1. It was confirmed that normal subjects can detect an increase in airways resistance of 1.2 cmH2O 1−1 s when this is presented during a sequence of otherwise unresisted breaths.
2. In contrast when such subjects meet the same resistance presented unexpectedly during a sequence of breaths against a larger resistance (2.5 cmH2O 1−1 s), they commonly fail to detect it, indicating that they believe no external resistance remains.
3. Subjects breathing continuously against a given external resistance frequently during the course of the study indicate that they believe that a decrease in resistance has been made.