Scaling of added loads to breathing: magnitude estimation vs. handgrip matching

Six healthy male adults were studied at five levels of suprathreshold added resistance (delta R) applied three times to inspiration in a random sequence. Subjects squeezed an isometric handgrip dynamometer coincident with the breath to express the perceived magnitude of the load and also gave a numerical estimate after completing the loaded inspiration. Peak mouth pressure, grip deflection, and numerical estimate were analyzed to derive the exponents for Stevens' power law. The mean exponent and correlation coefficient obtained from numerical estimates were 1.11 +/- 0.16 and 0.94 +/- 0.04, respectively, while the exponent and correlation coefficient simultaneously obtained from handgrip matching was 0.73 +/- 0.10 and 0.91 +/- 0.05, respectively. Multiplying each subject's exponent obtained from handgrip matching by 1.7 yields a mean equated exponent of 1.23 +/- 0.17. The equated exponents were not statistically different (P greater than 0.05) from the exponents derived from numerical estimates. These results suggest that the use of cross-modality (handgrip) matching provides a reliable method for obtaining psychophysical magnitude functions of respiratory sensations and that exponents obtained using either technique can be equated for comparison.