perception and visual cognition: making sense of the senses

Question 1

The phenomenological approach

Answer 1

way of measuring perception by just describing what yu sense

Question 2

psychophysics

Answer 2

way of measuring perception
(Fechner, 1860: “Elements of Psychophysics”)
how its done:
 So, we try to relate
 a precisely defined physical stimulus, with
 a precisely measured behavioural response

Question 3

light

Answer 3

the agency that causes a visual sensation when it falls on the retina of the eye … it forms a narrow section of the electromagnetic spectrum

Question 4

electromagnetic radiation

Answer 4

waves of energy that are caused by the acceleration of charged particles.

Question 5

characterisation of light

Answer 5

wavelength

intensity

Question 6

intensity

Answer 6

as intensity increases so does the number of photons emit per second

Question 7

absolute threshold

Answer 7

 The smallest amount of stimulus energy

necessary for an observer to detect a stimulus  i.e. what’s the dimmest light that we can see?

Question 8

techniques for measuring thresholds

Answer 8

Method of constant stimuli
 Pre-determined set of stimuli
 Fit a
psychometric function to data
 Slow, but accurate

Question 9

signal detection theory: problem

Answer 9

Need to take account of observer

“decision criterion”

Question 10

metric conversions

Answer 10

Metric conversions: 30 miles = 50 km 20 feet = 6 metres 20 gallons = 7.5 litres

Question 11

difference thresholds: just noticable threshold

Answer 11

 The smallest difference between two stimuli that a person can detect
(e.g. line length)

Question 12

webbers law

Answer 12

The ratio of the JND (Δl) to the standard

stimulus (l) is constant:  ΔI/I=k

Question 13

sensory adaptation and sensory sensitivity

Answer 13

The exquisite sensitivity of our sensory systems is not always apparent
 The conditions have to be right

Question 14

sensory adapttation enhances sensitivity

Answer 14

 Most sensitive to light
 After half an hour in the dark
 Most sensitive to sound
 In the quietness of the night
 Most sensitive to taste
 After drinking plain water
 Absence of sensory stimulation  Increases sensitivity

Question 15

sensory adaptation reduces sensitivity

Answer 15

Can’t see stars in the daytime
 Can’t hear very well after rock concerts
 Can’t taste much after eating a hot curry
 Hot baths and cold swimming pools feel OK,
once you’ve been in for a while
 Strong, persistent stimulation
 Decreases sensitivity

Question 16

sensory adaptation: why

Answer 16

 Evolutionary advantages
 Allows us to cope with wide variety of environments
 Focuses sensory resources on the interesting stuff
Retinal Stabilisation
Stabilised images fade rapidly

Question 17

retinal stabilisation

Answer 17

Stabilised images fade rapidly

Question 18

retinal adaptation

Answer 18

If an image is stabilized on the retina … it fades.
 Normally our eyes are constantly in motion to prevent this.
 Serves to
 reduce visual clutter (e.g. blood vessels)  concentrate on changes
Principles & Measurements
Objectives
To enable you to:
Understand how we can measure sensory performance
Appreciate the exquisite sensitivity, and fitness for purpose, of human sensory systems
Understand the utility of sensory adaptation mechanisms

Question 19

function of the senses

Answer 19

 To detect various forms of energy
 Vision - electromagnetic radiation
 Hearing - mechanical vibrations
 Touch - mechanical perturbations of the skin
 Smell - chemical properties of gases
 Taste - chemical properties of solids and liquids in contact with the tongue

Question 20

phototransduction

Answer 20

 Photoreceptors (rods and cones) turn light into electricity – a process called phototransduction
 Photoreceptors -> bipolar cells -> retinal ganglion cells
 The axons of the retinal ganglion cells form the optic nerve

Question 21

Duplex theory

Answer 21

Rods and cones differ in structure, number and distribution across the retina.
Why?
Rods are neural substrate for night vision
(also called scotopic vision)
Cones are neural substrate for day vision (also called photopic vision)
rods
120 million in one adult human eye Sacrifice acuity for sensitivity
More common in periphery
Cones
6 million in one adult human eye Sacrifice sensitivity for acuity Commonest in central vision

Question 22

sound waves

Answer 22

long smooth waves have a lower freq and lower pitch

short sharp waves with more waves in a period have a higher freq and highr pitch

Question 23

transduction in the ear

Answer 23

 Sound waves travel down the external auditory canal and vibrate the eardrum (tympanic membrane)
 The middle ear (ossicles) transfer these vibrations and amplify them
 These vibrations are picked up by the hair cells in the fluid-filled cochlea, which transform them into electrical signals which are then passed down the auditory nerve

Question 24

place theory of audition

Answer 24

 Frequency is encoded according to position on the basilar membrane
 High frequencies are encoded near the tip of the cochlear spiral
 Low frequencies are encoded near the centre
 Famously discovered by Von Bekesy in his experiments on a dead elephantʼs cochlea
Transduction on the Tongue
 Chemicals dissolved in water stimulate taste buds on the tongue
sweet (sucrose) sour (acid)
salty (sodium) bitter (quinine)

Question 25

transduction in the nose

Answer 25

 Molecules carried in the air stimulate specific odour receptors in olfactory epithelium
 About 350 different receptor classes
 Electrical signals pass directly to olfactory bulb in the frontal lobe

Question 26

transduction of mechanoreceptors

Answer 26

Many different types:
 Light touch to hair -> Basket cells
 Light touch without hair -> Meissner corpuscles  Deep touch
 Pacinian Corpuscles
 Ruffini Endings
 Temperature and Pain -> Free Nerve Endings

Question 27

other senses

Answer 27

Proprioception (Perception of the body in space)  Kinaesthesis
 Sense of Muscle Movement
 Equilibrium and Balance (Vestibular System)
 Balance and Acceleration  Interoception
 Internal body senses  Linked to emotions?

Question 28

achromatopsia

Answer 28

true colour blindness

Question 29

tributes of colour

Answer 29

 Hue = blue vs. red, green, yellow, purple
 Brightness = light blue vs. dark blue
saturation = red vs. pink

Question 30

colour mixture: subtractive

Answer 30

mixing paint

looking through coloured filters

Question 31

colour mixing; additive

Answer 31

Mixing coloured lights T elevision

Pointillist painting

Question 32

Young-Helmholtz Theory (Trichromacy)

Answer 32

hree types of cone photoreceptor Long-, Medium-, Short-wavelength- preferring
Red = Lots of L, not very much M,S Blue = Lots of S, not very much M,L Yellow = About even in L,M, not much S etc. etc.

Question 33

problems with Trichromacy

Answer 33

Complementary Colours*
 Have you ever seen a reddish green?  Or a yellowish blue?
Simultaneous Colour Contrast
 A grey square surrounded by blue looks yellowish (and vice versa)
A red stimulus gives a green afterimage (and vice versa)

Question 34

opponent process theory

Answer 34

 Proponents: First Hering, then Hurvich and Jameson
 L, M, S cone outputs recoded into six primaries: red, green, blue, yellow, black, white
 Primaries are combined in antagonistic pairs: (red-green), (blue-yellow), (black-white)
 Hue perception from:
 Red-green (L-M)
 Blue-yellow (S- [L+M])

Question 35

forbidden colours

Answer 35

 Some authors have argued that it is possible to see reddish-greens and yellowish-blues
 See:
 Seeing Forbidden COLORS. By: Billock, Vincent A., Tsou, Brian H., Scientific American, 00368733, Feb2010, Vol. 302, Issue 2
 Livitz, G. et al (2011), Perceiving opponent hues in color induction displays. Seeing and Perceiving, 24, 1-17.

Question 36

colour deficiency

Answer 36

 8% of males are colour defective
 Colour blindness (achromatopsia)
 Cerebral (Sacks’ colour blind artist)
 No cones (“Island of the colour blind”)
 Commonest are
 Dichromats (two cones)
 Anomalous trichromats (different spectral sensitivities)

Question 37

why do we have colour

Answer 37

colour helps us recognise things and remember them better

Question 38

synesthesia

Answer 38

 A “merging” of the senses
 Experience unusual perceptions (e.g. colours, tastes)
while going about their everday lives
 Synaesthetic perceptions of colour can be triggered by
 Sound, Taste, Smell, touch
 Letters, numbers, words (written and spoken), music
 “Projectors” vs “Associators”
 4.4% of the population? (Simner et al, 2006)
 95% of these get colour sensations
 Thought to be to do with un-pruned neural connections
or reduced neural inhibition
 If this might apply to you – let me know!!