Is precise discrimination of low level motion needed for heading discrimination?

Normal observers judge heading well both when moving in a straight line and when moving along a curved path. Judgments of curved path motion require depth variations in the scene while judgments of straight line heading (pure translation) do not. Here we show that a stroke patient who is impaired in low level 2D motion discrimination tasks and cannot accurately judge 3D structure from motion can accurately judge heading for straight line self-motion. This patient is impaired in judgments of curved path self-motion. This suggests that accurate heading judgments for observer translation do not require accurate 2D motion perception or 3D reconstruction of the scene. Judgments of curved path motion appear more dependent on accurate 2D motion perception.