Upward Spread Research Articles

The effect of frequency-selective attenuation on the speech-reception threshold of sentences in conditions of low-frequency noise

Within a study on the merits of a multichannel automatic gain control in hearing aids, the effect of frequency-selective amplification on the masked speech-reception threshold (SRT) for sentences is measured in conditions of seriously disturbing low-frequency noise, with the effect of wideband amplification as a reference. Speech and noise are both spectrally shaped according to the bisector line of the listener's dynamic-range of hearing, but with the noise in a single octave band (0.25-0.5 or 0.5-1 kHz) increased by 20 dB relative to this line. The increase of noise level is steady state in the first experiment, and time varying in the second experiment. Results for 12 normal-hearing and 12 hearing-impaired listeners indicate that, in both experiments, frequency-selective compression of the signal in the octave band with the 20-dB increase of noise is more beneficial than wideband compression. For the hearing-impaired group, wideband compression does not give any systematic change in intelligibility. Frequency-selective compression in steady-state conditions may, for both groups of listeners, give a decrease of masked SRT (relative to a condition without compression) of up to 4 dB for a compression factor of 100%. Roughly comparable effects are seen for frequency-selective compression in time-varying conditions. The superiority of frequency-selective over wideband compression is attributed to a more effective reduction of upward spread of masking.

Predicting the spread rates of fires on vertical surfaces

A model is developed for the upward spread rate of the pyrolysis front of burning vertical slab. It is ignited with a flame from a line burner of user-specified strength, Qb(t). It can also be exposed to arbitrary, time-varying impinging external fluxes. It is assumed that the slab material has uniform, isotropic properties and that there is no lateral diffusion of heat within the slab. This model has been implemented as a computer program. The program has two options for the mass-loss rate. The first uses an algebraic submodel for the steady-state pyrolysis of simple, non-melting and non-charring materials. The second is based on Cone Calorimeter data: the mass-loss rate data found via the Cone at a given irradiance level is transformed into what the rate would be at those found during the actual experiment. The latter approach automatically includes the effects of charring, of transient heating, etc., to a first approximation. Expressions for the heating flux from the flame to the wall are found for all cases of interest. Runs were made assuming 2.5, 5, and 10 kW/m igniting burners and with a square-root dependence on Qb′ for the flame height, as well as with the usual 2/3 power dependence. The results of each run were compared with the results of upward spread experiments on PMMA carried out in 1975 by Orloff et al. The results, using either massloss rate option, were in excellent agreement with experiment when the square-root dependence was used.

Tiptoeing through the melanocytic minefield

Fortunately the histological diagnosis of most benign and malignant pigment cell tumours and of non melano-cytic tumours of skin is not difficult. A problem is usually due to one major feature. An axiom is that no one feature is diagnostic of malignant melanoma. More detailed analysis is required searching for features supporting or opposing the major feature. Some of the major problems are tumours of large epithelioid, spindle and giant cells where differential diagnoses are melanoma, Spitz naevus and cellular blue naevus. When the cells are of naevul size the diagnosis could be banal naevus, dysplastic naevus or melanoma of naevul like cells. Abnormalities of site such as deep dermal extension raise possibilities of congenital naevus, cellular blue naevus and desmoplastic melanoma. Other worrying features are upward epidermal spread, disruptive lymphocytic infiltration, fibrosis, mitotic activity, foamy cytoplasm and spindle cells especially in non pigmented tumours. Deeper levels is probably the most helpful proceedure. Useful stains are melanin, iron, reticulin, PAS, trichome S100, keratin and vimentin. Melanoma MOABs and AgNORs still require evaluation. Further clinical history such as duration of pre-existing lesion, especially if congenital, past and family history and mole status of the patient can be useful. Be prepared to recheck the clinical history especially the patients age.

Do “adaptive frequency response” (AFR) hearing aids reduce upward spread of masking?

Speech recognition scores in noise are improved for some subjects wearing hearing aids that reduce low‐frequency noise with an adjustable high‐pass filter circuit. Fabry and Van Tasell (1989) argued that because speech‐to‐noise ratios are not altered by AFR hearing aids, improvements in speech recognition may be related to a reduction in upward spread of masking experienced by the listener [D. Fabry and D. Van Tasell, J. Acoust. Soc. Am. Suppl. I 85, S25 (1989)]. To evaluate this hypothesis, pure‐tone masking patterns for a low‐frequency bandpass noise were measured in normal and hearing‐impaired subjects. The noise skirt of the masker was very steep, with attenuation above the 1000‐Hz cutoff greater than 100 dB/oct. Masking patterns for the same noise were also obtained in the presence of a high‐pass filter that simulated the effects of an AFR hearing aid. Differences in the masking patterns can be taken as a measure of upward spread of masking. Subjects with high‐frequency hearing loss tended to demonstrate greater amounts of upward spread of masking than did normal‐hearing listeners. Further, monosyllabic speech recognition in noise testing indicated improvements in performance of the hearing‐impaired subjects related to the decrease of upward spread of masking in the high‐pass filtering conditions.

Upward spread of masking, hearing loss, and speech recognition in young and elderly listeners

Upward spreading of masking, measured in terms of absolute masked threshold, is greater in hearing-impaired listeners than in listeners with normal hearing. The purpose of this study was to make further observations on upward-masked thresholds and speech recognition in noise in elderly listeners. Two age groups were used: One group consisted of listeners who were more than 60 years old, and the second group consisted of listeners who were less than 36 years old. Both groups had listeners with normal hearing as well as listeners with mild to moderate sensorineural loss. The masking paradigm consisted of a continuous low-pass-filtered (1000-Hz) noise, which was mixed with the output of a self-tracking, sweep-frequency Bekesy audiometer. Thresholds were measured in quiet and with maskers at 70 and 90 dB SPL. The upward-masked thresholds were similar for young and elderly hearing-impaired listeners. A few elderly listeners had lower upward-masked thresholds compared with the young control group; however, their on-frequency masked thresholds were nearly identical to the control group. A significant correlation was found between upward-masked thresholds and the Speech Perception in Noise (SPIN) test in elderly listeners.

Physiological mechanisms of psychophysical masking: Observations from auditory-nerve fibers

Masking might be due either to the spread of the excitation produced by the masker to the place of the tone signal along the cochlea or to the suppression of the response to the signal by the masker. In order to identify the contributions of these two mechanisms to tone-on-tone masking, masked thresholds of auditory-nerve fibers were measured in anesthetized cats using the same stimulus paradigms and detection criteria as in psychophysics. Suppressive masking was identified by comparing thresholds for simultaneous masking with those for a nonsimultaneous masking technique resembling pulsation thresholds. These nonsimultaneous thresholds do not include the contribution of suppression to masking because suppression only occurs for stimuli that overlap in time. For each masker and signal frequency, the fibers with the lowest (or "best") masked thresholds had characteristic frequencies (CF) slightly on the opposite side of the masker frequency with respect to the signal frequency, consistent with the psychophysical phenomenon of off-frequency listening. Patterns of best masked thresholds against signal frequency resembled psychophysical masking patterns in that they showed a maximum for signal frequencies close to the masker, and a skew toward high frequencies. Masking was found to be both excitatory and suppressive, with the relative contribution of the two mechanisms depending on the frequency separation between signal and masker. Suppressive masking was large for signal frequencies well above the masker. For these conditions, simultaneous thresholds grew more rapidly with masker level than did nonsimultaneous thresholds, suggesting that the upward spread of masking is largely due to the growth of suppression rather than to that of excitation.

Auditory Detection, Discrimination and Speech Processing in Ageing, Noise-sensitive and Hearing-impaired Listeners

The aims of this research were to document changes in hearing and speech intelligibility in noise that occur with ageing, noise sensitivity, and progressive bilateral sensorineural hearing loss. Five groups defined by age, clinical complaint and degree of hearing loss were tested. Each of 73 subjects participated in nine different procedures, including detection in quiet and in continuous 90 dB SPL helicopter noise, frequency and duration discrimination, consonant recognition and word identification. The effects of different types of background noise and speech-to-noise ratio were investigated. Ageing, without concomitant hearing loss, resulted in significantly greater DLs both for frequency and for duration with a 20 ms standard at both 500 Hz and 4,000 Hz. Hearing loss, unconfounded by ageing, affected masked detection and frequency discrimination at 4,000 Hz and speech intelligibility in noise. The sole finding for subjects with noise sensitivity was an upward spread of masking for detection. Across tests, the best predictors of speech processing decrements were the detection thresholds for 2,000 Hz and 4,000 Hz in quiet or in noise.

Perceptual, Acoustical, and Musical Aspects of the Tambūrā Drone

The basso continuo principle, as embodied in Rameau's theory of functional harmony, was paralleled by the introduction of drone instruments in the classical music of India. In order to understand how these two systems are tied together in human music perception, we studied the role of tambūrā interactions with North Indian rags played on the sitār. Raman (1914-1922) had applied his theory of discontinuous wave motion to mechanical and musical properties of the strings of the violin. He noted the remarkable, powerful harmonic series that arose from the nonlinear interaction of the tambürã string and grazing contact with its curved bridge. We analyzed the waveforms of the most common drone tunings. Each of the four strings was played with and without juari ("life-giving" threads). The upward transfer and spread of energy into higher partials imparts richness to tambūrā tones and underlies the use of different drone tunings for different rags. Specific notes of rāg scales are selectively and dynamically enhanced by different drone tunings. Based on coincident features of spectral and musical scale degrees, we computed an index of spectral complexity of the interactions of tambūrā tunings with rãg scales. We speculate that the use of juari contributes to stable pitch centers, implied scale modulation, and an improvisational flexibility.

Association of phenol-containing structures with Apium graveolens resistance to Fusarium oxysporum f.sp. apii race 2

Electron-opaque (EO) structures were studied, using light and electron microscopy, in the xylem parenchyma cells and vessels of both incompatible and compatible Apium graveolens L. var. rapaceum (celeriac) and compatible Apium graveolens L. var. dulce (celery) roots 24 h after inoculation with Fusarium oxysporum f.sp. apii race 2. Few small EO bodies were observed in the noninoculated hosts. Histological, cytochemical, and chemical tests indicated the presence of phenolic substances and polysaccharides in the EO materials. These EO structures increased both in number and size as infection progressed. The incompatible host produced three and five times more of the EO materials than the compatible celeriac and celery, respectively. The amount of the EO materials and host compatibility were related to the absence and presence of fungal hyphae in the vascular system. Hyphae either associated with or enveloped by the EO structures were vacuolated; their cytoplasm was restricted to the cell periphery. Occlusion of the xylem vessel pores of the incompatible host with the EO structures likely prevented upward spread of the pathogen throughout the entire plant.

The effect of varying the amplitude-frequency response on the masked speech-reception threshold of sentences for hearing-impaired listeners.

In an evaluation of frequency-dependent automatic gain-control systems in hearing aids, the effect of varying the amplitude-frequency response on the speech-reception threshold (SRT) for sentences in noise is studied for 20 hearing-impaired listeners. The noise has a spectrum identical to the long-term average spectrum of the sentences. Speech and noise are shaped by the same amplitude-frequency response; their spectra are varied relative to the bisector of the individual's dynamic range. In four experimental conditions, the effect of a steady-state amplitude-frequency response is studied. Steepening the negative spectral slope of speech and noise appears to cause an increase of masked SRT, possibly due to increased effect of upward spread of masking. The effect of a single transition of the amplitude-frequency response between 10 and -10 dB/oct halfway through the sentence seems to be related to the effect for the fixed -10-dB/oct condition. Two transition times are tested. For a transition time of 0.25 s, the SRT is only a little higher than for 1 s. The results suggest that the amplitude-frequency response may be varied in time without having a detrimental effect on the masked SRT of sentences for hearing-impaired listeners as long as strongly negatively sloping spectra are avoided.

Physiological mechanisms of masking and intensity discrimination

Recent electrophysiological studies in which stimulus paradigms were designed to mimic those of psychophysics suggest that a broad range of psychophysical data on masking and intensity discrimination can be simply explained by assuming that signal detection is primarily based on average discharge rate informal ion in auditory‐nerve fibers, provided that information from high‐threshold fibers is taken into account. These studies further suggest that tone‐on‐tone masking is due both to spread of the excitation produced by the masker to the signal place along the cochlea, and to suppression of the signal by the masker, with the relative importance of the two mechanisms depending on masker level and frequency separation between signal and masket. In particular, two‐tone rate suppression is largely responsible for the upward spread of masking at high masker levels and for differences between simultaneous and nonsimultaneous masking techniques. New results will also be presented on unmasking due to suppression of the masker by the signal, improvements in signal detectability by off‐frequency listening, and the role of olivocochlear efferents in signal detection. [Work supported by NIH Grant NS13126.]

Use of the Articulation Index to assess “noise reduction” hearing aids

The Articulation Index (AI) was used to evaluate a commercially available “noise reduction” hearing aid. First, a transfer function relating calculated AI to rated speech intelligibility was derived empirically for a group of normal‐hearing subjects. This function was used to predict speech recognition by 12 hearing‐impaired subjects wearing either the noise reduction hearing aid or conventional amplification. Subsequently, subjects rated the intelligibility of connected discourse presented under both aided conditions at five signal‐to‐noise (S/N) ratios in speech‐weighted noise. The AI transfer function predicted speech intelligibility accurately for half the subjects. For the remaining subjects, predicted scores were typically higher than observed scores. If the effects of upward spread of masking were included in the AI calculations, these differences were minimized. For all subjects, speech intelligibility increased monotonically with AI. AI scores and speech intelligibility ratings were similar between the two hearing‐aid conditions, suggesting that S/N ratio was not increased by the noise reduction hearing aid relative to conventional amplification. [Work supported by NINCDS NS 12125.]

The vertical thermohaline structure in the Argentine basin

The vertical thermohaline structure in the central Argentine basin is investigated on the basis of high‐resolution hydrographic data. Emphasis is placed on fronts, their horizontal gradients, vertical stability and associated fine structure. Horizontal thermohaline gradients vary strongly with depth, regions of strong gradients alternating with those of weak gradients. The strongest gradients occur often at depths below the upper mixed layer. The salinity gradient maximum occurs above the temperature gradient maximum. Enhanced gradients are found where warm, salty water moves over cooler, fresher water such as between the subtropical water (STW) and antarctic intermediate water (AAIW) and between the North Atlantic deep water (NADW) and the antarctic bottom water (AABW). Temperature, salinity, and density fronts do not always coexist. Density‐compensating temperature and salinity fronts occur in the surface layer of the subantarctic and at abyssal depth below 3500 m. Vertical profiles of the Väisälä frequency indicate much reduced hydrostatic stabilities in the Brazil current and subantarctic frontal zones. Potential vorticity minima indicate the formation of subantarctic mode water just north of the subantarctic front and its subsequent northward and upward spread across isopycnals. The thermohaline fine structure is vertically intermittent. The amplitude variances between the enhanced and quiet regions vary by almost 2 orders of magnitude. Enhanced fine structure amplitudes are found near the STW‐AAIW and NADW‐AABW interfaces, where large horizontal thermohaline gradients occur and the hydrostatic stability is low. The temperature and salinity fine structures are largely density compensating. The coherence between the temperature and salinity fine structure is strongly depth dependent and is highest in regions where warm, salty water moves over cooler, fresher water.

Spitz nevus (large spindle cell and/or epithelioid cell nevus)

The Spitz nevus (large spindle and/or epithelioid cell nevus) is a benign acquired melanocytic tumour found predominantly in children and adolescents. Depending on the architecture (junctional, compound, dermal) and cytology (predominance of spindle or epithelioid cells, or presence of both cell types) several variants have been distinguished. A histological feature occasionally leading to diagnostic difficulties is the involvement of the suprabasal epidermis. The present study details the occurrence of intraepidermal involvement (pagetoid spread, nesting of cells, trans-epidermal elimination) according to the age of the patients. 89 cases of Spitz nevus were reviewed. There were 19 compound Spitz nevi with evidence of epidermal involvement, 56 cases of compound Spitz nevi without evidence of epidermal involvement and 14 cases of dermal Spitz nevi. The epidermal involvement mainly consisted of nesting of nevus cells above the basal cell layer, 9 cases clearly showing evidence of transepidermal elimination of cell nests. Upward spread of single melanocytes (pagetoid spread) was minimal and always associated with nesting or trans-epidermal elimination. The mean age of patients was significantly lower in the group of compound nevi with intraepidermal involvement (7.16 +/- 4.52 years), than in the group of compound nevi without epidermal involvement (13.18 +/- 8.88 years). The age of the latter group was significantly lower than the group of pure intradermal nevi (30.14 +/- 11.25 years). Thus, involvement of the suprabasal epidermis is not a feature of Spitz nevi in adults; in such a case the diagnosis of malignant melanoma should be considered.

Susceptibility of zinc-deficient wheat plants to colonization byFusarium graminearum Schw. Group 1

Wheat plants were grown at three levels of zinc nutrition in potted soil under controlled conditions. The surface soil in half of the pots was inoculated with a thin layer of milled chaff colonized byFusarium graminearum Group 1. Forty days after sowing, the plants were assessed for dry matter production and the extent of colonization by the pathogen. The concentration of zinc in the plant tissues was also determined. The zinc status of the plants ranged from severe deficiency through subclinical deficiency to sufficiency. The extent of colonization above the point of infection was decreased significantly by increasing the level of zinc supply. However, colonization of the seminal or secondary roots was not affected by zinc supply, nor was the incidence of infected plants. The unidirectional effect on resistance suggests that zinc has modified the contribution of the xylem flux to the upward spread of the pathogen.

Excess masking among listeners with a sensorineural hearing loss.

Three experiments were conducted to determine whether listeners with a sensorineural hearing loss exhibited greater than normal amounts of masking at frequencies above the frequency of the masker. Excess masking was defined as the difference (in dB) between the masked thresholds actually obtained from a hearing-impaired listener and the expected thresholds calculated for the same individual. The expected thresholds were the power sum of the listener's thresholds in quiet and the average masked thresholds obtained from a group of normal-hearing subjects at the test frequency. Hearing-impaired listeners, with thresholds in quiet ranging from approximately 35-70 dB SPL (at test frequencies between 500-3000 Hz), displayed approximately 12-15 dB of maximum excess masking. The maximum amount of excess masking occurred in the region where the threshold in quiet of the hearing-impaired listener and the average normal masked threshold were equal. These findings indicate that listeners with a sensorineural hearing loss display one form of reduced frequency selectivity (i.e., abnormal upward spread of masking) even when their thresholds in quiet are taken into account.

The role of tambura spectra in drone tunings of North Indian ragas

As part of a program on the role of drone interactions with North Indian ragas played on the sitar, the waveforms of the tambura for the most common drone tuning of the four strings [pa, sa1, sa2, sa′ (low sa)] were analyzed. Each of the strings was played with and without juari threads that have the effect of separating the string slightly from the bridge. The resulting sound is referred to by Indian musicians as a buzz. Without juari the pitch heard is very close to the string fundamental and the partials fall linearly in decibels. With juari the pitch is heard at one or even two octaves above the base pitch and the partials have great power as far as the 20th partial. With juari the 4th, 7th, 11th, or 12th, and the 17th partials have more amplitude than the fundamental. Total harmonic distortion is on the order of 1 to 19 dB without juari but ranges from 12 to 44 dB with juari. The upward spread of energy into higher partials imparts richness to tambura tones, and underlies the use of different drone tunings for different ragas. The pitch and timbre changes with tambura are discussed in terms of the psychoacoustics of complex tones.

Frequency resolution at equivalent sound‐pressure levels in normal‐hearing and hearing‐impaired listeners

Forward‐masked psychophysical tuning curves (PTCs) were obtained for multiple‐level 1000‐Hz probe tones from 15 normal‐hearing and 23 hearing‐impaired ears with cochlear hearing loss. Comparisons between normal‐hearing and hearing‐impaired PTC characteristics were made at equivalent masker levels near the tips of PTCs. The low‐frequency slopes of PTCs from hearing‐impaired listeners were not different from those of normal‐hearing listeners, i.e., hearing‐impaired listeners did not demonstrate abnormal upward spread of masking when equivalent masker levels were compared. Only 8 of the 23 hearing‐impaired listeners demonstrated abnormally broad PTCs, due exclusively to abnormally gradual high‐frequency slopes to their PTCs. This demonstration of abnormal downward spread of masking was only observed in listeners with hearing losses greater than 40 dB HL. From these results, it would appear that some, but not all, cochlear hearing losses greater than 40 dB HL influence the sharp tuning capabilities usually associated with outer hair‐cell function. The restriction of abnormal findings in this study to the high‐frequency sides of PTCs alone is likely due to the use of equivalent masker‐level comparisons, and also to the use of flat‐envelope nonsimultaneous maskers rather than fluctuating‐envelope simultaneous masker. [Work supported by NINCDS.]

Spectral shaping and the intelligibility of speech in noise

Various studies have shown that attenuation of the first formant results in enhanced speech intelligibility in noise. One explanation (Nye et al., 1974) suggests that it is caused by upward spread of masking in normal speech perception. The other explanation proposed is that attenuating F1 increases the amount of intelligibility information relative to the total speech energy in the signal. The stimulus materials were phonetically balanced (PB) words produced by one male speaker. Stimuli were digitally filtered with a high-pass filter that had a passband from 1100–5000 Hz and a stopband from 0–850 Hz (the attenuation levels of the stopband were 10, 20, 40, and 80 dB relative to the unfiltered signal. Items were equated for rms energy after filtering. Processed stimuli were presented to subjects in a perceptual identification task at 0 dB S/N. Articulation index values were then computed for the test items. Fitting transfer functions to the data showed that the increased intelligibility obtained by high-pass filtering was not well predicted by the articulation index values. This supports the hypothesis that attenuating the F1 results in an increase in intelligibility due to a release from masking effect.

Frequency masking patterns and “excess masking” in normal‐hearing and hearing‐impaired listeners

The presence of “excessive upward spread of masking” in high‐frequency sensorineural hearing‐loss (HFSNHL) subjects has been previously demonstrated by other investigators. This excess masking, defined by predictions from a “noise” model of hearing loss, occurs in the transition region between normal and impaired hearing. To examine this phenomenon further, frequency masking patterns (FMPs) were obtained from two normal‐hearing subjects and one HFSNHL subject. Using a 200‐Hz narrow‐band noise (NBN) masker (90 dB SPL) with an upper edge at 520 Hz, FMPs from the impaired ear demonstrated excess masking, which it was hypothesized might be explained by an inability to “listen in the valleys” of the masker envelope because of poor temporal resolution. To test this notion, the experiment was repeated using a 40‐Hz NBN masker (90 dB SPL), which has less rapid envelope fluctuations. No differences in the upward spread of masking were seen between the 200‐ and 40‐Hz bandwidth‐equal SPL maskers. When the experiment was repeated with equal spectrum level maskers, the 40‐Hz NBN masker produced less upward spread of masking in both normal‐hearing and hearing‐impaired ears. These data suggest that, for the HFSNHL subject, excessive upward spread of masking cannot be completely explained by an inability to “listen in the valleys.” [Work supported by NINCDS.]