Horizontal and Vertical Distance Perception in Altered Gravity.

Area of Science:

• Human perception
• Spaceflight research
• Proprioception

Background:

• Understanding human spatial perception is crucial for space exploration and human-machine interaction.
• Gravity significantly influences sensory-motor functions, but its precise effect on egocentric distance perception remains incompletely understood.

Purpose of the Study:

• To investigate the effects of varying gravitational conditions (1g, 0g, 1.8g) on the perception of horizontal and vertical egocentric distances.
• To compare distance judgments obtained through verbal reports versus visually directed actions (blind pulling).

Main Methods:

• Experiments conducted during parabolic flights with alternating periods of normal, microgravity, and hypergravity.
• Participants made absolute judgments of distance using verbal reports and a blind pulling task towards a memorized visual target.

Main Results:

• Verbal distance reports were accurate between 0.6m and 6.0m across all gravity levels.
• Blind pulling showed underestimation of horizontal distances, which decreased in microgravity (0g).
• A vertical asymmetry (overestimation for 'up', underestimation for 'down') was observed in 1g and 1.8g, but absent in 0g.

Conclusions:

• Gravity independently influences verbal and action-based distance judgments.
• Reduced horizontal distance underestimation in microgravity supports the hypothesis that distance perception in action-based tasks relies on estimated motor effort.
• Gravity's absence eliminates vertical distance perception asymmetry, highlighting its role in spatial orientation.