Constant-speed straight motion is less uncomfortable than speed change

What it is

Once speed settles and heading does not change, discomfort falls back from its peak. Constant-velocity straight motion holds visual self-motion at a fixed rate with radial optic flow, and stops asking the otoliths for new acceleration. The motion is still fake, so discomfort does not drop to zero. It is only more tolerable than accel and brake at the same speed.

The comparison is the speed-change slices inside one continuous-locomotion scheme, not teleport, and not turning.

Why it happens

Otoliths encode acceleration and adapt back to baseline under constant linear velocity. Vision still reports forward speed, so conflict remains, but it becomes steady-state: there is no repeated “should have moved and did not” transient to refresh the error. People can partly habituate to steady flow; they rarely habituate to repeated accel pulses, each of which reopens the error signal.

Straight motion also constrains flow geometry. Radial expansion grows from the view centre; the periphery still has a tangential component, but the whole retina is not swept by rotation. Speed still matters: at the same “constant,” triple the rate and both flow area and flow speed rise, lifting the steady discomfort. The constant-versus-changing advantage is a profile claim at matched speed, not another way of saying “slower is better.”

Studying it

Use scripted translation: at one peak speed, compare a trapezoidal speed curve (long accel, short cruise) with a near-rectangular curve (brief accel, long cruise). Keep the path straight; test turns separately. Align FMS to accel slices and cruise slices and read the within-slice slope, not the session total.

If FMS still climbs during cruise, speed or flow density has already exceeded the habituable steady range. If it jumps only on the accel ramp and flattens or falls on cruise, the profile claim holds. Having people mark the moment “this started to feel bad,” then aligning that mark to the speed curve, splits the two slices more cleanly than a retrospective SSQ.

Where it stops holding

The advantage assumes motion that is actually constant and actually straight. Repeated stick recentring, micro-accels to hug a nav mesh, and automatic sidesteps for obstacle avoidance shatter the steady state. Even constant speed on a passive vehicle can open a second discomfort channel if the user cannot predict when it ends. Very high constant speeds (flight, vehicles) make the steady state itself intolerable and shrink the gap versus speed change. Real walking already uses gait accelerations; the claim that “virtual cruise is milder” has no counterpart there.

Applying it

• Map the stick to a fast entry into a locked cruise speed, not to continuous acceleration proportional to stick throw.
• On straight cruise, suppress automatic accel and lateral nudges. When a turn is required, interrupt cruise explicitly rather than layering a hidden wobble onto it.
• Prefer speed gears over an infinite analogue: walk and jog, constant inside each gear.
• How to check: on a straight corridor, run a trapezoid and a cruise profile at the same peak speed. If FMS rises only on the accel ramp and flattens on cruise, make cruise the default mapping; if cruise also climbs, drop a gear before arguing about profile.

Related

• Same group: N4.02.1 Continuous locomotion keeps spatial sense but readily causes discomfort · N4.02.2 Acceleration and turning are the strongest sources of discomfort
• Nearby: N4.07 Continuous Locomotion and Discomfort · N4.03 Cybersickness Mitigation
• Search terms: constant-velocity locomotion · steady-state optic flow · habituation to vection