F2 Transition Research Articles

Dissecting coarticulation: How locus equations happen

A programmatic series of studies aimed at expanding our understanding of coarticulation in V 1·CV 2 sequences is presented. The common thread was examining coarticulatory dynamics through the prism of locus equations (LEs). Multiple experimental methodologies (articulatory synthesis, X-ray film, Principal Component Analysis, and extraction of time constants for F2 transitions), guided by a few theoretical assumptions about speech motor planning and control, were used to uncover the articulatory underpinnings responsible for the trademark acoustic form of LE scatterplots. Specific findings were: (1) the concept of a stop consonantal ‘target’ was quantitatively derived as a vowel-neutral, ‘deactivated,’ tongue contour; (2) the linearity of LEs is significantly enhanced by the uniformity of F2 transition time constants, which normalize with respect to F2 transition extents, and an inherent linear bias created by the smaller frequency range of [F2 onset−F2 vowel] relative to F2 vowel frequencies; (3) realistic LE slopes and y-intercepts were derived by modeling different extents of V 2 overlap onto stop consonantal target shapes at closure; and (4) a conceptually simple model, viz. interpolation between successive articulatory target shapes, followed by derivation of their formant values expressed as LEs, came surprisingly close to matching actual LEs obtained from our speaker.

Site-selective time resolved laser fluorescence spectroscopy of Eu and Cm doped LaPO4

Abstract Samples of LaPO4 doped with Eu 3+ or Cm 3+ were synthesized by a hydrothermal process which resulted in a solid solution at temperatures less than conventional processing. Time resolved laser fluorescence spectroscopy was used to probe the incorporated Eu 3+ or Cm 3+ in order to gain structural information on its local environment. This revealed that Eu 3+ and Cm 3+ incorporate on the La site as expected. The emission spectrum of Eu 3+ resolves the fully degenerate 5-fold splitting of the peaks in the F2 transition due to the low symmetry of the site, confirming previous calculations. A minor site in the Eu 3+ doped sample is identified as coordinated with hydroxide contamination. Direct excitation of Cm 3+ doped samples show the presence of “satellite” species. Although these spectral features have been observed in Cm 3+ doped LuPO4 and YPO4, this is the first time that these satellites are resolved into their individual species. These are hypothesized to be due to a disturbance in the ideal structure which creates a break in the equivalence of the four lanthanum sites within a unit cell. The 4-fold ground state splitting of all species is identical, although slightly shifted, indicating similar environments. The fluorescence lifetimes were long (1.2 ms for Cm and 3.6 ms for Eu) indicating an absence of water in the immediate coordination sphere due to the incorporation of the doping ion.

Eu3+ and Dy3+ activated Sr2V2O7 phosphor for solid-state lighting

Eu 3+ and Dy 3+ doped strontium vanadium oxide (Sr2V2O7) phosphor has been successfully synthesized using solid state diffusion method and characterized by XRD as well as photoluminescence (PL) measurements. The PL emission of Eu 3+ ion was observed in Sr2V2O7 phosphor at 593 nm and 618 nm in orange and red region of the spectrum, which corresponds to 5 D0→ 7 F1, 5 D0→ 7 F2 transitions, at the excitation wavelength of 393 nm. The PL emission of Dy 3+ ion was observed in Sr2V2O7 phosphor at 484 nm and 575 nm in blue and yellow region of the spectrum, which corresponds to 4 F9/2→ 6 H15/2 and 4 F9/2 → 6 H13/2 transitions, at the excitation wavelength of 349 nm. The 300 – 400 nm is Hg free excitation, which is characteristic of solid state lighting. Hence, Sr2V2O7 :RE [RE = Eu 3+ and Dy 3+ ] phosphors may be efficient materials for solid state lighting.

Acoustic contrastivity in conversational and loud speech

Despite frequent clinical observations of improved speech intelligibility following high vocal intensity training in speakers with dysarthria, the mechanism by which loud speech results in increased speech intelligibility is little understood. Prior research has reported conflicting acoustic results of articulatory modifications in loud speech conditions such as changes in vowel durations, acoustic vowel space, and F2 transition duration/extent. More interestingly, the impact of an overall increase in amplitude of speech signals on perceptual judgment of speech intelligibility is unclear, especially when the entire speech signal is amplified as compared to the amplification of selected phonetic events (see Kim and Kuo, in press). This presentation focuses on the change of relative contrastivity within utterances that were produced at both conversational and loud levels to better understand the underlying mechanism of enhanced speech intelligibility secondary to greater vocal intensity. In this presentation, data on the ratio of vowel durations (long versus short), formant structures of vowels (tense versus lax), as well as the ratio of syllable intensity (stressed vs unstressed) will be compared between conversational and loud speech conditions produced by young adult speakers.

Preparation and Characterization of 3D Flower-like La2O3 Nanostructures

In this work, a facile route using a simple solvothermal reaction and sequential heat treatment process to prepare 3D La2O3 flower-like nanostructures without employing templates or matrices for self-assembly is presented. The as-synthesized products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), highresolution TEM (HRTEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TG), differential thermal analysis (DTA), and Fourier transformation IR (FTIR). SEM results demonstrate that the as-prepared flower-like precursor with average size of 5- 7 μm in diameter is composed of numerous nanoplates with a thickness of about 100 nm. Influencing factors such as solvothermal reaction temperature, surfactants, reaction time, and solvents were systematically investigated. 3D flower-like La2O3 nanostructures with many holes on the petals were obtained after calcinations of the flower-like precursor at 800 °C for 4 h. The BET surface area of the flower-like La2O3 nanostructures is 9.98 m2/g. Eu3+ doped flower-like La2O3 nanostructures were also prepared employing the same preparation process. The flower-like La2O3:Eu3+ nanostructures show a strong red emission corresponding to 5D0 -7F2 transition (625 nm) of Eu3+ under ultraviolet excitation (267 nm). The possible formation mechanism for the 3D flower-like precursor was briefly discussed. Keywords: Characterization, lanthanum oxide, nanomaterials, porous, self-assembly, solvothermal synthesis, rare earth, flower-like, nanostructures, photoluminescence

Enhanced Red Emission of LaVO4:Eu3+ Phosphors by Li-doping

LaVO4 phosphors were synthesized by using a solid state reaction, and were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). The XRD patterns of the Li-doped LaVO4:Eu 3+ powder phosphors revealed a mixture of tetragonal and monoclinic phases. The tetragonal phase of the LaVO4:Eu 3+ phosphor showed a higher PL intensity than the monoclinic one, despite the presence of both monoclinic and tetragonal structures. The Li-doped LaVO4:Eu 3+ powder phosphors absorbed strongly at 396 nm and exhibited strong red emission at approximately 619.5 nm due to the D0 → F2 transition. The incorporation of Li ions into the LaVO4:Eu 3+ powder can lead to a remarkable increase in photoluminescence. The enhanced luminescence is attributed to the incorporation of Li ions that may act as a sensitizers for effective energy transfer. This phosphor has promising applications in near-UV light-emitting diodes(LEDs).

Preparation and Photoluminescence Properties of Three-Dimensionally Ordered Macroporous ZrO<SUB>2</SUB>:Eu<SUP>3+</SUP>

Three-dimensionally ordered macroporous (3DOM) ZrO2:Eu3+ (0.5%, 1%, 2% and 5%) were successfully prepared using a polystyrene (PS) colloidal crystal template in combination with a sol-gel method. The structure, morphology, porosity, and optical properties of the materials were well characterized by X-ray diffraction (XRD), Field emission scanning electron micrograph (FESEM), N2 adsorption, and photoluminescence (PL) spectra. The results indicated that the closely packed material exhibited three-dimensional ordering of pores and a strong red (5)D0-->(7)F2 transitions under charge transfer excitation. Strong PL and abundant porosity are of particular interest and give this multifunctional material future potential.

A psychoacoustic method to find the perceptual cues of stop consonants in natural speech.

Synthetic speech has been widely used in the study of speech cues. A serious disadvantage of this method is that it requires prior knowledge about the cues to be identified in order to synthesize the speech. Incomplete or inaccurate hypotheses about the cues often lead to speech sounds of low quality. In this research a psychoacoustic method, named three-dimensional deep search (3DDS), is developed to explore the perceptual cues of stop consonants from naturally produced speech. For a given sound, it measures the contribution of each subcomponent to perception by time truncating, highpass/lowpass filtering, or masking the speech with white noise. The AI-gram, a visualization tool that simulates the auditory peripheral processing, is used to predict the audible components of the speech sound. The results are generally in agreement with the classical studies that stops are characterized by a short duration burst followed by a F2 transition, suggesting the effectiveness of the 3DDS method. However, it is also shown that /ba/ and /pa/ may have a wide band click as the dominant cue. F2 transition is not necessary for the perception of /ta/ and /ka/. Moreover, many stop consonants contain conflicting cues that are characteristic of competing sounds. The robustness of a consonant sound to noise is determined by the intensity of the dominant cue.

Transition characteristics in speakers with dysarthria and in healthy controls: Part IV: Additional data on vital capacity transitions and stroke patients.

Formant transitions are known to provide important cues for speech perception, sound identification, and inferences to articulatory behavior. This study describes and examines three types of formant transitions [consonant-vowel (CV), vowel-consonant (VC), and diphthong transitions] in four groups of speakers: healthy, ALS, Parkinson’s disease, and stroke. This is an extension from previous work by Weismer et al. [J. Acoust. Soc. Am. 121, 3135 (2007)] and Weismer et al. [J. Acoust. Soc. Am. 124, 2558 (2008)], who showed shallower slopes for CV and diphthong transitions in persons with dysarthria (ALS and PD). To better understand the characteristics of the different transition types in healthy and disordered populations, two questions are addressed here. First, are CV transitions associated with dysarthria different from those in healthy speakers in a way comparable to the observed differences in diphthong transitions? Second, do VC transitions show the same normal characteristics, and are the differences between healthy speakers and speakers with dysarthria the same as in CV transitions? Distributional analyses for 50-ms CV, 50-ms VC, and diphthong (highest-lowest/lowest-highest) F2 transition measures will be presented for 18 healthy speakers, 4 speakers with ALS, 4 speakers with PD, and 20 stroke patients. [Work supported by NIDCD R01 DC003723.]

Synthesis and Luminescence of Hollow Spherical Eu<SUP>3+</SUP>- or Tb<SUP>3+</SUP>-Doped MgAl<SUB>2</SUB>O<SUB>4</SUB> Phosphors

Eu3+- or Tb3+ -doped MgAl2O4 hollow spheres have been successfully synthesized via facile hydrothermal method by using carbon spheres as template followed by a subsequent heat treatment. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results showed that the hollow microspheres possessed diameters in the range of 1-2.5 microm and shell thickness of 60-80 nm. A possible formation mechanism for hollow spheres was proposed. MgAl2O4:Eu3+ show strong red emission at 619 nm corresponding to the forced electric dipole (5)D0-->(7)F2 transition of Eu3+, and MgAl2O4:Tb3+ exhibit strong green emission at 545 nm corresponding to 5D4-->(7)F5 transition of Tb3+.

A Duration-Dependent Account of Coarticulation for Hyper- and Hypoarticulation

Previous studies investigating anticipatory coarticulation in emphatically stressed CV sequences and during fast speaking rates reported that three factors contributed to the overall extent of the documented coarticulation. These factors were: (1) vowel identity, (2) vowel space expansion (emphasis) or reduction (fast rate), and a hypothesized (3) ‘deeper’ and ‘shallower’ stop closure contact in emphatic and faster speech, respectively. The objective of the current research was to conceptually and quantitatively unify these two studies. This was accomplished by showing that the opposite changes to frequency onsets of F2 transitions due to emphatic and rapid speech systematically vary as a function of the durational changes in the stop closure interval. Specifically, the decrease in coarticulation in emphatic speech is characterized by increases in F2 onsets and longer stop closures (relative to a normal baseline); the increase in coarticulation due to rapid speech shows concomitant decreases in F2 onsets coinciding with shorter stop closure intervals. Vocal tract area function simulations corresponding to emphatic and reduced speech implicitly support ‘deeper’ and ‘shallower’ closure contacts as a third factor contributing to the overall extent of anticipatory CV coarticulation.

A duration‐dependent account of coarticulation for hyper‐ and hypoarticulation.

Hyperarticulated and hypoarticulated speech are accompanied by spectral expansion and spectral reduction of vowel nuclei, respectively. These shifts in F1/F2 vowel space directly affect degree of anticipatory coarticulation in consonant + vowel sequences apart from traditional vowel context effects. Examining the opposite conditions of emphatic stress [Lindblom et al., J. Acoust. Soc. Am. 121, 3802–3813 (2007)] and faster speaking rates (Agwuele et al., Phonetica, in press) it was shown that coarticulatory effects could be documented independently of the expected vowel expansion/reduction effects. A modified locus equation regression metric was used in both studies to isolate alterations in F2 transition onsets due to prosodic and speech rate conditions apart from vowel space shifts per se. The current study provides a unified empirical and theoretical account for the opposite coarticulatory effects by providing duration data as the common variable tying both studies together. Articulatory and acoustic simulations of deeper (emphasis) and shallower (increased tempo) closures are provided to explain the shifts of observed F2 onsets relative to predicted F2 onsets due simply to expanded/reduced vowel space.

Hydrothermal synthesis and vacuum ultraviolet excited photoluminescence properties of (Y, La)VO4:Eu3+ phosphors

The Y0.95-xLaxVO4:5%Eu3+ (0≤x≤0.15) phosphors were synthesized successfully by mild hydrothermal method at 200°C and their photoluminescence properties under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation were studied. Monitoring at 619nm, a strong broad absorption was enhanced by co-doping of La3+ into the YVO4:Eu3+ lattices at about 260nm in the UV excitation spectra. The VUV excitation spectra also showed the enhanced excitation bands at about 156nm and 200nm. Under 254nm or 147nm excitation, it was found that Y0.95-xLaxVO4:Eu3+ phosphors showed strong red emission at about 615nm and 619nm corresponding to the electric dipole 5D0 -7F2 transition of Eu3+, resulting in good color purity. The improvement of luminescence intensity of YVO4:Eu3+ was also observed after partial substituting Y3+ by La3+ and the optimal luminescence intensity appeared with incorporation of 2.5mol% La3+. The reasons of this enhancement were investigated and discussed in details.

Effects of Hearing Loss and Spectral Shaping on Identification and Neural Response Patterns of Stop-Consonant Stimuli in Young Adults

The primary purpose of this study was to more clearly define the effects of hearing loss, separate from age, on perception, and neural response patterns of dynamic spectral cues. To do this, the study was designed to determine whether (1) hearing loss affects the neural representation and/or categorical perception of stop-consonant stimuli among young adults and (2) spectrally shaped amplification aimed at increasing the audibility of the F2 formant transition cue reduces any effects of hearing loss. It was predicted that (1) young adults with hearing loss would differ from young adults with normal hearing in their behavioral and neural responses to stop-consonant stimuli and (2) enhancing the audibility of the F2 formant transition cue relative to the rest of the stimulus would not overcome the effects of hearing loss on behavioral performance or neural response patterns. Behavioral identification and neural response patterns of stop-consonant stimuli varying along the /b-d-g/ place-of-articulation continuum were measured from seven young adults with mild-to-moderate hearing impairment (mean age = 21.4 yr) and compared with responses from 11 young adults with normal hearing (mean age = 27 yr). Psychometric functions and N1-P2 cortical-evoked responses were evoked by consonant-vowel (CV) stimuli without (unshaped) and with (shaped) frequency-dependent amplification that enhanced F2 relative to the rest of the stimulus. Behavioral identification and neural response patterns of stop-consonant CVs differed between the two groups. Specifically, to the unshaped stimuli, listeners with hearing loss tended to make low-frequency judgments more often (more /b/, fewer /g/) than listeners with normal hearing when categorizing along the /b-d-g/ continuum. Additionally, N1 amplitudes were larger and P2 latencies were longer to all phonemes in young adults with hearing impairment versus normal hearing. Enhancing the audibility of the F2 transition cue with spectrally shaped amplification did not alter the neural representation of the stop-consonant CVs in the young listeners with hearing loss. It did modify categorical perception such that listeners with hearing loss tended to make high-frequency judgments more often (more /g/, fewer /b/). However, shaping the stimuli did not make their psychometric functions more like those of the normal controls. Instead, young adults with hearing loss went from one extreme (low-frequency judgments with unshaped stimuli) to the other (high-frequency judgments with shaped stimuli), whereas judgments from the normal controls were more balanced. Hearing loss, separate from aging, seems to negatively impact identification and neural representation of time-varying spectral cues like the F2 formant transition. Enhancing the audibility of the F2 formant transition cue relative to the rest of the stimulus does not overcome the effects of hearing loss on behavioral performance or neural response patterns in young adults. Thus, the deleterious effects of hearing loss on stop-consonant perception along the place-of-articulation continuum may not only be due solely to decreased audibility but also due to improper coding by residual neurons, resulting in distortion of the time-varying spectral cue. This may explain, in part, why amplification cannot completely compensate for the effects of sensorineural hearing loss.

The Effect of Speaking Rate onConsonant Vowel Coarticulation

In 2007 Lindblom et al. introduced a methodological tool to disentangle consonant-vowel (CV) coarticulation attributable to emphatic stress apart from the vowel expansion effects known to accompany the prosodic overlay. After empirically accounting for the altered vowel positions, they reported small but consistent increases in F2 transition onsets in emphatically produced CVs that could not be attributed to vowel context influences, and that differed across stop place. At issue is whether the findings of these authors can be replicated, but in the opposite direction, for CVs produced at fast speaking rates. A modified locus equation regression metric was similarly used to account for rate-induced vowel reduction effects in predicting frequencies of F2 transition onsets in rapid speech. Six American-English speakers produced [V1.CV2] sequences embedded in a carrier sentence, at three speaking tempos: normal, fast, and fastest. Significant differences were found between ‘predicted’ and ‘observed’ F2 onsets across stops, with alveolars and velars showing greater decreases in F2 onsets during more rapid speech than labials. The complementary findings are discussed relative to a unified view of anticipatory coarticulation in CV production across a continuum of hyperarticulated spectral expansion to hypoarticulated spectral reduction.

Fractionation of Suwannee River Fulvic Acid and Aldrich Humic Acid on α-Al2O3: Spectroscopic Evidence

Sorptive fractionation of Suwannee River Fulvic Acid (SRFA) and Purified Aldrich Humic Acid (PAHA) on alpha-Al2O3 at pH 6 was probed in the supernatant using different spectroscopic techniques. Comparison of dissolved organic carbon (DOC) analysis with UV/vis spectrophotometric measurements at 254 nm, including specific UV absorbance (SUVA) calculation, revealed a decrease in chromophoric compounds for the nonsorbed extracts after a 24 h contact time. This fractionation, only observable below a certain ratio between initial number of sites of humic substances and of alpha-Al2O3, seems to indicate a higher fractionation for PAHA. C(1s) near-edge X-ray absorption fine structure spectroscopy (NEXAFS) confirmed this trend and points to a decrease in phenolic moieties in the supernatant and to an eventual increase in phenolic moieties on the surface. Time-resolved luminescence spectroscopy (TRLS) of Eu(III) as luminescent probe showed a decrease in the ratio between the (5)D0-->(7)F2 and (5)D0-->(7)F1 transitions for the fractionated organic matter (OM) that is thought to be associated with a lower energy transfer from the OM to Eu(III) due to the loss of polar aromatics. These modifications in the supernatant are a hint for the modification of sorbed humic extracts on the surface.

Spectroscopic Analysis of Ligand Binding to Lanthanide−Macrocycle Platforms

A high-affinity, binary Eu(3+) receptor site consisting of 1,4,7,10-tetraazacyclododecane-1,7-diacetate (DO2A) was constructed with the goal of improving the detection of dipicolinic acid (DPA), a major component of bacterial spores. Ternary Eu(DO2A)(DPA)(-) complex solutions (1.0 microM crystallographically characterized TBA x Eu(DO2A)(DPA)) were titrated with EuCl3 (1.0 nM-1.0 mM); increased Eu(3+) concentration resulted in a shift in equilibrium population from Eu(DO2A)(DPA)(-) to Eu(DO2A)(+) and Eu(DPA)(+), which was monitored via the ligand field sensitive (5)D0 --> (7)F3 transition (lambda(em) = 670-700 nm) using luminescence spectroscopy. A best fit of luminescence intensity titration data to a two-state thermodynamic model yielded the competition equilibrium constant (Kc), which in conjunction with independent measurement of the Eu(DPA)(+) formation constant (Ka) allowed calculation of the ternary complex formation constant (Ka'). With this binding affinity by competition (BAC) assay, we determined that Ka' = 10(8.21) M(-1), which is approximately 1 order of magnitude greater than the formation of Eu(DPA)(+). In general, the BAC assay can be employed to determine ligand binding constants of systems where the lanthanide platform (usually a binary complex) is stable and the ligand bound versus unbound states can be spectroscopically distinguished.

Spectral Integration of Dynamic Cues in the Perception of Syllable-Initial Stops

The present experiments examine the potential role of auditory spectral integration and spectral center of gravity (COG) effects in the perception of initial formant transitions in the syllables [da]-[ga] and [t^ha]-[k^ha]. Of interest is whether the place distinction for stops in these syllables can be cued by a ‘virtual F3 transition’ in which the percept of a frequency transition is produced by a dynamically changing COG. Listeners perceived the virtual F3 transitions comparably with actual F3 transitions although the former were less salient a cue. However, in a separate experiment, static ‘virtual F3 bursts’ were not as effective as actual F3 bursts in cueing the alveolar-velar place distinction. These results indicate that virtual F3 transitions can provide phonetic information to the perceptual system and that auditory spectral integration (completed by the central auditory system) may play a significant role in speech perception.

Modeling formant pattern in fricative-vowel sequences

MRI data indicate that there are two subject-dependent articulatory patterns in French post-alveolar sibilant fricative /'integral of'/. Each type of articulations can correspond to the Polish fricatives /'curled c'/ and /'underdotted s'/ on the basis of their articulatory similarity: palatalized for the former, and the presence of a sublingual cavity as well as lip protrusion for the latter. The F2 transitions, in part, reflect the acoustic contrast between these Polish fricatives, which exhibit a higher locus in the palatalized /'curled c'/ than in /'underdotted s'/. However, no systematic transitional characteristic could be found in French. We hypothesize that the subject-specific formant-cavity affiliation in the adjacent vowel /a/ and/or the difference of scale in vocal tract lengths manifest as the acoustic variation in French, whereas those VT morphological differences are articulatorily compensated in Polish to maintain the distinctiveness of these two post-alveolar fricatives. In order to assess this hypothesis, the F-patterns along /a 'integral of' a/ sequences are simulated for various vocal tract configurations. In calculations, the two different types of the fricative articulations are combined with the vocal-tract area functions appropriate for /a/ but different in shape and in size to taken into account for female and male speakers. The results will be discussed.

English /r/-/l/ pronunciation training for Japanese speakers

Previous studies have demonstrated that perceptual training improves both perception and production by adult second-language (L2) learners. The present study examined whether production training likewise improves both perception and production. Japanese speakers underwent ten sessions of production training for English /r/ and /l/. The training combined three methods: (1) subjects received audio-visual examples and pronunciation instructions for /r/ and /l/; (2) they produced mono syllables (i.e., /ra/ and /la/) and minimal-pair words, with online feedback about their formant frequencies using a real-time spectrogram as well as pronunciation feedback from an instructor; and (3) they made recordings of minimal-pair words and compared them to "enhanced" versions of these recordings (i.e., signal-processed versions with the correct F3 frequencies and transition durations). All participants completed a battery of pre/post training tests (i.e., English /r/-/l/ identification, discrimination, perceptual mapping of best exemplars, and production). The preliminary results indicate that this training approach improves production; the results will be further discussed in terms of its effect on perception and the underlying representation of these categories.