effect of variability in level on forward masking and on increment detection in the first of four experiments all with the same four subjects varying the level of a forward masker from interval to interval in a two interval forced choice 2ifc adaptive procedure had little effect on threshold in the second experiment the signal level was fixed and performance was measured in units of d varying the level of the forward masker again had little effect analyses of trial by trial data indicated that subjects did not vote for the interval with the higher level masker as would an energy detector performance was better on trials where the masker level in the interval with the signal was lower and was relatively independent of masker level in the nonsignal interval in the third experiment these results were replicated for a wider range of masker variability and with maskers lower in frequency than the signal in the fourth experiment the same range of variability from interval to interval was imposed on the level of the pedestal in an increment detection task results were sim

relative contributions of specific frequency bands to the loudness of broadband sounds listeners with normal hearing nh and sensorineural hearing loss snhl were asked to compare pairs of noise stimuli and choose the louder noise in each pair each noise was made up of 15 two erbn equivalent rectangular bandwidth wide frequency bands that varied independently over a 12 db range from one presentation to the next mean levels of the bands followed the long term average speech spectrum ltass or were set to 43 51 or 59 db sound pressure level spl the relative contribution of each band to the total loudness of the noise was determined by computing the correlation between the difference in levels for a given band on every trial and the listener s decision on that trial weights for snhl listeners were governed by audibility and the spectrum of the noise stimuli with bands near the spectral peak of the ltass noise receiving greatest weight nh listeners assigned greater weight to the lowest and highest bands an effect that increased with overall level but did not assign greater weight to bands near the ltass peak additional loudness matching and paired comparison studies using stimuli missing one of the 15 bands showed a significant contribution by the highest band but properties other than loudness may have contributed to the decisions

two procedures for estimating internal noise internal noise was measured in two paradigms simultaneously in one method the listener s agreement in choosing the same masker as the one in a pair that sounds most signal like is used to estimate internal noise d m green psych rev 71 392 407 1964 in the other the increment in detection performance on those trials having identical as opposed to different maskers is used to estimate internal noise r a siegel unpublished master s thesis m i t 1979 most results place the estimate of additive internal noise as nearly equal to the external noise variability the estimates from the agreement method can be adversely affected by uncertainty regarding the observation interval and interval biases whereas the estimates obtained with the detection method are highly sensitive to measurement errors

stability and attractivity of periodic solutions of parabolic systems with time delays abstract this paper is concerned with the existence stability and global attractivity of time periodic solutions for a class of coupled parabolic equations in a bounded domain the problem under consideration includes coupled system of parabolic and ordinary differential equations and time delays may appear in the nonlinear reaction functions our approach to the problem is by the method of upper and lower solutions and its associated monotone iterations the existence of time periodic solutions is for a class of locally lipschitz continuous reaction functions without any quasimonotone requirement using schauder fixed point theorem while the stability and attractivity analysis is for quasimonotone nondecreasing and mixed quasimonotone reaction functions using the monotone iterative scheme the results for the general system are applied to the standard parabolic equations without time delay and to the corresponding ordinary differential system applications are also given to three lotka volterra reaction diffusion model problems and in each problem a sufficient condition on the reaction rates is obtained to ensure the stability and global attractivity of positive periodic solutions

possible generalization of boltzmann gibbs statistics with the use of a quantity normally scaled in multifractals a generalized form is postulated for entropy namelys q k 1 i 1 w p i q q 1 whereq characterizes the generalization andp i are the probabilities associated withw microscopic configurations w the main properties associated with this entropy are established particularly those corresponding to the microcanonical and canonical ensembles the boltzmann gibbs statistics is recovered as theq 1 limit

complex earthquake networks hierarchical organization and assortative mixing to characterize the dynamical features of seismicity as a complex phenomenon the seismic data are mapped to a growing random graph which is a small world scale free network here hierarchical and mixing properties of such a network are studied the clustering coefficient is found to exhibit asymptotic power law decay with respect to connectivity showing hierarchical organization this structure is supported by not only main shocks but also small shocks and may have its origin in the combined effect of vertex fitness and deactivation by stress release at faults the nearest neighbor average connectivity and the pearson correlation coefficient are also calculated it is found that the earthquake network has assortative mixing this is a main difference of the earthquake network from the internet with disassortative mixing physical implications of these results are discussed

psychometric functions for pure tone intensity discrimination slope differences in school aged children and adults previous work on pure tone intensity discrimination in school aged children concluded that children might have higher levels of internal noise than adults for this task j acoust soc am 120 2777 2788 2006 if true this would imply that psychometric function slopes are shallower for children than adults a prediction that was tested in the present experiment normal hearing children 5 9 yr and adults were tested in a two stage protocol the first stage used a tracking procedure to estimate 71 correct for intensity discrimination with a gated 500 hz pure tone and a 65 db sound pressure level standard level the mean and standard deviation of these tracks were used to identify a set of five signal levels for each observer in the second stage of the experiment percent correct was estimated at these five levels psychometric functions fitted to these data were significantly shallower for children than adults as predicted by the internal noise hypothesis data from both stages of testing are consistent with a model wherein performance is based on a stable psychometric function with sensitivity limited by psychometric function slope across observers the relationship between slope and threshold conformed closely to predictions of a simple signal detection model

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

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

psychometric functions for level discrimination to determine the form of psychometric functions for 2i 2afc level discrimination ten increment levels were presented in random order within blocks of 100 trials stimuli were chosen to encompass a wide range of conditions and difference limens eight 10 ms tones had frequencies of 0 25 1 8 or 14 khz and levels of 30 60 or 90 db spl two 500 ms stimuli also were tested a 1 khz tone at 90 db spl and a white noise at 63 db spl for each condition at least 20 blocks were presented in mixed order results for three normal listeners show that the sensitivity d is nearly proportional to l 20 log p p p where p is pressure over the entire range of difference limens when d is plotted against weber fractions for pressure p p or intensity i i exponents of the best fitting power functions decrease with increasing difference limens and are less than one for large difference limens these results indicate that the transformation from stimulus intensity to decision variable may be approximately lo

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

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

a phenomenological model for the responses of auditory nerve fibers i nonlinear tuning with compression and suppression a phenomenological model was developed to describe responses of high spontaneous rate auditory nerve an fibers including several nonlinear response properties level dependent gain compression bandwidth and phase properties were implemented with a control path that varied the gain and bandwidth of tuning in the signal path filter by making the bandwidth of the control path broad with respect to the signal path the wide frequency range of two tone suppression was included by making the control path filter level dependent and tuned to a frequency slightly higher than the signal path filter other properties of two tone suppression were also included these properties included the asymmetrical growth of suppression above and below the characteristic frequency and the frequency offset of the suppression tuning curve with respect to the excitatory tuning curve the implementation of this model represents a relatively simple phenomenological description of a single mechanism that underlies several important nonlinear response properties of an fibers the model provides a tool for studying the roles of these nonlinearities in the encoding of simple and complex sounds in the responses of populations of an fibers

finite data size scaling of clustering in earthquake networks abstract an earthquake network is known to be of the small world type the values of the network s characteristics however depend not only on the cell size i e the scale of coarse graining needed for constructing the network but also on the size of a seismic data set here discovery of a scaling law for the clustering coefficient in terms of the data size which is referred to here as finite data size scaling is reported its universality is shown to be supported by the detailed analysis of the data taken from california japan and iran effects of setting a threshold of magnitude are also discussed

a measure of internal noise based on sample discrimination internal noise is often inferred from the difference between observed performance and optimum performance in detection and discrimination tasks it can be measured directly in some cases by observing the extent to which a change in external variability impacts performance in the studies reported here external variability was added to an intensity discrimination task by adding a gaussian random variable with zero mean to the overall level presented in each interval of a two interval forced choice task the standard deviation of the random variable was set to half the mean difference between the levels in the two intervals resulting in d ideal 2 as the mean difference and the corresponding standard deviation of the random variable decreased in size performance was increasingly limited by internal noise permitting a reliable estimate of internal noise to be obtained this can be viewed as a sample discrimination task with one component per sample in the first study performance was measured using 2 khz tones presented at an average level of 70 db spl with mean differences between distributions ranging from 0 1 to 2 2 db in steps of 0 3 db the distributions were either gaussian in level or in power conditions with no external variability were used to obtain a psychometric function in the second study performance was measured using 2 khz tones presented at average levels of 50 and 90 db spl with mean differences ranging from 0 4 to 2 2 db in steps of 0 6 db in both studies the measure of internal noise was highly reliable and in good agreement with the intensity difference limen dl estimated from the psychometric function analyses suggest that this measure could be used to estimate the mean difference between the decision distributions as well as the amount of internal noise in cases where the mean difference between the distributions is unknown

decision rules of listeners in spectral shape discrimination with or without signal frequency uncertainty a correlation technique was used to assess the decision rules of three listeners in two cases of spectral shape discrimination tasks in one case the signal frequency was fixed and in the other it was randomly varied within each block of trials in order to estimate the decision rule of the listeners the experimenter superimposed random level perturbations on each frequency component upon each stimulus presentation over many trials correlation coefficients were computed between the random perturbations and the binary responses of the listeners and were expressed as a function of signal level for both the fixed and random signal cases the measured correlation functions were in reasonably good agreement with those predicted based on the likelihood ratio decision rules thus the listeners appeared to use information nearly optimally in discriminating spectral shapes this investigation demonstrated that the correlation technique can be used to reveal the decision rules for cases where the decision statistics are nonlinear functions of the observations

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

nonextensivity measure for earthquake networks studying earthquakes and the associated geodynamic processes based on the complex network theory enables us to learn about the universal features of the earthquake phenomenon in addition we can determine new indices for identification of regions geophysically it was found that earthquake networks are scale free and its degree distribution obeys the power law here we claim that the q exponential function is better than power law model for fitting the degree distribution we also study the behavior of q parameter nonextensivity measure with respect to resolution it was previously asserted in eur phys j b 2012 85 23 that the topological characteristics of earthquake networks are dependent on each other for large values of the resolution a peak in the plot of q against resolution determines the beginning of the assertion range

the decision process in forward masked intensity discrimination evidence from molecular analyses in a two interval forced choice intensity discrimination task presenting a fixed increment the level of the forward masker in interval 1 and interval 2 was sampled independently from the same normal distribution on each trial mean and standard deviation of the distribution were varied correlational analyses of the trial by trial data revealed different decision strategies depending on the relation between mean masker level and standard level if the two levels were identical listeners tended to select the interval containing the higher level masker behaving like an energy detector at the output of a temporal window of integration for mean masker level higher than the standard level most listeners showed a negative correlation between the masker level in a given interval and the probability of selecting this interval indicating a strategy of comparing the masker loudness and the target loudness in each of the two observation intervals and voting for the interval where the loudness difference was s