THE EFFECTS OF MASKING ON THE GROWTH OF VIBROTACTILE SENSATION MAGNITUDE AND ON THE AMPLITUDE DIFFERENCE LIMEN - A TEST OF THE EQUAL SENSATION MAGNITUDE EQUAL DIFFERENCE LIMEN HYPOTHESIS

In this study, the hypothesis that the difference limen (DL) for the d etection of differences in amplitude of vibrotactile stimuli is indepe ndent of the slope of the sensation magnitude function was tested. The slope of the sensation magnitude function was varied by presenting te st stimuli in the presence of or in the absence of vibrotactile noise. The slopes of the sensation magnitude functions were determined throu gh a matching technique in which the subject adjusted stimulus amplitu des of a 250-Hz stimulus presented alone and a 250-Hz stimulus present ed simultaneously with a masking noise, so that their sensation magnit udes were equated. The slope of the matching function was found to inc rease as a function of the intensity of the masking noise. In the seco nd phase of the experiment, the amplitude DL was measured by the gated -pedestal method for test stimuli presented under the same stimulus co nditions as used in the matching procedure. At all levels bf stimulus intensity, the DL was found to be independent of the masking condition provided the sensation magnitudes of the stimuli were the same. This finding supports the hypothesis that the size of the DL is independent of the slope of the sensation magnitude function, provided the sensat ion magnitudes of stimuli are the same. The generality of this princip le, first discovered in hearing, is thus extended to another sense mod ality.