Flexible human speech recognition

In describing human performance in sound perception, in word recognition, in speech understanding and in dialogue handling, we generally test human limits under controlled conditions and try to understand the underlying mechanisms. However, the human system itself has already been built by nature. In speech and language technology, we would like to equal, or perhaps even outrank, human performance, but we would then first have to design the system and we would have to develop the modules according to certain specifications. This paper emphasizes the flexibility, robustness and efficiency of human performance at various levels, and tries to indicate lessons to be learned for designing speech and language technology systems.