9.2.1 A Limited Generalization of the Results
Prototyping is a universal method that is used extensively in various disciplines and wherever interactive technology is developed. Characteristics such as fidelity, resolution and interac-tivity have been established to describe prototypes on an abstract level independent from underlying technologies. Thus, I formulated the best practices derived from my exploratory research in a context-independent way. However, the insights on Experience Prototyping presented in this thesis result from a three-year project in the automotive domain focusing on experiences in future electric vehicles. Thus, the presented case studies focus on a par-ticular application area with clearly defined goals. Furthermore, the applications explored in the case studies deal with specific scenarios and driving situations and the implemented devices represent different in-car functions. For these reasons, a generalization of the results is limited. I believe that the reported best practices can be transferred in other application areas. However, the specific tools and methods of Experience Prototyping have to be utilized in other domains in further case studies to analyze whether they can be applied in a similar way. We suggest a process to design and develop interactive applications triggering mean-ingful experiences and invite practitioners in the field to apply this process with its tools and methods in various applications areas.
Furthermore, I point to the fact that our Experience Design process cannot be seen as a complete process for developing automotive applications. Obviously, in-vehicle systems need to meet numerous requirements and are therefore far more complex. Our approach must be seen as a first attempt to integrate the focus on the interaction experience into very early development phases. Considering the automotive domain, further work attempting to integrate our findings into the internal development processes has do be done.
9.2.2 The Evaluation of Experience Prototypes is Challenging
The evaluation of meaningful experiences triggered during the interaction with prototypes has been one of the greatest challenges in the project and has caused intensive discussion. We agreed that both quantitative as well as qualitative results need consideration to capture inter-action experiences, which are in the end subjective impressions of individuals including their prior experiences, possible biases, emotions and feelings. Quantitative results are needed to show that experiential values of prototypes can be evaluated in a statistically meaningful way.
Qualitative statements can support these results and additionally add further inspiration to the design process. However, in our project we concentrated one a particular way to eval-uate experience prototypes. We measured the fulfillment of specific psychological needs as well as aroused positive affect and analyzed correlations between these scales. When desired needs were addressed during the interaction and this caused positive emotion, we interpreted our experience design as successful. Three limitations are induced by our approach.
First, we developed our evaluation methods in parallel to the implementation of the proto-types. Thus, especially the questionnaires were adapted based on the results and observations
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of user studies. This needs to be considered when comparing the results of our evaluations of the Heartbeat and the Periscope concepts. An exception is GestShare, were we followed the same procedure and used identical evaluation methods in both studies to ensure comparable results.
Second, especially the UXNQ measuring the satisfaction of psychological needs seems to be prone to certain circumstances during the user studies. One example are the items com-prising the need for Relatedness. For instance, "being close to people I care for" and "being part of a group" are both parts of this need, but result in different ratings whenever a proto-type is used by people who did not know each other prior the experiment. They might both feel as part of the group during interaction, but they are not close to each other, causing the reliability of the scale to drop to an unacceptable level. A further exploration and validation of this evaluation method or the introduction of new methods will be necessary to be able to achieve more meaningful results when evaluating experience prototypes.
Third, in our iterative and agile process, we immediately evaluated new prototypes to re-ceive quick results and short development cycles. The disadvantage of this approach is that designed experiences and the interaction experience with prototypes was not evaluated over a long period of time. Our user studies usually lasted between 30 and 60 minutes, providing sufficient time for participants to experience the prototype. However, long-term studies are necessary to analyze the durability of designed experiences. For instance, one interesting question is whether an interactive system based on the need for Relatedness is still able to trigger meaningful experiences after it has been used several times over days, weeks, months or even years.
9.2.3 The Drawbacks of Prototyping
Despite all advantages mentioned in this work, prototyping is not suitable to solve all re-maining problems and open questions in the discipline of Experience Design. Please keep in mind that per definition any prototype only represents an unfinished part of a future in-teractive product. When implementing prototypes, several trade-offs in terms of fidelity, resolution, interactivity and underlying technology are necessary. These decisions depend on the targeted audience, time as well as financial budget, available prototyping tools, eval-uation purposes and management decisions, just to name a view. A prototype can only demonstrate certain functions or design aspects of an envisioned system and thus results of evaluations and any qualitative feedback must always be handled with care. Thus, Ex-perience Prototypers must be aware of the context in which a prototype is developed and consider influencing factors carefully. Further work analyzing the influence of certain as-pects of experience prototypes on the subjective experience of people interacting with it is needed.