This video contains looping sinusoidal motion examples. Viewers affected by this type of motion, like those with vestibular disorders, should be advised.
What is a vestibular disorder?
The vestibular system is made up of sensory organs in the inner ear, which help you maintain balance. Individuals with vestibular disorders have a condition that affects the way the brain processes incoming signals about head position and movement.
You or someone you know may have had your vestibular system affected when there is a difference between the actual movement of your body and the movement of perceived visuals.
[A figure moves forward, while an arrow pointing in a different direction passes across the eyes]
For example, some people experience car sickness, particularly while reading, where you are perceiving physical movement in one direction, forward, but your eyes are focused on text that is not moving. This is also common for people using virtual reality headsets, where you visually perceive movement, but are not in motion physically.
What is sinusoidal motion?
Linear motion is when an object moves at a constant, steady pace.
[A graph appears on screen with an line that extends from one point to the next]
If this movement were plotted on a graph, it would appear as a straight line that ramps from one point to the next. Sinusoidal motion refers to when an object moves in a repeating pattern of acceleration and deceleration. This type of movement would create a wave of curves on the graph, called a sine wave.
To picture this, think of a boat rocking on the ocean continuously. This movement over waves causes the common ailment of seasickness for many individuals. When digital content is animated with this type of movement, this can cause dizziness or nausea in some individuals.
Let’s view some examples comparing linear motion and sinusoidal motion.
Here is an animation of a line moving in a circle that might be used commonly as a loading indicator in an app or website. This first example is moving in a linear fashion, where the line moves at a continuous rate. This second example is the same animation with a speed up and slowdown, often called ease in/ease out in animation software, applied to the movement of the line creating sinusoidal motion. Here are the two movements side by side for comparison.
Zooming in and out on the z-axis can also create this kind of motion. In this first example, a circle zooms in, the content pauses, and then it zooms out. Because there is this pause, and the in and out movement does not repeat, this is much less likely to trigger these feelings of seasickness. However, in this second example, where the circle zooms in and repeatedly scales in a grow then shrink motion, this creates the type of motion we need to avoid.
Rapid forms of this type of movement, which can occur from using zoom transitions in video editing software, or from creating flip transitions where your object spins quickly on the Y axis, can also create these feelings of motion sickness.
The short version of this concept is: There is not a problem with creating animations, nor to using ease-in or ease-out type movements. Avoid looping those movements, or having multiple objects using that type of movement in rapid succession on the screen.
[Bullet points on screen
- No problem with animations
- Eas in/eas out is good
- Avoid looping eased animations
- Avoid many simultaneous eased objects]
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