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# Spine Drift Illusion - Some Explanations - Page-1

This illusion was first introduced By Kitaoka, A., 2010 [link]

# Illusory motion in two-dimensional space:

- The motion direction changes depending on: (A) eye movements; (B) how the eyes detect and locate changes during movements.
- The illustration shows the illusory motion direction for a circle when you scroll down. If you scroll up, the direction becomes reversed.
- The motion directions cancel each other out:
Because of the circle's symmetrical structure, it appears stable and not in illusory motion.

- The circle can be divided into four (4) parts, where two (2) of them induce clockwise motion and the other two (2) induce counterclockwise motion.

- Illustrates the direction of movement of spines by placing them in the circle model.
- Contrast inversion does not change the direction (white spine vs black spine).

# Part Extraction

- Type of spine with its own elements.
- The pattern that the brain tries to read and define its position.

Element - Definition:

- The various components of a spine.
- The image illustrates a spine with three (3) different parts.

# Part one - color interaction

- Part 1 strengthens the illusion.

# Part two

Motion Trigger points (MTP) - Definition:

- Different directional terminal points that defines the start and the end points for the illusory motions.

- To be marked at the beginning and end of an element.

Unspeciffied Motion Trigger points (uMTP) - Definition:

- Motion trigger point with:(A) non-predefined distance, (B) Unspecified marking place.

- It can be used to segment the spine and can be defined as the start or endpoint of a segment.

- The motion intensity can be observed by: (A) placing the MTP at crucial points on the element and (B) dividing the element into several segments, so that they can be observed separately.

# Demo:

Relative Illusory Motion (IM) intensity:

- The intensity of the different parts can be graded relative to each other and not in comparison to other reading patterns.

- The intensity can change depending on which element the segment is connected to.

# Part three

Segmentation:

Comment:

- The spine can be placed in a coordinate system with radius 10.
Every 22.5 degrees can be marked with a uMTP. The x and y values of each point can be obtained from the coordinate system.

Comment:

- These five trigger points corresponds to four segments of equal length.

Calculating the slope, distance and angle for every segment:

Comment:

- The distance between the segments is equal (rounded).

-  When the angle (θ) is minus (-), the illusory motion direction is clockwise, while when the angle (θ) is plus (+), the illusory motion direction is anti-clockwise.

-  when the slope increases the intensity increases.

Relative Illusory Motion (IM) intensity - Part 3:

# Imaginary Frames - Part 3

Comment:

- The Illusion Works like a flip book: When you are scrolling down you scrolling through different frames.

- Every frame have different illusory motion intensity/direction. The intensity is Relative.

Comment:

- The intensity reverses if you scroll left-/or right-ward. The image illustrates the intensity when scrolling down.

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