 Results showed a linear decline in performance with increasing age of exposure; those exposed to ASL from birth performed best, and 'late learners' worst, on all production and comprehension tests.Their study thus provides direct evidence for language learning ability decreasing with age, but it does not add to Lenneberg's CP hypothesis as even the oldest children, the 'late learners', were exposed to ASL by age four, and had therefore not reached puberty, the proposed end of the CP.In addition, the declines were shown to be linear, with no sudden 'drop off' of ability at a certain age, as would be predicted by a strong CP hypothesis.