Testing Modes

The Yes/No Method is based on protocols used in audiometry. The assessor is presented with six random presentations per dilution level. Three of the presentations are odorous samples diluted to the dilution ratio while the other three are blanks.

The assessor sniffs the presentation port whenever the sniff light activates. Each time they detect an odor the assessor presses the detect ("D") button. The test automatically stops when the assessor completes level 14 or after the assessor has correctly identified the odorous and blank presentations for 2 consecutive dilution levels (12 correct presentations).

The Forced Choice mode is the most common testing method utilized in olfactometry. The assessor is presented with a series of presentations at increasing dilutions levels (decreasing dilution ratios). At each level the assessor is presented with one presentation of the dilute odor and one blank presentation (binary testing). The assessor must select the presentation which contains the odor by declaring to the test administrator whether the selection is a "Guess", "Detection", or "Recognition", as defined by ASTM E679-04. This method of declaration is called "forced choice."

The test begins with the concentration of the one odor presentation below the odor threshold (subthreshold). Each succeeding level has an odor concentration two times higher. The assessor continues to each dilution level until they detect (and possibly recognize) the odor (super-threshold). For example, the assessor begins at level 4 and sniffs both presentations. The assessor then is forced to make a selection by guessing if necessary. The assessor then continues to level 5, sniffs both presentations, and makes a selection. The assessor continues to level 6, 7, and so on. This statistical approach of increasing levels of sample presentation is called "ascending concentration series."

The Forced Choice mode is the most common testing method utilized in olfactometry. The assessor is presented with a series of presentations at increasing dilutions levels (decreasing dilution ratios). At each level the assessor is presented with one presentation which contains the odor and two blank presentations (triangular testing). The assessor must select the presentation which is different from the other two by declaring to the test administrator whether the selection is a "Guess", "Detection", or "Recognition", as defined by ASTM E679-04.  This method of declaration is called "forced choice."

The test begins with the concentration of the one odor presentation below the odor threshold (subthreshold). Each succeeding level has an odor concentration two times higher. The assessor continues to each dilution level until they detect (and possibly recognize) the odor (super-threshold). For example, the assessor begins at level 4 and sniffs all three presentations. The assessor then is forced to make a selection by guessing if necessary. The assessor then continues to level 5, sniffs all three presentations, and makes a selection. The assessor continues to level 6, 7, and so on. This statistical approach of increasing levels of sample presentation is called "ascending concentration series."

The Direct Presentation Method is a method for presenting an odor sample at a specific concentration to an assessor for a specified amount of time. One application for this method is to monitor physiological functions (i.e. heart rate) before, during, and after the presentation.

In the Direct Presentation Mode the test administrator specifies the sniff time for the presentation. The test administrator then initiates the presentation and completes any other desired operations (i.e. monitor heart rate). Once the presentation is complete the test administrator can select a new dilution level for testing or they can stop the test.