The effect of neural adaptation of population coding accuracy

Most neurons in the primary visual cortex initially respond vigorously when a preferred stimulus is presented, but adapt as stimulation continues. The functional consequences of adaptation are unclear. Typically a reduction of firing rate would reduce single neuron accuracy as less spikes are available for decoding, but it has been suggested that on the population level, adaptation increases coding accuracy. This question requires careful analysis as adaptation not only changes the firing rates of neurons, but also the neural variability and correlations between neurons, which affect coding accuracy as well. We calculate the coding accuracy using a computational model that implements two forms of adaptation: spike frequency adaptation and synaptic adaptation in the form of short-term synaptic plasticity. We find that the net effect of adaptation is subtle and heterogeneous. Depending on adaptation mechanism and test stimulus, adaptation can either increase or decrease coding accuracy. We discuss the neurophysiological and psychophysical implications of the findings and relate it to published experimental data.Comment: 35 pages, 8 figure

Comfort seats: Influence of laptop and tablet use for seat design

This seminar was delivered on 18th April 2012 by Prof dr Peter Vink from the faculty of Industrial Design Engineering at the Delft University of Technology, where he guides 10 PhD students active in the field of interior design. He is also principle scientist at TNO (the second largest applied scientific research organization in Europe), where he specializes in leading research in design of work, work environments, interior design and work systems. In his group projects are carried out in the field of Participatory Ergonomics (how and who to involve in a design process), Comfort (hand tools, seats, vehicle interiors and improving working conditions) and Intelligent Manufacturing (developing simulation systems to improve the design of the organization and lay-out of assembly lines). Professor Vink has in excess of 200 publications in the field of interior design and has been a consulatant and advisor for companies including Boeing, BMW, Gispen and SNCF. The presentation was hosted at Brunel University as part of the Human Centred Design Institute (HCDI) Research Seminar Series. HCDI is a University Research Centre (URC) that brings together expertise in Human-centred Design which combines methodologies and technologies from design, engineering, computer science, artificial intelligence and philosophy. Human-centred Design leads to machines, systems and products which are physically, cognitively and emotionally intuitive to their users. The Human Centre Design seminar series are events designed to encourage communication and teamwork with colleagues across the university and experts leaders in human-centred related topics.The use of laptops and tablets is increasing. In 2008 more laptops than desk tops are sold and tablet sales is increasing as well. This has influence on the design of office and vehicle interiors. However, the ideal tablet office or laptop aircraft seat, which results in an optimal position and experience, is hard to establish as for reading, typing and touchscreen activities other positions are experienced as comfortable. These changes in work devices have their consequences for the interior. For instance, in the office the desk top is not often used. In using the current desk top PC the keyboard, mouse and screen can be placed on every position. The guidelines prescribe for instance the screen height and the keyboard position. For a notebook this is more difficult as the keyboard and mousepad are connected to the screen. Sometimes a docking station or seperate screens, mouses and keyboards are connected. Or a notebook standard with keyboard and mouse is used. In this case the work station can be designed in such a way the VDU guidelines are met. Using a tablet with a touchscreen the human body position is completely different. For a train, car or aircraft seat this device use has its consequences as well. In this presentation several devices and environmental designs will be shown, background information and effect studies will be presented showing consequences for seat and environment design

Abnormal reward valuation and event-related connectivity in unmedicated major depressive disorder

BACKGROUND: Experience of emotion is closely linked to valuation. Mood can be viewed as a bias to experience positive or negative emotions and abnormally biased subjective reward valuation and cognitions are core characteristics of major depression. METHODS: Thirty-four unmedicated subjects with major depressive disorder and controls estimated the probability that fractal stimuli were associated with reward, based on passive observations, so they could subsequently choose the higher of either their estimated fractal value or an explicitly presented reward probability. Using model-based functional magnetic resonance imaging, we estimated each subject's internal value estimation, with psychophysiological interaction analysis used to examine event-related connectivity, testing hypotheses of abnormal reward valuation and cingulate connectivity in depression. RESULTS: Reward value encoding in the hippocampus and rostral anterior cingulate was abnormal in depression. In addition, abnormal decision-making in depression was associated with increased anterior mid-cingulate activity and a signal in this region encoded the difference between the values of the two options. This localised decision-making and its impairment to the anterior mid-cingulate cortex (aMCC) consistent with theories of cognitive control. Notably, subjects with depression had significantly decreased event-related connectivity between the aMCC and rostral cingulate regions during decision-making, implying impaired communication between the neural substrates of expected value estimation and decision-making in depression. CONCLUSIONS: Our findings support the theory that abnormal neural reward valuation plays a central role in major depressive disorder (MDD). To the extent that emotion reflects valuation, abnormal valuation could explain abnormal emotional experience in MDD, reflect a core pathophysiological process and be a target of treatment

A simple proof of the Markoff conjecture for prime powers

We give a simple and independent proof of the result of Jack Button and Paul Schmutz that the Markoff conjecture on the uniqueness of the Markoff triples (a,b,c), where a, b, and c are in increasing order, holds whenever $c$ is a prime power.Comment: 5 pages, no figure

Quantum computing of semiclassical formulas

We show that semiclassical formulas such as the Gutzwiller trace formula can be implemented on a quantum computer more efficiently than on a classical device. We give explicit quantum algorithms which yield quantum observables from classical trajectories, and which alternatively test the semiclassical approximation by computing classical actions from quantum evolution. The gain over classical computation is in general quadratic, and can be larger in some specific cases.Comment: 8 pages, 1 figur

A hierarchical model for aging

We present a one dimensional model for diffusion on a hierarchical tree structure. It is shown that this model exhibits aging phenomena although no disorder is present. The origin of aging in this model is therefore the hierarchical structure of phase space.Comment: 10 pages LaTeX, 4 postscript-figures include

Direct flux and current vector control for induction motor drives using model predictive control theory

The study presents the direct flux and current vector control of an induction motor (IM) drive, which is a relatively newer and promising control strategy, through the use of model predictive control (MPC) techniques. The results highlight that the fast flux control nature of direct flux control strategy is further enhanced by MPC. Predictive control is applied in two of its variants, namely the finite control set and modulated MPC, and the advantages and limitations of the two are underlined. This work also highlights, through experimental results, the importance of prioritising the flux part of the cost function which is particularly significant in the case of an IM drive. The performance of the MPC-based approach is compared with the proportional-integral controller, which also prioritises the flux control loop, under various operating regions of the drive such as in the flux-weakening regime. Simulations show the performance expected with different control strategies which is then verified through experiments