Day 63 of 150 Pattern Difficulty 4/10
The phi phenomenon turns alternating flashes into motion
Quick answer
The phi phenomenon turns alternating flashes into motion. Today's question (Apparent motion) asks about a finding from Wertheimer, M. in 1912. The correct option is The phi phenomenon (apparent motion) — full explanation, primary source, and glossary cross-links below.
Today's question
When two stationary lights flash in rapid alternation at the right separation and timing, observers perceive a single light moving back and forth. What is this illusion called?
Reveal the answer and explanation
Correct: A — The phi phenomenon (apparent motion)
Wertheimer (1912) demonstrated that when two stationary stimuli alternate at intervals of roughly 60 ms (with appropriate spacing), observers see continuous motion rather than two discrete flashes — the phi phenomenon. This founding observation of Gestalt psychology revealed that perception is constructive: the brain fills in motion that does not physically exist. The same mechanism underlies cinema, animation, and traffic-arrow signs. Wertheimer distinguished beta motion (the percept of an object actually traveling between the two locations) from pure phi (a sense of motion without an identifiable moving object). All forms exploit the visual system's bias to assume that nearby flashes belong to a single moving object.
About the source
Wertheimer, M. (1912). Experimentelle Studien über das Sehen von Bewegung. Zeitschrift für Psychologie, 61, 161–265.
Every Cognition Bible question cites a primary source — a paper, book chapter, or monograph that exists, that we can point to on Google Scholar, and whose finding the question accurately summarizes. No fabricated authority strings, no name-drops without paper-level grounding.
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