Final answer:
Gravity is the correct answer since it is a physical force, not a psychological influence like motivation, perception, and attitude.
Step-by-step explanation:
Among the options provided, gravity is the factor that is not a psychological influence. Psychological influences include factors such as motivation, which drives behavior; perception, which is how we interpret sensory information; and attitude, which is our evaluation of a person, idea, or object, often categorized as positive or negative. Gravity, on the other hand, is a physical force that attracts objects toward one another, particularly the pull of the Earth that gives us weight and stability, but it does not affect our psychological processes in the way that social and individual psychology factors do.