Tactile perceptions in products other than food. How to measure them?

Carine Egoroff

PSA Peugeot Citroën

2 route de Gisy

78 943 Vélizy Villacoublay

France

Tel : (+33) 01 57 59 69 28

Fax : (+33) 01 57 59 62 74

 Carine.egoroffmpsa.com

One of the main preoccupations of car manufacturers is to better specify the comfort and the quality of vehicles. Traditionally, product specifications result from a know-how combining knowledge and expertise in the fields of mechanics, physics, marketing and design. However, in an increasing competitive context, manufacturers need nowadays to better answer to consumer expectations. They need to offer interior designs that match the vehicle identity and provide a real sensory coherence. But how to characterize this global character or this coherence?

The judgment of car comfort or character goes through sensory information (sound, tactile, visual, olfactory, thermal… stimulations) and its cognitive integration, either consciously or not. To access to this information, sensory analysis methods, initially developed for the food and cosmetic industries, are used. The most frequently used technique is the quantitative descriptive analysis which can be applied to the different sensory stimulations involved. For the tactile characterisation of seat fabrics or plastics for dash boards, we use a panel composed of twelve sensory experts. During each particular study, the panelists are trained to describe and evaluate the sensory differences perceived among the products. Thus, they first elaborate by consensus the list of descriptors with precise definitions and gestures for each term. Then, they are trained to develop their sensory acuity and to use the evaluation scale. The final evaluations, always performed in blind condition and replicated twice, give the positioning of the different products as well as their quantified sensory characteristics.

The sensory profile method however requires a long training period. Several weeks are necessary to perform a study. A faster method has then been tested to characterize large sets of fabrics : the free sorting task. Based on categorization process, this method is supposed to be simple and more natural for the subjects. Panelists are asked first to sort a set of products according to their similarities and then to describe the resulting groups. The studies show that the perceptual space obtained with this tool is close from the profile’s one. But the product discrimination appears less accurate.

Further studies (collaboration PSA/CESG) have then been conducted to evaluate if this limitation could be overcome using new instructions. We proposed the hierarchical sorting task. In this method, panelists have to realize successive divisions of the set of fabrics. Starting with two groups, they carry on the divisions until they find no more differences between products. Compared with a free sorting task, this method shows improvement in the discriminability of the products. In addition, this condition allows to better understand the strategy used by the subjects to categorize products by keeping track of the order of apparition of the sensory characteristics.

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