Bottom-Up Processing

Imagine you're stumped on what to eat at the food court until a waft of tangy citrus catches your attention. As the scent draws you in, you catch a hint of spicy pepper luring you toward a part of the dining area you haven't perused yet. Is that cilantro? Garlic? Fish sauce? As you search for the source, you notice a Thai food stall serving Spicy Garlic Lime Chicken—yep, that sounds exactly like what you were looking for.

Detecting individual scents, then combining them to identify a dish without context from the bigger picture, is bottom-up processing in action. In this type of attention, we break down our environment's sensory information into its fundamental components, then assemble it to figure out what the scent could be. Notice that in the food court, you didn't use any previous knowledge to arrive at Spicy Garlic Lime Chicken; it was simply the combination of aromas that piqued your interest. This exemplifies how bottom-up processing tends to follow a sort of “what you see is what you get” belief—no learning is required to perceive new stimuli. 

Our perceptions, according to bottom-up processing, are built from direct sensory input without higher processes getting involved. But in reality, once we receive inputs, we also interpret them using prior knowledge, previous experience, and guiding thoughts, which refers to the other side of the coin, top-down processing. For example, smelling a toasted bun and instantly thinking “burgers!” would be exercising top-down processing because past experiences allow you to assume what's letting off that scent by speculating the type of dish that typically accompanies it. In short, bottom-up processing is like building a puzzle piece by piece from the individual elements, while top-down processing is like having the picture on the front of the box to guide you and using that knowledge to piece the puzzle together faster.

Highlighting the key differences between bottom-up and top-down processing can also help to grasp the concept:¹

• Data-driven vs. knowledge-driven processing of information: The brain focuses on the direct data presented by sensory systems in bottom-up processing vs primarily using previously acquired knowledge and context clues in top-down processing. 
• Physical vs. psychological: Bottom-up is linked to the physical stimulation of sensory receptors and transmission of neural signals, whereas top-down taps into cognitive processes like memory retrieval that are much more psychological in nature. 

During bottom-up processing, different physical stimuli—sight, sound, smell, touch, and taste, but also submodalities like temperature, pressure, and proprioception (our ability to sense our position and movement in space)—are detected by our sensory receptors: eyes, ears, nose, skin, and tongue. This input is converted into neural impulses and then sent to the brain and spinal cord for interpretation, a process known as transduction. Different senses have their own respective pathways. As an example, the visual transduction pathway includes the retina, optic nerve, optic chiasm, optic tract, lateral geniculate body, optic radiations, and finally the visual cortex of the brain.²² 

Bottom-up processing is relevant across theoretical explorations of human perception and practical applications in areas such as social cognition, technological innovation, and law enforcement. Over time, research has deepened our understanding of how this perceptual mechanism operates, highlighting both bottom-up's strengths and limitations. As studies have demonstrated the process’s reliability in certain contexts and shortcomings in others, the evolving insights into bottom-up processing have shaped how—and when—we can rely on automatic responses. Since bottom-up processing happens subconsciously without our control, the real choice lies in whether we trust our instincts or decide to seek additional information from top-down processes to confirm them.