Horizontal stabilization of upper and lower borders of the comfortable zone.

Using a screw jack device the upper and lower borders of the comfortable zone were recorded in a two step procedure designed to counteract bias inherent in previous measurements. In these measurements, successively increasing and decreasing values of zonal borders were recorded corresponding to a fully closed or fully opened starting position of the screw. Both of these positions are outside the comfortable zone. The two step procedure used a starting position which was supposed to lie inside the comfortable zone. However, the procedure did not achieve its aim fully. It succeeded only in stabilizing the lower border values. In the discussion hypothetical considerations are made concerning the neurophysiological mechanism underlying recordings of the borders of the comfortable zone, which might explain the differential behaviour of the zonal borders.