🧠 CHAPTER 4 – SENSATION & PERCEPTION

Sensation

Process where sense organs detect energy (like light or sound) and send info to the brain.

Example: Eyes detect light waves.

Psychophysics

Study of how physical energy relates to our experience of it.

Example: How bright a light has to be for you to notice it.

Absolute Threshold

The smallest amount of a stimulus you can detect 50% of the time.

Example: The faintest sound you can hear in a quiet room.

Just-Noticeable Difference (JND)

Smallest change in a stimulus that you can notice.

Example: Slightly turning up your phone volume and hearing the difference.

Weber’s Law

To notice a difference, the change must be proportional to the original amount.

Example: Adding 1 lb to a 5-lb weight is noticeable, but not to a 50-lb weight

Signal Detection Theory

Detecting a stimulus depends on the signal’s strength and your state (alertness, expectations).

Example: You “hear” your phone buzz when waiting for a text.

Adaptation (Sensory Adaptation)

Reduced sensitivity after constant exposure to a stimulus.

Example: Stop noticing a strong smell after a few minutes.

Transduction

Turning sensory energy into brain signals.

Example: Light waves become electrical signals in the retina.

👁️ VISION

Wavelength

Determines color.

Example: Short = blue

Amplitude

Determines brightness.

Example: Tall wave = bright light.

Purity (Saturation)

Determines how vivid or dull a color is.

Example: Pure red = vivid; mixed wavelengths = dull red/pink.

Retina

Light-sensitive layer in the back of the eye that detects light and sends info to the brain.

Rods

Detect light and dark; work in low light; found in the periphery of the retina.

Example: Seeing shapes in the dark.

Cones

Detect color and fine detail; work in bright light; concentrated in the fovea.

Example: Reading or seeing bright colors during the day.

Fovea

The central area of the retina with the most cones; it provides the sharpest vision.

Example: Looking directly at something to see it clearly.

Photopigments

Light-sensitive chemicals in rods and cones help convert light to neural signals.

Example: Rhodopsin in rods helps with night vision.

Optic Nerve

Carries visual info from the retina to the brain.Note: Creates a “blind spot” where it exits the eye.

Trichromatic Theory (Young-Helmholtz)

Color vision is based on three types of cones: red, green, and blue.

Example: RGB pixels on a screen.

Opponent-Process Theory

Color vision works in opposite pairs: red–green, blue–yellow, black–white.

Example: After staring at red, you see a green afterimage.

Depth Cues

Ways the brain judges distance and depth.

👁️‍🗨️ Monocular Depth Cues (One Eye)

Texture Gradient

Close = more detail; far = smoother.

Example: Grass looks rough close up

Linear Perspective

Parallel lines appear to meet in the distance.

Example: Train tracks converge on the horizon.

Interposition (Overlap)

Closer objects block farther ones.

Example: A tree blocking a house = the tree is closer.

Relative Height

Objects higher in your view look farther away.

Example: Mountains higher in your view seem distant.

Relative Size

Smaller-looking object = farther away.

Example: Two people same size → the smaller one looks farther back.

Relative Motion (Motion Parallax)

Close objects move faster across your view; far ones move slowly.

Example From a car, fence posts zoom by, mountains barely move.

Monocular Memory Trick:

“Tiny Lions In Real Races Run”

Texture, Linear, Interposition, Relative Height, Relative Size, Relative Motion.

👀 Binocular Cues (Two Eyes)

Retinal Disparity

Each eye sees a slightly different image; brain combines them for depth.

Example: Hold up a finger and close one eye, then the other — it “moves.”

Convergence

Eyes turn inward to focus on close objects.Example: Cross-eyed when looking at your nose.

Pathway to Occipital Cortex

Retina → Optic Nerve → Thalamus (LGN) → Occipital Lobe (Visual Cortex)

Feature Detectors

Neurons in visual cortex that respond to specific features like edges or motion.

Example: Some neurons fire only for vertical lines.

👂 SOUND

Sound Localization

Ability to tell where a sound is coming from based on which ear hears it first/loudest.

Example: Someone calls from your right; your right ear hears it first.

Conductive Hearing Loss

Damage to the outer or middle ear prevents sound from being conducted.

Example: Ear infection or wax buildup.

Treatment: Hearing aid.

Sensorineural Hearing Loss

Damage to the inner ear (cochlear hair cells) or auditory nerve.

Example: Loud concerts cause permanent damage.

Treatment: Cochlear implant.

👃 SMELL (Olfaction)

Epithelium

The receptor area in the nose that detects odor molecules.

Example: Cells activate when you smell coffee.

Glomeruli

Clusters of neurons in the olfactory bulb that process smell signals.

Example: Each glomerulus responds to certain scent types.

Olfactory Bulb

Brain structure that receives smell info and sends it to the brain (like the amygdala for emotion).

Example: Smells can bring back strong memories.

The vestibular system

Consists of fluid-filled semicircular canals in the inner ear that relay information about body and head movements to the brain to help maintain balance

Taste

Taste Buds

The small bumps on the tongue contain the sensory receptors for taste.

Taste Pores

Tiny, invisible openings within the taste buds that catch food particles dissolved in saliva.

Taste Receptors

Sensory cells (50-100 per taste bud) that detect chemical molecules from food and send signals to the brain.

The Five Basic Tastes

The five chemical categories of taste: sweet, salty, sour, bitter, and savory (umami).

Umami

The taste sensation meaning "savory," often associated with protein-rich foods and MSG.

Taste Coding (Pattern Recognition)

The process by which the brain identifies a specific flavor by recognizing the unique pattern of activation across the five different types of taste receptors.

Sensory Integration

The process by which the brain combines information from different senses (like sight and sound) to form a unified perception.

Ventriloquist Effect

An example of sensory integration where visual cues inform auditory signals, making a sound appear to come from a different location, such as a dummy's moving mouth.

McGurk Effect

A more striking example of sensory integration in which a speaker's lip movements actually change what we hear, illustrating the dominance of vision in speech perception.

Example: Hearing the syllable "bah" while watching a mouth pronounce "gah" results in the perception of a blended sound, such as "dah."

Speech Perception Ratio

For face-to-face conversations, speech perception is described as multiple parts hearing to one part seeing, indicating that vision plays a significant, though secondary, role.