Perception of Spatially Distributed Sound Sources

Äänen suunnan havaitsemisen tutkimukset ovat paljolti keskittyneet yhden äänilähteen tapaukseen. Useamman samanaikaisen tilassa sijaitsevan äänilähteen havaitsemisesta on kuitenkin myös tutkimuksia. Suuri osa noista tutkimuksista on tehty kuulokkeilla, mutta kaiuttimiakin on käytetty. On havaittu, että äänen leveyden havaitsemiseen vaikuttavat esimerkiksi äänenvoimakkuus, taajuus ja ajallinen pituus. Tässä diplomityössä tilaäänen havaitsemista tutkittiin tekemällä kaksi kuuntelukoetta. Painopiste oli tilassa hajautetusti sijaitsevien äänilähteiden suuntien havaitsemisen tarkkuudessa. Kokeet suoritettiin kaiuttomassa huoneessa, jossa 15 kaiutinta oli asetettu horisontaalitasoon, kaikki samalle etäisyydelle koehenkilöstä. Ensimmäisessä kuuntelukokeessa käytettiin erilaisia laajalle jakautuneita äänilähdekokonaisuuksia. Mukana oli esimerkiksi yksittäinen leveä äänilähde, jonka leveys vaihteli tapauksesta toiseen sekä leveitä äänilähteitä, joiden jakaumassa oli aukkoja. Koehenkilöiden tehtävänä oli kussakin tapauksessa oman havaintonsa mukaan erottaa, mitkä kaiuttimet lähettivät ääntä. Tulosten mukaan äänilähteessä olleita pieniä aukkoja ei havaittu täsmällisesti ja leveät äänilähteet havaittiin kapeampina kuin ne oikeasti olivat. Tulokset viittaavat myös siihen, että tilajakauman yksityiskohtien havaitsemisen tarkkuus on huonompi kuin 15 astetta, kun äänilähde on leveä. Toisessa kuuntelukokeessa testiääninä käytettiin kohinasignaaleja eri kaistanleveyksillä sekä siniaaltoja, jotka jaettiin eri kaiuttimiin. Näitä ääniä esitettiin koehenkilöille käyttämällä eri kaiutinyhdistelmiä, joiden kaiutintiheys vaihteli. Kaiutinyhdistelmiä esitettiin kaksi kerrallaan, ja koehenkilöiden tehtävä oli erottaa, kumpi kahdesta kosketusnäytöllä kuvatusta yhdistelmästä oli käytössä jälkimmäisessä testiäänessä. Tulosten mukaan havaitsemisen tarkkuus pieneni, kun kaiuttimien tiheys kasvoi. Myös kohinasignaalien kaistanleveys vaikutti havaitsemisen tarkkuuteen.Sound localization studies have mostly been concentrating on the localization of a single source. Nevertheless, there are studies on the perception of several simultaneous sound sources in spatial conditions. A large number of those experiments have been done using headphones, but also loudspeakers have been used. It has been found out that spatial width perception is affected for example by signal loudness, frequency and temporal length. In this thesis, perception of spatial sound was investigated by conducting two listening tests. The focus was on the resolution of directional perception of spatially distributed sound sources. The tests were performed in an anechoic chamber using 15 loudspeakers that were placed in the horizontal plane equidistant from the listener. In the first listening test, various sound source distributions such as sound sources with varying widths and wide sound sources with gaps in the distribution were used. The subjects were asked to distinguish which loudspeakers emit sound according to their own perception. Results show that small gaps in the sound source were not perceived accurately and wide sound sources were perceived narrower than they actually were. The results also indicate that the resolution for fine spatial details is worse than 15 degrees when the sound source is wide. In the second listening test, noise signals with different bandwidths as well as sine waves divided to the loudspeakers were used as stimuli. These were presented to the subjects using loudspeaker combinations with different loudspeaker densities. Two loudspeaker combinations at a time were presented and the task of the subjects was to discriminate which of the two shown combinations was used in producing the latter of the two sound events. The results indicate that the perception accuracy decreased as the loudspeaker density increased. Also, the bandwidth of the noise signals affected the perception accuracy

Continuous 24-h Photoplethysmogram Monitoring Enables Detection of Atrial Fibrillation

Aim: Atrial fibrillation (AF) detection is challenging because it is often asymptomatic and paroxysmal. We evaluated continuous photoplethysmogram (PPG) for signal quality and detection of AF.Methods: PPGs were recorded using a wrist-band device in 173 patients (76 AF, 97 sinus rhythm, SR) for 24 h. Simultaneously recorded 3-lead ambulatory ECG served as control. The recordings were split into 10-, 20-, 30-, and 60-min time-frames. The sensitivity, specificity, and F1-score of AF detection were evaluated for each time-frame. AF alarms were generated to simulate continuous AF monitoring. Sensitivities, specificities, and positive predictive values (PPVs) of the alarms were evaluated. User experiences of PPG and ECG recordings were assessed. The study was registered in the Clinical Trials database (NCT03507335).Results: The quality of PPG signal was better during night-time than in daytime (67.3 +/- 22.4% vs. 30.5 +/- 19.4%, p < 0.001). The 30-min time-frame yielded the highest F1-score (0.9536), identifying AF correctly in 72/76 AF patients (sensitivity 94.7%), only 3/97 SR patients receiving a false AF diagnosis (specificity 96.9%). The sensitivity and PPV of the simulated AF alarms were 78.2 and 97.2% at night, and 49.3 and 97.0% during the daytime. 82% of patients were willing to use the device at home.Conclusion: PPG wrist-band provided reliable AF identification both during daytime and night-time. The PPG data's quality was better at night. The positive user experience suggests that wearable PPG devices could be feasible for continuous rhythm monitoring.Peer reviewe

Tilajakaumaltaan monimutkaisten äänitapahtumien havaitseminen ja havaitsemisen mallintaminen

The sound localization ability of humans is dominantly based on temporal differences and sound-pressure-level differences between the ears. Localization is most accurate with a single sound source in the frontal horizontal plane. However, natural scenarios typically consist of more than one sound source having narrower or broader spatial extent. The aim of this thesis was to study how humans perceive such complex scenarios and how various attributes of the sound scene contribute to the perception.  In all of the listening experiments of this thesis, the perception of widely distributed sound scenarios was studied on the horizontal plane. Sounds were presented from varying loudspeaker setups with up to thirteen loudspeakers close to one another. With noise signals, the directions of only up to three individual sound sources were accurately perceived at their original locations, and widely distributed sound source groups were perceived as narrower than they were. With monophonic music and ambient-noise signals that were synthesized to be spatially extended, the perception was found to be yet slightly narrower than with the noise cases. The effects of changes in the temporal domain were investigated as well. First, peaks in the signal envelope were shown to aid in the directional discrimination of a sound in the presence of two other simultaneous spatially non-overlapping sounds. Second, accurate spatial perception of temporally successive sounds was shown to be difficult, as the inter-stimulus-interval was required to be high in order to perceive the correct spatial distribution of the presented sounds. In addition to studying human perception, a binaural auditory model was developed to mimic human spatial hearing performance. The design of the model was motivated by knowledge on neurophysiology and psychoacoustics. A binaural activity map produced by the model showed performance matching that of humans in various listening scenarios. Importantly, spatially wide or complex sound scenarios can be analyzed as well, a feature uncommon in auditory modeling. Furthermore, the model was applied in the assessment of spatial sound reproduction techniques and showed differences in activation when there were perceivable differences in the reproduced scenarios.  The results give new insight on spatial sound perception. Overall, spatial hearing is not accurate in localizing multiple simultaneous sounds as opposed to accuracy in vision. Obtained results help in the development of parametric spatial sound reproduction techniques, as the techniques do not need to reproduce details that are not perceived by human listeners.Äänten paikallistaminen perustuu ihmisillä ennen kaikkea korvienvälisiin aika- ja äänenvoimakkuuseroihin. Tarkimmillaan paikallistamiskyky on silloin, kun yksittäisiä ääniä esitetään horisontaalitasolla etusuunnassa. Luonnollisissa tilanteissa on kuitenkin yleensä useampi kuin yksi äänilähde, ja kukin näistä lähteistä saattaa muodostaa äänitapahtuman, joka havaitaan pistemäisenä tai leveämpänä. Tämän väitöskirjan tavoitteena oli tutkia ihmisten kykyä havaita tilajakaumaltaan monimutkaisia äänitapahtumia sekä sitä, miten äänten eri ominaisuudet vaikuttavat havaintoon. Väitöskirjan kaikissa kuuntelukokeissa tutkittiin horisontaalitasossa laajojen äänitapahtumien havaitsemista. Äänet esitettiin erilaisista kaiutinkokonaisuuksista, ja yhtäaikaisesti käytössä oli yhdestä kolmeentoista lähekkäin sijoitettua kaiutinta. Tutkimukset osoittivat, että kohinasignaaleilla enimmillään vain kolmen erillisen äänilähteen suunnat oli mahdollista havaita tarkasti. Laajalle levitetyt äänilähderyhmät vuorostaan havaittiin kapeampina kuin ne oikeasti olivat. Havainto oli vielä kapeampi, kun testiäänenä oli synteettisesti levitettyä musiikkia tai meren kohinaa. Ajallisten muutosten vaikutuksia tutkittiin käyttämällä testiääntä, jonka verhokäyrässä oli lyhyitä piikkejä. Piikikkyyden lisääntyminen helpotti tehtävää, jossa pyrittiin havaitsemaan kohdeäänen suunta kahden eri suunnista tulevan häiriöäänen välistä. Lyhyiden peräkkäin esitettyjen äänten suuntien tarkka havaitseminen osoittautui haastavaksi, sillä äänten tarkka tilajakauma havaittiin vasta, kun äänten välinen aikaero oli huomattavan suuri. Ihmisen havaintokyvyn tutkimisen lisäksi väitöskirjassa kehitettiin binauraalinen kuulomalli, jonka tehtävänä on jäljitellä ihmisen tilakuulon toiminnallisuutta. Sen toteutuksessa käytettiin pohjana neurofysiologian ja psykoakustiikan tietoja. Mallin suorituskyvyn osoitettiin olevan samankaltainen kuin ihmisten kyky useissa erilaisissa kuuntelutilanteissa. Myös tilajakaumaltaan leveiden tai monimutkaisten äänitapahtumien analysointi toimii, mikä on toistaiseksi harvinainen ominaisuus kuulomalleissa. Lisäksi testattiin mallin kykyä analysoida tilaäänentoistomenetelmiä, ja mallin tuottamassa aktivaatiossa oli nähtävissä muutoksia silloin, kun ihminenkin pystyi toistetuista äänitapahtumista sellaisia havaitsemaan. Väitöskirjan tulokset antavat uusia näkemyksiä tilaäänen havaitsemiseen. Yleisesti ottaen voidaan sanoa, että useiden samanaikaisten äänten paikantaminen on epätarkkaa verrattuna näkökyvyn tarkkuuteen. Tuloksista on hyötyä parametristen tilaäänentoistomenetelmien kehityksessä, sillä kyseiset tekniikat perustuvat ihmisen havaintokyvyn puutteiden hyödyntämiseen

Expertise in using the Rorschach Comprehensive System in personality assessment

The aim of the present study has been to investigate how differently skilled clinical psychologists use the Rorschach Comprehensive System (RCS) when they assess personality. There are no earlier studies in this area, and therefore the nature of this study is exploratory, aiming at the discovery of new knowledge that can act as a basis for further investigations. The subjects comprised three skill groups (expert, intermediate, and novice groups), each of which included 10 participants. They were to assess the personality of two real patients, using the anamnesis, the WAIS-R profile, and the RCS-materials. The assessments were carried out thinking aloud and the transcribed verbal protocols (610 pages) were used as data. The relevant categories were found using a datadriven approach. They were as follows: items used from the RCS-materials, inferences made from items, integration of information, errors in using the RCS, and content and structure of personality characteristics. The first key result was that experts differed mostly from other groups by making more inferences from RCS-materials, integrating more, making fewer errors and constructing more complex personality characteristics, and skilled use of the RCS in personality assessment is thus primarily seen to be connected to these activities. The second main result was that there were no differences between the intermediate and novice groups, which raises discussion about the development of skills in this area

Spatial Perception of Sound Source Distribution in the Median Plane

Spatial perception of concurrently active sound sources was investigated in an exploratory listening experiment. Incoherent noise source distributions of varying spatial characteristics were presented from loudspeaker arrays in anechoic conditions. The arrays were coinciding with the +/- 45 degrees angular sectors in the frontal median and horizontal planes. The task of the immobile subjects was to report the directions of loudspeakers they perceived emitting sound. The results from median plane distributions suggest that two concurrent sources located along the vertical midline can be perceived individually without resorting to head movements when they are separated in elevation by 60 degrees or more. With source pairs separated by less than 60 degrees. and with more complex physical distributions, the distributions were perceived inaccurately, biased, and spatially compressed but nevertheless not as point-like auditory images.Peer reviewe

Effect of spectral overlap on the echo suppression threshold for single reflection conditions

In performing arts venues, the spectra of direct and reflected sound at a receiving location differ, due to seat dip effect, diffusive and absorptive surfaces, and source directivity. This paper examines the influence of differing lead and lag spectral contents on echo suppression threshold. The results indicate, that for a highpass filtered direct sound and a broadband reflection, attenuation of low frequencies initially results in an increase in echo suppression threshold, while for higher cutoff frequencies echo suppression threshold drastically decreases. For broadband direct sound and filtered reflections, the echo suppression threshold is inversely related to high frequency content. (C) 2013 Acoustical Society of Americ

Neural realignment of spatially separated sound components

Natural auditory scenes often consist of several sound sources overlapping in time, but separated in space. Yet, location is not fully exploited in auditory grouping: spatially separated sounds can get perceptually fused into a single auditory object and this leads to difficulties in the identification and localization of concurrent sounds. Here, the brain mechanisms responsible for grouping across spatial locations were explored in magnetoencephalography (MEG) recordings. The results show that the cortical representation of a vowel spatially separated into two locations reflects the perceived location of the speech sound rather than the physical locations of the individual components. In other words, the auditory scene is neurally rearranged to bring components into spatial alignment when they were deemed to belong to the same object. This renders the original spatial information unavailable at the level of the auditory cortex and may contribute to difficulties in concurrent sound segregation.Peer reviewe

Auditory localization by subjects with unilateral tinnitus

Tinnitus is associated with changes in neural activity. How such alterations impact the localization ability of subjects with tinnitus remains largely unexplored. In this study, subjects with self-reported unilateral tinnitus were compared to subjects with matching hearing loss at high frequencies and to normal-hearing subjects in horizontal and vertical plane localization tasks. Subjects were asked to localize a pink noise source either alone or over background noise. Results showed some degree of difference between subjects with tinnitus and subjects with normal hearing in horizontal plane localization, which was exacerbated by background noise. However, this difference could be explained by different hearing sensitivities between groups. In vertical plane localization there was no difference between groups in the binaural listening condition, but in monaural listening the tinnitus group localized significantly worse with the tinnitus ear. This effect remained when accounting for differences in hearing sensitivity. It is concluded that tinnitus may degrade auditory localization ability, but this effect is for the most part due to the associated levels of hearing loss. More detailed studies are needed to fully disentangle the effects of hearing loss and tinnitus.Peer reviewe