Complex sentence: According to Dickens (1990), critics of the 1979 film "The Corn is Green" mentioned the "palsy that kept her head trembling"; her tremor became more noticeable in the 1980s (when Hepburn was in her 70s to 80s).
Split into simpler sentences: According to Dickens (1990), the tremor was noticeable by the time of her performance in the 1979 film "The Corn is Green", when critics mentioned the "palsy that kept her head trembling". Hepburn's tremor worsened in the 1980s (when she was in her 70s to 80s).