critical period were topographic representations of the contralateral side of the new whisker patterns when visualized by a cytochrome oxidase or Nissle staining method, supporting the instructive role of the extrinsic mechanism.

Afferent Pathways↗
PubMedDate not supplied

The binding of visual patterns in bumblebees.

Bees navigating between their nests and foraging sites rely on their ability to learn and to recall many complex visual patterns [1-4]. How are the elements that make up one of these patterns bound together so that the whole pattern can be recalled when it is required? Consider the sentence: 'Dons nod off.' The words in it can be distinguished by the pattern of elements or letters that they contain. Words may contain the same elements arranged in different orders (don, nod), or contain elements of different types, or vary in both these respects (nod, off). We show here that bumblebees (Bombus terrestris) can learn to group the elements of a pattern together, such that different identifiable patterns contain the same elements in different combinations--analogous to the grouping of letters found in words. Our results suggest that pattern binding in bees is achieved in part by linking pattern elements directly together and in part by associating the elements with cues that are related to the context in which the pattern is seen.

Animals↗
PubMed1991

Some observations on the perception of Marroquin patterns.

Demonstrations are presented to show that the perception of structure in Marroquin patterns is disrupted if the dots comprising the pattern have opposite contrast polarity, and also if the dots comprising the pattern are separated in stereoscopic depth. It is also demonstrated that the perception of structure in a Marroquin pattern is made possible if the pattern is separated in stereoscopic depth from 'noise' dots, where the pattern structure cannot be perceived in either half of the unfused stereogram. In these respects the perception of Marroquin patterns is similar to the perception of Glass patterns. These findings are thus consistent with the proposal that the perception both of Marroquin and of Glass patterns is based on the construction of virtual lines.

Attention↗
PubMed1993

Focal visual attention and pattern discrimination.

Pattern discrimination in the presence of distractor patterns is improved when the stimulus display is preceded by a precue designating the location of the target pattern. Experiments were conducted to determine how big an improvement the precue produced. The specific question of whether the observer is able to process selectively the stimulus pattern in the cued location of the display and ignore the patterns of the noncued locations was addressed. In order to study this, reaction time for pattern discrimination on a blank background (no distractors) was compared with the reaction time when the observer performed the same discrimination task in the presence of distractors and a precue had indicated the location of the stimulus pattern to be discriminated. The results showed that these two reaction times were equal if the cue preceded the stimulus patterns at intervals which were longer than some minimum time. Hence, stimuli outside the 'aperture' of focal attention can be ignored. These results could not be attributed to eye movements, because the longest duration of the whole sequence of precue and stimulus patterns was only 200 ms.

Adult↗
PubMed1996

Qualitative cues in the discrimination of affine-transformed minimal patterns.

An important factor in judging whether two retinal images arise from the same object viewed from different positions may be the presence of certain properties or cues that are 'qualitative invariants' with respect to the natural transformations, particularly affine transformations, associated with changes in viewpoint. To test whether observers use certain affine qualitative cues such as concavity, convexity, collinearity, and parallelism of the image elements, a 'same-different' discrimination experiment was carried out with planar patterns that were defined by four points either connected by straight line segments (line patterns) or marked by dots (dot patterns). The first three points of each pattern were generated randomly; the fourth point fell on their diagonal bisector. According to the position of that point, the patterns were concave, triangular (three points being collinear), convex, or parallel sided. In a 'same' trial, an affine transformation was applied to one of two identical patterns; in a 'different' trial, the affine transformation was applied after the point lying on the diagonal bisector was perturbed a short, fixed distance along the bisector, inwards for one pattern and outwards for the other. Observers' ability to discriminate 'same' from 'different' pairs of patterns depended strongly on the position of the fourth, displaced, point: performance varied rapidly when the position of the displaced point was such that the patterns were nearly triangular or nearly parallel sided, consistent with observers using the hypothesised qualitative cues. The experimental data were fitted with a simple probabilistic model of discrimination performance that used a combination of these qualitative cues and a single quantitative cue.

Adult↗
PubMed1998

The effects of visual discomfort and pattern structure on visual search.

Unpleasant somatic and perceptual side effects can be induced when viewing striped repetitive patterns, such as a square wave or a page of text. This sensitivity is greater in participants with higher scores on a scale of visual discomfort. In three experiments the effect that this sensitivity has on performance efficiency in a reading-like visual search task was investigated. In experiments 1 and 2, the 'global' structure of the patterns was manipulated to produce a square-wave, a checkerboard, and a plaid pattern. It was found that the group that suffered severe visual discomfort took significantly longer than other groups to perform the task, with interference greatest with presentation of the square-wave-like pattern. This supports the prediction of greatest distraction of visual attention from the local target elements with presentation of the pattern structure inducing greatest visual discomfort. In experiment 3, the internal pattern components were manipulated and task difficulty reduced. A no-interference and two interference patterns, one with a global characteristic only and the second made up of distracting line elements, containing global and local components were used. The global pattern structure produced interference effects on the visual-search task. All groups performed with the same speed and accuracy on the task involving the no-interference pattern, a finding attributed to reduced task difficulty. McConkie and Zola's model of visual attention was used to explain these results.

Asthenopia↗
PubMed2002

Finding composite regulatory patterns in DNA sequences.

Pattern discovery in unaligned DNA sequences is a fundamental problem in computational biology with important applications in finding regulatory signals. Current approaches to pattern discovery focus on monad patterns that correspond to relatively short contiguous strings. However, many of the actual regulatory signals are composite patterns that are groups of monad patterns that occur near each other. A difficulty in discovering composite patterns is that one or both of the component monad patterns in the group may be 'too weak'. Since the traditional monad-based motif finding algorithms usually output one (or a few) high scoring patterns, they often fail to find composite regulatory signals consisting of weak monad parts. In this paper, we present a MITRA (MIsmatch TRee Algorithm) approach for discovering composite signals. We demonstrate that MITRA performs well for both monad and composite patterns by presenting experiments over biological and synthetic data.

Algorithms↗
PubMedDate not supplied

Visual memory, visual imagery, and visual recognition of large field patterns by the human brain: functional anatomy by positron emission tomography.

We measured the regional cerebral blood flow (rCBF) in 11 healthy volunteers with PET (positron emission tomography). The main purpose was to map the areas of the human brain that changed rCBF during (1) the storage, (2) retrieval from long-term memory, and (3) recognition of complex visual geometrical patterns. A control measurement was done with subjects at rest. Perception and learning of the patterns increased rCBF in V1 and 17 cortical fields located in the cuneus, the lingual, fusiform, inferior temporal, occipital, and angular gyri, the precuneus, and the posterior part of superior parietal lobules. In addition, rCBF increased in the anterior hippocampus, anterior cingulate gyrus, and in several fields in the prefrontal cortex. Recognition of the patterns increased rCBF in 18 identically located fields overlapping those activated in learning. In addition, recognition provoked differentially localized increases in the pulvinar, posterior hippocampus, and prefrontal cortex. Learning and recognition of the patterns thus activated identical visual regions, but different extravisual regions. A surprising finding was that the hippocampus was also active in recognition. Recall of the patterns from long-term memory was associated with rCBF increases in yet different fields in the prefrontal cortex, and the anterior cingulate cortex. In addition, the posterior inferior temporal lobe, the precuneus, the angular gyrus, and the posterior superior parietal lobule were activated, but not any spot within the occipital cortex. Activation of V1 or immediate visual association areas is not a prerequisite for visual imagery for the patterns. The only four fields activated in storage recall and recognition were those in the posterior inferior temporal lobe, the precuneus, the angular gyrus, and the posterior superior parietal lobule. These might be the storage sites for such visual patterns. If this is true, storage, retrieval, and recognition of complex visual patterns are mediated by higher-level visual areas. Thus, visual learning and recognition of the same patterns make use of identical visual areas, whereas retrieval of this material from the storage sites activates only a subset of the visual areas. The extravisual networks mediating storage, retrieval, and recognition differ, indicating that the ways by which the brain accesses the storage sites are different.

Adult↗
PubMed2000

Farey sequences of spatiotemporal patterns in video feedback.

In this paper we present an experimental and theoretical description of the dynamic of spatial patterns obtained in a video feedback loop. A video camera monitors the screen to which it is connected and can turn around its optical axis at an angle alpha. Under certain conditions of brightness and magnification, this optoelectronic system produces spatiotemporal patterns in the form of spots located on a circle on the screen. These patterns are very similar to the spatial transverse modes obtained in other optical devices such as lasers or photorefractive media. It is possible to generate stationary patterns of n-fold symmetries for angles alpha=2pi/n. When the angle alpha varies around 2pi/n, the pattern rotates with a certain frequency proportional to the difference between 2pi/n and alpha. We discover more general patterns at angles 2pi/(p/k) with p-fold symmetry, following the hierarchy of the Farey algorithm which theoretically can produce stationary patterns at any angle alpha. Very accurate experiments were performed to observe these patterns up to the level k=6. This is the first time a Farey tree has been observed as a sequence of spatial patterns to our knowledge. Previous observations of this hierarchy were made only in the temporal domain.

Animals↗
PubMed2005

Style consistent classification of isogenous patterns.

In many applications of pattern recognition, patterns appear together in groups (fields) that have a common origin. For example, a printed word is usually a field of character patterns printed in the same font. A common origin induces consistency of style in features measured on patterns. The features of patterns co-occurring in a field are statistically dependent because they share the same, albeit unknown, style. Style constrained classifiers achieve higher classification accuracy by modeling such dependence among patterns in a field. Effects of style consistency on the distributions of field-features (concatenation of pattern features) can be modeled by hierarchical mixtures. Each field derives from a mixture of styles, while, within a field, a pattern derives from a class-style conditional mixture of Gaussians. Based on this model, an optimal style constrained classifier processes entire fields of patterns rendered in a consistent but unknown style. In a laboratory experiment, style constrained classification reduced errors on fields of printed digits by nearly 25 percent over singlet classifiers. Longer fields favor our classification method because they furnish more information about the underlying style.

Algorithms↗
PubMed1994

Patterned light flash evoked short latency activity in the visual system of visually normal and in amblyopic subjects.

In a previous experimental study on anaesthetized cat it was shown that a short latency (35-40 ms) cortical potential changed polarity due to the presence or absence of a pattern in the flash stimulus. The results suggested one pathway of neuronal activation in the cortex to a pattern that was within the level of resolution and another to patterns that were not. It was implied that a similar difference in impulse transmission to pattern and non-pattern stimuli may be recorded in humans. The present paper describes recordings of the short-latency visual evoked response to varying light flash checkerboard pattern stimuli of high intensity in visually normal and amblyopic children and adults. When stimulating the normal eye a visual evoked response potential with a peak latency between 35 to 40 ms showed a polarity change to patterned compared to non-patterned stimulation. The visual evoked response resolution limit could be correlated to a visual acuity of 0.5 and below. In amblyopic eyes the shift in polarity was recorded at the acuity limit level. The latency of the pattern depending potential was increased in patients with amblyopia compared to normal, but not directly related to amblyopic degree. It is concluded that the short latency, visual evoked response that mainly represents the retino-geniculo-cortical activation may be used to estimate visual resolution below 0.5 in acuity level.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Balance between pattern and flicker sensitivities in the visual fields of ophthalmological patients.

We measured the balance between visual sensitivities to pattern and to flicker rather than measuring absolute sensitivities to pattern or flicker. The test target was a 2-cycle deg-1 sinewave grating that was counterphase modulated at 8 Hz. Seventeen points in the visual field were tested out to eccentricities of 24 degrees. We examined 10 control subjects, 6 patients with glaucoma 10 with ocular hypertension, and 10 with multiple sclerosis. For controls pattern sensitivity was lower than flicker sensitivity in central vision. The converse held in peripheral vision. The balance between pattern sensitivity and flicker sensitivity was markedly abnormal in part or all of the visual field for many patients. There were examples in all patient groups. In some patients flicker sensitivity was depressed relative to pattern. In others the converse was true. Of 10 patients with ocular hypertension and no perimetric field loss 8 had a significantly abnormal ratio between pattern sensitivity and flicker sensitivity at some point in the visual field. The balance between pattern and flicker sensitivity was more sensitive to visual pathology than absolute sensitivity to either pattern or flicker. We conclude that the relationship between pattern and flicker sensitivity may be more sensitive to visual field damage than is conventional perimetry or visual acuity perimetry.

Adult↗
PubMed1983

Favored patterns in spike trains. II. Application.

In this paper we apply the two methods described in the companion paper (4) to experimentally recorded spike trains from two preparations, the crayfish claw and the cat striate cortex. Neurons in the crayfish claw control system produced favored patterns in 23 of 30 spike trains under a variety of experimental conditions. Favored patterns generally consisted of 3-7 spikes and were found to be in excess by both quantized and template methods. Spike trains from area 17 of the lightly anesthetized cat showed favored patterns in 16 of 27 cases (in quantized form). Some patterns were also found to be favored in template form; these were not as abundant in the cat data as in the crayfish data. Most firing of the cat neurons occurred at times near stimulation, and the observed patterns may represent stimulus information. Favored patterns generally contained up to 7 spikes. No obvious correlations between identified neurons or experimental conditions and the generation of favored patterns were apparent from these data in either preparation. This work adds to the existing evidence that pattern codes are available for use by the nervous system. The potential biological significance of pattern codes is discussed.

Action Potentials↗
PubMed1993

Relationships between color, shape, and pattern selectivities of neurons in the inferior temporal cortex of the monkey.

1. To examine the way in which information from different visual submodalities is integrated in the inferior temporal (IT) cortex of the monkey, we studied the relationships between the color, shape, and pattern selectivities of individual neurons in IT cortex of two awake macque monkeys. Neurons were recorded while each animal performed a visual fixation task. For each neuron, we analyzed selectivity for the visual submodalities of color, contour shape, and textural pattern using preselected standard sets of visual stimuli, namely colored geometrical shapes with certain patterns. 2. About two thirds (62%) of single neurons whose activities were recorded from the anterior part of IT cortex, which included the ventral bank of the superior temporal sulcus, responded to one or more of the stimuli in the standard sets of stimuli used. An index (stimulus selectivity index) was calculated for each neuron to quantify how well a cell discriminated the preferred stimulus from the least preferred stimulus in each set of stimuli. The stimulus selectivity index, as well as the statistical significance of the variation in the responses to the stimuli within a given set, was used to classify a cell as selective or not selective in a given submodality. Of the neurons whose responses were analyzed quantitatively, 69% were selective for color, 68% were selective for shape, and 82% were selective for pattern. 3. Of the neurons that were tested with respect to the selectivity for color and for shape, 45% were selective both for color and shape, 50% were selective for either color or shape, and only 5% were not selective for color or shape. These frequencies were not significantly different from those predicted from the occurrence of the selective and nonselective neurons in each submodality if the independence of the selectivities for color and shape is assumed. We also found that the color preference of individual neurons does not depend on the shape of the stimulus. These results indicate that there was no overt interaction between the selectivities for color and shape in these IT neurons. 4. Of the neurons that were compared with respect to the selectivity for color and for pattern, 58% were selective both for color and pattern, 38% were selective for either color or pattern, and only 4% were not selective for color or pattern. There was no correlation between the degree of color selectivity and the degree of pattern selectivity of individual neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗