Chapter 4: Sensation and perception Slides prepared by Randall E. Osborne, Texas State University-San Marcos, adapted by Dr Mark Forshaw, Staffordshire University, UK 1

What do these famous people have in common? Duke Ellington Stevie Wonder Richard Feynman Tori Amos 2

Synaesthesia 3

When there are links between different sensory modalities; for example… Seeing letters and numbers as coloured or sounds with flavours Ramachandran’s hypothesis: in early neonatal development, brain sensory regions are linked, then separate off later...so maybe some links are retained in synaesthetes 4

Perceiving and Sensing Topics covered: Sensation Perception Transduction Psychophysics 5

Perceiving and Sensing Measuring thresholds –boundary between two psychological states Absolute threshold –minimal intensity needed to just barely detect a stimulus Just noticeable difference (JND) –Weber’s Law (constant proportion) 6

Signal Detection Signal detection –sensory signals face competition for detection –both outside and inside the person Signal detection theory Perceptual sensitivity 7

Signal detection criteria 8

Sensory Adaptation Sensory adaptation –Over time, we adapt to current conditions –We stop ‘perceiving’ certain things after a while –Useful to prevent us constantly feeling our clothes or noticing the sound of our own breathing 9

Vision: More than meets the eye 10

Vision Visual acuity Sensing light Properties of light waves –length –amplitude –purity 11

The Human Eye Cornea Pupil Light adaptation Retina Accommodation Cones Rods Fovea 12

The Human Eye Blind spot Receptive field Lateral inhibition Seeing in colour –additive colour mixing –subtractive colour mixing Trichromatic colour representation Colour-opponent system 13

Visual Pathway From Eye Through Brain 14

Pathways Visual streams Ventral (below) stream –across occipital lobe into lower levels of temporal lobes (shape and identity) Dorsal (above) stream –travels up from occipital lobe to parietal lobes (location and motion) 15

Recognizing Objects by Sight Visual-form agnosia The importance of object recognition –without it, all information would require effortful processing Feature detectors –modular view (specialized cells help us detect specific items like houses or trees) –distributed representation view (pattern of activity across cells ‘adds up’ to a perception/recognition of the object) 16

Recognizing Objects by Sight fMRI studies of the 1990s –some brain regions do respond selectively to specific object categories Perceptual constancy –sensitive to change but notice the differences 17

Principles of Perceptual Organization Before object recognition can occur, grouping of images must occur Gestalt perceptual grouping rules 18

Principles of Perceptual Organization Grouping involves visually separating an object from its surroundings Separating “figure” from “ground” –size –edge assignment 19

Theories of Object Recognition Image-based –template –what if we’ve never seen it before? Parts-based –brain deconstructs image into parts 20

Perceiving Depth and Size Monocular cues to depth: –Linear perspective –Texture gradient –Interposition –Relative height in the image 21

Perceiving Depth and Size Binocular depth cues binocular disparity having space between the eyes means that each eye registers a slightly different view of the world the difference in these views provides the brain with important and direct information about depth 22

Motion-Based Depth Cues Motion parallax –Based on the movement of your head through space and time Optic flow –The movement of visual data that flows past you as you move forward 23

Illusions of Depth and Size Ames Room –Trapezoidal room decorated to look like a normal room Moon illusion –The moon only looks larger on the horizon –It seems that way because the sight of it is in context with buildings, trees etc, but high in the sky we have no comparison objects 24

Perceiving Motion Waterfall illusion Phi phenomenon Common fate Apparent motion 25

Audition: More than meets the ear 26

Sensing Sound Three physical dimensions of sound –frequency –amplitude –complexity These determine what we hear –pitch –loudness –timbre 27

The Human Ear 28

Auditory Transduction Cochlea Basilar Membrane Hair cells 29

Perceiving Pitch Area A1 – a portion of the temporal lobe that contains the primary auditory cortex Normal range ,000 Hz Place code –the cochlea encodes different frequencies at different locations along the basilar membrane. Temporal code – the cochlea registers low frequencies via the firing rate of action potentials entering the auditory nerve. 30

The body senses: more than skin deep 31

Touch Haptic perception – using the hands to explore our environment Thermoreceptors Neural representation of the body’s surface –contralateral organization –somatosensory representation (fingers vs. back) 32

Pain A-delta fibres (fast acting pain) C fibres (longer lasting pain) Referred pain Gate-control theory –periaqueductal grey –bottom-up control –top-down control 33

Body Position, Movement, and Balance Vestibular system –semicircular canals 34

The chemical senses: adding flavour 35

Smell Only sense directly connected to forebrain 10 million olfactory receptor neurons (ORNs) –glomerulus –350 different ORN types (humans) Olfactory bulb Pheromones 36

Taste Identifying things that are “bad” for you Taste buds (5 different types) –salt –sour –bitter –sweet –umami (savoury) Each taste bud contains several types of taste receptors (microvilli) that react with tastant molecules in food 37