Visual search and eye movements: Studies of perceptual span

In visual search one tries to find the currently relevant item among other, irrelevant items. In the present study, visual search performance for complex objects (characters, faces, computer icons and words) was investigated, and the contribution of different stimulus properties, such as luminance contrast between characters and background, set size, stimulus size, colour contrast, spatial frequency, and stimulus layout were investigated. Subjects were required to search for a target object among distracter objects in two-dimensional stimulus arrays. The outcome measure was threshold search time, that is, the presentation duration of the stimulus array required by the subject to find the target with a certain probability. It reflects the time used for visual processing separated from the time used for decision making and manual reactions. The duration of stimulus presentation was controlled by an adaptive staircase method. The number and duration of eye fixations, saccade amplitude, and perceptual span, i.e., the number of items that can be processed during a single fixation, were measured. It was found that search performance was correlated with the number of fixations needed to find the target. Search time and the number of fixations increased with increasing stimulus set size. On the other hand, several complex objects could be processed during a single fixation, i.e., within the perceptual span. Search time and the number of fixations depended on object type as well as luminance contrast. The size of the perceptual span was smaller for more complex objects, and decreased with decreasing luminance contrast within object type, especially for very low contrasts. In addition, the size and shape of perceptual span explained the changes in search performance for different stimulus layouts in word search. Perceptual span was scale invariant for a 16-fold range of stimulus sizes, i.e., the number of items processed during a single fixation was independent of retinal stimulus size or viewing distance. It is suggested that saccadic visual search consists of both serial (eye movements) and parallel (processing within perceptual span) components, and that the size of the perceptual span may explain the effectiveness of saccadic search in different stimulus conditions. Further, low-level visual factors, such as the anatomical structure of the retina, peripheral stimulus visibility and resolution requirements for the identification of different object types are proposed to constrain the size of the perceptual span, and thus, limit visual search performance. Similar methods were used in a clinical study to characterise the visual search performance and eye movements of neurological patients with chronic solvent-induced encephalopathy (CSE). In addition, the data about the effects of different stimulus properties on visual search in normal subjects were presented as simple practical guidelines, so that the limits of human visual perception could be taken into account in the design of user interfaces.

Luonto, tiede ja teknologia : Kansanvalistuksen Suomi-kuva 1870-1920

Nature, science and technology. The image of Finland through popular enlightenment texts 1870-1920 This doctoral thesis looks at how Finnish popular enlightenment texts published between 1870 and 1920 took part in the process of forming a genuine Finnish national identity. The same process was occurring in other Nordic countries at the time and the process in Finland was in many ways influenced by them, particularly Sweden. In Finland the political realities under Russian rule especially during the Russification years, and the fact that its history was considered to be short compared to other European countries, made this nation-building process unique. The undertaking was led by members of the national elite, influential in the cultural, academic as well as political arenas, who were keen to support the foundation of a modern Finnish identity. The political realities and national philosophy of history necessitated a search for elements of identity in nature and the Finnish landscape, which were considered to have special national importance: Finland was very much determined as a political entity on the basis of its geography and nature. Nature was also used as means of taking a cultural or political view in terms of, for example, geographical facts such as the nation s borders or the country s geographical connections to Western Europe. In the building of a proper national identity the concept of nature was not, however, static, but was more or less affected by political and economic progress in society. This meant that nature, or the image of the national landscape, was no longer seen only as a visual image of the national identity, but also as a source of science, technology and a prosperous future. The role of technology in this process was very much connected to the ability to harness natural resources to serve national interests. The major change in this respect had occurred by the early 20th century, when indisputable scientific progress altered the relationship between nature and technology. Concerning technology, the thesis is mainly interested in the large and at the time modern technological manifestations, such as railways, factories and industrial areas in Finland. Despite the fact that the symbiosis between national nature and international but successfully localized technology was in Finnish popular enlightenment literature depicted mostly as a national success story, concerns began to arise already in last years of the 19th century. It was argued that the emerging technology would eventually destroy Finland s natural environment, and therefore the basis of its national identity. The question was not how to preserve nature through natural science, but more how to conserve such natural resources and images that were considered to be the basis of national identity and thus of the national history. National parks, isolated from technology, and distant enough so as to have no economic value, were considered the solution to the problem. Methodologically the thesis belongs to the genre of science and technology studies, and offers new viewpoints with regard to both the study of Finnish popular enlightenment literature and the national development process as a whole.

Visual completion in an illusory figure

The visual systems of humans and animals represent physical reality in a modified way, depending on the specific demands that the species in question has for survival. The ability to perceive visual illusions is found in independently evolved visual systems, from honeybees to humans. In humans, the ability emerges early, at the age of four months. Thus the perception of illusion is likely to reflect visual processes of fundamental importance for object perception in natural vision. The experiments reported in this thesis employed various modifications of the Kanizsa triangle, a drawn configuration composed of three black disks with missing sectors on a white background. The sectors appear to form the tips of a triangle. The visual system completes the physically empty area between the disks, generally called inducers, with giving the perception of an illusory triangle. The illusory triangle consists of an illusory surface bounded by illusory contours; the triangle appears brighter than and to lie above the background. If the sectors are coloured, the colour fills the illusory area, a phenomenon known as neon colour spreading . We investigated spatial limitations on the perception of Kanizsa-type illusions and how other stimuli and viewing parameters affected these limitations. We also studied complex configurations thick, bent, mobile and chromatic inducers - to determine whether illusions combining several attributes can be perceived. The results suggest that the visual system is highly effective in completing a percept. The perception of an illusory figure is spatially scale invariant when perceived at threshold. The processing time and the number of fixations modify the percept, making the perception of the illusion more probable in various viewing conditions. Furthermore, the fact that the illusion can be perceived when only one inducer is physically present at any given moment indicates the potential of single inducers. Apparently, modelling illusory figure perception will require a combination of low-level, local processes and higher-level integrative processes. Our studies with stimuli combining several attributes relevant to object perception demonstrate that the perception of an illusory figure is flexible and is maintained also when it contains colour and volume and when shown in movement. All in all, the results confirm the assumed importance of the visual processes related with the perception of illusory figures in everyday viewing. This is indicated by the variety of inducer modifications that can be made without destroying the percept. Furthermore, the illusion can acquire additional attributes from such modifications. Due to individual differences in the perception of illusory figures, universal values for absolute performance are not always meaningful, but stable trends and general relations do exist.

Dynamics of contour, object and face processing in the human visual cortex

The neural basis of visual perception can be understood only when the sequence of cortical activity underlying successful recognition is known. The early steps in this processing chain, from retina to the primary visual cortex, are highly local, and the perception of more complex shapes requires integration of the local information. In Study I of this thesis, the progression from local to global visual analysis was assessed by recording cortical magnetoencephalographic (MEG) responses to arrays of elements that either did or did not form global contours. The results demonstrated two spatially and temporally distinct stages of processing: The first, emerging 70 ms after stimulus onset around the calcarine sulcus, was sensitive to local features only, whereas the second, starting at 130 ms across the occipital and posterior parietal cortices, reflected the global configuration. To explore the links between cortical activity and visual recognition, Studies II III presented subjects with recognition tasks of varying levels of difficulty. The occipito-temporal responses from 150 ms onwards were closely linked to recognition performance, in contrast to the 100-ms mid-occipital responses. The averaged responses increased gradually as a function of recognition performance, and further analysis (Study III) showed the single response strengths to be graded as well. Study IV addressed the attention dependence of the different processing stages: Occipito-temporal responses peaking around 150 ms depended on the content of the visual field (faces vs. houses), whereas the later and more sustained activity was strongly modulated by the observers attention. Hemodynamic responses paralleled the pattern of the more sustained electrophysiological responses. Study V assessed the temporal processing capacity of the human object recognition system. Above sufficient luminance, contrast and size of the object, the processing speed was not limited by such low-level factors. Taken together, these studies demonstrate several distinct stages in the cortical activation sequence underlying the object recognition chain, reflecting the level of feature integration, difficulty of recognition, and direction of attention.

Temporal acuity in developmental dyslexia across the life span : Tactile, auditory, visual, and crossmodal estimations

Taustaa Kehityksellinen dysleksia (lukivaikeus) on erityinen lukemaan oppimisen vaikeus, johon liittyy usein myös vaikeuksia kirjoittamaan oppimisessa. Lukivaikeuden oletetaan useissa tapauksissa johtuvan vaikeudesta käsitellä kielen äännerakenteita (fonologinen prosessointi). Tämä poikkeavuus voi olla joko lukivaikeuden perimmäinen syy tai vaihtoehtoisesti ongelmat äänteiden käsittelyssä voivat heijastaa jotain vielä perustavamman tason vaikeutta. Eräs tällainen ehdotettu perustavan tasoin syy on poikkeavuus aistien toiminnoissa, erityisesti aistien aikatarkkuudessa. Aikatarkkuudella tarkoitetaan kykyä ja rajoja siinä, kuinka nopeasti esitettyä aistitiedon virtaa henkilö kykenee vastaanottamaan ja käsittelemään. Monet arjen toiminnot lukemisen rinnalla edellyttävät aistien erittäin tarkkaa ajallista erottelukykyä (esimerkiksi kuulo puheen ymmärtämisessä, tunto pintamateriaalin tunnistamisessa). Aikatarkkuusvaikeuksien esiintyvyyttä lukivaikeudessa on tutkittu aiemminkin, mutta yksimielisyyteen ei ole päästy siitä, onko kaikilla lukivaikeuksisilla näitä ongelmia tai mihin aisteihin vaikeudet mahdollisesti rajoittuvat. Myöskään ei tiedetä, havaitaanko aikatarkkuuden ongelmia kaiken ikäisillä lukivaikeuksisilla vai vaihteleeko mahdollinen ongelmien kuva iän mukana. Lisäksi on epäselvää, kuinka aikatarkkuuden ongelmat itseasiassa ovat yhteydessä kielen käsittelyn ja varsinaisen lukemisen vaikeuksiin. Tutkimussarjan aihe Tässä tutkimussarjassa aikatarkkuutta tutkittiin kolmessa yksittäisessä aistissa, joita olivat tunto, näkö ja kuulo, sekä kolmessa aistien välisessä yhdistelmässä, joita olivat audiotaktiilinen (kuulo-tunto), visuotaktiilinen (näkö-tunto) ja audiovisuaalinen (näkö-kuulo). Aikatarkkuutta arvioitiin kahdella eri menetelmällä, jotta saataisiin lisää tietoa siitä, missä tietyssä aikatarkkuuden osa-alueessa lukivaikeuksisilla mahdollisesti on vaikeuksia. Ensimmäisessä tehtävässä tutkittavan tuli arvioida, ovatko esitetyt ei-kielelliset ärsykkeet samanaikaisia vai eriaikaisia. Toisessa tehtävässä koehenkilön tuli arvioida esitettyjen ei-kielellisten ärsykkeiden esitysjärjestys. Molemmissa tehtävissä määriteltiin millisekuntitasolla (sekunnin tuhannesosa) se esitysnopeus, jolla koehenkilö kykeni arvioimaan ärsykkeiden ajalliset suhteet oikein. Englanninkielinen demonstraatio aikatarkkuustehtävistä löytyy internetistä (http://www.helsinki.fi/hum/ylpsy/neuropsy). Itse aikatarkkuustehtävien lisäksi tutkimussarjassa arvioitiin tutkimushenkilöiden päättelykykyä, kielellisiä toimintoja ja lukemista. Tutkimushenkilöt Tutkimuksiin osallistui 53 lukivaikeuksista ja 66 sujuvaa lukijaa, jotka oli jaettu kolmeen pääikäryhmään: lapset (8-12 vuotta), nuoret aikuiset (20-36 vuotta) ja ikääntyneemmät aikuiset (20-59 vuotta). Ikääntyneempien aikuisten ryhmä oli edelleen jaettu ikävuosikymmenluokkiin, mikä mahdollisti sen tutkimisen, vaikuttaako lisääntyvä aikuisikä lukivaikeuksisten aikatarkkuuteen (20-29, 30-39, 40-49 ja 50-59 -vuotiaat). Tutkimussarjan tulokset Aikatarkkuuden ongelmat lukivaikeuksisilla olivat yleistyneitä yli iän, aistien ja tehtävien Lukivaikeuksiset kaikissa pääikäryhmissä (lapset, nuoret aikuiset, ikääntyneemmän aikuiset) tarvitsivat samanikäisiä sujuvia lukijoita hitaamman esitystahdin, jotta he kykenivät arvioimaan ei-kielellisten ärsykkeiden ajallisen esitystavan oikein. Tämä aikatarkkuuden ongelma havaittiin lukivaikeuksisilla kaikissa aisteissa (tunto, kuulo, näkö) ja niiden yhdistelmissä (audiotaktiilinen, visuotaktiilinen, audiovisuaalinen). Lukivaikeuksisten aikatarkkuusongelmat ilmenivät edelleen molemmissa tehtävätyypeissä (samanaikaisuuden ja järjestyksen arvioinnissa). Aikatarkkuus ja sen ongelmat olivat yhteydessä äänteiden käsittelyyn Aikatarkkuus oli yhteydessä äänteiden käsittelykykyyn (fonologiseen prosessointiin), niin lapsilla kuin aikuisillakin, kaikissa aisteissa, niiden yhdistelmissä ja tehtävätyypeissä. Yhteys ei-kielellisen aikatarkkuuden ja kielellisten toimintojen välillä oli kuitenkin selkeämpi lukivaikeuksisilla kuin sujuvilla lukijoilla. Tämä tarkoittaa, että etenkin lukivaikeuksisilla ryhmätason huono aikatarkkuus oli yhteydessä huonoon äänteiden käsittelyyn (fonologiseen prosessointiin) ja päinvastoin. Suoraa yhteyttä lukemisen ja aikatarkkuuden välillä ei kuitenkaan havaittu. Lisääntyvä aikuisikä heikensi lukivaikeuksisten aikatarkkuutta suhteettoman paljon Tiedonkäsittelyn nopeuden on toistuvasti osoitettu hidastuvan normaalissa ikääntymisessä. Lisääntyvä aikuisikä (20-59 -vuotiailla) heikensikin sekä sujuvien että lukivaikeuksisten aikatarkkuutta. Toisin sanoen, mitä iäkkäämmästä aikuisesta oli kysymys, sitä hitaammin hänelle tuli esittää ärsykkeet, jotta hän kykeni arvioimaan niiden ajalliset suhteet oikein. Tämä ikään liittyvä tavanomainen hidastuminen oli kuitenkin yllättäen suhteettoman nopeaa lukivaikeuksisilla. Toisin sanoen, jo nuorilla lukivaikeuksisilla havaittu aikatarkkuuden vaikeus (ryhmäero verrattuna sujuviin lukijoihin) ei pysynyt saman suuruisena, vaan ryhmien ero kasvoi aikuisiän lisääntyessä. Tulosten merkitys Lukivaikeuden osoitettiin tässä tutkimussarjassa olevan yhteydessä yleistyneeseen vaikeuteen käsitellä ajassa nopeasti muuttuvaa ei-kielellistä aistitietoa (yli aistien ja niiden yhdistelmien, tehtävätyyppien, tutkittavien iän). Tämä osoittaa, että lukivaikeus ei ole ongelma, joka rajoittuu vain kielellisen materiaalin käsittelyn vaikeuksiin (äänteiden käsittely, lukeminen, kirjoittaminen). Nyt havaitut vaikeudet eivät myöskään rajoittuneet vain niihin aisteihin, jotka selkeimmin liittyvät lukemiseen (näkö) ja puhuttuun kieleen (kuulo); Ongelmia esiintyi myös muissa aisteissa (tunto). Lukivaikeuksisten lukijoiden ryhmätasolla havaittu aikatarkkuuden ongelma ei kuitenkaan heijastunut yksilötasolle; Jokainen lukivaikeuksinen ei ollut huono aikatarkkuustehtävissä. Näin ollen ei siis voida väittää, että kaikkien lukivaikeuksisten äänteiden käsittelyn tai lukemaan oppimisen vaikeudet voisivat selittyä aistien toimintojen poikkeavuudella. Aikatarkkuuden ongelmat eivät olleet yhteydessä varsinaiseen lukemiseen. Sekä lukivaikeuksisilla lapsilla että aikuisilla todettiin kuitenkin selkeä yhteys aikatarkkuuden ongelmien ja lukemaan oppimisen keskeisen ennakkoehdon, fonologisen prosessoinnin, välillä. Saattaa siis olla, että synnynnäinen aistien toimintojen poikkeavuus vaikuttaa yksilön suoriutumiseen jo ennen varsinaista lukemaan oppimista, kun ne taidot kehittyvät (fonologinen prosessointi), joille myöhempi lukemaan oppiminen perustuu. Ikäännyttäessä havaittu lukivaikeuksisten suhteettoman nopea aikatarkkuuden heikkeneminen osoittaa, että lukivaikeus ei voi olla ongelma, joka koskee vain lapsuusikää, tai vaikeus, joka johtuu vain kehityksen viivästymästä joka kurottaisiin iän myötä umpeen. Tulosten ymmärtämiseksi onkin muistettava kaksi seikkaa. Lukivaikeus on ensinnäkin yhdistetty synnynnäisiin, pieniin, poikkeavuuksiin aivojen rakenteissa ja toiminnoissa. Toisaalta tavanomaiseen ikääntymiseen liittyy se, että aivot kykenevät yhä huonommin korjaamaan ja kiertämään (kompensoimaan) pieniä vaurioita. Tämän perusteella tutkimussarjan tuloksista voidaan päätellä, että lukivaikeuksisten jo synnynnäisesti heikentyneet aivojen kompensointimahdollisuudet eivät ole yhtä tehokkaita puskuroimaan ikääntymisen tavanomaisia vaikutuksia kuin sujuvilla lukijoilla. Yllättävää kuitenkin on, että tämä korostunut heikkeneminen havaittiin jo suhteellisen nuorilla, työikäisillä, lukivaikeuksisilla, ennen 60 ikävuotta. Samanlaista ikäännyttäessä korostuvaa vaikeutta ei lukivaikeuksilla kuitenkaan havaittu päättelyssä, kielellisissä toiminnoissa tai itse lukemisessa. Vaikuttaakin siis siltä, että ne toiminnot, joita on harjaannutettu aktiivisesti, eivät heikkene kasvavan aikuisiän myötä yhtä suhteettomasti. Alkuperäiset artikkelit Laasonen M, Tomma-Halme J, Lahti-Nuuttila P, Service E, and Virsu V (2000) Rate of information segregation in developmentally dyslexic children, Brain and Language, 75(1), 66-81. Laasonen M, Service E, and Virsu V (2001) Temporal order and processing acuity of visual, auditory, and tactile perception in developmentally dyslexic young adults, Cognitive, Affective, and Behavioral Neuroscience, 1(4), 394-410. Laasonen M, Service E, and Virsu V (2002) Crossmodal temporal order and processing acuity in developmentally dyslexic young adults, Brain and Language, 80(3), 340-354. Laasonen M, Lahti-Nuuttila P, and Virsu V (2002) Developmentally impaired processing speed decreases more than normally with age, NeuroReport, 13(9), 1111-1113.

Auditory - Visual Matching in Learning Disabilities : Intervention Studies from Finland and Sweden

The present thesis discusses relevant issues in education: 1) learning disabilities including the role of comorbidity in LDs, and 2) the use of research-based interventions. This thesis consists of a series of four studies (three articles), which deepens the knowledge of the field of special education. Intervention studies (N=242) aimed to examine whether training using a nonverbal auditory-visual matching computer program had a remedial effect in different learning disabilities, such as developmental dyslexia, Attention Deficit Disorder (ADD) and Specific Language Impairment (SLI). These studies were conducted in both Finland and Sweden. The intervention’s non-verbal character made an international perspective possible. The results of the intervention studies confirmed, that the auditory-visual matching computer program, called Audilex had positive intervention effects. In Study I of children with developmental dyslexia there were also improvements in reading skills, specifically in reading nonsense words and reading speed. These improvements in tasks, which are thought to rely on phonological processing, suggest that such reading difficulties in dyslexia may stem in part from more basic perceptual difficulties, including those required to manage the visual and auditory components of the decoding task. In Study II the intervention had a positive effect on children with dyslexia; older students with dyslexia and surprisingly, students with ADD also benefited from this intervention. In conclusion, the role of comorbidity was apparent. An intervention effect was evident also in students’ school behavior. Study III showed that children with SLI experience difficulties very similar to those of children with dyslexia in auditory-visual matching. Children with language-based learning disabilities, such as dyslexia and SLI benefited from the auditory-visual matching intervention. Also comorbidity was evident among these children; in addition to formal diagnoses, comorbidity was explored with an assessment inventory, which was developed for this thesis. Interestingly, an overview of the data of this thesis shows positive intervention effects in all studies despite learning disability, language, gender or age. These findings have been described by a concept inter-modal transpose. Self-evidently these issues need further studies. In learning disabilities the aim in the future will also be to identify individuals at risk rather than by deficit; this aim can be achieved by using research-based interventions, intensified support in general education and inclusive special education. Keywords: learning disabilities, developmental dyslexia, attention deficit disorder, specific language impairment, language-based learning disabilities, comorbidity, auditory-visual matching, research-based interventions, inter-modal transpose

Developmental, functional brain imaging and electrophysiological evidence of visual and auditory working memory

Intact function of working memory (WM) is essential for children and adults to cope with every day life. Children with deficits in WM mechanisms have learning difficulties that are often accompanied by behavioral problems. The neural processes subserving WM, and brain structures underlying this system, continue to develop during childhood till adolescence and young adulthood. With functional magnetic resonance imaging (fMRI) it is possible to investigate the organization and development of WM. The present thesis aimed to investigate, using behavioral and neuroimaging methods, whether mnemonic processing of spatial and nonspatial visual information is segregated in the developing and mature human brain. A further aim in this research was to investigate the organization and development of audiospatial and visuospatial information processing in WM. The behavioral results showed that spatial and nonspatial visual WM processing is segregated in the adult brain. The fMRI result in children suggested that memory load related processing of spatial and nonspatial visual information engages common cortical networks, whereas selective attention to either type of stimuli recruits partially segregated areas in the frontal, parietal and occipital cortices. Deactivation mechanisms that are important in the performance of WM tasks in adults are already operational in healthy school-aged children. Electrophysiological evidence suggested segregated mnemonic processing of visual and auditory location information. The results of the development of audiospatial and visuospatial WM demonstrate that WM performance improves with age, suggesting functional maturation of underlying cognitive processes and brain areas. The development of the performance of spatial WM tasks follows a different time course in boys and girls indicating a larger degree of immaturity in the male than female WM systems. Furthermore, the differences in mastering auditory and visual WM tasks may indicate that visual WM reaches functional maturity earlier than the corresponding auditory system. Spatial WM deficits may underlie some learning difficulties and behavioral problems related to impulsivity, difficulties in concentration, and hyperactivity. Alternatively, anxiety or depressive symptoms may affect WM function and the ability to concentrate, being thus the primary cause of poor academic achievement in children.

Search for genetic variants influencing human height

Human growth and attained height are determined by a combination of genetic and environmental effects and in modern Western societies > 80% of the observed variation in height is determined by genetic factors. Height is a fundamental human trait that is associated with many socioeconomic and psychosocial factors and health measures, however little is known of the identity of the specific genes that influence height variation in the general population. This thesis work aimed to identify the genetic variants that influence height in the general population by genome-wide linkage analysis utilizing large family samples. The study focused on analysis of three separate sets of families consisting of: 1) 1,417 individuals from 277 Finnish families (FinnHeight), 2) 8,450 individuals from 3,817 families from Australia and Europe (EUHeight) and 3) 9,306 individuals from 3,302 families from the United States (USHeight). The most significant finding in this study was found in the Finnish family sample where we a locus in the chromosomal region 1p21 was linked to adult height. Several regions showed evidence for linkage in the Australian, European and US families with 8q21 and 15q25 being the most significant. The region on 1p21 was followed up with further studies and we were able to show that the collagen 11-alpha-1 gene (COL11A1) residing at this location was associated with adult height. This association was also confirmed in an independent Finnish population cohort (Health 2000) consisting of 6,542 individuals. From this population sample, we estimated that homozygous males and females for this gene variant were 1.1 and 0.6 cm taller than the respective controls. In this thesis work we identified a gene variant in the COL11A1 gene that influences human height, although this variant alone explains only 0.1% of height variation in the Finnish population. We also demonstrated in this study that special stratification strategies such as performing sex-limited analyses, focusing on dizygous twin pairs, analyzing ethnic groups within a population separately and utilizing homogenous populations such as the Finns can improve the statistical power of finding QTL significantly. Also, we concluded from the results of this study that even though genetic effects explain a great proportion of height variance, it is likely that there are tens or even hundreds of genes with small individual effects underlying the genetic architecture of height.

Search For Susceptibility Genes In Schizophrenia

Schizophrenia is a severe mental disorder affecting 0.4-1% of the population worldwide. It is characterized by impairments in the perception of reality and by significant social or occupational dysfunction. The disorder is one of the major contributors to the global burden of diseases. Studies of twins, families, and adopted children point to strong genetic components for schizophrenia, but environmental factors also play a role in the pathogenesis of disease. Molecular genetic studies have identified several potential positional candidate genes. The strongest evidence for putative schizophrenia susceptibility loci relates to the genes encoding dysbindin (DTNBP1) and neuregulin (NRG1), but studies lack impressive consistency in the precise genetic regions and alleles implicated. We have studied the role of three potential candidate genes by genotyping 28 single nucleotide polymorphisms in the DNTBP1, NRG1, and AKT1 genes in a large schizophrenia family sample consisting of 441 families with 865 affected individuals from Finland. Our results do not support a major role for these genes in the pathogenesis of schizophrenia in Finland. We have previously identified a region on chromosome 5q21-34 as a susceptibility locus for schizophrenia in a Finnish family sample. Recently, two studies reported association between the γ-aminobutyric acid type A receptor cluster of genes in this region and one study showed suggestive evidence for association with another regional gene encoding clathrin interactor 1 (CLINT1, also called Epsin 4 and ENTH). To further address the significance of these genes under the linkage peak in the Finnish families, we genotyped SNPs of these genes, and observed statistically significant association of variants between GABRG2 and schizophrenia. Furthermore, these variants also seem to affect the functioning of the working memory. Fetal events and obstetric complications are associated with schizophrenia. Rh incompatibility has been implicated as a risk factor for schizophrenia in several epidemiological studies. We conducted a family-based candidate-gene study that assessed the role of maternal-fetal genotype incompatibility at the RhD locus in schizophrenia. There was significant evidence for an RhD maternal-fetal genotype incompatibility, and the risk ratio was estimated at 2.3. This is the first candidate-gene study to explicitly test for and provide evidence of a maternal-fetal genotype incompatibility mechanism in schizophrenia. In conclusion, in this thesis we found evidence that one GABA receptor subunit, GABRG2, is significantly associated with schizophrenia. Furthermore, it also seems to affect to the functioning of the working memory. In addition, an RhD maternal-fetal genotype incompatibility increases the risk of schizophrenia by two-fold.

Plant species diversity of buffer zones in agricultural landscapes: in search of determinants from the local to regional scale

Buffer zones are vegetated strip-edges of agricultural fields along watercourses. As linear habitats in agricultural ecosystems, buffer strips dominate and play a leading ecological role in many areas. This thesis focuses on the plant species diversity of the buffer zones in a Finnish agricultural landscape. The main objective of the present study is to identify the determinants of floral species diversity in arable buffer zones from local to regional levels. This study was conducted in a watershed area of a farmland landscape of southern Finland. The study area, Lepsämänjoki, is situated in the Nurmijärvi commune 30 km to the north of Helsinki, Finland. The biotope mosaics were mapped in GIS. A total of 59 buffer zones were surveyed, of which 29 buffer strips surveyed were also sampled by plot. Firstly, two diversity components (species richness and evenness) were investigated to determine whether the relationship between the two is equal and predictable. I found no correlation between species richness and evenness. The relationship between richness and evenness is unpredictable in a small-scale human-shaped ecosystem. Ordination and correlation analyses show that richness and evenness may result from different ecological processes, and thus should be considered separately. Species richness correlated negatively with phosphorus content, and species evenness correlated negatively with the ratio of organic carbon to total nitrogen in soil. The lack of a consistent pattern in the relationship between these two components may be due to site-specific variation in resource utilization by plant species. Within-habitat configuration (width, length, and area) were investigated to determine which is more effective for predicting species richness. More species per unit area increment could be obtained from widening the buffer strip than from lengthening it. The width of the strips is an effective determinant of plant species richness. The increase in species diversity with an increase in the width of buffer strips may be due to cross-sectional habitat gradients within the linear patches. This result can serve as a reference for policy makers, and has application value in agricultural management. In the framework of metacommunity theory, I found that both mass effect(connectivity) and species sorting (resource heterogeneity) were likely to explain species composition and diversity on a local and regional scale. The local and regional processes were interactively dominated by the degree to which dispersal perturbs local communities. In the lowly and intermediately connected regions, species sorting was of primary importance to explain species diversity, while the mass effect surpassed species sorting in the highly connected region. Increasing connectivity in communities containing high habitat heterogeneity can lead to the homogenization of local communities, and consequently, to lower regional diversity, while local species richness was unrelated to the habitat connectivity. Of all species found, Anthriscus sylvestris, Phalaris arundinacea, and Phleum pretense significantly responded to connectivity, and showed high abundance in the highly connected region. We suggest that these species may play a role in switching the force from local resources to regional connectivity shaping the community structure. On the landscape context level, the different responses of local species richness and evenness to landscape context were investigated. Seven landscape structural parameters served to indicate landscape context on five scales. On all scales but the smallest scales, the Shannon-Wiener diversity of land covers (H') correlated positively with the local richness. The factor (H') showed the highest correlation coefficients in species richness on the second largest scale. The edge density of arable field was the only predictor that correlated with species evenness on all scales, which showed the highest predictive power on the second smallest scale. The different predictive power of the factors on different scales showed a scaledependent relationship between the landscape context and local plant species diversity, and indicated that different ecological processes determine species richness and evenness. The local richness of species depends on a regional process on large scales, which may relate to the regional species pool, while species evenness depends on a fine- or coarse-grained farming system, which may relate to the patch quality of the habitats of field edges near the buffer strips. My results suggested some guidelines of species diversity conservation in the agricultural ecosystem. To maintain a high level of species diversity in the strips, a high level of phosphorus in strip soil should be avoided. Widening the strips is the most effective mean to improve species richness. Habitat connectivity is not always favorable to species diversity because increasing connectivity in communities containing high habitat heterogeneity can lead to the homogenization of local communities (beta diversity) and, consequently, to lower regional diversity. Overall, a synthesis of local and regional factors emerged as the model that best explain variations in plant species diversity. The studies also suggest that the effects of determinants on species diversity have a complex relationship with scale.

Mining Sequential Data – in Search of Segmental Structures

Segmentation is a data mining technique yielding simplified representations of sequences of ordered points. A sequence is divided into some number of homogeneous blocks, and all points within a segment are described by a single value. The focus in this thesis is on piecewise-constant segments, where the most likely description for each segment and the most likely segmentation into some number of blocks can be computed efficiently. Representing sequences as segmentations is useful in, e.g., storage and indexing tasks in sequence databases, and segmentation can be used as a tool in learning about the structure of a given sequence. The discussion in this thesis begins with basic questions related to segmentation analysis, such as choosing the number of segments, and evaluating the obtained segmentations. Standard model selection techniques are shown to perform well for the sequence segmentation task. Segmentation evaluation is proposed with respect to a known segmentation structure. Applying segmentation on certain features of a sequence is shown to yield segmentations that are significantly close to the known underlying structure. Two extensions to the basic segmentation framework are introduced: unimodal segmentation and basis segmentation. The former is concerned with segmentations where the segment descriptions first increase and then decrease, and the latter with the interplay between different dimensions and segments in the sequence. These problems are formally defined and algorithms for solving them are provided and analyzed. Practical applications for segmentation techniques include time series and data stream analysis, text analysis, and biological sequence analysis. In this thesis segmentation applications are demonstrated in analyzing genomic sequences.