Effects Of Frequency Separation Research Articles

Low-high-low or high-low-high? Pattern effects on sequential auditory scene analysis.

Sequential auditory scene analysis (ASA) is often studied using sequences of two alternating tones, such as ABAB or ABA_, with "_" denoting a silent gap, and "A" and "B" sine tones differing in frequency (nominally low and high). Many studies implicitly assume that the specific arrangement (ABAB vs ABA_, as well as low-high-low vs high-low-high within ABA_) plays a negligible role, such that decisions about the tone pattern can be governed by other considerations. To explicitly test this assumption, a systematic comparison of different tone patterns for two-tone sequences was performed in three different experiments. Participants were asked to report whether they perceived the sequences as originating from a single sound source (integrated) or from two interleaved sources (segregated). Results indicate that core findings of sequential ASA, such as an effect of frequency separation on the proportion of integrated and segregated percepts, are similar across the different patterns during prolonged listening. However, at sequence onset, the integrated percept was more likely to be reported by the participants in ABA_low-high-low than in ABA_high-low-high sequences. This asymmetry is important for models of sequential ASA, since the formation of percepts at onset is an integral part of understanding how auditory interpretations build up.

On the Effect of Frequency Separation, Mass Ratio, Solidity, and Aerodynamic Resonances in Coupled Mode Flutter of a Linear Compressor Cascade

Abstract At a low mass ratio of structure to air, the work-per-cycle approach, or better known as the energy method, will lead to nonconservative results as aerodynamic coupling of modeshapes acts destabilizing. Using the p–k method to solve the aeroelastic stability equation, the effects of various structural aspects are investigated for a two-dimensional compressor cascade in subsonic and transonic flow conditions. The investigated key parameters are frequency separation, mass ratio, and solidity. Furthermore, the effect of a high frequency dependency of the aerodynamic forces is presented. Such phenomena can happen in case of aerodynamic or acoustic resonances. If the resonance peaks are close to the aeroelastic frequency, a discontinuous behavior of the frequency or damping solution can lead to a rapid destabilization of the system, once the aeroelastic frequency moves from one side to the other of the peak. In these regimes, it is crucial to have a high quality representation of the frequency-dependent generalized aerodynamic forces (GAFs) for an accurate prediction of the flutter onset.

An ERP Study on the Auditory Stream Segregation in Cochlear Implant Simulations: Effects of Frequency Separation and Time Interval.

Auditory stream segregation is an important function of the auditory system, and the extent to which this function works has a major impact on listener's ability to recognize auditory objects in complex listening environments. However, cochlear implant (CI) listeners are poorly equipped for this challenge, mainly owing to the impoverished sensory information available via their implants. The purpose of this study was to examine two factors, i.e., frequency separation and time interval, affecting the auditory stream segregation in vocoder simulations simulating CI speech processing based on an event-related potential (ERP) experiment. The pure-tone stimuli were processed by a vocoding process, and presented to normal-hearing listeners in an ERP experiment. Experimental results showed that a large frequency separation or a short time interval led to a larger mismatch negativity (MMN) response. The MMN results in this work suggested that the degree of auditory stream segregation was affected by frequency separation and time interval, and MMN could serve as a potential index for future ERP studies on auditory stream segregation in CI users.

Effects of frequency separation and fundamental frequency on perception of simultaneity of the tones

Present study investigated the range of perceptual simultaneity, within which listeners perceive two asynchronous tones as simultaneous, as a function of frequency separation and fundamental frequency of the tones. This function was obtained with frequency separations ranging from 0.03 to 5.00 octaves, and fundamental frequencies ranging from 100 to 800 Hz. Listener’s task was to judge whether the two asynchronous pure tones were perceptually simultaneous or not. Results showed a V-shaped function for the perceptual simultaneity range against the frequency separation regardless of fundamental frequency. The perceptual simultaneity range steeply decreased and then gradually increased with the increment of frequency separation. The breakpoint of the V-shaped function was appeared at around the critical bandwidth. This breakpoint was best predicted by CB (Critical Bandwidth) scale, rather than by ERB (Equivalent Rectangular Bandwidth) or octave scales. These findings supported the notion (Okazaki & Ichikawa,...

Effects of Frequency Separation and Diotic/Dichotic Presentations on the Alternation Frequency Limits in Audition Derived from a Temporal Phase Discrimination Task.

Temporal phase discrimination is a useful psychophysical task to evaluate how sensory signals, synchronously detected in parallel, are perceptually bound by human observers. In this task two stimulus sequences synchronously alternate between two states (say, A-B-A-B and X-Y-X-Y) in either of two temporal phases (ie A and B are respectively paired with X and Y, or vice versa). The critical alternation frequency beyond which participants cannot discriminate the temporal phase is measured as an index characterizing the temporal property of the underlying binding process. This task has been used to reveal the mechanisms underlying visual and cross-modal bindings. To directly compare these binding mechanisms with those in another modality, this study used the temporal phase discrimination task to reveal the processes underlying auditory bindings. The two sequences were alternations between two pitches. We manipulated the distance between the two sequences by changing intersequence frequency separation, or presentation ears (diotic vs dichotic). Results showed that the alternation frequency limit ranged from 7 to 30 Hz, becoming higher as the intersequence distance decreased, as is the case with vision. However, unlike vision, auditory phase discrimination limits were higher and more variable across participants.

A Neurocomputational Model of Stimulus-Specific Adaptation to Oddball and Markov Sequences

Stimulus-specific adaptation (SSA) occurs when the spike rate of a neuron decreases with repetitions of the same stimulus, but recovers when a different stimulus is presented. It has been suggested that SSA in single auditory neurons may provide information to change detection mechanisms evident at other scales (e.g., mismatch negativity in the event related potential), and participate in the control of attention and the formation of auditory streams. This article presents a spiking-neuron model that accounts for SSA in terms of the convergence of depressing synapses that convey feature-specific inputs. The model is anatomically plausible, comprising just a few homogeneously connected populations, and does not require organised feature maps. The model is calibrated to match the SSA measured in the cortex of the awake rat, as reported in one study. The effect of frequency separation, deviant probability, repetition rate and duration upon SSA are investigated. With the same parameter set, the model generates responses consistent with a wide range of published data obtained in other auditory regions using other stimulus configurations, such as block, sequential and random stimuli. A new stimulus paradigm is introduced, which generalises the oddball concept to Markov chains, allowing the experimenter to vary the tone probabilities and the rate of switching independently. The model predicts greater SSA for higher rates of switching. Finally, the issue of whether rarity or novelty elicits SSA is addressed by comparing the responses of the model to deviants in the context of a sequence of a single standard or many standards. The results support the view that synaptic adaptation alone can explain almost all aspects of SSA reported to date, including its purported novelty component, and that non-trivial networks of depressing synapses can intensify this novelty response.

Relative importance of different spectral bands to consonant identification: Relevance for frequency transposition in hearing aids

Listeners with high-frequency dead regions (DRs) benefit from amplification of frequencies up to 1.7 times the edge frequency, fe, of the DR. Better consonant identification might be achieved by replacing the band from fe to 1.7fe with a higher spectral band. We aimed to identify the optimal band, using simulations with normal-hearing listeners. In experiment 1, nonsense syllables were lowpass filtered to simulate DRs with fe of 0.5, 0.75, and 1.0 kHz. Identification was measured for each of these base bands alone and with a bandpass-filtered band added (but not transposed). The added band either extended from fe to 1.7fe or its center frequency was increased, keeping bandwidth fixed in ERBN-number. Performance improved with increasing center frequency and then reached an asymptote or declined. Experiment 2 used a mid-frequency base band, and a lower-frequency added band. The results also showed a beneficial effect of frequency separation of the added and base bands. Experiment 3 resembled experiment 1, but with bandwidth fixed in Hertz. For higher-frequency added bands, the benefit was lower than for experiment 1.

Effects of frequency separation in periodic active noise control systems

In many practical active noise control (ANC) applications, the primary noise contains multiple closely-spaced harmonics. A narrow-band feedforward ANC system consists of an adaptive filter excited by a composite reference signal, which is the sum of multiple sinusoids corresponding to the harmonic frequencies of the primary noise. This paper analyzes and shows that the convergence of this direct-form controller is dependent on the frequency separation between two adjacent sinusoids in the reference signal. The analysis also proves that the length of the adaptive filter required for achieving the same convergence speed decreases with an increase in frequency separation. This paper also performs mathematical analysis of the direct/parallel-form controller, which significantly improves the convergence speed and reduces filter length by increasing the frequency separation in the individual reference signal for each adaptive filter. Computer simulations are conducted to verify the analysis presented in the paper

The role of predictive models in the formation of auditory streams

Sounds provide us with useful information about our environment which complements that provided by other senses, but also poses specific processing problems. How does the auditory system distentangle sounds from different sound sources? And what is it that allows intermittent sound events from the same source to be associated with each other? Here we review findings from a wide range of studies using the auditory streaming paradigm in order to formulate a unified account of the processes underlying auditory perceptual organization. We present new computational modelling results which replicate responses in primary auditory cortex [Fishman, Y.I., Arezzo, J.C., Steinschneider, M., 2004. Auditory stream segregation in monkey auditory cortex: effects of frequency separation, presentation rate, and tone duration. J. Acoust. Soc. Am. 116, 1656–1670; Fishman, Y. I., Reser, D. H., Arezzo, J.C., Steinschneider, M., 2001. Neural correlates of auditory stream segregation in primary auditory cortex of the awake monkey. Hear. Res. 151, 167–187] to tone sequences. We also present the results of a perceptual experiment which confirm the bi-stable nature of auditory streaming, and the proposal that the gradual build-up of streaming may be an artefact of averaging across many subjects [Pressnitzer, D., Hupé, J. M., 2006. Temporal dynamics of auditory and visual bi-stability reveal common principles of perceptual organization. Curr. Biol. 16(13), 1351–1357.]. Finally we argue that in order to account for all of the experimental findings, computational models of auditory stream segregation require four basic processing elements; segregation, predictive modelling, competition and adaptation, and that it is the formation of effective predictive models which allows the system to keep track of different sound sources in a complex auditory environment.

Auditory stream segregation in monkey auditory cortex: effects of frequency separation, presentation rate, and tone duration.

Auditory stream segregation refers to the organization of sequential sounds into "perceptual streams" reflecting individual environmental sound sources. In the present study, sequences of alternating high and low tones, "...ABAB...," similar to those used in psychoacoustic experiments on stream segregation, were presented to awake monkeys while neural activity was recorded in primary auditory cortex (A1). Tone frequency separation (AF), tone presentation rate (PR), and tone duration (TD) were systematically varied to examine whether neural responses correlate with effects of these variables on perceptual stream segregation. "A" tones were fixed at the best frequency of the recording site, while "B" tones were displaced in frequency from "A" tones by an amount = delta F. As PR increased, "B" tone responses decreased in amplitude to a greater extent than "A" tone responses, yielding neural response patterns dominated by "A" tone responses occurring at half the alternation rate. Increasing TD facilitated the differential attenuation of "B" tone responses. These findings parallel psychoacoustic data and suggest a physiological model of stream segregation whereby increasing delta F, PR, or TD enhances spatial differentiation of "A" tone and "B" tone responses along the tonotopic map in A1.

Effect of frequency separation and stimulus rate on the mismatch negativity: an examination of the issue of refractoriness in humans

Refractoriness of the generators of the mismatch negativity (MMN) was examined in two experiments in which two deviant tones occurred in a row. In Experiment 1, the size of the MMN elicited by the first deviant was manipulated by using deviants that were close to or far from the standard in frequency. In Experiment 2, the time between two identical deviants was varied. It was found that neither the size of the MMN elicited by the first deviant, nor the time between two deviants, affected the amplitude of the MMN elicited by the second deviant. It was concluded that refractoriness played no role in the amplitude of the MMN for the parameters used.

Echo suppression or localization masking?

A brief dichotic conditioner (C) has been shown to effectively disrupt lateralization of a brief probe (P) presented after a short interval (4–7 ms, onset to onset) with an interaural time delay that is perfectly audible in the absence of the C [P. M. Zurek, J. Acoust. Soc. Am. 66, 1750–1757 (1980)], even when the C and the P are different sounds [P. L. Divenyi and J. Blauert, in Auditory Processing of Complex Sounds, edited by W. A. Yost and C. S. Watson (Erlbaum, Hillsdale, NJ, 1987), pp. 146–155]. An echo suppression mechanism responsible for this effect would predict (1) suppression to be strongest when the C and the P are identical and to decrease monotonically as the spectra of the two sounds are made different, and (2) a monotonic falloff of suppression when the temporal separation between the two sounds is increased beyond a certain minimum. In the present experiments, the effects of frequency separation and temporal separation between a narrow-band P centered at 2 kHz and a C were systematically explored. Contrary to the predictions, low-frequency (0.8 < 1.3 kHz) C's were more effective in suppressing the lateralization of the P than those closer to the P frequency, and lateralization performance was nonmonotonically related to temporal separation between C and P. The results suggest that a dichotic stimulus with a relatively high localization strength could “mask” the localization of another, subsequent dichotic stimulus. [Work supported by the Veterans Administration.]

The effect of frequency separation on the correlation of bearing errors measured on ionospherically propagated HF signals from colocated transmitters

Simultaneous bearing observations are made on colooated HF transmitters radiating on different frequencies and, out of many days' measurement, the results for one day are presented. The bearing data clearly show the presence of bearing fluctuations with periodicities ranging from about 12 to 20 minutes. Those with the longer periodicities show a good correlation with one another at relatively wide separations (about 4.5 MHz) of the radiated frequencies; furthermore, they exhibit a phase advancement with height which would be expected from theory if the bearing perturbations arose from gravity waves. However, the fluctuations with periodicities of the order of 12 minutes are only well correlated when the radiated frequencies differ by less than about 2 MHz and it is suggested that they are, physically, very much smaller disturbances.

Discrimination of the order of the components of repeating tone sequences: Effects of frequency separation and extensive practice

The Ss’ task was to identify repeating sequences of pure tones that differed only with respect to the order in which the tones occurred. With tones occurring at a constant rate of 5/sec, performance was better when the tones were widely spaced in frequency than when they were less widely spaced. One S was able, after considerable practice, to distinguish among different sequences whose component tones were presented at rates up to 500/sec. It was tenatively concluded that, in this case, performance was based on temporal (order) information at the slowest presentation rates, primarily on spectral information at the highest rates, and on both order and spectral information at intermediate rates.