Vertical-horizontal illusory effects with gaze restrictions do not change length estimations using the lower limb

Area of Science:

• Perception and Motor Control
• Human Locomotion
• Visual-Motor Integration

Background:

• The vertical-horizontal (V-H) illusion demonstrates how visual perception can be distorted.
• Previous research shows gaze direction and visual feedback influence manual estimates of the V-H illusion.
• The extent to which these visual illusions affect lower limb movements is less understood.

Purpose of the Study:

• To investigate if the V-H illusion influences lower limb movement planning and execution.
• To examine the effects of different gaze conditions on stepping performance.
• To differentiate between movement planning and movement completion in response to visual illusions.

Main Methods:

• Participants performed a stepping task, attempting to match their foot distance to a projected inverted T (IT) shape under three gaze conditions: target fixation (TF), movement fixation (MF), and remembered target fixation (RTF).
• Kinematic and kinetic variables were measured, including step displacement, peak velocity (PV), normalized ground reaction force amplitude (GRFampN), and center of pressure (COP) parameters (COPtime, COPamp).

Main Results:

• Gaze conditions significantly affected PV, GRFampN, COPtime, and COPamp, with lower values observed during movement fixation (MF) compared to target fixation (TF) and remembered target fixation (RTF).
• Step displacement was not significantly affected by gaze conditions.
• No significant correlations were found between step displacement and other measured kinematic or kinetic variables.

Conclusions:

• Visual illusions, like the V-H illusion, can influence the planning and initial execution of lower limb movements.
• However, these deceptive visual cues do not appear to affect the final accuracy of the step length estimation.
• The findings suggest a dissociation between the processes involved in movement planning and movement completion.