numerical calculation of equivalent grid block permeability tensors for heterogeneous porous media a numerical procedure for the determination of equivalent grid block permeability tensors for heterogeneous porous media is presented the method entails solution of the fine scale pressure equation subject to periodic boundary conditions to yield upon appropriate averaging of the fine scale velocity field the coarse scale or equivalent grid block permeability when the region over which this coarse scale permeability is computed constitutes a representative elementary volume rev the resulting equivalent permeability may be interpreted as the effective permeability of the region solution of the pressure equation on the fine scale is accomplished through the application of an accurate triangle based finite element numerical procedure which allows for the modeling of geometrically complex features the specification of periodic boundary conditions is shown to yield symmetric positive definite equivalent permeability tensors in all cases the method is verified through application to a periodic model problem and is then applied to the scale up of areal and cross sections with fractally generated permeability fields the applicability and limitations of the method for these more general heterogeneity fields are discussed

a numerical upscaling method for an elliptic equation with heterogeneous tensorial coefficients the aim of this paper is to develop a new numerical method to determine the effective permeability on a coarse scale level of problems with strongly heterogeneous tensorial coefficients defined on a fine scale this method stems from a primal dual mixed formulation and the upscaled permeability is obtained by imposing the continuity of the numerical flux across the lines of discontinuities moreover a finite volume scheme is built to numerically solve elliptic equations with this kind of coefficients finally the method is illustrated by several numerical experiments copyright 2002 john wiley sons ltd

linear free resolutions and minimal multiplicity let s k x x be a polynomial ring over a field and let a4 a m be a finitely generated graded module in the most interesting case a4 is an ideal of s for a given natural number p there is a great interest in the question can m be generated by homogeneous elements of degree p no simple answer say in terms of the local cohomology of m is known but somewhat surprisingly the stronger question can the jth syzygy of m be generated by elements of degree qp j for all j 0 l n does admit a simple response the following is neither new nor difficult to prove though it seems not well known

temporal integration and multiple looks revisited weights as a function of time this study tests the hypothesis that temporal integration for detection of tone bursts with various durations can be explained by optimally combining multiple looks of brief signal segments whose contribution to detection increases over time detectability was measured for signals consisting of six consecutive 25 ms 1 khz tone pulses presented in a 50 hz wide masker or in maskers consisting of seven 50 hz wide noises one critical band apart with either coherent or incoherent envelopes the level of each signal pulse varied randomly around masked threshold according to a gaussian distribution the slopes of conditional psychometric functions plotted in terms of d 2 as a function of the squared signal pulse intensity for pulses in a particular temporal position yielded estimates of the contribution to detection provided by each pulse results for three normal listeners showed a small but significant effect of the temporal location of the pulse multiple looks predictions of temporal integration functio

effect of component relative entropy on the discrimination of simultaneous tone complexes results are reported from a number of experiments investigating the effects of stimulus uncertainty on the discrimination of simultaneous multitone complexes with few exceptions the data were well described by a model in which average threshold for the detection of a change in one or more components varies with the components relative entropy core in the complex r a lutfi j acoust soc am 94 748 758 1993 in different experiments thresholds for the detection of a change in target level were found to be linearly related to core for manipulations in the number of targets the number of context tones and the relative degree of level perturbation on tones from trial to trial the slopes of the functions did not change with measures taken at different points on the psychometric function and in most cases were close to the theoretical value of b 1 0 as predicted by strict application of the model also as predicted but for the exception of one listener increasing the level of the target beyond that of the context had little or no effect on threshold a correlational analysis of the trial by trial data revealed a tendency of listeners to give negative weight to frequencies immediately above the target and to adjust weights in response to changes in the relative degree of level perturbation though inconsistent with the basic premise of the model the variation in weights was not so great as to materially affect the predictions for mean thresholds

multiple bursts multiple looks and stream coherence in the release from informational masking in the simultaneous multitone masking paradigm introduced by neff and green percept psychophys 41 409 415 1987 the masker typically is a small number of tones having frequencies and levels that are randomly drawn on every presentation large amounts of masking for a pure tone signal often occur that are thought to reflect central rather than peripheral limitations on processing previous work from this laboratory has indicated that playing a rapid succession of randomly drawn multitone maskers in each observation interval dramatically reduces the amount of masking that is observed relative to a single burst sb in this multiple bursts different mbd procedure the signal tone is the only constant frequency component during the sequence of bursts and tends to perceptually segregate from the masker in this study the number of masker bursts and the interburst interval ibi were varied the goals were to determine how the release from masking relative to the sb condition depends on the number of bursts and to examine whether increasing the ibi would cause each burst to be processed independently if the latter were true it might disrupt the perception of signal stream coherence thereby diminishing the mbd advantage however multiple independent looks could also lead to an improvement in performance for those subjects showing large amounts of informational masking in the sb condition substantial reduction in masked thresholds occurred as the number of masker bursts increased while masking increased as ibi lengthened the results were not consistent with a simple version of a multiple look model in which the information from each burst was combined optimally but instead appear to be attributable to mechanisms involved in the perceptual organization of sounds

the effect of spatial separation on informational and energetic masking of speech the effect of spatial separation of sources on the masking of a speech signal was investigated for three types of maskers ranging from energetic to informational normal hearing listeners performed a closed set speech identification task in the presence of a masker at various signal to noise ratios stimuli were presented in a quiet sound field the signal was played from 0 azimuth and a masker was played either from the same location or from 90 to the right signals and maskers were derived from sentences that were preprocessed by a modified cochlear implant simulation program that filtered each sentence into 15 frequency bands extracted the envelopes from each band and used these envelopes to modulate pure tones at the center frequencies of the bands in each trial the signal was generated by summing together eight randomly selected frequency bands from the preprocessed signal sentence three maskers were derived from the preprocessed masker sentences 1 different band sentence which was generated by summing together six randomly selected frequency bands out of the seven bands not present in the signal resulting in primarily informational masking 2 different band noise which was generated by convolving the different band sentence with gaussian noise and 3 same band noise which was generated by summing the same eight bands from the preprocessed masker sentence that were used in the signal sentence and convolving the result with gaussian noise resulting in primarily energetic masking results revealed that in the different band sentence masker the effect of spatial separation averaged 18 db at 51 correct while in the different band and same band noise maskers the effect was less than 10 db these results suggest that in these conditions the advantage due to spatial separation of sources is greater for informational masking than for energetic masking

estimates of effective frequency selectivity based on the detection of a tone added to complex maskers in experiment 1 the validity of parameters associated with the roex p r auditory filter shape was examined for three different types of maskers a a noise masker b a random 12 tone masker whose frequencies varied on a burst by burst basis multiple burst different mbd and c a random 12 tone masker whose frequencies were the same across bursts multiple burst same mbs first the power spectrum model of masking was used to estimate auditory filter shapes for four observers second the resulting auditory filter shapes were used in a computer simulation that provided an estimate of internal noise for each observer third relative weights across frequency were estimated for each observer and each masker type for the noise masker these analyses provided predictions and relative weights that were consistent across the three analyses for the mbd and mbs maskers there was little consistency neither the estimated internal noise nor the estimated relative weights reliably supported a single f

effective properties of composite materials with periodic microstructure a computational approach abstract this study reviews several problems which are specific of composites with periodic microstructure composed of linear or nonlinear constituents the theoretical background of the method is recalled first two different families of numerical methods are considered to solve the problem the first is based on the finite element method the concept of macroscopic degrees of freedom is presented the implementation of periodicity conditions is discussed a general framework permitting either a strain or stress control is proposed the second numerical method is based on fast fourier transforms it considers first the problem of a homogeneous linear reference material undergoing a nonhomogeneous periodic eigenstrain the solution of this problem is based on the explicit form of the periodic green s function of the reference medium the relative merits of the two methods are compared and several examples are discussed both methods give very comparable results on test examples and their domains of applications appear to be complementary

resolutions of determinantal ideals the submaximal minors for many years there has been considerable interest in finding a resolution of the ideal generated by the minors of order p of a generic m x n matrix to put the problem more precisely suppose r is a commutative ring and x are variables with 1 i m and 1 j q n if we let r r x be the polynomial ring over r then we have the generic matrix x and we may form the ideal zp in r generated by the p x p minors of this matrix the problem then is to find an explicit free resolution of the ideal zp over the ring r it was proved by eagon and hochster lo that r i has a resolution of length m p l n p l but their proof consisted in showing that the ideal zp is perfect it did not provide a construction of the resolution in fact it is not known whether the betti numbers of the ideal zp depend on the characteristic of the ground ring r in 121 lascoux succeeded in giving an explicit resolution provided that the ground ring r contained the field q of rational numbers his construction rests heavily on the theory of schur functors and the fact that in characteristic zero the schur functors are the irreducible representations of the general linear group over the integers however the construction breaks down despite the fact that one can define the schur functors over an arbitrary commutative ring see 1 2 14 151 for various constructions of schur functors in analyzing the work of lascoux and its subsequent reworking by nielsen 131 some basic facts seemed to clamor for attention one was that within a resolution of r z there appeared to be two types of boundary maps one of degree 1 and one of degree p the maps of degree 1 were maps between sums of schur functors of fixed durfee square k see section 2 for definitions while the maps of degree p were from sums of schur functors of

discriminating coherence in spectro temporal patterns this study examined the ability of trained listeners to discriminate coherent components in randomly varying spectral patterns in each observation interval the listener was presented with a sequence of bursts of multitone complexes having a fixed number of tones m in each burst in the standard interval the frequency of each tone in every burst was chosen randomly between 200 and 5000 hz in the signal interval the frequencies of n tones were repeated throughout the burst sequence while the remaining m n tones were chosen at random the n tones were coherent in the sense that they were perceived as sticking together to form a pattern the listener s task was to discriminate which burst sequence contained the n components the results indicated that discrimination improved with increasing n m with increasing number of bursts per interval and declined as the coherent components were increasingly perturbed in frequency further for a fixed value of the ratio n m discriminability was relatively independent of m a model incorporating multichannel filtering and an optimum decision rule was reasonably successful in accounting for the experimental results

examination of a linear model in an informational masking study when multitone maskers are used in a two interval forced choice experiment the amount of masking is larger when the masker is randomly chosen on each presentation interval compared to on each trial the same masker in the two listening intervals these conditions are referred to as having within versus between trial randomization if it is assumed that an observer s ultimate detection decision depends on a single decision variable dv it is probable that the dv s variance will be substantially larger in the within trial randomization condition compared to the between trial randomization condition the goal of the current experiment is to evaluate the degree to which this stimulus based change in dv variance can account for the difference in thresholds in the within versus between trial randomization conditions thresholds are measured for the detection of a tone added to a six component masker in between and within trial randomization conditions the slopes of the psychometric functions provide an estimate of the variance in the dv for the between and within trial randomization conditions additionally a channel model is fitted to the psychophysical results in the within trial randomization condition the resulting model is then used to predict the value of the dv for each trial and ultimately to estimate the proportion of the total variance in the within trial randomization condition that is attributable to changes in maskers across intervals the variance of the dv in the between trial randomization condition accounted for approximately 65 of the total variance in the dv in the within trial randomization condition stimulus based interval by interval masker randomization accounted for approximately 20 of the total variance of the within trial randomization dv the remaining 15 of the dv variance in the within trial randomization condition remained unaccounted for this result is fairly stable whether the maskers are drawn from a small versus large pool of potential maskers

spectral and temporal integration of brief tones both spectral and temporal integration of tones have been explored in detail but integration of tones varying across both dimensions has received little attention this study explores temporal integration of tone pulses that vary over a range of frequencies baseline thresholds were obtained for both spectral and temporal integration with the same signals and compared with prior research the signals were then varied on both dimensions in several ways with equivalent spectral and temporal step sizes different spectral and temporal step sizes and a random pattern of frequency presentation the data were also analyzed by spectral step size temporal step size frequency range direction and slope of frequency change and predictability the spectral and temporal integration conditions showed that the current procedures and signals yielded the same improvement in detection thresholds as prior studies the spectrotemporal integration conditions showed the improvement for overall detection of the signals to be limited by spectral integration with improvement related primarily to the number of tones regardless of timing and frequency surprisingly trial by trial random presentation of signal frequencies did not negatively influence detection these results support the multiple looks hypothesis viemeister n f and wakefield g h 1991 temporal integration and multiple looks j acoust soc am 90 858 865 as applied to spectrotemporal integration

homogenized behavior of two phase flows in naturally fractured reservoirs with uniform fractures distribution abstract we consider the behavior of two phase flow in a periodically fractured porous medium e denotes the parameter associated to the period size we deal with homogenization methods to find asymptotic flow behavior as e tends to zero the homogenized porosity and permeability depend no longer on heterogeneities this limit gives the behavior of two phase flows in globally equivalent homogeneous media in some special cases we compute the arithmetic and harmonic means which are used classically in simulation codes

dependence of post masking on masker duration and its relation to temporal effects in loudness temporal masking of tones by noise was investigated using a post forward masking paradigm the masker level and duration were varied for every masker level employed the rate of decay of masking was found to depend on the duration of the masker specific loudness values were computed from the forward masking functions and an electronic device which simulates these loudness functions is presented in the simulation a series of integrators or a single integration with one long time constant was utilized the effect of the proposed integrators on loudness meters is discussed

informational masking for simultaneous nonspeech stimuli psychometric functions for fixed and randomly mixed maskers sensitivity d and response bias were measured as a function of target level for the detection of a 1000 hz tone in multitone maskers using a one interval two alternative forced choice 1i 2afc paradigm ten such maskers each with eight randomly selected components in the region 200 5000 hz with 800 1250 hz excluded to form a protected zone were presented under two conditions the fixed condition in which the same eight component masker is used throughout an experimental run and the random condition in which an eight component masker is chosen randomly trial to trial from the given set of ten such maskers differences between the results obtained with these two conditions help characterize the listener s susceptibility to informational masking im the d results show great intersubject variability but can be reasonably well fit by simple energy detector models in which internal noise and filter bandwidth are used as fitting parameters in contrast the results are not well fit by these models in addition to presentation of new data and its relation to energy detector models this paper provides comments on a variety of issues problems and research needs in the im area 2005 acoustical society of america doi 10 1121 1 2032748

observer efficiency and weights in a multiple observation task a sequence of seven tones sampled from one of two distributions differing in mean frequency is presented to observers who try to report which distribution was sampled estimates are obtained of the weight or importance given to each tone as a function of its temporal position in five experiments the reliability of the information is varied by changing the variance of the distributions tones with high reliability are sampled from distributions with relatively small variance whereas tones with low reliability are sampled from distributions with relatively large variance results show that the observations are weighted more efficiently when the tones have equal rather than unequal reliability and when the most reliable tones have the greater intensity additional results show that the most intense tones often receive the greatest weight even when those tones have the least reliability

similarity uncertainty and masking in the identification of nonspeech auditory patterns this study examined whether increasing the similarity between informational maskers and signals would increase the amount of masking obtained in a nonspeech pattern identification task the signals were contiguous sequences of pure tone bursts arranged in six narrow band spectro temporal patterns the informational maskers were sequences of multitone bursts played synchronously with the signal tones the listener s task was to identify the patterns in a 1 interval 6 alternative forced choice procedure three types of multitone maskers were generated according to different randomization rules for the least signal like informational masker the components in each multitone burst were chosen at random within the frequency range of 200 6500 hz excluding a protected region around the signal frequencies for the intermediate masker the frequency components in the first burst were chosen quasirandomly but the components in successive bursts were constrained to fall in narrow frequency bands around the frequencies of the components in the initial burst within the narrow bands the frequencies were randomized this masker was considered to be more similar to the signal patterns because it consisted of a set of narrow band sequences any one of which might be mistaken for a signal pattern the most signal like masker was similar to the intermediate masker in that it consisted of a set of synchronously played narrow band sequences but the variation in frequency within each sequence was sinusoidal completing roughly one period in a sequence this masker consisted of discernible patterns but not patterns that were part of the set of signals in addition masking produced by gaussian noise bursts thought to produce primarily peripherally based energetic masking was measured and compared to the informational masking results for the three informational maskers more masking was produced by the maskers comprised of narrow band sequences than for the masker in which the frequencies were not constrained to narrow bands also the slopes of the performance level functions for the three informational maskers were much shallower than for the gaussian noise masker or for no masker the findings provided qualified support for the hypothesis that increasing the similarity between signals and maskers or parts of the maskers causes greater informational masking however it is also possible that the greater masking was a consequence of increasing the number of perceptual streams that had to be evaluated by the listener

the role of masker fringes for the detection of coherent tone pips three experiments investigated the role of pre post exposure to a masker in a detection task with complex random spectro temporal maskers in the first experiment the masker was either continuously presented or pulsed on and off with the signal for most listeners thresholds were lower when the masker was continuously presented despite the fact that there was more uncertainty about the timing of the signal in the second experiment the signal bearing portion of the masker was preceded and followed by masker fringes of different durations consistent with the findings of experiment 1 for some listeners shorter duration fringes led to higher thresholds than long duration fringes in the third experiment the masker fringe a preceded b followed or c both preceded and followed the signal relative to the middle signal conditions a late signal yielded lower thresholds and the early signal yielded higher thresholds these results indicate that listeners can use features of an ongoing sound to extract an added signal and that listeners differ in the importance of pre exposure for efficient signal extraction however listeners do not appear to perform this comparison retrospectively after the signal potentially indicating a form of backward masking

intensity perception xiii perceptual anchor model of context coding in our preliminary theory of intensity resolution e g see n i durlach and l d braida j acoust soc am 46 372 383 1969 two modes of memory operation are postulated the trace mode and the context coding mode in this paper we present a revised model of the context coding mode which describes explicitly a process by which sensations are coded relative to the context and which predicts a resolution edge effect l d braida and n i durlach j acoust soc am 51 483 502 1972 j e berliner l d braida and n i durlach j acoust soc am 61 1256 1267 1977 the sensation arising from a given stimulus presentation is coded by determining its distance from internal references or perceptual anchors the noise in this process combined with the sensation noise constitutes the limitation on resolution in the model in the revised model the probability density functions of the decision variable are not precisely gaussian and cannot be expressed analytically in closed form this p

informational processing of complex sound ii cross dimensional analysis a series of experiments investigated listeners ability simultaneously to process information across different acoustic dimensions on each trial the listener heard a pair of brief n tone sequences n 1 to 12 the frequency intensity and duration of each tone in the sequence varied randomly from trial to trial on average the values of these three parameters were greater for one sequence the target than the other the nontarget the listener s task was to identify the target on each trial for an ideal observer in this task d performance grows as the square root n obtained d grew at a rate slightly less than the square root of n close to cube root of n growth was observed when the average difference occurred in only one of the three tone parameter values within a block of trials although performance fell short of ideal optimum weights were consistently given to each tone and each parameter the results are consistent with a model in which performance depends predominantly on the information content of the sounds regardless of how the information is packaged in the stimulus transmitted information is estimated to be 0 9 2 0 bits within a single acoustic dimension 2 1 3 0 bits when distributed across dimensions

green lazarsfeld condition for toric edge ideals of bipartite graphs abstract previously ohsugi and hibi gave a combinatorial description of bipartite graphs g whose toric edge ideal i g is generated by quadrics showing that every cycle of g of length at least 6 must have a chord this corresponds to the green lazarsfeld condition n 1 in this paper we investigate the higher syzygies of i g and give combinatorial descriptions of the green lazarsfeld conditions n p of toric edge ideals of bipartite graphs for all p 1 in particular we show that i g is linearly presented i e satisfies condition n 2 if and only if the bipartite complement of g is a tree of diameter at most 3 we also investigate the regularity of linearly presented toric edge ideals and give criteria for polyomino ideals to satisfy the green lazarsfeld conditions

intensity discrimination in the presence of random frequency multicomponent maskers and broadband noise this study examined the effects of multicomponent random frequency maskers and broadband noise maskers on intensity discrimination at 1000 hz maskers and signals were 200 ms presented simultaneously in the first set of conditions thresholds were measured for the detection of a 1000 hz tone in the presence of 40 or 60 db spl random frequency or noise maskers with extensive training of listeners with the random frequency masker to assure stable effects of masker frequency uncertainty the random frequency maskers had two six or ten components chosen at random from a large frequency range 300 3000 hz excluding a 160 hz band around 1000 hz for these maskers performance across the four listeners was very similar showing large effects of masker frequency uncertainty for noise maskers performance matched predictions for energy based masking in the second and third sets of conditions intensity discrimination was measured at 1000 hz for pedestals ranging from 40 to 80 db spl first in isolation and then in the presence of the maskers the pattern of results for intensity discrimination in quiet showed the expected near miss to weber s law but poorer performance than typically observed the addition of broadband noise maskers had little effect on performance however random frequency maskers degraded performance in nearly all conditions with the size of the effect dependent on the level of the pedestal relative to the masker considering the pedestal as a tonal masker the data were fitted with various models of combined masking a simple power law model provided excellent fits with exponents ranging from 0 24 to 0 35 for the multicomponent maskers but 1 0 linear for the noise the results support models positing that the effects of individual maskers undergo nonlinear transformation before they are added independent of the mechanisms which produce these effects because random frequency maskers presumably produce informational uncertainty based masking the nonlinearity in this case appears central rather than peripheral

nonmonotonicity of informational masking neff and green percept psychophys 41 409 415 1987 report that the masking of single tones by random frequency multitone maskers varies nonmonotonically with number of masker components peaking at 10 50 components in this paper it is shown that such results are well predicted by a model the component relative entropy model core wherein thresholds increase linearly with the ensemble variance of masker spectra smoothed by peripheral auditory filters r a lutfi j acoust soc am 94 748 758 1993 three experiments were conducted in the first the nonmonotonic relation was replicated for 9 of 11 listeners in conditions similar to those of neff and green in the second the frequencies of masker components were fixed and the levels of components were varied randomly across presentations to simulate gaussian noise in this case the nonmonotonicity and the total amount of masking for these listeners were shown to be significantly reduced in the third experiment masked thresholds for the signal were found to vary monotonically with the frequency spacing of masker components for a fixed number of masker components large individual differences among listeners were obtained in some experimental conditions individual as well as mean thresholds were well predicted by the core model with an appropriate selection of the values of the two free parameters of the model for each listener

role of attention in overshoot frequency certainty versus uncertainty overshoot the elevation in the threshold for a brief signal that comes on close to masker onset was measured with signal frequency certain same frequency on every trial or uncertain randomized over trials in broadband noise thresholds were higher 2ms after masker onset than 200ms later by 9db with frequency certainty by 6 7db with uncertainty in narrowband noise centered on the signal frequency thresholds at 2ms were not elevated with certainty but were elevated 4 5db with uncertainty thus frequency uncertainty leads to less overshoot in broadband noise to more overshoot in narrowband noise reduced overshoot in broadband noise may come about because the masker given its many frequencies disrupts focusing at onset as much under certainty as uncertainty once the initial disruption dissipates threshold is lower with certainty so overshoot is greater in contrast a narrowband noise with frequencies only near the signal does not disrupt focusing when the signal frequency is known beforeha

excitation based and informational masking of a tonal signal in a four tone masker this study examined contributions of peripheral excitation and informational masking to the variability in masking effectiveness observed across samples of multi tonal maskers detection thresholds were measured for a 1000 hz signal presented simultaneously with each of 25 four tone masker samples using a two interval forced choice adaptive task thresholds were measured with each sample fixed throughout trial blocks for ten listeners average thresholds differed by as much as 26 db across samples an excitation based model of partial loudness moore b c j et al 1997 j audio eng soc 45 224 237 was used to predict thresholds these predictions accounted for a significant portion of variance in the data of several listeners but no relation between the model and data was observed for many listeners moreover substantial individual differences on the order of 41 db were observed for some maskers the largest individual differences were found for maskers predicted to produce minimal excitat

binaural advantage for sound pattern identification listeners learned to identify six tone patterns in continuous broadband noise the patterns consisted of eight sequential 48 ms tones having frequencies that were 1 constant 2 rising 3 falling 4 alternating 5 one step up or 6 one step down the frequency extent was 14 of the nominal center frequency masking level differences mlds were measured in a 2i2afc adaptive detection task by comparing thresholds for noso and nos conditions identification level differences ilds were measured in a 1i6afc fixed level identification task by comparing the psychometric functions for the two interaural conditions two center frequencies 500 and 3000 hz were used in addition for ilds the center frequency was randomly roved over the 2500 hz range average mlds and ilds were 12 db at 500 hz and 3 db at 3000 hz however in the roved condition the psychometric function for the nos condition was much shallower than for the noso condition so ilds decreased with increasing s n level this result is in good agreement with similar findings for speech h levitt and l r rabiner j acoust soc am 42 601 608 1967 the orderly relationship between detection and identification breaks down in certain conditions when an informational masker is used work supported by nih nindcd

individual differences in simultaneous masking with random frequency multicomponent maskers individual differences were examined for 49 listeners in a simultaneous masking task with random frequency multicomponent maskers and a 1000 hz signal across conditions the maskers were broadband noise or complexes of 2 100 sinusoids whose frequencies were randomly chosen with each presentation maskers were equal rms waveforms presented at 60 db spl thresholds for the multicomponent maskers spanned a range of up to 59 db across listeners within conditions without distinct groupings when divided into quartiles mean thresholds for listeners in the lowest quartile increased monotonically with the number of masker components and peaked below values produced by broadband noise listeners in the upper quartile had nonmonotonic functions with a broad peak around 10 20 components with values above those produced by broadband noise quiet thresholds and masked thresholds for the broadband noise masker did not distinguish high from low threshold groups lowering masker uncertainty frequencies randomized between but not within trials or introducing temporal differences by shortening the signal both improved performance by as much as 40 db dependent on the masking produced with maximum uncertainty training effects within experiment excluding an initial training period were examined for all listeners and for five listeners across two consecutive experiments eleven of forty nine listeners 22 showed systematic improvement averaging 12 db within experiment independent of high or low original thresholds for the five tested longer four improved by 5 db or more in at least one condition but the change in performance occurred primarily during initial training for the second experiment the large individual differences documented present a challenge to the development of models for masking produced by masker frequency uncertainty

complexes associated with trace and evaluation another approach to lascoux s resolution i l th syzygy hence the length of a minimal free resolution of d is m p 1 n 1 although lascoux described explicitly maps between the consecutive syzygies he was unable to prove that this leads to a complex proofs of his lemmas 3 7 1 and 3 7 2 in s are incomplete we illustrate essential dif ficulties on the example of 1 x 1 minors in this case the lascoux s con struction gives the rth syzygy as c r lif lxg lascoux describes the differential as being composed from the maps la f lxg l fq l g for p c 1 j u i1 1 each of those maps is specified up to scalar and he does not say how to adjust them in order to get a complex even in the case p 1 when the rth syzygy equals a f g isomorphism a f g cll i l f lxg is quite complicated and it is difficult to compute these scalars roberts in his preprint 123 gave more down to earth construction of a complex but he was unable to prove that it is a resolution of d except in some special cases the purpose of this paper is to overcome these difficulties by presenting still another approach that allows us to get a complex and to prove easily that it is a minimal free resolution of d here are some essential features of our method the basic idea can be explained in case

spectral processing of two concurrent harmonic complexes in a concurrent profile analysis task each of the two observation intervals was the sum of two harmonic complexes in the first interval one of the harmonic complexes had a flat spectrum and the other had a broad spectral peak at 1 khz in the second interval the association between the spectral profiles and the complexes was either consistent with the first interval or inconsistent so that profile changes flat versus peaked could be created in both of the complexes in two experiments thresholds and psychometric functions for detecting the profile change were measured in terms of the spectral peak s magnitude as functions of three types of segregation cues difference in fundamental frequency onset asynchrony and difference in interaural time difference between the two complexes decreasing the magnitude of each cue led to higher thresholds and shallower psychometric functions whose upper asymptotes often failed to reach 100 correct the patterns of the threshold and psychometric functions varied across cue types and across individual listeners the results suggest that informational masking is present in the concurrent profile analysis task segregation cues appear to contribute to the release from informational masking but the process depends on listening strategies adopted by individual listeners

signal uncertainty and psychometric functions in profile analysis experiment 1 was conducted to compare the effects of signal frequency uncertainty on the detection of a change in spectral shape and on the detection of a tone in wideband noise results indicate that for both tasks the uncertainty effect was small being on average about 3 db in a second experiment psychometric functions were measured for the detection of changes in the spectral shape of multicomponent complexes psychometric functions for profile tasks have a 25 db range and are similar to those measured for the detection of an increment in the level of a single sinusoid these psychometric functions are different from those found when detecting a signal in noise which typically have a 10 db range three equations for the shape of the psychometric functions were compared the difference in the resulting fits was small thus preventing an unambiguous choice of functional form

informational masking with small set sizes informational masking refers to interference in the detectability of a sound or discrimination of some property of a sound beyond that which can be attributed to interactions at the auditory periphery in the current experiments the signal to be detected was a tone added to a 6 tone masker and informational masking was introduced by randomly choosing the frequencies of the tones that comprise the masker the primary question was whether small numbers of maskers could replace randomly drawn maskers without sacrificing the underlying detection schemes adopted by observers similar to the method used by wright and saberi j acoust soc am 105 1765 1775 1999 detection thresholds were measured for different masker set sizes where set size refers to the number of 6 tone maskers from which any one masker was drawn set sizes of 3 6 12 and 24 were tested as well as conditions in which the maskers were chosen at random in addition observers memory for maskers was coarsely evaluated large differences in thresholds were found across observers and across different masker sets even for set sizes of 24 the memory test suggests some recognition of maskers for some observers post hoc analysis of the data included an evaluation of the relative contribution of different frequencies using a single linear model as a base for comparison a linear model fitted to each condition was also evaluated although the data were fitted better using many rather than one linear model the reduction in quality of fit was modest this result suggests substantial consistency in decision strategies regardless of masker set size

the extent to which a position based explanation accounts for binaural release from informational masking detection was measured for a 500hz tone masked by noise an energetic masker or sets of ten randomly drawn tones an informational masker presenting the maskers diotically and the target tone with a variety of interaural differences interaural amplitude ratios and or interaural time delays resulted in reduced detection thresholds relative to when the target was presented diotically binaural release from masking thresholds observed when time and amplitude differences applied to the target were reinforcing favored the same ear resulting in a lateralized position for the target were not significantly different from thresholds obtained when differences were opposing favored opposite ears resulting in a centered position for the target this irrelevance of differences in the perceived location of the target is a classic result for energetic maskers but had not previously been shown for informational maskers however this parallellism between the patterns of binaural release for energet

strategies used to detect auditory signals in small sets of random maskers detection performance for a masked auditory signal of fixed frequency can be substantially degraded if there is uncertainty about the frequency content of the masker a quasimolecular psychophysical approach was used to examine response strategies in masker uncertainty conditions and to investigate the influence of uncertainty when the number of different masker samples was limited to ten or fewer the task of the four listeners was to detect a 1000 hz signal that was presented simultaneously with one of ten ten tone masker samples the masker sample was either fixed throughout a block of two interval forced choice trials or was randomized across or within trials the primary results showed that 1 when the signal level was low and the masker sample differed between the two intervals of a trial most listeners based their responses more on the presence of specific masker samples than on the signal 2 the detrimental effect of masker uncertainty was clearly evident when only four maskers were randomly presented and grew as the size of the masker set was increased from two to ten 3 the slopes of psychometric functions measured with the same masker samples differed among the fixed and two random masker conditions 4 there were large differences in the influence of masker uncertainty across masker samples and listeners these data demonstrate the great susceptibility of human listeners to the influence of masker uncertainty and the ability of quasimolecular investigations to reveal important aspects of behavior in uncertainty condition

existence uniqueness and approximation for generalized saddle point problems extensions of the well known results of brezzi on saddle point problems are presented the class of problems is generalized to include the unsymmetric case and the known stability and approximation results are strengthened and applied to the generalized problem an application to the solution of certain exterior interface problems is indicated

a molecular description of profile analysis decision weights and internal noise systematic inefficiencies and internal noise in a spectral profile discrimination task were investigated listeners detected a 1000 hz sinusoid added in phase to the central component of a complex consisting of 11 equal intensity sinusoids parameters for a channel model that employs decision weights and internal noise were estimated with molecular psychophysical techniques maximum likelihood predictions of the model were generally within a few decibels of observed thresholds the degree to which an assumption of ideal weights leads to overestimation of internal noise was also assessed

psychometric functions and temporal integration in electric hearing temporal integration functions and psychometric functions for detection were obtained in eight users of the nucleus 22 electrode cochlear implant stimuli were 100 hz 200 microseconds phase trains of biphasic pulses with durations ranging from 0 44 to 630 4 ms 1 to 64 pulses temporal integration functions were measured for 21 electrodes slopes of these functions were considerably shallower than the 2 5 db doubling slopes typically observed in acoustic hearing they varied widely across subjects and for different electrodes in a given subject ranging from 0 06 to 1 94 db doubling of stimulus pulses with a mean standard deviation s d value of 0 42 0 38 psychometric functions were measured for 11 of the same 21 electrodes slopes of psychometric functions also varied across subjects and electrodes and were 2 20 times steeper than those reported by other investigators for normal hearing and cochlear impaired acoustic listeners slopes of individual psychometric functions for 1 2 4 and 8 pulse stimuli ranged from 0 20 to 1 84 log d db with a mean s d value of 0 77 0 45 psychometric function slopes did not vary systematically with stimulus duration in most cases a clear inverse relation between slopes of psychometric functions and slopes of temporal integration functions was observed this relation was reasonably well described by a hyperbolic function predicted by the multiple looks model of temporal integration viemeister and wakefield j acoust soc am 90 858 865 1991 psychometric function slopes tended to increase with absolute threshold and were inversely correlated with dynamic range suggesting that observed differences in psychometric function slopes across subjects and electrodes may reflect underlying differences in neural survival

a model of auditory pattern analysis based on component relative entropy recently results from detection and information theory have been used to predict performance of human observers in experiments involving the discriminability of changes in individual components of unfamiliar or uncertain tone patterns r a lutfi j acoust soc am 91 3391 3401 1992 in this paper the theoretical analysis is expanded to yield a general rule of pattern analysis that accounts for nearly all of the major results of such experiments conducted over the last 18 years the rule can be stated as follows component discriminability in an unfamiliar tone pattern profile or sequence is a linearly increasing function of the component s relative entropy core in the pattern ancillary the threshold for detection of a change decreases by one order of magnitude factor of 10 for each one bit increase in core this precise relation of threshold to core is demonstrated repeatedly in a review of past studies and is shown to account for the relative effects of a variety of important variables and their interactions such variables include the total duration of the pattern the number of tones in the pattern the number of tones subject to change the relative level and duration of individual tones in the pattern the relative variability and the physical dimension of the tones parameters that are subject to change the number and position of targets in the pattern the psychophysical procedure used method of adjustment versus same different the type of discrimination task frequency versus intensity discrimination and the manner of presentation of the tones simultaneous or sequential the core rule seems to reflect a general property of auditory analysis wherein the perception of patterns in an ensemble is dominated by those features that dominate the variance of the ensemble

binaural processing of noisy stimuli internal external noise ratios for diotic and dichotic stimuli a set of ten digitized statistically similar gaussian maskers was used in one internal tone in noise detection experiments under diotic noso and dichotic nos interaural conditions stimulus response matrices were generated for each masker in the presence or absence of a target 500 hz tone for both noso and nos nonparametric analyses show that response probabilities and sensitivities vary significantly across noise waveforms indicating a considerable external noise component in subject response variability a parametric model is developed that maps individual stimulus waveforms onto a decision axis facilitating evaluation of internal external noise variance ratios for both noso and nos internal and external noise variance are of similar magnitude

temporal limits of level dominance in a sample discrimination task level dominance refers to the effect where attention is automatically directed to the loudest part of an auditory display in a sample discrimination task the frequencies of five 50ms tones were sampled from normal distributions with means of 1000 and 1100hz and presented sequentially with the tones alternating in intensity observers decide from which distribution the sample was drawn the informativeness of the even numbered tones d 2 was greater than the informativeness of the odd numbered tones d 1 estimates of decision weights and performance levels d show that when the more informative tones were less intense observers attended to the louder tones rather than the more informative tones this effect extends well beyond the temporal limits expected from forward masking studies

perceiving sequential dependencies in auditory streams this study examined the ability of human listeners to detect the presence and judge the strength of a statistical dependency among the elements comprising sequences of sounds the statistical dependency was imposed by specifying transition matrices that determined the likelihood of occurrence of the sound elements markov chains were constructed from these transition matrices having states that were pure tones noise bursts that varied along the stimulus dimensions of frequency and or interaural time difference listeners reliably detected the presence of a statistical dependency in sequences of sounds varying along these stimulus dimensions furthermore listeners were able to discriminate the relative strength of the dependency in pairs of successive sound sequences random variation along an irrelevant stimulus dimension had small but significant adverse effects on performance a much greater decrement in performance was found when the sound sequences were concurrent likelihood ratios were computed based on the transition matrices to specify ideal observer performance for the experimental conditions preliminary modeling efforts were made based on degradations of ideal observer performance intended to represent human observer limitations this experimental approach appears to be useful for examining auditory stream formation and maintenance over time based on the predictability of the constituent sound elements

level dominance in sound source identification impact sounds were synthesized according to standard textbook equations given for the motion of simply supported metal plates in a two interval forced choice procedure highly practiced listeners identified from these sounds a predefined class of target plates based on their particular material and geometric properties the effects of two factors on identification were examined the relative level of partials comprising the sounds and the relative amount of information given as the difference in d each partial provided for identification in different conditions one factor was fixed while the other either increased or decreased with frequency the effect on listener identification in each case was determined from a logistic discriminant analysis of trial by trial responses yielding a vector of listener decision weights on the frequency and decay of individual partials the weights increased proportionally with relative level but were largely uninfluenced by relative information content a result exactly opposite to that expected from a maximum likelihood observer the dominant effect of relative level was replicated for other sound sources clamped bars and stretched membranes and was not diminished by randomizing the relative level of partials across trials the results are taken to underscore the importance of relative level in the identification of rudimentary sound sources

sample discrimination of frequency by hearing impaired and normal hearing listeners in a multiple observation sample discrimination experiment normal hearing nh and hearing impaired hi listeners heard two multitone complexes each consisting of six simultaneous tones with nominal frequencies spaced evenly on an erbn logarithmic scale between 257 and 6930hz on every trial the frequency of each tone was sampled from a normal distribution centered near its nominal frequency in one interval of a 2ifc task all tones were sampled from distributions lower in mean frequency and in the other interval from distributions higher in mean frequency listeners had to identify the latter interval decision weights were obtained from multiple regression analysis of the between interval frequency differences for each tone and listeners responses frequency difference limens an index of sensorineural resolution and decision weights for each tone were used to predict the sensitivity of different decision theoretic models results indicate that low frequency tones were given much greater perceptu

the deterioration of hearing with age frequency selectivity the critical ratio the audiogram and speech threshold the frequency selectivity of the auditory system was measured by masking a sinusoidal signal 0 5 2 0 or 4 0 khz or a filtered speech signal with a wideband noise having a notch or stopband centered on the signal as the notch was widened performance improved for both types of signal but the rate of improvement decreased as the age of the 16 listeners increased from 23 to 75 years indicating a loss in frequency selectivity with age auditory filter shapes derived from the tone in noise data show a that the passband of the filter broadens progressively with age and b that the dynamic range of the filter ages like the audiogram that is the range changes little with age before 55 but beyond this point there is an accelerating rate of loss the speech experiment shows comparable but smaller effects the filter width measurements show that the critical ratio is a poor estimator of frequency selectivity because it confounds the tuning of the system with the efficiency of the signal detection and speech processing mechanisms that follow the filter an alternative one point measure of frequency selectivity which is both sensitive and reliable is developed via the filter shape model of masking

psychometric functions for multicomponent maskers with spectral uncertainty previous experiments used a two alternative forced choice adaptive procedure to measure thresholds for a 1000 hz signal in the presence of maskers composed of multiple sinusoids these sinusoids were drawn at random from a 300 to 3000 hz range excluding the signal frequency and frequencies within a critical band around the signal this experiment examined psychometric functions for 50 of the original 200 maskers with 10 components using signal levels from 10 80 db spl the psychometric functions were well fitted in d by signal level coordinates but individual functions typically spanned a 30 to 40 db range corresponding adaptive thresholds did not differ from thresholds based on 200 maskers and were in agreement with the average of the predicted thresholds across the 50 maskers although individual maskers could differ in effectiveness by 10 15 db the majority produced similar masking overall the adaptive procedure adequately characterizes performance in these conditions work supported by nih

level discrimination of single tones in a multitone complex by normal hearing and hearing impaired listeners a conditional on a single stimulus coss analysis procedure j acoust soc am 86 1743 1746 1989 was used to estimate how well normal hearing and hearing impaired listeners selectively attend to individual spectral components of a broadband signal in a level discrimination task on each trial two multitone complexes consisting of six octave frequencies from 250 to 8000 hz were presented to listeners the levels of the individual tones were chosen independently and at random on each presentation the target tone was selected within a block of trials as the 250 1000 or 4000 hz component on each trial listeners were asked to indicate which of the two complex sounds contained the higher level target as a group normal hearing listeners exhibited greater selectivity than hearing impaired listeners to the 250 hz target while hearing impaired listeners showed greater selectivity than normal hearing listeners to the 4000 hz target which is in the region of their hearing loss both groups of listeners displayed large variability in their ability to selectively weight the 1000 hz target trial by trial analysis showed a decrease in weighting efficiency with increasing frequency for normal hearing listeners but a relatively constant weighting efficiency across frequency for hearing impaired listeners interestingly hearing impaired listeners selectively weighted the 4000 hz target which was in the region of their hearing loss more efficiently than did the normal hearing listeners

discrimination of random time varying spectra with statistical constraints in the present study a sample discrimination procedure is used to examine how various statistical constraints on random time varying spectra might aid listeners in discriminating among these signals time varying spectra were constructed by adding five sequences of tones five tones in each sequence centered at the octave frequencies from 250 to 4000 hz the levels frequencies and durations of the tones varied randomly from one presentation to the next the signal to be detected was an increment in the level of tones comprising the sequence centered at 1000 hz the target sequence three main conditions were examined in which the parameter values of tones varied independently of one another equal variance condition covaried across tone sequences cross channel covariance condition or covaried among themselves for each tone cross parameter covariance condition for the latter two conditions two special cases were examined in which the target sequence varied independently of nontarget sequence

relative dominance of individual partials in determining the pitch of complex tones these experiments were conducted to determine the dominance of each partial in determining the residue pitch of a complex tone subjects were required to make pitch matches to a complex tone which had one partial slightly mistuned from its correct harmonic value the shift in residue pitch was measured as a function of the frequency shift of the harmonic for each harmonic in turn for mistunings up to 2 3 the shift in residue pitch was approximately a linear function of the shift in the harmonic but for greater mistunings the shift in residue pitch was reduced the degree to which a given harmonic can influence residue pitch gives a measure of the dominance of that harmonic the dominant harmonics were always contained within the lowest six harmonics for fundamental frequencies of 100 200 and 400 hz but there were marked individual differences in the exact distribution of dominance across harmonics the level of a harmonic relative to adjacent harmonics can have a significant effect on its dominance the implications of the results for theories of pitch perception are discussed

correlation coefficients and correlation ratios as estimates of observer weights in multiple observation tasks advantages of correlational methods are described for estimating the relative reliance or weight observers give to different elements of a complex display when performing auditory or visual discriminations correlational methods differ from other such methods by providing a least squares estimate of weights rather than a maximum likelihood estimate based on a presumed model the main benefit is that these methods can be generally applied in cases where the statistical properties of elements are unknown where correlations exist between elements or where it is necessary to evaluate decision models that are inherently nonlinear

effective properties of multicomponent simultaneous maskers under conditions of uncertainty when more than one sinusoid is used as a masker more masking is observed than would be predicted by a simple combination of their individual effects this masking is dramatically increased when the masker components vary in frequency and intensity with each presentation these studies manipulated several masker parameters under conditions of high masker uncertainty examining the effect of excluding critical band components fixing or randomizing component amplitudes and frequencies and narrowing the frequency range of the components the signal was always a 200 ms 1000 hz sinusoid presented simultaneously with the 200 ms masker removing critical band components reduced the amount of masking but considerable masking remained that appears to be nonperipheral in origin fixing masker frequencies across the two intervals of a trial greatly reduced the masking observed whereas fixing masker amplitudes had no effect reducing the frequency range from 5000 to 2700 hz generally increased the masking obser

cuing effects for informational masking the detection of a tone added to a random frequency multitone masker can be very poor even when the maskers have little energy in the frequency region of the signal this paper examines the effects of adding a pretrial cue to reduce uncertainty for the masker or the signal the first two experiments examined the effect of cuing a fixed frequency signal as the number of masker components and presentation methods were manipulated cue effectiveness varied across observers but could reduce thresholds by as much as 20 db procedural comparisons indicated observers benefited more from having two masker samples to compare with or without a signal cue than having a single interval with one masker sample and a signal cue the third experiment used random frequency signals and compared no cue signal cue and masker cue conditions and also systematically varied the time interval between cue offset and trial onset thresholds with a cued random frequency signal remained higher than for a cued fixed frequency signal for time intervals between the cue and trial of 50 ms or longer thresholds were approximately the same with a signal or a masker cue and lower than when there was no cue without a cue or with a masker cue analyses of possible decision strategies suggested observers attended to the potential signal frequencies particularly the highest signal frequency with a signal cue observers appeared to attend to the frequency of the subsequent signal

a non mortar mixed finite element method for elliptic problems on non matching multiblock grids abstract we consider the approximation of second order elliptic equations on domains that can be described as a union of sub domains or blocks we assume that a grid is defined on each block independently so that the resulting grid over the entire domain need not be conforming i e match across the block boundaries several techniques have been developed to approximate elliptic equations on multiblock grids that utilize a mortar finite element space defined on the block boundary interface itself we define a mixed finite element method that does not use such a mortar space the method has an advantage in the case where adaptive local refinement techniques will be used in that there is no mortar grid to refine as is typical of mixed methods our method is locally conservative element by element it is also globally conservative across the block boundaries theoretical results show that the approximate solution converges at the optimal rate to the true solution we present computational results to illustrate and confirm the theory

discrimination of frequency variance for tonal sequences real world auditory stimuli are highly variable across occurrences and sources the present study examined the sensitivity of human listeners to differences in global stimulus variability in a two interval forced choice task variance discrimination was measured using sequences of five 100 ms tone pulses the frequency of each pulse was sampled randomly from a distribution that was gaussian in logarithmic frequency in the non signal interval the sampled distribution had a variance of stan2 while in the signal interval the variance of the sequence was sig2 with sig2 stan2 the listener s task was to choose the interval with the larger variance to constrain possible decision strategies the mean frequency of the sampling distribution of each interval was randomly chosen for each presentation psychometric functions were measured for various values of stan2 although the performance was remarkably similar across listeners overall performance was poorer than that of an ideal observer io which perfectly compares interval variances however like the io weber s law behavior was observed with a constant ratio of sig2 stan2 to stan2 yielding similar performance a model which degraded the io with a frequency resolution noise and a computational noise provided a reasonable fit to the real data

relative estimates of combination weights decision criteria and internal noise based on correlation coefficients a means by which relative combination weights may be determined is described for a signal detection model in which the decision variable is a weighted linear combination of several independent normally distributed random variables xi s the first theorem presents the correlation between the binary response variables signal versus no signal and the component xi the second theorem presents a parallel result for the case that additive internal noise is present thus in psychophysical experiments the relative combination weights may be obtained by correlating the observers responses and the input random variables third three numerical methods which allow the evaluation of the relative magnitude of the decision criterion and the variance of a hypothetical additive internal noise are considered

the incorporation of level and level invariant cues for the detection of a tone added to noise the potential contribution of level dependent and level invariant cues for the detection of a tone added to narrow bands of noise was assessed in two experiments in the first experiment three masker bandwidths 40 120 and 360 hz and three center frequencies 600 1800 and 5400 hz were tested for the tone in noise detection task the signal to be detected was a tone with a frequency equal to the center frequency of the noise masker the level of the added tone was adjusted so as to generate d scores of approximately 2 in a two alternative forced choice procedure then the distributions of across interval changes in level were measured the distribution of differences in level was applied to either the noise alone or the tone plus noise stimuli allowing the measurement of sensitivity to changes in level for a two interval forced choice intensity discrimination task for one of the four observers there was a good correspondence between the d values obtained in the tone in noise task and the d

observer weighting strategies in interaural time difference discrimination and monaural level discrimination for a multi tone complex two experiments measured listeners abilities to weight information from different components in a complex of 553 753 and 953 hz the goal was to determine whether or not the ability to adjust perceptual weights generalized across tasks weights were measured by binary logistic regression between stimulus values that were sampled from gaussian distributions and listeners responses the first task was interaural time discrimination in which listeners judged the laterality of the target component the second task was monaural level discrimination in which listeners indicated whether the level of the target component decreased or increased across two intervals for both experiments each of the three components served as the target ten listeners participated in both experiments the results showed that those individuals who adjusted perceptual weights in the interaural time experiment could also do so in the monaural level discrimination task the fact that the same individuals appeared to be analytic in both tasks is an indication that the weights measure the ability to attend to a particular region of the spectrum while ignoring other spectral regions

sources of variation in profile analysis i individual differences and extended training this study investigated two sources of variance in the ability to discriminate auditory profiles individual differences and extended training the goals of the study were 1 to determine the range and origins of individual differences in profile analysis and 2 to determine whether those who initially had poor sensitivity to changes in spectral shape could eventually acquire finer sensitivity profile stimuli had 11 components with equal log spacing from 200 2200 hz thresholds ranged from 1 to 25 db signal level relative to the context level across 46 listeners the correlation between spectral shape discrimination thresholds after 2000 trials and pure tone intensity discrimination thresholds was 0 36 the range of individual differences for pure tone intensity discrimination and spectral shape discrimination was about the same two groups of listeners were given extended practice on the profile task one group that showed low thresholds after an initial 2000 trials of practice and another that showed much higher initial thresholds all listeners improved during the course of the first 2000 trials of training most of the poor listeners continued to improve during 9000 trials of training individual differences in the listeners sensitivity to changes in spectral shape still existed after the extended practice

successive versus simultaneous comparison in auditory intensity discrimination the ability to discriminate between two brief sounds having identical frequency components but differing in the intensity of one or more of the components is studied the stimulus manipulations include randomizing the overall intensity of the sounds varying the number and spacing of the components and varying the interval of time between the sounds the results from the experiment in which interstimulus interval is manipulated clearly support a profile analysis mechanism that computes two rough spectral analyses stores a classification of these spectra in memory and compares the two stores this profile mechanism involves a simultaneous comparison of different components of the complex some remote from the signal frequency rather than a successive comparison of the difference in intensity at the signal frequency the simultaneous comparison process is more sensitive when the profile is composed of many components spaced over a wide frequency range

effects of masker waveform and signal to masker phase relation on diotic and dichotic masking by reproducible noise the proportions of hits and false alarms were estimated for the detection of a 500 hz sinusoidal signal in each of 25 reproducible samples of wideband white gaussian noise the effects of signal phase were investigated under diotic moso and dichotic mos conditions and compared to the predictions of two major models of binaural hearing averaging the data over samples obscured important across sample and across subject differences in performance the proportions of hits and false alarms for individual noise samples presented under the moso condition were highly correlated with those for the same noise samples under the dichotic mos condition suggesting that the cues determining performance under these conditions are related signal to masker phase had a large effect on the proportion of hits under the moso condition but only a small effect under the mos condition the vector model predicts a large effect of signal phase under the mos condition and is therefore imcompatible with this aspect of the data the expected value of the decision variable of the ec model is independent of signal phase however when the variance of the decision variable is also considered the ec model does predict changes in the proportion of hits with the phase of the signal comparable to those observed here further it was shown that if minor changes in the form of the ec model s decision variable or in the distribution of the internal noise parameters are assumed the expected value of the decision variable also changes with the phase of the signal

informational masking by everyday sounds tone in noise detection is severely degraded when only a few spectral components of the noise are presented at random on each trial neff and green percept psychophys 41 409 415 1987 the elevations in threshold are attributed to uncertainty regarding the noise caused by sparse sampling of noise components informational masking is the term used to describe the result the present experiment was undertaken to determine how informational masking is affected when sparse sampling is from a set of common everyday sounds instead of noise on each presentation a different masker waveform of constant total power was synthesized from the magnitude and phase of a fixed number m of spectral components m 2 921 across blocks of trials the components were selected at random from 1 of 50 common environmental sounds e g baby crying door slamming phone ringing or 1 of 50 samples of gaussian noise masked thresholds for a 1 0 khz signal in the presence of both types of maskers were obtained using an adaptive two interval forced choice procedure results with noise replicated earlier results showing largest elevations in threshold for 10 20 sampled components results with everyday sounds showed a similar pattern with thresholds elevated above those for noise by as much as 10 db at the larger values of m the differences in masked thresholds were systematically related to differences in the ensemble variance of masker spectra as predicted by a model previously applied to noise lutfi j acoust soc am 94 748 758 1993 not predicted was the result of a subsequent trial by trial analysis in which 9 11 db less masking was observed for samples from everyday sounds rated as easily recognized by listeners the results suggest that listeners fail to exploit lawful dependencies among spectral components of everyday sounds to aid detection unless enough information is available for the sound to be easily recognized

auditory discrimination of material changes in a struck clamped bar the principles of theoretical acoustics were applied to approximately reconstruct the sound pressure waveform at the ear as would be generated by an idealized struck clamped bar the result is an inharmonic sum of damped sinusoids whose individual acoustic parameters frequency intensity and decay modulus are for a fixed geometry and fixed driving force uniquely determined by the material composition of the bar in the standard 2ifc procedure listeners were asked to discriminate changes in material composition based on their perception of the acoustic waveform listener strategies for discriminating such changes were estimated by perturbing slightly the individual acoustic parameters from trial to trial and computing correlations with the listener s response cf r a lutfi and e oh j acoust soc am 95 2963 a 1994 in general the correlations reveal that listeners fail to make optimal use of the information in the acoustic waveform by tending to give undue weight for a given material change to changes in component frequency in some case the accompanying reduction in performance efficiency amounted to 80

informational processing of complex sound i intensity discrimination this paper reports on some initial experiments using the sample discrimination paradigm to investigate normal hearing listeners ability to process information in complex nonspeech sounds an important feature of the sample discrimination experiment is that the value of the d i f f e r e n c e to be discriminated randomly varies from trial to trial it is this variation that yields potential information in the present study listeners heard a pair of multitone complexes or sequences on each trial the individual levels of the tones were drawn from two normal distributions differing only in mean the listener s task was to identify the sound having the higher mean tone level for an ideal observer in these experiments performance in d grows as the square root n where n is the number of tones obtained d grew more nearly as the cube root of n regardless of whether the tones were played sequentially or simultaneously or whether they were increased in number from high frequencies to low or from low frequencies to high a preliminary model is proposed in which discrimination performance depends predominantly on the information content of the sounds and is largely independent of the physical dimensions along which the sounds vary information content is defined in terms of the variance of the underlying stimulus distributions and a stimulus equivocation factor that is derived from the data based on this model transmitted information is estimated to be between 1 0 and 2 6 bits

multiple observations and internal noise a multiple observation task was used to evaluate models of internal noise on each trial n tones n 1 2 3 4 6 8 10 or 12 within a block were independently sampled from one of two probability density functions on frequency each was normal in form with a standard deviation of 100 hz the two distributions had means of 1000 and 1100 hz respectively the sample was presented through headphones as n 50 ms tone bursts separated by 50 ms the subjects task was to decide from which of the two distributions the tones were sampled a model partitioning internal variance into peripheral variance added to each observation prior to formulating a decision statistic and central variance added to the decision statistic provided a good description of the data of all four subjects a subsequent study counterbalanced two levels of the difference between distribution means 100 or 150 hz with two levels of the standard deviation 100 or 150 hz increasing did not affect estimates of internal variance however increasing resulted in increased estimates of internal variance for both levels of one interpretation of this result is that external and internal variance are not independent work supported by afosr and nmrdc

spectral and temporal weights in spectral shape discrimination the coss analysis b g berg j acoust soc am 86 1743 1746 1989 was used to estimate spectral and temporal weights of a three component amplitude modulated stimulus in a spectral shape discrimination task in all experiments the task of the observer was to detect an increment in the level of the center component a spectral temporal weight quantifies the relative influence of a spectral component on the decisions of an observer during a specified segment of the total stimulus duration in the first two experiments the signal was added to all three temporal segments of the center component the ideal weights for each component should be the same across temporal segments spectral temporal weights were obtained for four conditions with different stimulus durations in general the estimated weights for each component were not equal at different temporal segments in the third experiment the signal was added to only one of three segments of the center component ideally weight patterns should have changed when the temporal position of the signal segment was altered two stimulus durations 300 and 15 ms were used for the 300 ms condition the signal was added to only the end segment and for all three observers the weight patterns are different from that obtained in experiment 1 with the signal added to all segments for the 15 ms conditions altering the signal position changed the estimated weights for only one observer

generalized inf sup conditions for chebyshev spectral approximation of the stokes problem a mixed problem and its approximation in an abstract framework are considered they are proved to be well posed if and only if several inf sup conditions are satisfied these results are applied to the stokes equations in a square formulated in chebyshev weighted sobolev spaces and their approximations two kinds of spectral discretizations are analyzed a galerkin method and a collocation method at the chebyshev nodes

sample discrimination of frequency differences with distracters this study examined the effect of the type and frequency range of remote frequency distracters on sample discrimination of frequency differences sd f for baseline sd f conditions normal hearing listeners judged frequency differences between pairs of target tones drawn from gaussian frequency distributions near 2000 hz in experiment 1 the distracters were pairs of random frequency tones fixed frequency tones or noise bands with one distracter above and one below the target region three frequency separations of targets and distracters were tested none overlapping the target region effects of fixed frequency or noise band distracters were small compared to that of random frequency distracters which drove performance to near chance in experiment 2 dominance of the low frequency distracter was supported by the effects of changing distracter level by presenting only the higher or lower frequency distracter and by the pattern of weights derived from trial by trial responses performance recovered only when the lower frequency distracter was attenuated 40 50 db relative to the targets in experiment 3 all stimulus distributions were shifted 2 octaves higher in frequency the stronger influence of the distracter frequency below the target remained the results demonstrate the importance of both stimulus variability and frequency relationships in the interaction of targets and distracters for sd f

masker first advantage for cues in informational masking the detectability of a pure tone signal may be reduced by adding a small number of randomly drawn masker tones remote from the signal frequency an effect attributed to informational masking a pretrial cue consisting of either the upcoming signal or masker releases informational masking but a pretrial cue of the signal plus masker stimulus does not in these experiments the relative potency of pre and posttrial cues in releasing informational masking was examined in separate conditions the masker alone and signal plus masker stimuli were cues the results indicated a masker first advantage i e sensitivity was superior when a masker cue preceded a yes no trial interval compared to a when a signal plus masker preceded the trial and b when either cue type followed the yes no trial interval a masker first advantage was also obtained when the results from a two interval forced choice same different task were examined in contrast a masker first advantage was not obtained when the frequency of the signal to be detected was random for detection tasks using random multi tone maskers there may be differences in processing efficiency depending on the order in which stimuli are presented the masker first advantage may depend in part on observers maintaining their attention at the signal frequency

schur functors and schur complexes the study of schur functors has a relatively long history its main impetus derived from representation theory originally in characteristic zero over the years however with the development of modular representations and algebraic geometry over fields of positive characteristic the need for a theory of universal polynomial functors increased and since the mid 1960s approaches to a characteristic free treatment of schur functors have been developing see for instance the recent book of green 1 l in which the treatments by carter and lusztig 6 higman 12 and towber 20 among others are discussed our own interest in such a treatment was awakened by the work of lascoux 141 on resolutions of determinantal ideals although his thesis treated only the characteristic zero case it suggested that a general and elementary theory of schur functors could be developed using only the rudiments of multilinear algebra involving the hopf algebra structures of the symmetric exterior and divided power algebras moreover this elementary development admitted of a natural generalization to the idea of schur complexes whose usefulness was demonstrated for instance in our construction of a universal minimal

informational processing of complex sound iii interference in this study theoretical results from information theory and detection theory are applied to provide a formal analysis of the interaction of target and context uncertainty on the discrimination of brief multitone sequences the experiments employ a sample discrimination task in which the performance of an ideal observer is held constant while the relative variability of the target t and context c is varied listener performance in these experiments was less than ideal but increased monotonically with t c whether the task was to discriminate the frequency or the intensity of the target performance was also constant for a constant t c regardless of the target s position in the sequence the results are consistent with a class of models in which the decision variable is a weighted sum of the tone values comprising the sequence weighting functions computed from the trial by trial data suggest that limits in performance result from trial by trial variability in the weights the decision variable also

informational masking increases the costs of monitoring multiple channels this study examined the costs of simultaneously monitoring two frequency regions listeners detected low and high frequency tones in a 2i4afc procedure on every trial each signal was presented in either the first or second interval independently comparison of thresholds in single and dual signal conditions provided an estimate of the costs thresholds were obtained in quiet in notched filtered noise and in randomized multitone maskers no cost was found in quiet whereas large costs were found for the masked conditions especially for the multitone masker these results suggest that costs of dividing attention in frequency depend on both signal and nonsignal channels

growth of forward masking for sinusoidal and noise maskers as a function of signal delay implications for suppression in noise the first two experiments were designed to determine whether mutual suppression in broadband noise increases in strength with increasing overall level in experiment i masking functions signal threshold versus masker level were measured in forward masking as a function of the delay time of a 10 ms signal both for a broadband noise masker low pass filtered at 8 khz and for sinusoidal maskers at 1 2 and 4 khz in the latter case the signal frequency equaled the masker frequency for short signal delays the masking functions were steeper for the sinusoidal masker than for the noise masker at longer delays the slopes for both masker types decreased and the slopes for the two masker types became more nearly equal in experiment ii we investigated the effect of gating a low level noise cue with the sinusoidal masker at the longer signal delays the masking functions had equal slopes for the broadband noise masker and the sinusoidal masker with cue at short signal delays the masking functions for sinuso