xRead - Olfactory Disorders (September 2023)

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of concentrations of a given odorant. Just noticeable dif ferences are sensitive to age and have been measured in clinical settings, 1102 but have not been standardized. A number of investigators define odor discrimination as the ability to differentiate between the quality of dif ferent odorants presented at suprathreshold levels. Such tests do not require overt identification of the stimuli, only a determination of whether they differ from one another in quality. In some tests, the task is to identify the “odd” or different stimulus in a series of stimulus presenta tions. When three stimuli are presented, two same and one different, this is commonly termed a triangle test. In other tests, a same:different response is obtained, eg, two stimuli are presented on a given trial and the task is to report, for a given set, whether they are the same or dif ferent. Other tests require either matching an odorant to a sample or sorting odorants into specific categories. Still others have participant’s rate the similarity of numerous odorants. Such similarity ratings are then assessed using sophisticated statistical algorithms that show the similari ties and differences in multidimensional coordinates, with similar odorants falling into the same spatial regions. The latter tests require many trials and are rarely employed clinically. Moreover, most of these tests lack standardized normative data. Odor memory tests There are numerous types of tests designed to assess a patient’s ability to remember and recall an odor. The most straightforward of such tests simply add delay intervals between the inspection set and response set of an odor dis crimination test. Clinically, it is most common that a single odorant is presented and the task is to identify that odor from a small set of odorants after different time delays. A dozen or more such “match-to-sample” trials are per formed. Such tests were developed following the classi cal Peterson and Peterson short-term memory test for ver bal material. 620 Other memory tests require a participant to smell a series of odorants (the “inspection set”) and to pick out the odors from a larger set of odors presented at a later time. Unfortunately, in many memory tests it is the verbal label that is being remembered, eg, “I recall smelling rose,” rather than the specific odor, per se, which is well known and is present in long-term memory. In an effort to interfere with the verbal rehearsal of the inspec tion odor or odors, verbal tasks are often interspersed, with varying success, during the delay interval, such as count ing backwards in threes from a large number. Attempts have been made to develop odor memory tests using stim uli that are not readily identified or categorized, although such tests have not been developed for clinical assessment.

Odor memory tests have been shown to be more sensitive to effects of alcohol ingestion than odor identification tests and general threshold tests. 1103 In general, however, short term memory is rather robust and is only impacted by brain damage. Odor intensity rating tests Numerous tests employ rating scales or other assessments of the buildup of perceived intensity as a function of increases in odorant concentration. Such tests appear to measure physiological processes somewhat separate from those measured by tests of odor threshold, identification, discrimination, and memory. 1104 The most common rat ing scales used clinically are category scales and visual analog scale (VAS) or line scales. In category scaling, the perceived intensity is indicated according to specific cate gories (eg, weak, moderate, and strong); in VAS, responses are placed along a line with such descriptors as “no smell” and “extremely strong smell” typically located at the ends of the line. Unfortunately, responses to such scales can be problematic and can lead to biased measures. For example, not all segments of the scale are used by all patients and bunching of responses at the higher end of the continuum commonly occurs. To minimize such problems, scales have been developed that provide logarithmic spaced descrip tors at different points along the line to better mimic the known geometric progression of suprathreshold intensity sensations. More sophisticated procedures, such as cross modal matching and magnitude estimation, provide more “ratio-like” response alternatives but are rarely used clin ically for practical reasons, as reviewed elsewhere. 1105 It should be noted that, unlike tests that require forced choice responses (eg, forced-choice questions in identifi cation tests) or employ signal detection procedures, most intensity rating tests do not control for response biases.

Tests of basal odor sensitivity Odor threshold tests

Besides odor identification tests, the most widely used clin ical olfactory tests involve discerning the lowest concen tration of an odorant that can either be detected ( detection threshold ) or recognized ( recognition threshold ). Thresh old tests are intuitively accepted by clinicians, regulatory agencies, and insurance companies given their similar ity to widely accepted auditory pure-tone threshold tests. Moreover, since they do not require language or knowl edge of specific odors, they are not culture-dependent and their scores can be directly compared among different cul-