Complex sentence: Prior to mid- 1974 she invented gestures to indicate specific phonemes and homonyms regardless of semantic context, unlike previous observations of invented signing systems in which individual gestures exclusively communicated semantic meaning.
Split into simpler sentences: Prior to mid- 1974 she invented gestures to indicate specific phonemes and homonyms, which she used regardless of semantic context. By contrast, previous observations of invented signing systems found that individual gestures exclusively communicated semantic meaning.