Complex sentence: They also observed that tangible symbols may serve as a bridge to other symbol systems, including abstract symbol systems such as speech or sign language, and that learning to use tangible symbols to communicate does not hinder the acquisition of natural speech and may even promote it.
Split into simpler sentences: They also observed that tangible symbols may serve as a bridge to other symbol systems, including abstract symbol systems such as speech or sign language. They found learning to use tangible symbols to communicate does not hinder the acquisition of natural speech, and may even promote it.