  This text presents the cognitive-ergonomics approach to design, in both its
individual and collective form. It focuses on collective design with respect to
individual design. The theoretical framework adopted is that of information
processing, specified for design problems. The cognitive characteristics of
design problems are presented: the effects of their ill-defined character and
of the different types of representation implemented in solving these problems,
amongst others the more or less "satisficing" character of the different
possible solutions. The text first describes the cognitive activities
implemented in both individual and collective design: different types of
control activities and of the executive activities of solution development and
evaluation. Specific collective-design characteristics are then presented:
co-design and distributed-design activities, temporo-operative and cognitive
synchronisation, and different types of argumentation, of co-designers'
intervention modes in the design process, of solution-proposals evaluation. The
paper concludes by a confrontation between the two types of design, individual
and collective.
