CW) Or Counterclockwise Research Articles

Spatial realignment in sensorimotor adaptation: Taking the efficiency into account.

The present study reviewed the modular approach in adaptive motor control by taking cognitive efficiency into account. Three experiments were conducted to compare different visuomotor learning mechanisms (modular adaptation, use-dependent plasticity, and spatial realignment) in response to visuomotor rotations. During exposure, the visual feedback of flicking movements in a single-target scenario was rotated either 30° clockwise (CW) or counterclockwise (CCW) at the left and right starting locations, respectively. Exposure to the CW and CCW rotations was carried out in an alternating order. After adaptation to the rotations, generalization was evaluated by assessing aftereffects from a set of untrained starting locations to the target (Experiments 1 and 2) or from the trained starting locations to a set of new targets (Experiment 3). Predictions made based on the different visuomotor learning mechanisms were compared to the empirical data. In spite of evidential advantages of modular structure, the current work could show a particular case of visuomotor transformation, in which modularity lacks efficiency. Results indicate that the adaptive motor control system employed the spatial realignment to accomplish adaptation more efficiently.

Structural Insight into the Rotational Switching Mechanism of the Bacterial Flagellar Motor

Author SummaryThe bacterial flagellum is a rotating organelle that governs cell motility. At the base of each flagellum is a motor powered by the electrochemical potential difference of specific ions across the cytoplasmic membrane. In response to environmental stimuli, rotation of the motor switches between counterclockwise and clockwise, with a corresponding effect on the swimming direction of the cell. Switching is triggered by the binding of the signaling protein phospho-CheY to FliM and FliN, and achieved by conformational changes in the rotor protein FliG. The actual switching mechanism, however, remains unclear. In this study, we characterized a fliG mutant of Salmonella that shows an extreme clockwise-biased rotation, and determined the structure of a fragment of FliG (FliGMC) of the equivalent mutant variant of Thermotoga maritima. FliGMC is composed of two domains and covers the regions essential for torque generation and FliM binding. We showed that the mutant structure has a conformational change in the helix connecting the two domains, leading to a domain orientation distinct from that of the wild-type FliG. On the basis of this structure, we propose a new model for the arrangement of FliG subunits in the rotor that is consistent with the previous mutational studies and explains how cooperative switching occurs in the motor.

The Functional Benefits of Tilt Adaptation

Many have argued that effects of adaptation, such as aftereffects from motion or tilt, reflect that the visual system hones its responses in on the characteristics of the adapting stimulus. This view entails that on average, the discrimination of the characteristics of an adapting stimulus should become easier as viewing time increases since the variation in the response gradually adapts to the range and variation in the stimulus. Here this was tested for adaptation to tilt. Observers viewed a Gabor patch which varied in contrast from 0 to 74% at a rate of 0.6 Hz, for 4, 8, 16 or 32 s, after which the Gabor patch changed orientation (at the point when contrast was 0). The results show that the longer the observers adapt to the dynamic Gabor, the better they become at discriminating between clockwise (CW) or counterclockwise (CCW) changes in tilt (orientation) of the same patch. Experiment 2 confirms that both the direct and indirect tilt aftereffects are seen with this contrast varying Gabor patch and Experiment 3 shows that the aftereffects are only slightly smaller than in other studies with stimuli such as lines and sinusoidal gratings. These results show that adaptation to tilt leads to better discrimination around the orientation of the adapting stimulus itself, and that discrimination performance improves steadily with increased adaptation time. The results support proposals that the visual system adjusts its response characteristics to the properties of the visual input at a given time.

Effects of lateral head inclination on multimodal spatial orientation judgments in neglect: Evidence for impaired spatial orientation constancy

Recent research revealed that patients with spatial hemineglect show deficits in the judgment of the subjective vertical and horizontal. Systematic deviations in the subjective axes have been demonstrated in the visual and tactile modality, indicating a supramodal spatial orientation deficit. Further, the magnitude of the bias was shown to be modulated by head- and body-position. The present study investigated the effect of passive lateral head inclination on the subjective visual and tactile vertical and horizontal in neglect patients, control patients with left- or right-sided brain damage without neglect and healthy controls. Subjects performed visual- and tactile-spatial judgments of axis orientations in an upright head orientation and with lateral head inclination 25° in clockwise (CW) or counterclockwise (CCW) direction. Neglect patients displayed a marked variability as well as a systematic tilt in their spatial judgments. In line with a multisensory spatial orientation deficit their subjective vertical and horizontal was tilted CCW in the visual and in the tactile modality, while such a tilt was not evident in any other subject group. Furthermore, lateral head inclination had a differential effect in neglect patients, but not in control subjects. Neglect patients’ judgments were modulated in the direction of the head tilt (‘A-effect’). That is, a CCW inclination further increased the CCW spatial bias whereas a CW inclination decreased the spatial bias and thus led to approximately normal performance. The increased A-effect might be caused by a pathologically strong attraction of the subjective vertical by an idiotropic vector relying on the actual head orientation, as a consequence of impaired processing of gravitational information in neglect patients.

Peri-equatorial paleolatitudes for Jurassic radiolarian cherts of Greece

Radiolarian-rich sediments dominated pelagic deposition over large portions of the Tethys Ocean during middle to late Jurassic time as shown by extensive bedded chert sequences found in both continental margin and ophiolite units of the Mediterranean region. Which paleoceanographic mechanisms and paleotectonic setting favored radiolarian deposition during the Jurassic, and the nature of a Tethys-wide change from biosiliceous to biocalcareous (mainly nannofossil) deposition at the beginning of Cretaceous time, have remained open questions. Previous paleomagnetic analyses of Jurassic red radiolarian cherts in the Italian Apennines indicate that radiolarian deposition occurred at low peri-equatorial latitudes, similar to modern day deposition of radiolarian-rich sediments within equatorial zones of high biologic productivity. To test this result for other sectors of the Mediterranean region, we undertook paleomagnetic study of Mesozoic (mostly middle to upper Jurassic) red radiolarian cherts within the Aegean region on the Peloponnesus and in continental Greece. Sampled units are from the Sub-Pelagonian Zone on the Argolis Peninsula, the Pindos–Olonos Zone on the Koroni Peninsula, near Karpenissi in central Greece, and the Ionian Zone in the Varathi area of northwestern Greece. Thermal demagnetization of samples from all sections removed low-temperature viscous and moderate-temperature overprint magnetizations that fail the available fold tests. At Argolis and Koroni, however, the cherts carry a third high-temperature magnetization that generally exhibits a polarity stratigraphy and passes the available fold tests. We interpret the high-temperature component to be the primary magnetization acquired during chert deposition and early diagenesis. At Kandhia and Koliaky (Argolis), the primary declinations and previous results indicate clockwise vertical-axis rotations of ∼ 40° relative to “stable” Europe. Due to ambiguities in hemispheric origin (N or S) and thus paleomagnetic polarity, the observed declinations could indicate either clockwise (CW) or counterclockwise (CCW) vertical-axis rotations. Thus at Adriani (Koroni), the primary declinations indicate either CW or CCW rotations of ∼ 95° or ∼ 84°, depending on paleomagnetic polarity and age. The primary inclinations for all Peloponnesus sites indicate peri-equatorial paleolatitudes similar to those found for coeval radiolarian cherts exposed in other Mediterranean orogenic belts. Our new paleomagnetic data support the interpretation that Mesozoic radiolarites within the Tethys Ocean were originally deposited along peri-equatorial belts of divergence and high biologic productivity.

Multiferroics – from frustrated lattice to tailored interface

This is a copy of the slides presented at the meeting but not formally written up for the volume. Highly efficient control of magnetism in terms of genuinely-electric action in a solid has been a big challenge in condensed matter science and will also widen the bottle-neck of the state-of-art spin-electronics technology. Multiferroics, the materials in which both ferromagnetism and ferroelectricity can coexist, are the prospective candidate which can potentially host the gigantic ME effect. A useful hint to designing of the strong M-P coupling has been gained by the recent discovery of the ferroelectricity in the frustrated magnets, such as perovskite manganites, spinel chromites, etc. The direction of the polarization can be totally determined by the clockwise (CW) or counter-clockwise (CCW) rotation of the transverse-spiral (cycloidal) spin in proceeding along the spiral propagation axis, that is called spin helicity or vector chirality. In those compounds, the spontaneous P can be easily controlled by an external magnetic field of specific direction, such as the generation and/or flopping of the spontaneous polarization. Conversely, the spin helicity, CW or CCW, can be controlled with genuine electric field via the reversal of spontaneous polarization. Furthermore, the clamping between the magnetic and ferroelectric domains can show up, enabling the magnetic (electric) control of the ferroelectric (ferromagnetic) domains. Multiferroics with the strong M-P correlation may also provide a unique arena to test new optical effects, say the magnetoelectic optical effects. This includes the so-called magnetization-induced second harmonic generation (MSHG) and the nonreciprocal dichroism dependent on the light propagation direction (but not on the light polarization). The former can be applied to probe the interface magnetism as well, while the latter may have potential of producing new optical devices with nonreciprocal functions. Strategy for exploring such multiferroics as showing strong M-P coupling and novel optical functions is argued in terms of the designed spin superstructure and tailor-made materials.

On the effective number of tracked trajectories in normal human vision

Z. W. Pylyshyn and R. W. Storm (1988) have shown that human observers can accurately track four to five items at a time. However, when a threshold paradigm is used, observers are unable to track more than a single trajectory accurately (S. P. Tripathy & B. T. Barrett, 2004). This difference between the two studies is examined systematically using substantially suprathreshold stimuli. The stimuli consisted of one (Experiment 1) or more (Experiments 2 and 3) bilinear target trajectories embedded among several linear distractor trajectories. The target trajectories deviated clockwise (CW) or counterclockwise (CCW) (by 19 degrees, 38 degrees, or 76 degrees in Experiments 1 and 2 and by 19 degrees, 38 degrees, or 57 degrees in Experiment 3), and observers reported the direction of deviation. From the percentage of correct responses, the "effective" number of tracked trajectories was estimated for each experimental condition. The total number of trajectories in the stimulus and the number of deviating trajectories had only a small effect on the effective number of tracked trajectories; the effective number tracked was primarily influenced by the angle of deviation of the targets and ranged from four to five trajectories for a +/-76 degrees deviation to only one to two trajectories for a +/-19 degrees deviation, regardless of whether the different magnitudes of deviation were blocked (Experiment 2) or interleaved (Experiment 3). Simple hypotheses based on "averaging of orientations," "preallocation of resources," or pop-out, crowding, or masking of the target trajectories are unlikely to explain the relationship between the effective number tracked and the angle of deviation of the target trajectories. This study reconciles the difference between the studies cited above in terms of the number of trajectories that can be tracked at a time.

Implicit learning of sequential bias in a guessing task: Failure to demonstrate effects of dopamine administration and paranormal belief

Previous research suggests that implicit sequence learning (ISL) is superior for believers in the paranormal and individuals with increased cerebral dopamine. Thirty-five healthy participants performed feedback-guided anticipations of four arrow directions. A 100-trial random sequence preceded two 100-trial biased sequences in which visual targets (arrows) on trial t tended to be displaced 90° clockwise (CW) or counter-clockwise (CCW) from those on t − 1. ISL was defined as a positive change during the course of the biased run in the difference between pro-bias and counter-bias responses. It was hypothesized that this difference would be greater for believers in the paranormal than for skeptics, for those who received dopamine than for those who received placebo, and for believers who received dopamine than for the other groups. None of the hypotheses were supported by the data. It is suggested that a simple binary guessing task with a focus on prediction accuracy during early trials should be considered for future explorations.

How 34 Pegs Fit into 26 + 8 Holes in the Flagellar Motor

How 34 Pegs Fit into 26 + 8 Holes in the Flagellar Motor

Multi-resolution analysis of the large-scale coherent structure in a turbulent separation bubble affected by an unsteady wake

Abstract Multi-resolution analysis (MRA) was applied to the large-scale coherent structure in a turbulent separation bubble affected by an unsteady wake. The unsteady wake was generated using a spoked-wheel type wake generator, which was installed in front of the separation bubble. The wake generator was rotated either clockwise (CW) or counter-clockwise (CCW) with a normalized passing frequency of StH=0.2. The Reynolds number based on the half-thickness of the blunt body was ReH=5600. To show the unsteady dynamic flow structures between the ‘cutting’ and ‘wrapping’ regimes, a MRA using the maximal overlap discrete wavelet transform (MODWT) was performed. This method enabled delineation of the coherent structure of the turbulent separation bubble through a scale-resolved analysis. Reconstruction of the flow field in combination with conditional averaging was attempted. Flapping motions as well as sawtooth movements of the unsteady separation bubble were analyzed using the MODWT. The unsteady wakes decayed faster in the system with CCW rotation than in that with CW rotation.

How White Noise Generates Power-Law Switching in Bacterial Flagellar Motors

The clockwise (CW) or counterclockwise (CCW) spinning of a bacterial flagellar motor is controlled by the concentration [Y] of a phosphorylated protein, CheY-P. Representing the stochastic switching behavior of the motor by a dynamical two-state (CW and CCW) model, whose energy levels fluctuate in time (t) as [Y](t) fluctuates, we show that temporal fluctuations in [Y](t) can generate a power-law distribution for the durations of the CCW states, in agreement with recent experiments. Correlations between the duration times of nearby CCW (CW) intervals are predicted by our model, and shown to exist in the experimental data and to affect the power spectrum for motor switching.

Vorticity patterns of sunspot H α whirls

We study vorticity patterns of 897 superpenumbral filaments (in 142 sunspots) using Hα (BBSO) observations from July 2000 – April 2001. A majority (69%) of filaments show noticeable curvature in clockwise (CW) or counter-clockwise (CCW) sense. 73% of all sunspots contain both CW and CCW filaments in their superpenumbrae. Only 27% of sunspots have all their superpenumbral filaments twisted in the same direction. The average sunspot vorticity exhibits well-known hemispheric preference, but the dependence is weaker than in the previous studies: 34 (54%) out of 63 sunspots in the northern hemisphere exhibit CCW pattern of superpenumbral whirls, and 45 (69%) of 65 sunspots in the southern hemisphere show CW pattern. We suggest that the local distribution of magnetic fields around sunspots may affect the curvature of superpenumbral filaments and, hence, weaken the hemispheric helicity rule.

Smooth Pursuit of a Partially Occluded Object

There has long been qualitative evidence that humans can pursue an object defined only by the motion of its parts (eg Steinbach, 1976 Vision Research16 1371 – 1375). We explored this quantitatively using an occluded diamond stimulus (Lorenceau and Shiffrar, 1992 Vision Research32 263 – 275). Four subjects (one naive) tracked a line-figure diamond moving along an elliptical path (0.9 Hz) either clockwise (CW) or counterclockwise (CCW) behind either an X-shaped aperture (CROSS) or two vertical rectangular apertures (BARS), which obscured the corners. Although the stimulus consisted of only four line segments (108 cd m−2), moving within a visible aperture (0.2 cd m−2) behind a foreground (38 cd m−2), it is largely perceived as a coherently moving diamond. The intersaccadic portions of eye-position traces were fitted with sinusoids. All subjects tracked object motion with considerable temporal accuracy. The mean phase lag was 5°/6° (CROSS/BARS) and the mean relative phase between the horizontal and vertical components was +95°/+92° (CW) and −85°/−75° (CCW), which is close to perfect. Furthermore, a \chi2 analysis showed that 56% of BARS trials were consistent with tracking the correct elliptical shape ( p<0.05), although segment motion was purely vertical. These data disprove the main tenet of most models of pursuit: that it is a system that seeks to minimise retinal image motion through negative feedback. Rather, the main drive must be a visual signal which has already integrated spatiotemporal retinal information into an object-motion signal.

Salmonella typhimurium fliG and fliN mutations causing defects in assembly, rotation, and switching of the flagellar motor

FliG, FliM, and FliN are three proteins of Salmonella typhimurium that affect the rotation and switching of direction of the flagellar motor. An analysis of mutant alleles of FliM has been described recently (H. Sockett, S. Yamaguchi, M. Kihara, V. M. Irikura, and R. M. Macnab, J. Bacteriol. 174:793-806, 1992). We have now analyzed a large number of mutations in the fliG and fliN genes that are responsible for four different types of defects: failure to assembly flagella (nonflagellate phenotype), failure to rotate flagella (paralyzed phenotype), and failure to display normal chemotaxis as a result of an abnormally high bias to clockwise (CW) or counterclockwise (CCW) rotation (CW-bias and CCW-bias phenotypes, respectively). The null phenotype for fliG, caused by nonsense or frameshift mutations, was nonflagellate. However, a considerable part of the FliG amino acid sequence was not needed for flagellation, with several substantial in-frame deletions preventing motor rotation but not flagellar assembly. Missense mutations in fliG causing paralysis or abnormal switching occurred at a number of positions, almost all within the middle one-third of the gene. CW-bias and CCW-bias mutations tended to segregate into separate subclusters. The null phenotype of fliN is uncertain, since frameshift and nonsense mutations gave in some cases the nonflagellate phenotype and in other cases the paralyzed phenotype; in none of these cases was the phenotype a consequence of polar effects on downstream flagellar genes. Few positions in FliN were found to affect switching: only one gave rise to the CW mutant bias and only four gave rise to the CCW mutant bias. The different properties of the FliM, FliG, and FliN proteins with respect to the processes of assembly, rotation, and switching are discussed.

Rotation of elastic shear waves in laminated, structurally chiral composites

We present experimental and theoretical data to support the hypothesis that elastic shear waves can sense the microstructural handedness, if any, in a material. Structurally chiral composites are constructed by stacking identical uniaxial plates, their symmetry axes describing either a left- or a right-handed spiral. Four glass-reinforced laminated composites-left- and right-handed, pure uniaxial and random-were made to verify the effect of form or structural chirality on elastic shear wave propagation. The composites were characterized by using shear wave transducers in an ultrasonic through-transmission experiment. Test results indicate that shear waves transmitted through left- and right-handed chiral composites have polarization states that are rotated clockwise (CW) or counter-clockwise (CCW) with respect to the incident linearly polarized wave. The uniaxial sample and the random sample did not show this effect. This effect is similar to the rotation of the plane of polarization of electromagnetic waves in “optically” (electromagnetically) active media. Wave propagation in the samples was also analyzed numerically using a matrix representation method. The experimental data compares with the numerical results qualitatively.

An SS1-SS2 beta-barrel structure for the voltage-activated potassium channel.

To examine the feasibility of a beta structure for the pore-lining region of the voltage-gated potassium channel, we have characterized a family of 12 antiparallel beta-barrels. Each is comprised of four identical pairs of beta-strands organized with approximate 4-fold symmetry about a channel axis. The C- and N-termini of the beta-strand pairs are assumed to be at the extracellular end of the channel, and each pair is connected by a hairpin turn at the intracellular end of the channel. The models differ in the residues located in the hairpin turn and in the orientation of the two strands of each pair in the barrel, i.e. whether the C-terminus of a pair is clockwise (CW) or counterclockwise (CCW) from the N-terminus when the channel is viewed from outside the cell. Following known structure precedents and potential energy predictions, the barrel is assumed to be right-twisting in all cases. All models have crowded layers of inward-projecting aromatic side-chains near the center of the channel which could regulate channel selectivity. The models with an odd number of amino acids in the hairpin turn have the advantage of predicting that F433 points into the barrel, but the disadvantage that V438 does not. Of these models, two of the models are most consistent with the external tetraethylammonium (TEA) block data, and of those, one (T439 CCW 3:5) is most consistent with the internal TEA block data.

Ionospheric equivalent current systems of low-latitude Pc3 pulsations

Ionospheric equivalent current systems of low-latitude Pc3 pulsations observed on 7 June 1980 were studied using data from the AFGL (Air Force Geophysics Laboratory) magnetometer network. The network, which covers four hours in longitude, consists of seven stations: five along 55°N and two along 40°N geomagnetic latitude. Pulsations studied had a period between 11 and 23 s and were observed simultaneously at all seven stations. A cross spectral analysis of the interstation signals showed a phase structure in longitude as well as in latitude. In longitude, the apparent phase propagated eastward or westward, but was not always consistent between the H- and D-components. In latitude, on the other hand, the apparent phase was always poleward for both components. Ionospheric equivalent current systems were drawn by combining the results of the cross spectral analysis of the interstation signals with the phase differences of the H- and D-components at each station. Two different types of the current systems, namely Type A and Type B were found. Type A indicates that either a clockwise (CW) or counterclockwise (CCW) ionospheric current cell appears at the North-East end of the activity Region, moves toward the West, and then disappears at the North-West end of the activity region. This type of event has a spectral peak between 12 and 16 s and is observed between 6:00 and 10:00 M.L.T. Type B consists of two sub-cells moving from North to South independently. This type has a spectral peak between 11 and 23 s, a range much broader than that of Type A and is commonly seen between 7:30 and 15:00 M.L.T. The structure and movement of the current system associated with low-latitude Pc3 pulsations is discussed in relation to the field-line resonance model.

Homing pigeons subjected to section of the anterior commissure can build up two olfactory maps in the deflector lofts.

Pigeons kept in two cages with screens which deflect the wind clockwise (CW) or counter-clockwise (CCW) show corresponding deflections in their initial orientation. In order to determine the nature of this phenomenon, experimental birds were treated as follows: The anterior commissure of the forebrain (AC), which mediates the interhemispheric transfer of olfactory input was sectioned; After surgery, each experimental bird was kept alternately in a CW cage with its right nostril plugged, and in a CCW cage with its left nostril plugged; the two treatments were alternated every 3 days for 69 days before test releases began. In 23 out of 28 cases the experimentals showed CW deflections when released with the right nostril plugged and CCW deflections when released with the left nostril plugged. The controls were intact, and their nostrils were free in each phase of the experiment. They were subdivided into two groups: one group was kept in the CW cage when the experimentals were in the same cage, the other group in the CCW cage when the experimentals stayed there. In the remaining time each group was kept in a fenced loft. The behaviour of controls demonstrated that the time the experimentals had spent in each kind of deflector cage had been long enough to produce the corresponding deflections in initial orientation. Control experiments were then performed on pigeons with the AC sectioned (2 series) and on intact birds (1 series), both maintained in lofts which did not deflect the wind, and released with one nostril plugged. They did not show deflections similar to those of the experimentals.(ABSTRACT TRUNCATED AT 250 WORDS)

Depth perception in moving line patterns.

By means of a computer system, the two-dimensional projections of a three-dimensional random wire figure, rotated clockwise (CW) or counterclockwise (CCW) about the vertical axis, were produced and displayed on a CRT. Generally the stimulus display appeared as an object rotating in depth, changing direction of movement frequently from clockwise rotation to counterclockwise, and vice versa. In the experiment, the three subjects observed the displays of three different types of projection, two polar projections and a parallel one. They were instructed to judge the direction of the seen motion and asked to report it using the button-switches. Both duration of the rotation perceived in either direction and frequency of the apparent reversals between those two were measured from the output sheets of a pen-recorder. The results showed the effects of the type of projection. (1) The veridical motions were perceived more continuously and durably in the polar projections than in the parallel one, (2) the opposite relation was found with the nonveridical motions, and (3) the reversals of moving direction were seen more frequently in the parallel projection than in the polar ones.

The subjective vertical under "dry" and "wet" conditions at clockwise and counterclockwise changed positions and the effect of a parallel-lined background field.

The dependence of the subjective vertical (SV, the angle β between a subjective vertical line and body median plane) on the gravity vertical (body tilt position, angle α) and on the ‘optical vertical’ (i.e., a field of parallel lines seen as background to the line to be adjusted) was investigated. The SV was measured under ‘dry’ and ‘wet’ conditions at different degrees of body tilt attained in either clockwise (CW) or counterclockwise (CCW) progression.