Final answer:
The concept where speakers perceive distinct stimuli as identical due to an underlying classificatory system is known as top-down processing. This phenomenon occurs when our perception is influenced by our prior knowledge, experiences, and expectations.
Step-by-step explanation:
Speakers perceive physically distinct stimuli as identical because their perceptions are assisted by knowledge of the underlying classificatory system. This phenomenon is known as top-down processing. Essentially, top-down processing refers to the interpretation of sensations being influenced by available knowledge, experiences, and thoughts. This concept is a key feature in Gestalt psychology and explains how a person's cognitive factors can affect the way they perceive sensory information.
People apply this perceptual set to generate a bias or predisposition when interpreting ambiguous figures or in determining the complete shape of partial or incomplete stimuli through what is known as the Gestalt principle of closure.
Perception is not solely based on the sensory input but also on our expectations, previous knowledge, and experiences that guide the brain in making interpretations. For example, when we look at a color, and all agree it is 'blue', it could be because we have learned to classify that particular wavelength of light under the label 'blue'. Motivations can also influence our perception, as seen in cases where desire or expectancy can cause us to 'detect' a stimulus that isn't present, a principle known as signal detection theory.