Cue validity and object-based attention

In a previous study, Egly, Driver, and Rafal (1994) observed both space- and object-based components of visual selective attention. However, the mechanisms underlying these two components and the relationship between them are not well understood. In the present research, with a similar paradigm, these issues were addressed by manipulating cue validity. Behavioral results indicated the presence of both space- and object-based components under high cue validity, similar to the results of Egly et al.'s study. In addition, under low cue validity, the space-based component was absent, whereas the object-based component was maintained. Further event-related potential results demonstrated an object-based effect at a sensory level over the posterior areas of brain, and a space-based effect over the anterior region. The present data suggest that the space- and object-based components reflect mainly voluntary and reflexive mechanisms, respectively

The role of spatial frequency information for ERP components sensitive to faces and emotional facial expression

To investigate the impact of spatial frequency on emotional facial expression analysis, ERPs were recorded in response to low spatial frequency (LSF), high spatial frequency (HSF), and unfiltered broad spatial frequency (BSF) faces with fearful or neutral expressions, houses, and chairs. In line with previous findings, BSF fearful facial expressions elicited a greater frontal positivity than BSF neutral facial expressions, starting at about 150 ms after stimulus onset. In contrast, this emotional expression effect was absent for HSF and LSF faces. Given that some brain regions involved in emotion processing, such as amygdala and connected structures, are selectively tuned to LSF visual inputs, these data suggest that ERP effects of emotional facial expression do not directly reflect activity in these regions. It is argued that higher order neocortical brain systems are involved in the generation of emotion-specific waveform modulations. The face-sensitive N170 component was neither affected by emotional facial expression nor by spatial frequency information

Elektrophysiologische und bildgebende Untersuchungen zum Einfluss visueller Aufmerksamkeit auf die Objektwahrnehmung des Menschen

Attention is essential component of visual perception. The present thesis contains experimental results of several studies investigating the influence of selective attention mechanisms on visual perception using electrophysiological and functional neuroimaging recordings in humans. Feature-based attention represents the focusing of visual perception towards a specific feature attribute (e.g. blue ) and facilitates its processing throughout the visual field. Two studies provide evidence that feature-based attention comprises two distinct mechanisms acting in a global manner. While the attribute-specific process enables the discrimination of feature attributes ( blue ) within the behaviorally relevant dimension, the dimension-specific process was shown to be likewise acting in a global way enhancing the processing of non-target attributes assigned to the relevant dimension ( color ). Differences in event-related potentials (ERPs) were found both for the processing of color- and motion-defined objects. The dimension of color can further be subdivided into categories providing the categorical perception of color. The third study investigated neural correlates of categorical color perception using functional magnetic resonance imaging (fMRI). The results show a faster/more accurate discrimination of colors assigned to different categories (e.g. blue and green ) than to the same category (e.g. blue1 and blue2 ). FMRI analysis revealed correlates of color category effects in language related brain regions as well as the primary visual cortex. While performing a visual attention task, temporal expectation can be very useful in order to optimize behavior. Preliminary results of an additional study show that the stimulus structure itself can also be a critical factor. Both behavioral and ERP data were strongly influenced by different probability distributions and illustrate the impact of temporal expectation on the experimental design of a spatial-cueing task

Electrophysiological correlates of event segmentation: how does the human mind process ongoing activity?

The human mind decodes, processes, and makes sense of a continual flow of dynamic information, taken from an array of sensory inputs. Compelling behavioural and neuroimaging evidence reveals that humans segment activities into meaningful chunks for processing, and this phenomenon has profound implications for learning, memory and understanding the world around us (Newtson, 1973; Zacks and Tversky, 2001; Zacks et al., 2001). Whilst the existence of event segmentation is widely accepted, it remains unclear what cognitive mechanisms drive this ability.This thesis constitutes a series of behavioural and neuroimaging experiments that investigate top-down and bottom-up influences on event segmentation. The neuroimaging studies presented here are novel; they extend the field by investigating event segmentation using scalp-recorded electroencephalography (EEG). Event Related Potentials (ERPs, derived from EEG using signal-averaging procedures) showed that the perceptual processing of event boundaries is differentially sensitive to the segmentation of activities into small or large chunks, consistent with findings from previous neuroimaging research (Zacks et al., 2001). In contrast with previous findings, the electrophysiological investigations elicited responses that were clearly affected by manipulating top-down information (e.g., participant's knowledge about the activity being segmented). The results from the studies reported in the thesis support an account of the perceptual processing of event boundaries, which incorporates both top-down and bottom-up influences

Detecting the neural correlates of episodic memory with mobile EEG: Recollecting objects in the real world

Episodic memory supports recognition of the details of complex real world experiences, providing a continuous record of events embedded within spatial and temporal context. Despite the inherently dynamic nature of real events, the bulk of neuroscientific research to date examines recognition in absence of the detailed contextual information that is known to be a defining characteristic. Given the importance of environmental context for episodic memory, examining ERP correlates of memory in more naturalistic settings is vital for progress in understanding how retrieval operates in daily life. The current study capitalized on recent advances in mobile EEG technology to address this issue and is the first to investigate ERP correlates of episodic retrieval in real world contexts. Participants were guided around a pre-defined route inside a building on campus, while performing a recognition memory task, which paired images of objects with actual physical locations in the building to provide context. Importantly, the findings clearly demonstrate that it is possible to observe reliable neural correlates of memory in real world contexts. Replicating two well established ERP correlates of episodic retrieval reported in prior laboratory based studies, we detected FN400 old/new effects traditionally associated with familiarity between 300 and 500 ms, and a late posterior negativity (LPN) often linked to reconstructive processing or evaluation of retrieval outcomes between 500 and 800 ms. Moreover, the FN400 effect was found to be sensitive to retrieval of context, with more sustained effects for objects encountered in a different context at study and test. Overall, the current work highlights the power of mobile EEG technology for examining complex cognitive functions in more naturalistic real world settings

Nägemistaju automaatsete protsesside eksperimentaalne uurimine

Väitekirja elektrooniline versioon ei sisalda publikatsiooneVäitekiri keskendub nägemistaju protsesside eksperimentaalsele uurimisele, mis on suuremal või vähemal määral automaatsed. Uurimistöös on kasutatud erinevaid eksperimentaalseid katseparadigmasid ja katsestiimuleid ning nii käitumuslikke- kui ka ajukuvamismeetodeid. Esimesed kolm empiirilist uurimust käsitlevad liikumisinformatsiooni töötlust, mis on evolutsiooni käigus kujunenud üheks olulisemaks baasprotsessiks nägemistajus. Esmalt huvitas meid, kuidas avastatakse liikuva objekti suunamuutusi, kui samal ajal toimub ka taustal liikumine (Uurimus I). Nägemistaju uurijad on pikka aega arvanud, et liikumist arvutatakse alati mõne välise objekti või tausta suhtes. Meie uurimistulemused ei kinnitanud taolise suhtelise liikumise printsiibi paikapidavust ning toetavad pigem seisukohta, et eesmärkobjekti liikumisinformatsiooni töötlus on automaatne protsess, mis tuvastab silma põhjas toimuvaid nihkeid, ja taustal toimuv seda eriti ei mõjuta. Teise uurimuse tulemused (Uurimus II) näitasid, et nägemissüsteem töötleb väga edukalt ka seda liikumisinformatsiooni, millele vaatleja teadlikult tähelepanu ei pööra. See tähendab, et samal ajal, kui inimene on mõne tähelepanu hõlmava tegevusega ametis, suudab tema aju taustal toimuvaid sündmusi automaatselt registreerida. Igapäevaselt on inimese nägemisväljas alati palju erinevaid objekte, millel on erinevad omadused, mistõttu järgmiseks huvitas meid (Uurimus III), kuidas ühe tunnuse (antud juhul värvimuutuse) töötlemist mõjutab mõne teise tunnusega toimuv (antud juhul liikumiskiiruse) muutus. Näitasime, et objekti liikumine parandas sama objekti värvimuutuse avastamist, mis viitab, et nende kahe omaduse töötlemine ajus ei ole päris eraldiseisev protsess. Samuti tähendab taoline tulemus, et hoolimata ühele tunnusele keskendumisest ei suuda inimene ignoreerida teist tähelepanu tõmbavat tunnust (liikumine), mis viitab taas kord automaatsetele töötlusprotsessidele. Neljas uurimus keskendus emotsionaalsete näoväljenduste töötlusele, kuna need kannavad keskkonnas hakkamasaamiseks vajalikke sotsiaalseid signaale, mistõttu on alust arvata, et nende töötlus on kujunenud suuresti automaatseks protsessiks. Näitasime, et emotsiooni väljendavaid nägusid avastati kiiremini ja kergemini kui neutraalse ilmega nägusid ning et vihane nägu tõmbas rohkem tähelepanu kui rõõmus (Uurimus IV). Väitekirja viimane osa puudutab visuaalset lahknevusnegatiivsust (ingl Visual Mismatch Negativity ehk vMMN), mis näitab aju võimet avastada automaatselt erinevusi enda loodud mudelist ümbritseva keskkonna kohta. Selle automaatse erinevuse avastamise mehhanismi uurimisse andsid oma panuse nii Uurimus II kui Uurimus IV, mis mõlemad pakuvad välja tõendusi vMMN tekkimise kohta eri tingimustel ja katseparadigmades ning ka vajalikke metodoloogilisi täiendusi. Uurimus V on esimene kogu siiani ilmunud temaatilist teadustööd hõlmav ülevaateartikkel ja metaanalüüs visuaalsest lahknevusnegatiivsusest psühhiaatriliste ja neuroloogiliste haiguste korral, mis panustab oluliselt visuaalse lahknevusnegatiivsuse valdkonna arengusse.The research presented and discussed in the thesis is an experimental exploration of processes in visual perception, which all display a considerable amount of automaticity. These processes are targeted from different angles using different experimental paradigms and stimuli, and by measuring both behavioural and brain responses. In the first three empirical studies, the focus is on motion detection that is regarded one of the most basic processes shaped by evolution. Study I investigated how motion information of an object is processed in the presence of background motion. Although it is widely believed that no motion can be perceived without establishing a frame of reference with other objects or motion on the background, our results found no support for relative motion principle. This finding speaks in favour of a simple and automatic process of detecting motion, which is largely insensitive to the surrounding context. Study II shows that the visual system is built to automatically process motion information that is outside of our attentional focus. This means that even if we are concentrating on some task, our brain constantly monitors the surrounding environment. Study III addressed the question of what happens when multiple stimulus qualities (motion and colour) are present and varied, which is the everyday reality of our visual input. We showed that velocity facilitated the detection of colour changes, which suggests that processing motion and colour is not entirely isolated. These results also indicate that it is hard to ignore motion information, and processing it is rather automatically initiated. The fourth empirical study focusses on another example of visual input that is processed in a rather automatic way and carries high survival value – emotional expressions. In Study IV, participants detected emotional facial expressions faster and more easily compared with neutral facial expressions, with a tendency towards more automatic attention to angry faces. In addition, we investigated the emergence of visual mismatch negativity (vMMN) that is one of the most objective and efficient methods for analysing automatic processes in the brain. Study II and Study IV proposed several methodological gains for registering this automatic change-detection mechanism. Study V is an important contribution to the vMMN research field as it is the first comprehensive review and meta-analysis of the vMMN studies in psychiatric and neurological disorders

Aerospace Medicine and Biology: A continuing bibliography with indexes (supplement 314)

This bibliography lists 139 reports, articles, and other documents introduced into the NASA scientific and technical information system in August, 1988

Combining EEG and Eye Tracking: Using Fixation-Locked Potentials in Visual Search

Visual search is a complex task that involves many neural pathways to identify relevant areas of interest within a scene. Humans remain a critical component in visual search tasks, as they can effectively perceive anomalies within complex scenes. However, this task can be challenging, particularly under time pressure. In order to improve visual search training and performance, an objective, process-based measure is needed. Eye tracking technology can be used to drive real-time parsing of EEG recordings, providing an indication of the analysis process. In the current study, eye fixations were used to generate ERPs during a visual search task. Clear differences were observed following performance, suggesting that neurophysiological signatures could be developed to prevent errors in visual search tasks

Elektroentsefalograafiline vaade emotsionaalse tähelepanu mehhanismidele

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Miks ilus inimene rahvasummas silma jääb? Või ka kauguses kostuv pidurikrigin liiklusmürast üle kostab? Tartu Ülikoolis valminud doktoritöö kohaselt võib põhjuseks olla emotsionaalse informatsiooni kiirendatud töötlus. Aju on varustatud tähelepanumehhanismidega, mis valivad meeleorganite vahendatud infotulvast välja kõige olulisema teabe. Näiteks tahtlik tähelepanu aitab keskenduda käesolevale ning tahtmatu tähelepanu märgata ootamatusi. Neile sekundeerib ka kolmas süsteem, mis tõstab esile emotsionaalse tähendusega infot. Just afektiivne tähelepanu viib fookuse potentsiaalsetele hüvedele nagu kaunis kaaslane ja ohtudele nagu liiklusõnnetus. Seni on aga lahendamata küsimus, mis täpselt toimub ajus siis, kui erinevad tähelepanusüsteemid omavahel konkureerivad. Näiteks kui veebiuudise lugeja silm haarab ühtaegu nii pooleliolevat teksti kui mahlakat kõmupealkirja külgribal. Mõnikord jääb võitjaks emotsionaalne tähelepanu ning kõmulugu saab oodatud kliki. Teinekord suudab aga tahtlik tähelepanu ebaolulise ahvatluse kõrvale tõrjuda ja loo lugemine võib jätkuda. Oma doktoritöös uuris Andero Uusberg lähemalt võimalust, et tähelepanulises võistluses toimub esimese sekundikolmandiku jooksul liidritevahetus. Emotsionaalne tähelepanu reageerib stardis kiiremini, kuid umbes 350 ms järel on tahtlik süsteem seisu viigistanud ning aju fookust juhitakse edaspidi koostöös. Mitmed selle mõttemudeli ennustused leidsid kinnitust emotsionaalse sisuga fotode vaatamise ajal mõõdetud aju elektrilise aktiivsuse analüüsimisel. Üldisemalt aitab tähelepanusüsteemide erinev stardikiirus seletada, miks tegelikkuses ohutud stiimulid nagu kauge pidurikrigin kipuvad siiski tähelepanu haarama – kulub hetk, ette kui konteksti arvestav tahtlik tähelepanu jõuab korrigeerida primitiivsema emotsionaalse süsteemi esialgset valikut. Doktoritööst leiab ka vihjeid igapäevaseks emotsioonide reguleerimiseks. Ebameeldiva raviprotseduuri või muu ärevust tekitava olukorraga toimetulemiseks soovitatakse vahel mõelda millestki muust. Uusbergi uurimistöö näitas aga, et selline strateegia on suurema tõenäosusega edukas siis, kui mõte juhitakse millelegi piisavalt keerukale. Näiteks kui katseisikutel paluti võimalikult detailirohkelt kujutleda jalutamist kodulinnas, vähenes samal ajal esitletud emotsionaalsete piltide sisusse süvemine ning neile reageerimise intensiivsus. Kui ülesandeks oli aga keskenduda emotsionaalsete piltide neutraalsetele omadustele, vähenes afektiivne tähelepanu vaid mõnevõrra.Why does a beautiful face stand out from a crowd? Or even a distant braking screech captures attention? A recent doctoral thesis suggests the reason may be faster processing of emotional information. The brain is equipped with various attention mechanisms for sorting out important information from potentially overwhelming sensory input. While top-down attention enables us to concentrate and bottom-up attention to remain vigilant for unexpected aspects of the environment, there is also a third system sensitive to emotional information. This affective attention is responsible for spotting opportunities such as a valuable mate or threats such as a traffic accident. Scientists do not fully comprehend however, how does competition between attention systems is resolved in the brain. As an example, consider a reader of an online news story whose eyes also capture a juicy headline at a sidebar. Sometimes affective attention succeeds in breaking the concentration on the story in favour of the emotional distraction. At other times however, top-down attention prevails and reading continues uninterrupted. In his thesis, Andero Uusberg investigated the idea that the competition between attentional systems changes across time. More specifically, affective attention may be faster off the mark while after about a third of a second however, top-down attention catches up and the subsequent focus is determined in co-operation. This framework explained several aspects of electrical brain activity measured while participants viewed emotionally evocative photographs. More broadly, different onsets can explain why safe stimuli such as a distant braking screech still captivates us – it takes a moment for the more context-aware top-down attention system to correct the early reaction of the more primitive affective attention. The thesis also has implications for everyday emotion regulation. To cope with unpleasant events such as medical procedures, people are sometimes advised to distract themselves by thinking of something else. In this regard, the present findings imply that this strategy requires the distractive mental activity to be reasonably difficult. For instance, when participants were asked to imagine their neighbourhoods with high level of detail, they indeed paid less attention to unpleasant photographs as well as experienced less intense emotional reactions. When they merely thought of nonaffective features of affective images however, emotional attention was attenuated only modestly