Usually of smaller dimension. Receive the wall covering. Studs are usually mortise and tenoned into the sill and plate at the outer edge so that the exterior face is flush with the outside edge of the sill. Run diagonally between horizontal and vertical members that triangulates the forces of the load on a frame either through compression or tension. Narrow timbers set at even distances that support the flooring.
Joists run from girts to summers or tie beams.
In New England a sleeper is a foundation level replacement for joists. Sleepers are larger than joists and could span a greater distance. The sleeper may actually be laying on the ground, especially in post in ground construction where the floor is not tied to the sills.