How humans learn and represent networks

Humans communicate, receive, and store information using sequences of items -- from words in a sentence or notes in music to abstract concepts in lectures and books. The networks formed by these items (nodes) and the sequential transitions between them (edges) encode important structural features of human communication and knowledge. But how do humans learn the networks of probabilistic transitions that underlie sequences of items? Moreover, what do people's internal maps of these networks look like? Here, we introduce graph learning, a growing and interdisciplinary field focused on studying how humans learn and represent networks in the world around them. We begin by describing established results from statistical learning showing that humans are adept at detecting differences in the transition probabilities between items in a sequence. We next present recent experiments that directly control for differences in transition probabilities, demonstrating that human behavior also depends critically on the abstract network structure of transitions. Finally, we present computational models that researchers have proposed to explain the effects of network structure on human behavior and cognition. Throughout, we highlight a number of exciting open questions in the study of graph learning that will require creative insights from cognitive scientists and network scientists alike.Comment: 9 pages, 6 figure

Broadband acoustic backscatter from crude oil under laboratory-grown sea ice

Author Posting. © Acoustical Society of America, 2016. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 140 (2016): 2274–2287, doi:10.1121/1.4963876.In ice-covered seas, traditional air-side oil spill detection methods face practical challenges. Conversely, under-ice remote sensing techniques are increasingly viable due to improving operational capabilities of autonomous and remotely operated vehicles. To investigate the potential for under-ice detection of oil spills using active acoustics, laboratory measurements of high-frequency, broadband backscatter (75–590 kHz) from crude oil layers (0.7–8.1 cm) under and encapsulated within sea ice were performed at normal and 20 incidence angles. Discrete interfaces (water-oil, oil-ice, and ice-oil) are identifiable in observations following oil injections under the ice and during the subsequent encapsulation. A one-dimensional model for the total normal incidence backscatter from oil under ice, constrained by oil sound speed measurements from 10 C to 20 C and improved environmental measurements compared to previous studies, agrees well with preencapsulation observations. At 20 incidence angles echoes from the ice and oil under ice are more complex and spatially variable than normal incidence observations, most likely due to interface roughness and volume inhomogeneities. Encapsulated oil layers are only detected at normal incidence. The results suggest that high-frequency, broadband backscatter techniques may allow under-ice remote sensing for the detection and quantification of oil spills.Funding for this research was provided by the International Oil and Gas Producers Arctic Oil Spill Technology Joint Industry Programme under Contract No. 28-13-14. C.B. was supported by the WHOI Postdoctoral Scholar Program with funding from the United States Geological Survey. A.C.L. was supported in part by the Ocean Acoustics Program at the Office of Naval Research

Restoring the sting to metric preheating

The relative growth of field and metric perturbations during preheating is sensitive to initial conditions set in the preceding inflationary phase. Recent work suggests this may protect super-Hubble metric perturbations from resonant amplification during preheating. We show that this possibility is fragile and sensitive to the specific form of the interactions between the inflaton and other fields. The suppression is naturally absent in two classes of preheating in which either (1) the vacua of the non-inflaton fields during inflation are deformed away from the origin, or (2) the effective masses of non-inflaton fields during inflation are small but during preheating are large. Unlike the simple toy model of a $g^2 \phi^2 \chi^2$ coupling, most realistic particle physics models contain these other features. Moreover, they generically lead to both adiabatic and isocurvature modes and non-Gaussian scars on super-Hubble scales. Large-scale coherent magnetic fields may also appear naturally.Comment: 6 pages, 3 ps figures, RevTex, revised discussion of backreaction and new figure. To appear Phys. Rev. D (Rapid Communication

Structure from noise: Mental errors yield abstract representations of events

Humans are adept at uncovering abstract associations in the world around them, yet the underlying mechanisms remain poorly understood. Intuitively, learning the higher-order structure of statistical relationships should involve complex mental processes. Here we propose an alternative perspective: that higher-order associations instead arise from natural errors in learning and memory. Combining ideas from information theory and reinforcement learning, we derive a maximum entropy (or minimum complexity) model of people's internal representations of the transitions between stimuli. Importantly, our model (i) affords a concise analytic form, (ii) qualitatively explains the effects of transition network structure on human expectations, and (iii) quantitatively predicts human reaction times in probabilistic sequential motor tasks. Together, these results suggest that mental errors influence our abstract representations of the world in significant and predictable ways, with direct implications for the study and design of optimally learnable information sources.Comment: 62 pages, 7 figures, 10 table

Acoustic characterization of sensors used for marine environmental monitoring

Acknowledgements The authors wish to acknowledge Benjamin Brand for his assistance with the Acoustic Test Facility set-up, Jessica Noe for her assistance designing sonar mounts, James Joslin for his assistance with cables for sonar operation, and Mark Wood for his assistance with icListen hydrophones. This study would not have been possible without their contributions. Funding This work was funded by the US Department of Energy [grant number DE-EE0007827]. Emma Cotter is supported by a National Science Foundation Graduate Research Fellowship [grant number DGE-1762114].Peer reviewedPostprin

Exploiting signal processing approaches for broadband echosounders

© International Council for the Exploration of the Sea, 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in ICES Journal of Marine Science 74 (2017): 2262–2275, doi:10.1093/icesjms/fsx155.Broadband echosounders, which transmit frequency-modulated pulses, increase the spectral characterization of targets relative to narrowband echosounders, which typically transmit single-frequency pulses, and also increase the range resolution through broadband matched-filter signal processing approaches. However, the increased range resolution does not necessarily lead to improved detection and characterization of targets close to boundaries due to the presence of undesirable signal processing side lobes. The standard approach to mitigating the impact of processing side lobes is to transmit tapered signals, which has the consequence of also reducing spectral information. To address this, different broadband signal processing approaches are explored using data collected in a large tank with both a Kongsberg–Simrad EK80 scientific echosounder with a combination of single- and split-beam transducers with nominal centre frequencies of 18, 38, 70, 120, 200, and 333 kHz, and with a single-beam custom-built echosounder spanning the frequency band from 130 to 195 kHz. It is shown that improved detection and characterization of targets close to boundaries can be achieved by using modified replica signals in the matched filter processing. An additional benefit to using broadband echosounders involves exploiting the frequency dependence of the beam pattern to calibrate single-beam broadband echosounders using an off-axis calibration sphere.This research was supported by the NOAA Office of Science and Technology, Advanced Sampling Technology Working Group. G.L.L. was partially supported by NOAA Cooperative Agreements NA09OAR4320129 and NA14OAR4320158 through the NOAA Fisheries Quantitative Ecology and Socieconomics Training (QUEST) program. A.C.L. was partially supported through the Office of Naval Research Ocean Acoustics Program

The efficacy of medial patellofemoral ligament reconstruction combined with tibial tuberosity transfer in the treatment of patellofemoral instability

A systematic review of the literature was undertaken to evaluate the efficacy of medial patellofemoral ligament (MPFL) reconstruction combined with tibial tuberosity transfer (TTT) in the treatment of patellofemoral instability. Using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, a systematic search was carried out to identify and review the published literature pertinent to MFPL reconstruction combined with TTT. Relevant studies were critically appraised with narrative data synthesis. Studies that met the eligibility criteria were suitable for appraisal and consisted of case series and therapeutic series (levels IV & III). All studies had inherent variations in outcomes reporting and limited follow-up. Combined treatment offers restoration of normal anatomy, thus adding clinical value to the currently recommended anatomic approach to MPFL reconstruction. Nevertheless, the current body of evidence does not determine the threshold at which patellofemoral axis requires the need for adjunctive distal realignment as opposed to MPFL reconstruction alone. This review highlighted numerous recurring limitations in the conduct and presentation of the studies, which inadvertently mitigated the interpretation of their results. Future priority should be awarded to larger randomised controlled trials utilising validated patient reported outcome measures