time-to-contact

Compiled with AI assistance and selectively reviewed. Please consult the cited passages; the books remain the authoritative source. About this companion

Editorial synthesis · provisional

Definition

Time-to-contact is the prospective interval to contact specified by optical information from an approaching surface or object. AB uses it to illustrate forward-aimed perception in diving and braking. RB2 identifies Lee's tau as the inverse relative rate of image expansion that specifies this interval, allowing action timing without separately computing distance and velocity, with unchanged speed explicitly qualifying the collision forecast.

Explanation

AB presents time-to-contact within active looking: a diving gannet folds its wings in response to the expanding surface, and a braking driver reads the same prospective quantity. The point is that optical information can guide action toward what is about to happen unless something changes, rather than requiring calculation of a final location.

RB2 gives the technical attribution to David Lee and names the invariant tau. Its description connects braking and landing to prospective control, then situates that example within Gibson's account of environmental information specific to affordances and action needs. The forecast is conditional on speed remaining unchanged. Time-to-contact therefore names what is specified, while tau names the optical invariant used to specify it; neither is a general synonym for anticipation or every kind of predictive model.

Scope and attribution

Positive support is restricted to AB and RB2. Searches for time-to in PB, RB1 and RB3 returned no matches. Tau remains a related separate concept, not an alias collapsing measure and specified interval.

AB — The Actual Book

Gannet diving and driver braking illustrate forward-directed looking guided by an optical signature of what will happen unless something changes.

Occurrence locators: 94; Notes: 242.

RB2 — The Real Book, Volume II: Becoming Is Being

Lee's tau specifies time-to-contact without separate distance and velocity computations. The unchanged-speed qualification and prospective-control setting are explicit.

Occurrence locators: 65, 66.

Background used in the editorial explanation

Named theories and mechanisms are distinguished from neighboring background, homonyms and the author’s own synthesis. Reproduced AI passages retain their separate voice.