Browsing by Author "Sams, Mikko"
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Item Acoustic model and language model adaptation for a mobile dictation service(Aalto University, 2010) Mansikkaniemi, André; Kurimo, Mikko; Elektroniikan, tietoliikenteen ja automaation tiedekunta; Sams, MikkoAutomatisk taligenkänning är en maskinstyrd metod genom vilken tal omvandlas till text. MobiDic är en mobil dikteringstjänst som använder ett serverbaserat automatiskt taligenkänningssystem för att omvandla tal inspelat på en mobiltelefon till läsbara och editerbara textdokument. I detta arbete undersöktes förmågan hos Tekniska Högskolans taligenkänningssystem att omvandla juridik-relaterat tal inspelat på en mobiltelefon med MobiDics klientprogram till korrekt text. Det fanns skillnader mellan test- och träningsdata gällande både akustik och språk. De akutiska bakgrundsmodellerna var tränade med tal som hade spelats in på en datormikrofon. Språkmodellerna var tränade med text från olika tidningar och nyhetstjänster. På grund av testdatans speciella karaktär har tyngdpunkten i arbetet legat på att förbättra taligenkänningsförmågan hos systemet genom adaptering av akustiska modeller och språkmodeller. Adaptering av akustiska modeller ger de bästa och pålitligaste resultaten i syftet att förbättra taligenkänningsförmågan. Genom att använda den globala cMLLR-metoden och endast 2 minuter av adapteringsdata kan man förminska antalet feltolkade ord med 15-22%. Genom att använda den regressionsklassbaserade cMLLR-metoden kan man uppnåytterligare förbättringar i taligenkänningsförmågan om det finns större mängder av adapteringsdata (> 10 min.) tillgängligt. Adaptering av språkmodellen gav ingen betydande förbättring av taligenkännings förmågan. Det främsta problemet var de stora skillnaderna mellan språkadapteringsdata och språket som förekom i de juridik-relaterade talinspelningarna.Item ACT OF FICTION : Simultaneously experienced multiple perspectives of (un)reality when engaging with narrative-based art(M I T PRESS, 2023-08-01) Amir, Einat; Sofaer, Joshua; Sams, Mikko; Department of Art and Media; National Cheng Kung University; Department of Computer Science; Department of Neuroscience and Biomedical EngineeringThe authors propose a new conception of the mechanism that occurs during a narrative-based art experience—the “Act of Fiction.” They claim that there is no “suspension of disbelief” but rather something more similar to our decision-making systems, enabling us to simultaneously be present in the real and the unreal (fictional). The article’s first part contains a narrative account in which an Act of Fiction takes place; it exemplifies what it also describes. The second part provides an analysis of this phenomenon through a review of current literature and our position on it. The third part proposes an outline for a primary examination of what might be happening in the brain in the experience of an Act of Fiction. The authors conclude by suggesting directions for future research.Item Action in Perception: Prominent Visuo-Motor Functional Symmetry in Musicians during Music Listening(2015) Burunat, Iballa; Brattico, Elvira; Puolivali, Tuomas; Ristaniemi, Tapani; Sams, Mikko; Toiviainen, Petri; Department of Neuroscience and Biomedical EngineeringMusical training leads to sensory and motor neuroplastic changes in the human brain. Motivated by findings on enlarged corpus callosum in musicians and asymmetric somatomotor representation in string players, we investigated the relationship between musical training, callosal anatomy, and interhemispheric functional symmetry during music listening. Functional symmetry was increased in musicians compared to nonmusicians, and in keyboardists compared to string players. This increased functional symmetry was prominent in visual and motor brain networks. Callosal size did not significantly differ between groups except for the posterior callosum in musicians compared to nonmusicians. We conclude that the distinctive postural and kinematic symmetry in instrument playing cross-modally shapes information processing in sensory-motor cortical areas during music listening. This cross-modal plasticity suggests that motor training affects music perception.Item Adapting a Gaze Tracking System to Mobile Environments(2012) Meriläinen, Arto; Jagadeesan, Sharman; Lääketieteellisen tekniikan ja laskennallisen tieteen laitos; Sams, MikkoGaze tracking has traditionally been performed in controlled laboratory environments. The experiment setups have commonly been limited to study only computer-human interaction. Recently, the need to perform experiments in natural environments has emerged in different areas of science. This thesis overviews the structure of a mobile gaze tracking system, that was developed in the Ganzheit project. The goal of the gaze tracking system is to offer an open alternative for commercial systems. The developed gaze tracker utilizes model-based gaze tracking. The approach is accurate and robust against movements of the head. In order to utilize model-based gaze tracking, it is vital to identify the pupil and corneal reflections from an eye image. The constructive part of the thesis focuses on developing a method for identifying the features from the eye image. The developed method is tested with experimental data. The results show that the method for finding the pupil is accurate and robust against differences in facial features and changing lighting conditions. The goodness of recognizing the corneal reflections varies between test subjects. The mobile gaze tracking system is experimented in an ordinary office room. The results indicate that the developed method works adequately.Item Attending to and neglecting people(2016-05-05) Hari, Riitta; Sams, Mikko; Nummenmaa, Lauri; Department of Neuroscience and Biomedical Engineering; Department of ArtHuman behaviour is context-dependent—based on predictions and influenced by the environment and other people. We live in a dynamic world where both the social stimuli and their context are constantly changing. Similar dynamic, natural stimuli should, in the future, be increasingly used to study social brain functions, with parallel development of appropriate signal-analysis methods. Understanding dynamic neural processes also requires accurate time-sensitive characterization of the behaviour. To go beyond the traditional stimulus–response approaches, brain activity should be recorded simultaneously from two interacting subjects to reveal why human social interaction is critically different from just reacting to each other. This theme issue on Attending to and neglecting people contains original work and review papers on person perception and social interaction. The articles cover research from neuroscience, psychology, robotics, animal interaction research and microsociology. Some of the papers are co-authored by scientists who presented their own, independent views in the recent Attention and Performance XXVI conference but were brave enough to join forces with a colleague having a different background and views. In the future, information needs to converge across disciplines to provide us a more holistic view of human behaviour, its interactive nature, as well as the temporal dynamics of our social world.Item Auditory representation of learned sound sequences in motor regions of the macaque brain(NATL ACAD SCIENCES, 2020-06-30) Archakov, Denis; DeWitt, Iain; Kuśmierek, Paweł; Ortiz-Rios, Michael; Cameron, Daniel; Cui, Ding; Morin, Elyse L.; VanMeter, John W.; Sams, Mikko; Jääskeläinen, Iiro P.; Rauschecker, Josef P.; Department of Neuroscience and Biomedical Engineering; Georgetown UniversityHuman speech production requires the ability to couple motor actions with their auditory consequences. Nonhuman primates might not have speech because they lack this ability. To address this question, we trained macaques to perform an auditory-motor task producing sound sequences via hand presses on a newly designed device ("monkey piano"). Catch trials were interspersed to ascertain the monkeys were listening to the sounds they produced. Functional MRI was then used to map brain activity while the animals listened attentively to the sound sequences they had learned to produce and to two control sequences, which were either completely unfamiliar or familiar through passive exposure only. All sounds activated auditory midbrain and cortex, but listening to the sequences that were learned by self-production additionally activated the putamen and the hand and arm regions of motor cortex. These results indicate that, in principle, monkeys are capable of forming internal models linking sound perception and production in motor regions of the brain, so this ability is not special to speech in humans. However, the coupling of sounds and actions in nonhuman primates (and the availability of an internal model supporting it) seems not to extend to the upper vocal tract, that is, the supralaryngeal articulators, which are key for the production of speech sounds in humans. The origin of speech may have required the evolution of a "command apparatus" similar to the control of the hand, which was crucial for the evolution of tool use.Item Automated recognition of young conifer trees using machine vision in mechanical point cleaning of young stands(2008) Luoma, Matti; Visala, Arto; Elektroniikan, tietoliikenteen ja automaation tiedekunta; Teknillinen korkeakoulu; Helsinki University of Technology; Sams, MikkoTässä diplomityössä tutkittiin havupuun taimen automaattista tunnistamista todellisessa metsäympäristössä. Tutkimuksen tavoitteena on tehostaa taimikon koneellista reikäperkausta helpottamalla koneen ohjaajan työtä konenäkömenetelmin. Työssä keskityttiin kuusen taimen segmentoimiseen digitaalisesta kuvasta. Segmentointiin kokeiltiin useita erilaisia tekstuurianalyysialgoritmejä: yhteisesiintymämatriisi, reunataajuus, fraktaalidimensiot, local binary patterns ja Gabor-filtterit. Lisäksi väri-informaation käyttöä segmentointiin tutkittiin laskemalla värikanavista EGRB muunnokset. Paras segmentointitulos saatiin local binary pattern (LBP) menetelmällä lasketuista tekstuuripiirteistä sekä kynnystämällä värikanavista lasketulla excessive green (EG) arvolla. Näillä menetelmällä algoritmi onnistui estimoimaan havupuun taimen keskikohdan sijainnin oikein yli 80 %:ssa testikuvista.Item Behavioral and physiological correlates of empathy and empathic accuracy in human-centered design(2020-12-14) Piispanen, Matias; Alho, Jussi; Perustieteiden korkeakoulu; Sams, MikkoHuman-centered design (HCD) employs various empathetic techniques in order to enhance designers’ understanding of the user experience. Thus, enables them to create products and designs that truly meet users’ needs as well as are inclusive for all of them. However, the field currently lacks measures to quantify empathy’s role in the design process, nor is it well known how accurately designers understand the user experience. For this reason, this thesis evaluated the feasibility of measuring the autonomic nervous system (ANS) synchrony by comparing changes in heart rate (HR) between a designer and users in a semi-structured design interview. This is due to interpersonal synchrony which has been suggested to be an important mechanism supporting empathy. In addition, the thesis assesses the designer’s capability to correctly infer the users’ thoughts and feelings using the empathic accuracy (EA) method, as well as tests whether ANS synchrony can be used to predict the designer’s capability to understand the users. A statistically significant HR synchrony was found in 40% of all the designer- user dyads. The designer on average correctly inferred 47% of the users’ reported thoughts and feelings. The results showed no relation between HR synchrony and the designer’s EA scores. In conclusion, the results suggest that it is possible to detect significant HR synchrony between a designer and a user during a design interview. However, the study demonstrated that designer can only partially understand the users’ experience, thus highlighting the importance of these results for the design field. Nevertheless, further research is needed to verify the findings and the role of empathy in HCD.Item Behavioural activation system sensitivity is associated with cerebral μ-opioid receptor availability(Oxford University Press, 2016-04-06) Karjalainen, Tomi; Tuominen, Lauri; Manninen, Sandra; Kalliokoski, Kari K.; Nuutila, Pirjo; Jääskeläinen, Iiro; Hari, Riitta; Sams, Mikko; Nummenmaa, Lauri; Department of Neuroscience and Biomedical Engineering; Department of Art; Turku PET CentreThe reinforcement-sensitivity theory proposes that behavioural activation and inhibition systems (BAS and BIS, respectively) guide approach and avoidance behaviour in potentially rewarding and punishing situations. Their baseline activity presumably explains individual differences in behavioural dispositions when a person encounters signals of reward and harm. Yet, neurochemical bases of BAS and BIS have remained poorly understood. Here we used in vivo positron emission tomography with a μ-opioid receptor (MOR) specific ligand [11C]carfentanil to test whether individual differences in MOR availability would be associated with BAS or BIS. We scanned 49 healthy subjects and measured their BAS and BIS sensitivities using the BIS/BAS scales. BAS but not BIS sensitivity was positively associated with MOR availability in frontal cortex, amygdala, ventral striatum, brainstem, cingulate cortex and insula. Strongest associations were observed for the BAS subscale ‘Fun Seeking’. Our results suggest that endogenous opioid system underlies BAS, and that differences in MOR availability could explain inter-individual differences in reward seeking behaviour.Item Bodily maps of musical sensations across cultures(National Academy of Sciences, 2024-01-25) Putkinen, Vesa; Zhou, Xinqi; Gan, Xianyang; Yang, Linyu; Becker, Benjamin; Sams, Mikko; Nummenmaa, Lauri; Department of Neuroscience and Biomedical Engineering; University of Turku; Sichuan Normal University; University of Electronic Science and Technology of China; Sichuan University; University of Hong KongEmotions, bodily sensations and movement are integral parts of musical experiences. Yet, it remains unknown i) whether emotional connotations and structural features of music elicit discrete bodily sensations and ii) whether these sensations are culturally consistent. We addressed these questions in a cross-cultural study with Western (European and North American, n = 903) and East Asian (Chinese, n = 1035). We precented participants with silhouettes of human bodies and asked them to indicate the bodily regions whose activity they felt changing while listening to Western and Asian musical pieces with varying emotional and acoustic qualities. The resulting bodily sensation maps (BSMs) varied as a function of the emotional qualities of the songs, particularly in the limb, chest, and head regions. Music-induced emotions and corresponding BSMs were replicable across Western and East Asian subjects. The BSMs clustered similarly across cultures, and cluster structures were similar for BSMs and self-reports of emotional experience. The acoustic and structural features of music were consistently associated with the emotion ratings and music-induced bodily sensations across cultures. These results highlight the importance of subjective bodily experience in music-induced emotions and demonstrate consistent associations between musical features, music-induced emotions, and bodily sensations across distant cultures.Item Brain activation networks during natural viewing conditions(2007) Koskentalo, Katri; Jääskeläinen, Iiro; Pomren, Cajus; Sähkö- ja tietoliikennetekniikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Sams, MikkoPerinteisesti aivotutkimuksessa on keskitytty tutkimaan tiettyä aivojen toiminnan osa-aluetta kerrallaan käyttämällä hyvin keinotekoisia ja yksinkertaistettuja ärsykkeitä. Tässä kokeessa annoimme koehenkilöiden katsella vapaasti monimuotoista ärsykettä, elokuvaa, samalla kun heidän aivotoimintaansa tallennettiin toiminnallisella magneettikuvauksella, fMRI:llä. Pyrkimyksenämme oli selvittää millaiset samankaltaiset aivojen verkostot aktivoituvat tällaisissa luonnollisen kaltaisissa olosuhteissa eri koehenkilöillä. Luonnollisen kaltaiset olosuhteet paljastavat todennäköisesti enemmän aivojen toiminnasta jokapäiväisessä elämässä. Koehenkilöille esitettiin elokuva Crash (2005). Ensimmäiset 72 minuuttia elokuvasta esitettiin koehenkilöille pimennetyssä huoneessa ja loput 36 minuuttia magneettikuvauslaitteessa. Koehenkilöitä ohjeistettiin katsomaan elokuvaa vapaasti. Magneettikuvauksen jälkeen koehenkilöt katsoivat loput 36 minuuttia elokuvasta uudelleen pimennetyssä huoneessa ja arvioivat kokemiaan emootioita valenssi- ja virittävyysasteikoila. Analyysimenetelminä käytettiin korrelaatioanalyysiä ja riippumattomien komponenttien analyysiä (ICA), jotta voitaisiin selvittää millaiset samankaltaiset hermoverkostot aktivoituivat eri koehenkilöiden kesken. Kokeen tulokset paljastivat suuren korrelaation eri koehenkilöiden aivojen aktivaation välillä. Eri koehenkilöiden aivot näyttivät vastaavan hyvin samankaltaisesti jopa niin monimuotoiseen ärsykkeeseen kuin käytetty elokuva. Riippumattomien komponenttien analyysillä löydettiin useita eri koehenkilöillä samankaltaisia aktivaatiokomponentteja, joista suurin osa luokiteltiin visuaalisiksi tai auditorisiksi. Kokeessa löydettiin myös selektiivinen auditorinen komponentti, joka antoi suurimmat vasteet elokuvan kohdille, joissa esiintyi puhetta. Emootioarviointien tulokset olivat vaikeammin tulkittavissa, eikä yhteneviä johtopäätöksiä pystytty vetämään. Ainoastaan tiettyjen pikkuaivojen alueiden aktivaation havaittiin korreloivan virittävyysarviointien kanssa useimmilla koehenkilöillä.Item Brain-to-brain hyperclassification reveals action-specific motor mapping of observed actions in humans(2017-12-11) Smirnov, Dmitry; Lachat, Fanny; Peltola, Tomi; Lahnakoski, Juha; Koistinen, Olli-Pekka; Glerean, Enrico; Vehtari, Aki; Hari, Riitta; Sams, Mikko; Nummenmaa, Lauri; Department of Neuroscience and Biomedical Engineering; Department of Computer Science; Department of ArtSeeing an action may activate the corresponding action motor code in the observer. It remains unresolved whether seeing and performing an action activates similar action-specific motor codes in the observer and the actor. We used novel hyperclassification approach to reveal shared brain activation signatures of action execution and observation in interacting human subjects. In the first experiment, two "actors" performed four types of hand actions while their haemodynamic brain activations were measured with 3-T functional magnetic resonance imaging (fMRI). The actions were videotaped and shown to 15 "observers" during a second fMRI experiment. Eleven observers saw the videos of one actor, and the remaining four observers saw the videos of the other actor. In a control fMRI experiment, one of the actors performed actions with closed eyes, and five new observers viewed these actions. Bayesian canonical correlation analysis was applied to functionally realign observers' and actors' fMRI data. Hyperclassification of the seen actions was performed with Bayesian logistic regression trained on actors' data and tested with observers' data. Without the functional realignment, between-subjects accuracy was at chance level. With the realignment, the accuracy increased on average by 15 percentage points, exceeding both the chance level and the accuracy without functional realignment. The highest accuracies were observed in occipital, parietal and premotor cortices. Hyperclassification exceeded chance level also when the actor did not see her own actions. We conclude that the functional brain activation signatures underlying action execution and observation are partly shared, yet these activation signatures may be anatomically misaligned across individuals.Item The brains of high functioning autistic individuals do not synchronize with those of others(2013) Salmi, Juha; Roine, Ulrika; Glerean, Enrico; Lahnakoski, Juha; Nieminen-von Wendt, Taina; Tani, P; Leppämäki, S; Nummenmaa, Lauri; Jääskeläinen, Iiro P.; Carlson, Synnöve; Rintahaka, P; Sams, Mikko; Department of Neuroscience and Biomedical EngineeringMultifaceted and idiosyncratic aberrancies in social cognition characterize autism spectrum disorders (ASDs). To advance understanding of underlying neural mechanisms, we measured brain hemodynamic activity with functional magnetic resonance imaging (fMRI) in individuals with ASD and matched-pair neurotypical (NT) controls while they were viewing a feature film portraying social interactions. Pearson's correlation coefficient was used as a measure of voxelwise similarity of brain activity (InterSubject Correlations—ISCs). Individuals with ASD showed lower ISC than NT controls in brain regions implicated in processing social information including the insula, posterior and anterior cingulate cortex, caudate nucleus, precuneus, lateral occipital cortex, and supramarginal gyrus. Curiously, also within NT group, autism-quotient scores predicted ISC in overlapping areas, including, e.g., supramarginal gyrus and precuneus. In ASD participants, functional connectivity was decreased between the frontal pole and the superior frontal gyrus, angular gyrus, superior parietal lobule, precentral gyrus, precuneus, and anterior/posterior cingulate gyrus. Taken together these results suggest that ISC and functional connectivity measure distinct features of atypical brain function in high-functioning autistic individuals during free viewing of acted social interactions. Our ISC results suggest that the minds of ASD individuals do not ‘tick together’ with others while perceiving identical dynamic social interactions.Item Changes in the activation of human auditory cortex during visual speech perception and soudless vowel production: an fMRJ study(2009) Kari, Heini; Balk, Marja; Jääskeläinen, Iiro; Lääketieteellisen tekniikan ja laskennallisen tieteen laitos; Teknillinen korkeakoulu; Helsinki University of Technology; Sams, MikkoInformation from different senses is integrated in the human brain. The purpose of this study was to examine how the activation in the human auditory cortex changes during audio-visual stimulus. Visual speech and nonlinguistic auditory stimuli were presented simultaneously and activation in auditory cortex was measured using functional magnetic resonance imaging (fMRI). The effect of soundless vowel production in mind was studied as well. In the experiment, two nonlinguistic auditory stimuli were presented at the middle frequencies 250 Hz (low) and 2 000 Hz (high). Duration of the tone was 100 ms and stimuli were repeated every 500 ms in 30-s periods. Low and high frequency tones and silent period were presented in random order. Visual stimuli were videos, 10 minutes in length. In the first video a woman was articulating silently four Finnish language vowels (/a/, /i/, /o/, /y/). In the second, control experiment, there was a still face image of the same woman and moving circles (directions vertical, horizontal, right, left) were superimposed on the mouth region. The third visual stimulus was a still face image and during the condition subject was instructed to soundlessly produce vowels in mind. The results show that lip-reading activated auditory cortex more than control stimuli (moving circles), especially at lower frequencies (250 Hz). Activation was seen in both hemispheres. Furthermore, our results suggest greater activation during control experiment than during lip-reading at higher frequencies (2 000 Hz). During soundless vowel production there was no meaningful activation at either of the frequencies. Our results are consistent with previous findings that there are multiple frequency-dependent (i.e. tonotopically organized) areas in the human auditory cortex. Activation was stronger in the left than in the right hemisphere. Further experiments at different frequency ranges should he carried out to examine tonotopical organization more precise. In the future, higher magnetic field fMRI scanners and combining several experimental study techniques to same investigation might reveal much more about tonotopic organization of the auditory cortex and activation areas during various audio-visual stimuli.Item Cholesterol and lipoproteins in Alzheimer's disease - Comprehensive meta-analysis of the role of serum cholesterol in disease developmet(2007) Hokkanen, Johanna; Sähkö- ja tietoliikennetekniikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Sams, MikkoItem Classification of emotion categories based on functional connectivity patterns of the human brain(ACADEMIC PRESS INC ELSEVIER SCIENCE, 2022-02-15) Saarimäki, Heini; Glerean, Enrico; Smirnov, Dmitry; Mynttinen, Henri; Jääskeläinen, Iiro P.; Sams, Mikko; Nummenmaa, Lauri; Department of Neuroscience and Biomedical Engineering; Department of Computer Science; Aalto University; University of TurkuNeurophysiological and psychological models posit that emotions depend on connections across wide-spread corticolimbic circuits. While previous studies using pattern recognition on neuroimaging data have shown differences between various discrete emotions in brain activity patterns, less is known about the differences in functional connectivity. Thus, we employed multivariate pattern analysis on functional magnetic resonance imaging data (i) to develop a pipeline for applying pattern recognition in functional connectivity data, and (ii) to test whether connectivity patterns differ across emotion categories. Six emotions (anger, fear, disgust, happiness, sadness, and surprise) and a neutral state were induced in 16 participants using one-minute-long emotional narratives with natural prosody while brain activity was measured with functional magnetic resonance imaging (fMRI). We computed emotion-wise connectivity matrices both for whole-brain connections and for 10 previously defined functionally connected brain subnetworks and trained an across-participant classifier to categorize the emotional states based on whole-brain data and for each subnetwork separately. The whole-brain classifier performed above chance level with all emotions except sadness, suggesting that different emotions are characterized by differences in large-scale connectivity patterns. When focusing on the connectivity within the 10 subnetworks, classification was successful within the default mode system and for all emotions. We thus show preliminary evidence for consistently different sustained functional connectivity patterns for instances of emotion categories particularly within the default mode system.Item Complex networks analysis of white matter tracts in Asperger syndrome(2010) Roine, Ulrika; Sams, Mikko; Saramäki, Jari; Elektroniikan, tietoliikenteen ja automaation tiedekunta; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Sams, MikkoItem A computational approach to estimation of crowding in natural images(2008) Ahonen, Lauri; Näsänen, Risto; Elektroniikan, tietoliikenteen ja automaation tiedekunta; Teknillinen korkeakoulu; Helsinki University of Technology; Sams, MikkoÄrsyketungos on ilmiö, jonka vuoksi ääreisnäössä olevien kohteiden tunnistus heikkenee, mikäli kohteen läheisyydessä on häiriöärsykkeitä. Ärsyketungos on siis havaintokentän, eli yhdellä fiksaatiolla havaittavan kohdemäärän, kokoa rajoittava tekijä. Tämä johtuu näköjärjestelmän korkeammilla tasoilla tapahtuvasta laajasta piirreintegraatiosta kohteen ympäristössä. Kriittisestä roolistaan huolimatta ärsyketungos-ilmiötä ei ole tutkittu monimutkaisilla luonnollisilla kuvilla (mikä tahansa valokuva). Tässä tutkimuksessa tutkittiin, kuinka ärsyketungos vaikuttaa kohteen havaitsemiseen monimutkaisissa luonnollisissa kuvissa. Lisäksi haluttiin selvittää voidaanko ilmiön voimakkuutta ennustaa näköjärjestelmä malleja ja kuvien tilastollisia ominaisuuksia käyttäen. Ärsyketungos-ilmiön voimakkuus määritettiin kokeellisesti, mittaamalla kontrasti kynnyksiä erikokoisille kirjainkohteille, jotka sijaitsivat luonnollisen kuvan päällä. Kokeellisen osan tuloksilla validoitiin kehitettyjä metodeja. Metodit perustuivat kuvan tilastollisiin ominaisuuksiin ja `clutter-malleihin' Tilastolliset ominaisuudet ja 'clutter-mallit' yhdistettiin sekä tutkimustietoon ärsyketungoksen ominaisuuksista, että näköjärjestelmän tunnettuihin ominaisuuksiin. Näköjärjestelmä huomioimalla pyrittiin arvioimaan spatiaalisesta näöntarkkuuden vaihtelusta aiheutuvia muutoksia kuvan tilastollisiin ominaisuuksiin. Kehitetyt metodit ennustivat mielivaltaisen kuvan aiheuttaman ärsyketungos-ilmiön voimakkuuden. Myös näköjärjestelmän malli vaikutti tuloksiin. Erot eri laskentamallien välillä olivat kuitenkin merkityksettömiä. Täten yksinkertaisinta metodia, jossa laskettiin kontrastienergiaa, voidaan pitää tehokkaimpana. Luonnolliset kuvat voivat aiheuttaa voimakkaan ärsyketungos-ilmiön. Pääteltiin, että ilmiö voidaan ennustaa kohtuullisella tarkkuudella jo nykyisellä tietämyksellä, mutta lisätuntemus ilmiön syistä ja mekanismeista mahdollistaisi tarkempien mallien kehittämisen. Tällaisilla malleilla on sovellutuskohteita esimerkiksi käyttöliittymien suunnitellussa, informaation visualisoinnin arvioinnissa ja lisätyn todellisuuden sovellusten kehityksessä.Item Computational features of neonatal EEG monitoring after asphyxia(2017-02-13) Jaatela, Julia; Tokariev, Anton; Stevenson, Nathan; Perustieteiden korkeakoulu; Sams, MikkoThe aim of this thesis was to find out if computational electroencephalography (EEG) features can be used in the automated monitoring of newborns after asphyxia. EEG is already widely used in the neonatal intensive care units but there is a need for quantitative measures that can be obtained without the presence of a clinical expert. One of the biggest challenges in the treatment of newborns with asphyxia is also to correctly estimate the severity of the resulting neurological problems. Eight different feature classes were computed for 42 full-term babies from periods of quiet and active sleep. These feature classes measured correlations of amplitude and phase, interhemispheric synchrony, multifractality and spectral properties. We then studied the ability of these features to distinguish between different severity groups and also tested a classification algorithm to predict the outcome of the babies. Quiet sleep was noted to be more sensitive when separating groups with different grades of severity and most of the used feature classes showed significant results in statistical testing between the groups. The babies with the normal outcome were classified more accurately with the EEG based classification algorithm, than with only the clinical estimation.Item Consistency of Regions of Interest as nodes of fMRI functional brain networks(2017) Korhonen, Onerva; Saarimäki, Heini; Glerean, Enrico; Sams, Mikko; Saramäki, Jari; Department of Neuroscience and Biomedical Engineering; Department of Computer ScienceThe functional network approach, where fMRI BOLD time series are mapped to networks depicting functional relationships between brain areas, has opened new insights into the function of the human brain. In this approach, the choice of network nodes is of crucial importance. One option is to consider fMRI voxels as nodes. This results in a large number of nodes, making network analysis and interpretation of results challenging. A common alternative is to use predefined clusters of anatomically close voxels, Regions of Interest (ROIs). This approach assumes that voxels within ROIs are functionally similar. Because these two approaches result in different network structures, it is crucial to understand what happens to network connectivity when moving from the voxel level to the ROI level. We show that the consistency of ROIs, defined as the mean Pearson correlation coefficient between the time series of their voxels, varies widely in resting-state experimental data. Therefore the assumption of similar voxel dynamics within each ROI does not generally hold. Further, the time series of low-consistency ROIs may be highly correlated, resulting in spurious links in ROI-level networks. Based on these results, we recommend that averaging BOLD signals over anatomically defined ROIs should be carefully considered.
