A motion effect, the vestibular stimulus generated by a moving chair, is crucial in improving user experiences in many virtual reality (VR) and entertainment applications. However, the perceptual characteristics of motion effects remain unexplored to a great extent. This paper constructs a perceptual space that accounts for many motion effects based on their perceptual distances and then demonstrates smooth-rough and irregular-regular as its two primary perceptual dimensions. An authoring space is constructed with these two pairs as the axes. We also present methods for synthesizing new motion effects with a specific property in the authoring space. The contributions of this work are with new insights into the perceptual characteristics of motion effects and the first design methods of motion effects achieving desired perceptual properties.