Gravity-dependent change in the 'light-from-above' prior.

Area of Science:

• Visual perception
• Neuroscience
• Human orientation

Background:

• The visual system relies on prior knowledge, like the assumption of light from above, to interpret ambiguous visual information.
• Understanding how body and retinal orientation affect these visual priors is crucial for object recognition and spatial orientation.

Purpose of the Study:

• To investigate how body and retinal orientation influence the
• light from above
• prior in shape-from-shading perception.
• To determine the contribution of vestibular signals to these orientation-dependent visual biases.

Main Methods:

• Seven male observers judged shape-from-shading stimuli under varying body orientations (roll-tilt, supine) using a robotic arm.
• Stimuli simulated 24 illumination directions to assess the
• light from above
• prior (maximum convexity judgment).
• A modeling approach integrated retinal and vestibular (utricle, saccule) signals to predict observed biases.

Main Results:

• The
• light from above
• prior significantly changed with body orientation relative to gravity.
• Retinal orientation and a component at twice its frequency also influenced the prior.
• Model predictions incorporating retinal and vestibular inputs accurately reflected the experimental data.

Conclusions:

• Visual priors, such as
• light from above
• , are dynamically updated by neural processes monitoring self-orientation.
• This adaptation optimizes object recognition for moderate deviations from upright posture.
• Extreme body tilts relative to gravity lead to impaired shape-from-shading perception.