A seat assembly forms a substantially horizontal plane for an exposed surface of each of a lower seat cushion and a seatback cushion of a seatback. The seat assembly comprises a lifter mechanism for a rearward edge of the lower seat cushion. The lifter mechanism further comprises a main lift arm coupled to the edge, a slotted support arm having a distal end thereof pivotally coupled to a distal end of the main lift arm, a linkage arm pivotably coupled with the main lift arm and a slot in the slotted support arm, and a translational arm coupled with the linkage arm. The rearward edge of the lower seat cushion is raised by the translational arm being displaced to a fully displaced position to thereby raise a distal end of the linkage arm and the lift arm.