Complex sentence: Touch is the earliest sense to develop in the fetus, and the development of infants' haptic senses, and how that relates to the development of the other senses such as vision, has been the target of much research.
Split into simpler sentences: Touch is the earliest sense to develop in the fetus. The development of an infant's haptic senses and how it relates to the development of the other senses such as vision has been the target of much research.