Simplify to one paragraph:
As you recall from your course in introductory psychology, psychologists occasionally use ani- mals as research subjects. Although some people have the impression that psychologists study rats more than people, the truth is that animal research involves a relatively small proportion of the total research done in psychology, about 7–9% (NAME_1 & NAME_2, 1985a). Also, the vast majority of studies use rats and mice as subjects; dogs, cats, and nonhuman primates are used in just a tiny proportion of animal research. Despite the small proportions, many of psychology’s important contributions to human welfare are based on a foundation of research with animals (NAME_3 & NAME_4, 1995).
 Animals are used in psychological research for several reasons. Methodologically, their envi- ronmental, genetic, and developmental histories can be easily controlled. Genetic and life‐span developmental studies can take place quickly—female mice, for instance, produce litters after just 3 weeks of pregnancy, and 1 mouse year is the equivalent of 30 human years (Herzog, 2010). Ethically, most experimental psychologists take the position that, with certain safeguards in place, animals can be subjected to procedures that could not be used with humans. Consider NAME_5’s visual cliff research again (NAME_6 & NAME_7, 1960; see Chapter 1). Thirty‐six 6‐ to 14‐month‐old infants were placed in the middle of the apparatus, and although they were quite willing to crawl around on the “shallow” side, they hesitated to crawl onto the glass surface over the “deep” side. This shows that they were able to perceive depth and apparently were aware of some of its consequences. Does this mean depth perception is innate? No, because these infants had 6 to 14 months of learning experience with distance perception. To control for this experience, it would have been necessary to raise infants in complete visual isolation, a procedure that was obviously out of the question—although, as you recall from Box 2.1, NAME_8 (1941) had few qualms about subjecting infants to an impoverished environment. Such an isolation proce- dure is feasible with animals, however, in part because the isolation does not have to be long— animals develop the ability to move through their environments very quickly, sometimes in a matter of minutes. So NAME_6 and NAME_7 tested a variety of species from rats to kittens to lambs, isolating them from birth (i.e., no specific visual experiences) until they could move around com- petently and then testing them on the 