Inductive reasoning is of remarkable interest as it plays a crucial role in many human activities, including hypotheses evaluation in scientific inquiry, learning processes, prediction of future events, and diagnosis of a phenomenon (e.g., medical diagnosis). Despite the relevance of these cognitive processes in a variety of settings, there still remains much to understand about the basis of human inductive inferences. For example, it is not yet clear whether the same psychological mechanisms underlie both inductive reasoning and deductive reasoning or, on the contrary, whether induction and deduction correspond to distinct mental processes. The study of inductive reasoning has been a traditional topic in epistemology, and is more recently being explored in cognitive psychology as well. In the present contribution, I focus on both the epistemological and the psychological accounts. To begin with, I illustrate the state-of-art of research on inductive reasoning. On one hand, epistemologists have been working to develop normative theories in which the notion of inductive strength (or confirmation) is formalized. I discuss some of the alternative Bayesian measures of confirmation proposed in the literature on inductive logic. On the other hand, psychologists have been empirically investigating inductive reasoning, discovering important phenomena such as systematic effects of similarity, typicality, and diversity. I illustrate some of the most significant models of induction proposed in the psychological literature to account for such phenomena. Both lines of inquiry – epistemological and psychological – have focused on a restricted kind of induction problem: when assessing the inductive strength of arguments, premises are assumed to be true, that is, ascertained with the maximum degree of probability. However, inductive arguments occurring in real settings often depart from this pattern. Indeed, in a variety of situations, one may need to assess the impact of a piece of evidence whose probability may have significantly changed while not attaining certainty. Evidential uncertainty in inductive inferences is at the core of the present research. After exploring a selection of psychological phenomena concerning uncertainty, I address the epistemological problem of how to extend Bayesian confirmation theory to include cases where the evidence is not certain. A straightforward solution is proposed for a major class of confirmation measures called P-incremental. The solution proposed is based on Jeffrey conditionalization, an essential formal principle discussed below in greater detail. On the psychological account, I discuss two experimental studies conducted to test whether and how people’s judgments of inductive strength depend on the degree of evidential uncertainty. In the first study the uncertainty of evidence is explicitly manipulated by means of numerical values, whereas in the second study uncertainty is implicitly manipulated by means of ambiguous pictures. The results show that people’s judgments are highly correlated with those predicted by two normatively sound Bayesian measures of confirmation. This sensitivity to the degree of evidential uncertainty supports the centrality of inductive reasoning in cognition, and opens the path to further investigations on induction in real contexts.

Human mental life is accompanied by oscillatory signals that send information across distributed neural networks. Whether a stimulus reaches or escapes our conscious experience is influenced by the state of the brain in that moment, reflected in cerebral electrophysiology. Our understanding of this brain activity has grown vastly in recent years, thanks to leading advances in electro- and magneto-encephalography (EEG and MEG, or M-EEG, which enable us to monitor the electric brain signal) and recent developments allowing the direct modulation of endogenous oscillatory components that underlie cortical functions. Transcranial current stimulation, particularly the variant with alternating current (tACS), putatively lets us assess and gauge the role of oscillations on cognition. Several studies have confirmed that tACS can influence neural mechanisms and behavior, even conscious access. Until recently, cerebral activity during stimulation could not be assessed and observations were limited to the aftereffects. The aim of the project described in this dissertation is to investigate the validity of a pioneering procedure that can recover brain signal during simultaneous MEG and tACS. Then, exploiting this approach, we furthered our grasp of how the neural system is altered by transcranial stimulation and the complex relationship between the external current and the internal mechanisms of the brain. The overall goal is to explore our ability to manipulate neural signatures in ongoing activity and the conscious perception of an upcoming stimulus. Chapter 1 provides the reader with a general introduction of current studies and theories behind tACS influence on cognition and behavior. After a description of what tACS is and what it does, the focus is mostly on cutting-edge methods combining tACS and M-EEG, network connectivity and graph theoretical frameworks to study cognitive processes. At the end of the introductory chapter, we indulge on applications and consequences of these approaches, as well as open questions about our understanding of the prerequisites of conscious perception that drove the experiments described in the following chapters. Chapter 2 reports the first study in which we addressed the feasibility of concurrent tACS and MEG, the prerequisite for the rest of the project. Chapter 3 and 4 present studies that better delineated what happens in the brain in terms of oscillatory phase, connectivity and the dependency of tACS effects with the ongoing brain state during electrical stimulation. We addressed some key issues on the mechanisms of action of tACS and its sensitivity to in-vivo brain networks. Chapter 5 provides preliminary results of a study employing a near-threshold task paired with tACS and MEG in the context of conscious perception. We stimulated prestimulus brain rhythms in sensory cortices to see if their strength and connectedness with the rest of the brain could determine whether a stimulus will be perceived or not. Chapter 6, after a recapitulation of the main results in a broader perspective, discusses the meaning and the limitations of the experimental findings and how these extend our current knowledge.

The work presented here is at the meeting point of two branches of visual search research, one of which focuses on the proposition that visual search is guided by preparatory internal representations of targets (i.e., search templates: e.g., Bravo & Farid, 2009; 2012; Castelhano & Heaven, 2010; Duncan & Humphreys, 1989; Malcolm & Henderson 2009; 2010; Schmidt & Zelinsky, 2009; Vickery, King, & Jiang, 2005; Wolfe, 2007; Wolfe, Cave, & Franzel, 1989; Yang & Zelinsky, 2009), and the other of which focuses on investigating target detection in naturalistic search environments (e.g., Delorme, Richard, & Fabre-Thorpe, 2010; Delorme, Rousselet, Macé, & Fabre-Thorpe, 2004; Li, VanRullen, Koch, & Perona, 2002; Peelen, Fei-Fei, & Kastner, 2009; Peelen & Kastner, 2011; Thorpe, Fize, & Marlot, 1996; VanRullen & Thorpe, 2001). The search template for objects presented in naturalistic scenes is relatively unknown in terms of its content and characteristics, neural underpinnings, and individual differences in its representation. This thesis explores these topics in depth using behavioral and neurostimulation methods in four experimental chapters.

In everyday situations humans are continuously confronted with complex and cluttered visual environments that contain a large number of objects. Despite this complexity, performance in real-life tasks is surprisingly efficient. As a novel explanation for this efficiency, we propose that the brain uses typical regularities between objects (e.g., lamps are typically appearing above dining tables) to group these objects to reduce complexity and thereby facilitate behavioral performance. In a series of experiments, we show that object regularities reduce competitive interactions in visual cortex, and we relate this benefit to improved detection of target objects among regular distracter groups. Furthermore, we show that this inter-object grouping also enhances performance in visual working memory and determines how fast objects enter visual awareness in the first place. Altogether, our findings demonstrate that inter-object grouping effectively reduces the number of competing objects and thus can facilitate perception in cluttered, but regular environments.

Interacting with the external environment is an inherently multisensory experience. Therefore, understanding how unisensory deprivations occurring early in life affect this interaction has always been a hot topic of research. In this thesis I aim to contribute to this prolific debate by further investigating the effects on behavior exerted by early-acquired bilateral deafness. In the past decades many studies have extensively investigated this topic, focusing mainly on explaining the changes occurring within the visual modality of deaf people, ultimately aiming at understanding to what extent the intuitive assumption that deaf adults ‘see better’ than hearing controls is really true. This approach proved highly informative, yet many fundamental aspects of behavior remained largely overlooked. The aim of this thesis was to identify these missing aspects and try to address them as systematically as possible. In particular I focused on four critical domains: (i) the investigation of the behavioral reorganization that occurs within the tactile modality of deaf adults (Chapter 2, Study 1; Study 2); (ii) the possible modifications of the interactions between two intact sensory systems (i.e., vision and touch) as a consequence of auditory deprivation (Chapter 3); (iii) the finer-grained definition of which mechanisms of visual attention are modified by bilateral deafness (Chapter 4, Study 1; Chapter 5); (iv) the further understanding of the role of extensive visual training in driving the behavioral improvements reported in the deaf population compared to hearing controls (Chapter 2, Study 3; Chapter 4, Study 1; Study 2; Chapter 5). This set of results highlight that deafness-related plasticity exerts multifaceted effects on behavior, which extend selectively to certain functions but not to others, and that even produced selective aspects of impaired behaviors. Importantly, these data also provide initial evidence that vision and touch might to a certain extent, reorganize independently from one another as a consequence of early bilateral deafness and that also the way they interact with each other shows some modified aspects. Finally, the majority of the behavioral modifications I documented in this thesis depended from deafness per se and was not ascribable to training-related effects. Unexpectedly but very interestingly, what clearly emerged from this set of results is the remarkable flexibility of which are capable the reorganized sensory systems, and in particular the reorganized visual system of deaf adults.

Il presente lavoro ha lo scopo di studiare in dettaglio l’interazione genitore-bambino in famiglie con bambini con Disturbo dello Spettro Autistico (che verranno sintetizzati con l’acronimo ASD dalla definizione inglese “Autism Spectrum Disorder”). I disturbi dello spettro autistico sono disordini del neurosviluppo che alterando nei primi anni di vita la capacità di mettersi in relazione con gli altri, determinano gravi effetti cognitivi, affettivi e comportamentali. Le ricerche condotte negli ultimi decenni nell'ambito della psicologia dello sviluppo hanno evidenziato il ruolo centrale delle relazioni genitoriali nello sviluppo del bambino, sia in bambini con sviluppo tipico che con sviluppo atipico. Questo lavoro di tesi ha l’obiettivo di osservare alcuni aspetti peculiari dell’interazione genitore-bambino in bambini con disturbo dello spettro autistico, considerando come il deficit a livello del “cervello sociale” si ripercuote sullo strutturarsi e il mantenersi di questa relazione. Nel presente lavoro si collocano quattro studi. In particolar modo saranno analizzate nel primo studio le caratteristiche del gioco in diadi madre-bambino con ASD confrontandole con diadi madre-bambino in cui il bambino presenta la Sindrome di Down o lo sviluppo tipico al fine di evidenziare similitudini e differenze sia nelle abilità manifestate dalle madri sia per quelle espresse dai bambini. Nel secondo studio, verrà approfondito l’aspetto del gioco specificatamente in interazione madre-bambino e padre-bambino in famiglie con bambini con ASD, al fine di osservare se la capacità di gioco manifestate dal bambino si differenzino in base alla figura genitoriale con cui stanno interagendo e per evidenziare se madre e padre evidenziano delle caratteristiche peculiari in base al ruolo genitoriale rivestito. Il terzo studio, invece, si è concentrato sull’analisi dello scambio sincronico all’interno delle diadi madre-bambino con disturbo dello spettro autistico confrontandolo con interazioni con bambini con sviluppo tipico e sindrome di Down, con lo scopo di osservare più in dettaglio la struttura dello scambio diadico per evidenziare i contribuiti specifici di entrambi i membri della diade, mostrando come possano differire in base alla presenza o meno di una patologia. Infine nel quarto studio sarà osservata la disponibilità emotiva diadica all’interno di famiglie di bambini con disturbo dello spettro autistico, analizzando sia i comportamenti del bambino sia i comportanti delle due figure genitoriali.

For decades, works in psychology of thinking and decision making have been reporting suboptimal performance and systematic departures from the axioms of probability theory in people’s probability judgments. In these first works, poor performance was often attributed to people making normatively wrong intuitions because of their limited cognitive resources and lack of statistical skills. Over the last years, studies that considered various Bayesian models of inductive reasoning but also other high and lower-level cognitive processes provided a more optimistic picture by showing that, despite departing from the normative benchmark, people’s reasoning skills lead to adaptive and sound performance in everyday life. Different explanatory accounts for this suboptimal but sound reasoning have been proposed, some being more compelling than others. The present thesis is aimed at exploring one of these accounts that is based on confirmation relations and suggests that human inductive ability might rely more on estimating evidential impact than posterior probability. So far, this account has been applied to classical probabilistic reasoning errors, linguistic and psycholinguistic phenomena and probabilistic inferences with verbal stimuli. In this study, we tried to see whether the implicit estimation of confirmation relations can affect probability judgments also when the link between evidence and hypotheses is operationalized as the arbitrary association between visual features in briefly presented figures. First, we expected participants to consider confirmed hypotheses more probable than corresponding (in terms of posterior probability) disconfirmed ones; second, we expected them to choose the more likely option (i.e. the normatively correct one) more often when it was confirmed by the evidence provided than when it was disconfirmed. Four computer-based experiments were conducted using the same methodology. Experimental stimuli consisted of inductive arguments concerning 40 sets of figures composed of two features with two possible values each. By varying the probabilistic association between the two values of the features, sets were generated to have, for each possible combination of the two features, two arguments with the same posteriors and opposite impacts. In each trial, participants first looked at a set of figures. One of these figures was then randomly drawn. Participants were informed about the value of one feature of the drawn figure (e.g., that it was a “circle”) and had to guess the value of the other feature (“white” vs. “black”). Throughout the four experiments, we used three different combinations of features: color and shape (exp.1: black/white; exp 2: light/dark grey), pattern and shape (exp 3) and type and orientation of line (exp 4). In all four experiments, participants systematically chose the confirmed alternative over the equally probable, but disconfirmed one, and chose the normatively incorrect (i.e. less likely) alternative more often when it was confirmed (vs. disconfirmed) by the evidence provided. These results provided a first empirical evidence of the effect of confirmation relations on probability judgment with perceptual stimuli, but also highlighted a significant influence of the experimental material itself on choice patterns. In fact, in experiments 1 to 3 the obtained results showed that color (or pattern) was a more compelling evidence than shape in determining participants’ choices. The combination of line curvature and orientation used in experiment 4 proved to be the more balanced among those employed in the present research. Only in this last experiment, indeed, the type of evidence did not affect the choice for the confirmed alternative, nor the amount of errors. The results we found supported our experimental claims showing that confirmation relations can affect probability judgments even in absence of any semantic element, but also suggested the existence of a mutual influence between perceptual features and probability judgments. Our experimental results have theoretical as well as applied implications. On a theoretical level, they extend the results coming from works involving verbal and linguistic material to perceptual stimuli with no semantic background. Additionally, they show that high-level relations, which are completely unknown to the subject, affect the way people perceive relations within a visual set of perceptual items. This might have interesting and noteworthy implications for studies on visual cognition, and, on a broader level, contingency learning and stereotypical judgments.

The current thesis aims to investigate cascaded processing in visual word recognition by testing the predictions of the Dual Route Cascaded (DRC) model of reading. Despite widespread acceptance of the idea that visual language processing is cascaded, there are circumstances in which such an account is not easily reconciled with the data produced by skilled readers. Recent experiments involving factorial manipulations in reading showed, in particular, additive effects of stimulus quality (i.e., clear vs. degraded stimuli) with letter string length and orthographic neighbourhood size in nonword reading and with word frequency and lexicality when words and nonwords were mixed in the task, thus suggesting that information processing implicated in visual word recognition must be at least partially thresholded. Six experiments have been presented in this thesis: on one hand, a new variable that has a role when the stimuli are degraded – the Total Letter Confusability – has been introduced; on the other hand, the effects due to list composition have been analyzed when the stimuli were degraded in the task. In general, the results obtained suggest a novel interpretation of the additivities previously observed; these findings have been explained within the DRC model which also correctly simulates a significant amount of the data. The empirical evidence collected so far clearly indicates that there is currently no need to assume thresholded processing in the reading system.

Reward is a strong determinant of human and non-human behavior, influencing the exploration of the world around us and our interactions with it. Interestingly, the impact of reward and reward-associated objects is not limited to strategic changes in approach behavior or attention deployment, but also extends to situations in which prioritizing processing of such objects is not necessarily advantageous for current goals. In spite of converging evidence for the automatic influence of reward on attentional deployment, less is known about the impact of reward on other cognitive processes. In this thesis I describe a first attempt to investigate the influence of reward in encoding and maintenance of visual representations in working memory. Throughout this thesis I argue that once objects have been associated with a positive outcome in past encounters, they are preferentially encoded and maintained in visual working memory (VWM) even when reward is no longer provided or when there is no consistent pairing between reward feedback and target identity. In Chapters 2 and 3 I demonstrate that reward associated objects interfere with the visual representations of less valuable items maintained in VWM. This interference was already present starting 10 ms from the offset of the memory display suggesting that valuable objects directly affected the encoding of less valuable items. This robust phenomenon was observed at different delays, both when reward-associated objects were task-relevant and when they were not, and was independent of object salience. However, the interference disappeared when task requirements for target selection increased suggesting that items with a positive reward history can effectively capture attention and interfere with VWM representations only when cognitive resources are not exhausted by the main task (Chapter 3). In the last study presented in this thesis I explored the possibility that reward could impact VWM beyond target selection and encoding, namely influencing the active maintenance process. To investigate this hypothesis I measured reward priming effects on event-related potential (ERP) indices of selective attention – the N2pc - and visual working memory maintenance – the CDA (contralateral delay activity). Results indicate that reward modulated CDA only, speaking for a discrete effect of reward on VWM maintenance. While the precise nature of such modulation is still unknown, these results suggest that reward history might influence the precision or the duration of visual representations maintained in VWM. Further studies are necessary to directly test this hypothesis, but these initial results suggest an interesting direction for future research in better characterizing the nature and extent of the influence of reward history on visual cognition.

Cross-modal processing and multisensory integration (MSI) can be observed at early stages of sensory processing in the cortex. However, the neurophysiological mechanisms underlying these processes and how they vary across sensory systems remain elusive. The aim of this study was to investigate how cross-modal processing and MSI are reflected in power and phase of oscillatory neuronal activity at different temporal scales in different sensory cortices. To this goal, we recorded stereo-electroencephalographic (SEEG) responses from early visual (calcarine and pericalcarine) and auditory (Heschl’s gyrus and planum temporale) regions in patients with drug-resistant epilepsy while performing an audio-visual oddball task. To Investigate crossmodal processing and MSI in the power domain of oscillatory activity, we explored a wide range of frequency bands (theta/alpha band: 5-13Hz; beta band: 13-30 Hz; gamma band: 30-80 Hz; high-gamma band: 80-200 Hz) during the first 150 ms post-stimulus onset. Differently, to investigate crossmodal processing and MSI in the phase domain of oscillatory activity, we explored a narrow range of frequency bands (theta/alpha band: 5-13Hz; beta band: 13-30 Hz; gamma band: 30-80 Hz) during the first 300 ms post-stimulus onset. In the power domain, we showed that cross-modal processing occurs mainly in the high-gamma band (80-200Hz) in both cortices. However, we evidenced that the way MSI is expressed across modalities differs considerably: in the visual cortex, MSI relies mainly on the beta band, however it is also evident, to a lesser extent, in the gamma and high-gamma band, while the auditory cortex reveals widespread MSI in the high-gamma band and, to a lesser extent, across the gamma band and the other investigated frequency bands. In the phase domain, we showed that cross-modal processing is differently expressed across modalities: in the auditory cortex it induces an increased phase concentration index (PCI) in ongoing oscillatory activity across all the investigated frequency bands, while, in the visual cortex, it induces an increased PCI particularly evident in the theta/alpha band with few or no effect respectively in the gamma and beta band. Importantly in both cortices, the most part of the COIs showing increased PCI, were not accompanied by a concomitant increase in power. These results indicate that in both auditory and visual cortex, cross-modal processing induces a pure phase resetting of the oscillatory activity. During MSI processing we observed, in both cortices, a stronger increase in PCI, in comparison to the intramodal processing, in the theta/alpha band and in the gamma band. Our results confirm the presence of cross-modal information representations at neuronal populations level and conform to a model where the cross-modal input induces phase-locked modulation of the ongoing oscillations. Importantly, our data showed that the way MSI is expressed in power modulations differs between the investigated sensory cortices suggesting the presence of different types of neurophysiological interactions during this process. These results are discussed in the framework of the current literature.