Dernières publications HAL

Children are limited in visual search accuracy and this ability increases from childhood to adolescence. Developmental limitations in visual search could be related to children's difficulties in efficiently planning and executing their search, often assessed with cancellation tasks. However, few studies have examined age-related changes in visual search strategies. In the present study, 135 French participants between the ages of 7 to 16 years performed a complex cancellation task. Results showed that the participants improved not only in visual search accuracy and speed with age, but they also organized better their visual search as they got older. Moreover, this improvement seemed linear from age 7 to age 16, suggesting that visual search strategies still improve during adolescence. This finding may be linked to the maturation of specific cerebral networks and opens new perspectives for future studies to better understand visual search processes.

Introduction Sensorimotor adaptation has often been studied in the visual modality through the Prism Adaptation (PA) paradigm. In this paradigm, a lateral shift in visual pointing was found after wearing prismatic goggles. An effect of PA has sometimes been observed on hearing, in favor of a cross-modality recalibration. However, no study has ever shown if a biased auditory-motor adaptation could induce this lateral shift, which appears essential to a better understanding of the mechanisms of auditory adaptation. The present study aimed at inducing an auditory prism-like effect. Methods Sixty healthy young adults underwent a session of active audio-proprioceptive training in immersive virtual reality based on Head Related Transfer Functions (HRTF). This training consisted of a game in which the hand-held controller emitted sounds either at its actual position in a control group or at 10° or 20° to the right of its actual position in two experimental groups. Sound localization was assessed before and after the training. Results The difference between both localization tests was significantly different between the three groups. As expected, the difference was significantly leftward for the group with a 20° deviation compared to the control group. However, this effect is due to a significant rightward deviation in the control group whereas no significant difference between localization tests emerged in the two experimental groups, suggesting that other factors such as fatigue may have cumulated with the training after-effect. Discussion More studies are needed to determine which angle of deviation and which number of sessions of this audio-proprioceptive training are required to obtain the best after-effect. Although the coupling of hearing and vision in PA still needs to be studied, adding spatial hearing to PA programs could be a promising way to reinforce after-effects and optimize their benefits.

The assessment of unilateral spatial neglect (USN) primarily relies on paper-and-pencil tests, which do not fully represent daily life difficulties. To address this limitation, ecological tests, like the Baking Tray Test (BTT), have been developed. However, the original BTT identifies the presence of USN without providing information on its severity. In this aim, a new severity measure, the Centre of Mass (CoM), has been proposed, but its calculation in real environments poses challenges. Immersive virtual reality (VR) offers a promising solution for implementing a BTT in which measures are automatically calculated. This study aimed to assess the feasibility and relevance of an immersive VR BTT. Nineteen right brain-damaged patients with and without USN and 25 healthy participants were included. Group analyses showed an equivalence between the two BTT versions. Individual analyses revealed that all USN patients, except one, had pathological results in both versions. They also underlined pathological scores in patients without USN signs on paper-and-pencil tests. Finally, the CoM strongly correlated with paper-and-pencil tests and appeared to be a good indicator of USN severity. These findings support the relevance of implementing the BTT in an immersive VR version, suggesting its potential to enhance USN assessment.

Peripherally located objects are often perceived to be smaller than centrally located objects. This perceptual phenomenon, known as the Size-Eccentricity Effect (SEE), is mainly due to the structural properties of the visual system and is further modulated by covert attention. In this study, we evaluated whether pre-saccadic attention could also compensate for this effect. Participants performed a judgment task where they compared a test disk of varying size, briefly presented in peripheral vision, to a reference disk appearing 450 ms later in foveal vision. When no saccade was made toward the location of the test disk, the SEE was observed. However, when participants initiated saccades about 200 ms after the test disk extinction, points of subjective equality were close to objective equality. The second experiment aimed at excluding an explanation involving non-specific arousal mechanisms, also known to enhance visual perception. Participants executed a keypress or an antisaccade instead of a saccade. The size-eccentricity disappeared only in the saccade condition, confirming the crucial role of pre-saccadic attention shifts in this SEE compensation. Therefore, pre-saccadic attention improves not only the processing of orientation, contrast and spatial frequency (as previously demonstrated), but also the processing of peripheral object size.

Voluntary actions, such as pressing a button, can affect the loudness of the sounds produced. To date, the role of intentional motor-sensory coupling and the involvement of more general prediction mechanisms remain unclear. Asking participants to make ocular saccades (which do not naturally produce sounds: weak coupling) instead of pressing a button (which frequently produces sounds: strong coupling) allowed us to investigate this question. Two independent groups of participants performed either a saccade task (N=42) or a keypress task (N=43). In a short movement-sound delay condition, a tone of variable intensity was presented 150 ms after movement onset. In a long delay condition, the tone was presented 1500 ms after movement onset, in order to dissociate it from possible motor-based effects. We also manipulated motor-sensory coupling within each task by presenting the tones after every movement in one subgroup, whereas in another subgroup, tones were delivered randomly after 50% of the movements. A reference tone was presented 800-1200 ms after the variable tone, and participants indicated which of the two tones was louder. The only significant effect we observed on the psychometric functions was a larger JND in the 150-ms delay condition of the saccade task compared to all other experimental conditions. We found no significant effects of the movement-tone contingency. A reinforcement learning model was then used to compute a prediction error regarding tone occurrence for each trial (in the 50% movement-tone contingency). Prediction error affected the judgment of saccade generated tones (GLMM analysis, p = .005), but not the judgment of keypress generated tones (p = .285). These results suggest that motor-based effects on the perception of self-generated tones depend critically on the strength of the previously learned association between a movement and the sound it produces. This may explain the inconsistent results found in the literature.