Final answer:
The psychologist's perspective is the Developmental perspective of psychology, which focuses on studying how humans change and grow across the lifespan.
Step-by-step explanation:
The psychologist's perspective in this case is the Developmental perspective of psychology. Developmental psychology focuses on studying how humans change and grow across the lifespan, including physical, cognitive, and psychosocial development. In this case, the psychologist is interested in observing and recording infants' temperaments as they evolve into personalities for 18 years, which falls under the domain of developmental psychology.