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.

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.

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.

The present thesis investigates the effects of auditory deafferentation and reafferentation with a unimodal and multisensory perspective. Aim of the thesis is the understanding of issues concerning functional plasticity resulting from long-term auditory deprivation, and the effects of reafferentation through a cochlear implant (CI) on audition, vision, and their interaction. The thesis is divided into three parts: Part I explores the effects of auditory deafferentation on the visual modality to understand whether a long-term sensory deprivation leads one of the remaining senses to reorganise in a cross-modal fashion. In particular, Chapter 1 reviews animal and human findings on cross-modal plasticity after sensory deafferentation and introduces the particular case of deafness, focusing on the sensory modality that seems to reorganise the most after profound deafness: vision. In Chapter 2 I present the study we conducted to explore an underinvestigated issue of cross-modal reorganisation after long-term auditory deprivation. We investigated visual temporal processing in a group of profoundly deaf individuals by testing their ability to make temporal order judgments. Our results show comparable accuracy in processing visual temporal sequences in deaf individuals and hearing controls, but an enhanced reactivity in the deaf population particularly when responding to stimuli appearing towards the periphery of the visual field. Our findings suggest that long-term auditory deprivation does not alter temporal processing abilities, and that the reactivity observed in the deaf group may instead constitute a central aspect of the functional changes occurring after auditory deafferentation. Part II of the thesis addresses the effects of auditory reafferentation through a cochlear implant on the adult auditory system. Chapter 3 reviews findings that document plasticity in the adult brain and the role of experience in determining the extent for plasticity to occur. In addition, a review on auditory spatial hearing introduces the two studies we conducted to investigate the recovery of sound localisation abilities after bilateral and unilateral cochlear implantation (chapter 4 and 5, respectively). Results from the first study show that partial recovery of spatial hearing after bilateral implantation occur with different time course as a function of the recipient’s experience with auditory cues. Results from the second study show that some sound localisation abilities can emerge even in prelingually deafened adults fitted with a single implant, at least in a laboratory setting. Importantly, this ability appears to be constraint by the years of experience with the CI, and again as a function of previous auditory experience of the CI recipient. Part III addresses the question of the effects of auditory reafferentation on the visual system and its interaction with audition. Chapter 6 reviews the issue of cross-modal plasticity after auditory reafferentation. In particular, we investigated whether visual abilities are modified after cochlear implantation in a group of prelingual and postlingual deaf recipients (Chapter 7). In this study we found that prelingual deaf recipients, compared to postlingual deaf, had an advantage in detecting the onset of rapidly presented visual stimuli in the periphery of the visual field. In a further experiment (Chapter 8) we investigated whether auditory and visual information are integrated after cochlear implantation in prelingual and postlingual deaf recipients and found that their abilities are comparable to hearing controls. Finally, Chapter 9 summarises all the presented results and draws the major conclusions.

How humans perceive everyday reality is one of the most fascinating and enduring interest of different scientific disciplines. The aim of the present dissertation is to investigate - from both a theoretical and an empirical perspective - some aspects concerning the crossmodal interactions between hearing and vision. In the first part of the introduction special attention is given to the cortical and subcortical neural substrate involved in integrating different sensory modalities, and more specifically, audiovisual stimuli. Experimental studies in the literature designed to empirically investigate different aspects of audiovisual interaction and the potential existence of a sensory dominance between hearing and vision will be presented. In the last part, the introduction will be focalized to discuss some of the principal models aimed to predict the outcome of audiovisual integration and its relation with sensory dominance. The following chapters present the experimental studies designed to empirically investigate different aspects of audiovisual interactions and the role of eye movements in auditory cognition. In a first study, the effects of eye movements on auditory spatial representation will be explored. The aim is to disentangle controversial results in the literature emerged in two studies that used different type of sounds (i.e., free field sounds provided through loudspeakers vs. sounds provided intracranially through headphones) and different tasks. In a second study, the disputed relation between perception and action will be investigated in presence of a crossmodal audiovisual illusion. The aim is to verify whether participants’ visuo-motor behaviour might be biased by the visual illusion as emerged for perception, and eventually, whether perceptive and motor biases are correlated. The last study presented in this dissertation will explore the effects of crossmodal audiovisual stimulation in low vision patients and the relation between the visual pathology. More precisely, the possible visual detection enhancement provided by a sound coupled with a visual stimulus will be investigated. To this purpose, in a first experiment, the effect of spatial disparity between audiovisual stimuli will be deepened while the last two experiments will be focalized on the effects of temporal audiovisual disparities of crossmodal stimuli. The results of the studies described in the present dissertation provide evidence of an effect of eye movements in the auditory spatial cognition and a relation between the perceptive and visuo-motor systems in presence of an illusion induced by a sound. Moreover the presented findings report for the first time a significant crossmodal effect of audition on visual perception in low vision patients.

Oscillatory neuronal activity in the alpha band has been associated with both conscious perception and attention. Firstly, conscious perception of a weak sensory stimulus is preceded by alpha power decreases. Secondly, attention to a sensory event reduces alpha activity in the corresponding sensory regions. According to the widely accepted functional inhibition hypothesis, oscillatory neural activity in the alpha band reflects cortical excitability; in other words, a sensory region with low alpha power levels is more excitable. Several questions regarding the relationship between conscious perception, attention and alpha band activity have not been addressed so far. Firstly, it remained unclear whether brain states predisposing consciousness only comprise local pre-stimulus alpha power decreases, or also global network states. Secondly, it remained unclear whether alpha power decreases prior to conscious perception are confounded by fluctuations of attention or not. The goal of the current thesis is to address these two open questions in the tactile modality with two magnetoencephalography studies. The first study explored brain states predisposing conscious tactile perception, with a particular focus on functional connectivity patterns in addition to alpha power modulations. To this end, a simple near-threshold detection paradigm was conducted, with weak tactile stimuli to the participants’ left index finger. Findings revealed that conscious perception is preceded by a) a relative alpha power decreases in the somatosensory cortex contralateral to stimulation, and b) a spectrally specific pattern of functional connectivity in the primary somatosensory cortex. Based on the first study, it can be concluded that brain states predisposing consciousness comprise local cortical excitability changes as well as frequency-specific network patterns. The second study focused on alpha power changes prior to conscious perception in the context of spatial attention. To this end, a near-threshold detection paradigm with a double-pulse target stimulus was combined with a spatial attention task. The results showed a) that spatial tactile attention modulates pre-stimulus alpha power, and b) that spontaneous alpha power fluctuations not explained by attention influence perception. These findings indicate that – while attention does affect pre-stimulus alpha power levels – spontaneous alpha power fluctuations predispose consciousness. Taken together, we conclude that brain states predisposing conscious perception comprise spectrally specific functional connectivity patterns, and alpha power fluctuations distinct from attention-induced alpha power modulations.