the influence of stimulus envelope and fine structure on the binaural masking level difference a masking level difference mld paradigm was used to investigate the influence of stimulus envelope and stimulus fine structure characteristics on monaural and binaural hearing the degree of masker envelope fluctuation was manipulated by selecting narrow band noises 50 hz on a continuum of values of the normalized fourth moment of the envelope the noises were specified as low noise noise lnn medium noise noise mnn and high noise noise hnn fine structure cues were studied by measuring thresholds at 500 and 4000 hz regions in which the availability of such cues to the auditory system differ substantially in addition thresholds were measured for gaussian noise maskers gn and for maskers having a flat magnitude spectrum termed equal magnitude noise emn maskers the results indicated lower noso thresholds for lnn than for the other four masker types furthermore there were no differences in threshold for maskers having moderate and high degrees of envelope fluctuation mnn and hnn the

the connection matrix theory for morse decompositions the connection matrix theory for morse decompositions is introduced the connection matrices are matrices of maps between the homology indices of the sets in the morse decomposition the connection matrices cover in a natural way the homology index braid of the morse decomposition and provide information about the structure of the morse decomposition the existence of connection matrices of morse decompositions is established and examples illustrating applications of the connection matrix are provided

short term temporal integration evidence for the influence of peripheral compression thresholds for a 6 5 khz sinusoidal signal temporally centered in a 400 ms broadband noise masker were measured as a function of signal duration for normally hearing listeners and listeners with cochlear hearing loss over a range of masker levels for the normally hearing listeners the slope of the function relating signal threshold to signal duration integration function was steeper at medium masker levels than at low or high levels by a factor of nearly 2 for signal durations between 2 and 10 ms while no significant effect of level was found for signal durations of 20 ms and more no effect of stimulus level was found for the hearing impaired listeners at any signal duration for signal durations greater than 10 ms consistent with many previous studies the slope of the integration function was shallower for the hearing impaired listeners than for the normally hearing listeners however for shorter durations there was no significant difference in slope between the results from the hearing impaired listeners and those from the normally hearing listeners in the high and low level masker conditions a model incorporating a compressive nonlinearity representing the effect of basilar membrane bm compression and a short term temporal integrator postulated to be a more central process can account well for changes in the short term integration function with level if it is assumed that the compression is greater at medium levels than at low or high levels by a factor of about 4 this is in reasonable agreement with physiological measurements of bm compression and with previous psychophysical estimates

almost planar homoclinic loops in r3 in this paper we study homoclinic loops of vector fields in 3 dimensional space when the two principal eigenvalues are real of opposite sign which we call almost planar we are interested to have a theory for higher codimension bifurcations almost planar homoclinic loop bifurcations generically occur in two versions non twisted and twisted loops we consider high codimension homoclinic loop bifurcations under generic conditions the generic condition forces the existence of a 2 dimensional topological invariant ring non necessarily unique which is a topological cylinder in the non twisted case and a topological mobius band in the twisted case if the third eigenvalue is negative resp positive the limit set resp limit set of trajectories starting in a neighborhood of the loop is contained in the invariant ring the dynamics is then given by fixed points or periodic points of period 2 of a 1 dimensional map which admits a nice asymptotic expansion allowing to treat homoclinic loop bifurcations of arbitrarily high codimension in the non twisted case

analytical expressions for the envelope correlation of certain narrow band stimuli analytical solutions are presented for the correlation between the envelopes of certain narrow band stimuli which are typically used in binaural research these stimuli are either the sum of an in phase masker and an out of phase signal or they are two partially correlated noises because an envelope has a nonzero mean the solutions differ depending on whether the envelope correlation is expressed as the normalized cross correlation or as the normalized cross covariance pearson product moment correlation the envelope correlation depends on the statistics of the masker and the signal whereas the waveform correlation depends on neither this influence only disappears for the normalized envelope cross correlation provided that the correlation is close to one in this case the normalized envelope cross correlation is equal to the square root of the waveform correlation the results for two partially correlated noise bands are also of relevance for experiments dealing with monaural envelope discrimination and comodulation masking release

generalized hopf bifurcation and its dual generalized homoclinic bifurcation we show the duality between the generalized hopf bifurcation ghb and the generalized homoclinic bifurcation ghb this duality is twofold 1 the poincare normal forms at a weak focus and at a weak saddle 2 the bifurcation diagrams of the ghb and the ghb since the ghb is well known the ghb may be considered as the heart of the article

intensity discrimination and detection of amplitude modulation thresholds for detection of low rate sinusoidal amplitude modulation and for detection of intensity increments were measured over a wide range of levels in an examination of the relationship between these fundamental aspects of intensity processing as expected thresholds measured with a continuous 1 khz tone decrease with increasing carrier pedestal level for levels between 6 and 85 db spl the data are well described by 10 log i i 0 44 20 log m d fm where i i is the weber fraction for increment detection m is the modulation index at threshold and d fm depends on modulation rate fm the relationship between the psychometric functions for modulation and increment detection is also consistent with this equation the data indicate a clear relationship between modulation and increment detection and thus provide an important additional consideration for models of modulation processing no existing models provide an adequate account of this relationship

suggested formulae for calculating auditory filter bandwidths and excitation patterns recent estimates of auditory filter shape are used to derive a simple formula relating the equivalent rectangular bandwidth erb of the auditory filter to center frequency the value of the auditory filter bandwidth continues to decrease as center frequency decreases below 500 hz a formula is also given relating erb rate to frequency finally a method is described for calculating excitation patterns from filter shapes

the generalized homoclinic bifurcation abstract in this article we study a family x of vector fields having at 0 a homoclinic loop with multiplicity n we give conditions for the displacement function to have the same zeros as all those of p x 0 1 x n 1 xn 1 xn in a positive neighborhood of x 0 where is continuous these conditions determine the versality of the family x in a neighborhood of the loop to obtain the result we use the concept of chebychev systems

interaural correlation discrimination ii relation to binaural unmasking many theoretical models of binaural interaction assume that sensitivity to interaural correlation underlies binaural unmasking this paper explores the extent to which sensitivity to changes in interaural correlation implied by results from binaural detection experiments are consistent with sensitivity to changes in interaural correlation measured directly in correlation discrimination experiments the vehicle for this exploration is a simplified model of the underlying processes assumed by many models of binaural unmasking for the detection of narrow band signals in the presence of broadband noise consideration is given to psychometric function slopes detection thresholds bandwidth effects duration effects level effects and interaural parameter effects although many of the results obtained from our analysis are consistent with the notion that the cue in binaural detection tasks is a change in interaural correlation some significant inconsistencies are noted

rigorous computation of the global dynamics of integrodifference equations with smooth nonlinearities topological tools such as conley index theory have inspired rigorous computational methods for studying dynamics these methods rely on the construction of an outer approximation a combinatorial representation of the system that incorporates small bounded error in this work we present an automated approach to constructing outer approximations for systems in a class of integrodifference operators with smooth nonlinearities chebyshev interpolants and galerkin projections form the basis for the construction while analysis and interval arithmetic are used to incorporate explicit error bounds this represents a significant advance to the approach given by day junge and mischaikow siam j appl dyn syst 3 2004 pp 117 160 extending the nonlinearities that may be studied from low degree polynomials to smooth functions and the studied portion of phase space from a simulated attracting region to the global maximal invariant set as a demonstration of the techniques a morse decomposition of the

detection of partially filled gaps in noise and the temporal modulation transfer function results of experiments on the detection of silent intervals or gaps in broadband noise are reported for normal hearing listeners in some preliminary experiments a gap threshold of about 2 ms was measured this value was independent of the duration of the noise burst variation of the noise level on each presentation or the temporal position of the gap within the noise burst in the main experiments the thresholds for partial decrements in the noise waveform as well as brief increments were determined as predicted by a model that assumes a single fixed peak to valley detection ratio thresholds for increments are slightly higher than thresholds for decrements when the signal is measured as the change in rms noise level a first order model describes the temporal properties of the auditory system as a low pass filter with a 7 to 8 ms time constant temporal modulation transfer functions were determined for the same subjects and the estimated temporal parameters agreed well with those estimated from the gap detection data more detailed modeling was carried out by simulating viemeister s three stage temporal model simulations using an initial stage bandwidth of 4000 hz and a 3 ms time constant for the low pass filter generate data that are very similar to those obtained from human subjects in both modulation and gap detection

on the use of the normalized correlation as an index of interaural envelope correlation the purpose of the present study was to obtain new empirical observations that would help determine the form of interaural envelope correlation that accounts for listeners sensitivity to binaural information conveyed by high frequency stimuli in a four interval two alternative task listeners detected which interval contained a 4 khz tone added antiphasically to diotic 200 hz wide noise nos the nonsignal intervals contained the tone added homophasically noso discriminability d was measured as a function of s n for values between 30 and 30 db for all s ns overall level was 70 db spl using a similar procedure listeners were also tested in direct discrimination tasks where changes in envelope correlations were produced in one of two manners first changes in the normalized interaural envelope correlation were produced by varying the degree to which the envelopes covaried this was accomplished by mixing two independent gaussian noises second changes in the normalized interaural envelope correlation were produced by adding dc values to the envelopes of the stimuli overall in both experiments listeners ability to discriminate changes in interaural envelope correlation from a base correlation of 1 0 was well accounted for by the normalized correlation it is also shown that the normalized correlation of the envelope accounts for classic data concerning discriminability of interaural time differences at high frequencies as a function of depth of modulation

using machine learning to predict catastrophes in dynamical systems nonlinear dynamical systems which include models of the earth s climate financial markets and complex ecosystems often undergo abrupt transitions that lead to radically different behavior the ability to predict such qualitative and potentially disruptive changes is an important problem with far reaching implications even with robust mathematical models predicting such critical transitions prior to their occurrence is extremely difficult in this work we propose a machine learning method to study the parameter space of a complex system where the dynamics is coarsely characterized using topological invariants we show that by using a nearest neighbor algorithm to sample the parameter space in a specific manner we are able to predict with high accuracy the locations of critical transitions in parameter space

conley index of poincare maps in isolating segments abstract we calculate the discrete time conley index of the poincare map of a time periodic ordinary differential equation in an isolated invariant set generated by a periodic isolating segment as an application we present results on the existence of bounded solutions of some planar equations

investigation of perceptual constancy in the temporal envelope domain the ability to discriminate complex temporal envelope patterns submitted to temporal compression or expansion was assessed in normal hearing listeners an xab matching to sample procedure was used x the reference stimulus is obtained by applying the sum of two inharmonically related sinusoids to a broadband noise carrier a and b are obtained by multiplying the frequency of each modulation component of x by the same time expansion compression factor 0 35 2 83 for each trial a or b is a time reversed rendering of x and the listeners task is to choose which of the two is matched by x overall the results indicate that discrimination performance degrades for increasing amounts of time expansion compression i e when departs from 1 regardless of the frequency spacing of modulation components and the peak to trough ratio of the complex envelopes an auditory model based on envelope extraction followed by a memory limited template matching process accounted for results obtained withou

topology in dynamics differential equations and data abstract this special issue is devoted to showcasing recent uses of topological methods in the study of dynamical behavior and the analysis of both numerical and experimental data the twelve original research papers span a wide spectrum of results from abstract index theories over homology and persistence based data analysis techniques to computer assisted proof techniques based on topological fixed point arguments

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

on the similarity of two theories of comodulation masking release it is observed that two theories of comodulation masking release mr namely the envelope correlation theory and the equalization and cancellation theory are nearly the same

analytical expressions for the envelope correlation of narrow band stimuli used in cmr and bmld research analytical solutions are presented for the correlation between the envelopes of certain narrow band stimuli that are typically used in experiments on binaural unmasking and on comodulation masking release cmr these stimuli consist of two maskers with identical envelopes and a signal that is added to one of the maskers if the two maskers have the same center frequency and are presented to the right and left ear the stimulus resembles a binaural mosm condition if the two maskers have different center frequencies we have a cmr condition with one flanking band the solutions for the envelope correlation differ depending on whether the envelope correlation is expressed as normalized cross correlation or as normalized cross covariance pearson product moment correlation the envelope correlation depends on the statistics of the masker and the signal whereas the waveform correlation depends on neither this influence only disappears for the normalized envelope cross correlation provided that the masker level is much higher than the signal level in this case the envelope cross correlation is approximately equal to the square root of the waveform correlation it is argued that the different properties of both types of envelope correlation are of relevance for cmr research

temporal integration at 6 khz as a function of masker bandwidth thresholds were measured for a 6 khz sinusoidal signal presented within a 500 ms masker the masker was either a bandpass gaussian noise of varying bandwidth or a sinusoid of the same frequency as the signal the spectrum level of the noise masker was kept constant at 20 db spl and the level of the sinusoidal masker was 40 db spl thresholds for signal durations between 2 and 300 ms were measured for masker bandwidths ranging from 60 to 12 000 hz the masker was spectrally centered around 6 khz for masker bandwidths less than 600 hz the slope of the temporal integration function decreased with decreasing masker bandwidth the results are not consistent with current models of temporal integration or temporal resolution it is suggested that the results at narrow bandwidths can be understood in terms of changes in the power spectrum of the stimulus envelope or modulation spectrum according to this view the onset and offset ramps of the signal introduce detectable high frequency components into the modulation spectrum which provide a salient cue in narrowband maskers for broadband maskers these high frequency components are masked by the inherent rapid fluctuations in the masker envelope additionally for signal durations between 7 and 80 ms signal thresholds decreased by up to 5 db as the masker bandwidth increased from 1200 to 12 000 hz the mechanisms underlying this effect are not yet fully understood

infinite series in cohomology attractors and conley index in this paper we study the cohomological conley index of arbitrary isolated invariant continua for continuous maps f u subseteq mathbb r d rightarrow mathbb r d by analyzing the topological structure of their unstable manifold we provide a simple dynamical interpretation for the first cohomological conley index describing it completely and relate it to the cohomological conley index in higher degrees a number of consequences are derived including new computations of the fixed point indices of isolated invariant continua in dimensions 2 and 3 our approach exploits a certain attractor repeller decomposition of the unstable manifold reducing the study of the cohomological conley index to the relation between the cohomology of an attractor and its basin of attraction this is a classical problem that in the present case is particularly difficult because the dynamics is discrete and the topology of the unstable manifold can be very complicated to address it we develop a new method that may be of independent interest and involves the summation of power series in cohomology if z is a metric space and k subseteq z is a compact global attractor for a continuous map g z rightarrow z we show how to interpret series of the form sum j ge 0 a j g j as endomorphisms of the cohomology group of the pair z k

chaos near a resonant inclination flip abstract horseshoes play a central role in dynamical systems and are observed in many chaotic systems however most points in a neighborhood of the horseshoe escape after finitely many iterations in this work we construct a new model by re injecting the points that escape the horseshoe we show that this model can be realized within an attractor of a flow arising from a three dimensional vector field after perturbation of an inclination flip homoclinic orbit with a resonance the dynamics of this model without considering the re injection often contains a cuspidal horseshoe with positive entropy and we show that for a computational example the dynamics with re injection can have more complexity than the cuspidal horseshoe alone

indices of the iterates of r 3 homeomorphisms at lyapunov stable fixed points abstract given any positive sequence c n n n we construct orientation preserving homeomorphisms f r 3 r 3 such that fix f per f 0 0 is lyapunov stable and lim sup i f m 0 c m we will use our results to discuss and to point out some strong differences with respect to the computation and behavior of the sequences of the indices of planar homeomorphisms

zagreb indices of transformation graphs and total transformation graphs the first zagreb index of a graph g is the sum of squares of the degrees of the vertices of g expressions for the first zagreb index and first zagreb coindex are obtained for total semitotal line or middle and semitotal point graphs as well as of eight distinct types of total transformation graphs g xyz

conley index for random dynamical systems conley index theory is a very powerful tool in the study of dynamical systems in this paper we generalize conley index theory to discrete random dynamical systems our constructions are basically the random version of franks and richeson in j franks d richeson shift equivalence and the conley index trans amer math soc 352 2000 3305 3322 for maps and the relations of isolated invariant sets between time continuous random dynamical systems and corresponding time h maps are discussed two examples are presented to illustrate results in this paper

monaural envelope correlation perception for bands narrower or wider than a critical band monaural envelope correlation perception concerns the ability of listeners to discriminate stimuli based on the degree of correlation between the temporal envelopes of two or more frequency separated bands of noise richards j acoust soc am 82 1621 1630 1987 previous work has examined this ability for relatively narrow bandwidths generally 100 hz or less the present experiment explored a wide range of bandwidths from 25 to 1600 hz which included bands narrower and wider than a critical bandwidth stimuli were pairs of noise bands separated by a 500 hz wide spectral gap centered on 2250 hz the magnitude spectra of the pair of comodulated bands were either identical or reflected around the midpoint of the band and performance was assessed with and without a low pass noise masker although discrimination was best for intermediate bandwidths mean performance was above chance for all bandwidths tested data were similar for stimuli with identical and reflected magnitude spectra and for stimuli with and without the low pass masker the one exception was particularly good performance for intermediate bandwidth stimuli with identical spectra for which some listeners reported hearing a tonal cue results indicate that listeners are flexible in selecting spectral regions upon which to base across frequency comparisons

across frequency envelope correlation discrimination and masked signal detection this study compared the dependence of comodulation masking release cmr and monaural envelope correlation perception mecp on the degree of envelope correlation for the same narrowband noise stimuli envelope correlation across noise bands was systematically varied by mixing independent bands with a base set of comodulated bands the magnitude of cmr fell monotonically with reductions in envelope correlation and cmr varied over a range of envelope correlations that were not discriminable from each other in the mecp paradigm for complexes of 100 hz wide noise bands discrimination thresholds in the mecp task were similar whether the standard was a comodulated set of noise bands or a completely independent set of noise bands this was not the case for 25 hz wide noise bands although the data demonstrate that cmr and mecp exhibit different dependencies on the degree of envelope correlation some commonality across the two phenomena was observed specifically for 25 hz wide bands of noise there was a robust relationship between individual listeners sensitivity to decorrelation from an otherwise comodulated set of noise bands and the magnitude of cmr measured for those same comodulated noise bands

isolating blocks and epsilon chains for maps abstract the relationship between the outputs and computer simulations of dynamical systems and their true orbit structures is explored epsilon chains are used as a mathematical representation of computer generated pseudo orbits the question when is a pseudo orbit shadowed by a true orbit is discussed isolated invariant sets are defined and are shown to be contained in special neighborhoods called isolating blocks the conley index is extended and applied to maps

detection of time and bandlimited increments and decrements in a random level noise the purpose of this study was to compare detection of increments and decrements occurring over limited regions of time and frequency within a 500 ms broadband 0 6000 hz noise three listeners tracked detection thresholds adaptively in a two interval two alternative forced choice task thresholds were measured for both increments and decrements in level l 10 log10 1 n0 n0 db where n0 is the spectral power density of the noise as a function of signal duration t 30 500 ms for a range of signal bandwidths w 62 6000 hz that were logarithmically centered around 2500 hz listeners were forced to rely on temporal and spectral profile cues for detection due to randomization of overall presentation level from interval to interval which rendered overall energy an inconsistent cue increments were detectable for all combinations of w and t whereas decrements were not consistently detectable for w 500 hz narrow band decrements were not detectable due to spread of excitation from the spectral edges of

on extremal zagreb indices of trees with given domination number first m1 and second m2 zagreb indices are graph invariants that originate from chemical researches on total electron energy of conjugated molecules there is a legion of articles dealing with these two indices this paper presents upper bounds on zagreb indices of trees in terms of domination number these are strict bounds and extremal trees are characterized in addition a lower bound for the first zagreb index of trees with a given domination number is determined and the extremal trees are characterized as well finally using previously known upper bound for harary index h in terms of m1 and m2 a unique tree with given domination number that maximizes h is characterized

the influence of interaural stimulus uncertainty on binaural signal detection this paper investigated the influence of stimulus uncertainty in binaural detection experiments and the predictions of several binaural models for such conditions masked thresholds of a 500 hz sinusoid were measured in an n s condition for both running and frozen noise maskers using a three interval forced choice 3ifc procedure the nominal masker correlation varied between 0 64 and 1 and the bandwidth of the masker was either 10 100 or 1000 hz the running noise thresholds were expected to be higher than the frozen noise thresholds because of stimulus uncertainty in the running noise conditions for an interaural correlation close to 1 no difference between frozen noise and running noise thresholds was expected for all values of the masker bandwidth these expectations were supported by the experimental data for interaural correlations less than 1 0 substantial differences between frozen and running noise conditions were observed for bandwidths of 10 and 100 hz two additional conditions were tested to further investigate the influence of stimulus uncertainty in the first condition a different masker sample was chosen on each trial but the correlation of the masker was forced to a fixed value in the second condition one of two independent frozen noise maskers was randomly chosen on each trial results from these experiments emphasized the influence of stimulus uncertainty in binaural detection tasks if the degree of uncertainty in binaural cues was reduced thresholds decreased towards thresholds in the conditions without any stimulus uncertainty in the analysis of the data stimulus uncertainty was expressed in terms of three theories of binaural processing the interaural correlation the ec theory and a model based on the processing of interaural intensity differences iids and interaural time differences itds this analysis revealed that none of the theories tested could quantitatively account for the observed thresholds in addition it was found that in conditions with stimulus uncertainty predictions based on correlation differ from those based on the ec theory

the effect of temporal placement on gap detectability the detectability of a masked sinusoid increases as its onset approaches the temporal center of a masker this study was designed to determine whether a similar change in detectability would occur for a silent gap as it was parametrically displaced from the onset of a noise burst gap thresholds were obtained for 13 subjects who completed five replications of each condition in 3 to 13 days six subjects were inexperienced listeners who ranged in age from 18 to 25 years seven subjects were highly experienced and ranged in age from 20 to 78 years the gaps were placed in 150 ms 6 khz low passed noise bursts presented at an overall level of 75 db spl the bursts were digitally shaped at onset and offset with 10 ms cosine squared rise fall envelopes the gated noise bursts were presented in a continuous unfiltered white noise floor attenuated to an overall level of 45 db spl gap onsets were parametrically delayed from the onset of the noise burst defined as the first nonzero point on the waveform envelope by 10 11 13 15 20 40 60 110 120 and 130 ms results of anovas indicated that the mean gap thresholds were longer when the gaps were proximal to signal onset or offset and shorter when the gaps approached the temporal center of the noise burst also the thresholds of the younger highly experienced subjects were significantly shorter than those of the younger inexperienced subjects especially at placements close to signal onset or offset the effect of replication short term practice was not significant nor was the interaction between gap placement and replication post hoc comparisons indicated that the effect of gap placement resulted from significant decreases in gap detectability when the gap was placed close to stimulus onset and offset

discrimination of interaural envelope correlation and its relation to binaural unmasking at high frequencies listeners sensitivity to interaural correlation of the envelope of high frequency waveforms and whether such sensitivity might account for detectability in a masking level difference paradigm were assessed thresholds of interaural envelope decorrelation from a reference correlation of 1 0 were measured for bands of noise centered at 4 khz and bandwidths ranging from 50 1600 hz decorrelation of the envelope was achieved by mixing two independent narrow band noises separately with the same listeners noso and nos detection thresholds were measured for maskers of the same center frequency and bandwidths for bandwidths of noise up to about 400 hz listeners were similarly sensitive to interaural decorrelation in both types of task however for bandwidths greater than 400 hz or so while sensitivity in the discrimination task was unaffected sensitivity was reduced in the nos conditions additional data suggested that listeners were able to maintain their sensitivity independent of bandwidth in the discrimination task by focusing on binaural information within select spectral regions of the stimuli

leray functor and cohomological conley index for discrete dynamical systems we introduce the leray functor on the category of graded modules equipped with an endomorphism of degree zero and we use this functor to define the cohomological conley index of an isolated invariant set of a homeomorphism on a locally compact metric space we prove the homotopy and additivity properties for this index and compute the index in some examples as one of applications we prove the existence of nonconstant bounded solutions of the euler approximation of a certain system of ordinary differential equations

realization of all dold s congruences with stability the main goal of this paper is to prove that for each n 2 every sequence of integers satisfying dold s congruences is realized as the sequence of fixed point indices of the iterates of an orientation preserving r n homeomorphism at an isolated stable fixed point

index filtrations and the homology index braid for partially ordered morse decompositions abstract on a morse decomposition of an invariant set in a flow there are partial orderings defined by the flow these are called admissable orderings of the morse decomposition the index filtrations for a total ordering of a morse decomposition are generalized in this paper with the definition and proof of existence of index filtrations for admissable partial orderings of a morse decomposition it is shown that associated to an index filtration there is a collection of chain complexes and chain maps called the chain complex braid of the index filtration the homology index braid of the corresponding admissable ordering of the morse decomposition is obtained by passing to homology in the chain complex braid keywords morse decomposition conley index index filtration

saddle quantities and applications abstract in this paper we make the connection between the theoretical study of the generalized homoclinic loop bifurcation ghb and the practical computational aspects for this purpose we first compare the dulac normal form with the joyal normal form these forms were both used to prove the ghb theorem but the second one is far more practical from the algorithmic point of view we then show that the information carried by these normal forms can be computed in a much simpler way using what we shall call dual lyapunov constants the coefficients of a normal form or the dual lyapunov quantities are particular cases of what we shall call saddle quantities we calculate the saddle quantities for quadratic systems and we show that no more than three limit cycles can appear in a homoclinic loop bifurcation we also study the homoclinic loop bifurcation of order 5 appearing in a 6 parameter family close to a hamiltonian system to our knowledge this is the first time that one can find a complete description of a ghb of such high order finally we calculate the saddle quantities for a symmetric cubic vector field and we deduce a bound for the number of limit cycles that appear in a ghb

some factors affecting the magnitude of comodulation masking release this paper examines some of the factors that can affect the magnitude of comodulation masking release cmr in experiment i psychometric functions were measured for the detection of a 1 khz sinusoidal signal in a multiplied narrow band noise centered at 1 khz reference condition and the same noise with two comodulated flanking bands added the functions were slightly steeper for the comodulated than for the reference masker thus cmrs measured at a high percent correct point were slightly 0 4 db larger than cmrs measured at a low percent correct point large individual differences were found for the reference masker but not for the comodulated masker experiment ii compared cmrs obtained with narrow band gaussian noise and multiplied noise using a single flanking band for a flanking band remote from the signal frequency the cmrs were smaller and more variable for the multiplied noise than for the gaussian noise this variability arose mainly from individual differences in the reference condition experiment iii compared growth of masking functions for a signal centered in gaussian noise and multiplied noise thresholds were lower for the multiplied than for the gaussian noise and the differences were greatest at high noise levels the results are consistent with the idea that for multiplied noise some subjects can detect a change in the distribution of the envelope of the stimulus when the signal is added to the masker such subjects have low thresholds in the reference condition and give small cmrs other subjects are relatively insensitive to this cue they have higher thresholds in the reference condition and give larger cmrs for gaussian noise thresholds for the reference condition are relatively stable across subjects and cmrs tend to be substantial even for flanking band frequencies remote from the signal frequency

the effects of frequency region and bandwidth on the temporal modulation transfer function temporal modulation transfer functions tmtfs were measured using narrow band am and qfm noises with upper spectral edges from 0 6 to 4 8 khz and spectrum levels of 10 and 40 db spl the cutoff frequency of the tmtf increases as the upper spectral edge is increased up to 4 8 khz at low levels and is constant at higher levels sensitivity increases with bandwidth if frequency region is constant in a second experiment these results were compared to predictions of a model incorporating peripheral and central limitations to modulation detection to obtain an estimate of peripheral filtering frequency selectivity was measured using the notched noise method with probe frequencies and levels chosen to parallel those in the first experiment the tmtf data were then predicted using the model predicted cutoff frequencies as a function of the upper spectral edge of the test stimulus were lower than but parallel to those of the subjects at the lower stimulus level the model predicted only a slight increase in cutoff frequency with level and thus predicted an increase in cutoff frequency with frequency region at the higher level as well in contrast to the measured data these results suggest that there are peripheral and central limitations to temporal resolution but the psychoacoustically derived auditory filter may be only an indirect measure of peripheral filtering and or a more complex model may be needed

the role of envelope fluctuations in spectral masking two experiments are reported in this study in the first experiment the masking effect of five different types of narrow band maskers was compared the masker was either a tone a narrow band gaussian noise or a multiplication noise obtained by multiplying a sinusoid with a low pass gaussian noise the noise maskers had a bandwidth of either 20 or 100 hz in all cases the masker had a center frequency of 1 3 khz and a duration of 500 ms five point growth of masking functions were measured using a 2 khz tonal target with a duration of 400 ms temporally centered in the masker six subjects participated in the experiment although considerable intersubject differences were observed the data of all subjects showed several common trends first the tonal maskers produced more masking than the noise maskers second gaussian noise maskers produced more masking than multiplication noise maskers of the same bandwidth finally 100 hz wide noise maskers produced more masking than 20 hz wide maskers of the same

detection of renewal system factors via the conley index let n be an isolating neighborhood for a map f if we can decompose n into the disjoint union of compact sets n 1 and n 2 then we can relate the dynamics on the maximal invariant set inv n to the shift on two symbols by noting which component of n each iterate of a point x inv n lies in we examine a method based on work by mischaikow szymczak et al for using the discrete conley index to detect explicit subshifts of the shift associated to n in essence we measure the difference between the conley index of inv n and the sum of the indices of inv n 1 and inv n 2

the contribution of static and dynamically varying itds and iids to binaural detection this paper investigates the relative contribution of various interaural cues to binaural unmasking in conditions with an interaurally in phase masker and an out of phase signal mos pi by using a modified version of multiplied noise as the masker and a sinusoid as the signal conditions with only interaural intensity differences iids only interaural time differences itds or combinations of the two were realized in addition the experimental procedure allowed the presentation of specific combinations of static and dynamically varying interaural differences in these conditions with multiplied noise as masker the interaural differences have a bimodal distribution with a minimum at zero iid or itd additionally by using the sinusoid as masker and the multiplied noise as signal a unimodal distribution of the interaural differences was realized through this variation in the shape of the distributions the close correspondence between the change in the interaural cross correlation and the size of the interaural differences is no longer found in contrast to the situation for a gaussian noise masker domnitz and colburn j acoust soc am 59 598 601 1976 when analyzing the mean thresholds across subjects the experimental results could not be predicted from parameters of the distributions of the interaural differences the mean the standard deviation or the root mean square value a better description of the subjects performance was given by the change in the interaural correlation but this measure failed in conditions which produced a static interaural intensity difference the data could best be described by using the energy of the difference signal as the decision variable an approach similar to that of the equalization and cancellation model

on extremal multiplicative zagreb indices of trees with given domination number abstract for a molecular graph the first multiplicative zagreb index 1 is equal to the product of squares of the vertex degrees and the second multiplicative zagreb index 2 is equal to the product of the products of degrees of pairs of adjacent vertices in this paper we explore the multiplicative zagreb indices in terms of domination number sharp upper and lower bounds of 1 and 2 are given in addition the corresponding extreme graphs are characterized and our conclusions enrich and extend some known results