Psych 1010: Unit 4

Week 4: Sensation and Perception and test question

Sensation and perception are connected but not the same

Sensation: detection of physical energy by the sense organs

Perception is how the brain interprets the raw sensory data

Forms of sensory information

Photoreception: light; eyes

Mechanoreception: pressure, vibration, movement; physical such as hands

Chemoreception: chemical; tastes

Transduction: conversion of one energy form into another (light energy into action potentials to the brain)

Bottom-up: perception based on simple input

Top-down: perceptual processes derived from cognitive and memory processes for interpreting information

Sensory adaptation:

  • Sensory functions adaptive for important function (such as putting off shoes, you forget about them until something changes

    • Psychophysics: the measurement of sensation

      • Absolute threshold minimum intensity of a stimulus that a person can detect half the time (for instance, low volume music)

      • Subliminal perception: stimuli that are presented at below absolute threshold 

Just Noticeable difference (Difference threshold):

The perceptual experience where someone can observe a difference

Weber’s law: Just noticeable difference between 2 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 

JND in Marketing

  • Any changes they want to make are discernible (at or above the JND)

  • Negative change (below the JND; example, chips and volume of chips in a bag)

The role of attention in Sensation and Perception

Flexible attention is critical

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

Attention as a bottleneck: Cocktail party effect; despite many stimuli in a party, we are able to recognize our names

The role of attention in Sensation and perception

We are poor at detecting stimuli in plain sight if our attention is focused elsewhere

Change blindness: failure to detect changes in your environment; constrained by age and distractions

Senses: Sight and hearing

Vision starts with light, the physical energy which stimulate the eye; tranductions; photoreceptors

Iris: control light that enters by eye also adjusts to imaginary light

Rods and cone are retina receptors

Rods (100 million) detect black , white and grey and are sensitive to movement

  • Peripheral and twilight vision

  • Low light

  • Located in periphery 

Cones (5-6 mil): sharp focus, colour perception, detail

  • Work well in daylight

  • Cluster around fovea

Feature detectors: cells in visual cortex that respond/are sensitive to specific features of environment

Colour vision:

  • Trichromatic theory” retain contains red, green and blue receptors but when stimulated, they produce perception of any colour

  • Consistent three types of cones in eye

  • Does not explain afterimage

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

Colour processing has both trichromatic theory and the opponent processing theory

When we can’t see

blindness can result in reorganisation of other sensory cortices and changes in other sense 

Echolocation might improve following blindness 

Visual agnosia: object recognition deficit: damage to higher visual cortical areas

Blindsight: above-chance visual performance of cortically blind individuals with damage to area VI

Gestalt principles: principles that determine how we organise information into meaningful wholes (We are born with built in tendencies to organise incoming sensory information in certain ways)


“The whole is more than the sum of the parts” we conceptualise sensory information as a whole like images, looking at a whole image instead of certain parts


Perceptual constancy: the recognition that objects are constant and unchanging even through sensory input about them is changes (like a door opening and closing, it is the same shape)


How do we perceive depth:

Our brain uses cues to determine depth (retina is flat)

  • Texture gradient: near objects have more texture 

  • Relative size: bigger images are perceive as closer 

  • Superimposition: if an object is cover another object, we perceive it as closer/covering the other object


Depth and distance: binocular depth cues require both eyes (Convergence, Disparity)

Culture shapes depth perception (the way people process certain things like images have different interpretations)

Hearing: sound is movement of air molecules brought about by vibration of an object

Physical aspects of sound

  • Frequently (pitch)

  • Amplitude (loudness

Outer ear (pinna): funnels sound towards eardrum

Eardrum: part of the ear that vibrates when waves make contact

Middle ear: tiny chamber containing 3 tiny bones that act as mechanical amplifier

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 cant hear

  • Conductive deafness: malfunction of the year, failure of eardrum

  • Nerve damage: damage in auditory nerve

  • Nerve induced hearing loss: damage hair cells due to repeated loud noises 

Sociocultural effects; McGurk effect: Visual and auditory senses being manipulated causes a third sound (saying ba, but changing face makes it seem like fa)