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PubMed2000

Prototype neural semicircular canal prosthesis using patterned electrical stimulation.

The design of a prototype semicircular canal prosthesis is presented along with preliminary results. This device measures angular velocity of the head (+/-500 degrees/s) using a piezoelectric vibrating gyroscope. With a digital filter this velocity is filtered to match the dynamic characteristics of the semicircular canals, which are the physiological rotation sensors of the vestibular system. This digitally filtered signal is used to modulate the pulse rate of electrical stimulation. The pulse rate is varied between 50 and 250 Hz via a sigmoidal lookup table relating pulse rate to angular velocity; the steady-state rate is 150 Hz. A current source utilizes these timing pulses to deliver charge balanced, cathodic-first, biphasic, current pulses to the nerves innervating the semicircular canal via platinum electrodes. Power is supplied via lithium batteries. dc/dc converters are used to generate regulated +/-5 V supplies from the batteries. All of the components are contained in a small, lightweight, Nylon box measuring roughly 43 mm x 31 mm x 25 mm, which can be mounted on the top of an animal's head. This device has been tested in guinea pigs having surgically implanted platinum electrodes, and the results show that the prosthesis can provide a rotational cue to the nervous system.

Animals↗
PubMed2004

Computational Fluid Dynamics (CFD) study of the 4th generation prototype of a continuous flow Ventricular Assist Device (VAD).

The continuous flow ventricular assist device (VAD) is a miniature centrifugal pump, fully suspended by magnetic bearings, which is being developed for implantation in humans. The CF4 model is the first actual prototype of the final design product. The overall performances of blood flow in CF4 have been simulated using computational fluid dynamics (CFD) software: CFX, which is commercially available from ANSYS Inc. The flow regions modeled in CF4 include the inlet elbow, the five-blade impeller, the clearance gap below the impeller, and the exit volute. According to different needs from patients, a wide range of flow rates and revolutions per minute (RPM) have been studied. The flow rate-pressure curves are given. The streamlines in the flow field are drawn to detect stagnation points and vortices that could lead to thrombosis. The stress is calculated in the fluid field to estimate potential hemolysis. The stress is elevated to the decreased size of the blood flow paths through the smaller pump, but is still within the safe range. The thermal study on the pump, the blood and the surrounding tissue shows the temperature rise due to magnetoelectric heat sources and thermal dissipation is insignificant. CFD simulation proved valuable to demonstrate and to improve the performance of fluid flow in the design of a small size pump.

Blood Flow Velocity↗
PubMed1992

[Studies on tsutsugamushi diseases in Gifu Prefecture. 5. Characterization of monoclonal antibodies to prototype strains of Rickettsia tsutsugamushi and immunological grouping of newly isolated strains using the antibodies].

We characterized 8 monoclonal antibodies (MAbs) to Karp, Kato, and Gilliam strains of Rickettsia tsutsugamushi, and analysed 17 isolates from patients with Tsutsugamushi disease using these MAbs. These were divided into 3 strain-specific (Kp/D11, Kt/2D9, and Gi/E4) and 5 cross-reactive MAbs (Kp/1F11, Kp/1C10, Kp/C6, Kt/3B2, and Kt/3C2). All MAbs recognized characteristic protein antigens using the indirect fluorescent-antibody test (IFA) and proteinase K treatment. Analysis by polyacrylamide gel electrophoresis and immunoblotting techniques revealed that Kato-specific MAb Kt/2D9 recognized a polypeptide with a molecular mass of 54 kilodalton (kDa) of the homologous strain, and cross-reactive MAbs Kp/1F11, Kp/C6, and Kt/3B2 recognized those of 46-47 kDa, 46-47 KDa, and 60 kDa, respectively to the homologous and heterologous strains. MAbs Kp/1C10 which exhibited a high IFA titer against the Karp strain and only low titers against heterologous strains recognized only the 110 kDa polypeptide of the homologous strain. MAb Kt/3C2 which reacted with both Karp and Kato strains recognized a 54 to 56 kDa polypeptide band of the two prototype strains as well as several other polypeptides, however, each molecular mass was present in only one of two strains. Testing by the plaque reduction technique showed another characteristic of MAb Kt/3C2 to neutralize both Karp and Kato Strains. Fourteen isolated strains from patients in the south and west regions of Gifu Prefecture, the Shimokoshi stain isolated in Niigata Prefecture, and Kawasaki and Kuroki stains isolated in Miyazaki Prefecture were examined for reactivities to 8 MAbs by IFA to classify their antigenicities. No isolated strains reacted with Karp-specific Kp/D11, Kato-specific Kt/2D9, or Gilliam-specific Gi/E4.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

Determination of the detective quantum efficiency of a prototype, megavoltage indirect detection, active matrix flat-panel imager.

After years of aggressive development, active matrix flat-panel imagers (AMFPIs) have recently become commercially available for radiotherapy imaging. In this paper we report on a comprehensive evaluation of the signal and noise performance of a large-area prototype AMFPI specifically developed for this application. The imager is based on an array of 512 x 512 pixels incorporating amorphous silicon photodiodes and thin-film transistors offering a 26 x 26 cm2 active area at a pixel pitch of 508 microm. This indirect detection array was coupled to various x-ray converters consisting of a commercial phosphor screen (Lanex Fast B, Lanex Regular, or Lanex Fine) and a 1 mm thick copper plate. Performance of the imager in terms of measured sensitivity, modulation transfer function (MTF), noise power spectra (NPS), and detective quantum efficiency (DQE) is reported at beam energies of 6 and 15 MV and at doses of 1 and 2 monitor units (MU). In addition, calculations of system performance (NPS, DQE) based on cascaded-system formalism were reported and compared to empirical results. In these calculations, the Swank factor and spatial energy distributions of secondary electrons within the converter were modeled by means of EGS4 Monte Carlo simulations. Measured MTFs of the system show a weak dependence on screen type (i.e., thickness), which is partially due to the spreading of secondary radiation. Measured DQE was found to be independent of dose for the Fast B screen, implying that the imager is input-quantum-limited at 1 MU, even at an extended source-to-detector distance of 200 cm. The maximum DQE obtained is around 1%--a limit imposed by the low detection efficiency of the converter. For thinner phosphor screens, the DQE is lower due to their lower detection efficiencies. Finally, for the Fast B screen, good agreement between calculated and measured DQE was observed.

Biophysical Phenomena↗
PubMed2003

System performance of a prototype flat-panel imager operated under mammographic conditions.

The results of an empirical and theoretical investigation of the performance of a high-resolution, active matrix flat-panel imager performed under mammographic conditions are reported. The imager is based upon a prototype, indirect detection active matrix array incorporating a discrete photodiode in each pixel and a pixel-to-pixel pitch of 97 microm. The investigation involved three imager configurations corresponding to the use of three different x-ray converters with the array. The converters were a conventional Gd2O2S-based mammographic phosphor screen (Min-R) and two structured CsI:Tl scintillators: one optimized for high spatial resolution (FOS-HR) and the other for high light output (FOS-HL). Detective quantum efficiency for mammographic exposures ranging from approximately 2 to approximately 40 mR at 26 kVp were determined for each imager configuration through measurements of x-ray sensitivity, modulation transfer function (MTF), and noise power spectrum (NPS). All configurations were found to provide significant presampling MTF at frequencies beyond the Nyquist frequency of the array, approximately 5.2 mm(-1) , consistent with the high spatial resolution of the converters. In addition, the effect of additive electronic noise on the NPS was found to be significantly larger for the configuration with lower system gain (FOS-HR) than for the configurations with higher gain (Min-R, FOS-HL). The maximum DQE values obtained with the CsI:Tl scintillators were considerably greater than those obtained with the Min-R screen due to the significantly lower Swank noise of the scintillators. Moreover, DQE performance was found to degrade with decreasing exposure, although this exposure-dependence was considerably reduced for the higher gain configurations. Theoretical calculations based on the cascaded systems model were found to be in generally good agreement with these empirically determined NPS and DQE values. In this study, we provide an example of how cascaded systems modeling can be used to identify factors limiting system performance and to examine trade-offs between factors toward the goal of maximizing performance.

Computer Simulation↗
PubMed2004

Dosimetry of a prototype retractable eMLC for fixed-beam electron therapy.

An electron multileaf collimator (eMLC) has been designed that is unique in that it retracts to 37 cm from the isocenter [63-cm source-to-collimator distance (SCD)] and can be deployed to distances of 20 and 10 cm from the isocenter (80 and 90 cm SCD, respectively). It is expected to be capable of arc therapy at 63 cm SCD; isocentric, fixed-beam therapy at 80 cm SCD; and source-to-surface distance (SSD), fixed-beam therapy at 90 cm SCD. In all positions, its leaves could be used for unmodulated or intensity-modulated therapy. Our goal in the present work is to describe the general characteristics of the eMLC and to demonstrate that its leakage characteristics and dosimetry are adequate for SSD, fixed-beam therapy as an alternative to Cerrobend cutouts with applicators once the prototype's leaves are motorized. Our eMLC data showed interleaf electron leakage at 15 MeV to be less than 0.1% based on a 0.0025 cm manufacturing tolerance, and lateral electron leakage at 5 and 15 MeV to be less than 2%. X-ray leakage through the leaves was 1.6% at 15 MeV. Our data showed that beam penumbra was independent of direction and leaf position. The dosimetric properties of square fields formed by the eMLC were very consistent with those formed by Cerrobend inserts in the 20 x 20 cm2 applicator. Output factors exhibited similar field-size dependence. Airgap factors exhibited almost identical field-size dependence at two SSDs (105 and 110 cm), consistent with the common assumption that airgap factors are applicator independent. Percent depth-dose curves were similar, but showed variations up to 3% in the buildup region. The pencil-beam algorithm (PBA) fit measured data from the eMLC and applicator-cutout systems equally well, and the resulting two-dimensional (2-D) dose distributions, as predicted by the PBA, agreed well at common airgap distance. Simulating patient setups for breast and head and neck treatments showed that almost all fields could be treated using similar SSDs as when using applicators, although head and neck treatments require placing the patient's head on a head-holder treatment table extension. The results of this work confirmed our design goals and support the potential use of the eMLC design in the clinical setting. The eMLC should allow the same treatments as are typically delivered with the electron applicator-cutout system currently used for fixed-beam therapy.

Air↗
PubMed2005

Physical characterization of a prototype selenium-based full field digital mammography detector.

The purpose of this study was to measure experimentally the physical performance of a prototype mammographic imager based on a direct detection, flat-panel array design employing an amorphous selenium converter with 70 microm pixels. The system was characterized for two different anode types, a molybdenum target with molybdenum filtration (Mo/Mo) and a tungsten target with rhodium filtration (W/Rh), at two different energies, 28 and 35 kVp, with approximately 2 mm added aluminum filtration. To measure the resolution, the presampled modulation transfer function (MTF) was measured using an edge method. The normalized noise power spectrum (NNPS) was measured by two-dimensional Fourier analysis of uniformly exposed mammograms. The detective quantum efficiencies (DQEs) were computed from the MTFs, the NNPSs, and theoretical ideal signal to noise ratios. The MTF was found to be close to its ideal limit and reached 0.2 at 11.8 mm(-1) and 0.1 at 14.1 mm(-1) for images acquired at an RQA-M2 technique (Mo/Mo anode, 28 kVp, 2 mm Al). Using a tungsten technique (MW2; W/Rh anode, 28 kVp, 2 mm Al), the MTF went to 0.2 at 11.2 mm(-1) and to 0.1 at 13.3 mm(-1). The DQE reached a maximum value of 54% at 1.35 mm(-1) for the RQA-M2 technique at 1.6 microC/kg and achieved a peak value of 64% at 1.75 mm(-1) for the tungsten technique (MW2) at 1.9 microC/kg. Nevertheless, the DQE showed strong exposure and frequency dependencies. The results indicated that the detector offered high MTFs and DQEs, but structured noise effects may require improved calibration before clinical implementation.

Equipment Design↗
PubMed2006

Intraoperative cone-beam CT for guidance of head and neck surgery: Assessment of dose and image quality using a C-arm prototype.

Cone-beam computed tomography (CBCT) with a flat-panel detector represents a promising modality for intraoperative imaging in interventional procedures, demonstrating sub-mm three-dimensional (3D) spatial resolution and soft-tissue visibility. Measurements of patient dose and in-room exposure for CBCT-guided head and neck surgery are reported, and the 3D imaging performance as a function of dose and other acquisition/reconstruction parameters is investigated. Measurements were performed on a mobile isocentric C-arm (Siemens PowerMobil) modified in collaboration with Siemens Medical Solutions (Erlangen, Germany) to provide flat-panel CBCT. Imaging dose was measured in a custom-built 16 cm cylindrical head phantom at four positions (isocenter, anterior, posterior, and lateral) as a function of kVp (80-120 kVp) and C-arm trajectory ("tube-under" and "tube-over" half-rotation orbits). At 100 kVp, for example ("tube-under" orbit), the imaging dose was 0.059 (isocenter), 0.022 (anterior), 0.10 (posterior), and 0.056 (lateral) mGy/ mAs, with scans at approximately 50 and approximately 170 mAs typical for visualization of bony and soft-tissue structures, respectively. Dose to radiosensitive structures (viz., the eyes and thyroid) were considered in particular: significant dose sparing to the eyes (a factor of 5) was achieved using a "tube-under" (rather than "tube-over") half-rotation orbit; a thyroid shield (0.5 mm Pb-equivalent) gave moderate reduction in thyroid dose due to x-ray scatter outside the primary field of view. In-room exposure was measured at positions around the operating table and up to 2 m from isocenter. A typical CBCT scan (10 mGy to isocenter) gave in-air exposure ranging from 29 mR (0.26 mSv) at 35 cm from isocenter, to <0.5 mR (<0.005 mSv) at 2 m from isocenter. Three-dimensional (3D) image quality was assessed in CBCT reconstructions of an anthropomorphic head phantom containing contrast-detail spheres (11-103 HU; 1.6-12.7 mm) and a natural human skeleton. The contrast-to-noise ratio (CNR) was evaluated across a broad range of dose (0.6-23.3 mGy). CNR increased as the square root of dose, with excellent visualization of bony and soft-tissue structures achieved at approximately 3 mGy (0.10 mSv) and approximately 10 mGy (0.35 mSv), respectively. The prototype C-arm demonstrates CBCT image quality sufficient for guidance of head and neck procedures based on soft-tissue and bony anatomy at dose levels low enough for repeat intraoperative imaging, with total dose over the course of the procedure comparable to or less than the effective dose of a typical (2 mSv) diagnostic CT of the head.

Dose-Response Relationship, Radiation↗
PubMed2006

The response of prototype plane-parallel ionization chambers in small megavoltage x-ray fields.

Accurate small-field dosimetry has become important with the use of multiple small fields in modern radiotherapy treatments such as IMRT and stereotactic radiosurgery. In this study, we investigate the response of a set of prototype plane-parallel ionization chambers, based upon the Exradin T11 chamber, with active volume diameters of 2, 4, 10, and 20 mm, exposed to 6 MV stereotactic radiotherapy x-ray fields. Our goal was to assess their usefulness for accurate small x-ray field dose measurements. The relative ionization response was measured in circular fields (0.5 to 4 cm diameter) as compared to a 10 x 10 cm2 reference field. A large discrepancy (approximately 40%) was found between the relative response in the smallest plane-parallel chamber and other small volume dosimeters (radiochromic film, micro-metal-oxide-semiconductor field-effect transistor and diode) used for comparison. Monte Carlo BEAMnrc simulations were used to simulate the experimental setup in order to investigate the cause of the under-response and to calculate appropriate correction factors that could be applied to experimental measurements. It was found that in small fields, the air cavity of these custom-made research chambers perturbed the secondary electron fluence profile significantly, resulting in decreased fluence within the active volume, which in turn produces a chamber under-response. It is demonstrated that a large correction to the p(fl) correction factor would be required to improve dosimetric accuracy in small fields, and that these factors could be derived using Monte Carlo simulations.

Dose-Response Relationship, Radiation↗
PubMedDate not supplied

A 4-MV CT scanner for radiation therapy: the prototype system.

A Varian 4-MV isocentric therapy accelerator has been modified to perform also as a CT scanner. The goal is to provide a computed tomography capability for use in radiotherapy at low cost. We envision three principal uses for the system. These are (i) to provide two and three-dimensional maps of electron density distribution for CT assisted therapy planning; (ii) to aid in patient set up by providing sectional views of the treatment volume and high contrast scout-mode verification images; and (iii) to provide a means for periodically checking the patients anatomical conformation against that which was used to generate the original therapy plan. The machine was modified by mounting an array of detectors on a frame that is bolted to the counterweight end of the gantry in such a manner as to define a "third generation" CT scanner geometry. Details of the detectors and data acquisition electronics are provided. We present results of phantom studies which demonstrate that this prototype system has a spatial resolution of 4 mm and the ability to discriminate electron density differences of less than 1%. We also show that the system is exactly linear over a wide range of electron densities corresponding to those found in body tissues.

Particle Accelerators↗
PubMedDate not supplied

A xenon ionization detector for scanned projection radiography: 95-channel prototype evaluation.

We have designed, constructed, and tested a 95-channel prototype xenon ionization detector for use in scanned projection radiography (SPR). This detector has higher spatial resolution, is more dose efficient, and is easier to construct than computed tomography (CT) xenon ionization detectors. It consists of two parallel plates separated by a 2-mm gap filled with xenon gas at 2 MPa (20 atm). One plate is a high-voltage electrode while the other is a circuit board etched to form an array of metal collector strips focused on the x-ray source. The resulting detector channels are 0.5 mm wide and 6 cm long. In this paper we present results from measurements of system noise and detector channel calibration. We compared the detector system to a screen/film system and found that it allows the detection of structures with 0.17% radiographic contrast compared to 2% contrast required for detection with screen/film when tested by imaging a 10-cm-thick Lucite phantom with a 10 X 10(-6) C/kg exposure. From images of resolution test patterns, the limiting resolution of the detector is 2.0 1p/mm at 1.6 magnification. Images of reduction mammoplasty tissue samples, obtained with 1/17 the exposure of screen/film images, had the same low-contrast sensitivity but contained less high-contrast detail than the film images.

Radiographic Image Enhancement↗
PubMedDate not supplied

Evaluation of a prototype dual-energy computed tomographic apparatus. II. Determination of vertebral bone mineral content.

A prototype dual-energy computed tomographic (CT) scanner (Siemens Somatom DR3) with rapid kVp switching and prereconstruction processing has been used to measure vertebral bone mineral density. With this approach misregistration and beam hardening inaccuracies can be reduced considerably. Basis material images of aluminum- and Lucite-equivalent density enable measurements of bone mineral density that are nearly independent of the amount of marrow fat. To simulate variable marrow fat, alcohol-water mixtures were used as media in calibration standards. A section of dried trabecular bone was also scanned immersed in varying alcohol-water mixtures. In both simulations it was shown that the dual-energy measurement is nearly independent of marrow composition whereas the single-energy measurement would be strongly influenced by marrow fat. Dual-energy CT was compared to dual-photon absorptiometry (153Gd) for the measurement of bone mineral mass of ten excised human vertebrae. There was a high degree of correlation between the two measurements (r = 0.97). Dual-energy and single-energy CT measurements on 17 patients with suspected metabolic bone disease strongly support the conclusion that the influence of fat can lead to significant errors in single-energy determinations of the mineral density of trabecular bone.

Bone Marrow↗
PubMedDate not supplied

Evaluation of a prototype dual-energy computed tomographic apparatus. I. Phantom studies.

We report the evaluation of a prototype dual-energy implementation using rapid kVp switching on a clinical computed tomographic scanner. The method employs prereconstruction basis material decomposition of the dual-energy projection data. Each dual-energy scan can be processed into conventional single-kVp images, basis material density images, and monoenergetic images. Phantom studies were carried out to qualitatively and quantitatively evaluate and validate the approach.

Biometry↗
PubMedDate not supplied

A prototype amorphous selenium imaging plate system for digital radiography.

This paper summarizes the results of research and development of a prototype amorphous selenium digital imaging system. The first phase of this project consists of the preliminary design and fabrication of the system. In this system the conventional film-screen photon receptor is replaced by a charged amorphous selenium imaging plate. After exposure, the latent electrostatic image on the selenium surface is scanned with multiple microelectrometer probes forming a 1024 X 1024 X 12 bit digital image. The second phase investigates the system's physical imaging characteristics and clinical feasibility. X-ray exposure latitude comparable to 200-speed calcium-tungstate film-screen system are shown for three typical diagnostic kVp settings with total filtration of 3 mm aluminum and 9 cm Lucite. Using the modulation transfer function (MTF), resolving power of approximately 1.0 line pair per millimeter and detective quantum efficiency values of approximately 5% have been measured. The clinical evaluation consists of preliminary images of a 16-kg female dog and a 4.5-kg rabbit and comparisons to film-screen images are offered.

Animals↗
PubMedDate not supplied

Electronic scanning-slit fluorography: design and performance of a prototype unit.

Electronic scanning-slit fluorography involves replacing paired fore and aft slits for scatter rejection with only one beam-defining tantalum fore aperture. Since the video signal within the projection of the aperture on the image intensifier is much more intense than behind the tantalum, one can discriminate electronically between these two signals and thus eliminate the unwanted x-ray scatter and veiling glare. The general features of a prototype unit are described along with the rationale for the choice of design factors employed. Imaging time of 1-2 s has been achieved using multiple scanning slits. Small focal-spot size and large number of pixels are favored for higher dose utilization, shorter imaging time, and lower x-ray tube loading, as well as for better spatial resolution. Images of a chest phantom show better visibility of low-contrast details, especially in poorly penetrated areas, when compared with the image obtained and displayed under the same conditions, but using a conventional grid to reject scattered radiation.

Biophysical Phenomena↗
PubMedDate not supplied

A prototype beam delivery system for the proton medical accelerator at Loma Linda.

A variable energy proton accelerator was commissioned at Fermi National Accelerator Laboratory for use in cancer treatment at the Loma Linda University Medical Center. The advantages of precise dose localization by proton therapy, while sparing nearby healthy tissue, are well documented [R. R. Wilson, Radiology 47, 487 (1946); M. Wagner, Med. Phys. 9, 749 (1982); M. Goitein and F. Chen, Med. Phys. 10, 831 (1983)]. One of the components of the proton therapy facility is a beam delivery system capable of delivering precise dose distributions to the target volume in the patient. To this end, a prototype beam delivery system was tested during the accelerator's commissioning period. The beam delivery system consisted of a beam spreading device to produce a large, uniform field, a range modulator to generate a spread out Bragg peak (SOBP), and various beam detectors to measure intensity, beam centering, and dose distributions. The beam delivery system provided a uniform proton dose distribution in a cylindrical volume of 20-cm-diam area and 9-cm depth. The dose variations throughout the target volume were found to be less than +/- 5%. Modifications in the range modulator should reduce this considerably. The central axis dose rate in the region of the SOBP was found to be 0.4 cGy/spill with an incident beam intensity of 6.7 x 10(9) protons/spill. With an accelerator repetition rate of 30 spills/min and expected intensity of 2.5 x 10(10) protons/spill for patient treatment, this system can provide 50 cGy/min for a 20-cm-diam field and 9-cm range modulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Equipment Design↗
PubMed1995

Radiological properties of a prototype multi-rod collimator for producing irregular fields in photon radiation therapy.

A prototype multi-rod collimator for producing irregular fields in photon radiation therapy has been designed and built. The mechanical details of the design and operation of the multi-rod collimator are discussed. Beam profiles for an approximately 10 x 10 cm2 field have been measured at various depths in phantom, and compared with profiles obtained using the secondary collimator jaws alone and with cast metal blocks. The ability of the collimator to produce irregular fields is demonstrated with reference to some commonly encountered therapy fields and the ability to produce central blocks and island blocks is discussed. Isodose curves for selected irregular fields are presented.

Models, Structural↗
PubMed1992

Phonetic prototypes: influence of place of articulation and speaking rate on the internal structure of voicing categories.

In this investigation, the effects of context on the perception of voicing contrasts specified by voice-onset-time (VOT) in syllable-initial stop consonants were examined. In an earlier paper [J.L. Miller and L.E. Volaitis, Percept. Psychophys. 46, 505-512 (1989)], it was reported that the listener's adjustment for one contextual variable, speaking rate, was not confined to the region of the phonetic category boundary, but extended throughout the phonetic category. The current investigation examines whether this type of perceptual remapping also occurs for another contextual variable, the place of articulation of the syllable-initial consonant. In a preliminary experiment that involved acoustic measurement of natural speech, it was confirmed that as place of articulation moves from labial to velar, VOT increases, and it was established that this occurs across a range of speaking rates (syllable durations). In the main experiments, which focused on the voiceless category, it was found that this acoustic change was reflected in perception not only as a shift in the location of the voiced-voiceless category boundary, but also a change in both the specific range of stimuli identified as members of the voiceless category and the set of stimuli judged to be the best exemplars, or prototypes, of the category. These findings extend earlier research by showing that a change in place of articulation, like a change in speaking rate, systematically alters the internal perceptual structure of voicing categories.

Adult↗