Criticality of mostly informative samples: A Bayesian model selection approach

We discuss a Bayesian model selection approach to high dimensional data in the deep under sampling regime. The data is based on a representation of the possible discrete states $s$, as defined by the observer, and it consists of $M$ observations of the state. This approach shows that, for a given sample size $M$, not all states observed in the sample can be distinguished. Rather, only a partition of the sampled states $s$ can be resolved. Such partition defines an {\em emergent} classification $q_s$ of the states that becomes finer and finer as the sample size increases, through a process of {\em symmetry breaking} between states. This allows us to distinguish between the $resolution$ of a given representation of the observer defined states $s$, which is given by the entropy of $s$, and its $relevance$ which is defined by the entropy of the partition $q_s$. Relevance has a non-monotonic dependence on resolution, for a given sample size. In addition, we characterise most relevant samples and we show that they exhibit power law frequency distributions, generally taken as signatures of "criticality". This suggests that "criticality" reflects the relevance of a given representation of the states of a complex system, and does not necessarily require a specific mechanism of self-organisation to a critical point.Comment: 31 pages, 7 figure

Mothers' experience of parent-infant psychotherapy: a qualitative analysis

Aims: This research investigates how mothers experience parent-infant psychotherapy (PIP). The study uses a collaborative exploration of mothers' lived experience and the meaning they attach to it. The intention is to develop insights into mothers' variety of experience of PIP and how their subjectivity impacts their perception of the therapeutic process. Using their in-depth descriptions, this study develops an understanding of the themes inherent in the experience of women in motherhood. Design: This research uses phenomenology, hermeneutics and idiography as a philsosophical base, and applies interpretative phenomenological analysis methodology, drawing upon Jonathan Smith's concept of experiential qualitative research in psychology (2009). This approach was chosen in order to develop an understanding of the insider perspective by engaging directly with mothers' own descriptive accounts of PIP. Method: Seven women, aged between 27 and 43 years old, voluntarily participated in this study. The volunteers were recruited from among participants of a group of PIP course delivered by a National Health Service (NHS) clinic. In-depth semi-structured interviews were conducted to develop an understanding of participants' lived experience and their meaning-making processes. Findings: Three master themes emerged from across the participants' accounts: (1) from a negative to a positive experience of motherhood, (2) PIP as a nurturing experience, (3) PIP as a humanising experience, and (4) PIP as a transformative experience. The findings highlight the significant change in mothers' perception of motherhood (their state of being a mother) - from a sense of inability, detachment, isolation and depression to feeling different, competent, maternal and relationally attached - which they attribute to their experience of PIP. It gave them a different vantage point from which to feel, behave, think, understand and engage with themselves and the world. Conclusion: PIP is valued by mothers as a potentially powerful therapeutic intervention and vehicle for change for themselves, their children and the generations to come. The mothers, psychotherapists, the group setting are all essential to the success of the therapeutic encounter. Mothers should be given the opportunity to access such treatment at this precious and formative time in their and their children's lives

Problemas en torno a la composicionalidad de los proxitipos

Según la teoría neo-empirista de conceptos de Prinz (2002), los conceptos son proxitipos, construcciones temporales formadas por captas de representaciones perceptivas, que se activan en la memoria de trabajo para representar una categoría. Estas representaciones son altamente variables y su activación resulta sensible al contexto, ¿pueden entonces dar lugar a pensamiento productivo y sistemático

Cómo organizar las representaciones en una mente neo-empirista: Un análisis de la individuación de conceptos en la teoria de Prinz

En Furnishing the mind, Prinz sostiene que los conceptos son proxitipos, i.e. "representaciones derivadas perceptivamente que son usadas para detectar categorías" (Prinz 2002, p. 237). Según esta propuesta los conceptos son "copias almacenadas de representaciones producidas por la percepción" (Prinz 2002, p. 272). Las copias de representaciones preceptivas se almacenan en memoria a largo plazo formando redes de representaciones ligadas entre sí. Por otra parte, Prinz también sostiene que los conceptos son "construcciones altamente variables en memoria de trabajo" (Weinberg et al., p. 297). Los conceptos así caracterizados oscilan entre dos niveles distintos: la memoria de trabajo- como construcciones temporarias- y la memoria a largo plazo como redes de representaciones perceptivas. Esto resulta problemático. ¿Los conceptos son representaciones perceptivas almacenadas o construcciones variables, sensibles al contexto? ¿O hay una definición plausible que permita que sean ambas? A continuación analizaré cada una de estas alternativas

Towards a statistical mechanics of macroscopic brain states

Esta tesis estudia la naturaleza de las fluctuaciones espontáneas de la actividadcerebral humana, medida a gran escala. Dichas fluctuaciones se organizan enun repertorio de patrones espacio temporales que se repiten en diversas condiciones,tanto en la ejecución de tareas como en reposo y tanto en el sueño como enla vigilia. La relación entre los "estados físicos", definidos por las interaccionesneuronales que forman estos patrones, y los "estados mentales" asociados a cambiosen la consciencia, el procesamiento de información y los diferentes procesoscognitivos que realiza el cerebro, es una pregunta abierta y fundamental en laneurociencia. Desde un punto de vista físico, el problema consiste en entender los mecanismosdinámicos responsables de la emergencia de dichos patrones. En este trabajo,usamos herramientas de la mecánica estadística para describir y modelar la actividadcerebral espontánea, en experimentos de resonancia magnética funcional enestado de reposo. Nuestra hipótesis principal es que la complejidad observada sepuede entender por analogía a los fenómenos críticos observados en sistemas físicosque presentan una transición de fase de segundo orden. En el caso particulardel cerebro, con sus cientos de miles de millones de neuronas interactuando, resultaimportante determinar qué relación existe entre la complejísima estructurade conexiones y la dinámica colectiva que de ellas emerge. Aquí abordamos esteproblema mediante la construcción de un modelo híbrido basado en conexionesaxonales empíricas y una dinámica de masas neuronales. Desde el punto de vista de la neurociencia, la pregunta más interesante está relacionadacon la naturaleza funcional de los patrones espacio temporales observados. Es decir, tratar de entender la relación entre los estados físicos y los estadosmentales mencionados previamente. En este trabajo presentamos una conexiónentre ambos niveles de descripción al estudiar los cambios en la dinámica cerebralde sujetos al quedarse dormidos. De esta manera exploramos la hipótesisde que el origen neurobiológico de las uctuaciones espontáneas de la actividadesté relacionado con cambios en el estado de vigilia de los sujetos. Tanto en la neurociencia como en cualquier disciplina que estudie sistemascomplejos, el problema de modelado tiene una dificultad inherente y es que, dadala alta dimensionalidad del sistema, los datos experimentales se encuentraninevitablemente subsampleados. Por este motivo, resulta necesario definir representacionesreducidas del sistema que al mismo tiempo resulten informativas. Enesta tesis incluimos una discusión teórica sobre este problema general, usandoelementos de la teoría de la información para cuantificar la relevancia de distintasrepresentaciones de los datos experimentales y su relación con la hipótesis decriticalidad.In this thesis we study the nature of spontaneous large scale fluctuations ofhuman brain activity. These fluctuations are organised into a set of spatiotemporalpatterns that emerge in different conditions, such as during a task or at rest,and during wakefulness and sleep. The relationship between the "physical states"of the brain, dfined by the interacting neurons forming these patterns, and the 'mental states' associated with changes in consciousness, information processingand cognitive processes, is a fundamental open question in neuroscience. From a physicist point of view, the problem lies in understanding the dynamicalmechanisms responsible for the emergence of the aforementioned patterns. We approach this problem using tools from statistical mechanics to describe andmodel the spontaneous fluctuations of brain activity, measured with functionalmagnetic resonance imaging (fMRI) in resting state experiments. Our main hypothesisis that the observed complexity can be explained by analogy with criticalphenomena, known in physical systems undergoing a second order phase transition. In the particular case of the brain, with its hundred billion neurons interacting,it is important to determine the relationship between the complex structureof connections and the collective dynamics that emerge from them. Here we studythis using a hybrid model based on an empirical structure of axonal connectionsand neural mass dynamics. From the point of view of neuroscience, the most interesting question is relatedto the functional nature of the observed spatiotemporal patterns. Thatmeans understanding the relation between the aforementioned physical and mentalstates. In this work we present a connection between both levels of descriptionby studying the changes in the brain dynamics when subjects fall asleep. In thisway we explored the hypothesis that the neurobiological origin of spontaneousactivity fluctuations is related with changes in the state of sleep or wakefulnessof the subjects. In neuroscience as in any other complex system science, the problem of buildingmodels from the data has a fundamental difficulty which comes from thefact that complex systems are extremely high dimensional and therefore the relevantvariables for their description are usually strongly under sampled in theexperiments. Thus, in order to get a meaningful model one has to find reducedrepresentations while keeping relevant information about the system. We discussa general framework to choose between different representations of the limiteddata, using information theoretical measures to quantify their relevance, andanalyse how this affects the hypothesis of criticality.Fil: Haimovici, Ariel. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Trophic relationships of the long-finned squid loligo Sanpaulensis on the southern Brazilian shelf

The diet and predators of Loligo sanpaulensis (Cephalopoda: Loliginidae) on the southern Brazilian shelf were studied by examining the stomach contents of 668 long-finned squid (12–184 mm mantle length) caught by bottom trawl and the stomach contents of 47 potential predators, including stranded penguins and marine mammals as well as fish and cephalopods caught with diverse fishing gears in the region. Of 313 long-finned squid stomachs containing food, fish occurred in 36.4% of stomachs, crustaceans in 23.3% and cephalopods in 6.4%. Identified prey included demersal fish, shrimps and conspecifics. Loligo sanpaulensis was preyed on by 31 of the 47 potential predatory species examined. The frequency of occurrence (FO) was high (>20%) in the stomach contents of La Plata dolphins Pontoporia blainvillei, penguins Spheniscus magellanicus, fur seals Arctocephalus spp., the benthic shark Mustelus canis and the benthic finfish Astroscopus sexpinosus and Percophis brasiliensis. It was less important (5–20% FO) for the benthic and demersal fish Helicolenus lahillei, Paralichthys isosceles, P. patagonicus, Merluccius hubbsi and Urophycis mystacea, and of minor importance (2–5% FO) in the diet of the finfish Trichiurus lepturus, Cynoscion guatucupa, Macrodon ancylodon, Pagrus pagrus and Pomatomus saltatrix. Loligo sanpaulensis seems to be a link in the pelagic and benthic foodwebs of the southern Brazilian shelf, because it is preyed on by such high-level predators as marine mammals and penguins, and by several of the most abundant fish found in the region

Larvae of Illex argentinus from five surveys on the continental shelf of southern Brazil

Three types of rhynchoteuthion larvae and one of small juvenile ommastrephid were collected in 116 of 371 samples obtained in five surveys on the shelf of southern Brazil. The cruises were between Santa Marta Grande Cape (28°30'S) and Chui (34°40'S); one cruise in autumn 1980-1982, one in winter, and three in spring. Samples were collected with a bongo net of 0.33-mm mesh in oblique hauls from bottom to surface between the coast and approximately the 200-m isobath line. Juveniles and the type of larvae that accounted for over 90% of the total were identified as Illex argentinus. They were found mostly in winter and spring in association with the western boundary of the Brazil Current and Subtropical Waters and rarely with Coastal and Subantarctic Waters. Their abundance in southern Brazil may be explained by spawning in the region and northward transport of egg masses

Reproductive cycle of Loligo sanpaulensis Brakoniecki, 1984 (Cephalopoda; Loliginidae) in southern Brazil

Loligo sanpaulensis the most abundant coastal squid in southern Brazil. The reproduction of the species was studied from 2,340 specimens obtained in eight groundfish surveys from 198 1 to 1987 along the coast of southern Brazil (28"35' S to 34"40' S), at depths from 10 to 587 m. On the shelf,' ripe specimens and mated females were found in all seasons, being less frequent in autumn. Most squids caught on the slope during all seasons were immature. The high frequency of fully mature females, and the occurrence of spent males, egg masses and loliginid paralarvae suggested that the species spawns off Southern Braz il. Mature individuals were mostly smaller than 80 mm mantle length (ML) in summer and autumn. In winter and spring, two spawning groups, with 50 - 80 mm ML and larger than 100 mm ML, were detected at depths under and over 40 m respectively. Off southern Brazil , the species has a long spawning period, with peaks in summer and winter/spring. The squid migrates across and along the shelf, taking advantage of the Brazil and Malvinas currents system to reach suitable spawning and feeding grounds. It is hypothesized that summer spawners may find adequate feeding grounds in winter in the outer shelf while winter spawners may recruit in part to the southern range of the species in northern Argentina in spring, eventually returning northward to reproduce

Reproductive biology of winter-spring spawners of Illex argentinus (Cephalopoda: Ommastrephidae) off Southern Brazil

The reproduction and fecundity of winter-spring spawners of the shortfin squid Illex argentinus off southern Brazil (27°S-34°S) were studied in samples from bottom trawl surveys on the outer shelf and upper slope from 1986 to 1992. The mantle length-total weight relationships were for males: TW = 0.00002456 ML2.974 for females: TW = 0.00004265 ML 2.842 and pooled: TW = 0.00005376 ML 2.809. Males were heavier than females at the same ML. Fully mature squids were found from July to October. Mantle length and total weight of fully mature males ranged from 188 to 296 mm (mean 252.2 mm) and 195.5 to 611 g (mean 382.7 g) and for females from 225 to 356 mm (mean 307.4 mm) and 234 to 772 g (mean 558.4 g). Total weight was maximum at full maturity and decreased in the subsequent stages of both sexes. Mean weight and mean major axis length of ripe oocytes in the oviducts were 0.48 mg (sd= 0.10 mg) and 1.27 mm (sd= 0.08 mm), respectively. Total and oviduct mean fecundities, in thousands of oocytes larger than 0.4 mm, in ten fully mature females (294-336 mm ML) were 177.2 (93.0 to 294.3) and 118.4 (51.5 to 233.9), respectively. Spawning season in this region seems to be more protracted than in higher latitudes. Our results suggest that a northward migration could take place prior to spawning and that in winter and spring, southern Brazil may be a major spawning ground of Illex argentinus that contributes to the local and to the Uruguay and northeastern Argentina recruitment