Partial loss of taste function can take a variety of forms. Losses can be specific to one taste quality or to one tongue locus. In addition, the shapes of psychophysical functions can be altered so that taste intensity no longer grows normally with concentration. Magnitude matching, an efficient psychophysical scaling method (based on magnitude estimation of stimuli from two sensory continua), can provide a relatively quick assessment of a patient's ability to taste the four taste qualities--sweet, salty, sour, and bitter. When taste intensity and loudness are scaled in the same session, a person with normal hearing who has taste loss will match taste intensities to abnormally weak sounds. Spatial losses are detected by placing pieces of filter paper soaked in taste solutions on specific tongue loci. Dysgeusia, the presence of a chronic taste in the mouth, can result from abnormal substances in the mouth (e.g., via saliva or from poor oral hygiene) or can reflect disorders of the central nervous system.