Comparison of level discrimination, increment detection, and comodulation masking release in the audio- and envelope-frequency domains

In general, the temporal structure of stimuli must be considered to account for certain observations made in detection and masking experiments in the audio-frequency domain. Two such phenomena are (1) a heightened sensitivity to amplitude increments with a temporal fringe compared to gated level discrimination performance and (2) lower tone-in-noise detection thresholds using a modulated masker compared to those using an unmodulated masker. In the current study, translations of these two experiments were carried out to test the hypothesis that analogous cues might be used in the envelope-frequency domain. Pure-tone carrier amplitude-modulation (AM) depth-discrimination thresholds were found to be similar using both traditional gated stimuli and using a temporally modulated fringe for a fixed standard depth (m(s)=0.25) and a range of AM frequencies (4-64 Hz). In a second experiment, masked sinusoidal AM detection thresholds were compared in conditions with and without slow and regular fluctuations imposed on the instantaneous masker AM depth. Release from masking was obtained only for very slow masker fluctuations (less than 2 Hz). A physiologically motivated model that effectively acts as a first-order envelope change detector accounted for several, but not all, of the key aspects of the data

The effects of background noise and test subject on the perceived amount of bass in phase-modified harmonic complex tones

Äänenvärin havaitseminen liittyy läheisesti äänen tuottamiin suhteellisiin tasoihin simpu- kassa eri taajuuskaistoilla, joita kutsutaan kriittisiksi kaistoiksi. Äänen magnitudispektri määrittää sen taajuuskomponenttien suhteelliset voimakkuudet ja vaihespektri niiden suhteelliset vaiheet. Äänenväri siis riippuu usein pelkästään magnitudispektristä. Tutki- mustulokset ovat kuitenkin osoittaneet, että tietyn tyyppisten äänien äänenväriä voidaan muuttaa myös pelkästään vaihespektriä muuttamalla. Tämän lisäksi aiempi tutkimus on osoittanut, että muuttamalla harmonisen äänen vaihespektriä tietyllä tavalla havaittu bassokkuus muuttuu. Tällaiset äänet ovat siis ’vaiheherkkiä’. Kyseisessä tutkimuksessa käytettiin kahta tällaista vaihemuokattua ääntä, joista toisessa taajuuskomponenttien välillä oli -90 asteen ja toisessa 90 asteen vaihe- ero, ja perustaajuuskomponentti oli molemmissa kosinivaiheessa. Tutkimus osoitti, että suurin bassokkuusero havaitaan matalilla perustaajuuksilla ja se vastaa keskimäärin 2 – 4 dB:n vahvistusta magnitudispektrissä matalilla taajuuksilla. Tämä ilmiön suuruus riippui kuitenkin huomattavasti testihenkilöstä. Lisäksi huomattiin, että bassokkuuserot ovat helpompia kuulla taustakohinan kanssa. Tämän työn tavoitteena oli tutkia edelleen taustakohinan merkitystä ja yksilöllisiä eroja tällaisten vaiheherkkien äänien bassokkuuden havaitsemisessa. Kaksi formaalia kuuntelu- koetta järjestettiin käyttäen kuulokkeita. Ensiksi tutkittiin taustakohinan vaikutusta kyseisten äänien bassokkuuserojen kuulemiseen olettaen, että nämä erot ovat kuultavissa äänekkyyseroina. Tulokset viittaavat, että taustakohinan tason nousun vaikutus testiäänien äänekkyyseroon ei ole tilastollisesti merkittävä, mutta on lähellä merkittävyyden rajaa ja trendi on nähtävissä äänekkyyseron kasvulle. Lisäksi nähdään, että kyseisten vaiheherkkien äänien yleinen äänekkyys laskee kun taustakohinan tasoa voimistetaan. Toiseksi tutkittiin sitä, minkä vaihespektrin omaavan äänen eri ihmiset kuulevat bassokkaimpana. Tulokset osoittavat, että testihenkilöt eroavat siinä, minkä vaihespektrin omaavan äänen he kuulevat bassokkaimpana, ja että tämä ero on tilastollisesti merkittävä.The perception of timbre is closely related to the relative levels produced by a sound in each frequency band, called ‘critical band’, in the cochlea. The magnitude spectrum defines the relative levels and phase spectrum the relative phases of the frequency components in a complex sound. Thus, the timbre of sound depends often only on the magnitude spectrum. However, several studies have shown that the timbre of certain complex sounds can be affected by modifying only the phase spectrum. Moreover, a recent study has shown that with certain modifications of only the phase spectrum of a ‘phase-sensitive’ harmonic complex tone, the perceived level of bass changes. That experiment was conducted using two synthetic harmonic complex tones in which adjacent frequency components have a phase-shift of -90◦ and 90◦, respectively, and the fundamental component is in cosine-phase. The greatest difference in perceived level of bass was found at the fundamental frequency of 50 Hz and it corresponds to a 2 – 4-dB amplification of the magnitude spectrum at low frequencies. However, this effect was reported to vary substantially between individuals. Moreover, the differences were found to be easier to detect in the presence of background noise. The aim of this thesis was to investigate further the roles of background noise and the individual in the perceived level of bass in the phase-sensitive tones. Two formal listening tests were conducted accordingly using headphones. Firstly, the effect of background noise on the discrimination of the phase-sensitive tones based on the perceived level of bass was studied. The effect of increasing background noise level on the perceived loudness difference was found not to be statistically significant, but a trend could be seen towards increasing loudness difference. Additionally, the results indicate that the overall perceived loudness of the test tones decreases with increasing level of background noise. Secondly, an experiment was conducted to find the preferred value of the constant phase shift between adjacent components that produces a tone with the perceptually loudest bass for different individuals. The results show that individuals hear the phase spectrum required to produce the perception of the loudest bass statistically significantly differently from each other

The spike train statistics for consonant and dissonant musical accords

The simple system composed of three neural-like noisy elements is considered. Two of them (sensory neurons or sensors) are stimulated by noise and periodic signals with different ratio of frequencies, and the third one (interneuron) receives the output of these two sensors and noise. We propose the analytical approach to analysis of Interspike Intervals (ISI) statistics of the spike train generated by the interneuron. The ISI distributions of the sensory neurons are considered to be known. The frequencies of the input sinusoidal signals are in ratios, which are usual for music. We show that in the case of small integer ratios (musical consonance) the input pair of sinusoids results in the ISI distribution appropriate for more regular output spike train than in a case of large integer ratios (musical dissonance) of input frequencies. These effects are explained from the viewpoint of the proposed theory.Comment: 22 pages, 6 figure

Considering the Case for Biodiversity Cycles: Reexamining the Evidence for Periodicity in the Fossil Record

Medvedev and Melott (2007) have suggested that periodicity in fossil biodiversity may be induced by cosmic rays which vary as the Solar System oscillates normal to the galactic disk. We re-examine the evidence for a 62 million year (Myr) periodicity in biodiversity throughout the Phanerozoic history of animal life reported by Rohde & Mueller (2005), as well as related questions of periodicity in origination and extinction. We find that the signal is robust against variations in methods of analysis, and is based on fluctuations in the Paleozoic and a substantial part of the Mesozoic. Examination of origination and extinction is somewhat ambiguous, with results depending upon procedure. Origination and extinction intensity as defined by RM may be affected by an artifact at 27 Myr in the duration of stratigraphic intervals. Nevertheless, when a procedure free of this artifact is implemented, the 27 Myr periodicity appears in origination, suggesting that the artifact may ultimately be based on a signal in the data. A 62 Myr feature appears in extinction, when this same procedure is used. We conclude that evidence for a periodicity at 62 Myr is robust, and evidence for periodicity at approximately 27 Myr is also present, albeit more ambiguous.Comment: Minor modifications to reflect final published versio

Doctor of Philosophy

dissertationAmplitude modulation (AM) detection measures a listener's sensitivity to temporal envelope fluctuations. AM signals are ecologically relevant because the amplitude of speech fluctuates over time. The post-cochlear representation of AM may be influenced by processes that occur in the cochlea, where signals are subject to cochlear compression and adaptive mechanisms that modulate the cochlear response such as the medial olivocochlear (MOC) reflex. Specifically, cochlear compression may reduce the difference between high-intensity peaks and low-intensity valleys (i.e., effective modulation depth) of AM. Furthermore, gain reduction of the cochlear amplifier via the MOC reflex is hypothesized to decompress the cochlear input-output function and thus improve the AM effective modulation depth at moderate levels. To test these hypotheses, AM detection was measured for a narrow-band, high-frequency carrier (5000 Hz) for conditions that do or do not elicit the MOC reflex. These conditions take advantage of the sluggish onset of the reflex, which exhibits an onset delay (?25 ms) upon stimulation. Specifically, AM detection was measured as a function of level for a 50 ms carrier in the presence and absence of a long ipsilateral notched-noise precursor. A longer carrier (500 ms) without a precursor was also included. For no-precursor condition, AM detection thresholds at moderate carrier levels are poorer compared to low and high levels, consistent with a reduced effective modulation depth due to cochlear compression. In the precursor condition, AM thresholds improved monotonically with carrier level, with the largest improvements seen at moderate levels. This improvement is consistent with decompression of the cochlear input-output function via the MOC reflex. For 500 ms carriers, AM detection thresholds improved by a constant (across all carrier levels) relative to AM thresholds with a precursor, consistent with the longer carrier providing more "looks" to detect the AM signal. In a second experiment, AM thresholds were measured as a function of modulation frequency to examine whether the effects of the precursor depend on the modulation frequency. The results showed that the improvement in AM detection with compared to without a precursor is limited to low modulation frequencies (<60Hz). The experiment in Chapter 3 was designed to examine the effects of cochlear compression on the inherent fluctuations of narrow-band noise carriers. To test this, AM detection was measured for short and long, high- and low-fluctuating noise carriers as a function of carrier level. The results showed that AM thresholds for short, low-fluctuating noise carriers worsened as carrier level increased from low to mid carrier levels and then improved with further increases in carrier level, as found in the previous experiment. This is consistent with greater cochlear compression at moderate levels. For high-fluctuating carriers, AM thresholds were roughly constant across carrier levels. For high-fluctuating carriers, low-level linear and mid-level compressive cochlear response growth may have resulted in constant envelope signal-to-noise ratios, due to the cochlear response growth equally affecting the target modulation and inherent carrier fluctuations. Thus, AM detection for high-fluctuating carriers is constant as a function of carrier level

Dynamics of Vocalization-Induced Modulation of Auditory Cortical Activity at Mid-utterance

Background: Recent research has addressed the suppression of cortical sensory responses to altered auditory feedback that occurs at utterance onset regarding speech. However, there is reason to assume that the mechanisms underlying sensorimotor processing at mid-utterance are different than those involved in sensorimotor control at utterance onset. The present study attempted to examine the dynamics of event-related potentials (ERPs) to different acoustic versions of auditory feedback at mid-utterance. Methodology/Principal findings: Subjects produced a vowel sound while hearing their pitch-shifted voice (100 cents), a sum of their vocalization and pure tones, or a sum of their vocalization and white noise at mid-utterance via headphones. Subjects also passively listened to playback of what they heard during active vocalization. Cortical ERPs were recorded in response to different acoustic versions of feedback changes during both active vocalization and passive listening. The results showed that, relative to passive listening, active vocalization yielded enhanced P2 responses to the 100 cents pitch shifts, whereas suppression effects of P2 responses were observed when voice auditory feedback was distorted by pure tones or white noise. Conclusion/Significance: The present findings, for the first time, demonstrate a dynamic modulation of cortical activity as a function of the quality of acoustic feedback at mid-utterance, suggesting that auditory cortical responses can be enhanced or suppressed to distinguish self-produced speech from externally-produced sounds

The Bird's Ear View: Audification for the Spectral Analysis of Heliospheric Time Series Data.

The sciences are inundated with a tremendous volume of data, and the analysis of rapidly expanding data archives presents a persistent challenge. Previous research in the field of data sonification suggests that auditory display may serve a valuable function in the analysis of complex data sets. This dissertation uses the heliospheric sciences as a case study to empirically evaluate the use of audification (a specific form of sonification) for the spectral analysis of large time series. Three primary research questions guide this investigation, the first of which addresses the comparative capabilities of auditory and visual analysis methods in applied analysis tasks. A number of controlled within-subject studies revealed a strong correlation between auditory and visual observations, and demonstrated that auditory analysis provided a heightened sensitivity and accuracy in the detection of spectral features. The second research question addresses the capability of audification methods to reveal features that may be overlooked through visual analysis of spectrograms. A number of open-ended analysis tasks quantitatively demonstrated that participants using audification regularly discovered a greater percentage of embedded phenomena such as low-frequency wave storms. In addition, four case studies document collaborative research initiatives in which audification contributed to the acquisition of new domain-specific knowledge. The final question explores the potential benefits of audification when introduced into the workflow of a research scientist. A case study is presented in which a heliophysicist incorporated audification into their working practice, and the “Think-Aloud” protocol is applied to gain a sense for how audification augmented the researcher’s analytical abilities. Auditory observations are demonstrated to make significant contributions to ongoing research, including the detection of previously unidentified equipment-induced artifacts. This dissertation provides three primary contributions to the field: 1) an increased understanding of the comparative capabilities of auditory and visual analysis methods, 2) a methodological framework for conducting audification that may be transferred across scientific domains, and 3) a set of well-documented cases in which audification was applied to extract new knowledge from existing data archives. Collectively, this work presents a “bird’s ear view” afforded by audification methods—a macro understanding of time series data that preserves micro-level detail.PhDDesign ScienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111561/1/rlalexan_1.pd