Ternus Illusion

The Ternus Illusion is a phenomenon in visual perception where the perceived motion direction of a single element is influenced by the presence or absence of another element. It was first described by the German psychologist Joseph Ternus in 1926.

Key Characteristics

  • Sequential Presentation: The Ternus Illusion involves the sequential presentation of two or more frames containing multiple elements.
  • Motion Perception: Depending on the specific configuration and timing of the frames, the motion perception of the individual elements can change.
  • Apparent Motion: The illusion often gives rise to an illusion of apparent motion, where the elements appear to move independently from frame to frame.
  • Contrast Enhancement: The illusion is typically enhanced when there is a higher contrast between the elements and the background.

Types of Ternus Illusion

Over the years, various types of Ternus Illusion have been identified:

  1. Element-Based: The perceived motion direction is influenced by the displacement of individual elements (e.g., dot or shape) from one frame to the next.
  2. Blob-Based: Motion perception is influenced by the displacement of entire blobs (a group of connected elements) from one frame to the next.
  3. Grouping Influence: The presence of additional elements can influence the perceived motion direction of the main element.

Underlying Mechanisms

The Ternus Illusion challenges our understanding of motion perception and involves complex cognitive processes such as multi-element integration, temporal integration, and attentional mechanisms. Multiple theories and computational models have been proposed to explain the underlying mechanisms, including the parallel-pathway model, feature-tracking model, and temporal capture model.


The Ternus Illusion has been extensively studied in the field of visual perception and provides valuable insights into the mechanisms of motion perception, object tracking, and visual attention. The knowledge gained from studying this illusion has potential applications in various domains such as animation, computer graphics, virtual reality, and human-robot interaction.