Figure 17. Using the impulse response functions (IRFs) to predict the motion with pulsed L′ and M′ gratings in spatial quadrature phase.

Motion was previously generated on the orange field with a pair of pulsed L′ and M′ gratings, where the L′ grating was varied in SOA relative to M′ (Fig. 8, ○). The L′ and M′ impulse response functions for observer C.F.S. measured on the orange field can be used to predict the motion responses. L′ and M′ IRFs are represented on the vertical and horizontal axes respectively since the gratings were in quadrature spatial phase. Data points show the orthogonal vector sum of the two IRFs at 2 ms increments, representing the moving LUM grating signal – the vector angle indicates the spatial phase of the LUM grating and vector length indicates its effective contrast. At 0 ms SOA (A) the vector rotates anticlockwise (starting at the origin and proceeding from vector a and pass b) producing motion in the forward direction. At 35 ms SOA (B), the vector rotates anticlockwise (from vector a to b) but later reverses, yielding little net directional motion response. At 60 ms SOA (C) the vector rotates clockwise producing reversed motion.