Psychophysical Laws of Perception

Abstractions that relate physical stimulus magnitude to perceived experience via lawful functions — Weber's and Stevens's power laws, Fitts's law — and cross-modal binding illusions (ventriloquism, kappa effect, common fate) where the brain infers a shared source or object.

10 abstractions in this family — domain-specific abstractions that sit near one another in structural-signature space (k-means over structural-signature embeddings). Each is shown with its short description.

• Bezold Effect — The color-perception phenomenon in which a target's apparent hue shifts toward a finely interspersed surround rather than away from it — assimilation, gated by whether the surround falls inside the visual system's spatial integration window.
• Common Fate — Group visual elements that change together — moving, flickering, or co-varying synchronously — into one perceived object, on the inference that things sharing a fate usually share an origin.
• Fitts's Law — Predict how long an aimed reach takes as a logarithmic function of target distance over target width — MT = a + b·log₂(2D/W) — treating the movement as transmission across a finite-throughput motor channel.
• Kappa effect — A psychophysical illusion in which the perceived duration between two stimuli lengthens when they are farther apart in space and shortens when closer, because the perceptual system reconstructs elapsed time from spatial layout under an implicit constant-velocity prior.
• Perceptual Constancy — The phenomenon by which a perceiver holds an object's properties — size, shape, color, identity — stable despite large variation in the proximal stimulus, by inferring the distal property and implicitly factoring out the viewing condition.
• Purkinje Effect — Explain why red darkens and blue seems to glow at dusk: as light falls, the eye hands off from cones (peaking ~555 nm) to rods (peaking ~507 nm), so a whole different sensitivity curve — not the surfaces — reweights apparent brightness.
• Stevens's Power Law — Relate the perceived magnitude of a sensation to the physical intensity of the stimulus by a power function ψ = k·I^β, whose modality-characteristic exponent β compresses the sense (β < 1), expands it (β > 1), or leaves it near-linear — recovered as the slope of magnitude estimates plotted on log-log axes.
• Temporal Binding — Bind events that fall within a characteristic time window into a single perceived unit by attributing them to a shared source, warping subjective time and location to keep the percept consistent with that attribution.
• Ventriloquism Effect — A sound is mislocalised toward a synchronised visual event when the brain infers a common cause, because vision's lower spatial uncertainty pulls the merged location estimate toward it by inverse-variance weighting — gated by temporal and spatial binding windows beyond which the percept splits.
• Weber's Law — The just-noticeable difference in a stimulus is a constant fraction of the baseline magnitude, not a fixed absolute amount (ΔI/I = k), so a perceiving system compares ratios rather than differences across its dynamic range.