Complex sentence: The visual cliff apparatus was created by psychologists Eleanor J. Gibson and R.D. Walk to investigate depth perception in human and animal species, which allowed them to experimentally adjust the optical and tactical stimuli associated with a simulated cliff while protecting the subjects from injury.
Split into simpler sentences: The visual cliff apparatus was created by psychologists Eleanor J. Gibson and R.D. Walk to investigate depth perception in human and animal species. This appartatus allowed them to experimentally adjust the optical and tactical stimuli associated with a simulated cliff while protecting the subjects from injury.