Suprathreshold testing involves assessment of the patientâ€™s perceptions of taste intensities at levels above threshold. The method of measuring this quality is by revealing a sensory loss in the sense of taste for one or all of the gustatory modalities (salty, sour, sweet or bitter) through psychophysical procedure known as magnitude matching. The logic behind magnitude matching is that a deficiency in one sensory modality (in this case, hearing) can be revealed if it is compared to another, presumably normal, modality on the same scale. Several concentrations of sodium chloride, sucrose, citric acid, and quinine HCl, along with several loudness levels of a 1000-Hz tone are provided for the magnitude matching task. The taste solutions are presented in medicine cups, which the patient sips and then expectorates, and the tones are presented through headphones. The patient is asked to assign numbers to the perceived intensities of the several concentrations of sucrose, sodium chloride, citric acid and quinine HCL, comparing the intensity to the auditory referent, in a cross-modality matching paradigm. The numbers assigned by the patients are converted to logarithms and plotted on log-log coordinates by the examiner. The slopes of the derived concentration-response functions can indicate abnormalities of threshold or of the perception of supra-threshold intensities. The results are scaled in relation to loudness functions to reveal abnormalities of taste as depressed psychophysical functions. In other words, patients with hypogeusia associate stronger taste concentrations with weaker tones than normal patients do.
This test also serves to document an intact sense of taste in patients who complain of flavor loss due to olfactory deficits. The 20 stimuli are presented in a random order over about a 45-minute period.