Oral Proprioceptive Sensitivity and Upper Limb Kinesthetic Acuity: A Pilot Study

This observational, descriptive, cross-sectional study investigates the possible relationship between oral proprioceptive sensitivity and kinesthetic acuity of the upper limbs in children younger than 15 years.

The study consists of two main assessments:

Upper-Limb Kinesthetic Acuity

Upper-limb kinesthetic acuity is assessed using a matching task based on the method described by Proske and Gandevia. With their eyes covered, participants reproduce the position of one forearm with the other. The angular position of both forearms is measured using digital inclinometers, and the difference between the reference and indicator arms is recorded across repeated trials. The procedure is performed five times for forearm flexion and five times for extension.

Oral Proprioceptive Sensitivity and Visual Perception

The effect of oral proprioceptive stimulation on visual perception is assessed using the Perceptive Maddox Test. Participants lie on a rigid examination table, with the head position maintained by the examiner. The test produces binocular dissociation, allowing the participant to perceive a horizontal red line and a point of light as separate visual images.

The assessment is performed in three phases. First, participants are exposed to auditory stimulation alone, consisting of five 10-second sequences of simultaneous 500-Hz whistles presented to both ears at approximately 50 dB. The occurrence and characteristics of transient visual losses (visual pseudoscotomas) are recorded.

Second, auditory stimulation is combined with different oral proprioceptive stimuli involving the incisors, including tongue contact and examiner-applied pressure. The effect of these stimuli on the visual perception of the red line is recorded.

Third, calibrated pressure or traction stimuli are applied to the incisors using a dynamometer, according to the oral stimulus that produced a visual effect in the previous phase. The temporal and spatial characteristics of the response, as well as the variability in the pressure or traction required, are recorded.

The study is exploratory and aims to characterize the possible relationship between oral proprioceptive responses and upper-limb kinesthetic acuity, as well as the interaction between oral and auditory sensory stimulation and visual perception.

• Upper-Limb Kinesthetic Acuity Assessment (Other), also known as Phase 1, Kinesthetic Matching Task: Participants performed a matching task with both forearms while their eyes were covered. One forearm was positioned by the examiner at a predetermined angle, and the participant moved the other forearm to match its perceived position. The angular position of both forearms was measured using digital inclinometers. The procedure was repeated five times for forearm flexion and five times for extension to assess the variability of upper-limb kinesthetic acuity.
• Effect of Auditory Stimulation on Visual Perception (Other), also known as Phase 2, Perceptive Maddox Test and Auditory Stimulation: Participants underwent the Perceptive Maddox Test while receiving bilateral auditory stimulation consisting of simultaneous 500-Hz whistles presented through wireless headphones at approximately 50 dB. Five 10-second sequences were presented. Participants reported whether the red line disappeared completely or partially and, when applicable, indicated the location and changes in location of the visual loss. The occurrence and temporal and spatial characteristics of transient visual losses (visual pseudoscotomas) were recorded.
• Oral Proprioceptive Sensitivity Assessment (Other), also known as Phase 3, Perceptive Maddox Test and Oral Proprioceptive Stimulation: The effect of oral proprioceptive stimulation on visual perception was assessed using the Perceptive Maddox Test in combination with auditory stimulation. Oral stimuli consisted of examiner-applied pressure to the vestibular surfaces of the incisors. When an oral stimulus produced a visual effect, calibrated pressure or traction was applied to the incisors using a dynamometer. The temporal and spatial characteristics of the visual response and the variability in the pressure or traction required were recorded.

Primary outcomes

• Correlation between upper-limb kinesthetic acuity and oral proprioceptive sensitivity [Day 1]: Correlation between variability in upper-limb kinesthetic acuity, assessed by the matching task, and variability in the visual response to oral proprioceptive stimulation during the Perceptive Maddox Test.

Secondary outcomes

• Occurrence of auditory-induced visual pseudoscotomas [Day 1]: Proportion of participants who experience transient visual losses (visual pseudoscotomas) during bilateral auditory stimulation in the Perceptive Maddox Test.
• Effect of oral proprioceptive stimulation on auditory-induced visual pseudoscotomas [Day 1]: Proportion of participants in whom oral proprioceptive stimulation suppresses auditory-induced visual pseudoscotomas, and characterization of the oral stimuli producing this effect.
• Lability of the visual response to oral proprioceptive stimulation [Day 1]: Temporal and spatial lability of the visual response to oral proprioceptive stimulation and variability in the pressure or traction intensity required to suppress visual pseudoscotomas.

Sex: All, ages: any to 15 Years, accepts healthy volunteers

Inclusion Criteria:

* Children younger than 15 years.
* Presence of all eight permanent incisors.
* Voluntary agreement to participate in the study.

Exclusion Criteria

* Neurological, sensory, or motor conditions that could interfere with the performance or interpretation of the study procedures.
* Treatment with psychotropic medication.
* Hearing loss in one or both ears.
* Visual acuity below 20/20 in either eye.
* Stereoacuity below 120 arc seconds.
* Vertical phoria greater than 0.75 prism diopters.
* Strabismus, whether previously operated or not.
* Ongoing optometric rehabilitation.
* History of amblyopia.
* Absence of one or more permanent incisors.