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At least 55 records · Page 3Linked to original sources

PubMed2001

Practising orientation identification improves orientation coding in V1 neurons.

The adult brain shows remarkable plasticity, as demonstrated by the improvement in fine sensorial discriminations after intensive practice. The behavioural aspects of such perceptual learning are well documented, especially in the visual system. Specificity for stimulus attributes clearly implicates an early cortical site, where receptive fields retain fine selectivity for these attributes; however, the neuronal correlates of a simple visual discrimination task remained unidentified. Here we report electrophysiological correlates in the primary visual cortex (V1) of monkeys for learning orientation identification. We link the behavioural improvement in this type of learning to an improved neuronal performance of trained compared to naive neurons. Improved long-term neuronal performance resulted from changes in the characteristics of orientation tuning of individual neurons. More particularly, the slope of the orientation tuning curve that was measured at the trained orientation increased only for the subgroup of trained neurons most likely to code the orientation identified by the monkey. No modifications of the tuning curve were observed for orientations for which the monkey had not been trained. Thus training induces a specific and efficient increase in neuronal sensitivity in V1.

Animals↗

PubMed1973

Orientation of intermediates in the bleaching of shear-oriented rhodopsin.

Cattle rhodopsin can be highly oriented by shearing a wet paste of digitonin micelles of this visual pigment between two quartz slides. This orients the rhodopsin micelles so that their chromophores lie mainly parallel to the direction of shear. In such preparations the orientation of rhodopsin and intermediates of its bleaching by light have been measured with plane-polarized light from -195 degrees C to room temperature. The chromophore maintains essentially the same orientation as in rhodopsin in all the intermediates of bleaching: bathorhodopsin (prelumirhodopsin), lumirhodopsin, and metarhodopsins I and II. When, however, the retinaldehyde chromophore is hydrolyzed from opsin in the presence of hydroxylamine, the retinaldehyde oxime that results rotates so as to lie mainly across the direction of shear. That is, the retinal oxime, though free, orients itself upon the oriented matrix of the opsin-digitonin micelles. These experiments show the rhodopsin-digitonin micelle to be markedly asymmetric, with the chromophore lying parallel to its long axis. The asymmetry could originate in the formation of the micelle, in rhodopsin itself, or by its linear polymerization under the conditions of the experiment. If rhodopsin itself is markedly asymmetric, for which there is some evidence, then, since in the rod outer segments its chromophores lie parallel to the disk membranes, the molecules themselves must lie with their long axes parallel to the membranes.

Animals↗

PubMed2000

CGG/CCG repeats exhibit orientation-dependent instability and orientation-independent fragility in Saccharomyces cerevisiae.

An expansion to >200 CGG/CCG repeats (hereafter called CGG) in the 5' region of the FMR1 gene causes fragile X syndrome, and this locus becomes a folate-sensitive fragile site. We used Saccharomyces cerevisiae as a model system to study the stability and fragility of CGG repeats. Tracts of (CGG)(81)and (CGG)(160)were integrated onto a yeast chromosome in both orientations relative to the nearest replication origin. Tracts of this length are pre-mutation alleles in humans, with a high probability of expansion in future generations. The CGG tracts in yeast colonies showed a length-dependent instability with longer tracts being more prone to contraction than shorter tracts. In addition, there was an orientation bias for tract stability with tracts having fewer contractions when the CCG strand was the template for lagging strand synthesis. Expansions of the CGG tracts also occurred in an orientation-dependent manner, although at a lower frequency than contractions. To determine whether CGG tracts are fragile sites in yeast, the CGG tracts were flanked by direct repeats, and the rate of recombination between the repeats determined. Strains carrying the (CGG)(160)tract in either orientation had a large increase in their rate of recombination compared with a no-tract control strain. Because this increase was dependent on genes involved in double-strand break repair, recombination was likely to be initiated by CGG tract-induced breakage between the direct repeats. The observation of orientation-dependent instability and orientation-independent fragility suggests that at least some aspects of their underlying mechanisms are different.

Chromosome Fragile Sites↗

PubMed2000

Orientational ordering in fluids with partially constrained molecule orientations

Molecular orientations in anisotropic fluids can be partially constrained as a result of electric or magnetic fields or interface influences. A statistical approach for the investigation of the orientational ordering in such systems is proposed. The long-range correlations are taken into account consistently. The method is illustrated for the well-known thermotropic nematic model in an infinite disorienting field W, when the molecules are constrained to orient perpendicularly to the field direction. For this problem the analytical solution of the anisotropic Ornstein-Zernike equation is obtained, and the asymptotic expression for the long-range correlations on large distances is given. The phase diagram and elastic constants are calculated for W-->infinity and are compared with the usual case of a uniaxial nematic ordering at W=0. In the case W-->infinity when the temperature decreases the orientational phase transition of the second order becomes the one of the first order at a tricritical point. The disorienting field W increases much the region of an ordered fluid. It is shown that at a given pressure the orientational ordering temperature for W-->infinity is higher about 1.2-1.5 times than the one at W=0. The orientational ordering pressure is less about 4-5 times than the pressure of the uniaxial nematic ordering (W=0) at the same temperature. The disorienting field increases elastic properties of the model under consideration.

Journal Article↗

PubMed1995

The role of attention in the shift from orientation-dependent to orientation-invariant identification of disoriented objects.

In two experiments, the naming of rotated line drawings of natural objects was examined after a training phase in which the objects were either attended or ignored. In the training phase of Experiment 1, subjects were presented with objects in a number of orientations over five repeated blocks of trials. In the center of each object, seven letters (Xs and Ts, colored red or blue) were presented in rapid succession. Half the subjects named aloud the rotated object and ignored the changing letter display (object-attend). The other half ignored the object and counted the number of red Ts, and then used this number to perform a simple multiplication (object-ignore). In the test phase, all subjects named the rotated objects. The results showed that in the first block of trials in the training phase, mean naming time in the object-attend condition increased the further an object was rotated from the upright. This effect of orientation for attended objects was much reduced in the later presentations of the test phase. In contrast, there was no such benefit of prior presentation observed for the naming of objects that had previously been ignored. Instead, a substantial orientation effect was shown for the naming of previously ignored objects, which was similar to the orientation effect observed for attended objects named in the first block. Similar results were found in Experiment 2, in which object-attend subjects in training covertly named the objects and then performed a letter count and multiplication task. In both experiments, performance on the letter count and multiplication task varied with the angle of the ignored object. The results suggest that full attentional resources must be allocated in order for orientation-invariant representations to be formed and used in the identification of rotated objects.

Adult↗

PubMed1995

Active control in interrupted dynamic spatial orientation: the detection of orientation change.

Gibson (1966, 1979) suggested that an important property of perception is that the observer is active. Two experiments were conducted to examine the benefits of active observation in determining dynamic spatial orientation. Subjects were presented with displays simulating locomotion through a three-dimensional environment. Active observers continuously controlled locomotion, whereas passive observers viewed the display. During the trial, the display was blacked out for a brief period, followed by a static image that was at either the correct or the incorrect orientation following the blackout. Subjects were required to indicate whether they were positioned at the correct extrapolated orientation. The presence or absence of orientation change, the type of change (changes in rotation about the depth axis [roll], horizontal axis [pitch], or forward translation), the duration of the blackout, and the consistency of change were varied. In addition, the experiments used either a compensatory or a pursuit tracking task. Active observers had greater sensitivity than did passive observers in detecting a change for both tracking tasks. Subjects in both experiments exhibited greater sensitivity in detecting inconsistent changes (relative to consistent changes), suggesting that the dynamics specified by optical flow were incorporated in extrapolated orientation. In addition, sensitivity decreased with an increase in blackout duration. The results are discussed in terms of an extrapolation model of perception that incorporates the responses executed by active observers.

Attention↗

PubMed1985

Orientation sensitivity and texture segmentation in patterns with different line orientation.

Orientation sensitivity (OS) and the ability of human subjects to discriminate structured areas of different texture orientation (DOT) were investigated using line arrays of varying line length. In general, OS was mediated by shorter lines than was DOT; lines can be distinguished by their orientation before they give the impression of a texture border between adjacent regions with lines differing in orientation. This difference was found to hold over a range of retinal eccentricities from 5 degrees nasal to 30 degrees temporal. Decreasing visual acuity, associated with increasing distance from the fovea, cannot, however, account for the higher threshold of DOT, even taking into account that DOT requires a larger area for analysis than OS. When angle of orientation between adjacent texture areas was varied instead of line length, DOT thresholds at different retinal locations were reached at similar values. The difference between OS and DOT, found consistently at all retinal positions, suggests that they are mediated by distinct neural mechanisms.

Adolescent↗

PubMed1999

A comparison of grain imaging and measurement using horizontal orientation and colour orientation contrast imaging, electron backscatter pattern and optical methods.

The problems associated with the definition of a grain, grain size measurement, and the issues associated with making one- and two-dimensional measurements on a three-dimensional structure are discussed. The relatively new scanning electron microscope (SEM)-based techniques of colour orientation contrast imaging (COCI) and automated electron backscatter pattern (EBSP) are explained and examples given. Comparisons with conventional (horizontal) orientation contrast imaging (HOCI) in the SEM are made. A direct comparison is made between conventional metallographic methods and these new techniques on precisely the same region of an interstitial free iron specimen. Both optical imaging and HOCI were found to miss a large number of grain boundaries (7 and 12%, respectively), and to create boundaries ( approximately 2%). COCI was found to be reliable, with only 3% of boundaries missed. EBSP was taken to be the standard against which the others were compared, as it unambiguously measured changes in crystallographic orientation. Errors in the number of grain boundaries that are detected have a considerable effect on grain size measurements, e.g. mean linear intercept, and a follow-on effect on the modelling of mechanical properties. New methods for increasing the acquisition speed of orientation maps are discussed, along with examples. The combination of COCI (for grain location) and EBSP (for orientation measurement) is promising, but requires improvements in either imaging or image analysis to be totally reliable.

Journal Article↗

PubMed1984

Effects of three non-insight-oriented treatment methods on agoraphobic women suitable for insight-oriented psychotherapy.

Twenty-three agoraphobic women rated suitable for insight-oriented psychotherapy received one of three randomly assigned non-insight-oriented types of treatment for 3 months and the effect was followed up after 9 months. All patients received basal therapy (B) in the form of standardized information, self-exposure instructions and anxiolytic medication. One group received this treatment only with monthly appointments. The others, in addition, received either therapist-directed prolonged exposure in vivo (PE) or relaxation therapy (R). The effects of insight-oriented psychotherapy could not be studied due to the small numbers in this group. All groups showed clinically relevant improvement, which indicates a favourable prognosis of patients suitable for insight-oriented psychotherapy irrespective of mode of treatment. However, since the PE group was least improved in some neurotic symptoms and had two treatment drop-outs and two cases of symptom substitution this mode of treatment cannot be recommended for insight-suitable patients. R patients came out favourably, which was contrary to the poor outcome with this therapy in patients not suitable for insight-oriented psychotherapy.

Adolescent↗

PubMed1985

Measurement of erythrocyte orientation in flow by spin labeling II--phenomenological models for erythrocyte orientation rate.

We present two phenomenological models describing the flowing erythrocyte orientation rate. The first concerns the onset of a stable orientation in a very dilute erythrocyte suspension. It is based on a simple formula for erythrocyte elongation as a function of shear stress, and we assume that beyond a threshold of elongation, erythrocytes take on a stable orientation, while below this threshold, they have a flipping motion. We extend this model to high hematocrit values assuming that the effect of red cell collisions imposes a random moment to each erythrocyte, shifting it from its stable orientation. We obtain an approximate expression for erythrocyte orientation rate as a function of shear rate and then we compare these results to our experimental data in part III of this series.

Biomechanical Phenomena↗

PubMed1991

Problem-oriented training promotes spontaneous analogical transfer: memory-oriented training promotes memory for training.

Spontaneous analogical transfer is the use of information from one problem to solve another problem, without an explicit hint to use the previous information. The results of five experiments were that if subjects tried to solve a training problem before hearing its solution, or tried to explain a training story's solution before hearing the correct explanation, spontaneous transfer was more likely than it was if subjects had studied the same training passage for memory before hearing its solution or explanation. The advantage of problem-oriented processing over memory-oriented processing occurred even though solution attempts nearly always failed, and the advantage was not reduced if the target problem was tested 15 min later rather than immediately after training. We propose that problem-oriented processes performed at study are appropriate processes to use at test. Further support for the account comes from subjects' memory for the training passages; the advantage for problem-oriented processing on solution tasks was mirrored by an equally substantial advantage for the memory-oriented subjects on a recall task.

Adult↗

PubMed1995

Part-whole information is useful in visual search for size x size but not orientation x orientation conjunctions.

In visual search tasks, subjects look for a target among a variable number of distractor items. If the target is defined by a conjunction of two different features (e.g., color x orientation), efficient search is possible when parallel processing of information about orientation is used to guide the deployment of attention to the target. Another type of conjunction search has targets defined by two instances of one type of feature (e.g., a conjunction of two colors). In this case, search is inefficient when the target is an item defined by parts of two different colors but much more efficient if the target can be described as a whole item of one color with a park of another color (Wolfe, Friedman-Hill, & Bilsky, 1994). In this paper, we show that the same distinction holds for size. "Part-whole" size x size conjunction searches are efficient; "part-part" searches are not (Experiments 1-3). In contrast, all orientation x orientation searches are inefficient (Experiments 4-6). This difference between preattentive processing of color and size, on the one hand, and orientation, on the other, may reflect structural relationships between features in real-world objects.

Adolescent↗

PubMed1975

The effects of lesions of the superior colliculus on locomotor orientation and the orienting reflex in the rat.

The effects of bilateral removal of the superior colliculus or visual cortex on visually guided locomotor movements in rats performing a brightness discrimination task were investigated directly with the use of cine film. Rats with collicular lesions showed patterns of locomotion comparable to or more efficient than those of normal animals when approaching one of 5 small doors located at one end of a large open area. In contrast, animals with large but incomplete lesions of visual cortex were distinctly impaired in their visual control of approach responses to the same stimuli. On the other hand, rats with collicular damage showed no orienting reflex or evidence of distraction in the same task when novel visual or auditory stimuli were presented. However, both normal and visual-decorticate rats showed various components of the orienting reflex and disturbance in task performance when the same novel stimuli were presented. These results suggest that although the superior colliculus does not appear to be essential to the visual control of locomotor orientation, this midbrain structure might participate in the mediation of shifts in visual fixation and attention. Visual cortex, while contributing to visuospatial guidance of locomotor movements, might not play a significant role in the control and integration of the orienting reflex.

Acoustic Stimulation↗

PubMed2000

Validity of the Orientation Log, relative to the Galveston Orientation and Amnesia Test.

OBJECTIVE: To establish the validity of the Orientation Log (O-Log) by comparison with the Galveston Orientation and Amnesia Test (GOAT). DESIGN: Correlation of daily measures of orientation. SETTING: Acute rehabilitation hospital. SUBJECTS: Sixty-eight inpatients receiving rehabilitation following traumatic brain injury (TBI). PRIMARY MEASURES: The O-Log and GOAT. RESULTS: There was a significant correlation between the GOAT and O-Log (r = .901, P<.001). A cutoff of 25 on the O-Log was found to be comparable with the 75 cutoff on the GOAT. The scales were equivalent in measuring duration of posttraumatic amnesia. CONCLUSIONS: The O-Log is a valid measure of orientation for people with TBI and offers some advantages in administration over the GOAT.

Adolescent↗

PubMed1985

[Cardiac anxiety syndrome. Etiologic significance of orientation crises and orientation conflicts and their consequences for therapeutic practice].

In the framework of a phenomenological approach to cardiac neurosis the author investigated 20 patients suffering from this disease regarding their kind of communication disorder and conflicts in order to find out the main conditions for etiology. This study is based on the conception of so-called "Anthropological-integrative Psychotherapy" developed by D. Wyss. He conceptualized fundamental structures of communication representing the structural aspect of a psychosomatic disease and modi of communication in order to show its dynamic aspect. The purpose of this investigation was to examine disproportions, deficiencies, compensatory hypertrophy and conflicts in the six fundamental structures of communication (Living Space, Orientation, Order, Time, Body, Performance). In accordance with many other publications separation anxiety, ambivalence between tie and separation, aggressive restraint, sexual disorders and conflicts in the structure of "performance" are confirmed as significant etiological factors. In addition, conflicts, crises and deficiency of orientation have proved to be of major importance. This is the essential result of this study and an important new contribution to our understanding of cardiac neurosis. The therapies of 3 patients suffering from cardiac neurosis are reviewed to illustrate the three main kinds of disorders in orientation. Finally the therapeutic consequences are discussed. The constitution of new orientation in an intersubjective and dialogic process seems to be an essential aim for psychotherapeutic treatment of cardiac neurosis.

Adaptation, Psychological↗

PubMed1979

The orientational freedom of molecular probes. The orientation factor in intramolecular energy transfer.

The measurement of the efficiency of Förster long-range resonance energy transfer between donor (D) and acceptor (A) luminophores attached to the same macromolecular substrate can be used to estimate the D-A separation, R. If the D and A transition dipoles sample all orientations with respect to the substrate (the isotropic condition) in a time short compared with the transfer time (the dynamic averaging condition), the average orientation factor less than K2 greater than is 2/3. If the isotropic condition is not satisfied but the dynamic averaging condition is, upper and lower bounds for less than K2 greater than, and thus R, may be obtained from observed D and A depolarizations, and these limits may be further narrowed if the transfer depolarization is also known. This paper offers experimental protocols for obtaining this reorientational information and presents contour plots of less than K2 greater than min and less than K2 greater than max as functions of generally observable depolarizations. This permits an uncertainty to be assigned to the determined value of R. The details of the D and A reoreintational process need not be known, but the orientational distributions are assumed to have at least approximate axial symmetry with respect to a stationary substrate. Average depolarization factors are derived for various orientational distribution functions that demonstrate the effects of various mechanisms for reorientation of the luminophores. It is shown that in general the static averaging regime does not lend itself to determinations of R.

Energy Transfer↗

PubMed1981

Orientation of emitting dipoles of chlorophyll A in thylakoids: considerations on the orientation factor in vivo.

Orientation angles of five emitting dipoles of chlorophyll a in thylakoids were estimated from low temperature fluorescence polarization ratio spectra of magnetically oriented chloroplasts. A simple expression is given also for the evaluation of data from linear dichroism measurements. It is shown that the Qy dipoles of chlorophylls lie more in the plane of the membranes and span a larger angular interval than was previously thought. Values for the orientation factor are calculated using various models corresponding to different degrees of local order of the Qy dipoles of chlorophylls in the thylakoid. We show that the characteristic orientation pattern of the Qy dipoles of chlorophylls in the membrane, i.e., increasing dichroism toward longer wavelengths, may favour energy transfer between the antenna chlorophylls as well as funnel the excitation energy into the reaction centers.

Chlorophyll↗

PubMed1998

Orientation dependency for foveal line stimuli: detection and intensity discrimination, resolution, orientation discrimination and vernier acuity.

Thresholds were measured for five tasks: line detection, intensity discrimination, two-line resolution, vernier acuity and line-orientation discrimination. For each task, 30 arcmin lines were presented foveally in eight retinal meridians to assess similarities in orientation anisotropies across tasks in the same observer. Three observers were tested. The pattern of the orientation anisotropy differs across tasks. Meridional anisotropies exist in detection, increment discrimination thresholds, and vernier acuity but the classical oblique effect is consistently found only in orientation discrimination.

Discrimination, Psychological↗