ASTM E1909-97(2003)

The purpose of time-intensity measurements is to establish the pattern of development and decline of a particular sensory characteristic under study. T-I evaluations are applicable when measurements at a single time point (an averaging process) are not sufficient to distinguish products that have very different temporal characteristics. As pointed out by Lee and Pangborn (1)³ , “This averaging process results in the masking or complete loss of important information such as rate of onset of stimulation, time and duration of maximum intensity, rate of decay of perceived intensity, time of extinction, and total duration of the entire process.”

Products rated similarly using traditional single point techniques of product profiling may provide very different temporal sensory experiences to the consumer. Acceptability of the product may be affected, and traditional descriptive methodology does not reflect the changes in an attribute’intensity over time.

T-I has applications for a variety of products. Examples include: food products, ranging from short-term sweetness in a beverage to long-term elasticity in chewing gum; personal care products, measuring the development and longevity of shampoo lather and the residual skin feel of a skin cream; household care products, monitoring the intensity of scents over time; pharmaceuticals, monitoring skin cooling after application of a topical analgesic. Auditory signals or visual changes in products can also be evaluated by the T-I technique.

1.1 This guide covers procedures for conducting and analyzing time-intensity (T-I) evaluations of products or other sensory stimuli. Time-intensity is the measurement of the intensity of a single sensory sensation over time in response to a single exposure to a product or other sensory stimulus.

1.2 This guide utilizes a specially trained panel to measure the intensity of a single continuous sensation during the time from initial exposure:

1.2.1 To its extinction,

1.2.2 To a specified intensity, or

1.2.3 To a predetermined limit of time.

1.3 Applications not covered in this guide include measuring:

1.3.1 Multiple sensations,

1.3.2 Multiple exposures within a single measurement, and

1.3.3 Qualitative or hedonic changes in the perceived sensation.

1.4 This guide includes protocols for the selection and training of judges, descriptions and use of physical data collection devices, and methods of data handling, summarization, and statistical analysis. Illustration of two different data handling and analysis approaches are included in the appendixes.

1.5 This guide is not applicable to measure product shelf life or stability that require evaluations at discrete time intervals.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.