Models of speech production postulate that, in order to facilitate rapid and precise control of articulation, the predicted auditory feedback is sent to the auditory system to be compared with incoming sensory data. If this is so, an 'error' signal may be observed when the predicted auditory feedback and the sensory consequences of vocalization do not match. I used event-related fMRI to look for the neural concomitants of such an error signal. In two conditions volunteers whispered 'ted'. In one of these, voice-gated noise implemented in our real-time processing system was used to mask the auditory feedback, which should result in an error signal. Two other conditions were yoked to the production conditions (either clearly heard or masked), but were listen-only and therefore no error signal would be expected. I acquired whole-brain EPI data from 21 subjects using a fast-sparse design. Activity in the superior temporal gyrus bilaterally was significantly greater for clear than masked speech during the listen-only trials (F(1,20)≥12.84, p<0.002), and significantly higher for masked than for clear speech in the production trials (F(1,20)≥6.68, p<0.02). This crossover interaction indicates that speech production results in corollary discharge in the auditory system and furthermore suggests that this corollary discharge reflects expectations about the sensory concomitants of speech acts. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2007-09-26 10:02:35.972

Perception and action are coupled via bidirectional relationships between sensory and motor systems. Motor systems influence sensory areas by imparting a feedforward influence on sensory processing termed “motor efference copy†(MEC). MEC is suggested to occur in humans because speech preparation and production modulate neural measures of auditory cortical activity. However, it is not known if MEC can affect auditory perception. We tested the hypothesis that during speech preparation auditory thresholds will increase relative to a control condition, and that the increase would be most evident for frequencies that match the upcoming vocal response. Participants performed trials in a speech condition that contained a visual cue indicating a vocal response to prepare (one of two frequencies), followed by a go signal to speak. To determine threshold shifts, voice-matched or -mismatched pure tones were presented at one of three time points between the cue and target. The control condition was the same except the visual cues did not specify a response and subjects did not speak. For each participant, we measured f0 thresholds in isolation from the task in order to establish baselines. Results indicated that auditory thresholds were highest during speech preparation, relative to baselines and a non-speech control condition, especially at suprathreshold levels. Thresholds for tones that matched the frequency of planned responses gradually increased over time, but sharply declined for the mismatched tones shortly before targets. Findings support the hypothesis that MEC influences auditory perception by modulating thresholds during speech preparation, with some specificity relative to the planned response. The threshold increase in tasks vs. baseline may reflect attentional demands of the tasks. / acase@tulane.edu

The phenomenon of somatosensory attenuation describes the perception that self-generated touch feels weaker than externally generated touch of identical intensity. Previous studies have shown that besides intensity, self-generated touches feel less pleasant and less ticklish than identical externally generated touches. However, previous studies did not systematically assess attenuation across a range of stimuli that can elicit intensity, pleasantness, and ticklishness more efficiently. This thesis aims to replicate these previous observations across a range of tactile stimuli of different intensities and velocities and investigate whether people who attenuate their self-generated touches to a greater extent do so for all aforementioned qualities. Previous studies have shown that participants with lower levels of somatosensory attenuation have more schizotypal personality traits. Twelve volunteers participated in three perceptual tasks where they received touches on their sole generated either by a robot(External) or the participants(Self). Following the strokes, participants had to rate the sensation from 0(not at all) to 100(extremely). For the intensity task, we manipulated the intensity of the applied forces (1,2,3,4N). For the pleasantness and ticklishness tasks, we manipulated the velocity of the applied strokes (0.3,1,10,30cm/s). After the tasks, participants completed a Schizotypal Personality Questionnaire (SPQ). Significant somatosensory attenuation was observed in all tasks, but for specific, not all, stimuli: forces of 4N in terms of intensity, strokes of 1cm/s in terms of pleasantness, and strokes of 10cm/s and 30cm/s in terms of ticklishness. These results suggest that the ability to suppress the tactile consequences of self-generated touch occurs in all three tactile qualities.

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Nos entrées sensorielles, comme nos mouvements, sont entachés d’incertitudes. Pourtant, notre système nerveux central semble être aussi précis que possible compte tenu de ces incertitudes: il les gère de manière optimale, par exemple en pondérant des informations sensorielles redondantes en fonction de leur fiabilité, ou en prenant en compte ses incertitudes motrices lors de la réalisation de mouvements. Si les modalités des combinaisons d’informations redondantes sont bien connues lors de tâches statiques, elles le sont moins en conditions dynamiques, lors de mouvements. La partie expérimentale de cette thèse a permis de confirmer l’existence de mécanismes d’estimation et de contrôle optimaux des mouvements chez l’humain. En effet, nous avons mis en évidence l’intégration optimale d’information visuelle lors de la réalisation de saccades à la lumière: lors de séquences de saccades, le système visuomoteur est capable d’utiliser l’information visuelle pour mettre à jour ses estimations internes de la position de l’œil. Une étude complémentaire des sources de variabilité des saccades suggère un rôle similaire pour la proprioception extra-oculaire. Par une troisième expérience, novatrice, nous avons montré que le toucher est pris en compte en temps réel lors de mouvements de la main en contact avec une surface. Nous avons également inféré une mesure de la variance de l'information tactile. Enfin, à partir des connaissances sur la représentation des variables sensorimotrices dans le système nerveux, nous avons construit plusieurs réseaux de neurones qui implémentent de manière proche de l'optimum statistique la planification et le contrôle de mouvements / Our sensory inputs, as well as our movements, are uncertain. Nevertheless, our central nervous systems appears to be as accurate as possible: these uncertainties are handled in an optimal fashion. For example, redundant sensory signals are weighted according to their accuracy, and motor uncertainties are taken in account when movements are made. The characteristics of the combination of redundant sensory signals are well known for static tasks. However, they are less known in dynamic conditions. The experimental part of this thesis allowed to confirm the use of statistically optimal sensorimotor processes during movements. We showed that visual information can be integrated during sequences of saccades, the oculomotor system being able to use visual information to update its internal estimate of eye position. A complementary study on the sources of variability for saccadic eye movements suggests a similar role for extra-ocular proprioception. In a third original experiment, we showed that tactile input is optimally taken in account for the on-line control of arm movements during which fingertips are in contact with a textured surface. Last, we built several neuronal networks models simulating optimal movement planning. These networks were based on current knowledge about probabilistic representations in the nervous system

Ce travail dans le domaine de la « neuropsychanalyse » propose une spéculation théorique sur la structure physiologique de l’inconscient psychanalytique en recoupant les observations expérimentales et cliniques des deux cadres. L’écoute clinique indique une insistance de phonèmes récurrents dans ce qui fait conflit, appelés « phonèmes fantômes ». En effet, tel un membre fantôme, le signifiant refoulé est investi d’une intention mais son articulation est bloquée. Or, du fait de la structure ambiguë du langage, un même mouvement d’articulation peut radicalement changer de signification. C’est ce mécanisme qui donne lieu au retour du refoulé dans le signifiant et permet la survie de fantômes phonémiques qui tisseraient la structure linguistique de l’inconscient. Cette question du signifiant est présentée en écho à une question plus fondamentale, celle de l’émergence du psychique en réponse à la contrainte de l’organisme de faire la distinction entre intérieur et extérieur. Pour cette distinction, il faut supposer l’existence d’un système d’inhibition ciblé puisqu’il doit faire ressortir précisément ce qui dans la façon d’appréhender le monde extérieur n’a pas été anticipé. Cette précision est offerte par le modèle sensorimoteur des copies d’efférence, qui présentifie le mouvement avant qu’il ne se fasse et montre comment l’inhibition est condition de la représentation, constitutif du psychique. Pour l’humain la nécessité de la distinction intérieur-extérieur est impérieuse du fait précisément du langage qui rend complexe l’identification du lieu d’où ça parle. Elle mène au mouvement de refoulement, qui par inhibition fait apparaitre les fantômes phonèmiques comme les représentations en négatif des fragments de paroles refoulés. Cette réflexion théorique est précédée d’une mise en contexte élaborée dans l’histoire et l’épistémologique parfois controversée de la neuropsychanalyse et revendique pour sa méthodologie une approche transcendantale. / This study in the domain of « neuropsychoanalysis » proposes a theoretical speculation on the physiological structure of the psychoanalytic unconscious by cross-checking the experimental and clinical observations from both domains. Clinical listening indicates the insistence of recurring phonemes when it comes to conflictual topics, called “phonemic phantoms”. Indeed, as is the case in a phantom limb, the repressed signifier is invested by an intention while its articulation is blocked. However, due to the ambiguous structure of language, a same articulation movement can radically change signification. It is this mechanism that causes the return of the repressed in the signifier and allows for the survival of phonemic phantoms which are thought to weave the linguistic structure of the unconscious. The question of the signifier is presented as an instantiation of a more fundamental question, the emergence of the psychic realm in response to the constraint of the organism to distinguish interior from exterior. For this distinction, the existence of an accurate system of inhibition must be postulated since it has to be able to delineate precisely what in the way of apprehending the world was not anticipated by the organism. This precision is allowed by the sensorimotor model of efference copies, which presentifies the movement before its realisation and shows how inhibition is a condition for representation. For humans, the necessity of the interior-exterior distinction is imperious due to language which renders complex the identification of the locus from where speech is initiated (from where “id” speaks). This necessity leads to the movement of repression, which by inhibition induces phonemic phantoms in the form of negative representations of repressed speech. This work is preceded by an introduction which contextualises the theoretical reflexion in the sometimes controversial history and epistemology of neuropsychoanalysis and which claims a transcendental approach for its methodology.