The brightness of a target depends on its surround, which exerts influence through lateral interactions mediated by interneurons: A time lag is introduced between the registration of the surround and its effect on target brightness. DeValois et al. (1986, Vision Research, 26, 887-897) used a matching technique and found that induced brightness modulations existed only at temporal frequencies below 2.5 Hz. Paradiso & Nakayama (1991, Vision Research, 31 1221-1236) and Rossi & Paradiso (1996, Vision Research, 36, 1391-1398) suggested that brightness percepts are determined by a “fill-in” process whose signals propagate at 110-150^o/sec (6.7-9.2 ms/degree). We sinusoidally counterphased the inducing grating of a grating induction display (McCourt, 1982, Vision Research, 22, 119-134) to create a counterphasing induced grating within the test field. Adding a second (luminance) counterphasing grating in temporal and spatial quadrature phase to the induced grating transforms the brightness modulation into a traveling wave (motion). Varying the temporal phase of the added luminance grating permits a precise estimate of the temporal phase lag of induction. Results indicate that induction lag is remarkably short, on the order of a few milliseconds, and does not vary with inducing field height in a manner that suggests the operation of a fill-in process.