Dissociable processes underlying decisions in the Iowa Gambling Task: a new integrative framework

<p>Abstract</p> <p>Background</p> <p>The Iowa Gambling Task (IGT) is a common paradigm used to study the interactions between emotions and decision making, yet little consensus exists on the cognitive process determining participants' decisions, what affects them, and how these processes interact with each other. A novel conceptual framework is proposed according to which behavior in the IGT reflects a balance between two dissociable processes; a cognitively demanding process that tracks each option's long-term payoff, and a lower-level, automatic process that is primarily sensitive to loss frequency and magnitude.</p> <p>Methods</p> <p>A behavioral experiment was carried out with a modified version of IGT. In this modified version, participants went through an additional phase of interaction, designed to measure performance without further learning, in which no feedback on individual decisions was given. A secondary distractor task was presented in either the first or the second phase of the experiment. Behavioral measures of performance tracking both payoff and frequency sensitivity in choices were collected throughout the experiment.</p> <p>Results</p> <p>Consistent with our framework, the results confirmed that: (a) the two competing cognitive processes can be dissociated; (b) that learning from decision outcomes requires central cognitive resources to estimate long-term payoff; and (c) that the decision phase itself can be carried out during an interfering task once learning has occurred.</p> <p>Conclusion</p> <p>The experimental results support our novel description of the cognitive processes underlying performance in the Iowa Gambling Task. They also suggest that patients' impairments in this and other gambling paradigms can originate from a number of different causes, including a failure in allocating resources among cognitive strategies. This latter interpretation might be particularly useful in explaining the impairments of patients with ventromedial prefrontal cortex lesions and, by extension, the contribution of this brain region to human decision making.</p

A penalisation approach to simulate root compressors

The simulation of the unsteady flow field in root compressors requires to deal with several challenges related to the presence of moving parts and complex geometries. In the present work a penalisation approach applied to the compressible Navier- Stokes equations is investigated as a possible technique to perform this kind of simulations. In particular, the compressible Navier- Stokes equations are augmented by source terms which represent the effects of the body on the fluid and then they are integrated in both the fluid and solid domains. The presence of moving bodies is taken into account by a level set function. A validation based on a grid convergence study is performed on the flow around an impulsively started cylinder. A preliminary simulation of the flow field inside a root compressor is performed in order to predict the unsteady mass flow rate through the machine

Il ruolo della "legge dell'effetto" nei compiti di scelta iterata: un'analisi sperimentale dei giochi a una e due persone

2009/2010Lo scopo di questa tesi è studiare i meccanismi di raccolta ed integrazione delle informazioni nell'ambiente e la loro influenza sulle scelte negli esseri umani. Lo strumento sperimentale utilizzato è il Multi – Armed Bandit Task (MAB), un paradigma di scelta iterata nel quale i partecipanti affrontano la stessa situazione per un numero di trial predeterminato. Dopo ogni trial il partecipante vince o perde un certo numero di punti in funzione della scelta compiuta. Per poter massimizzare il proprio punteggio deve quindi integrare i feedback ricevuti per capire quali sono le alternative più remunerative. Per modellare i risultati dei MAB si è utilizzato il Reinforcement Learning (Sutton & Barto, 1998). La mia analisi dei MAB si è rivolta prevalentemente all'Iowa Gambling Task (IGT; Bechara, Damasio, Damasio, & Anderson, 1994), ideato come strumento diagnostico per lesioni della corteccia orbitofrontale. La peculiarità di questo paradigma è che i partecipanti incrementano il proprio punteggio con ogni scelta, ma a volte, per effetto della stessa scelta, ricevono anche una punizione e perdono una certa quantità di punti. Gli autori ritengono che il comportamento dei partecipanti sia guidato da due circuiti cerebrali: uno, con sede sottocorticale, che fa preferire le alternative più proficue a breve termine, ed un altro, con sede nella corteccia orbitofrontale, che permette ai partecipanti di integrare le informazioni sulle vincite e sulle perdite al fine di identificare le alternative più remunerative a lungo termine. Inizialmente i nostri esperimenti si sono concentrati esclusivamente sull'effetto della frequenza delle perdite – un fattore mai preso in considerazione da Bechara e colleghi – ed abbiamo concluso che è possibile spiegare buona parte del comportamento dei partecipanti in base alla legge dell'effetto, ovvero in base alla probabilità di perdita e vincita associata a ciascun mazzo, senza tenere conto delle grandezze degli esiti. Per poter spiegare alcuni dati sperimentali abbiamo in seguito elaborato una teoria a due processi. Il primo è governato dalla legge dell'effetto, e solitamente guida il comportamento; il secondo, che si occupa dell'integrazione delle informazioni relative alla grandezza di perdite e vincite, si attiva ed influenza le scelte dei partecipanti solo in alcune situazioni. I fattori che favoriscono – o impediscono – l'attivazione del secondo processo sono analizzati nell'ultima parte della tesi. Al fine di valutare la generalizzabilità del processo governato dalla legge dell'effetto abbiamo confrontato i MAB con le scelte iterate in situazioni di interazione strategica. In queste situazioni il punteggio ricevuto dipende dalle decisioni di un altro agente – come nei paradigmi utilizzati in Teoria dei Giochi (Camerer, 2003). Nelle due situazioni sperimentali che abbiamo studiato (Dilemma del Prigioniero e Sasso – Carta – Forbice) abbiamo confrontato il comportamento dei partecipanti in tre condizioni: interazione strategica con il computer; interazione strategica con un altro essere umano; MAB isomorfo alle prime due condizioni. I dati sperimentali e la modellazione dimostrano che, nella maggior parte delle situazioni da noi studiate, la legge dell'effetto può interpretare sia i MAB che le interazioni strategiche.XXIII Cicl

ASSESSMENT OF KINETICS FOR BUTANOL PRODUCTION BY CLOSTRIDIUM ACETOBUTYLICUM

The economic scenario established at the beginning of the third millennium has revived the interest in Acetone-Butanol-Ethanol (ABE) fermentations. Recent developments in molecular techniques applied to solventogenic microrganisms in combination with recent advances in fermentation systems and downstream processing have contributed to improve ABE fermentation processes feasibility and competitiveness. The challenges raised over the last years as regards ABE production may be synthesized in: i) use of renewable resources as substrate; ii) selection of strains characterized by high ABE productivity; iii) development of new fermentation systems; iv) development of new downstream strategies for enhanced solvent recovery. The selection of unconventional substrates is favoured by the ability of clostridia strains to metabolize a wide range of carbohydrates like glucose, lactose, etc...., typically present in wastewater streams e.g. from food industries. Even though clostridia have been proven successful to produce ABE, information about kinetics of substrate conversion, cell growth and butanol production is still lacking. Studies available in literature most typically regard batch tests whose results do not apply easily to continuous processes. The strong interaction between the growth/acidogenesis phase and the solventogenesis phase should be taken into account. The reactor systems investigated for the ABE fermentation belong to the batch and fed-batch typologies. Some attempts are reported in literature regarding continuous fermentation by means of clostridia strains confined in the reactor by immobilization or cell-recycling. The present study reports the preliminary results of a research activity aiming at investigating the feasibility of the ABE production by Clostridium acetobutylicum ATCC824 in a continuous biofilm reactor adopting cheese whey as feedstock. The contribution regards the characterization of the kinetics related to the ABE production process by free C. acetobutylicum ATCC824 adopting as medium lactose solutions, in order to emulate the cheese whey. The conversion process is characterized in terms of cells, acids, solvents, pH, gas composition and total organic compounds as a function of time. Results are worked out to assess the kinetics of the cells growth and of the ABE production. The yields of the carbon source in cells, acids and solvents are also assessed. The investigation is carried out adopting both batch reactors and two continuous reactors. In particular, the continuous reactors are equipped to operate under controlled conversion regimes, acidogenesis or solventogenesis. Tests carried out under batch conditions show that: i) cells growth follows the Monod kinetics for lactose concentration (CL) smaller than 100 g/L; ii) the butanol specific production rate increases linearly with CL; iii) the lactose conversion - measured at the end of the solventogenesis phase - decreases with CL; iv) the selectivity of butanol with respect to total solvents increases with CL and stabilizes at about 72%W for CL larger than 30 g/L. Preliminary tests carried out with the continuous reactor operated under solventogenesis regime show that steady state establishes with respect to cells and metabolites concentration at dilution rate of about 0.04 h-1

Quality of Transmission Estimation for Planning of Disaggregated Optical Networks

Modern optical networks depend upon advanced software-defined networking (SDN) technologies, which in turn rely on a network abstraction to infer the quality of transmission (QoT). In general, the QoT estimation is based upon the generalized signal-to-noise ratio (GSNR), which takes into account the ASE noise, cross-phase modulation (XPM) and self-phase modulation (SPM) components of the nonlinear interference (NLI). Uniquely, the SPM accumulates coherently, causing the total amount of SNR degradation to depend upon the physical lightpath (LP) history, preventing a fully disaggregated GSNR degradation evaluation. As the current signal symbol rate are increasing, the SPM will provide a progressively more significant contribution to the SNR degradation. We propose a method to evaluate the equivalent SPM component of the NLI that is generated in each fiber span within an optical line system (OLS), independent of the history or configuration of the optical network

Modelling non-linear interference in non-periodic and disaggregated optical network segments

We investigate the generation of nonlinear interference (NLI) within two disaggregated transmission scenarios, each considering a chain of three distinct optical line systems that contain fibers with different dispersion values, with 400G-ZR+ 64 GBd transmission simulated using the split-step Fourier method. Firstly, by separating the NLI into its main constituents: the self- and cross-phase modulations, we investigate the impact of accumulated dispersion upon NLI generation and compensate for the coherent accumulation of the former to produce a model that is fully spectrally and spatially separable, including for alien wavelengths. Considering ideal and optimized in-line amplification, we calculate the amplified spontaneous emission noise and combine this value with the recovered NLI to obtain the generalized signal-to-noise ratio. We show that this disaggregated model provides accurate and conservative results for both transmission scenarios, showing that abstracting these signals with a Gaussian noise approximation always results in a conservative prediction, even for non-uniform fiber dispersion scenarios

Simulative assessment of non-linear interference generation within disaggregated optical line systems

Lightpaths within optical line systems (OLS)s that deploy coherent optical technologies are mainly impaired by two additive Gaussian disturbances: the amplified spontaneous emission (ASE) noise from the optical amplifiers and the non-linear interference (NLI) from fiber propagation, together with some amount of phase noise, typically compensated for bythe carrier phase estimator module within the digital signal processing (DSP) unit. The main obstacle in accurately modelling the physical layer of a disaggregated optical network arises from the spatially-coherent and spectrally-aggregated general behavior of the NLI generation.Within this paper, we perform an accurate split-step Fourier method (SSFM) physical layer simulation campaign over a wide range of fiber chromatic dispersion values that range from 2to 16.7 ps / (nm·km) and channel symbol rates from 32 GBd to 85 GBd. For all the explored scenarios, we first show that the NLI generation in an OLS can be spectrally disaggregated in a practical manner by considering a superposition of self-channel (SC) and cross-channel (XC) NLI components only. Secondly, by considering the span-by-span generalized signal-to-noise ratio (GSNR) deterioration, we show that the XC-NLI accumulation components can also be considered as spatially disaggregated, leaving the SC-NLI as the only spatial coherency contribution. Consequently, by appropriately managing these coherent NLI contributions, we find that it is possible to produce a conservative physical layer model that is both spectrally and spatially disaggregated