Gravity dependence of subjective visual vertical variability.

Area of Science:

• Neuroscience
• Vestibular System
• Human Perception

Background:

• The brain integrates multiple sensory inputs to determine orientation relative to gravity.
• Otolith organs are crucial for sensing the gravito-inertial force vector, informing perception of head-roll.
• Subjective visual vertical (SVV) variability increases with head roll, indicating roll-angle dependence.

Purpose of the Study:

• To investigate if subjective visual vertical (SVV) variability correlates with the spatial distribution of otolithic sensors.
• To determine if SVV variability reflects otolith-derived acceleration estimates.
• To model the relationship between head-roll angle and SVV precision.

Main Methods:

• Subjects were tested at various head-roll orientations (0-360 degrees).
• Participants aligned an arrow to their perceived vertical to measure SVV.
• Otolith-dependent variability was modeled using otolith afferent distribution and firing rates, incorporating an internal bias.

Main Results:

• SVV variability was minimal when upright, peaked around 120-135 degrees of head roll, and decreased at 180 degrees.
• A model assuming an efficient otolith estimator did not fully match experimental data, particularly for upright and inverted positions.
• Simulated variability improved when the otolith estimator's effectiveness was reduced with increasing head roll.

Conclusions:

• Modulations in SVV precision during head roll are linked to otolith sensor properties.
• Central computational mechanisms may not be optimally tuned for head-roll angles far from upright.
• The brain's processing of otolith signals for orientation is complex and angle-dependent.