Sensation and perception

Sensory psychology

• How we know about the world • General principles

– Transduction • receptors

– Adequate stimulus – Law of specific nerve energies

• Battery experiment

– Physical properties give rise to perceptual features • Color is NOT a property of light

Physical versus perceptual characteristics

• Need to determine relationship between physical and perceptual characteristics

• Vision – light travels in waves – Definition of wavelength

Wave characteristic of light

Differences in wavelength are perceived as differences in color

Wave characteristic of light

A and B have same wavelength

B has higher amplitude

Differences in amplitude are perceived as differences in brightness

Relationship between physical and perceptual characteristics of light

Physical feature How it is perceived

Wavelength Color

Amplitude Brightness

Visual transduction

• Cornea – Light enters eye

• Pupil – Contraction and

dilation • Iris

– Pigmented part • Lens

– Focuses light on retina

Visual transduction

• Optic disc – How to find

your blind spot • Retina

– Photoreceptors • Rods • Cones

Rods and cones

Visual transduction

• Photochemicals in rods and cones respond to light – Fire action potential – Are carrots really good for your eyes?

Properties of rods and cones

• Cones (about 7 million in each retina) – Respond best to bright light – Respond to color – Difficult to see color in dark

• Rods (about 120 million in each retina)

– Respond best to dim illumination – Do not respond to color

From retina to perception

• Optic nerve • Occipital lobe • Feature detectors in the brain

– Respond (fire action potential) only for very specific stimuli

• Some will fire if see horizontal but not vertical line • Some will fire if see “L” but not for straight line

Perception of letter “t”

Summary of visual transduction

• Adequate stimulus for vision is light • Enters the eye and is focused on retina • Retina has receptors (neurons) with

photochemicals • Fire action potential when exposed to light • AP to occipital lobe via optic nerve

Color perception

• Not in the stimulus – Species differences – No brain; no color – Different brain; different color

• Question: What processes give PERCEPTION of color?

The spectrum of light

• White light combination of all colors • ROYGBIV

– Longest to shortest wavelenths • Red, orange, yellow, green, blue, indigo, violet • Infrared and ultraviolet

Theories of color vision

• Do not know exactly how perceive color • Trichromatic theory (Young-Helmholtz)

– Found three different kinds of cones – Each has different photochemical – 3 different photochemicals respond best to 3 primary

colors (red, green blue) – Any color can be made from combination of primary

colors

Trichromatic theory of color vision

• Show a color (pink) – All three cones types respond (fire) – Cone type most responsive to red fires most – Cone types most responsive to green and blue fire less – INTERPRETATION of pattern is pink

Examples of color perception

Trichromatic theory and color blindness

• How does color blindness result according to theory?

• Selective color blindness

• Problems for the trichromatic theory – After images

The opponent process theory

• Photochemicals in cones arranged in opposed pairs – Red-Green – Blue-Yellow – Black – White

• Colors oppose one another

– When see red prevents from seeing green

The opponent process theory

Opponent process theory

• Explanation for after images

Factors affecting color blindness

• Gender

• Race

• Age

Hearing

• General questions same as for vision (and all other senses) – What is adequate stimulus ? – How does adequate stimulus get transduced (cause

action potential) – Physical properties map on to perceptual characteristics

Adequate stimulus

• Changes in air pressure • Tuning fork example • Compression and expansion of air molecules

Physical properties of sound

• Changes in air pressure can be fast or slow – Many or few cycles (compression-expansion) per

second (Hertz –Hz) – Frequency

• Air pressure changes can be high or low

– Amplitude – Measured in decibels (after AGB)

Physical and perceptual properties of sound

Relationship between physical and perceptual features

Physical property Perceptual property

Frequency – cycles per second (Hz)

Pitch

Amplitude – decibels Loudness

Different pitches

200 Hz 2000 Hz

10,000 (10 kHz)

16,000 Hz

Species differences in perceiving frequencies

Changes in loudness

Base sound 10 dB louder 20 dB louder

30 dB louder

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Decibel value of some sounds

Pinna

The outer ear

• Pinna • External auditory canal

Pinna

The middle ear

• Tympanic membrane (ear drum) • Ossicles – hammer, anvil and stirrup

Pinna

The inner ear

• The cochlea- filled with fluid not air – Basilar membrane – Hair cells on the basilar membrane

Pinna

Hair cells

Transduction in the auditory system

• Changes in air pressure enter the external auditory canal

• Vibrate the tympanic membrane • Vibrate the ossicles • Ossicles “bang” on the cochlea

– Movement of fluid in cochlea – Bending of hair cells

The process of auditory transduction

Hearing without hair cells

• Cochlear implants – Electrodes implanted in cochlear next to auditory nerve – Microphone (on belt) receives sound and transmits to

electrodes – Electrodes directly stimulate the auditory nerve

Cochlear implants

Cochlear implants

• What do they sound like?

Implant Normal

Cochlear implants

• Who should get them • Potential disadvantages

• Controversy in deaf community

Factors that can affect hearing

• Things that can’t control – Age – Gender

• Things that can control – Noise

• Duration and amplitude both important – Frequency

• What frequencies important for speech • What frequencies noise damages • Environmental noise vs. loud music • “walkman” phenomenon

Damaged hair cells

Age and hair cell damage

The “minor” senses

• Smell, taste, and touch • Are they really minor

– Which sense would you LEAST like to lose

Smell and taste

• Both chemical senses – Adequate stimulus is specific chemical compound

• Smell – Transducers are receptors in nasal passage – Respond only to specific shape of chemical compounds

• Taste – Transducers are taste buds on tongue – Respond to 4 primary sensations

Tastes are interpreted

• Overall taste determined by combinations of firing of taste buds

• Taste after effects – Similar to visual after effects

• Due to fatiguing of specific taste buds

• Drink distilled water after very sweet water • Orange juice immediately after brushing teeth

Age and taste

• Very young – Prefer very sweet foods

• Older adults

– Lose sensitivity to sweets – Many no longer like chocolate

Smell

• Receptors in nasal passages respond to specific chemicals

• Humans relatively poor at identifying smells • Large gender differences • Males better at identifying

– Musk – active ingredient in most perfumes – Brut after aftershave

• Females better at – Juicy fruit gum, coconut, and prune juice

Pheromones

• What are they? • Importance in other species • Importance in humans?

– Coordination of menstrual cycles in women living together?

– Males 100,00 times more sensitive to musk than women

Perception

• Difference between sensation and perception – Receptors transduce information (sensation) – Brain interprets that information (perception)

• Prosopagnosia – inability to recognize familiar

faces – Can identify facial features (nose, eyes, etc.) – Can’t recognize as “Bob”

Depth perception

• Should we see in depth? – Image on retina

• Binocular disparity • Demonstration

– while holding finger near nose alternate blinking – Move finger to arm’s length – More computation needed when object closer

• Demo – hard to demonstrate but here goes

Explanation of demo

• Created by combining two different views using a special camera – When focus behind (relax or defocus) you can reinstate

the slightly different views – Brain will then combine

Monocular cues to depth

• Can perceive depth even with one eye – Based on experience in real world

• Size of retinal image

– In real world smaller images on retina mean object is further

– Can simulate this in two dimensions

Retinal image as cue to depth

Is the image of man in tie the same size?

With depth cues Without depth cues

Is the man in the blue shirt the same size in both images?

Monocular cues to depth (cont’d)

• Texture gradients – More densely packed regions appear to be further

Monocular cues to depth

• Linear perspective – lines in picture converge to a vanishing point

Monocular cues to depth

• Interposition – one object blocking another

Monocular cues to depth

• Motion parallax – when moving more distant objects move slower

Summary of depth perception

• Depth is perceived (created by brain) – Not in stimulus

• Stimulus is 2-D image on retina

• Cues we use based on experience in real world • Both monocular and binocular cues

Perceptual constancy

• Critical for maintaining constant perception of world

• Knowledge of world contributes to perception – Two people stand next to one another – One starts to move away – We do not perceive the moving person as getting

smaller

• Example of size constancy – Know that people don’t shrink – So perceive constant size – Despite change in size on

retina (image gets smaller as moves away)

Example of shape constancy

• Image on retina changes as angle of opening changes – Still perceive door as same

Illusions

• Use assumptions we make to fool us • Ames room example

Explanation of Ames room

• Assumption is that room is rectangular

• Actual shape is trapezoid

Perceptual organization

• Idea of perception – “what you see is NOT necessarily what you get”

• Perception based on

– Sensation – Knowledge and experience

• Understanding how we organize our world

– Visual experience not just series of action potential in rods and cones

Gestalt Psychologists

• School lasted from 1920-1950 – Developed principles about how organize perception – Many still hold today

• Some Gestalt principles

– Principles of perceptual grouping – Figure ground relationships

Perceptual grouping -similarity

Perceptual grouping -principle of continuation

Perceptual grouping - principle of proximity

• Is this organized in rows or columns?

Perceptual grouping - principle of closure

• Complete stimuli to form objects

Importance of figure-ground separation

• What is this a picture of ?

Importance of figure-ground separation

• Importance of separating background and foreground

Figure-ground confusions

• Ambiguous figures • No clear cues to

figure vs. ground

Pattern recognition

• Bottom up theories – Pattern we see determined by features of object – Similar to idea of feature detectors

• Biederman’s Geon model

– Limited set of geons – Combine to form all objects

Geons and pattern recognition

Importance of context

• Context – surrounding elements, angle of viewing, motion – Things other than the stimulus itself

• Bottom-up theories predict same stimulus, same pattern – But not necessarily true – Importance of context

Context – same stimulus different perception

Effects of context – the moon illusion

• Moon illusion • Explanation of

moon illusion

The importance of context

Viewed as is faces are similar

Rotated 180

The importance of context

A giant bird with a little person in mouth or a man in a canoe being attacked by giant fish

Motion as context

Effects of context

• Context can make us see things that are not really in the stimulus – Maybe most powerful

effect of context

Perception in infants

• Nature vs. nurture – Importance of learning for perception – Is there learning with sensation?

• Not all of one or the other • Some likely nature

– Binocular disparity • Some likely nurture

– Interposition, linear perspective

Testing depth perception in infants The visual cliff

Learning and perception

• Visual cliff – certain perceptual abilities learned • Cochlear implants

– Sensations are not speech – Can learn to interpret as speech

• Restored sight

– Blind – learn to identify object by touch – Operation to eliminate blindness – Will they be able to identify object by sight – Limitations on these studies

Visual deprivation studies

• Normal kittens have neurons in occipital lobe respond to diagonal lines

• Effects of contact lenses that only allow kittens to see vertical and horizontal (not diagonal lines) – Remove prior to age of 3 months – Remove after age of 3 months

Visual distortion studies

• Glasses that invert the world – Early effects – Later effects – Perceptual experience

• Video on inverted vision