AP Psychology Unit 2.1 - Cognition Perception

Perception- How We Interpret the World

Perception relies on...

● Bottom-up processing: relying on external sensory information

● Top-down processing: relying on internal expectations

○ Explains why people see the same things differently despite the same stimuli.

● Ex: You might see a vague figure in the distance and, based on prior expectations, assume it's a person, but your friend sees a bear

Schemas and Perceptual Sets

Internal factors that filter our perceptions and fill in gaps based on what we expect.

● Schema: your way to organize cognitive information.

● Perceptual Set: your expectations of what you will see, based on environmental context, emotions, culture.

● Example: If you expect to see a face in an abstract painting, your brain may interpret random shapes as facial features.

Context and Cultural Influences on Perception

● Perception isn’t just individual—our physical surroundings, cultural background, the environment we are are, heavily shape what we notice or ignore.

Gestalt Principles of Perception: Closure

Explains how we organize perceptions into meaningful wholes, making quick sense of our environments

● 1st principle of Gestalt:

○ Closure: Our brain fills in gaps to create a complete image.

● Ex: We assume that the circles are complete but partially blocked by the (illusory) triangle

● Add nothing more than little line segments to close off the circles and your brain stops constructing a triangle.

Gestalt Principles of Perception: Figure Ground

● Figure and Ground: We distinguish objects from their background.

● the organization of the visual field into objects (the figures) that stand out from their surroundings (the ground)

● Also: auditory.

○ example: clearly hearing the electric guitar melody despite the drums, singing, etc.

Gestalt Principles of Perception: Proximity and Similarity

● Proximity: we perceive objects as grouped together if they are close

● Similarity: we perceive objects as grouped together if they are alike

Attention and Perception

Attention is a combination of sensation and perception, affected by internal and external factors.

● Selective attention: Focusing on one stimulus and filtering the rest out

○ Cocktail party effect: auditory selection. Ex: hearing your name in a noisy room, or being at a loud party and being able to hear the person next to you

○ Inattentional blindness: Failing to notice a change because you're focused elsewhere.

○ Change Blindness: Not noticing a large change in a scene because you're distracted, blink, or have another visual interruption

Some research on selective attention...

fMRI scans show a 37% decrease in brain activity in areas vital to driving when a driver is listening to a conversation. (Just et al., 2008)

University of Sydney researchers found that cell phone users were four times more at risk of a car crash. (McEvoy et al., 2005, 2007)

The National Safety Council found that 28% of traffic accidents occur when drivers are chatting on cell phones or texting. (NSC, 2010)

Depth Perception - introduction

● Binocular cues like retinal disparity and convergence help us perceive depth using both eyes.

● Monocular cues like relative size, linear perspective, and texture gradient give the illusion of depth even with one eye.

● Allows us to navigate the world safely and understand spatial relationships.

● Example: When you see objects in the distance they look smaller, which your brain interprets as them being farther away.

Binocular Depth Cue - retinal disparity

You can tell how far something is by how different the object appears to the left vs. the right eye. A large disparity indicates the object is close, a small disparity indicates it is far

Binocular Depth Cue - convergence

With both eyes, you can tell how far something is by how much your eyes turn inward.

Monocular Cue - relative size

With just one eye, you can tell how far away something is by how big it appears compared to how big you know it actually is, or how it looks compared to other objects you know about.

Monocular Cue - texture gradient

With just one eye, you can tell how far away something is by whether its texture gets smoother and smoother (farther away) or more defined (closer)

Monocular Cue - linear perspective

With just one eye, you can tell how far away something is by lines converging in the distance. The mountains are close to where the lines converge, thus they are far.

Monocular Cue - interposition

With just one eye, you can tell how far away something is by whether other objects get in the way of it or not

Visual Perceptual Constancies

Perceptual constancies: allow us to maintain a stable perception of objects even when their appearance changes in our visual field.

● Size constancy: We perceive an object as having the same size, even if its image on the retina gets smaller as it moves away.

● Shape constancy: Pictured above. We recognize an object’s shape even if its angle changes, like seeing a door open or close.

● These constancies help us recognize objects in a constantly changing environment, ensuring our perception remains consistent and reliable.

● Example: You see a person walking away from you, but you don’t perceive them shrinking, even though their retinal image gets smaller.

Apparent Motion- Seeing Motion When There Is None

Apparent movement occurs when we perceive motion even though objects aren’t

actually moving.

● Helps explain phenomena like animations, optical illusions, and even certain neurological conditions.

● Example: When you watch a movie, your brain perceives continuous motion, even though it's just a series of still frames shown in quick succession.