Study of the Effect of Proprioceptive Stimuli in the Stomatognathic Area on Visual Perception, With and Without Sound

Proprioception plays a well-established role in postural control and motor coordination, but increasing evidence supports its involvement in higher-level sensory processing, including spatial localization and multisensory integration. Given the anatomical overlap of trigeminal afferents innervating both oculomotor and orofacial structures, this study focused on the potential interplay between the stomatognathic and visual systems.

This study is an observational investigation with an experimental within-subject design with repeated measures in healthy volunteers.

The aim is to investigate the influence of oral proprioceptive stimuli on visual perception and audiovisual integration in healthy young adults, and explore whether non-invasive oral stimuli could modulate the occurrence of transient visual distortions-specifically Visual pseudo-Scotomas (VS)-when binocular vision is altered, and whether these stimuli could counteract the effects induced by auditory input.

Participants have been screened to ensure normal hearing, vision, and dental status, and underwent testing using the Vertical Maddox Test, which induces a dissociation in binocular vision that relies heavily on proprioceptive cues.

The experimental protocol was composed of four phases:

• Baseline evaluation with no stimuli.
• Application of auditory stimuli (500 Hz tones delivered through headphones) to assess their influence on visual perception.
• Application of simultaneous auditory and Oral Proprioceptive Stimuli (OPS), including both Combined Oral Stimuli (COS, such as specific tongue and lip positions) and Dental Stimuli (DS, consisting of gentle pressure/traction on central incisors using a calibrated probe).
• Application of Oral Proprioceptive Stimuli (OPS) alone, without sound.

Participants were asked to report the occurrence and location of any Visual pseudo-Scotomas (VS) observed during each phase. These were defined as functional visual field losses detected via the Vertical Maddox Test, with no underlying ocular pathology.

This protocol was developed based on prior work investigating ocular and oral proprioception and its role in multisensory integration. No pharmacological agents, devices, or therapeutic interventions were used. The study is observational in nature, and no biospecimens were collected or retained.

Exclusion criteria

• General criteria:

• Treatment with psychotropic drugs
• Hearing loss in one or both ears
• Visual criteria:

• Visual acuity worse than 20/20 in one or both eyes
• Stereopsis (three-dimensional vision) less than 120 arc sec
• Vertical phoria greater than 0.75 Δ
• Strabismus operated on or not
• Ongoing optometric rehabilitation
• History of amblyopia
• Dental criteria:

• Missing one or more incisors
• Presence of conservative, prosthetic or orthodontic treatment on one or more incisors (fillings, root canal treatments, veneers, crowns, brackets, Invisalign type attachments...).