Measurements of the fine structure of laser intensity correlations near threshold

The correlation function of the intensity fluctuations of a single mode laser in the threshold region has been measured with a fast digital correlator. The various exponential components have been separated for the first time, by exploiting the nonlinear characteristics of the correlator. The results are in quantitative agreement with the theoretical predictions.     

Coding of spectral fine structure in the auditory nerve. II: Level-dependent nonlinear responses

Phase-locked discharge patterns of single cat auditory-nerve fibers were analyzed in response to complex tones centered at fiber characteristic frequency (CF). Signals were octave-bandwidth harmonic complexes defined by a center frequency F and an intercomponent spacing factor N, such that F/N was the fundamental frequency. Parameters that were manipulated included the phase spectrum, the number of components, and the intensity of the center component. Analyses employed Fourier transforms of period histograms to assess the degree to which responses were synchronized to the frequencies present in the acoustic stimulus. Several nonlinearities were observed in the response as intensity was varied between threshold and 80-90 dB SPL. Response nonlinearities were strong for all signals except those with random phase spectra. The most commonly observed nonlinearity was an emphasis of one or more stimulus components in the response. The degree of nonlinearity usually increased with intensity and signal complexity and decreased with fiber frequency selectivity. Half-wave rectification introduced synchronization to the missing fundamental. The strength of the response at the fundamental was related to stimulus crest factor. Signals with low center frequencies and high crest factors often elicited instantaneous discharge rates at the theoretical maximum of pi CF. This suggests that the probability of spike generation approaches one during high-amplitude waveform segments. Response nonlinearity was interpreted as arising from three sources, namely, cochlear mechanics, compression of instantaneous discharge rate, and saturation of average discharge rate. At near-threshold intensities, fibers with high spontaneous rates exhibited responses that were linear functions of stimulus waveshape, whereas fibers with low spontaneous spike rates produced responses that were best described in terms of an expansive nonlinearity.     

Estimation of detection threshold of system latency of virtual auditory display

When a virtual auditory display (VAD) is responsive to a listener’s head movement, high precision of sound localization can be obtained. However, when the system latency (SL) is detectable to the listener, he/she feels that the virtual world is unnatural. Therefore, SL should be sufficiently smaller than the detection threshold (DT). Few researchers have examined DT and little information on the inter-subject differences has been reported. Thus, DT was investigated in more detail in this study. We conducted two kinds of experiments and examined the DT and difference limen (DL). Findings showed the estimated average DT and DL for listeners to be 45 ms and 59 ms, respectively. It was confirmed that the respective sensitivities d′ derived from each of the two experiments are strongly correlated with each other (r = 0.90 (p < .01)).     

Coding of spectral fine structure in the auditory nerve. I. Fourier analysis of period and interspike interval histograms

The temporal fine structure of discharge patterns of single auditory-nerve fibers in adult cats was analyzed in response to signals consisting of a variable number of equal-intensity, in-phase harmonics of a common low-frequency fundamental. Two analytic methods were employed. The first method considered Fourier spectra of period histograms based on the period of the fundamental, and the second method considered Fourier spectra of interspike interval histograms (ISIH's). Both analyses provide information about fiber tuning properties, but Fourier spectra of ISIH's also allow estimates to be made of the degree of resolution of individual stimulus components. At low intensities (within 20-40 dB of threshold), indices of synchronization to individual components of complex tones were similar to those obtained for pure tones. This was true even when fibers were capable of responding to several signal components simultaneously. Response spectra obtained at low intensities resembled fibers' tuning curves, and fibers with low spontaneous discharge rates tended to provide better resolution of stimulus components than fibers with high spontaneous rates. Strongly nonlinear behavior existed at higher stimulus intensities. In this, information was transmitted about progressively fewer signal components and about frequencies not present in the acoustic stimulus, and the component eliciting the largest response shifted away from the fiber's characteristic frequency and toward the edges of the stimulus spectrum. This high-intensity "edge enhancement" can result from the combined effects of a compressive input-output nonlinearity, suppression, and the fortuitous addition of internally generated combination tones. The data indicate that sufficient information exists for the auditory system to determine the frequencies of narrowly spaced stimulus components from the temporal fine structure of nerve fiber's responses.     

The effect of auditory feedback on phonation threshold pressure measurement

The effect of auditory feedback on phonation threshold pressure (Pth) measurement was investigated in 14 females with normal, untrained voices. Two measurement systems (Glottal Enterprises MS 100--circumferentially vented mask and Kay Elemetrics Aerophone II--non-circumferentially vented mask) were examined under three conditions: (1) masked, (2) no mask, and (3) masked with enhanced auditory feedback-acoustic signal placed at ears through headphones. Masked with enhanced auditory feedback, in addition to subject training, significantly lowered Pth values regardless of mask design. The amount of auditory feedback provided by different mask designs was investigated and revealed a significant difference. Clinical significance of different auditory feedback levels provided by the two mask designs was investigated. Direct comparison of the mean values between systems was not possible because of each system's design and calibration. Comparisons were accomplished by subtracting means of select-paired conditions (masked/no mask; masked/masked plus masked with enhanced auditory feedback) within each system and then comparing these difference scores from the same paired conditions between each system. No clinical significance in difference scores was revealed because of varying amounts of auditory feedback provided by the masks. Results support the use of enhanced auditory feedback, in addition to subject training, when measuring Pth.     

The fine structure of the isoharic analogue resonances

The distribution of an isobaric analogue resonance over the numerous surrounding states of different isobaric spin is studied analytically in the frame of the Fano-Weidenmüller shell-model theory of nuclear reactions. The doorway state wave function is described byLane's coupled equations. The matrix element of the residual nuclear interaction between this doorway state and a complicated state of different isobaric spin exhibits a particular energy dependence. A sum rule is established: the sum of the fine structure widths is larger than the width of the doorway state, as calculated fromLane's model. The residual Coulomb interactions are neglected. When perturbation theory holds, the distribution of the fine structure peaks is shown to have a characteristic asymmetrical shape. The connection withRobson's R-matrix treatment is discussed.     

人耳听阈曲线的测定实验设计

介绍了用听觉实验仪测定听阈曲线的原理和方法,并对实验效果进行了分析。     

The Casimir effect and the fine structure constant

We consider the electron as a charged sphere that completely absorbs any radiation with wave number less than somek _m . The Casimir effect then provides a self stress which can balance the mutual repulsion of the distinct parts of the finite charge distribution. From this equilibrium condition and connecting, by quantum arguments, the value ofk _m to the radius of the electron, we obtain a good estimate for the value of the fine-structure constant.     

On the fine structure constant

In the framework of a particle model based on a classical minimum action principle a number α′ is derived which is shown to be the analogue of the fine structure constant $\text{α = e}{}^2\text{/}\text{h}\text{?}\text{c}$. To compute α′, a pair of coupled partial differential equations of the second order must be solved. No exact result has been obtained as yet, but it is likely that α′ ? 1. The analogy between α′ and α opens a clear insight into the meaning of the fine structure constant.     

The fine structure of the spectrum of the electronic NO laser

The spectrum of the electronic NO laser has been photographed with high resolution in the region 10 100–10 500 Å. It shows the band system F²Δ-C²Π whose upper and lower states are both Rydberg states configurationally mixed with valence states. Only predissociated rotational levels of the lower state appear in the spectrum. For v = 0 of C²Π a single mixed level $\text{T}{}_{\mathrm{y}}\text{(J = 5}\text{1}\text{2}\text{) = 52431}\text{cm}{}^{\mathrm{?1}}$, very close to the dissociation limit, gives rise to laser lines.     

The fine structure of coelomocytes in the sipunculid Phascolosoma esculenta

Ultrastructural characteristics of coelomocytes of the sipunculid Phascolosoma esculenta were studied by transmission electron microscopy. There are several cell types in the coelomic fluid, including three kinds of granulocytes, vesicular cells, germ cells, amoebocytes, phagocytes, and erythrocytes; there are also a new cell complex which is composed of podocytes and granular cells. And several other cell types (erythrocyte and different kinds of granulocytes) gathering together was discovered in the coelomic fluid of P. esculenta. Functional interpretations were provided for these cells using morphological evidence. The coelomocytes from different sipunculid genera and Annelida were compared. The structural diversity of coelomocytes provides both taxonomic characteristics for discriminative identification and phylogenetic markers in Phascolosoma and other sipunculid taxa.     

Suppression of auditory nerve responses. II. Suppression threshold and growth, iso-suppression contours

Two-tone "synchrony suppression" was studied in responses of single auditory nerve fibers recorded from anesthetized cats. Suppression thresholds for suppressor tones set to a fiber's characteristic frequency (CF) were approximately equal to discharge rate thresholds for CF tones. Suppression thresholds above and below CF were usually lower than the corresponding discharge rate thresholds. However, at all frequencies studied (including CF), suppression thresholds were higher than the corresponding thresholds for discharge synchronization. Across fibers, rates of suppression growth for suppressors at CF were greatest in low-CF fibers and least in high-CF fibers, and there was a systematic decrease in suppression growth rate at CF as CF increased. Within fibers, rates of suppression growth above CF were typically less than at CF, and slopes were monotonically decreasing functions of frequency. Within-fiber rates of suppression growth below CF were variable, but they usually were greater than rates of growth at CF. Iso-suppression contours (frequencies and intensities producing criterion amounts of suppression) indicated that tones near CF are the most potent suppressors at near-threshold intensities, and that the frequency producing the most suppression usually shifts downward as the amount of suppression increases. These data support the notion that synchrony suppression arises primarily as a passive consequence of hair cell activation.     

The influence of middle-ear muscle contraction on auditory threshold for selected pure tones

The influence of middle-ear muscle (MEM) contraction on auditory threshold has been measured for pure tones of 0.25, 0.5, and 1.5 kHz. The reflex-activating signal was a 3-kHz pure tone. Signal paradigms were chosen to reduce or eliminate the effects of binaural loudness summation, contralateral direct masking, and contralateral remote and backward masking effects, and to maximize the influence of MEM contraction. Results indicate that under no condition was behavioral threshold affected by the MEM contraction induced using a pure-tone stimulus of 3 kHz, 105 dB SPL.