Measuring the sensitivity of tactile temporal order judgments in sighted and blind participants using the adaptive psi method

Spatial locations of somatosensory stimuli are coded according to somatotopic and spatiotopic reference frames, representing somatic sensations according to the anatomical distribution of the sensory receptors on the skin surface, and according to the relative position of the body parts in external space, respectively. This was mostly evidenced by means of temporal order judgment (TOJ) tasks in which participants discriminate the temporal order of two tactile stimuli applied on the two hands. Because crossing the hands generates a conflict between anatomical and spatial responses, TOJ performance is typically decreased in such posture, except for congenitally blind people, suggesting a role of visual experience in somatosensory perception. In most previous TOJ studies, stimuli were presented using the method of constant stimuli, i.e. the constant repetition of a predefined sample of stimulus-onset asynchronies (SOA) separated the two stimuli. This method has the disadvantage that an important number of trials is needed to obtain reliable data, and to dissociate performances of distinct groups characterized by different cognitive abilities. Therefore, this study aimed to replicate previous tactile TOJ data with the adaptive psi method. Such method adapts the SOA presented in each trial according to the participant’s performance in all the previous trials, allowing to precisely estimate the temporal sensitivity of each participant while the presented stimuli are adapted to the participant’s individual discrimination threshold. We successfully replicated previous findings in both sighted and blind participants, corroborating previous data on spatial representations of somatosensory inputs using a more robust psychophysical tool

Danger in the dark : the role of visual experience in the spatial mapping of nociception : neuropsychological studies in congenitally blind and normally sighted individuals

This thesis was aimed to investigate how the position of a nociceptive stimulus applied on the body is coded in the brain and what is the role of visual experience in the development of these localization mechanisms. This was investigated by comparing the abilities of normally sighted people to those of people who never experienced vision, i.e. congenitally blind, in perceiving and localizing radiant-heat stimuli applied on two separate body parts. We showed that sighted participants localize nociceptive stimuli according to both their position on the body surface but also according to the location of the stimulated body part in external space. On the contrary, although congenitally blind participants are also able to use a spatial external coordinate system, they preferentially rely on the location of the stimuli according to their position on the body. This suggests that the way we perceive and localize nociceptive stimuli is shaped by visual experience.(PSYE - Sciences psychologiques et de l'éducation) -- UCL, 202

Testing the exteroceptive function of nociception: the role of visual experience in shaping the spatial representations of nociceptive inputs

Adequately localizing pain is crucial to protect the body against physical damage and react to the stimulus in external space having caused such damage. Accordingly, it is hypothesized that nociceptive inputs are remapped from a somatotopic reference frame, representing the skin surface, towards a spatiotopic frame, representing the body parts in external space. This ability is thought to be developed and shaped by early visual experience. To test this hypothesis, normally sighted and early blind participants performed temporal order judgment tasks during which they judged which of two nociceptive stimuli applied on each hand’s dorsum was perceived as first delivered. Crucially, tasks were performed with the hands either in an uncrossed posture or crossed over body midline. While early blinds were not affected by the posture, performances of the normally sighted participants decreased in the crossed condition relative to the uncrossed condition. This indicates that nociceptive stimuli were automatically remapped into a spatiotopic representation that interfered with somatotopy in normally sighted individuals, whereas early blinds seemed to mostly rely on a somatotopic representation to localize nociceptive inputs. Accordingly, the plasticity of the nociceptive system would not purely depend on bodily experiences but also on crossmodal interactions between nociception and vision during early sensory experience

La représentation numérique et spatiale chez les enfants dyspraxiques

L’objectif de ce mémoire est d’étudier l’impact des troubles visuo-spatiaux sur la représentation numérique et spatiale. Les enfants dyspraxiques présentent régulièrement des troubles visuo-spatiaux. Ils constituent donc une population d’intérêt dans l’étude de ce lien. Depuis plusieurs années, de nombreuses preuves d’une association entre la représentation des nombres et de l’espace ont été mises en évidence dans la littérature scientifique. En effet, les magnitudes numériques seraient organisées spatialement sur une ligne numérique mentale orientée de gauche à droite. Les petits nombres seraient représentés à gauche sur cette ligne et les grands nombres à droite. Cette relation spatio-numérique se manifeste précocement dans le développement de l’enfant. Sur le plan clinique, un déficit visuo-spatial a fréquemment été mis en lien avec des troubles en arithmétique chez des enfants en apprentissage scolaire. Cependant, l’origine spécifique de ces difficultés numériques reste à ce jour incertaine. Un groupe d’enfants dyspraxiques et un groupe d’enfants contrôles ont été comparés sur différents types de tâches numériques et spatiales dans le but d’investiguer cette question. Les résultats ont mis en avant des difficultés dès le traitement de la magnitude numérique chez les enfants dyspraxiques, suggérant que leurs difficultés avec l’espace s’étendent au caractère spatial de la ligne numérique mentale. Le manque de précision de la représentation des magnitudes numériques sur la ligne provoquerait un traitement inadéquat des nombres. Cette découverte argumente le débat actuel sur la question de l’origine des difficultés numériques chez les enfants souffrant d’un trouble visuo-spatial.Mémoire de master [120] en sciences psychologiques, Université catholique de Louvain, 201

Investigating crossmodal influence between nociception and vision in the peripersonal space of the limb using temporal order judgments

In order to adapt behaviors to a potentially damaging threat, it is crucial to coordinate the perception of the location of the threat in external space and the perception of the location of the damage on the body surface. In this study, we investigate how a nociceptive stimulus applied to the hand affects the perception of visual stimuli occurring near the hand, placed either near or far from the body trunk according to the anteroposterior axis. In a temporal order judgement task, participants judged which of two visual stimuli had been perceived first. Each pair of visual stimuli was preceded by one nociceptive stimulus applied on one of the two hands (unilateral) or two nociceptive stimuli one applied on each hand at the same time (bilateral). Results show that, as compared to the bilateral condition, participant’s judgments were shifted towards the visual stimuli having occurred near the hand on which the nociceptive stimulus was applied, independently of its position in space (near or far from the trunk). These results suggest the existence of cortical representations of each limb that extend slightly from their corporeal boundaries to external space, and are used as an interplay to integrate somatosensory and non-somatosensory information

Danger in the dark! Localization of nociceptive stimuli in normally sighted and congenitally blind people

To defend our body against potential physical threats, it is crucial to identify which body part is being damaged, but also to locate the threatening stimulus in its surroundings. Therefore, the brain coordinates the representation of the body with that of external space. To this aim, somatosensory inputs are remapped from the somatotopic towards a spatiotopic representation. The development of this spatial remapping would mainly rely on early visual experience. To test this hypothesis, we compared the ability of normally sighted and congenitally blind individuals to localize nociceptive stimuli. Participants performed temporal order judgement tasks during which they had to discriminate the temporal order of two nociceptive stimuli, one applied on each hand, with either their hands uncrossed or crossed over the body midline. While congenitally blinds were not affected by the posture, the performance of the sighted decreased in the crossed as compared to the uncrossed condition. This indicates that nociceptive stimuli are automatically remapped into a spatiotopic representation (where are the hands?) that interferes with the somatotopic representation (which hand is stimulated first?), whereas congenitally blinds seemed to only rely on a somatotopic map. This suggests that the way we perceive nociceptive stimuli is shaped by visual experience