Flight motion simulator seats having controls for shifting body position and pressure exerted are known in the art.  U.S. Pat.  No.  3,270,440 to Radosevic is an early example of a pneumatically controlled flight simulation seat which simulates the tactile sensations that would be felt by a pilot during flight.  The seat pneumatic controls are connected to the flight simulation computer so as to provide realistic sensations which correspond to the flight situation being simulated.  U.S. Pat.  No.  3,983,640 to Cardullo et al.  is an early example of a modern style aircraft simulator seat. 
A human being subjected to accelerations will perceive movement from different indications coming from his sensory system, the main one being the vestibular system, on which the conventional motion platforms act.  G-seats or dynamic seats act on alternative sensory paths which are mainly visual perspective changes, and changes from the sensory system referred as the haptic system by Cardullo.  As described in U.S. Pat.  No.  3,983,640, changes in the following items are perceived by the haptic sensory system: skeletal attitude, muscle tonus, pressure gradients, and touch or area of contact.  Skin tension, amongst others, could be added to this list.  Since most of the seats act on the same sensory paths to create the illusion of acceleration, conventional seats are differentiated by the sensory path they emphasize and by how the various sensory paths are combined with each other.  Another important aspect in the evaluation of dynamic seats is side effects that can be created, while trying to stimulate a specific sensory path.  For example, a device could generate an eye height change which would correspond to an upwards acceleration and generate a gradient of pressure that would correspond to a downwards acceleration as a side effect. 
U.S. Pat.  No.  4,030,207 to Kron discloses a simulator "G-seat" including a skin tension cue generator in which the seat fabric may be displaced in a parallel direction to the cushion surface onto which it is installed, and all or part of the seat pan may move from side to side and front to back.  The tactile cue in Kron is a skin tension change for which the amplitude can be modulated and localized on specific parts of the body, in the seat back and pan areas.  In Kron, the backrest skin tension change is meant to occur in the lateral direction but not in the vertical direction. 
In the prior art simulator seats, heave(vertical) acceleration was simulated by a seat pan vertical movement which induces at the same time "back scrubbing"(i.e.,  tension change on the skin of the user's back) due to the back rest remaining vertically stationary.  Therefore, the amount of back scrubbing generated is not controlled.  Applicants have discovered that a pitch movement of the seat pan coordinated with a the back rest vertical displacement, which is to be described in the present document, generates cues on the haptic sensory system along with an eye height change which provide realistic heave acceleration cues.