Psychometric functions (response vs. stimulus) are usually S-shaped, reflecting the fact that people's perceptual responses are variable. Describe, one source of bottom-up noise and one source of top-down noise that might affect a person's perceptual decision on a fingertip pressure sensing task. Note: "noise" doesn't mean auditory stimuli or sound. Noise, in this context, means variability. Hint: ANYTHING that comes from the environment is bottom-up ... cold hands, variable action potential rates because neurons aren't computers, additional stimuli, distraction. ANYTHING that comes from inside your head is top-down ... wandering thoughts, tiredness