Elements of Perception

• Perception is the process of recognizing, organizing, and making sense of sensations received from environmental stimuli

James Gibson

• Provided a useful framework for studying perception
• Introduced the concepts of
  • Distal (external) object
  • Informational medium
  • Proximal stimulation
  • Perceptual object

Elements of Perception

• Distal Stimulus: The object in the external world
• Informational Medium: Reflected light, sound waves, chemical molecules, or tactile information from the environment
• Proximal Stimulus: Representation of the distal stimulus in sensory receptors
• Perceptual Object: Mental representations of the distal stimulus

Example: Adobo Elements of Perception

• Distal Stimulus: A plate of adobo
• Informational Medium: Aroma of garlic and vinegar, steam, light reflecting off sauce, texture when touched
• Proximal Stimulus: Sensory input of dark sauce, savory smell, salty-sour-umami flavors, tender meat texture
• Perceptual Object: Brain recognizes and interprets "adobo"

Example: Queen Yasmin Elements of Perception

• Distal Stimulus: Queen Yasmin physically falling from the tree
• Informational Medium: Rustling leaves, scream, visual movement, vibrations on the ground
• Proximal Stimulus: Light waves, sound waves, feeling the ground shake
• Perceptual Object: Brain recognizes "Queen Yasmin is falling from the tree!", interpreting it as an accident, dangerous situation, or unexpected event

Sensory Adaptation

• Receptor cells adapt to constant stimulation by not firing until a change occurs
• This allows us to stop detecting a stimulus

Example: Sensory Adaptation - Urine

• Initially, a strong urine smell is overwhelming
• After a few minutes, the smell seems to fade due to sensory receptors adapting
• A new person entering immediately notices the smell

Ganzfeld Effect

• Unstructured visual field
• Eyes exposed to a uniform stimulus will stop perceiving it after a few minutes, seeing only gray
• Occurs because eyes adapt to the stimulus

Example: Ganzfeld effect

• Holding red plastic spoons over your eyes while shining a flashlight
• Initially, a bright red color is seen due to light passing through the spoons
• After a few minutes, your eyes adapt to the red light, and your brain ignores the stimulus
• Eventually, you stop perceiving red and see gray because the visual system adjusts to the unchanging red light

Parts of Human Eye

• Cornea: A clear dome that protects the eye
• Pupil: The opening in the center of the iris
• Vitreous Humor: A gel-like substance making up most of the eye
• Fovea: A small, thin region of the retina, the size of a pinhead
• Retina: Where electromagnetic light energy is transduced
  • First Layer: Ganglion cells
  • Second Layer: Amacrine cells, horizontal cells, and bipolar cells
  • Third Layer: Photoreceptor cells
    • Rods: Responsible for night vision, sensitive to light and dark
    • Cones: Allow for color perception

How Visual System Works

• Light passes through the cornea, then to the pupil
• Continues through the crystalline lens and vitreous humor
• Eventually, light focuses on the retina

Dorsal and Ventral Pathways

• Dorsal Pathway
  • "Where" pathway
  • Processes location and motion information
• Ventral Pathway
  • "What" pathway
  • Processes color, shape, and identity of visual stimuli

Example: Apple and pathaways

• Ventral Pathway
  • When you see an apple, your ventral pathway helps you recognize what it is
  • You process its color (red or green), shape (round), and identity (apple, a type of fruit)
  • This pathway helps you distinguish the apple from other objects, like a ball or a tomato
• Dorsal Pathway
  • If you decide to reach for the apple, your dorsal pathway helps with that
  • You process its location (on a table, in a fruit bowl) and motion (if it's rolling or still)
  • Your brain calculates how far your hand needs to move and coordinates your actions to grab it

Discovering Dorsal and Ventral Pathways

• Discovered through lesion studies in monkeys in the 1970s and 1980s by Ungerleider and Mishkin
• Scientists knew the temporal lobe and parietal lobe were involved in visual processing, but wanted to understand their specific roles of each

Studying Pathways Using Monkeys

• To study the pathways using monkeys, scientists used two steps:
  • Step 1: Identifying Brain Areas
  • Step 2: Lesion Studies (Damaging Specific Areas)
• Experiments involved surgically damaging specific brain areas in monkeys and testing their ability to perform different tasks

Findings: Ventral and Dorsal Pathways

Ventral Pathway ("What" Pathway) - Temporal Lobe

• When researchers damaged the temporal lobe, monkeys could no longer recognize objects
• Example: monkeys could no distinguish objects
• However, they could still reach for the object correctly, meaning their spatial awareness was intact

Dorsal Pathway ("Where" Pathway) - Parietal Lobe

• When researchers damaged the parietal lobe, monkeys could recognize objects but struggled with spatial tasks
• Example: If food was hidden in a specific location, they could not remember where to find it or had trouble reaching for it
• However, they could still identify objects, they knew the difference between a cube and a sphere

Bottom-Up Theories

• Describes approaches where perception starts with the stimuli taken in through your eye
• Data-driven (i.e., stimulus-driven) theories

Gibson's Theory of Direct Perception

• Information in sensory receptors is all we need to perceive anything
• The environment supplies us with all the information we need for perception

Example: Direct Perception - UPUAN VERSION

• According to Gibson, perception is direct and does not require complex mental processing
• Instead, we pick up information directly from the environment through affordances (what objects allow us to do)
• You immediately perceive the chairs affordance - something you can sit on
• perception directly informs you that the chair is for sitting based on its size, shape, and structure

Example: Direct Perception - Crossing the street

• No need to perform calculations about distance, speed, or physics
• Seeing moving cars and immediately perceiving the time to Cross the street
  • The walk signal (green light or pedestrian sign) directly tells you it is safe to go
  • The speed of approaching cars helps you judge whether to stop or move
• No need to analyze individual details consciously, perception is direct and action-oriented
• Emphasis is that we don’t "construct" perception, we directly perceive what the environment offers (affordances) and take action accordingly

Template Theories

• We store detailed templates in our minds

Example: YOU SAW UR FRIEND AT THE CROWD

• Brain has a stored mental template of what Esnyr looks like
• Compare each face to your stored template of Esnyr
• Once you find a match (someone with Esnyr exact features), you recognize him instantly
• If someone looks similar but not identical, your brain rejects them because they don’t fit the template perfectly
• Suggests storing specific, detailed mental patterns

Feature-Matching Theory: Oliver Selfridge's Pandemonium Model

• Step 1: Image Demon (photographer)
  • See the letter "A" on a piece of paper
  • The image demon captures the raw visual input of the letter as it appears
• Step 2: Feature Demons (detective agency)
  • Different feature demons analyze the basic lines, angles, and curves of the letter "A"
  • One demon detects two diagonal lines meeting at a point (/)
  • Another detects a horizontal line in the middle (-)
• Step 3: Cognitive Demons (guesser)
  • Cognitive demons shout out when they recognize a combination of features that match stored mental representations
  • The "A" demon recognizes that the detected features match the stored pattern for "A"
  • Other demons (for letters like "H" or "V") may shout, but with less confidence because they don’t match as closely
• Step 4: Decision Demon (Judge)
  • The decision demon listens to the cognitive demons and chooses the loudest one
  • Since the "A" demon is the loudest, brains correctly identifies the letter as "A."
• This is a bottom-up approach, meaning recognition starts from basic features and builds up to complete understanding

Recognition-by-Components Theory

• Developed by Irving Biederman (1987)
• Quickly recognize objects by observing their edges and then decomposing the objects into geons (geometrical ions)
• Geons can be recomposed into alternative arrangements

Example: Recognizing a bike

1. Detect Edges: brain first sees the bike’s outline
2. Break into Geons: decomposed into basic 3D shapes:

• Frame - Triangle + Cylinders
• Wheels - Circles
• Handlebars - Curved Cylinder
• Seat & Pedals - Small curved and rectangular shapes

3. Recognize the Bike: Even if tilted or partially hidden, brain reassembles the geons to identify it

• Recognize objects by breaking them into geons and reconstructing them, allowing recognition from different angles

Top-Down Theories

• Perception driven by high-level cognitive processes, existing knowledge, and expectations, which influence perceptions

Theory of Constructive Perception

• The perceiver builds (constructs), a cognitive understanding (perception) of stimulus
• Concepts of the perceiver and cognitive processes influence what they see
• This viewpoint also is known as intelligent perception

Example: Constructive Perception

1. See a shadow in a dimly lit room and ask yourself, “What is that?”
2. Raw perception alone doesn’t give a clear answer, so brain starts constructing meaning
3. Use pre-existing knowledge—you know your room and remember there’s a plant in that corner
4. Brain analyzes the shadow’s shape and position and concludes, “That’s just my plant.”
5. Final Perception: perceive the shadow not as something unknown, but as plant, thanks to cognitive processing and prior knowledge

Viewer-Centered Representation

• Individual stores how the object looks to them; what matters is its appearance to the viewer
• The object's shape changes depending on the angle

Example: Viewer-centered representation - Tekken

1. In Tekken, when you control a fighter, example is si Jin. The character’s appearance changes depending on the camera angle
2. the camera is behind fighter, you see their back and stance
3. If the camera shifts to the side, you see a profile view of character
4. Despite these different views, your brain recognizes the character as the same person based on stored viewer-centered representations

Object-Centered Representation

• Individual stores a representation of the object, independent of its appearance to the viewer
• The object's shape will stay stable across different orientations

Landmark-Centered Representation

• Information is characterized by its relation to a well-known or prominent item

Example: landmark

• Visiting friend’s house for the first time relying on landmarks
• the red church - found friend's house easily using only this information

Gestalt Laws

• Continuity- Tend to perceive smoothly flowing or continuous forms rather than disrupted or discontinuous ones
• Closure- Tend to perceptually close up, or complete, objects that are not, in fact, complete

Gestalt Laws

• Proximity- When perceive an assortment of objects, tend to see objects close to each other as forming a group
• Similarity -Tend to group objects on the basis of their similarity

Recognizing Patterns

• Suggests that humans have 2 systems
• Feature Analysis System - Recognition of parts of objects and in assembling those parts into distinctive wholes
• Configural System - Recognizing larger configurations

EXAMPLES- Two Systems

1 Feature Analysis System (Individual Features)

• You recognize a person by focusing on specific features, such as their eyes, their nose and/or their mouth

2. Configural System (Whole Pattern) Instead of focusing on separate features, you recognize a face by its overall structure and spatial arrangement

Face Recognition

• Fusiform gyrus of the temporal lobe, this brain area responds intensely when look at faces Inability to recognize faces Prosopagnosia Inability to recognize faces, would imply damage of some kind to the configural system

Perceptual Constancies

• Perception of an object remains the same even when the proximal sensation of the distal object changes

Size Constancy

• Perception is that an object maintains the same size despite changes in the size of the proximal stimulus

Shape Constancy

• Perception is that an object maintains the same shape despite changes in the shape of the proximal stimulus

Depth Perception: Monocular Depth Cues

• Represented in just two dimensions and observed with just one eye

Relative Size

• Larger objects appear closer, while smaller objects seem far away

Interposition/Overlap

• When one object blocks another, the blocked object is perceived as farther

Depth Perception: Binocular Depth Cues

• Receipt of sensory information in three dimensions from both eyes

Binocular Disparity

Each eye sees a slightly different image, Brain combines these images

• CLOSE - HIGH DISPARITY and FAR - LOW DISPARITY

Binocular Convergence

• Degree of convergence helps determine distance
• Capable of converging on the eyes

Deficits in Perception Agnosia

• Perceive sensory information (impaired "what"

Optic Ataxia

• Impairment in the ability to use the visual system to guide movement

Multatognosia

• Disturbance - cortex
• Individual is unable to pay attention

Color perception anomalies

• Inherited or vision deficiency.

Simulatgnosia

• Disturbance, cortex
• Individual cannot pay attention

Prosopagnosia

• Severely to recognize human faces

Rod

• Color blindness

Dichromacy

• 2/3 cones work, one malfuctioning

Monochromacy

• No working cones