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Archive for the ‘Ph.D. defense’ Category

Thomas Alrik Sørensen will defend his thesis entitled:

Investigations into Capacity-limitations in Visual Processing of the Human Observer.

June 20th at the University of Copenhagen.

The defence will begin at 3 pm and will be conducted in Udvalgsværelse 3 Nørregade 10 and will be evaluated by:

  • Associate Professor, Thomas Habekost, Department of Psychology, University of Copenhagen, (chairman).
  • Professor, Werner X. Schneider, Universität Bielefeld, Fakultät für Psychologie und Sportwissenshaft, Germany.
  • Dr. rer. nat., Antje Kraft, Charité Universitätsmedizin Berlin, Klinik für Neurologie, Germany.

Thesis abstract

Navigating in the environment seems to offer the viewer a rich sensation containing a wealth of information about different objects. However, in a controlled experimental setting it is possible to demonstrate that the short-term memory is severely limited in a human observer. This rich experience is in sharp contrast with the three to four objects that can be retained in visual short-term memory. It has been known for a long time that the human visual short-term memory is limited and within the last 10-15 years a consensus on the number of objects that can be retained seems to have been reached. The focus on a limitation in terms of number of objects has probably formed the basis for a description of short-term memory as a store consisting of a limited number of slots where objects can be encoded. However, whether there is empirical evidence to support the hypothesis that the short-term memory consists of a fixed number of slots is still open for debate.

This thesis presents two studies that investigate how manipulations of training and expertise (Study 1) or the general level of activation (arousal; Study 2) influence the capacity limitation in short-term memory.

In Study 1 the effects of training are investigated. Since it is time consuming to achieve a level of expertise where effects conceivably would show, groups with different levels of expertise were studied in a change detection task. By contrasting stimulus material with which participants had received different levels of overt training with stimulus material that was novel for all participants, it was demonstrated that short-term memory capacity is affected by level of expertise. The results indicate that the number of objects that can be retained in visual short-term memory is influenced by the strength of the mental representations of the observer; as categories become more established fewer resources seem to be required (as reflected in a larger short-term memory capacity).

Study 2 is based on an experimental investigation of repeated measures of short-term memory and investigates whether modulation of arousal affects the number of objects maintained in short-term memory. This manipulation also appears to systematically influence the number of objects encoded into short-term memory. As arousal increases the number of objects that can be maintained in short-term memory is lowered. The data suggest that this effect reflects a change in the focus of attention, which seems to narrow during heightened arousal. Two mechanisms are proposed to account for how arousal influences attentional processes; the scaling mechanism and the accentuation mechanism.

Both studies suggest an embrace of the concept that objects are maintained in short-term memory. However, short-term memory should not be viewed as a static concept consisting of a fixed number of slots. The number of objects that can be maintained in short-term memory is determined partly by how well the object is known and partly by the general level of activation (arousal) in an observer.

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Signe Vangkilde will defend her thesis entitled:

May I have your attention, please? Modulations of Visual Attention in Time and Space.

November 24th at the University of Copenhagen.

The defence will begin at 4 pm and will be conducted in Auditorium 1 Gothersgade 140 and will be evaluated by:

  • Associate Professor, Søren Kyllingsbæk, Department of Psychology, University of Copenhagen, (chairman).
  • Dr. Kathrin Finke, Neuro-cognitive Psychology Unit, Department Psychologie, LMU, Munich, Germany.
  • Professor Lars-Göran Nilsson, Department of Psychology, University of Stockholm, Sweden.

Thesis abstract

This thesis comprises a theoretical review and three empirical investigations of human visual attention aiming to increase our knowledge about the dynamics of visual attention in time and space.

In Study I (Vangkilde, Coull, & Bundesen, 2011) a new empirical paradigm is used to investigate how different levels of attentional intensity, expressed as specific expectations of events to come, influence visual attention. The results provide the first direct demonstration that our expectations of future events influence our attention by modulating the speed with which we process information.

Study II (Vangkilde, Bundesen, & Coull, 2011) investigates the attentional effect of the cholinergic neurotransmitter nicotine by use of the new CombiTVA paradigm, which provides estimates of independent subcomponents of attention. It is shown that acute nicotine in non-smokers and chronic nicotine in smokers enhances the visual threshold of perception but slows down the rate of information processing and compromises selectivity. These results challenge and differentiate the claim of nicotine as cognitive enhancer.

Study III (Vangkilde & Habekost, 2010) is an empirical evaluation of the efficacy of a rehabilitation strategy, prism adaptation, claimed to ameliorate symptoms of visual neglect after right hemisphere brain injuries. The study addresses several methodological problems pertaining to previous investigations of prism adaptation, and it establishes that short-term and long-term beneficial effects of prism adaptation could, in part, be realised through a functionally significant change in eye movements.

In the theoretical review all three investigations are related to the empirical and theoretical framework of a Theory of Visual Attention (TVA; Bundesen, 1990) and its neural interpretation (NTVA; Bundesen, Kyllingsbæk, & Habekost, 2005). Furthermore, it is discussed how the investigations provide information which can help bridge the gap between traditional theories focusing on selectivity and capacity of attention within the spatial domain and a more recent trend emphasising the importance of attentional intensity, which concerns the impact of arousal and the deployment of attention in time.

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Maria Norfang will defend her thesis entitled:

The importance of being relevant. Capturing effects of relevance and contrast in visual selection

November 18th at the University of Copenhagen.

The defence will begin at 1 pm and will be conducted in Auditorium 1 Gothersgade 140 and will be evaluated by:

  • Associate professor, Thomas Habekost, Department of Psychology, University of Copenhagen, (Chairman).
  • Professor, Jan Theeuwes, Cognitive Psychology, Vrije Universiteit, Amsterdam, Netherlands.
  • Professor Bruno Laeng, CSHC, University of Oslo, Norway.

Thesis abstract

Every second, more information reach our eyes than can be processed within the limited capacity of the human brain. We are therefore forced to select among the available information. Attentional mechanisms work to ensure that the most important elements are selected for processing. Both the physical properties of the stimulus and the current goal of the observer influence this selection process. However, it has been widely debated whether both components play a role in the initial allocation of visual attention. This thesis explores the role of contrast and of relevance in initial visual attention through a series of behavioral experiments.

In the first line of experiments, contrast was varied independently from relevance. The data demonstrated that task relevance influenced attention for presentation times down to 20 ms. In addition, feature contrast had a significant effect on report accuracy, despite being completely irrelevant to the task. The data confirmed that both contrast and relevance influence initial attentional selection. Furthermore, an interaction between local feature contrast and task relevance was revealed. In the thesis, a new equation of attentional weights that can account for the observed relation is proposed. In the second line of experiments, the complexity of relevance‐based visual selection was explored. Data from a triple conjunction search revealed that the number of conjunction‐types in a display significantly influence visual attention. This result challenge several existing theories of visual attention. Overall, both lines of experiments point towards overlaps between two of the major theories of visual attention today, namely the Guided Search model and the Theory of Visual Attention.

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