What Sets Apart Top-Down and Bottom-Up Processing?
As we are aware, our sensory receptors continuously collect information from our surroundings. However, how we make sense of this gathered information determines our interaction with it. In the realm of perception, it encompasses our ability to arrange, interpret, and consciously engage with sensory data. The process of perception involves two distinct approaches: bottom-up processing and top-down processing. But what exactly distinguishes these two processes? Let’s delve into their differences:
Top-down processing occurs when pattern recognition is influenced by contextual information. In this approach, perception begins with a broad overview and gradually becomes more specific. Our perceptions are significantly shaped by our expectations and prior knowledge. In simpler terms, our brains fill in the gaps and anticipate what comes next based on the knowledge we possess. For instance, if you encounter a paragraph written in illegible handwriting, it’s easier to understand the author’s message by reading the entire paragraph rather than individual words. The brain leverages the context provided by the surrounding words to grasp the essence of the paragraph.
Renowned psychologist Richard Gregory proposed that the perception process relies on top-down processing. He explained that drawing inferences based on prior experience and knowledge of a stimulus plays a pivotal role. According to Gregory, perception is essentially one’s best guess or hypothesis about the surrounding world. In the context of visual perception, Gregory argued that 90% of visual information is lost before reaching the brain. The brain constructs the stimulus based on related memories and experiences, forming a perceptual hypothesis. Gregory’s perspective suggests that the brain may generate incorrect hypotheses when confronted with visual illusions like the Necker cube, leading to inaccurate perceptions.
In contrast to the top-down approach, bottom-up processing commences with sensory input—the stimulus. This approach is often described as “data-driven” perception. For instance, if a football is placed at the center of a person’s field of vision, the visual data related to the football and all other information about the stimulus are transmitted from the retina to the brain’s visual cortex. The signal travels in only one direction.
Psychologist E.J. Gibson criticized Gregory’s explanation, particularly regarding visual illusions, which he viewed as atypical and not representative of normal visual experiences. Gibson firmly supported the bottom-up approach to perception and argued that perception is not shaped by hypotheses but is a direct phenomenon (“What you see is what you get”). In his theory, he emphasized that the environment can provide sufficiently detailed information about the stimulus (e.g., shape, size, distance) without being influenced by prior knowledge or past experiences. Motion parallax, for instance, supports this idea. When we are on a fast-moving train, objects closer to us appear to pass by rapidly, while those farther away move more slowly. Thus, we can determine the distance between us and objects passing by by observing their relative speeds. In summary:
This involves collecting input from the environment to construct perceptions using the sensory information received. It is data-driven and relies on the sensory information.
This is the interpretation of incoming information based on prior knowledge, experiences, and expectations. It is schema-driven and heavily dependent on one’s past knowledge, experiences, and expectations.