Precedence effect at horizontal and vertical plane and moving lagging signal

The precedence effect refers to the fact that humans are able to localize sound sources in reverberant environments. In this study, sound localization was studied with dual sound source: stationary (lead) and moving (lag) for two planes: horizontal and vertical. Duration of lead and lag signals was 1s. Lead-lag delays ranged from 1-40 ms. Testing was conducted in free field, with broadband noise busts (5-18 kHz). The listeners indicated the perceived location of the lag signal. Results suggest that at delays above to 25 ms in horizontal plane and 40 ms in vertical plane subjects localized correctly the moving signal. At short delays (up to 8-10 ms), regardless of the instructions, all subjects pointed to the trajectory near the lead. The echo threshold varied dramatically across listeners. Mean echo thresholds were 7.3 ms in horizontal plane and 10.1 ms in vertical plane. Statistically significant differences were not observed for two planes [F(1, 5) = 5.52; p = 0.07].     

The precedence effect in the horizontal and vertical planes in experiments with a moving lagging signal

The precedence effect in the localization of a moving lagging sound source was studied in experiments on humans under the free field conditions in the presence of a stationary (lead) sound source. Broad-band noise (5–18 kHz) bursts 1 s in duration presented in the horizontal and vertical planes were used as signals. The lead-lag delays ranged from 1 to 40 ms. The results showed that, if the signals were presented in the horizontal plane, the probability of correct localization of the moving lagging signal was decreased for delays shorter than 25 ms; if the signals were presented in the vertical plane, it was decreased for delays shorter than 40 ms. If the delays were shorter than 8–10 ms, the subjects could not localize the moving lagging signal at all. In this interval of delays, the subjects could localize only the lead signal. The mean echo threshold for signals presented in the horizontal plane was smaller than for signals presented in the vertical plane (7.3 and 10.1 ms, respectively). However, comparison of these values across the sample of subject did not show significant differences [F(1, 5) = 5.52, p = 0.07]. The results of the study suggest that the precedence effect causes a tendency towards a stronger suppression of a moving lagging signal in the vertical plane than in the horizontal plane.     

An evaluation of head position and craniofacial reference line variation

Natural head position (NHP) is the usual, balanced position of the head which is adopted for viewing the horizon or an object at eye level. Determination of NHP is useful when reconstructing facial form in art, forensics, orthodontic diagnosis and treatment planning for surgical management of craniofacial dysmorphic conditions. When NHP is uncertain, correction such as orientation to Frankfurt horizontal (FH) has been advocated. However, FH angulation varies between individuals and is subject to landmark identification error. Previous studies have measured FH and other craniofacial planes in relation to the true horizontal (HOR) with subjects in NHP and have found similar variation to that found with FH. This study measured craniofacial planes in 40 Aboriginal Australians (20 male, 20 female, aged 17 years or greater) from lateral cephalographs and compared its results with classical previous studies. Four planes, the neutral horizontal axis (NHA), FH, Krogman-Walker line (KW line), and palatal plane (P plane) demonstrated near parallelism and averaged between −1° and −2° from HOR. The combined use of NHA, FH, KW line, and P plane enables more effective corrected head position (CHP).     

Echo thresholds of the precedence effect in the vertical plane

Echo thresholds were measured for two configurations of loudspeakers in the vertical plane. The first configuration was characterized by the lead sound presentation from a loudspeaker placed in front of a subject, whereas the lag sound was presented from the loudspeaker above the subject's head. In the second configuration, the lead and lag sounds were presented from the same loudspeakers but in reverse order. All the stimuli were broadband noise bursts in the frequency range of 5-20 kHz. Burst durations were 5, 10, 20, and 100 ms. Average echo thresholds differences were significant only for the signals of 100 ms in duration (F (1, 16) = 6.28; p < 0.05). For the other signals (5, 10, 20 ms), there was no significant effect of location of lead and lag signals (p > 0.05).     

Discrimination of Velocity and Spectral Composition of a Sound Stimulus during Its Movement in the Vertical Plane

Differential sensitivity to the velocity of a sound source image in the vertical plane was studied by using two signals with different spectral bandwidths: 0.25–4 kHz (signal 1) and 4–12.5 kHz (signal 2). Five subjects were tested. Sequential switching of loudspeakers with similar frequency characteristics simulated movement of a sound source. Differential velocity thresholds were determined for two reference velocities: 58 and 115°/s. Significant differences in the absolute values of these thresholds were found for signals with different spectral compositions. The threshold for signal 1 (0.25–4.0 kHz) exceeded that for signal 2 (4.0–12.5 kHz) twofold at 58°/s and 1.6-fold at 115°/s.     

Spatial transformation of semicircular canal signals into abducens motor signals. A comparison between grass frogs and water frogs

The spatial transformation of semicircular canal signals to extraocular motor signals was studied by recording abducens nerve responses in grass and water frogs. Both species have similar vestibular canal coordinates but dissimilar orientations of their optic axes. Before sinusoidal oscillation in darkness the static head position was systematically altered to determine the planes of head oscillation in pitch and roll associated with minimal abducens nerve responses. Measured data and known canal plane vectors were used to calculate the abducens response vector in canal coordinates. The abducens vector deviated from the horizontal canal plane vector in grass frogs by 15° and in water frogs by 34° but was aligned with the pulling direction of the lateral rectus muscle in each of the two species. Lesion experiments demonstrated the importance of convergent inputs from the contralateral horizontal and anterior semicircular canals for the orientation of the abducens response vector. Thus, the orientation of the optic axis and the pulling directions of extraocular muscles are taken into account by the central organization of vestibulo-ocular reflexes. Horizontal and vertical canal signals are combined species-specifically to transform the spatial coordinates of sensory signals into appropriate extraocular motor signals. Accepted: 16 November 1997     

Responses of the Toad Bufo bufo (L.) to Stationary Prey Stimuli1

In the present work toads (Bufo bufo) are shown to respond with prey catching to stationary dummies without previous or accompanying visual or olfactory stimulation. The subjects very rarely showed jerky head movements which, therefore, cannot be necessary for perception of stationary objects. Size preference with respect to stationary stimuli is about the same as in experiments with moving stimuli. However, differences exist between the effects of stationary and moving stimuli with respect to shape and orientation. If a square measuring 10 times 10 mm and a rectangle measuring 5 times 20 mm, oriented either horizontally or vertically, are presented within the frontal-vertical plane, the square is preferred to the rectangles, and among these the horizontal rectangle is to the vertical one. This latter preference is due to the negative effect of the vertical extension: If the vertical rectangle is reduced in length, it becomes more effective as compared to the horizontal rectangle. In the horizontal (X-Z) plane the square and the rectangle oriented parallel to the Z-axis are equally superior to the bar oriented parallel to the X-axis. At presentation of a pair of stimuli in both planes, the one in the frontal-vertical plane is always preferred to that in the horizontal plane. Correspondences and differences of these results to those from experiments with moving prey dummies are discussed.     

Anisotropy in the chromatic channel: a horizontal-vertical effect

We compared the chromatic contrast thresholds of drifting (2Hz) red-green sine-wave gratings of horizontal, vertical, and two oblique orientations at three spatial frequencies (2, 4, 8 cpd). Luminance contrast thresholds for yellow-black gratings were also obtained. The classic oblique effect was found for high spatial frequency luminance and chromatic stimuli. For chromatic thresholds, a significant difference was found between the horizontal and vertical thresholds of all observers. One observer was retested with her head tilted 45 deg and demonstrated that the anisotropy was specific to retinal coordinates. These results give evidence for orientation selectivity in the chromatic channel which is at least partially independent of that in the luminance channel. We estimated the degree of lateral chromatic aberration in our observers' eyes and discuss the possible contribution of this aberration to the horizontal-vertical difference in the chromatic channel.     

The Video Head Impulse Test (vHIT) Detects Vertical Semicircular Canal Dysfunction

Background

The video head impulse test (vHIT) is a useful clinical tool to detect semicircular canal dysfunction. However vHIT has hitherto been limited to measurement of horizontal canals, while scleral search coils have been the only accepted method to measure head impulses in vertical canals. The goal of this study was to determine whether vHIT can detect vertical semicircular canal dysfunction as identified by scleral search coil recordings.

Methods

Small unpredictable head rotations were delivered by hand diagonally in the plane of the vertical semicircular canals while gaze was directed along the same plane. The planes were oriented along the left-anterior-right-posterior (LARP) canals and right-anterior-left-posterior (RALP) canals. Eye movements were recorded simultaneously in 2D with vHIT (250 Hz) and in 3D with search coils (1000 Hz). Twelve patients with unilateral, bilateral and individual semicircular canal dysfunction were tested and compared to seven normal subjects.

Results

Simultaneous video and search coil recordings were closely comparable. Mean VOR gain difference measured with vHIT and search coils was 0.05 (SD = 0.14) for the LARP plane and −0.04 (SD = 0.14) for the RALP plane. The coefficient of determination R² was 0.98 for the LARP plane and 0.98 for the RALP plane and the results of the two methods were not significantly different. vHIT and search coil measures displayed comparable patterns of covert and overt catch-up saccades.

Conclusions

vHIT detects dysfunction of individual vertical semicircular canals in vestibular patients as accurately as scleral search coils. Unlike search coils, vHIT is non-invasive, easy to use and hence practical in clinics.     

Optimization of the mechanical performance of a two-duct semicircular duct system--part 3: the positioning of the ducts in the head

In the majority of vertebrates, the horizontal duct of the vestibular system lies approximately in the yawing plane of the head. The positioning of the vertical ducts, however, is not in the pitch- and roll planes but the vertical ducts generally lie under an angle of about 30-45 degrees relative to the medial plane. Using the equations for a hydrodynamically interconnected two-duct system, optimal positions of the vertical and horizontal ducts in different vertebrate groups can be derived. It was stated that the mean response of the vertical ducts should be optimized. This leads to a symmetrical positioning of the vertical ducts with respect to the medial plane. In all observed vertebrate groups, a solution of mu =(pi-alpha)/2 is found (mu is the angle of the vertical ducts relative to the medial plane, alpha is the angle between the vertical duct planes). For alpha=90 degrees, this provides an equal sensitivity for pitch- and roll- movements. For alpha>90 degrees, a larger sensitivity for pitch movements is obtained, at the expense of a lower sensitivity for roll movements. It is argued that the angle alpha between the vertical ducts may vary from 90 to 120 degrees. In most vertebrates, the centre of mass is stabilized by e.g. fins, tri- or quadrupedal stability, a crawling body or upside-down resting positions (e.g. bats). Birds are generally biped, so in walking they are also rather sensitive to roll. These features are related to labyrinth positioning in the head.     

The importance of Planolites in the Cambrian substrate revolution

Early Cambrian subtidal shelf substrates were characterized by low water content and steep chemical gradients, conditions likely facilitated by the presence of microbial mats as reflected by an abundance of microbially-mediated sedimentary structures in Lower Cambrian strata. Such substrate conditions would have been unfavourable for burrowing by benthic metazoans. A combination of environmental restrictions and a lack of adaptations to vertical burrowing likely prevented most benthic metazoans from burrowing infaunally in Early Cambrian subtidal shelf substrates. The eventual acquisition of burrowing adaptations by benthic metazoans later in the Cambrian promoted an increase in the depth and intensity of bioturbation and initiated a transition toward well-hydrated substrates in which extensive infaunal activity was possible.Siliciclastic units of the Lower Cambrian succession in the White–Inyo Mountains, eastern California, contain abundant horizontal bioturbation on bedding planes, as documented by bedding plane bioturbation indices, but little vertical bioturbation, as shown by ichnofabric indices and x-radiography. Planolites, a simple horizontal trace fossil, represents the dominant type of bioturbation in these units. Planolites is found in a range of diameters, indicating that more than one species of tracemaker likely produced this type of trace. Although these Planolites do not have a vertical component, their abundance on bedding planes indicates that the activities of Planolites tracemakers had a significant impact on subtidal shelf substrates, represented by Lower Cambrian units in the White–Inyo Mountains, early in the Cambrian substrate revolution.     

Spatial distribution of soil penetration resistance as affected by soil compaction: The fractal approach

Using semivariograms and fractal dimension (D), we identified the spatial variation of penetration resistance (PR) in variously compacted silty loam in the Lublin region, South-East Poland. Four compaction treatments were as follows: zero traffic (0p), one pass of tractor (1p), three passes of tractor (3p), and (8p) eight passes. Penetration resistance was measured in a square net of 0.6 m × 0.6 m with grid density of 0.05 m, in horizontal planes at depths of 0.05, 0.15, 0.25, 0.35, 0.45 and 0.55 m in each traffic treatment. The data were analysed in 6 horizontal planes and 12 vertical planes. The vertical planes were obtained by transforming the measured data along one side of the square at every 0.05 m. Total number of penetrations was 864. Fractal dimension (D) was estimated from the slope of the log–log semivariogram plots. The semivariograms showed spatial autocorrelation of penetration resistance in the horizontal and vertical planes. Direction in space was important in this study. In the horizontal planes the differentiation of penetration resistance semivariance at different depths was considerable and not clearly related with traffic intensity. In the vertical planes the semivariograms showed spatial dependence of the PR and evident decreasing of semivariance with increasing traffic intensity. Kriging-interpolated maps revealed that the differentiation of penetration resistance was higher in the vertical than in the horizontal planes. The vertical differentiation was higher in 0p than in the remaining treatments. The overall mean fractal dimensions in the vertical planes increased with increasing compaction levels and can be a useful indicator of the compaction level. The opposite courses of fractal dimension in the vertical and horizontal planes indicate spatial anisotropy in distribution of penetration resistance.     

MPI CyberMotion Simulator: implementation of a novel motion simulator to investigate multisensory path integration in three dimensions

Path integration is a process in which self-motion is integrated over time to obtain an estimate of one's current position relative to a starting point (1). Humans can do path integration based exclusively on visual (2-3), auditory (4), or inertial cues (5). However, with multiple cues present, inertial cues - particularly kinaesthetic - seem to dominate (6-7). In the absence of vision, humans tend to overestimate short distances (<5 m) and turning angles (<30°), but underestimate longer ones (5). Movement through physical space therefore does not seem to be accurately represented by the brain. Extensive work has been done on evaluating path integration in the horizontal plane, but little is known about vertical movement (see (3) for virtual movement from vision alone). One reason for this is that traditional motion simulators have a small range of motion restricted mainly to the horizontal plane. Here we take advantage of a motion simulator (8-9) with a large range of motion to assess whether path integration is similar between horizontal and vertical planes. The relative contributions of inertial and visual cues for path navigation were also assessed. 16 observers sat upright in a seat mounted to the flange of a modified KUKA anthropomorphic robot arm. Sensory information was manipulated by providing visual (optic flow, limited lifetime star field), vestibular-kinaesthetic (passive self motion with eyes closed), or visual and vestibular-kinaesthetic motion cues. Movement trajectories in the horizontal, sagittal and frontal planes consisted of two segment lengths (1st: 0.4 m, 2nd: 1 m; ±0.24 m/s(2) peak acceleration). The angle of the two segments was either 45° or 90°. Observers pointed back to their origin by moving an arrow that was superimposed on an avatar presented on the screen. Observers were more likely to underestimate angle size for movement in the horizontal plane compared to the vertical planes. In the frontal plane observers were more likely to overestimate angle size while there was no such bias in the sagittal plane. Finally, observers responded slower when answering based on vestibular-kinaesthetic information alone. Human path integration based on vestibular-kinaesthetic information alone thus takes longer than when visual information is present. That pointing is consistent with underestimating and overestimating the angle one has moved through in the horizontal and vertical planes respectively, suggests that the neural representation of self-motion through space is non-symmetrical which may relate to the fact that humans experience movement mostly within the horizontal plane.     

Kinematics of Visually-Guided Eye Movements

One of the hallmarks of an eye movement that follows Listing’s law is the half-angle rule that says that the angular velocity of the eye tilts by half the angle of eccentricity of the line of sight relative to primary eye position. Since all visually-guided eye movements in the regime of far viewing follow Listing’s law (with the head still and upright), the question about its origin is of considerable importance. Here, we provide theoretical and experimental evidence that Listing’s law results from a unique motor strategy that allows minimizing ocular torsion while smoothly tracking objects of interest along any path in visual space. The strategy consists in compounding conventional ocular rotations in meridian planes, that is in horizontal, vertical and oblique directions (which are all torsion-free) with small linear displacements of the eye in the frontal plane. Such compound rotation-displacements of the eye can explain the kinematic paradox that the fixation point may rotate in one plane while the eye rotates in other planes. Its unique signature is the half-angle law in the position domain, which means that the rotation plane of the eye tilts by half-the angle of gaze eccentricity. We show that this law does not readily generalize to the velocity domain of visually-guided eye movements because the angular eye velocity is the sum of two terms, one associated with rotations in meridian planes and one associated with displacements of the eye in the frontal plane. While the first term does not depend on eye position the second term does depend on eye position. We show that compounded rotation - displacements perfectly predict the average smooth kinematics of the eye during steady- state pursuit in both the position and velocity domain.     

Modelling of the UV Index on vertical and 40° tilted planes for different orientations

In this study, estimated data of the UV Index on vertical planes are presented for the latitude of Valencia, Spain. For that purpose, the UVER values have been generated on vertical planes by means of four different geometrical models a) isotropic, b) Perez, c) Gueymard, d) Muneer, based on values of the global horizontal UVER and the diffuse horizontal UVER, measured experimentally. The UVER values, obtained by any model, overestimate the experimental values for all orientations, with the exception of the Perez model for the East plane. The results show statistical values of the MAD parameter (Mean Absolute Deviation) between 10% and 25%, the Perez model being the one that obtained a lower MAD for all levels. As for the statistic RMSD parameter (Root Mean Square Deviation), the results show values between 17% and 32%, and again the Perez model provides the best results in all vertical planes. The difference between the estimated UV Index and the experimental UV Index, for vertical and 40° tilted planes, was also calculated. 40° is an angle close to the latitude of Burjassot, Valencia, (39.5°), which, according to various studies, is the optimum angle to capture maximum radiation on tilted planes. We conclude that the models provide a good estimate of the UV Index, as they coincide or differ in one unit compared to the experimental values in 99% of cases, and this is valid for all orientations. Finally, we examined the relation between the UV Index on vertical and 40° tilted planes, both the experimental and estimated by the Perez model, and the experimental UV Index on a horizontal plane at 12 GMT. Based on the results, we can conclude that it is possible to estimate with a good approximation the UV Index on vertical and 40° tilted planes in different directions on the basis of the experimental horizontal UVI value, thus justifying the interest of this study.     

The visual field and visually guided behavior in the zebra finch (Taeniopygia guttata)

Summary Measurements were made of the physical properties of the visual system of the zebra finch, a bird with laterally placed eyes. The use of the visual system in pecking and courtship behavior was examined. It was demonstrated that the optical axis and the fovea of the eye point in a direction about 62° from the sagittal axis of the head. The visual field of each eye covers about 170° in the horizontal plane. In the frontal region there is an overlap of about 30°–40° where the birds can see binocularly; caudally there is a gap in the visual field of 60°. The point of best binocular viewing is in the sagittal plane at 16.5° below the beak.Concerning movement detection, the upper threshold is 540°/s for the binocular (frontal) part of the visual field and about 1100°/s for the monocular (lateral) part. Most fixations before pecking occur monocularly. A preference for one eye during pecking was not detected. During the courtship song, a male bird directs its head towards the female. The results are discussed in comparison with findings in pigeons and chickens.     

Terrestrial mosses as bioindicators of SO2 pollution stress

Summary The turf structure of terrestrial mosses was analysed in the understory of white spruce associations along two SO₂ stress gradients associated with a single SO₂ source. Changes in coverage, turf depth, biomass and percent living moss were followed. SO₂ stress initially caused changes in turf structure in the vertical plane (green turf depth, percentage and biomass) whereas changes in the horizontal plane (coverage) were most noticeable in areas of severe stress. The Index of Atmospheric Purity (IAP) reflected SO₂ stress only in these latter areas. Intrusion of weeds and increased prominence of subordinate species occurred in lightly stressed areas, but these perturbations were not reflected by the IAP. The effect of Q _i, frequency, and coverage factors in the IAP are discussed and the criteria of the Index of Community Vigor are proposed.     

Statocysts in crabs: short-term control of locomotion and long-term monitoring of hydrostatic pressure

Crabs show well-coordinated locomotion. They have proprioceptors similar to those of lobsters, but they differ in terms of their balancing systems and their condensed nervous system, which allows rapid interganglionic conduction. Typically they exhibit dynamically stable locomotion with a highly developed semicircular canal system that codes angular acceleration in each of three orthogonal planes (horizontal and vertical at 45 degrees and 135 degrees to the pitching plane). Left and right interneurons each code one direction of angular acceleration, carrying information between the brain and the thoracic ganglia. Cell A codes head-up vertical plane angular accelerations. Cell B codes rotations in the horizontal plane. Interneurons C and D code headdown vertical plane information, carrying it ipsilaterally and contralaterally respectively. These interneurons have a central role in locomotion. They are activated and have their responsiveness to angular acceleration enhanced before and during locomotion. Such simple activation pathways point to how an angular-acceleration-controlled robot (CRABOT) could be constructed. Hydrostatic pressure information carried by the thread hairs, which also sense angular acceleration, is filtered out from direct pathways onto the interneurons, but spectral analysis shows that it still has an influence via central pathways. Long-term recordings from equilibrium interneurons in free-walking crabs taken from the wild into constant conditions show tidally changing frequencies     

Polarotaxis,gravitaxis and vertical phototaxis in the green flagellate,Euglena gracilis

A fully automatic computer-controlled video analysis system has been used to study the movement of the green unicellular flagellate, Euglena gracilis in a horizontal or vertical cuvette. In darkness, in the absence of gaseous gradients, most cells swim straight upwards. While in a horizontal cuvette the transition between positive and negative phototaxis is found at about 1.5 W m^-2, an excess of 30 W m^-2 is required to reverse the upward swimming (due to the combined stimulus of negative gravitaxis and positive phototaxis) in a vertical cuvette. By studying the swimming direction in horizontal and vertical cuvettes in polarized light irradiated from above or from the side, respectively, the dichroic orientation of the photoreceptor molecules can be determined in three dimensions with respect to the axes of the cell: In a horizontal cuvette, in a linearly polarized beam from above, the cells orient predominantly at an angle of about 30° clockwise off the electric dipole transition moment as seen from above. The behavior in a vertical cuvette with polarized light entering from above indicates that the photoreceptor pigments are dichroically oriented 60° counterclockwise from the flagellar plane (seen from the front end of the cell). Experiments with horizontal polarized light indicate that the photoreceptor transition moment deviates 25° clockwise off the long axis of the cell.Abbreviation PFB paraflagellar body Dedicated to Prof. Dr. W. Nultsch on the occasion of his 60th birthday