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  • 1.
    Bachmann, Talis
    et al.
    Estonian Center of Behavioral and Health Sciences, University of Tartu, Estonia.
    Sikka, Pilleriin
    Estonian Center of Behavioral and Health Sciences, Estonian Center of Behavioral and Health Sciences, University of Tartu, Estonia.
    Perception of successive targets presented in invariant-item streams2005In: Acta Psychologica, ISSN 0001-6918, E-ISSN 1873-6297, Vol. 120, no 1, p. 19-34Article in journal (Refereed)
    Abstract [en]

    When two successive, spatially overlapping, targets (S1 and S2) are presented on a blank background, S2 typically dominates in explicit perception. We tested whether S2 dominance is also found for the conditions of presenting S1 and S2 in a stream of irrelevant objects. Successive target letters were presented within a stream of invariant stimulus items (capital Is). The stream items were presented either as a perceptually continuous object where both type and token appeared invariant (60-Hz stream) or as a flickering stream of successive replicas of the invariant stationary object where the type appeared invariant but the token appearance seemed intermittent (20-Hz condition). Compared to the control condition where targets were presented on a blank background we found that (1) recognition rate was lower for targets embedded in a perceptually continuous type-and-token object (60 Hz), but was unchanged for targets in a perceptually flickering sequence of the invariant-object tokens (20 Hz); (2) S1 recognition rate was higher compared to S2 recognition rate within the first epoch of stream (0-150 ms) while within the later stream-epochs S2 dominated over S1 as usual; (3) the overall difference in recognition rates between S1 and S2 was decreased. The results are discussed in the theoretical context of visual masking and attentional blink.

  • 2.
    Burnet, Phil W. J.
    et al.
    Department of Psychiatry, University of Oxford, Warneford Hospital.
    Eastwood, Sharon L.
    Department of Psychiatry, University of Oxford, Warneford Hospital.
    Bristow, Greg C.
    Department of Psychiatry, University of Oxford, Warneford Hospital.
    Godlewska, Beata R.
    Department of Psychiatry, University of Oxford, Warneford Hospital.
    Sikka, Pilleriin
    Department of Psychiatry, University of Oxford, Warneford Hospital.
    Walker, Mary
    Department of Psychiatry, University of Oxford, Warneford Hospital.
    Harrison, Paul J.
    Department of Psychiatry, University of Oxford, Warneford Hospital.
    D-amino acid oxidase activity and expression are increased in schizophrenia2008In: Molecular Psychiatry, ISSN 1359-4184, E-ISSN 1476-5578, Vol. 13, no 7, p. 658-660Article in journal (Refereed)
  • 3.
    Kallio, Sakari
    et al.
    University of Skövde, School of Humanities and Informatics. Centre for Cognitive Neuroscience, University of Turku, Turku, Finland / Department of Psychology, University of Turku, Turku, Finland.
    Hyönä, Jukka
    Department of Psychology, University of Turku, Turku, Finland.
    Revonsuo, Antti
    University of Skövde, School of Humanities and Informatics. Centre for Cognitive Neuroscience, University of Turku, Turku, Finland / Department of Psychology, University of Turku, Turku, Finland.
    Sikka, Pilleriin
    University of Skövde, School of Humanities and Informatics. Centre for Cognitive Neuroscience, University of Turku, Turku, Finland / Department of Psychology, University of Turku, Turku, Finland.
    Nummenmaa, Lauri
    Brain Research Unit, Low Temperature Laboratory, Aalto University School of Science, Espoo, Finland / Department of Biomedical Engineering and Computational Science, Aalto University School of Science, Espoo, Finland / Turku PET Centre, University of Turku, Turku, Finland.
    The Existence of a Hypnotic State Revealed by Eye Movements2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 10, article id e26374Article in journal (Refereed)
  • 4.
    Revonsuo, Antti
    et al.
    University of Skövde, School of Humanities and Informatics. Department of Psychology/Centre for Cognitive Neuroscience, University of Turku, Finland.
    Kallio, Sakari
    University of Skövde, School of Humanities and Informatics. Department of Psychology/Centre for Cognitive Neuroscience, University of Turku, Finland.
    Sikka, Pilleriin
    University of Skövde, School of Bioscience. Department of Psychology/Centre for Cognitive Neuroscience, University of Turku, Finland.
    What is an altered state of consciousness?2009In: Philosophical Psychology, ISSN 0951-5089, E-ISSN 1465-394X, Vol. 22, no 2, p. 187-204Article in journal (Refereed)
    Abstract [en]

    ‘‘Altered State of Consciousness’’ (ASC) has been defined as a changed overall pattern of conscious experience, or as the subjective feeling and explicit recognition that one’s own subjective experience has changed. We argue that these traditional definitions fail to draw a clear line between altered and normal states of consciousness (NSC). We outline a new definition of ASC and argue that the proper way to understand the concept of ASC is to regard it as a representational notion: the alteration that has happened is not an alteration of consciousness (or subjective experience) per se, but an alteration in the informational or representational relationships between consciousness and the world. An altered state of consciousness is defined as a state in which the neurocognitive background mechanisms of consciousness have an increased tendency to produce misrepresentations such as hallucinations, delusions, and memory distortions. Paradigm examples of such generally misrepresentational, temporary, and reversible states are dreaming, psychotic episodes, psychedelic drug experiences, some epileptic seizures, and hypnosis in highly hypnotizable subjects. The representational definition of ASC should be applied in the theoretical and empirical studies of ASCs to unify and clarify the conceptual basis of ASC research.

  • 5.
    Sikka, Pilleriin
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    How to Study Dream Experiences2019In: Dreams: Understanding Biology, Psychology, and Culture Volume 1 / [ed] Robert J. Hoss, Katja Valli, Robert P. Gongloff, Santa Barbara, CA: Greenwood, an Imprint of ABC-CLIO, LLC , 2019, 1, p. 153-166Chapter in book (Refereed)
    Abstract [en]

    In the scientific study of dreams, as in the scientific study of any other topic, it is important to first clearly define the phenomenon one is investigating. The definition determines what exactly is being studied. Then, the methods for collecting and analyzing data regarding this phenomenon need to be chosen. These methods determine what kind of results are obtained, to what extent the results reflect the phenomenon of interest, and whether the results can be trusted. This chapter gives an overview of how dream experiences are scientifically studied: how dreams and dreaming are defined, what kinds of methods are used to collect and analyze dream data, and what aspects need to be considered when conducting and reading studies that investigate dream experiences (see also Kahan & Horton, 2012, and Zadra & Domhoff, 2017).

    The full text will be freely available from 2020-02-01 00:01
  • 6.
    Sikka, Pilleriin
    et al.
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Feilhauer, Diana
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre.
    Valli, Katja
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Revonsuo, Antti
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    How You Measure Is What You Get: Differences in Self- and External Ratings of Emotional Experiences in Home Dreams2017In: American Journal of Psychology, ISSN 0002-9556, E-ISSN 1939-8298, Vol. 130, no 3, p. 367-384Article in journal (Refereed)
    Abstract [en]

    This study demonstrates that different methods for measuring emotional experiences in dreams — self-ratings of dreams using emotion rating scales versus external ratings in the form of content analysis of narrative dream reports — can lead to strikingly different results and contradicting conclusions about the emotional content of home dreams. During 3 consecutive weeks, every morning upon awakening, 44 participants (16 men, 28 women, average age 26.9± 5.1 years) reported their dreams and rated their emotional experiences in those dreams using the modified Differential Emotions Scale. Two external judges rated emotional experiences inthe same 552 (M = 12.55 ± 5.72) home dream reports using the same scale. Comparison of the 2 methods showed that with self-ratings dreams were rated as more emotional and more positive than with external ratings. Moreover, whereas with self-ratings the majority of dreams was rated as positively valenced, with external ratings the majority of dream reports was rated as negatively valenced. Although self- and external ratings converge, at least partially, in the measurement of negative emotional experiences, they diverge greatly in the measurement of positive emotional experiences. On one hand, this discrepancy may result from different biases inherent in the 2 measurement methods highlighting the need to develop better methods for measuring emotional experiences. On the other hand, self- and external ratings may capture different phenomena and should thus be considered complementary and used concurrently. Nevertheless, results suggest that negative emotional experiences can be measured in a more valid and reliable manner than positive emotional experiences.

  • 7.
    Sikka, Pilleriin
    et al.
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Department of Psychology and Speech-Language Pathology, Turku Brain and Mind Center, University of Turku, Turku, Finland.
    Pesonen, Henri
    Department of Mathematics and Statistics, University of Turku, Turku, Finland / Department of Computer Science, Aalto University, Helsinki, Finland.
    Revonsuo, Antti
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Department of Turku Brain and Mind Center, University of Turku, Finland.
    Peace of mind and anxiety in the waking state are related to the affective content of dreams2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 12762Article in journal (Refereed)
    Abstract [en]

    Waking mental well-being is assumed to be tightly linked to sleep and the affective content of dreams. However, empirical research is scant and has mostly focused on ill-being by studying the dreams of people with psychopathology. We explored the relationship between waking well-being and dream affect by measuring not only symptoms of ill-being but also different types and components of well-being. Importantly, this is the first time peace of mind was investigated as a distinct aspect of well-being in a Western sample and in relation to dream content. Healthy participants completed a well-being questionnaire, followed by a three-week daily dream diary and ratings of dream affect. Multilevel analyses showed that peace of mind was related to positive dream affect, whereas symptoms of anxiety were related to negative dream affect. Moreover, waking measures were better related to affect expressed in dream reports rather than participants’ self-ratings of dream affect. We propose that whereas anxiety may reflect affect dysregulation in waking and dreaming, peace of mind reflects enhanced affect regulation in both states of consciousness. Therefore, dream reports may possibly serve as markers of mental health. Finally, our study shows that peace of mind complements existing conceptualizations and measures of well-being.

  • 8.
    Sikka, Pilleriin
    et al.
    University of Skövde, The Systems Biology Research Centre. University of Skövde, School of Bioscience. Department of Psychology, University of Turku, Finland.
    Revonsuo, Antti
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Department of Psychology, University of Turku, Finland.
    Noreika, Valdas
    Department of Psychology, University of Cambridge, UK.
    Valli, Katja
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Department of Psychology, University of Turku, Finland.
    EEG Frontal Alpha Asymmetry and Dream Affect: Alpha Oscillations Over the Right Frontal Cortex During REM Sleep and Pre-Sleep Wakefulness Predict Anger in REM Sleep Dreams2019In: Journal of Neuroscience, ISSN 0270-6474, E-ISSN 1529-2401, Vol. 39, no 24, p. 4775-4784, article id 2884-18Article in journal (Refereed)
    Abstract [en]

    Affective experiences are central not only to our waking life but also to rapid eye movement(REM) sleep dreams. Despite our increasing understanding of the neural correlates of dreaming, we know little about the neural correlates of dream affect. Frontal alpha asymmetry (FAA) is considered a marker of affective states and traits as well as affect regulation in the waking state. Here, we explored whether FAA during REM sleep and during evening resting wakefulness is related to affective experiences in REM sleep dreams. EEG recordings were obtained from 17humanparticipants (7men)whospent 2 nights in the sleep laboratory. Participants were awakened 5minafter the onset of everyREMstage after which they provided a dream report and rated their dream affect. Two-minute preawakening EEG segments were analyzed. Additionally, 8 min of evening presleep and morning postsleep EEG were recorded during resting wakefulness. Mean spectral power in the alpha band (8 –13 Hz and correspondingFAAwere calculated over the frontal (F4-F3) sites. Results showed that FAA during REM sleep, and during evening resting wakefulness, predicted ratings of dream anger. This suggests that individuals with greater alpha power in the right frontal hemisphere may be less able to regulate (i.e., inhibit) strong affective states, such as anger, in dreams. Additionally, FAA was positively correlated across wakefulness and REM sleep. Together, these findings imply that FAA may serve as a neural correlate of affect regulation not only in the waking but also in the dreaming state.

    The full text will be freely available from 2019-12-13 00:01
  • 9.
    Sikka, Pilleriin
    et al.
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Revonsuo, Antti
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Sandman, Nils
    Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland / The Genomics and Biomarkers Unit, National Institute for Health and Welfare, Finland.
    Tuominen, Jarno
    Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Valli, Katja
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Dream emotions: a comparison of home dream reports with laboratory early and late REM dream reports2018In: Journal of Sleep Research, ISSN 0962-1105, E-ISSN 1365-2869, Vol. 27, no 2, p. 206-214Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to compare the emotional content of dream reports collected at home upon morning awakenings with those collectedin the laboratory upon early and late rapid eye movement (REM) sleep awakenings. Eighteen adults (11 women, seven men; mean age = 25.89 ± 4.85) wrote down their home dreams every morning immediately upon awakening during a 7-day period. Participants also spent two non-consecutive nights in the sleep laboratory where they were awoken 5 min into each continuous REM sleep stage, upon which they gave a verbal dream report. The content of a total of 151 home and 120 laboratory dream reports was analysed by two blind judges using the modified Differential Emotions Scale. It was found that: (1) home dream reports were more emotional than laboratory early REM dream reports, but not more emotional than laboratory late REM dream reports; (2) home dream reports contained a higher density of emotions than laboratory (early or late REM) dream reports; and (3) home dream reports were more negative than laboratory dream reports, but differences between home and early REM reports were larger than those between home and late REM reports. The results suggest that differences between home and laboratory dream reports in overall emotionality may be due to the time of night effect. Whether differences in the density of emotions and negative emotionality are due to sleep environment or due to different reporting procedures and time spent in a sleep stage, respectively, remains to be determined in future studies.

  • 10.
    Sikka, Pilleriin
    et al.
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Revonsuo, Antti
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. University of Turku, Finland.
    Valli, Katja
    Methodological Issues in Measuring Dream Emotions2016Conference paper (Refereed)
    Abstract [en]

    Emotions are central in dreams, specifically in rapid eye movement sleep dreams. Despite a wealth of research on the emotional content of dreams, there is little consensus about the overall emotionality and predominant valence of dreams or about the prevailing specific emotions in dreams. Previous contradictory findings are arguably due to unresolved methodological issues. However, studies that have directly investigated these methodological issues are scarce. In this presentation three studies that investigated the effect of study methodology on the frequency, valence and phenomenological content of dream emotions are discussed. The studies demonstrate that the use of different methods for rating dream emotions (participants who experience the dream vs external judges who analysed the respective dream report) and for collecting dream reports (home vs laboratory setting) leads to very different results and conclusions about the emotional content of dreams. As such, these studies highlight the importance of carefully considering study methodology when conducting and interpreting dream (emotional) content studies.

  • 11.
    Sikka, Pilleriin
    et al.
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Valli, Katja
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Virta, Tiina
    Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Revonsuo, Antti
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre.
    I know how you felt last night, or do I?: Self- and external ratings of emotions in REM dreams2014In: Consciousness and Cognition, ISSN 1053-8100, E-ISSN 1090-2376, Vol. 25, p. 51-66Article in journal (Refereed)
    Abstract [en]

    We investigated whether inconsistencies in previous studies regarding emotional experiencesin dreams derive from whether dream emotions are self-rated or externally evaluated.Seventeen subjects were monitored with polysomnography in the sleep laboratoryand awakened from every rapid eye movement (REM) sleep stage 5 min after the onsetof the stage. Upon awakening, participants gave an oral dream report and rated their dreamemotions using the modified Differential Emotions Scale, whereas external judges rated theparticipants’ emotions expressed in the dream reports, using the same scale. The twoapproaches produced diverging results. Self-ratings, as compared to external ratings,resulted in greater estimates of (a) emotional dreams; (b) positively valenced dreams;(c) positive and negative emotions per dream; and (d) various discrete emotions representedin dreams. The results suggest that this is mostly due to the underrepresentationof positive emotions in dream reports. Possible reasons for this discrepancy are discussed.

  • 12.
    Sikka, Pilleriin
    et al.
    University of Skövde, School of Humanities and Informatics. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Valli, Katja
    University of Skövde, School of Humanities and Informatics. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Virta, Tiina
    Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Revonsuo, Antti
    University of Skövde, School of Humanities and Informatics. Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
    Subjective and objective measures of affective states in REM sleep dreams2012Conference paper (Refereed)
  • 13.
    Sikka, Pilleriin
    et al.
    Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, United Kingdom.
    Walker, Rosie
    Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, United Kingdom.
    Cockayne, Rebecca
    Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, United Kingdom.
    Wood, Matthew J. A.
    Department of Physiology, University of Oxford, Warneford Hospital, Oxford, United Kingdom.
    Harrison, Paul J.
    Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, United Kingdom.
    Burnet, Philip W. J.
    Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, United Kingdom.
    D-Serine metabolism in C6 glioma cells: Involvement of alanine-serine-cysteine transporter (ASCT2) and serine racemase (SRR) but not D-amino acid oxidase (DAO)2010In: Journal of Neuroscience Research, ISSN 0360-4012, E-ISSN 1097-4547, Vol. 88, no 8, p. 1829-1840Article in journal (Refereed)
    Abstract [en]

    D-serine is an endogenous N-methyl-D-aspartate (NMDA) receptor coagonist. It is synthesized from L-serine by serine racemase (SRR), but many aspects of its metabolism remain unclear, especially in the forebrain, which lacks active D-amino acid oxidase (DAO), the major D-serine degradative enzyme. Candidate mechanisms include SRR operating in alpha,beta-eliminase mode (converting D-serine to pyruvate) and regulation by serine transport, in which the alanine-serine-cysteine transporter ASCT2 is implicated. Here we report studies in C6 glioma cells, which "simulate" the forebrain, in that the cells express SRR and ASCT2 but lack DAO activity. We measured D-serine, ASCT2, SRR, and DAO expression and DAO activity in two situations: after incubation of cells for 48 hr with serine isomers and after increased or decreased SRR expression by transfection and RNA interference, respectively. Incubation with serine enantiomers decreased [(3)H]D-serine uptake and ASCT2 mRNA and increased SRR immunoreactivity but did not alter DAO immunoreactivity, and DAO activity remained undetectable. SRR overexpression increased D-serine and pyruvate and decreased [(3)H]D-serine uptake and ASCT2 mRNA but did not affect DAO. SRR knockdown did not alter any of the parameters. Our data suggest that D-serine transport mediated by ASCT2 contributes prominently to D-serine homeostasis when DAO activity is absent. The factors regulating D-serine are important for understanding normal NMDA receptor function and because D-serine, along with DAO and SRR, is implicated in the pathogenesis and treatment of schizophrenia.

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