Linear acceleration perception: frequency dependence of the hilltop illusion

Area of Science:

• Vestibular System Neuroscience
• Human Perception and Psychophysics
• Spatial Orientation and Motion Sickness

Background:

• Linear acceleration stimulates otoliths, influencing motion perception and spatial orientation.
• The Hilltop Illusion is a perceptual phenomenon where horizontal motion is misinterpreted as movement over a hill.
• This illusion arises from reinterpreting linear acceleration as a gravitational vertical tilt.

Purpose of the Study:

• To investigate the dynamics of the Hilltop Illusion across eight frequencies.
• To explore the role of the Hilltop Illusion in spatial orientation perception.
• To quantify perceived tilt relative to gravity during linear acceleration.

Main Methods:

• Subjects experienced sinusoidal linear acceleration at various frequencies (0.0083–0.33 Hz).
• Participants dynamically adjusted a luminous line to their subjective vertical, indicating perceived tilt.
• Experiments utilized a linear acceleration sled and a sled centrifuge for high and low frequencies, respectively.

Main Results:

• The amplitude ratio of subjective vertical settings matched a lowpass filter with a 15-second time constant.
• Phase shifts during the illusion never exceeded a 40° lag.
• Observed dynamics suggest non-linear information processing, potentially predictive, underlies the Hilltop Illusion.

Conclusions:

• The Hilltop Illusion's dynamics are frequency-dependent and influenced by otolith stimulation.
• Perceived spatial orientation during linear acceleration involves complex neural processing.
• Evidence points towards non-linear and possibly predictive mechanisms in the human vestibular system.