Cross-sensory perception and deprivation

Tactile information is crucial for interacting with our environment; however, its interaction with other sensory modalities and inter-sensory processes is a topic that remains underexplored. The present doctoral thesis aims to i) explore the effects of active touch on tactile perception and the role of visual calibration; ii) define the role of active and passive touch in sensory integration; iii) investigate cross-modal interactions between audio-tactile cues that could enhance tactile perception; iv) provide the neuroscientific basis for developing technology aimed at assessing tactile perception in situations of sensory impairment or in sensory-deprived children. To achieve these objectives, we developed experiments involving sighted and blind adult participants, as well as children with hemiparesis and typically neurodeveloping ones. These experiments employed psychophysics methods and modelling. Experiments 1-2 particularly consisted on tasks involving passive and active tactile perceptions tasks, in unisensory settings (Experiment 1) or combined with acoustic feedback (Experiment 2), using a dynamic stimulus consisting of a moving wheel with a sinusoidal grid. Additionally, in Experiment 3, we involved active exploration with a haptic display capable of independently producing transient changes in both fingertip-surface friction (tactile stimulus) and transient sounds (auditory stimulus). In Experiment 4, we explored passive tactile perception on the forearm of children with hemiparesis and a control group, elicited by a haptic device (MSI Caterpillar). This could be presented alone or in addition to visual or auditory cues, in either a congruent or incongruent manner. i) Results from active and passive touch conditions revealed significantly lower precision in the blind group during active movements compared to passive perception, while no difference was observed in sighted participants. The reduced reliability of tactile feedback during active touch in blind individuals suggests that the lack of visual calibration might impact inter-sensory and motor-sensory processes required during an action. This further supports the role of visual calibration in active touch perception and highlights the need for intervention in this population. ii) When audio feedback was introduced, blind participants did not exhibit any differences between the unisensory and bimodal conditions, indicating a reduced interaction between senses. In contrast, sighted individuals were significantly negatively affected by the auditory cue in the active condition. This suggests that movement might introduce noise to the signal, making sighted participants more susceptible to auditory interference, spotlighting the importance of auditory features in tasks involving active exploration. iii) When typical participants engaged in tactile explorations of a haptic display with different pitched sounds, the high-pitched one was found to modulate the bias in the perceived localization of a tactile stimulus. This suggests that frequency can modulate the perceived location of a tactile stimulus in active touch conditions. Finally, iv) in the detection and localization of a tactile stimulus, there was a significant worse performance between the more affected arm of children with hemiparesis and the non-dominant one of the control group. Our results also suggest the presence of interaction between tactile and visual feedback in both groups. This finding supports the use of multimodal technology as an effective approach in the evaluation and potential rehabilitation of somatosensory impairments. Overall, the findings arising from my Ph.D. project provide new insights into the scientific understanding of tactile perception in active touch conditions, both in unisensory and multisensory contexts, delving into the role of visual calibration in this process. Furthermore, it expands knowledge of the impact of motor deficits on somatosensory perception and suggest new approaches for its evaluation and rehabilitation. The findings discussed here should be taken into consideration in the development of new haptic devices aimed at enhancing or substituting sensory information.