This paper focuses on the study of strategies implemented in a task that involves the assembly of a model of a building. Such a strategies approach is presented as an alternative to a performance approach, both for the purpose of creating task taxonomies and for ergonomic intervention. The main operational objective is to show that subjects change their strategies during a task and that this change -analysed at an intra-individual level- is in part predictable in terms of the level of spatial abilities (Spatial+ vs. Spatial-) and the multimedia presentation format used (“pop-up” vs. conventional). The use of behavioural protocols allows the identification of three types of strategies: global (operating by “trial and error”; synthetic (structural representations of the model); and analytical (“point-to-point” representations). The two dependent variables are the occurrence of strategies and change strategies. The key assumptions are framed in terms of both main effects and interactions: “abilities X formats.” It is expected that: (1) spatial ability has a differential effect on the occurrence of global/analytical strategies, (2) S- benefit more from using a “pop-up” format and thus are more analytical, (3) a “pop-up” format produces a higher number of stable subjects, (4) the amplitude of change is moderate, (5) the nature of the change depends on experimental factors.
The results show that the effect of the abilities factor is different depending on the modality of the format: in S+, the conventional format gives rise to an over-representation of analytical strategies and an under-representation of global strategies, while the opposite occurs in S-. As for the “pop-up” format, not only does it fail to increase the number of analytical strategies in S-, it also has a deleterious effect on S+ by bringing about twice as many global strategies as the conventional format.
The study of change shows that intra-individual variability is massive (two subjects out of three): however, on the one hand, the amplitude of change is low (a majority of unique changes) and, on the other, it is very sensitive to format (the “pop-up” format gives rise to more changes). Change is brought about in an orderly manner, mainly from the global to the analytic, and its precocity is positively sensitive to the spatial factor. The discussion highlights the advantages of the strategies approach, such as high consistency with regard to the subject’s activity, sensitivity to internal and external factors and therefore predictability, particularly in view of adaptive interfaces.