Supervised Learning in Spiking Neural Networks for Precise Temporal Encoding

Precise spike timing as a means to encode information in neural networks is biologically supported, and is advantageous over frequency-based codes by processing input features on a much shorter time-scale. For these reasons, much recent attention has been focused on the development of supervised learning rules for spiking neural networks that utilise a temporal coding scheme. However, despite significant progress in this area, there still lack rules that have a theoretical basis, and yet can be considered biologically relevant. Here we examine the general conditions under which synaptic plasticity most effectively takes place to support the supervised learning of a precise temporal code. As part of our analysis we examine two spike-based learning methods: one of which relies on an instantaneous error signal to modify synaptic weights in a network (INST rule), and the other one on a filtered error signal for smoother synaptic weight modifications (FILT rule). We test the accuracy of the solutions provided by each rule with respect to their temporal encoding precision, and then measure the maximum number of input patterns they can learn to memorise using the precise timings of individual spikes as an indication of their storage capacity. Our results demonstrate the high performance of FILT in most cases, underpinned by the rule's error-filtering mechanism, which is predicted to provide smooth convergence towards a desired solution during learning. We also find FILT to be most efficient at performing input pattern memorisations, and most noticeably when patterns are identified using spikes with sub-millisecond temporal precision. In comparison with existing work, we determine the performance of FILT to be consistent with that of the highly efficient E-learning Chronotron, but with the distinct advantage that FILT is also implementable as an online method for increased biological realism.Comment: 26 pages, 10 figures, this version is published in PLoS ONE and incorporates reviewer comment

A spatial capture-recapture model for territorial species

Advances in field techniques have lead to an increase in spatially-referenced capture-recapture data to estimate a species' population size as well as other demographic parameters and patterns of space usage. Statistical models for these data have assumed that the number of individuals in the population and their spatial locations follow a homogeneous Poisson point process model, which implies that the individuals are uniformly and independently distributed over the spatial domain of interest. In many applications there is reason to question independence, for example when species display territorial behavior. In this paper, we propose a new statistical model which allows for dependence between locations to account for avoidance or territorial behavior. We show via a simulation study that accounting for this can improve population size estimates. The method is illustrated using a case study of small mammal trapping data to estimate avoidance and population density of adult female field voles (Microtus agrestis) in northern England

U.S. Law of the Sea Cruise to Complete the Mapping of Necker Ridge, Central Pacific Ocean

U.S. Law of the Sea Cruise to Complete the Mapping of Necker Ridge, Central Pacific Ocean CRUISE KM1121 July 31, to August 10, 2011 Honolulu, HI to Honolulu, H

Milky Way Tomography with K and M Dwarf Stars: the Vertical Structure of the Galactic Disk

We use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey, to probe the structure of the Milky Way disk across the survey's footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin- and thick-disk subsamples in regions of some 200 square degrees within 2 kpc in vertical distance from the Galactic disk. These disk asymmetries present wave-like features as previously observed on other scales and at other distances from the Sun. We additionally explore the scale height of the disk and the implied offset of the Sun from the Galactic plane at different locations, noting that the scale height of the disk can differ significantly when measured using stars only above or only below the plane. Moreover, we compare the shape of the number density distribution in the north for different latitude ranges with a fixed range in longitude and find the shape to be sensitive to the selected latitude window. We explain why this may be indicative of a change in stellar populations in the latitude regions compared, possibly allowing access to the systematic metallicity difference between thin- and thick-disk populations through photometry.Comment: 41 pages, 17 figures, accepted for publication in ApJ; published version [oversight in Fig. 12 fixed

U.S. Law of the Sea Cruise to Map the Foot of the Slope of the Northeast U.S. Atlantic Continental Margin: Leg 6

U.S. Law of the Sea Cruise to Map the Foot of the Slope of the Northeast U.S. Atlantic Continental Margin: Leg 6 Cruise KNOX17RR May 1 – 31, 2008 Ft. Lauderdale, FL to Woods Hole, M

U.S. Law of the Sea Cruise to Map the Southern Flank of the Kingman Reef-Palmyra Atoll section of the Line Islands, Equatorial Pacific Ocean

U.S. Law of the Sea Cruise to Map the Southern Flank of the Kingman Reef-Palmyra Atoll section of the Line Islands, Equatorial Pacific Ocean CRUISE KM1009 May 17, to June 16, 2010 Pago Pago, American Samoa to Honolulu, H

The Grid Sketcher: An AutoCad-based tool for conceptual design processes

Sketching with pencil and paper is reminiscent of the varied, rich, and loosely defined formal processes associated with conceptual design. Architects actively engage such creative paradigms in their exploration and development of conceptual design solutions. The Grid Sketcher, as a conceptual sketching tool, presents one possible computer implementation for enhancing and supporting these processes. It effectively demonstrates the facility with which current technology and the computing environment can enhance and simulate sketching intents and expectations; Typically with respect to design, the position taken is that the two are virtually void of any fundamental commonality. A designer\u27s thoughts are intuitive, at times irrational, and rarely follow consistently identifiable patterns. Conversely, computing requires predictability in just these endeavors. The computing environment, as commonly defined, can not reasonably expect to mimic the typically human domain of creative design. In this context, this thesis accentuates the computer\u27s role as a form generator as opposed to a form evaluator. The computer, under the influence of certain contextual parameters can, however, provide the designer with a rich and elegant set of forms that respond through algorithmics to the designer\u27s creative intents. (Abstract shortened by UMI.)

Seafloor mapping in the Arctic: support for a potential U.S. extended continental shelf

For the United States, the greatest opportunity for an extended continental shelf under UNCLOS is in the ice-covered regions of the Arctic north of Alaska. Since 2003, CCOM/JHC has been using the icebreaker Healy equipped with a multibeam echosounder, chirp subbottom profiler, and dredges, to map and sample the region of Chukchi Borderland and Alpha-Mendeleev Ridge complex. These data have led to the discovery of several new features, have radically changed our view of the bathymetry and geologic history of the area, and may have important ramifications for the determination of the limits of a U.S. extended continental shelf under Article 76