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At least 217 records · Page 12Linked to original sources
PubMed2004

Sexual differentiation traits in functional males with female genital apertures (male symbol fga) in the woodlice Armadillidium vulgare Latr. (Isopoda, Crustacea).

This study reports the results of examination of the gonadal morphology and ultrastructural features of the androgenic hormone (AH)-producing androgenic gland cells of laboratory stocks of functional male woodlice, Armadillidium vulgare, with female genital apertures ( male symbol fga), with and without experimentally induced infections of the sex-ratio-distorting endobacterial parasite, Wolbachia. Males ( male symbol fga) have been reported in wild populations containing individuals infected with this maternally transmitted sex-ratio-distorting parasite. We report a reduction of testicular segment (utricle) number, androgenic gland cell hypertrophy, and electron-dense ultrastructural cytological features in male symbol fga males. The presence of the Wolbachia parasite had no effect on the features we examined. These results suggest that male symbol fga males are produced as the result of a delayed expression/action of the male sex-determining AH which causes a "lag-phase" delay in male differentiation in genetic males and is not due to the presence, in genetic females, of a hypothetical, epigenetic "M" gene as suggested by Rigaud and Juchault. Our results favor the interpretation of males as true genetic (ZZ) males in which the delayed AH action appears to involve cellular AH trafficking pathways which may be controlled by an impaired autosomal gene responsible for AH action.

Animals↗
PubMed1985

[Extraction of symbolic determinants common to a family of biological sequences].

A set of sequences can be defined by their common subsequences, and the length of these is a measure of the overall resemblance of the set. Each subsequence corresponds to a succession of symbols embedded in every sequence, following the same order but not necessarily contiguous. Determining the longest common subsequence (LCS) requires the exhaustive testing of all possible common subsequences, which sum up to about 2L, if L is the length of the shortest sequence. We present a polynomial algorithm (O(n X L4), where n is the number of sequences) for generating strings related to the LCS and constructed with the sequence alphabet and an indetermination symbol. Such strings are iteratively improved by deleting indetermination symbols and concomitantly introducing the greatest number of alphabet symbols. Processed accordingly, nucleic acid and protein sequences lead to key-words encompassing the salient positions of homologous chains, which can be used for aligning or classifying them, as well as for finding related sequences in data banks.

Amino Acid Sequence↗
PubMedDate not supplied

The physics of symbols: bridging the epistemic cut.

Evolution requires the genotype-phenotype distinction, a primeval epistemic cut that separates energy-degenerate, rate-independent genetic symbols from the rate-dependent dynamics of construction that they control. This symbol-matter or subject-object distinction occurs at all higher levels where symbols are related to a referent by an arbitrary code. The converse of control is measurement in which a rate-dependent dynamical state is coded into quiescent symbols. Non-integrable constraints are one necessary condition for bridging the epistemic cut by measurement, control, and coding. Additional properties of heteropolymer constraints are necessary for biological evolution.

Biological Evolution↗
PubMedDate not supplied

Symbols and dynamics in the brain.

The work of physicist and theoretical biologist Howard Pattee has focused on the roles that symbols and dynamics play in biological systems. Symbols, as discrete functional switching-states, are seen at the heart of all biological systems in the form of genetic codes, and at the core of all neural systems in the form of informational mechanisms that switch behavior. They also appear in one form or another in all epistemic systems, from informational processes embedded in primitive organisms to individual human beings to public scientific models. Over its course, Pattee's work has explored (1) the physical basis of informational functions (dynamical vs. rule-based descriptions, switching mechanisms, memory, symbols), (2) the functional organization of the observer (measurement, computation), (3) the means by which information can be embedded in biological organisms for purposes of self-construction and representation (as codes, modeling relations, memory, symbols), and (4) the processes by which new structures and functions can emerge over time. We discuss how these concepts can be applied to a high-level understanding of the brain. Biological organisms constantly reproduce themselves as well as their relations with their environs. The brain similarly can be seen as a self-producing, self-regenerating neural signaling system and as an adaptive informational system that interacts with its surrounds in order to steer behavior.

Animals↗
PubMed2003

Threshold visual acuity testing of preschool children using the crowded HOTV and Lea Symbols acuity tests.

PURPOSE: To compare the testability and threshold acuity levels for very young children on the crowded HOTV logMAR distance visual acuity test presented on the BVAT apparatus and the Lea Symbols logMAR distance visual acuity chart. METHODS: Subjects were 87 Head Start children from age 3 to 3.5 years. Testing consisted of binocular pretraining at near using a lap card as needed, binocular pretraining at 3 m, and threshold testing for each eye. The testing procedure, adapted from the Amblyopia Treatment Study, presented optotypes until the child was unable to correctly name or match three of three or three of four optotypes of a given size. Threshold acuity was the smallest size for which at least three optotypes were correctly identified. RESULTS: Both near and distance pretraining were completed by 71% of children for HOTV and by 75% for Lea Symbols (P =.39). The distribution of threshold acuities differed between the two tests. For the 69 eyes of 53 children who were successfully tested with both optotypes, results from the crowded HOTV acuity test were on average 0.25 logMar (2.5 lines) better than those from the Lea Symbols acuity test (P <.001). CONCLUSIONS: The proportion of children between 3 and 3.5 years of age whose monocular visual acuity could be assessed was high and was similar for the two charts tested. Crowded HOTV acuity results were better on average than results using Lea symbols. The different formats of the two tests may explain the observed differences in threshold acuity level.

Amblyopia↗
PubMed2003

Prototype symbolization in hooded crows.

Studies were undertaken to determine whether four crows previously trained to an image-based abstract selection rule could establish a relationship between the number of elements in a group and initially indifferent symbols (arabic numerals) and operate with these symbols, i.e., studies addressed the ability of these birds to symbolize. Unlike other similar studies, there was no use of special development of associative connections between the symbols and the corresponding arrays of elements, but conditions were created in which birds could observe these relationships on the basis of comparison with previously obtained information. Demonstration series were performed for this purpose, in which correct solutions by the crow resulted in receipt of a number of larvae corresponding to the number of elements in the array pictured or numeral imaged on the stimulus selected by the crow. Images belonged to the same category as the corresponding stimulus for selection (the second stimulus was another category): if the image was an array, then the corresponding picture for selection also bore an array, and vice versa. Crows could solve the task successfully by using an image-based selection rule. In test series, the image and both selection stimuli were initially from different categories: if the image was a numeral, then both selection stimuli were arrays, and vice versa. All four crows successfully coped with this task. Despite the absence of any similarity between the image and "correct" stimulus, they selected the array corresponding to the numeral and vice versa. It is suggested that the birds could achieve this result by comparing the information obtained during the presentation series--about the number of reinforcement units corresponding to each stimulus. Similar experiments showed that crows could use numbers to perform operations analogous to arithmetic addition.

Animals↗
PubMed2003

Symbolic control of visual attention: The role of working memory and attentional control settings.

This study examined how 1 symbol is selected to control the allocation of attention when several symbols appear in the visual field. In Experiments 1-3, the critical target feature was color, and it was found that uninformative central arrows that matched the color of the target were selected and produced unintentional shifts of attention (i.e., involuntary, initiated slowly, producing long-lasting facilitatory effects). Experiment 4 tested whether such selection is the result of an attentional filter or of a competition bias due to a match of incoming information against integrated object representations stored in working memory. Here, the critical feature was shape and color was irrelevant, but matching color arrows were still selected. Thus, features of objects in working memory will bias the selection of symbols in the visual field, and such selected symbols are capable of producing unintentional shifts of attention. ((c) 2003 APA, all rights reserved)

Adult↗
PubMed2001

Pigeons (Columba livia) learn to link numerosities with symbols.

After responding to each element in varying, successive numerosity displays, pigeons (Columba livia) had to choose, out of an array of symbols, the symbol designated to correspond to the preceding number of elements. After extensive training, 5 pigeons responded with significant accuracy to the numerosities 1 to 4, and 2 pigeons to the numerosities 1 to 5. Several tests showed that feedback tones accompanying element pecks, the familiarity of element configurations, and the shape of the elements were not crucial to this performance. One test, however, indicated that the number of pecks issued to the elements was important for numerosities above 2. An additional test confirmed that the birds chose the symbol that corresponded to a particular numerosity rather than the positions that the symbols had held during training.

Animals↗
PubMed2000

One-dimensional three-body problem via symbolic dynamics.

Symbolic dynamics is applied to the one-dimensional three-body problem with equal masses. The sequence of binary collisions along an orbit is expressed as a symbol sequence of two symbols. Based on the time reversibility of the problem and numerical data, inadmissible (i.e., unrealizable) sequences of collisions are systematically found. A graph for the transitions among various regions in the Poincare section is constructed. This graph is used to find an infinite number of periodic sequences, which implies an infinity of periodic orbits other than those accompanying a simple periodic orbit called the Schubart orbit. Finally, under reasonable assumptions on inadmissible sequences, we prove that the set of admissible symbol sequences forms a Cantor set. (c) 2000 American Institute of Physics.

Journal Article↗
PubMed1993

Visual recognition in the peripheral field: letters versus symbols and adults versus children.

The plot of the form-resolving field (FRF) was obtained by tachistoscopically presenting two figures in each stimulus, one in the center of gaze and the other in the peripheral field. The figures in the periphery were placed at various eccentricities in different presentations. The ensuing plot of average letter recognition as a function of eccentricity is the FRF. Only the horizontal components of the FRFs were used in the comparisons. Three sets of figures were used as stimuli: regular-size letters, large-size letters, and symbols. Three groups of subjects were compared: adult ordinary readers, reading children, and pre-reading-age children. The last were tested with symbols only. In letter recognition, the FRFs for young and adult ordinary readers are similar and fall off monotonically and symmetrically with eccentricity, hence conforming with the first Aubert-Foerster law (1857). However, the FRFs tested with symbols are narrower than those tested with letters of the same sizes and stroke widths, which is not in accordance with the first Aubert-Foerster law. In addition, the FRFs of symbols are different for each subject group. It is suggested that recognition in the peripheral field is not determined by visual acuity alone; rather, it is further confined or determined by the visual strategy employed to accomplish the task, and its associated distribution of lateral masking.

Adult↗
PubMed2001

Memory and motor skill components of the WAIS-III Digit Symbol-Coding subtest.

We examined motor skill and memory components of the Digit Symbol-Coding subtest of the WAIS-III in a clinical sample. Research using previous versions of the WAIS in non-clinical samples has suggested that the age-related decline in Digit Symbol-Coding scores is more related to motor ability rather than to the memory requirements of the test. Our results extend this conclusion to a clinical sample, using the WAIS-II. Copy scores measure motor skill on the Digit Symbol-Coding subtest, and Incidental Learning scores (Free Recall and Pairing) measure memory. A large proportion of Digit Symbol-Coding variance was explained by Copy scores with Incidental Learning scores controlled, but Incidental Learning scores explained little additional variance when Copy scores were controlled. The same pattern was found when we used the Immediate Memory and General Memory Indexes from the Wechsler Memory Scale-II as independent measures of memory.

Adult↗
PubMedDate not supplied

Symbolic dynamics applied to optokinetic nystagmus signals.

In this study symbolic dynamics is used to analyse the time evolution of the optokinetic nystagmus (OKN). The inter-saccadic nystagmus differences are transformed into a sequence of three equally numbered letters (symbols) which represents the temporal changes in the inter-saccadic signal: (a) a fall in the temporal change, (b) no changes and (c) a rise in temporal change. The complexity of the data series was then calculated as the entropy of the word length three probability distribution of the symbol sequence. The method was applied to OKN signals from ten healthy subjects and ten patients suffering from vertigo (four tests on each subject) and to 40 artificial white noise data series of the same length as the symbolic representation of the OKN data. Applying Student's t-test showed a statistically significant lower mean entropy value (p<0.05) for the patients.

Adult↗
PubMed1984

Age differences in response time to verbal and symbolic traffic signs.

It is well established that verbal skills are maintained at a high level into old age while visuo-spatial skills begin to decline at an earlier age. it was hypothesized that the elderly would therefore respond more quickly to verbal traffic signs than to symbolic ones. In a test of this hypothesis, response times (RT's) to symbolic and verbal traffic signs were obtained from subjects in two age groups (19-29 and 65-77 years). While the elderly responded more slowly than the young subjects, they were an average of .2 seconds quicker in response to verbal traffic signs than symbolic ones. There were no differences in RT for symbolic and verbal signs for the young subjects. It is clear that the impact of traffic signs changes on the elderly deserves more attention than it is currently being given.

Adult↗
PubMed2006

Preschoolers' speed of locating a target symbol under different color conditions.

A pressing decision in AAC concerns the organization of aided visual symbols. One recent proposal suggested that basic principles of visual processing may be important determinants of how easily a symbol is found in an array, and that this, in turn will influence more functional outcomes like symbol identification or use. This study examined the role of color on accuracy and speed of symbol location by 16 preschool children without disabilities. Participants searched for a target stimulus in an array of eight stimuli. In the same-color condition, the eight stimuli were all red; in the guided search condition, four of the stimuli were red and four were yellow; in the unique-color condition, all stimuli were unique colors. Accuracy was higher and reaction time was faster when stimuli were unique colors than when they were all one color. Reaction time and accuracy did not differ under the guided search and the color-unique conditions. The implications for AAC are discussed.

Attention↗
PubMed2006

Concomitant use of the matrix strategy and the mand-model procedure in teaching graphic symbol combinations.

Matrix strategies employing parts of speech arranged in systematic language matrices and milieu language teaching strategies have been successfully used to teach word combining skills to children who have cognitive disabilities and some functional speech. The present study investigated the acquisition and generalized production of two-term semantic relationships in a new population using new types of symbols. Three children with cognitive disabilities and little or no functional speech were taught to combine graphic symbols. The matrix strategy and the mand-model procedure were used concomitantly as intervention procedures. A multiple probe design across sets of action-object combinations with generalization probes of untrained combinations was used to teach the production of graphic symbol combinations. Results indicated that two of the three children learned the early syntactic-semantic rule of combining action-object symbols and demonstrated generalization to untrained action-object combinations and generalization across trainers. The results and future directions for research are discussed.

Child↗
PubMedDate not supplied

Uncertainty based approach for symbolic classification of numeric variables in intensive care units.

In intensive care units (ICUs), certain parameters must be interpreted taking into account the intrinsic characteristics of each patient or the peculiarities of the clinical case under consideration. Similar temporal evolutions of some parameters in different patients could have different interpretations. Artificial intelligence techniques can aid in resolving this problem through the construction of expert systems (ES). These systems are capable of performing contextual evaluations of the parameters typically monitored in ICUs. This contextual evaluation is usually carried out using symbolic elements. Thus, the symbolic processing of numeric data is an important task to perform. In any event, the assignment of semantic labels to numeric values is always an uncertain and arbitrary process. This suggests the convenience of defining and implementing representation schemes capable of dealing with uncertain knowledge. This paper presents a model for the symbolic processing of numeric variables in which the uncertainty associated with the assignment of literals appears spontaneously. The categorical approach for the symbolic classification of numeric values is a particular case of the proposed model.

Data Interpretation, Statistical↗
PubMed2005

Neural correlates of symbolic number processing in children and adults.

Using functional magnetic resonance imaging, we examined developmental differences in the functional neuroanatomy underlying symbolic number processing. Twelve adults and 12 children had to judge the relative magnitude of two single-digit Arabic numerals. We investigated which brain areas were significantly (P<0.005, uncorrected) more activated during processing of number pairs with small relative to large numerical distances. In the adult group, symbolic distance modulated bilateral parietal regions. In contrast, the group of children primarily engaged frontal regions. We conclude that the functional neuroanatomy underlying symbolic numerical magnitude processing undergoes an ontogenetic shift towards greater parietal engagement. This change may reflect maturation of underlying representations and increasing automaticity in mapping between numerical symbols and the magnitudes they represent.

Adult↗
PubMed2001

Estimating and improving the signal-to-noise ratio of time series by symbolic dynamics.

We investigate the effect of symbolic encoding applied to times series consisting of some deterministic signal and additive noise, as well as time series given by a deterministic signal with randomly distributed initial conditions as a model of event-related brain potentials. We introduce an estimator of the signal-to-noise ratio (SNR) of the system by means of time averages of running complexity measures such as Shannon and Rényi entropies, and prove its asymptotical equivalence with the linear SNR in the case of Shannon entropies of symbol distributions. A SNR improvement factor is defined, exhibiting a maximum for intermediate values of noise amplitude in analogy to stochastic resonance phenomena. We demonstrate that the maximum of the SNR improvement factor can be shifted toward smaller noise amplitudes by using higher order Rényi entropies instead of the Shannon entropy. For a further improvement of the SNR, a half wave encoding of noisy time series is introduced. Finally, we discuss the effect of noisy phases on the linear SNR as well as on the SNR defined by symbolic dynamics. It is shown that longer symbol sequences yield an improvement of the latter.

Journal Article↗