Social visual orienting in typical and atypical development.

This research deals with some perceptual aspects of shape and colour vision, and specifically with the relation between the widespread phenomenon of amodality in vision and the multifarious characteristics of colour appearances. The study is divided into a theoretical and an experimental part, and the rationale of the two experiments is discussed within the systematic framework illustrated in Chapter 1 and Chapter 2, respectively on the topics of colour and amodality. The third chapter describes an experiment carried out in order to study the effects of colour in dimensional phenomena. The results show that colour has an effect on amodal completion, and particularly regarding dark/light colours and harmonic and disharmonic configurations. The fourth chapter describes an experiment carried out in order to test the existence of a perceived natural relationship between shape and colour using non-geometrical figures. The aim of this study was to verify whether there is a natural relation between colours and natural shapes, and which elements or parts of the shapes – like orientation, type of shape, margins, texture or dimensionality – might be responsible for that relation and explain it. The results confirmed the initial hypothesis. Overall, one of the best achievements of the research reported, has been its demonstration of the feasibility of the phenomenological methods, complementary to psychophysical methods in the scientific analysis of visual perception.

Humans learn to trust new partners by evaluating the outcomes of repeated interpersonal interactions. However, available prior information concerning the reputation of these partners may alter the way in which outcomes affect learning. This thesis combines for the first time behavioral, computational, psychophysiological and neural models in a direct comparison of interaction-based and prior-based decision-to-trust mechanisms. Three studies are presented, in which participants played repeated and single trust games with anonymous counterparts. We manipulated several conditions: whether or not reputational priors were provided, the probability of reciprocation (trustworthiness) of each counterpart, and the time-horizon of the relationships. The thesis addresses several challenges involved in understanding the complex behavior of people in social contexts, by investigating whether and how they integrate reputation into decisions to trust unfamiliar others, by designing ways to combine reputation information and observed trustworthiness into unified models, and by providing insight into information on the brain processes underlying social cognition. Numerous models, algorithms, game theoretical and neuroscientific methods are used to examine these questions. The thesis presents several new reinforcement learning (RL) models and explores how well these models explain the behavioral and neural interactions between trust and reputation. The performance of the new models was tested using experiments of varying complexity. These experiments showed that model-based algorithms correlate better with behavioral and neural responses than model-free RL algorithms. More specifically, when no prior information was available our results were consistent with previous studies in reporting the neural detection of parametric estimates of RL models within the bilateral caudate nuclei. However, our work additionally showed that this correlation was modified when reputational priors on counterparts are provided. Indeed participants continued to rely on priors even when experience shed doubt on their accuracy. Notably, violations of trust from counterparts with high pro-social reputations elicited both stronger electrodermal responses and caudate deactivations when priors were available than when they were not. However, tolerance to such violations appeared to be mediated by priors-enhanced connectivity between the caudate nucleus and ventrolateral prefrontal cortex, which was anti-correlated with retaliation rates. Moreover, in addition to affecting learning mechanisms, violation of trust clearly influenced emotional arousal and increased subsequent recognition of partners who had betrayed trust.

In the last decade, a consistent body of research has shown that the correct identification of task-relevant items can cause a transitory increase in human perceptual sensitivity. In the present work I report evidence of short- and long-term changes in perceptual processing triggered by the recognition of visual targets. This collection of studies suggests that targets recognition may trigger internal signals of reinforcement which, in turn, would foster cortical plasticity. Interestingly, such endogenous signals seem to be modulated by the presence of external reward and by intrinsic aspects of task performance.

Attention is thought to alter appearance by intensifying the sensory impression of the attended stimulus. Current debates are about how this increases might operate and what are the underlying neural mechanisms. Three mechanisms have been proposed to account the effect of attention: contrast gain, response gain and baseline shift. However, psychophysical and neuroimaging studies produced results that are not always consistent. We used the functional magnetic resonance imaging (fMRI) to explore how attention alters the appearance of coherently moving dots. The first experiment assessed coherence response functions for different levels of contrast. This experiment showed which kind of pattern should be expected with attention altering appearance by means of contrast gain mechanism. The results showed that contrast produced a leftward shift of the coherence response function. By our knowledge, this is the first fMRI evidence for the assumption that processing of motion coherence is susceptible to contrast gain. The second experiment assessed the effect of attention on coherence response function. The results showed that attention affects the BOLD response with the same strength for all coherence levels. This pattern of response is compatible with the predictions of the baseline shift model. Finally, in order to explain the discrepancy between psychophysical and neuroimaging results, we suggested a signal detection account for the effect of baseline shift on the perceptual level, proposing that baseline shift may produce a leftward shift of the psychometric function although sensitivity remains unchanged.

In everyday life, our body gets in contact with multiple tactile stimuli from the outside world. How our somatosensory system identifies and localises these multiple stimuli entering in contact with our body surface, is the general framework to which the researches of the present thesis belong. Tactile stimuli on our body can be spatially coded and represented by using multiple reference frames. Touch is initially encoded into a sensory-space within primary somatosensory map and then further stages of processing can represent the location of tactile event with respect to the overall body structure (body-space) or to the outside world (external-space). In the present thesis we report first a series of behavioural experiments aimed at investigating which spatial reference frame is adopted in a special context of sensory stimulation, namely the double simultaneous stimulation (DSS). Then, we used functional magnetic resonance (fMRI) as a tool for delineating the neural bases of the cognitive processes sub-serving the elaboration and representation of concurrent stimuli for conscious tactile perception. In a first behavioural study using the tactile DSS paradigm, we defined the spatial coding used by observers when tactile stimuli are delivered with different fingers combinations (i.e., within vs. between hands) and hand postures (i.e., hands palm-down vs. palm-up). In a second behavioural work we tested the influence of different visual modulations (e.g., seeing body parts or objects) and visual-proprioceptive conflict (e.g., seeing body parts in a different position with respect to one adopted by the participant) on the spatial representation of touch. Furthermore, we investigated the effect of changes to the visual structural morphology of a body part on the spatial representation of touch. Finally, using a fMRI adaptation paradigm for touches at the fingers, we aimed to define the neural bases of tactile perception in a repeated stimulations context. In particular, we assessed the mutual interaction between tactile stimuli located at body parts that are clearly distinct in terms of the body-space (e.g., left and right index fingers), but proximal in terms of neural representations (due to some bilateral responses of the somatosensory cortices).

In each environment we experience in our daily life, we find ourselves surrounded by complex auditory soundscapes. These auditory scenes are often composed of many concurrent sound sources with both spatially and temporally overlapping spectral details, which humans are consistently able to parse seemingly effortlessly in order to navigate their surroundings. Two main aspects are involved in this capability: directing attention, first outlined by Cherry in 1953 in the form of a seminal paradigm, the so-called “cocktail party problem”, and parsing the sound scene, codified by Bergman in 1990 as “auditory scene analysis”. Attention, in every sensory domain, plays a fundamental role to efficiently select the relevant information and ignore the distracting inputs, with studies showing that it operates in the form of a “biased competition” between neural representation of perceptual objects. Objects were depicted in vision as the central “units”, on which non-spatial selective attention acts in many natural contexts, however in the auditory domain several questions remain to be addressed on that matter. Most notably it is indeed unclear how the attention mechanisms operate at both, the level of the auditory object formation and the level of the auditory object selection. More importantly where and how in the neural pathway an object-based representation of an attended sound emerges, is yet to be fully understood. In the present thesis we designed a novel paradigm to tackle the auditory selective attention at the level of object processing: a repetition target has been embedded in one of the two naturalistic streams in such a way that, after being cued, the participant necessarily had to build up representations of the auditory objects composing the scene across time in order to accomplish the task. This paradigm has been employed in both studies that compose the thesis. The first study was conducted to characterize the auditory selective attention system with a theoretical and empirical focus on high-level attentional modulations on the processing level of auditory objects. In line with studies of object-based attention in the visual domain, we reported a behavioral attentional facilitation effect in the validly cued trials, and an inhibition effect in the invalidly cued trials. In the second study, we focused on the neural activity during the repetition detection period by investigating the temporal dynamic of the cortical activity at the source level. These analyses were accomplished both in time (in form of evoked responses, ERFs) and frequency domain (in form of time-frequency spectrograms) providing not only insights into the time courses of events but also their exact spatial localization in cortex. We reported a significant stronger MEG response, mapped at the source cortical level, when the repetition segment was in the attended stream. The same has been found when the target repetition was detected, suggesting that the time course of the neural activity and its spatial distribution represent one aspect of the neural correlates of the object-based attention. Overall both studies show an attentional modulation effect operating indeed on the object-level in a naturalistic auditory scene supporting the biased competition theory.

What does it mean to be an emotion researcher? First of all, having no idea of what the object of study is. Indeed, there is still no general agreement about the definition of emotion, a vague concept that changes depending on the theoretical approach of each researcher. Given the important role they play in our lives influencing thoughts, behaviors, and social experiences, emotions have increasingly drawn the attention of several researchers in different domains. Specifically, the assumption that we are not slaves of our own emotions, but we can actively change them, has fostered a growing interest in emotion regulation. The field of affective neuroscience highlights the importance of integrating different methodological approaches (e.g., neuroimaging techniques, computational modeling, machine learning) to unveil the psychophysiological mechanisms and neural bases of emotional processes, providing insights about their impairments in mental disorders and the development of more accurate treatments. In light of this, in this thesis I will investigate the neural bases of emotion regulation, considering both its adaptive and detrimental aspects. The goal of the first part is to trace neurophysiological and brain structural representations of emotion regulation. In the second part, this construct will be explored by addressing its less adaptive counterparts, looking for morphometric evidence of emotion dysregulation. In the first study (Study I), I will investigate whether regulating emotions can leave a long-lasting trace in the brain, such as a neurophysiological ‘signature’ in the oscillatory activity, recording EEG signal at rest before and after applying an emotion regulation strategy. After exploring the physiological characterization of emotion regulation, the second study (Study II) will provide a morphometric representation of this process. A supervised machine-learning algorithm, namely Multi-Voxel Pattern Analysis (MVPA), will be applied on MRI images to identify structural networks predicting the use of specific cognitive strategies to regulate emotions. Studying mental disorders characterized by emotional difficulties can give us a direct window into neural mechanisms involved in emotion regulation. To address this issue, I will capitalize on Source-based Morphometry (SBM), a whole-brain multivariate approach to structural images based on Independent Component Analysis, a form of unsupervised machine learning to separate independent sources from a mixed-signal. In the third study (Study III), I will track down the neurostructural markers of emotion dysregulation focusing on Borderline Personality Disorder, whose core feature is dysfunctional emotion regulation, as compared to patients with Bipolar Disorder more characterized by mood disturbances and impulsive behavior. Along with emotions, the ability to control impulses can be dysregulated as well, representing a problematic symptom in many affective disorders. The fourth study (Study IV) will provide evidence of the neural bases of impulses dysregulation, investigating morphometric features of Bipolar Disorder. I will combine both subjective (self-report assessing impulsivity) and objective (MRI) measures, in order to gain a more comprehensive picture of this multifaceted dimension. These studies will be able to shed new light on emotion regulation processes, providing a wider overview of the underlying functional and dysfunctional mechanisms, thanks to the combination of neuroimaging techniques and subjective measures. According to a brain-behavioral approach, this will lead to build a model that can help to increase both scientific knowledge and everyday well-being.

There is a need to increase the efficacy and efficiency of aphasia rehabilitation protocols. In order to do this, we may rely on knowledge about how the language system may be changed by experience, including it’s plasticity to behavioral training and to neuromodulation. In this thesis, I study mechanisms of language facilitation in healthy individuals and mechanisms of language recovery in individuals with aphasia. I use both behavioral modification techniques (repeated naming in healthy individuals, and linguistically motivated aphasia therapy in individuals with aphasia), and neuromodulation (transcranial direct current stimulation, tDCS). The data in this thesis indicate that, in healthy individuals, language facilitation by repetition priming reflects changes in implicit processing of stimuli (at the level of lexical retrieval), and explicit episodic retrieval of the prior occurrence of the stimuli. In patients with aphasia, the data indicates that the observation of item-specific improvement after treatment depend on pre-treatment levels accessibility to the lexeme level via semantics, and also on short term memory skills and/or post-lexical processing skills. Generalization may occur when damage to abstract features is present(semantic and/or grammatical), and when knowledge of abstract features is engaged during treatment. tDCS has been successfully used in prior research to enhance language training and rehabilitation effects. However, our data from healthy individuals did not reveal effects of neuromodulation, and the data with patients was ambigous: it is not possible to discern whether tDCS indeed incrteased the effects of therapy or wether the data are better explained as reflecting a ceiling effect.

Every day we use actions, gestures and words to interact with other people and with the environment. Being able to understand people’s movements and communicative intentions is critical to our ability to act successfully in the world. Here we present three studies aiming at investigating the relationship between actions, gestures and words in the brain. In the first study we described and offer a standardized data set of 230 well-controlled stimuli of meaningful (pantomimes and emblems) and meaningless gestures together with norms, with the aim of promoting replicability between studies. One hundred and thirty raters (Italian and non-Italian speakers) rated the meaningfulness of the gestures, and provided a name and a description for each of them. To our knowledge, this is the first data set of meaningful and meaningless gestures presented in the literature. In the second study, we aimed 1) at characterizing the neural network associated with the processing of different categories of gestures (pantomimes, emblems and meaningless gestures) using fMRI, and 2) at contrasting the role of precentral and temporal areas in action understanding, using rTMS. In particular, we applied rTMS to the posterior middle temporal gyrus (pMTG) and to the ventral premotor cortex (PMv) in different sessions, while participants were performing either a semantic or a perceptual judgment task. According to motor theories of action understanding, rTMS applied to the PMv, but not to the pMTG, should impair performance during the semantic judgment task. By contrast, according to cognitive theories of action understanding, rTMS applied to pMTG, but not to PMv, should impair performance in this task. Results from the fMRI experiment revealed a sensitivity of the MTG to meaningful in comparison to meaningless gestures. Additionally, three different brain areas seemed to contribute to the processing of pantomimes and emblems: superior parietal lobe (SPL) and precentral gyrus (PCG) in the case of pantomimes and IFG in the case of emblems. Unfortunately, we did not observe any significant effect of rTMS in any condition. The third study aimed at investigating how pantomimes, emblems and words are organized in the middle temporal gyrus, using fMRI. We observed a posterior-to-anterior structure, both in the left and in the right hemisphere, that might reflect the input modality and also the arbitrariness of the relationship between form and meaning.