Direction Of Maximum Sensitivity Research Articles

Morphogenesis of free neuromasts in the larvae of brown-marbled grouper Epinephelus fuscoguttatus

Newly hatched larvae had one pair of free neuromasts behind the eyes. As the larvae grew, free neuromasts increased in number. The apical surface of sensory epithelium widened and subsequently elongated. The number of sensory hair cells increased and the directions of maximum sensitivity became both anteroposterior and dorsoventral on the trunk. Before notochord flexion, only the anteroposterior type was observed. After notochord flexion, two types of neuromasts were observed on the trunk. On the head, the orientation of free neuromasts formed a tangential line to concentric circles around the eyes and nostrils. Free neuromasts on the head could therefore receive stimuli from various angles from predators or zooplanktons. This suggests that these free neuromasts play a role in compensating for a dead angle of vision, and an important role in detecting zooplankton under scotopic vision. Canal organs were observed on the head and operculum in 40-d-old animals.

Structure and Development of Free Neuromasts in Barramundi, Lates calcarifer (Block)

This study was conducted to clarify the development of free neuromasts with growth of the barramundi, Lates calcarifer. A pair of free neuromasts was observed behind the unpigmented eyes in newly hatched eleutheroembryos with a mean total length of 1.93 mm, and two-hour-old eleuthero-embryos could respond to an approaching pipette. At 2 days after hatching, the egg yolk sac was mostly consumed, the eyes were pigmented, and the larvae commenced feeding on rotifers. Free neuromasts increased in number with growth and commenced developing into canal neuromasts in barramundi 15 days old with a mean total length of 8.07 mm. The average length of the major axis of the trunk free neuromasts attained approximately 12.9-15.5 microm, and the number of sensory cells was 15.4-17.5 at 15-20 days old. Developed cupulae of free neuromasts were observed in 1-day-old eleutheroembryos. The direction of maximum sensitivity of free neuromasts, determined from the polarity of the sensory cells, coincided with the minor axis of the lozenge-shaped outline of the apical surface of the free neuromasts. The polarity of trunk neuromasts was usually oriented along the antero-posterior axis of the fish body, but a few had a dorso-ventral direction. On the head, free neuromasts were oriented on lines tangential to concentric circles around the eye.

Search for gravitational waves from black-hole ringdowns using TAMA300 data

We report recent results of a search for gravitational waves radiated by black-hole ringdowns using TAMA300 data. A matched-filter search was performed for the data obtained in the observations in 2001 and 2003. A typical signal-to-noise ratio is expected to be 100 for a ringdown event at a distance of 10 kpc from the detector in the direction of maximum sensitivity. Our Monte Carlo study shows that the detection probability for Galactic ringdowns is 50–60% for black holes with masses greater than 25M⊙. Vetoing techniques for event selection and noise reduction are also studied. We found that by examining profiles of filter outputs, about 90% of spurious events arising from external disturbances or detector noises can be discriminated with the false dismissal probability of 5%.

Ear level noise rejection voice pickup method and apparatus

A highly discreet and accurate voice pickup device (1106) includes a standard miniature pressure gradient type microphone element provided and mounted very close to the side of the user's head (1100), preferably near the user's ear (1102). The microphone element is oriented so that direction of maximum sensitivity is parallel to the side of the user's head (1100), and points toward the user's mouth so that it will pick up the user's speech sounds (1108 and 1110) as the sounds diffract and travel along the side of the user's face and head, to the microphone element. The microphone element can be configured with low pass networks at front and rear ports (1210 and 1208) of the microphone element, which cooperate with air volume within the microphone to provide additional directional properties that advantageously vary with frequency and further enhance the noise-rejection capability of the microphone element.

Encoding of head acceleration in vestibular neurons. I. Spatiotemporal response properties to linear acceleration

1. Extracellular recordings were made in and around the medial vestibular nuclei in decerebrated rats. Neurons were functionally identified according to their semicircular canal input on the basis of their responses to angular head rotations around the yaw, pitch, and roll head axes. Those cells responding to angular acceleration were classified as either horizontal semicircular canal-related (HC) or vertical semicircular canal-related (VC) neurons. The HC neurons were further characterized as either type I or type II, depending on the direction of rotation producing excitation. Cells that lacked a response to angular head acceleration, but exhibited sensitivity to a change in head position, were classified as purely otolith organ-related (OTO) neurons. All vestibular neurons were then tested for their response to sinusoidal linear translation in the horizontal head plane. 2. Convergence of macular and canal inputs onto central vestibular nuclei neurons occurred in 73% of the type I HC, 79% of the type II HC, and 86% of the VC neurons. Out of the 223 neurons identified as receiving macular input, 94 neurons were further studied, and their spatiotemporal response properties to sinusoidal stimulation with pure linear acceleration were quantified. Data were obtained from 33 type I HC, 22 type II HC, 22 VC, and 17 OTO neurons. 3. For each neuron the angle of the translational stimulus vector was varied by 15, 30, or 45 degrees increments in the horizontal head plane. In all tested neurons, a direction of maximum sensitivity was identified. An interesting difference among neurons was their response to translation along the direction perpendicular to that that produced the maximum response ("null" direction). For the majority of neurons tested, it was possible to evoke a nonzero response during stimulation along the null direction always had response phases that varied as a function of stimulus direction. 4. These spatiotemporal response properties were quantified in two independent ways. First, the data were evaluated on the basis of the traditional one-dimensional principle governed by the "cosine gain rule" and constant response phase at different stimulus orientations. Second, the response gain and phase values that were empirically determined for each orientation of the applied linear stimulus vector were fitted on the basis of a newly developed formalism that treats neuronal responses as exhibiting two-dimensional spatial sensitivity. Thus two response vectors were determined for each neuron on the basis of its response gain and phase at different stimulus directions in the horizontal head plane.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of free and canal neuromasts and their directions of maximum sensitivity in the larvae of ayu,Plecoglossus altivelis

Development of free and canal neuromasts and their directions of maximum sensitivity in the larvae of ayu,Plecoglossus altivelis

Properties of periodontal mechanoreceptors supplying the cat's lower canine at short and long periods after reinnervation.

1. The properties of periodontal mechanoreceptors innervating the lower canine teeth of cats have been determined 6 weeks and 1 year after sectioning the inferior alveolar nerve. Recordings were made from single fibres dissected from the nerve central to the injury site, whilst forces were applied at right angles to the long axis of the tooth. 2. The range of directions over which each mechanosensitive unit responded (are of sensitivity) was established. Forces were then applied in the direction of maximum sensitivity and the maximum discharge frequency, dynamic index, adaptation rate, and the force threshold at three rates of force application (0.25, 2 and 20 N s-1) were determined. 3. Data from 115 units characterized 6 weeks after nerve section revealed a significantly reduced mean dynamic index and raised mean force threshold to forces applied at 2 and 0.25 N s-1, when compared with the controls. These units were, however, more sensitive than those examined 12 weeks after nerve section in a previous study (Loescher & Robinson, 1989b). 4. Data from 158 units characterized 1 year after nerve section revealed a significantly narrower mean are of sensitivity, reduced mean maximum discharge frequency, lower mean dynamic index and raised mean threshold to forces applied at 0.25 N s-1, when compared with the controls. 5. Bone overlying the roots of the reinnervated teeth was removed in order to localize receptors in the underlying periodontal ligament. Forty-six units were localized 6 weeks after nerve section and thirty-eight 1 year after nerve section. The mean conduction velocity of these units was significantly reduced both 6 weeks and 1 year after nerve section compared to the controls. One unit was found which branched to innervate receptors at two locations within the ligament, and one unit was found which branched to innervate a receptor in the ligament and another in the overlying skin. 6. The higher level of sensitivity of receptors when first reinnervated than at later stages is attributed to their immaturity. This immaturity may also contribute to the paraesthesia which is experienced by patients at a corresponding stage in recovery from nerve injury. The persistent reduction in sensitivity of units 1 year after nerve injury suggests that changes occur which have a permanent effect on their properties.

Dynamic polarization vector of spatially tuned neurons

The study of the dynamic properties of otolith neurons has been difficult previously because of the differing response sensitivities of individual cells to specific stimulus directions and the lack of a general mathematical scheme that could explain and account for all their response features. The present paper describes a method for estimating both the spatial and temporal properties of neurons like the otolith neurons that are spatially tuned to different stimulus directions. At each stimulus frequency, a response elipse can be constructed from the neural responses elicited by stimulation along three linear independent axes. The semimajor axis of the ellipse will specify the neuron's direction of maximum sensitivity (polarization vector), whereas the semiminor axis will provide its sensitivity in the perpendicular direction. The predictions of the method for nonzero length of the semiminor axis are qualitatively the same as the experimentally observed dependance of response phase on stimulus orientation.

Unidirectional, second-order gradient microphone

A second-order gradient microphone with unidirectional characteristics is described. The microphone consists of two commercially available, first-order gradient electret microphones that are properly baffled and arranged in antiphase with their rotational axes in line. The output of one of these transducers is added to the delayed output of the other transducer. The unidirectional microphone shows a directional characteristic that is relatively frequency independent, has a 3-dB beamwidth of the main lobe of 76 deg, and exhibits a toroidal sidelobe 10–20 dB below the main lobe. After equalization, the frequency response of the microphone in its direction of maximum sensitivity is within ±3 dB between 0.3 and 3 kHz. The output of the microphone, including equalization and amplification, is −60 dB re: 1 V/Pa at 1 kHz, and the equivalent noise level for the above frequency range amounts to 28 dB linear or an A-weighted level of 20 dB.

Receptor characteristics of periodontal mechanosensitive units supplying the cat's lower canine.

1. Forces have been applied to the lower canine teeth of cats, and the range of directions over which single periodontal mechanoreceptors are sensitive (arc of sensitivity) has been determined. We have further studied the response of each unit to forces applied in the direction of maximum sensitivity and investigated whether there is any relationship between the properties of the unit and its location within the periodontal ligament. 2. Recordings were made from 91 single units dissected from the inferior alveolar nerve in six cats. The mean arc of sensitivity to a 0.5 N force applied at right angles to the long axis of the tooth was 312 degrees. The arc of sensitivity was dependent on the force applied and the threshold of the receptor. 3. More units responded maximally to forces applied in a distolingual direction than would have been expected had the responses been evenly distributed around the tooth. Thirty-four of the units were bidirectionally sensitive, 28 became active when the force was removed, and 20 were spontaneously active. 4. The force threshold decreased with increasing rates of force application. 5. The majority of the units (81%) were slowly adapting. The rapidly adapting units had significantly higher force thresholds. 6. Twenty-eight of the receptors could be localized in the periodontal ligament after removing bone overlying the tooth root. There was no apparent relationship between the distance of the receptor from the fulcrum and its arc of sensitivity, threshold, maximum frequency of discharge, or adaptation properties.

Unidirectional, second-order gradient microphone

A second-order gradient microphone with unidirectional characteristics is described. The microphone consists of two commercially available, first-order gradient electret microphones that are properly baffled and arranged with their rotational axes in line. The output of one of these transducers is subtracted from the delayed output of the other transducer. The unidirectional microphone shows a directional characteristic that is relatively frequency independent, has a 3-dB beamwidth of the mainlobe of ± 40 degrees, and exhibits sidelobes 10–20 dB below the mainlobe. After equalization, the frequency response of the microphone in its direction of maximum sensitivity is within ± 3 dB between 0.3 and 4 kHz. The sensitivity of the microphone, including its equalization, is − 60 dBV/Pa at 1 kHz and the equivalent noise level for the above frequency range amounts to 28 dB linear or 20 dB(A).

Responses to head tilt in cat central vestibular neurons. I. Direction of maximum sensitivity.

Responses to head tilt were recorded from vestibular neurons in and around the lateral vestibular nucleus (LVN) of the decerebrate cat. Each animal had all six semicircular canals rendered nonfunctional by a plugging procedure. Each cell was studied by slowly tilting the cat, using one or both of two paradigms. In the first method, sinusoidal tilts (0.05 or 0.1 Hz) were used to produce bidirectional stimuli in up to 12 pairs of directions, including left/right (roll tilt) and fore/aft (pitch). The second method imposed a constant 10 degree tilt; the direction of the tilt was rotated around the animal by an appropriate combination of roll and pitch motions. Neurons responded by maximally increasing their discharge frequency in a particular direction of head tilt from the horizontal. Each cell's response could be described by a vector in the animal's horizontal plane whose orientation is given by the direction of the most effective stimulus and whose length represents the neuron's maximal sensitivity to tilt. The two methods of stimulation yielded equivalent response vectors. Response vectors were obtained for 100 neurons. The distribution of vector directions for these vestibular neurons was not uniform; there was a conspicuous absence of neurons with fore/aft-directed vectors. The sensitivity of these cells (length of the response vector) ranged from 10 to 230 impulses X s-1 X g-1 (median 50). Neurons whose vectors lay in the ipsilateral half-plane (which would be excited by ear-down tilt) tended to be less sensitive than those with contralateral vectors. Neurons excited by ear-up tilt tended to be located ventrally in the LVN, while those excited by ear-down tilt were more evenly distributed. There was no other obvious correlation of vector orientation with the anatomical locus of the cell in the LVN. The directional selectivity of the responses of these neurons to head tilts are similar to those previously reported tin utricular afferents. The broad distribution of response vector orientations provides an appropriate substrate for vestibulospinal reflexes to a wide variety of head tilts.

Differences between cosmic-ray intensities observed in polar and nonpolar regions

The directions of maximum sensitivity in space for the neutron monitors in polar regions (Resolute, Mawson, etc.) make large angles with the ecliptic plane in contrast with the neutron monitors at lower latitudes (Ottawa, Deep River, etc.). Hence a comparison of the intensities recorded in the two regions would reveal differential changes, if any, between the cosmic-ray intensity level inside and outside the ecliptic plane. Such an analysis was carried out and revealed differences as large as±2% in the daily means which were far outside the Poisson statistical erros. However, it was found that whereas the genuineness of some of these is not ruled out, a major part had to be attributed to unsatisfactory operation of instruments. This was so not only in the early part of I.G.Y. (1957) but even in 1963 and also for some super neutron monitors operating in 1964, thus nullifying to a great extent the advantages these would have had because of their high statistical accuracy. The need for operating at least three independent sections of a neutron pile and ensuring the parallel running of at least two of these all the time, is emphasized.

THE EFFECTIVE DIRECTIONAL SENSITIVITY OF COSMIC-RAY NEUTRON MONITORS

The direction of maximum sensitivity of a neutron monitor is calculated numerically for a set of points on the same geomagnetic meridian but extending in latitude from the equator to the pole. This leads to two master curves, one for the longitude, the other for the latitude of this direction. From these curves this direction is obtained in geographic co-ordinates for some 20 cosmic-ray stations. The method of calculation is described taking into account atmospheric absorption and the energy spectrum of the incident particles. The aperture of the sensitive cone, or source width, is also calculated. Finally the accuracy of the results is discussed and the application of the concept of effective direction is described.

Response of a model retinal receptor as a function of wavelength.

A polystyrene foam model of the ellipsoid of a retinal cone receptor was uniformly irradiated by a point source of microwave energy. The contribution of the model was determined when it was irradiated by a number of different wavelengths, and when it was oriented in different directions relative to the advancing wave front.The shorter the wavelength, the greater the ability of the model to concentrate the incident energy when the model was oriented in the direction of maximum sensitivity. Further, the directionality of the functions becomes greater the shorter the wavelength. That is, for the shorter wavelengths, the sensitivity falls off more rapidly (from the maximum) for equivalent obliquity of incidence of the wave front. The implications of these findings are discussed.