Multistable Perception

Necker Cube · Rubin Vase · Binocular Rivalry · Mutual inhibition & adaptation

Depth cue strength: 50%

Necker Cube (1832, L.A. Necker):
The wire-frame cube is geometrically ambiguous — two 3D interpretations are consistent with the 2D projection. Perception alternates between them spontaneously.

Flip rate: ~0.5–5 times/minute, log-normal distribution. Bimodal: brief dominance periods are rare (winner-take-all dynamics).

Key finding: you cannot perceive both simultaneously — only one interpretation dominates. This is the signature of mutual inhibition.

Figure-ground bias: 0

Currently seeing: Vase

Rubin's Vase (1915, E. Rubin):
Figure-ground separation: the same contour simultaneously defines the vase's edge (when vase is figure) and the faces' edges (when faces are figure).

A contour can only belong to one region at a time — the Gestalt "figure-ground rule." The two face silhouettes form a complementary pair.

Gestalt principles of figure:
· Smaller area tends to be figure
· Enclosed regions tend to be figure
· Symmetry promotes figure assignment

Left eye stimulus

Right eye stimulus

Perceived: Left eye

Left contrast: 80% Right contrast: 80%

Binocular rivalry: When each eye receives a different incompatible image, perception alternates between them (rather than merging). Higher-contrast image dominates more. Pupil dilation tracks rivalry state. Cross-orientation suppression is the key mechanism.

Mutual inhibition (w): 2.0 Adaptation rate: 0.05 Noise level: 0.2

Wilson (2003) mutual inhibition model:

τ·du₁/dt = −u₁ + I − w·f(u₂) − a₁ + noise
τ·du₂/dt = −u₂ + I − w·f(u₁) − a₂ + noise
da_i/dt = (f(u_i) − a_i) / τ_a

where f(u) = 1/(1+exp(−(u−θ))) is the gain function, w = inhibitory weight, a_i = adaptation variable.

Three regimes:
· Low inhibition: fusion (both active)
· Moderate inhibition + adaptation: alternation (bistability)
· High inhibition: winner-takes-all (one always wins)

Noise drives transitions; adaptation drives release from suppression.

MULTISTABLE PERCEPTION