the influence of age and high frequency hearing loss on sensitivity to temporal fine structure at low frequencies l sensitivity to temporal fine structure tfs at low frequencies may be adversely affected by hearing loss at high frequencies even when absolute thresholds at low frequencies are within the normal range however in several studies suggesting this the effects of hearing loss and age were confounded here interaural phase discrimination ipd thresholds for pure tones at 500 and 750 hz were measured for 39 subjects with ages from 61 to 83 yr all subjects had near normal audiometric thresholds at low frequencies but thresholds varied across subjects at high frequencies ipd thresholds were correlated with age ipd thresholds for the test frequency of 750 hz were weakly correlated with absolute thresholds at high frequencies but these correlations became non significant when the effect of age was partialed out the results do not confirm that sensitivity to tfs at low frequencies is influenced by hearing loss at high frequencies independently of age

factors influencing electrical place pitch perception in bimodal listeners factors that might affect perceptual pitch match between acoustic and electric stimulation were examined in 25 bimodal listeners using magnitude estimation pre operative acoustic thresholds in both ears and duration of severe profound loss were first examined as correlates with degree of match between the measured pitch and that predicted by the spiral ganglion frequency position model the degree of match was examined with respect to 1 the ratio between the measured and predicted pitch percept on the most apical electrode and 2 the ratio between the slope of the measured and predicted pitch function second effect of listening experience was examined to assess whether adaptation occurred over time to match the frequency assignment to electrodes pre experience pitch estimates on the apical electrode were within the predicted range in only 28 of subjects and the slope of the electrical pitch function was lower than predicted in all except one subject subjects with poorer hearing tended to have a lower pitch and a shallower electrical pitch function than predicted by the model pre operative hearing thresholds in the contralateral ear and hearing loss duration were not correlated with the degree of pitch match and there was no significant group effect of listening experience

the relationship between frequency selectivity and pitch discrimination sensorineural hearing loss this study tested the relationship between frequency selectivity and the minimum spacing between harmonics necessary for accurate fo discrimination fundamental frequency difference limens fo dls were measured for ten listeners with moderate sensorineural hearing loss snhl and three normal hearing listeners for sine and random phase harmonic complexes bandpass filtered between 1500 and 3500 hz with fo s ranging from 75 to 500 hz or higher all listeners showed a transition between small good fo dls at high fo s and large poor fo dls at low fo s although the fo at which this transition occurred fo tr varied across listeners three measures thought to reflect frequency selectivity were significantly correlated to both the fo tr and the minimum fo dl achieved at high fo s 1 the maximum fo for which fo dls were phase dependent 2 the maximum modulation frequency for which amplitude modulation and quasi frequency modulation were discriminable and 3 the equivalent rectangular bandwidth of the auditory filter estimated using the notched noise method these results provide evidence of a relationship between fo discrimination performance and frequency selectivity in listeners with snhl supporting spectral and spectro temporal theories of pitch perception that rely on sharp tuning in the auditory periphery to accurately extract fo information

effects of spectro temporal modulation changes produced by multi channel compression on intelligibility in a competing speech task these experiments are concerned with the intelligibility of target speech in the presence of a background talker using a noise vocoder stone and moore j acoust soc am 114 1023 1034 2003 showed that single channel fast acting compression degraded intelligibility but slow compression did not stone and moore j acoust soc am 116 2311 2323 2004 showed that intelligibility was lower when fast single channel compression was applied to the target and background after mixing rather than before and suggested that this was partly due to compression after mixing introducing comodulation between the target and background talkers experiment 1 here showed a similar effect for multi channel compression in experiment 2 intelligibility was measured as a function of the speed of multi channel compression applied after mixing for both eight and 12 channel vocoders with one compressor per channel intelligibility decreased as compression speed increased for the eight channel vocoder a compresso

psychometric functions for frequency discrimination from listeners with sensorineural hearing loss psychometric functions for pulsed pure tone frequency discrimination were obtained from hearing impaired listeners at frequencies with normal hearing and at frequencies with mild or moderate hearing losses the general form of psychometric functions at hearing impaired frequencies was found to be the same as at normal hearing frequencies i e d was linear with the frequency difference between tones in hz for all but one psychometric function the addition of an intercept term to the fitting equation did not account for significantly more variance than did the slope term alone therefore it was concluded that psychometric functions for frequency discrimination can be adequately described with only one parameter the slope of the psychometric function deficits in discrimination at hearing loss frequencies were manifested by more gradual slopes of psychometric functions procedures for normalizing psychometric functions are presented which facilitate comparisons of normal and impaired frequency discrimination data across studies and frequencies comparisons of dlf s difference limen for frequency obtained with adaptive and fixed procedures show a bias toward larger dlf s with adaptive procedures but only at higher frequencies a discussion of equal interval and equal ratio adaptive stepping rules indicates that an equal ratio rule may be preferable

frequency and intensity difference limens for harmonics within complex tones a two interval two alternative forced choice task was used to estimate frequency difference limens dls for individual harmonics within complex tones and dls for the periodicity i e number of periods per s of the whole complexes for complex tones with equal amplitude harmonics the dls for the lowest harmonics were small less than one percent the dls increased rather abruptly around the fifth to seventh harmonic the highest harmonic in each complex was also well discriminated and the discriminability of a single high harmonic was markedly improved by increasing its level relative to the other components the dl for a complex tone was generally smaller than the frequency dl of its most discriminable component the dl for a complex was found to be predictable from the dls of the harmonics comprising the complex using a formula derived by goldstein j acoust soc am 54 1496 1516 1973 from his optimum processor theory for the formation of the pitch of complex tones the dl for a complex i

enhancement of temporal cues to pitch in cochlear implants effects on pitch ranking the abilities to hear changes in pitch for sung vowels and understand speech using an experimental sound coding strategy etone that enhanced coding of temporal fundamental frequency f0 information were tested in six cochlear implant users and compared with performance using their clinical ace strategy in addition rate and modulation rate pitch difference limens dls were measured using synthetic stimuli with f0s below 300 hz to determine psychophysical abilities of each subject and to provide experience in attending to rate cues for the judgment of pitch sung vowel pitch ranking tests for stimuli separated by three semitones presented across an f0 range of one octave 139 277 hz showed a significant benefit for the experimental strategy compared to ace average d prime d values for etone d 1 05 were approximately three time larger than for ace d 0 35 similar scores for both strategies in the speech recognition tests showed that coding of segmental speech information by the exper

loudness perception and frequency discrimination in subjects with steeply sloping hearing loss possible correlates of neural plasticity loudness functions and frequency difference limens dlfs were measured in five subjects with steeply sloping high frequency sensorineural hearing loss the stimuli were pulsed pure tones encompassing a range of frequencies loudness data were obtained using a 2afc matching procedure with a 500 hz reference presented at a number of levels dlfs were measured using a 3afc procedure with intensities randomized within 6 db around an equal loudness level results showed significantly shallower loudness functions near the cutoff frequency of the loss than at a lower frequency where hearing thresholds were near normal dlfs were elevated on average relative to dlfs measured using the same procedure in five normally hearing subjects but showed a local reduction near the cutoff frequency in most subjects with high frequency loss the loudness data are generally consistent with recent models that describe loudness perception in terms of peripheral excitation patterns that are presumably restricted by a steeply sloping hearing loss however the dlf data are interpreted with reference to animal experiments that have shown reorganization in the auditory cortex following the introduction of restricted cochlear lesions such reorganization results in an increase in the spatial representation of lesion edge frequencies and is comparable with the functional reorganization observed in animals following frequency discrimination training it is suggested that similar effects may occur in humans with steeply sloping high frequency hearing loss and therefore the local reduction in dlfs in our data may reflect neural plasticity

temporal integration of loudness in listeners with hearing losses of primarily cochlear origin to investigate how hearing loss of primarily cochlear origin affects the loudness of brief tones loudness matches between 5 and 200 ms tones were obtained as a function of level for 15 listeners with cochlear impairments and for seven age matched controls three frequencies usually 0 5 1 and 4 khz were tested in each listener using a two interval two alternative forced choice 2i 2afc paradigm with a roving level up down adaptive procedure results for the normal listeners generally were consistent with published data e g j acoust soc am 99 1633 1644 1996 the amount of temporal integration defined as the level difference between equally loud short and long tones varied nonmonotonically with level and was largest at moderate levels no consistent effect of frequency was apparent the impaired listeners varied widely but most showed a clear effect of level on the amount of temporal integration overall their results appear consistent with expectations based on knowledge of the general properties of their loudness growth functions and the equal loudness ratio hypothesis which states that the loudness ratio between equal spl long and brief tones is the same at all spls the impaired listeners amounts of temporal integration at high spls often were larger than normal although it was reduced near threshold when evaluated at equal sls the amount of temporal integration well above threshold usually was in the low end of the normal range two listeners with abrupt high frequency hearing losses slopes 50 db octave showed larger than normal maximal amounts of temporal integration 40 to 50 db this finding is consistent with the shallow loudness functions predicted by our excitation pattern model for impaired listeners in modeling sensorineural hearing loss edited by w jesteadt erlbaum mahwah nj 1997 pp 187 198 loudness functions derived from impaired listeners temporal integration functions indicate that restoration of loudness in listeners with cochlear hearing loss usually will require the same gain whether the sound is short or long

relation between the growth of loudness and high frequency excitation to test the conjecture that cochlear impairment and a masking noise in normal ears produce analogous effects on the growth of loudness loudness was measured for 21 listeners all with bilateral symmetrical high frequency cochlear losses beyond the normal hearing region thresholds increased by 30 49 db octave for 10 listeners in group i and by 51 71 db octave for 11 listeners in group ii measured by absolute magnitude estimation and production at two frequencies where thresholds were normal the dynamic range over which loudness grows was not altered by the adjacent hearing loss this was not true however for the slope whereas the overall shape and slope of the loudness functions were essentially the same for group i the mid to high level slope for group ii was noticeably flatter for a tone at the cutoff frequency than for a lower frequency tone in contrast markedly steeper loudness functions characteristic of loudness recruitment were obtained for both groups at a frequency in the region of impaired hearing the reduced rate of loudness growth observed in the region of normal hearing for listeners with steep low pass losses like the reduction usually found for a tone masked by an adjacent high frequency noise is ascribed to the tone s restricted excitation pattern these results indicate that high frequency auditory cues are effectively eliminated by a steeply sloping high frequency hearing loss just as they are eliminated by the addition of an external noise to test the conjecture that cochlear impairment and a masking noise in normal ears produce analogous effects on the growth of loudness loudness was measured for 21 listeners all with bilateral symmetrical high frequency cochlear losses beyond the normal hearing region thresholds increased by 30 49 db octave for 10 listeners in group i and by 51 71 db octave for 11 listeners in group ii measured by absolute magnitude estimation and production at two frequencies where thresholds were normal the dynamic range over which loudness grows was not altered by the adjacent hearing loss this was not true however for the slope whereas the overall shape and slope of the loudness functions were essentially the same for group i the mid to high level slope for group ii was noticeably flatter for a tone at the cutoff frequency than for a lower frequency tone in contrast markedly steeper loudness functions characteristic of loudness recruitment were obtained for both groups at a frequency in the region of im

simulation of the effects of loudness recruitment and threshold elevation on the intelligibility of speech in quiet and in a background of speech these experiments simulated the threshold elevation and loudness recruitment associated with three different types of cochlear hearing loss moderate flat condition r2 severe flat condition r3 and moderate to severe sloping condition rx this was done to allow an examination of the effects of these factors on the intelligibility of speech in isolation from other factors that are normally associated with cochlear hearing loss such as reduced frequency selectivity the simulation was performed by splitting the input signal into 13 frequency bands and processing the envelope in each band so as to create loudness sensations in a normal ear that would resemble those produced in an impaired ear with recruitment the bands were then recombined all tests were performed using subjects with normal hearing for speech in quiet simulation of hearing loss produced a reduction in the ability to understand low level speech however speech at sufficiently high levels was highly intelligible in all conditions linear amplification according to the national acoustic laboratory nal prescription gave high intelligibility for speech at normal conversational levels for speech presented at a fixed input level of 65 db spl against a background of a single competing talker simulation of hearing loss produced substantial decrements in performance the speech to background ratios in conditions r2 and rx had to be 11 13 db higher than in the control condition unprocessed stimuli to achieve similar levels of performance linear amplification according to the nal prescription improved performance markedly for the conditions simulating flat losses but was less effective for the condition simulating a sloping loss this indicates that threshold elevation combined with recruitment produces a loss of intelligibility for speech in the presence of a single competing talker that is only partly compensated by linear amplification of the type typically used in hearing aids

the effect of tone vocoding on spatial release from masking for old hearing impaired listeners old hearing impaired listeners generally benefit little from lateral separation of multiple talkers when listening to one of them this study aimed to determine how spatial release from masking srm in such listeners is affected when the interaural time differences itds in the temporal fine structure tfs are manipulated by tone vocoding tvc at the ears by a master hearing aid system word recall was compared with and without tvc when target and masker sentences from a closed set were played simultaneously from the front loudspeaker co located and when the maskers were played 45 to the left and right of the listener separated for 20 hearing impaired listeners aged 64 to 86 srm was 3 7 db smaller with tvc than without tvc this difference in srm correlated with mean audiometric thresholds below 1 5 khz even when monaural tfs sensitivity discrimination of frequency shifts in identically filtered complexes was partialed out suggesting that low frequency audiometric thresholds may be a good indicator of candidacy for hearing aids that preserve itds the tvc difference in srm was not correlated with age pure tone itd thresholds nor fundamental frequency difference limens and only with monaural tfs sensitivity before control for low frequency audiometric thresholds

frequency resolution and discrimination of constant and dynamic tones in normal and hearing impaired listeners frequency resolution and three tasks of frequency discrimination were measured at 500 and 4000 hz in 12 normal and 12 hearing impaired listeners a three interval two alternative forced choice procedure was used frequency resolution was measured with an abbreviated psychoacoustical tuning curve frequency discrimination was measured for 1 a fixed frequency standard and target 2 a fixed frequency standard and a frequency transition target and 3 frequency transition standard and a frequency transition target the 50 ms frequency transitions had the same final frequency as the standards but the initial frequency was lowered to obtain about 79 discrimination performance there was a strong relationship between poor frequency resolution and elevated pure tone thresholds but only a very weak relationship between poor frequency discrimination and elevated pure tone thresholds several hearing impaired listeners had normal discrimination performance together with pure tone thresholds of 80 90 db hl a slight correlation was found between word recognition and frequency discrimination but a detailed comparison of the phonetic errors and either the frequency discrimination or frequency resolution tasks failed to suggest any consistent interdependencies these results are consistent with previous work that has suggested that frequency resolution and frequency discrimination are independent processes

a unitary model of pitch perception a model of the mechanism of residue pitch perception is revisited it is evaluated in the context of some new empirical results and it is proposed that the model is able to reconcile a number of differing approaches in the history of theories of pitch perception the model consists of four sequential processing stages peripheral frequency selectivity within channel half wave rectification and low pass filtering within channel periodicity extraction and cross channel aggregation of the output the pitch percept is represented by the aggregated periodicity function using autocorrelation as the periodicity extraction method and the summary autocorrelation function sacf as the method for representing pitch information it is shown that the model can simulate new experimental results that show how the quality of the pitch percept is influenced by the resolvability of the harmonic components of the stimulus complex these include i the pitch of harmonic stimuli whose components alternate in phase ii the increased frequency difference limen of tones consisting of higher harmonics and iii the influence of a mistuned harmonic on the pitch of the complex as a function of its harmonic number to accommodate these paradigms it was necessary to compare stimuli along the length of the sacf rather than relying upon the highest peak alone these new results demonstrate that the model responds differently to complexes consisting of low and high harmonics as a consequence it is not necessary to postulate two separate mechanisms to explain different pitch percepts associated with resolved and unresolved harmonics

auditory perceptual interpretation of the vowel an account of the simple vowels of american english will be given in terms of the author s auditory perceptual theory data from many sources will be used to illustrate and support this view in addition to theoretical suggestions concerning an auditory perceptual transformation and a segmentation rule the perceptualized spectral patterns associated with the nonretroflex vowels will be shown to fall into regions within a slab in a three dimensional auditory perceptual space these regions form a vowel map that by simple rotations can be related to various vowel charts such as those of jones pike or fant while the presentheory is an elaboration of traditional formant ratio theory it will be shown that a concept of a perceptual reference is needed not only for talker normalization but also to disambiguate vowels not distinguished by simple formant ratio theory additionally loci for the retroflex and nasalized vowels illustrate the utility of describing vowel spectra by five numbers combined into three dimensions simple f1 by f2 descriptions are not adequate except for enigmatophiles work supported by nincds and afosr

the importance for speech intelligibility of random fluctuations in steady background noise spectrally shaped steady noise is commonly used as a masker of speech the effects of inherent random fluctuations in amplitude of such a noise are typically ignored here the importance of these random fluctuations was assessed by comparing two cases for one speech was mixed with steady speech shaped noise and n channel tone vocoded a process referred to as signal domain mixing sdm this preserved the random fluctuations of the noise for the second the envelope of speech alone was extracted for each vocoder channel and a constant was added corresponding to the root mean square value of the noise envelope for that channel this is referred to as envelope domain mixing edm it removed the random fluctuations of the noise sinusoidally modulated noise and a single talker were also used as backgrounds with both sdm and edm speech intelligibility was measured for n 12 19 and 30 with the target to background ratio fixed at 7 db for sdm performance was best for the speech background and worst for the steady noise for edm this pattern was reversed intelligibility with steady noise was consistently very poor for sdm but near ceiling for edm demonstrating that the random fluctuations in steady noise have a large effect

phoneme recognition as a function of the number of auditory filter outputs it has been proposed that listeners take advantage of brief coups d oeil when processing speech in noise these glimpses can be characterized both in time and frequency the obligatory role of the auditory filters in determining the nature of any further processing suggests that the frequency extent of a glimpse should be equivalent to that of an auditory filter accordingly it is hypothesized that the spectral characteristics of glimpses primarily relate to the available number of auditory channels the present study investigated the number of auditory filter outputs needed to identify phonemes in quiet stimuli were first restricted to 80 8000 hz and then split into 30 contiguous auditory filter width bands normal hearing listeners were presented with n bands whose spectral location was selected randomly from trial to trial no signal was presented in the other bands consistent with previous studies performance gradually increased with the number of bands an asymptote was reached with 24 and 16 bands for vowels and consonants respectively while high levels of speech understanding are typically observed with as few as 4 channels of spectral information our results indicate that accurate phoneme recognition requires combination of a much larger number of auditory filter outputs

cross bifix free codes within a constant factor of optimality a cross bifix free code is a set of words in which no prefix of any length of any word is the suffix of any word in the set cross bifix free codes arise in the study of distributed sequences for frame synchronization we provide a new construction of cross bifix free codes which generalizes the construction by bajic to longer code lengths and to any alphabet size the codes are shown to be nearly optimal in size we also establish new results on fibonacci sequences which are used in estimating the size of the cross bifix free codes

the effect of interaural delay of the masker on masking level differences in young and old adults diotic sono thresholds and dichotic s pi n pi tau thresholds were measured for young and old adults using a 500 hz pure tone signal and broadband burst masking noise at 37 db spl hz in the dichotic condition both the signal and the masker were phase reversed and the masker was presented with an interaural delay of 0 25 0 5 0 75 1 1 25 1 5 1 75 2 3 or 5 ms masking level differences mlds were determined by subtracting dichotic thresholds from diotic thresholds the sono thresholds for the old subjects did not differ significantly from those for the young subjects however when mlds were plotted as a function of delay the pattern of results differed significantly between young and old subjects this difference in pattern was completely accounted for in terms of a delay line version of durlach s equalization and cancellation ec model n i durlach in foundations of modern auditory theory edited by j v tobias academic new york 1972 b a schneider and p m zurek j acoust soc am 86 1756 1763 1989 by assuming that temporal jitter increases with internal delay in young subjects but that it does not vary with the amount of internal delay in old subjects

dead regions and pitch perception the perception of pitch for pure tones with frequencies falling inside low or high frequency dead regions drs was examined subjects adjusted a variable frequency tone to match the pitch of a fixed tone matches within one ear were often erratic for tones falling in a dr indicating unclear pitch percepts matches across ears of subjects with asymmetric hearing loss and octave matches within ears indicated that tones falling within a dr were perceived with an unclear pitch and or a pitch different from normal whenever the tones fell more than 0 5 octave within a low or high frequency dr one unilaterally impaired subject with only a small surviving region between 3 and 4 khz matched a fixed 0 5 khz tone in his impaired ear with on average a 3 75 khz tone in his better ear when asked to match the 0 5 khz tone with an amplitude modulated tone he adjusted the carrier and modulation frequencies to about 3 8 and 0 5 khz respectively suggesting that some temporal information was still available overall the results indicate that the pitch of low frequency tones is not conveyed solely by a temporal code possibly there needs to be a correspondence between place and temporal information for a normal pitch to be perceived the perception of pitch for pure tones with frequencies falling inside low or high frequency dead regions drs was examined subjects adjusted a variable frequency tone to match the pitch of a fixed tone matches within one ear were often erratic for tones falling in a dr indicating unclear pitch percepts matches across ears of subjects with asymmetric hearing loss and octave matches within ears indicated that tones falling within a dr were perceived with an unclear pitch and or a pitch different from normal whenever the tones fell more than 0 5 octave within a low or high frequency dr one unilaterally impaired subject with only a small surviving region between 3 and 4 khz matched a fixed 0 5 khz tone in his impaired ear with on average a 3 75 khz tone in his better ear when asked to match the 0 5 khz tone with an amplitude modulated tone he adjusted the carrier and modulation frequencies to about 3 8 and 0 5 khz respectively suggesting that some temporal information was still available

the relative strength of the tone and noise components in iterated rippled noise rippled noise is constructed by delaying a random noise and adding it back to the original iterated rippled noise irn is constructed by repeating the delay and add process irn produces a two component perception i e a buzzy tone with a pitch equal to the reciprocal of the delay and a background noise that sounds like the original random noise the perceived tone noise ratio increases with the number of iterations the effective tone noise ratio in irn sounds with 1 16 iterations was measured in a discrimination matching experiment each irn was paired with a range of standard sounds having varying proportions of a broadband noise and a complex tone to find the point where their perceived tone noise ratios are the same the experiment shows that the tone noise ratio of the matching standard increases 3 8 db per doubling of the number of iterations in the irn stimulus spectral models of auditory perception explain the pitch of irn in terms of peaks in the region of the first five to eight harmonic

an autocorrelation model with place dependence to account for the effect of harmonic number on fundamental frequency discrimination fundamental frequency f0 difference limens dls were measured as a function of f0 for sine and random phase harmonic complexes bandpass filtered with 3 db cutoff frequencies of 2 5 and 3 5 khz low region or 5 and 7 khz high region and presented at an average 15 db sensation level approximately 48 db spl per component in a wideband background noise fundamental frequencies ranged from 50 to 300 hz and 100 to 600 hz in the low and high spectral regions respectively in each spectral region f0 dls improved dramatically with increasing f0 as approximately the tenth harmonic appeared in the passband generally f0 dls for complexes with similar harmonic numbers were similar in the two spectral regions the dependence of f0 discrimination on harmonic number presents a significant challenge to autocorrelation ac models of pitch in which predictions generally depend more on spectral region than harmonic number a modification involving a lag window is proposed and tested restricting the ac repr

a general equation describing frequency discrimination as a function of frequency and sensation level frequency discrimination thresholds for a wide range of stimulus frequencies and stimulus levels were obtained from three normal hearing listeners linear regression analyses of the present data and of data from two previous studies indicate that an sl 1 transformation of stimulus level and a square root f transformation of stimulus frequency yield linear dimensions that allow accurate predictions of frequency discrimination thresholds from normal hearing listeners over a wide range of stimulus frequencies 125 8000 hz and stimulus levels 5 8 db sl with a single prediction equation

frame synchronization for gaussian channels the problem of locating a periodically inserted frame synchronization pattern in random data for a m ary digital communication system operating over the additive white gaussian noise channel is considered the optimum maximum likelihood decision rule high signal to noise approximate maximum likelihood decision rule and ordinary correlation decision rule for frame synchronization are derived for both coherent and noncoherent phase demodulation a general lower bound on synchronization probability is derived for the coherent correlation rule monte carlo computer simulations of all three decision rules along with evaluations of the lower bound for the coherent correlation rule were performed for the coherent mpsk coherent and noncoherent m ary orthogonal and 16 qam signaling schemes these results show that in each case the high signal to noise maximum likelihood rules have a performance nearly equal to that of the maximum likelihood rules over a wide range of practically interesting signal to noise ratios snr s these high snr decision rules also provide significant performance improvement over the simple correlation rules moreover they are much simpler to implement than the maximum likelihood decision rules and in fact are no more complex than the correlation rules

the case of the missing delay lines synthetic delays obtained by cross channel phase interaction temporal models of pitch and harmonic segregation call for delays of up to 30ms to cover the full range of existence of musical pitch to date there is little anatomical or physiological evidence for delays that long we propose a mechanism by which delays may be synthesized from cross channel phase interaction phases of adjacent cochlear filter channels are shifted by an amount proportional to frequency and then combined as a weighted sum to approximate a delay synthetic delays may be used by pitch perception models such as autocorrelation segregation models such as harmonic cancellation and binaural processing models to explain sensitivity to large interaural delays the maximum duration of synthetic delays is limited by the duration of the impulse responses of cochlear filters itself inversely proportional to cochlear filter bandwidth maximum delay is thus frequency dependent this may explain the fact puzzling for temporal pitch models such as autocorrelation that pitch is more salient and eas

effects of spectral smearing and temporal fine structure degradation on speech masking release this study assessed the effects of spectral smearing and temporal fine structure tfs degradation on masking release mr the improvement in speech identification in amplitude modulated compared to steady noise observed for normal hearing listeners syllables and noise stimuli were processed using either a spectral smearing algorithm or a tone excited vocoder the two processing schemes simulated broadening of the auditory filters by factors of 2 and 4 simulations of the early stages of auditory processing showed that the two schemes produced comparable excitation patterns however fundamental frequency f0 information conveyed by tfs was degraded more severely by the vocoder than by the spectral smearing algorithm both schemes reduced mr but for each amount of spectral smearing the vocoder produced a greater reduction in mr than the spectral smearing algorithm consistent with the effects of each scheme on f0 representation moreover the effects of spectral smearing on mr produced by the two schemes were different for manner and voicing finally mr data for listeners with moderate hearing loss were well matched by mr data obtained for normal hearing listeners with vocoded stimuli suggesting that impaired frequency selectivity alone may not be sufficient to account for the reduced mr observed for hearing impaired listeners

perception of the envelope beat frequency of inharmonic complex temporal envelopes listeners can hear slow sinusoidal variations in the depth of sinusoidally amplitude modulated sam stimuli here the sam stimulus of frequency fm acts as the carrier and the slow variation in depth of frequency fm referred to as second order amplitude modulation corresponds to a beat in the temporal envelope recent studies have suggested that second order amplitude modulation perception is based on a modulation distortion component or the venelope the hilbert envelope of the ac coupled hilbert envelope both occurring at the envelope beat frequency fm this was tested by transposing to the modulation domain the matching paradigm used by schouten et al j acoust soc am 34 1418 1424 1962 listeners estimated the envelope beat frequency evoked by a 5 hz second order sam white noise with fm either an integer multiple of fm or shifted in frequency to make the complex envelope inharmonic the results indicate that the perception of the envelope beat frequency was affected by these shif

pitch discrimination by ferrets for simple and complex sounds although many studies have examined the performance of animals in detecting a frequency change in a sequence of tones few have measured animals discrimination of the fundamental frequency f0 of complex naturalistic stimuli additionally it is not yet clear if animals perceive the pitch of complex sounds along a continuous low to high scale here four ferrets mustela putorius were trained on a two alternative forced choice task to discriminate sounds that were higher or lower in f0 than a reference sound using pure tones and artificial vowels as stimuli average weber fractions for ferrets on this task varied from 20 to 80 across references 200 1200 hz and these fractions were similar for pure tones and vowels these thresholds are approximately ten times higher than those typically reported for other mammals on frequency change detection tasks that use go no go designs naive human listeners outperformed ferrets on the present task but they showed similar effects of stimulus type and refe

a signal detection analysis of auditory frequency discrimination in the rat the frequency discrimination behavior of rats in a simple go no go task was analyzed using the theory of signal detection discrimination acuity was studied and the receiver operating characteristic roc was generated in subjects by varying the reinforcement schedule and signal probability the detectability indices d a and sensitivity index si and response bias indices b and responsivity index ri were used to describe behavior a gave the most suitable psychometric functions while ri best described response bias behavior weber ratios were 6 25 0 23 at 5 khz in three subjects the best method to obtain the roc was to vary the probability with which subjects were reinforced the roc in two subjects demonstrated classical forms in another subject the function was asymmetric to the extent that detectability was not independent of response bias subjects altered their decision criterion in reporting a signal from trial to trial depending on previous trial events on any given trial subjects made a decision in one of several decision states variables that influenced decision states included previous reinforcement and timeouts the data indicate that timeouts may not be a useful feature in go no go tasks the identification of multiple decision states within a single behavioral session is a convenient method to generate the roc without expressly manipulating experimental conditions

pitch strength of iterated rippled noise when the pitch is ambiguous two versions of a cascade of delay gain following delay and add circuits were used to generate iterated rippled noise irn stimuli irn stimuli produce a repetition pitch whose pitch strength relative to the noise percept can be varied by changing the type of circuit the attenuation or the number of iterations in the circuit the repetition pitch of irn is different when the delayed noise is subtracted gain 0 to the undelayed noise in the case of subtraction irn pitch is often ambiguous having two or more pitches listeners were asked to use pitch strength to discriminate between various pairs of irn stimuli generated with different gains different network circuits and different number of iterations for most conditions the gain was less than one the data were described by a description based on an exponential function of the largest peak of the autocorrelation function of irn stimuli w a yost j acoust soc am 100 511 518 1996 processed such that the spectral dominance region is emphasized these results suggest that the strength of the pitch of irn stimuli can be described by temporal processing mechanisms as might be revealed by autocorrelation

effect of adaptive psychophysical procedure on loudness matches large variability in equal loudness matches has been observed across studies the purpose of the present study was to gain insight into the extent to which this variability results from differences in psychophysical procedures and or differences among listeners four adaptive two interval two alternatives forced choice procedures were used to obtain equal loudness matches between 5 and 200 ms 1 khz tones as a function of level for each of six normal listeners the procedures differed primarily in the sequence in which the stimuli were presented the variations tested were the ordering of stimuli by amplitude across blocks of trials both increasing and decreasing amplitudes randomizing the order across those blocks and randomizing the order within blocks the random within block procedure which sought to randomize any intertrial information yielded a significantly greater amount of temporal integration than the other three procedures the results show significant differences in temporal integration

psychoacoustic and phonetic temporal processing in normal and hearing impaired listeners four measures of auditory temporal processing were obtained from 16 normals and 16 individuals with a hearing loss of heterogeneous origin these measures were 1 temporal integration the difference in detection thresholds between signals of 10 and 1000 ms duration which was determined to provide an estimate of the ability to integrate energy over time 2 gap detection the shortest duration of silence between two noise bursts that can be discriminated from an uninterrupted noise 3 temporal difference limen the increment in duration necessary to detect a difference in the duration of a noise burst 4 gap difference limen the increment in duration necessary to detect a difference in the duration of a silent interval between two noise bursts each measure was obtained for stimuli centered both at 500 and at 4000 hz using a three alternative forced choice procedure in addition measures of identification and discrimination were obtained for two sets of synthetic speech syllables varying chiefly in a temporal parameter voice onset time from ba to pa and from bi to pi finally speech identification in noise was measured with the faaf test most of the hearing impaired listeners displayed poorer temporal analysis than the normals on all of the psychoacoustical tasks regardless of whether the two groups were compared at similar sound pressure levels or at similar sensation levels although the hearing impaired listeners displayed a reduction in the ability to discriminate subphonemic cues for the voiced voiceless distinction their identification of that distinction in stop consonants appeared to be normal the hearing impaired group made about twice as many errors as did the normals on each of the consonant features of place manner and voicing when identifying speech in noise increased temporal difference limen and longer gap detection thresholds were found to correlate significantly with reduced speech intelligibility in noise even when the effects of the pure tone threshold loss were partialed out

frame synchronization for optical overlapping pulse position modulation systems the maximum likelihood rules for locating data frames in direct detection optical communication systems utilizing overlapping pulse position modulation oppm are derived under two distinct assumptions of symbol and chip synchronization respectively various approximations to the optimal rules are identified as well as upper and lower bounds on the probability of correct synchronization further the problem of sequence design based on a maximum peak to sidelobe distance criterion is studied and upper bounds on peak to sidelobe distance for sequences of oppm symbols are derived some good sequences are obtained through a computer search

perception of the pitch of unresolved harmonics by 3 and 7 month old human infants three month olds discriminate resolved harmonic complexes on the basis of missing fundamental mf pitch in view of reported difficulty in discriminating unresolved complexes at 7 months and striking changes in the organization of the auditory system during early infancy infants ability to discriminate unresolved complexes is of some interest this study investigated the ability of 3 month olds 7 month olds and adults to discriminate the pitch of unresolved harmonic complexes using an observer based method stimuli were mf complexes bandpass filtered with a 12 db octave slope combined in random phase presented at 70 db sound pressure level spl for 650 ms with a 50 ms rise fall with a pink noise at 65 db spl the conditions were 1 low unresolved harmonics 2500 4500 hz based on mfs of 160 and 200 hz and 2 high unresolved harmonics 4000 6000 hz based on mfs of 190 and 200 hz to demonstrate mf discrimination participants had to ignore spectral changes in complexes with the same fundamental and respond only when the fundamental changed nearly all infants tested categorized complexes by mf pitch suggesting discrimination of pitch extracted from unresolved harmonics by 3 months adults also categorized the complexes by mf pitch although musically trained adults were more successful than musically untrained adults

on sequential frame synchronization in awgn channels we present a framework for the analysis of frame synchronization based on synchronization words sws where the detection is based on the following sequential algorithm the received samples are observed over a window of length equal to the sw over this window a metric e g correlation is computed an sw is declared if the computed metric is greater than a proper threshold otherwise the observation window is time shifted one sample we assume a gaussian channel antipodal signaling equally distributed data symbols and coherent detection where soft values are provided to the frame synchronizer we state the problem starting from the hypothesis testing theory deriving the optimum metric optimum likelihood ratio test lrt according to the neyman pearson lemma when the data distribution is unknown we design a simple and effective test based on the generalized lrt glrt we also analyze the performance of the commonly used correlation metric both with hard and soft values at the synchronizer input we show that synchronization can be greatly improved by using the lrt and glrt metrics instead of correlation and that among correlation based tests sometimes hard correlation is better than soft correlation the obtained closed form expressions allow the derivation of the receiver operating characteristic roc curves for the lrt and glrt synchronizers showing a remarkable gain with respect to synchronization based on correlation metric

growth of masking as a measure of response growth in hearing impaired listeners growth of masking functions were obtained from 19 normal and 5 hearing impaired listeners using a simultaneous masking paradigm when masker and probe frequency are identical the slope of masking approximates 1 0 for both normal hearing and impaired listeners for masker frequencies less than or greater than probe frequency the slopes for impaired listeners are shallower than those of normals these findings are consistent with previously reported physiological data single fiber rate versus level and ap masking functions for animals with induced cochlear lesions results are discussed in terms of a potential masking technique to estimate the growth of response in normal and impaired ears

optimal sequential frame synchronization we consider the ldquoone shot frame synchronization problem rdquo where a decoder wants to locate a sync pattern at the output of a memoryless channel on the basis of sequential observations the sync pattern of length n starts being emitted at a random time within some interval of size a where a characterizes the asynchronism level we show that a sequential decoder can optimally locate the sync pattern i e exactly without delay and with probability approaching one as n rarr infin if the asynchronism level grows as o enalpha with alpha below the synchronization threshold a constant that admits a simple expression depending on the channel if alpha exceeds the synchronization threshold any decoder sequential or nonsequential locates the sync pattern with an error that tends to one as nrarr infin hence a sequential decoder can locate a sync pattern as well as the nonsequential maximum likelihood decoder that operates on the basis of output sequences of maximum length a n 1 but with far fewer observations

good synchronization sequences for permutation codes for communication schemes employing frequency hopping multiple frequency shift keying modulation we present an algorithm for finding good non binary synchronization sequences which are permutations to be used with permutation codes to synchronize resynchronize data in channels with background noise and interference frequency jamming fading for the synchronization sequences new analytical expressions for the probability of false acquisition are also given using simulation results we show that our synchronization sequences perform better than some conventional non binary synchronization sequences in the presence of background noise and interference

pitch discrimination of diotic and dichotic tone complexes harmonic resolvability or harmonic number three experiments investigated the relationship between harmonic number harmonic resolvability and the perception of harmonic complexes complexes with successive equal amplitude sine or random phase harmonic components of a 100 or 200 hz fundamental frequency f0 were presented dichotically with even and odd components to opposite ears or diotically with all harmonics presented to both ears experiment 1 measured performance in discriminating a 3 5 5 frequency difference between a component of a harmonic complex and a pure tone in isolation listeners achieved at least 75 correct for approximately the first 10 and 20 individual harmonics in the diotic and dichotic conditions respectively verifying that only processes before the binaural combination of information limit frequency selectivity experiment 2 measured fundamental frequency difference limens f0 dls as a function of the average lowest harmonic number similar results at both f0 s provide further evidence that harmonic number not absolute frequency underlies the order of magnitude increase observed in f0 dls when only harmonics above about the 10th are presented similar results under diotic and dichotic conditions indicate that the auditory system in performing f0 discrimination is unable to utilize the additional peripherally resolved harmonics in the dichotic case in experiment 3 dichotic complexes containing harmonics below the 12th or only above the 15th elicited pitches of the f0 and twice the f0 respectively together experiments 2 and 3 suggest that harmonic number regardless of peripheral resolvability governs the transition between two different pitch percepts one based on the frequencies of individual resolved harmonics and the other based on the periodicity of the temporal envelope

pitch strength and pitch dominance of iterated rippled noises in hearing impaired listeners reports using a variety of psychophysical tasks indicate that pitch perception by hearing impaired listeners may be abnormal contributing to difficulties in understanding speech and enjoying music pitches of complex sounds may be weaker and more indistinct in the presence of cochlear damage especially when frequency regions are affected that form the strongest basis for pitch perception in normal hearing listeners in this study the strength of the complex pitch generated by iterated rippled noise was assessed in normal hearing and hearing impaired listeners pitch strength was measured for broadband noises with spectral ripples generated by iteratively delaying a copy of a given noise and adding it back into the original octave band pass versions of these noises also were evaluated to assess frequency dominance regions for rippled noise pitch hearing impaired listeners demonstrated consistently weaker pitches in response to the rippled noises relative to pitch strength in normal hearing listeners

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

frame synchronization in the presence of frequency offset a new frame synchronization technique which is robust to carrier frequency and phase errors is proposed for m ary psk systems this technique is derived through modification of the procedure used for obtaining the maximum likelihood ml rule in the paper by gansman et al 1997 the proposed rule is based on an operation called a double correlation which evaluates a correlation after properly multiplying the received signal with a sync pattern it was shown through computer simulation that the proposed rule generally outperformed the existing rules when a frequency offset existed

sequential frame synchronization based on hypothesis testing with unknown channel state information in this paper we propose a hypothesis testing based sequential frame synchronization technique that is robust against fluctuations and imperfect estimation of channel gain at the receiver the proposed detector uses division in the decision rule to cancel the effect of channel gain and therefore is called division based hypothesis testing dht we show that the receiver operating characteristic roc of dht is close to the optimal likelihood ratio test lrt while the optimal lrt requires perfect knowledge of noise and channel gain at the receiver further we use three performance metrics namely the probability of false synchronization p fs average reception duration l rx and probability of missed synchronization p ms to compare the performance of hypothesis testing against that of point estimation we analytically show that hypothesis testing can have better reliability and lower energy consumption than point estimation if the probability of false alarm of the hypothesis testing is lower than the minimum of two thresholds the cost of hypothesis testing is an arbitrarily small p ms while point estimation can have zero p ms a modified implementation of hypothesis testing is also introduced to further reduce the energy consumption

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

the importance of temporal fine structure information in speech at different spectral regions for normal hearing and hearing impaired subjects speech reception thresholds srts were measured for target and competing speech signals processed to contain variable amounts of temporal fine structure tfs information signals were filtered into 30 1 erb n wide channels where erb n refers to the bandwidth of normal auditory filters which were either tone vocoded preserving temporal envelope information extracted using the hilbert transform or left unprocessed containing both tfs and envelope information improvements in srt were compared when tfs was progressively introduced starting with the high or low frequency channels the results suggest some redundancy in the tfs information across frequency regions in a second experiment the signal was divided into five 6 erb n wide spectral regions four of which were tone vocoded the remaining region was either absent creating a spectral notch or was present and unprocessed srts were measured for normal hearing and hearing impaired subjects conditions where all channels were vocoded or unprocessed were also included normal hearing subjects benefited similarly when tfs information was added to each region suggesting that tfs information is important over a wide frequency range hearing impaired subjects benefited less although the benefit varied across subjects benefit from tfs information in speech was correlated with a psychophysical measure of tfs sensitivity obtained at two center frequencies

gap detection in normal and hearing impaired listeners temporal resolution estimated by measuring the minimum detectable gap t msec separating two successive signals was assessed in five normal hearing and five cochlear impaired listeners the signals were octave band noises 400 800 hz 800 1600 hz and 2000 4000 hz presented in a background of continuous broadband notched noise that was applied to eliminate unwanted spectral cues temporal resolution in all listeners showed systematic improvement with an increase in octave band center frequency resolution in the hearing impaired subjects was significantly poorer than normal regardless of whether the comparisons were made at equal sound pressure level or at equal sensation level

the role of stimulus complexity spectral overlap and pitch for gap detection thresholds in young and old listeners thresholds for detecting a gap between two complex tones were determined for young listeners with normal hearing and old listeners with mild age related hearing loss the leading tonal marker was always a 20 ms 250 hz complex tone with energy at 250 500 750 and 1000 hz the lagging marker also tonal could differ from the leading marker with respect to fundamental frequency f0 the presence versus absence of energy at f0 and the degree to which it overlapped spectrally with the leading marker all stimuli were presented with steeper 1 ms and less steep 4 ms envelope rise and fall times f0 differences decreases in the degree of spectral overlap between the markers and shallower envelope shape all contributed to increases in gap detection thresholds age differences for gap detection of complex sounds were generally small and constant when gap detection thresholds were measured on a log scale when comparing the results for complex sounds to thresholds obtained for pure tones in a previous study by heinrich and schneider 2006 j acoust soc am 119 2316 2326 thresholds increased in an orderly fashion from markers with identical within channel pure tones to different between channel pure tones to complex sounds this pattern of results was true for listeners of both ages although younger listeners had smaller thresholds overall

recent results on polyphase sequences a polyphase sequence of length n 1 a a sub j sub j 0 sup n is a sequence of complex numbers each of unit magnitude the unnormalized aperiodic autocorrelation function of a sequence is denoted by c spl tau associated with the sequence a the sequence polynomial f sub a z of degree n and the correlation polynomial g sub a z of degree 2n are defined for each root spl alpha of f sub a z 1 spl alpha is a corresponding root of f sub a z sup 1 transformations on the sequence a which leave c spl tau invariant are exhibited and the effects of these transformations on the roots of f sub a z are described an investigation of the set of roots a of the polynomial f sub a z has been undertaken in an attempt to relate these roots to the behavior of c spl tau generalized barker 1952 1953 sequences are considered as a special case of polyphase sequences and examples are given to illustrate the relationship described above

the effects of age and cochlear hearing loss on temporal fine structure sensitivity frequency selectivity and speech reception in noise temporal fine structure tfs sensitivity frequency selectivity and speech reception in noise were measured for young normal hearing nhy old normal hearing nho and hearing impaired hi subjects two measures of tfs sensitivity were used the tfs lf test interaural phase difference discrimination and the tfs2 test discrimination of harmonic and frequency shifted tones these measures were not significantly correlated with frequency selectivity after partialing out the effect of audiometric threshold suggesting that insensitivity to tfs cannot be wholly explained by a broadening of auditory filters the results of the two tests of tfs sensitivity were significantly but modestly correlated suggesting that performance of the tests may be partly influenced by different factors the nho group performed significantly more poorly than the nhy group for both measures of tfs sensitivity but not frequency selectivity suggesting that tfs sensitivity declines with age in the absence of elevated audiometric thresholds or broadened auditory filters when the effect of mean audiometric threshold was partialed out speech reception thresholds in modulated noise were correlated with tfs2 scores but not measures of frequency selectivity or tfs lf test scores suggesting that a reduction in sensitivity to tfs can partly account for the speech perception difficulties experienced by hearing impaired subjects

modeling the perception of concurrent vowels vowels with different fundamental frequencies if two vowels with different fundamental frequencies f0 s are presented simultaneously and monaurally listeners often hear two talkers producing different vowels on different pitches this paper describes the evaluation of four computational models of the auditory and perceptual processes which may underlie this ability each model involves four stages i frequency analysis using an auditory filter bank ii determination of the pitches present in the stimulus iii segregation of the competing speech sources by grouping energy associated with each pitch to create two derived spectral patterns and iv classification of the derived spectral patterns to predict the probabilities of listeners vowel identification responses the place models carry out the operations of pitch determination and spectral segregation by analyzing the distribution of rms levels across the channels of the filter bank the place time models carry out these operations by analyzing the periodicities in the wavef

relationship between frequency selectivity and frequency discrimination measured in subjects with unilateral and bilateral cochlear impairments frequency selectivity refers to the filtering processes which underlie our ability to detect a sound of one frequency in the presence of another sound with a different frequency frequency discrimination is our ability to detect changes in frequency over time it is a basic tenet of the place theory that frequency discrimination depends upon frequency selectivity in this paper we describe an experimental test of a place model put forward by zwicker 1956 in which frequency discrimination is explained in terms of excitation patterns the model is illustrated schematically in fig 1 which shows excitation patterns calculated using the method described by moore and glasberg 1983 for two sinusoids with frequencies 1180 and 1220 hz zwicker assumed that the frequencies of the two sinusoids can be discriminated if their excitation patterns differ at any point by more than a criterion amount he assumed a criterion of 1 db

further evidence that fundamental frequency difference limens measure pitch discrimination difference limens for complex tones dlcs that differ in f0 are widely regarded as a measure of periodicity pitch discrimination however because f0 changes are inevitably accompanied by changes in the frequencies of the harmonics dlcs may actually reflect the discriminability of individual components to test this hypothesis dlcs were measured for complex tones the component frequencies of which were shifted coherently upward or downward by f 0 25 37 5 or 50 of the f0 yielding fully harmonic f 0 strongly inharmonic f 25 37 5 or odd harmonic f 50 tones if dlcs truly reflect periodicity pitch discriminability they should be larger worse for inharmonic tones than for harmonic and odd harmonic tones because inharmonic tones have a weaker pitch consistent with this prediction the results of two experiments showed a non monotonic dependence of dlcs on f with larger dlcs for f s of 25 or 37 5 than for f s of 0 or 50 of f0 these findings are consistent with

on the search for a sequence from a predefined set of sequences in random and framed data streams in this paper we present a statistical analysis of the search for a set of predefined sequences in non equiprobable data streams both random and framed and derive a number of corresponding statistical parameters most importantly we derive the probability of occurrence of some sequence from the set at any given position from which all other statistical quantities of interest can be obtained the presented analysis is based on descriptors called cross bifices which express similarities among sequences in the set based on the obtained results we examine the problem of frame synchronization in synchronous transmission and derive parameters that could be used for the evaluation of the properties of frame synchronization sequences we introduce a survival probability of the search in a frame and a list miss probability for the list synchronizer which give exact bounds on the probability of correct frame synchronization when hard correlation is used as a sequence detection metric

on the relative influence of individual harmonics on pitch judgment spectral weighting functions were estimated in a pitch comparison task to assess the relative influence of individual harmonics on listeners pitch judgment the stimuli were quasi harmonic complex tones composed of the first 12 components with fundamental frequencies ranging from 100 to 800 hz on each stimulus presentation the frequency of each harmonic was randomly jittered by a small amount the perceptual weight for each harmonic was calculated as the correlation coefficient between the binary responses of the listener and the frequency jitters for that harmonic although in general the present results conform to previous ones showing the predominant role of several low ranked harmonics discrepancies exist in details contrary to some previous reports that the dominant harmonics were of fixed harmonic ranks regardless of their frequencies the current results showed that the dominant harmonics were best described as close to a fixed absolute frequency of 600 hz

simulation of the effect of threshold elevation and loudness recruitment combined with reduced frequency selectivity on the intelligibility of speech in noise the effect of loudness recruitment and threshold elevation together with reduced frequency selectivity have been simulated to examine the combined effect of the two major consequences of cochlear hearing loss on the intelligibility of speech in speech shaped noise in experiment 1 four conditions were simulated a moderate flat loss with auditory filters broadened by a factor of three b3r2 a moderate to severe sloping loss with auditory filters broadened by a constant factor of three b3rx and these conditions with linear amplification applied prior to the simulation processing b3r2 b3rx for conditions b3r2 and b3rx performance was markedly worse than for a control condition normal hearing condition r1 tested in a previous study for conditions b3r2 and b3rx linear amplification improved performance considerably however performance remained below that for condition r1 by between 5 and 19 in experiment 2 the broadening of the auditory filters was made more realistic by making it a function of the absolute threshold at the center frequency of the auditory filter three different hearing losses were simulated a moderate to severe sloping loss with variable broadening of the auditory filters bxrx the same moderate to severe sloping loss with linear amplification bxrx and the same broadening of the auditory filters but without the simulation of loudness recruitment and threshold elevation bx for condition bxrx performance was markedly worse than in condition r1 while performance in condition bx was somewhat worse than for condition r1 for condition bxrx linear amplification according to the nal procedure improved performance to a large extent but it remained worse than for condition r1 the results are consistent with previous evidence indicating that only part of the decrease of performance produced by actual cochlear hearing loss can be compensated by conventional linear hearing aids

temporal modulation transfer functions for listeners with real and simulated hearing loss a functional simulation of hearing loss was evaluated in its ability to reproduce the temporal modulation transfer functions tmtfs for nine listeners with mild to profound sensorineural hearing loss each hearing loss was simulated in a group of three age matched normal hearing listeners through spectrally shaped masking noise or a combination of masking noise and multiband expansion tmtfs were measured for both groups of listeners using a broadband noise carrier as a function of modulation rate in the range 2 to 1024 hz the tmtfs were fit with a lowpass filter function that provided estimates of overall modulation depth sensitivity and modulation cutoff frequency although the simulations were capable of accurately reproducing the threshold elevations of the hearing impaired listeners they were not successful in reproducing the tmtfs on average the simulations resulted in lower sensitivity and higher cutoff frequency than were observed in the tmtfs of the hearing impaired listeners discrepancies in performance between listeners with real and simulated hearing loss are possibly related to inaccuracies in the simulation of recruitment

auditory filter shapes of normal hearing and hearing impaired listeners in continuous broadband noise listeners with sensorineural hearing impairment typically exhibit auditory processing deficits such as reduced frequency and or temporal resolution such deficits may represent separate sequela of auditory pathology or may result directly from the sensitivity loss and the requirement to listen at high levels to assess the impact of increased thresholds on frequency resolution auditory filter characteristics were determined for hearing impaired and normal hearing listeners at 500 and 2000 hz in the presence of continuous broadband noise meant as a rough simulation of hearing loss in the fitting procedure the low frequency skirt of the derived auditory filter was allowed to vary as a function of signal level permitting different filter shapes to be estimated at high versus low signal levels listeners with moderate hearing losses at 2000 hz demonstrated near normal auditory filter shapes for lower signal levels but increasingly broad and asymmetric filters as signal level was raised at 500 hz where hearing losses were mild filter bandwidths increased little at the higher signal levels the presence of broadband noise had essentially no effect on filter shapes of either listener group the filter shape abnormalities demonstrated by listeners with moderate hearing loss which were not observed in normal hearing listeners at the same signal levels indicate that poor frequency resolution in these patients for high intensity stimuli does not follow directly from decreased sensitivity but instead reflects an independent pathology

pitch strength of iterated rippled noise two versions of a cascade add attenuate and delay circuit were used to generate iterated rippled noise irn stimuli irn stimuli produce a repetition pitch whose pitch strength relative to the noise percept can be varied by changing the type of circuit the attenuation or the number of iterations in the circuit listeners were asked to use pitch strength to discriminate between various pairs of irn stimuli which differed in the type of network used to generate the sounds the number of iterations and the attenuation in the network a description based on an exponential function of the first peak of the autocorrelation function of irn stimuli is consistent with the results the discrimination data were well fit by a function based on the difference in the exponential functions of the first peak of the autocorrelation functions a magnitude estimation experiment indicated that pitch strength was an exponential function of the height of the first peak in the autocorrelation function these results suggest that the strength of the pitch of irn stimuli is based on temporal processing as might be revealed by autocorrelation

effect of duration on the frequency discrimination of individual partials in a complex tone and on the discrimination of fundamental frequency thresholds for the discrimination of fundamental frequency fodls and frequency difference limens fdls for individual partials within a complex tone f0 250 hz harmonics 1 7 were measured for stimulus durations of 200 50 and 16 ms the fdls increased with decreasing duration although the results differed across subjects the effect of duration generally decreased as the harmonic number increased from 1 to 4 then increased as the harmonic number increased to 6 and finally decreased for the seventh harmonic for each duration fodls were smaller than the smallest fdl for any individual harmonic indicating that information is combined across harmonics in the discrimination of fo fodls predicted from the fdls corresponded well with observed fodls for the 200 and 16 ms durations but were significantly larger than observed fodls for the 50 ms duration a supplementary pitch matching experiment using two subjects indicated that the contribution of the seventh harmonic to the pitch of the 16 ms complex tone was smaller than would be predicted from the fdl for that harmonic the results are consistent with the idea that the dominant region shifts upward with decreasing duration but that the weight assigned to individual harmonics is not always adjusted in an optimal way

analysis of optimum frame synchronization based on periodically embedded sync words we present new tight bounds for evaluating the performance of sync word based frame synchronization algorithms in the periodically embedded case we consider antipodal signaling with coherent detection over additive white gaussian noise and both optimal and suboptimal search techniques our bounds are very close to results obtained through simulation and tend asymptotically for increasing signal to noise ratios to the exact performance

pitch of iterated rippled noise iterated rippled noise irn stimuli are generated by a cascade of delay d gain g and add networks the matched pitch of irn stimuli was determined as a function of the type of network used to generate irn stimuli the delay d 2 4 and 8 ms the number of iterations n 1 2 3 4 6 8 of the delay and add networks and whether the delayed noise was added g 1 to or subtracted g 1 from the undelayed noise the matched pitch of irn stimuli did not depend on the type of network when g 1 addition the matched pitch did not depend on the number of stages of iterations n and was always equal to the reciprocal of the delay 1 d when g 1 subtraction the match pitch depended on n when n 1 the matched pitch of irn stimuli was ambiguous having two pitches in the region of 1 d 10 when n 8 the match pitch was equal to 1 2d this change in the pitch occurred between n 2 and 6 the results are discussed in terms of spectral and temporal models of complex pitch processing a temporal model based on autocorrelation was able to provide quantitative predictions for the pitch of these irn stimuli however a spectral type of model can also account for the pitch of these irn stimuli

the effect of hearing loss on the resolution of partials and fundamental frequency discrimination the relationship between the ability to hear out partials in complex tones discrimination of the fundamental frequency f0 of complex tones and frequency selectivity was examined for subjects with mild to moderate cochlear hearing loss the ability to hear out partials was measured using a two interval task each interval included a sinusoid followed by a complex tone one complex contained a partial with the same frequency as the sinusoid while in the other complex that partial was missing subjects had to indicate the interval in which the partial was present in the complex the components in the complex were uniformly spaced on the erbn number scale performance was generally good for the two edge partials but poorer for the inner partials performance for the latter improved with increasing spacing f0 discrimination was measured for a bandpass filtered complex tone containing low harmonics the equivalent rectangular bandwidth erb of the auditory filter was estimated using the notched noise

a new approach to cross bifix free sets cross bifix free sets are sets of words such that no prefix of any word is a suffix of any other word in this paper we introduce a general constructive method for the sets of cross bifix free binary words of fixed length it enables us to determine a cross bifix free words subset which has the property to be non expandable

the role of excitation pattern temporal fine structure and envelope cues in the discrimination of complex tones the discrimination of bandpass filtered harmonic h from inharmonic i tones produced by shifting all components of the h tones upwards by a fixed amount in hz could be based on shifts in the pattern of ripples in the excitation pattern ep or on changes in the temporal fine structure evoked by the tones the predictions of two computational ep models were compared with measured performance one model used auditory filters with bandwidth values specified by glasberg and moore 1990 hear res 47 103 138 and one used filters that were twice as sharp stimulus variables were passband width fundamental frequency harmonic rank n of the lowest component within the passband component phase cosine or random signal to noise ratio snr and random perturbation in level of each component in the tones while the ep models correctly predicted the lack of an effect of phase and some of the trends in the data as a function of fundamental frequency and n neither model predicted the worsening in perfo

perception of missing fundamental pitch by 3 and 4 month old human infants a hallmark of complex pitch perception is that the pitch of a harmonic complex is the same whether or not the fundamental frequency is present by 7 months infants appear to discriminate on the basis of the pitch of the missing fundamental mf although electrophysiological cortical responses to mf pitch changes have been recorded in infants younger than 7 months no psychophysical studies have been published this study investigated the ability of 3 and 4 month olds to perceive the pitch of mf harmonic complexes based on fundamentals of 160 hz and 200 hz using an observer based method in experiment i to demonstrate mf pitch discrimination 3 and 4 month olds were required to ignore spectral changes in complexes with the same fundamental and to respond only when the fundamental changed in experiment ii a 60 260 hz noise was presented with complexes to mask combination tones at the fundamental frequency in experiment iii complexes were bandpass filtered with a 12 db octave slope to limit use of

comparisons of frequency selectivity in simultaneous and forward masking for subjects with unilateral cochlear impairments two experiments are described in which frequency selectivity was estimated in simultaneous and forward masking for each ear of subjects with moderate 25 60 db hl unilateral cochlear hearing losses in both experiments the signal level was fixed for a given ear and type of masking simultaneous or forward and the masker level was varied to determine threshold using an adaptive two alternative forced choice procedure in experiment i the masker was a noise with a spectral notch centered at the signal frequency either 1 0 or 1 5 khz threshold was determined as a function of notch width signal levels were chosen so that the noise level required at threshold for a notch width of zero was similar for the normal and impaired ear of each subject in both simultaneous and forward masking the function relating threshold to notch width had a steeper slope for the normal ear than for the impaired ear of each subject for the normal ears these functions were steeper in forward masking than in simultaneous masking this difference was interpreted as resulting from suppression for the impaired ears significant differences in the same direction were observed for three of the five subjects but the differences were smaller in experiment ii psychophysical tuning curves ptcs were determined in the presence of a fixed notched noise centered at the signal frequency 1 0 khz for the normal ears the ptcs were sharper in forward masking than in simultaneous masking for the impaired ears the ptcs were similar in simultaneous and forward masking but those in forward masking tended to be sharper at masker frequencies far removed from the signal frequency overall the results suggest that suppression is reduced but not completely absent in cases of moderate cochlear hearing loss

pitch discrimination and phase sensitivity in young and elderly subjects and its relationship to frequency selectivity frequency difference limens for pure tones dlfs and for complex tones dlcs were measured for four groups of subjects young normal hearing young hearing impaired elderly with near normal hearing and elderly hearing impaired the auditory filters of the subjects had been measured in earlier experiments using the notched noise method for center frequencies fc of 100 200 400 and 800 hz the dlfs for both impaired groups were higher than for the young normal group at all fc s 50 4000 hz the dlfs at a given fc were generally only weakly correlated with the sharpness of the auditory filter at that fc and some subjects with broad filters had near normal dlfs at low frequencies some subjects in the elderly normal group had very large dlfs at low frequencies in spite of near normal auditory filters these results suggest a partial dissociation of frequency selectivity and frequency discrimination of pure tones the dlcs for the two impaired groups were higher than those for the young normal group at all fundamental frequencies fo tested 50 100 200 and 400 hz the dlcs for the elderly normal group were intermediate at fo 50 hz dlcs for a complex tone containing only low harmonics 1 5 were markedly higher than for complex tones containing higher harmonics for all subject groups suggesting that pitch was conveyed largely by the higher unresolved harmonics for the elderly impaired group and some subjects in the elderly normal group dlcs were larger for a complex tone with lower harmonics 1 12 than for tones without lower harmonics 4 12 and 6 12 for fo s up to 200 hz some elderly normal subjects had markedly larger than normal dlcs in spite of near normal auditory filters the dlcs tended to be larger for complexes with components added in alternating sine cosine phase than for complexes with components added in cosine phase phase effects were significant for all groups but were small for the young normal group the results are not consistent with place based models of the pitch perception of complex tones rather they suggest that pitch is at least partly determined by temporal mechanisms

perception of the low pitch of frequency shifted complexes when all of the components in a harmonic complex tone are shifted in frequency by f the pitch of the complex shifts roughly in proportion to f for tones with a small number of components the shift is usually somewhat larger than predicted from pitch theories which has been attributed to the influence of combination tones smoorenburg j acoust soc am 48 924 941 1970 experiment 1 assessed whether combination tones influence the pitch of complex tones with more than five harmonics by using noise to mask the combination tones the matching stimulus was a harmonic complex test complexes were bandpass filtered with passbands centered on harmonic numbers 5 resolved 11 intermediate or 16 unresolved and fundamental frequencies f0s were 100 200 or 400 hz for the intermediate and unresolved conditions the matching stimuli were filtered with the same passband to minimize differences in the excitation patterns of the test and matching stimuli for the resolved condition the matching st

blind frame synchronization for error correcting codes having a sparse parity check matrix we present in this letter a blind frame synchronization method based on a maximum a posteriori probability map approach applied to coded communication systems this method is based on the calculation of the log likelihood ratios llr of the syndrome obtained according to the parity check matrix of the code after presenting the proposed method we compare it to an existing blind synchronization method previously introduced simulation results show that the proposed method outperforms the existing one and presents good performance when applied to codes having a sparse parity check matrix such as low density parity check ldpc codes and convolutional codes

moderate cochlear hearing loss leads to a reduced ability to use temporal fine structure information the ability of normally hearing and hearing impaired subjects to use temporal fine structure information in complex tones was measured subjects were required to discriminate a harmonic complex tone from a tone in which all components were shifted upwards by the same amount in hz in a three alternative forced choice task the tones either contained five equal amplitude components non shaped stimuli or contained many components but were passed through a fixed bandpass filter to reduce excitation pattern changes shaped stimuli components were centered at nominal harmonic numbers n 7 11 and 18 for the shaped stimuli hearing impaired subjects performed much more poorly than normally hearing subjects with most of the former scoring no better than chance when n 11 or 18 suggesting that they could not access the temporal fine structure information performance for the hearing impaired subjects was significantly improved for the non shaped stimuli presumably because they could benefit from spectral cues it is proposed that normal hearing subjects can use temporal fine structure information provided the spacing between fine structure peaks is not too small relative to the envelope period but subjects with moderate cochlear hearing loss make little use of temporal fine structure information for unresolved components

exploring the temporal mechanism involved in the pitch of unresolved harmonics this paper continues a line of research initiated by kaernbach and demany j acoust soc am 104 2298 2306 1998 who employed filtered click sequences to explore the temporal mechanism involved in the pitch of unresolved harmonics in a first experiment the just noticeable difference jnd for the fundamental frequency f0 of high pass filtered and low pass masked click trains was measured with f0 100 to 250 hz and the cut frequency 0 5 to 6 khz being varied orthogonally the data confirm the result of houtsma and smurzynski j acoust soc am 87 304 310 1990 that a pitch mechanism working on the temporal structure of the signal is responsible for analyzing frequencies higher than ten times the fundamental using high pass filtered click trains however the jnd for the temporal analysis is at 1 2 as compared to 2 3 found in studies using band pass filtered stimuli two further experiments provide evidence that the pitch of this stimulus can convey musical information a fourth experiment replicates the finding of kaernbach and demany on first and second order regularities with a cut frequency of 2 khz and extends the paradigm to binaural aperiodic click sequences the result suggests that listeners can detect first order temporal regularities in monaural click streams as well as in binaurally fused click streams

a time domain description for the pitch strength of iterated rippled noise two versions of a cascaded add attenuate and delay circuit were used to generate iterated rippled noise irn stimuli irn stimuli produce a repetition pitch whose strength relative to the noise can be varied by changing the type of circuit the attenuation or the number of iterations in the circuit listeners were asked to discriminate between various pairs of irn stimuli which differed in the type of network used to generate the sounds or the number of iterations n 1 2 3 4 7 and 9 performance was determined for irn stimuli generated with delays of 2 4 and 8 ms and for four bandpass filter conditions 0 2000 250 2000 500 2000 and 750 2000 hz some irn stimuli were extremely difficult to discriminate despite relatively large spectral differences while other irn stimuli produced readily discriminable changes in perception despite small spectral differences these contrasting results are inconsistent with simple spectral explanations for the perception of irn stimuli an explanation based on the first peak of the autocorrelation function of irn stimuli is consistent with the results simulations of the processing performed by the peripheral auditory system i e interval histograms and correlograms produce results which are consistent with the involvement of these temporal processes in the perception of irn stimuli

use of high rate envelope speech cues and their perceptually relevant dynamic range for the hearing impaired the ability of hearing impaired hi listeners to use high rate envelope information in a competing talker situation was assessed in experiment 1 signals were tone vocoded and the cutoff frequency fc of the envelope extraction filter was either 50 hz e filter or 200 hz p filter the channels for which the p or e filter was used were varied intelligibility was higher with the p filter regardless of whether it was used for low or high center frequencies performance was best when the p filter was used for all channels experiment 2 explored the dynamic range over which hi listeners made use of high rate cues in each channel of a vocoder the envelope extracted using fc 16 hz was replaced by the envelope extracted using fc 300 hz either at the peaks or valleys with a parametrically varied switching threshold for a target to background ratio of 5 db changes in speech intelligibility occurred mainly when the switching threshold was between 8 and 8 db relative to the channel root mean square level this range is similar in width to but about 3 db higher in absolute level than that found for normal hearing listeners despite the reduced dynamic range of the hi listeners

code aided maximum likelihood ambiguity resolution through free energy minimization in digital communication receivers ambiguities in terms of timing and phase need to be resolved prior to data detection in the presence of powerful error correcting codes which operate in low signal to noise ratios snr long training sequences are needed to achieve good performance in this contribution we develop a new class of code aided ambiguity resolution algorithms which require no training sequence and achieve good performance with reasonable complexity in particular we focus on algorithms that compute the maximum likelihood ml solution exactly or in good approximation with a tractable complexity using a factor graph representation the complexity of the proposed algorithm is discussed and reduced complexity variations including stopping criteria and sequential implementation are developed