Sensation and Perception: Foundations of Psychological Experience

Sensation and Perception

Introduction

Sensation and perception are fundamental processes in psychology that allow us to detect and interpret information from our environment. Sensation refers to the detection of physical energy by sensory organs, while perception is the brain's interpretation of this sensory data.

• Sensation: Detection of physical energy by the sense organs (e.g., sight, sound, smell, taste).

• Perception: The brain's interpretation of new sensory data; how our brain makes sense of things.

Transduction

Conversion of Energy

Transduction is the process by which sensory information is converted into neural impulses that the brain can interpret.

• Receive: Sensory information via sensory receptor.

• Transform: The stimulation into neural impulses (action potentials).

• Deliver: The neural information to the brain.

The Multitasking Brain

Bottom-up and Top-down Processing

The brain builds a coherent experience from multiple sources, using both bottom-up and top-down processing.

• Bottom-up: Perception based on building simple input into more complex perceptions.

• Top-down: A perceptual process in which memory and other cognitive processes are used for interpreting incoming sensory information. Example: If your brain expects to see a word, that’s most likely what you will see.

Sensory Adaptation

Adjusting to Constant Stimuli

Sensory adaptation refers to the process by which we become less sensitive to constant or unchanging stimuli.

• Activation is highest at first detection, then sensory adaptation occurs.

• Sensory receptor cells become less responsive to a stimulus that is unchanging, becomes less noticeable.

• Adaptive: Conserves energy, focuses on novelty and changes.

• Our body adapts to what we have touched earlier (so we don’t feel it anymore) and we become aware of it again when something changes (time, units, hair moves, etc.).

Psychophysics: The Measurement of Sensation

Absolute Threshold and JND

Psychophysics studies the relationship between physical stimuli and our psychological experience of them.

• Absolute threshold: Minimum intensity of a stimulus that a person can detect half the time.

• Minimum amount of sensory information that you can detect.

Subliminal Perception

• Perception of stimuli that are presented at below absolute threshold.

• Perception is not equal to persuasion. It has little practical application (e.g., self-help tapes).

• Hidden messages are below the threshold.

Weber’s Law

Weber’s Law states that the just noticeable difference (JND) between two stimuli is not an absolute amount, but an amount relative to the intensity of the first stimulus.

• The more intense the initial stimulus, the larger the difference needs to be to notice it.

• Example: One coin in one hand and two coins in the other vs. 10 coins and 11 coins.

Formula:

$\Delta I / I = k$

Where $\Delta I$ is the change in stimulus intensity, $I$ is the original intensity, and $k$ is a constant.

JND & Marketing

• Positive changes are discernible (at or just above JND).

• Negative changes are not discernible (below JND).

• Marketers use shrinking products and subtle changes to keep current customers.

Attention in Sensation and Perception

Selective Attention

Selective attention is the process of focusing on a specific aspect of sensory input while ignoring other stimuli in the environment.

• Attention as bottleneck: The other channels are still being processed at some level.

• Being able to focus on one aspect and ignore the others.

• We are always paying attention; we can decide what channels we switch to.

Change Blindness

• Failure to detect changes in your environment.

• Limited resources further constrained by age and distraction.

Intentional Blindness

• Failure to detect an unexpected stimulus in plain sight.

• Limited attentional resources; focus on what we deem important.

Vision

Introduction

Vision starts with light, the physical energy that stimulates the eye. Transduction occurs in the photoreceptors (rods and cones).

The Eye: Vision’s Window

• Cornea: Clear outer layer, like a window, helps to bend light.

• Pupil: Black hole, controls light.

• Iris: Controls the amount of light entering the eye and adjusts to emotional states.

How the Eye Works

1. Light enters your eye through your cornea.

2. Your iris dilates, changing the size of your pupil.

3. Your lens bends the light to the back of your eye; the image is flipped upside down.

4. Your retina sends the image as an electrical signal to your brain, and your brain flips it right side up.

Rods and Cones

• Rods (100-125 million): Detect black, white, and gray; sensitive to movement; peripheral and twilight vision; low light situations; located in periphery.

• Cones (5-6 million): Sharp focus, color perception, detail; work well in daylight; cluster around fovea.

Colour Vision

• Trichromatic theory: Retina contains red, green, and blue receptors; when stimulated, these receptors can produce perception of any colour.

• Opponent process theory: We perceive colours in terms of three pairs of opponent colours: red or green, blue or yellow, black or white.

Colour processing combines the trichromatic theory and the opponent processing theory.

Visual Perception

Visual Agnosia and Blindsight

• Visual agnosia: Object recognition deficit due to damage of higher visual cortical areas.

• Blindsight: Above-average visual performance of cortically blind individuals with damage to area V1; may respond to visual stimuli without conscious awareness.

Perceptual Organization

• We organize and interpret sights to become meaningful perceptions.

• Perception is a constructive process; we go beyond the stimuli that are presented to construct a meaningful situation.

Perceptual Constancy

• Recognition that objects are constant and unchanging even though sensory input about them is changing (e.g., constancy of shape, colour, etc.).

Colour Constancy

• The ability to perceive an object as having relatively the same colour under varying illumination conditions.

• Illusions can occur when adjustment leads to misperception of colour.

How We Perceive Depth

• Monocular depth cues: Rely on one eye (e.g., relative size).

• Binocular depth cues: Require both eyes (e.g., convergence, disparity).

Culture and Perception

Culture Shapes Visual Attention (Top-down)

• East Asians & Europeans/North Americans process visual information differently.

• Eastern: Holistically (context & relationships).

• Western: Analytically (salient objects).

Hearing (Audition)

Introduction

Sound starts with sound waves, the physical energy that stimulates the ear (vibration). Transduction is done by the hair cells in the cochlea.

Seeing Sound

• Outer ear (pinna): Funnels sound in toward eardrum.

• Eardrum (tympanic membrane): Vibrates when sound waves make contact; transmits vibrations to the middle ear.

• Middle ear: Tiny chamber containing three tiny bones (stirrup, anvil, hammer) that act as mechanical amplifier.

• Inner ear (cochlea): Coiled tube in ear filled with fluid that vibrates in response to sound.

• Basilar membrane: Runs through center of cochlea; divided into two chambers, covered with hair cells.

• Hair cells: Tiny cells that are bent by vibrations; transmit neural message (transduction happens here).

When We Can’t Hear

• Conductive deafness: Malfunctioning of the ear, especially a failure of eardrum or ossicles.

• Nerve deafness: Due to damage to auditory nerve.

• Nerve-induced hearing loss: Damage to hair cells due to repeated loud noises.

• Sudden sensorineural hearing loss: Sudden loss of hearing due to inner ear or nerve damage.

Context and Emotion in Perception

Context Effects

• Recall your own perceptions in different contexts (e.g., driver versus pedestrian).

• Context helps form perception and interpretation of a situation.

Emotions Can Sway Our Perceptions

• Sad music predisposes us to perceive sad meaning (mourning vs. morning).

• Anger increases likelihood that neutral items will be mistaken as a weapon.

• Worrying about panic leads to interpreting physical sensations as panic.

Summary Table: Types of Sensory Receptors and Their Functions

Sense	Receptor Type	Main Function
Vision	Rods & Cones	Detect light, color, movement
Hearing	Hair cells	Detect sound vibrations
Taste	Taste buds	Detect chemical substances
Smell	Olfactory receptors	Detect airborne chemicals
Touch	Various skin receptors	Detect pressure, temperature, pain

Additional info: Academic context and definitions have been expanded for clarity and completeness. All major topics from the original notes have been covered and organized for exam preparation.