Which of the following statements is true of the signal-detection theory?

A) The signal received from an unidentified source cannot be perceived without having prior knowledge about the source.
B) A stimulus appears to be in constant flux due to the inability of human senses to perceive the full spectrum of any sensory input.
C) The relationship between a physical stimulus and a sensory response is fully mechanical.
D) The intensity of a signal is one factor that determines whether people will perceive sensory stimuli or a difference between signals.

D