Introduction to Perception (College Board AP® Psychology): Revision Note

What is perception?

• Perception is the process by which the brain recognizes, interprets, and organizes sensory information

  • It is the second step in the sensation-perception process:

    • Sensation detects raw stimuli, e.g. your eyes detect light patterns

    • Perception gives those stimuli meaning, e.g. your brain interprets those patterns as the face of a friend

• Perception is not a passive, neutral process

  • It is actively shaped by both external sensory information and internal expectations and experiences

• Two types of processing describe how perception works:

  • Bottom-up processing

  • Top-down processing

Bottom-up processing

• Bottom-up processing builds a perception from the raw sensory data upward

  • It starts with the individual features of a stimulus and works toward a complete interpretation

• Bottom-up processing relies heavily on the sensory receptors and the physical features of the stimulus itself

  • E.g. when you encounter an unfamiliar word in a foreign language, you process each letter and sound individually to try to build meaning

    • There is no prior knowledge to draw on

Top-down processing

• Top-down processing starts with prior knowledge, expectations, and experience and works downward to interpret incoming sensory data

  • E.g. if you read a sentence with a letter missing, your brain fills in the gap automatically ("I h_pe you get an A on the AP exam") because your experience with language tells you what the word should be

• Top-down processing can cause people to perceive what they expect rather than what is actually there, which can lead to errors and illusions

• Both types of processing operate simultaneously

  • Perception is a combination of what our senses tell us and what our brain expects

Schemas and perceptual sets

• Schema is an organized mental framework or unit of knowledge about a subject, event, or concept built up through experience

  • Schemas influence what we notice, how we interpret it, and what we remember about it

    • E.g. if you have a schema for "library," you expect books, quiet, and desks. You would quickly notice a loud argument but might not notice a new painting on the wall

• Perceptual set is a predisposition or readiness to perceive something in a particular way based on prior experience, expectations, beliefs, and context

  • A perceptual set acts like a filter, as it makes certain interpretations more likely and others less likely

    • E.g. a nervous passenger on an airplane may perceive normal turbulence as a sign of danger, yet an experienced pilot with a different perceptual set perceives the same turbulence as routine

• Both schemas and perceptual sets are internal factors that shape perception

  • They are why two people can experience the same event and perceive it very differently

Cultural and contextual effects on perception

• Perception is also shaped by external factors , such as:

  • context

  • experience, and

  • cultural background

• Context can change how the same stimulus is perceived:

  • E.g., the same grey square appears darker against a white background and lighter against a black background because the surrounding context alters the perception

• Cultural experiences and expectations influence which perceptual rules feel natural and which do not, e.g.

  • Cultures that do not use rectangular buildings and right angles in their art and architecture are less susceptible to the Müller-Lyer illusion because they have not learned to use those visual cues to infer depth

  • People from cultures without a tradition of linear perspective in art may not perceive depth in the same way when looking at two-dimensional drawings

• This demonstrates that some perceptual rules that were once thought to be innate are at least partially learned through cultural experience

Attention

• Attention is the process of selectively focusing cognitive resources on a particular stimulus or task while filtering out others

• Attention is the interaction point between sensation and perception

  • It determines which sensory information gets processed further and which is ignored

• The brain cannot process all incoming sensory information simultaneously

  • Attention acts as a bottleneck or filter, channeling some information in and blocking the rest

    • E.g. in a noisy classroom, you can choose to focus on your teacher's voice and filter out the conversations happening around you

• Attentional resource theories propose that we have a fixed amount of attention that can be divided up and allocated

  • Only strong stimulation could capture your full attention

The cocktail party effect

• The cocktail party effect describes the phenomenon whereby a person can focus on one conversation in a noisy environment and yet still notice when their own name or a personally relevant topic is mentioned elsewhere in the room

  • E.g. you are deeply absorbed in a conversation at a loud party and suddenly hear your name spoken across the room, even though you were not consciously listening to that conversation

• This demonstrates that the brain continues to process unattended information at some level

  • The brain does not simply block everything outside of conscious focus; we are always effectively multitasking

• It provides evidence for filter theories of attention, which propose that information must pass through a filter before entering attention

  • Unattended information is attenuated (turned down) but not entirely eliminated, and personally meaningful stimuli can still break through

Inattentional blindness and change blindness

• Inattentional blindness occurs when a person fails to notice an unexpected stimulus that is in plain sight because their attention is focused elsewhere

  • E.g. in the famous gorilla experiment, participants asked to count basketball passes frequently failed to notice a person in a gorilla costume walking through the scene

• Change blindness occurs when a person fails to notice changes in their environment because they are not attending to the aspect of the scene that changed

  • E.g. in studies where a researcher stops to ask for directions and a different person continues the conversation after a brief obstruction, many participants do not notice that the person they are talking to has changed entirely

• Both phenomena demonstrate that perception is not a complete or accurate recording of the world

  • What we perceive is heavily determined by where we direct our attention