Week 8- Sensation and Perception 1

Question 1

Define sensation

Answer 1

The process by which the sense organs gather information about the environment and transmit the information to the brain for initial processing

Question 2

Define perception

Answer 2

The process by which the brain selects, organises and interprets sensations

Question 3

What are the three basic principles regarding sensation and perception?

Answer 3

1. There is no one-to-one correspondence between physical and psychological reality; measuring this is the realm of psychophysics
2. Sensation and perception are active processes
3. Sensation and perception are adaptive (facilitation of survival and reproduction)

Question 4

Outline the 5 features common to all sensory systems

Answer 4

1. Each sensory system has sensory receptors that:
   -Detect physical energy
   -Translate physical stimulation into neural signals (transduction)
2. Each sensory system requires a minimum amount of energy to activate the system (threshold)
   -All senses have threshold below which a person does not sense anything despite external stimulation
3. Sensation requires constant decision making
4. Sensing the world requires the ability to detect changes in stimulation
5. Efficient sensory processing requires “turning down the volume” or suppressing the redundant information

Question 5

Define absolute thresholds

Answer 5

Sensory systems require a minimum amount of energy for activation

Question 6

What affects the variation of thresholds between people and situations?

Answer 6

• External noise
• Internal noise- random firing of neurons
• Internal noise- psychological factors such as expectation, motivation, stress, fatigue

Question 7

Define the just noticeable difference threshold

Answer 7

• The lowest level of stimulation required to sense that a change in stimulation has occurred

Question 8

What is Weber’s law?

Answer 8

• The ratio of change in intensity required to produce a JND
• Object 1 weighs 100g. Difference noted at 103g. JND = 3g. WF = 3/100 = .03
• Object 2 weighs 1000g. Difference noted at 1030g. JND = 30g. WF = 30/1000 = .03
• WF is constant

Question 9

What is Fechner’s law?

Answer 9

The magnitude of a stimulus grows geometrically as the subjective experience of intensity grows arithmetically

Question 10

What is Steven’s power law?

Answer 10

As the perceived intensity of a stimulus grows arithmetically, the actual magnitude of the stimulus grows exponentially (squared, cubed etc)

Question 11

What do these laws tell us?

Answer 11

Sensation bears an orderly, predictable relation to physical stimulation, but psychological experience is not a photograph of external reality

Question 12

What is signal detection theory?

Answer 12

How to make a decision when there are only two possible decisions to make

Question 13

What are the four possible outcomes of signal detection theory?

Answer 13

1. Hit- a correct identification of something you should say “yes” to
2. Miss- you miss something you should have said “yes” to
3. Correct rejection- properly say “no” to something you should say “no” to
4. False alarm- you say “yes” to something you should have said “no” to

Question 14

Define transduction

Answer 14

The process of converting physical energy or stimulus information into neural impulses

Question 15

Outline light as a stimulus

Answer 15

• A form of electromagnetic energy that moves in waves
• The electromagnetic spectrum ranges from short wavelength gamma rays to long wavelength radio wave
• Visible spectrum: 400-750 nanometres (nm)

Question 16

Outline pupillary response

Answer 16

• Pupil dilates or contracts: to changes in ambient lighting
• Pupils dilate in the dark to allow more light, and constrict in light to prevent too much
• Constriction happens more quickly than dilation, to protect receptors on the retina from being burned out by unexpectedly strong light
• Emotions, motivation, arousal

Question 17

What is the cornea?

Answer 17

A tough, transparent tissue covering the front of the eyeball and protecting it from damage

Question 18

What is the aqueous humour?

Answer 18

A small area of clear fluid

Question 19

What is the pupil?

Answer 19

An opening in the centre of the iris

Question 20

Outline how light travels through the eye

Answer 20

• Light must enter the eyes and be focused on the retina
• Light enters through the cornea, and passes through the aqueous humour, then through the pupil
• Muscles in the iris cause the pupil to expand or contract (dilate or constrict) to control the amount of light that enters the eye
• Light is focused by the lens on the retina
• Retina is located at the very back of the eye and contains the receptors necessary to transmute light into neural impulses, allowing the light reflected off of objects to be translated into psychologically meaningful information

Question 21

Outline the structure of the retina

Answer 21

• At the back are photoreceptors
• The retina is as thin as a sheet of paper
• The retina contains two types of cells that transduce light, generating an electrical signal (action potential) when struck by light waves- rods and cones
• Rods and cones named for their distinctive shapes

Question 22

Outline the structure of rods

Answer 22

• More sensitive
• Good for dim light
• Not sensitive to wavelength and thus cannot distinguish colour

Question 23

Outline the structure of cones

Answer 23

• Less sensitive, need strong light
• In the centre of the retina (the fovea)
• Detailed vision
• Respond to wavelength (colour)

Question 24

Describe the layers of the retina and how light passes through them

Answer 24

• When a rod or cone is activated by light energy, it generates an electrical signal that stimulates the next layer up, which contains bipolar cells
• Bipolar cells synapse onto multiple rods and cones. Therefore, each bipolar cell integrates information from multiple photoreceptors
• Once a single bipolar cell is activated, it activates ganglion cells, which also integrate information from multiple bipolar cells
• The axons of the ganglion cells form the optic nerve, which carries visual information from the retina to the brain
• Given photoreceptors are located in the innermost layers, light had to pass through fluid in the eyeballs and blood vessels and all other retina layers

Question 25

Outline the structure of the fovea

Answer 25

• Area of clear vision
• About 1-2 degrees of visual angle in size
• Mostly cones
• Densely packed photoreceptors
• Small, central part of the retina
• Can richly represent colour
• Part of the retina used when reading

Question 26

Outline the Young-Helmholtz trichromatic theory

Answer 26

• Colour is explained by differential activation of three colour receptors in the eye
  -Accounts well for the colour vision experience of people who are born missing one or more types of cones (colour-blindness)
• There are certain phenomena that trichromacy cannot explain, e.g. after images in different colours after staring at something
• Processes in the retina

Question 27

Outline opponent-process theory

Answer 27

• Colours are derived from activity of three antagonistic systems (black-white, red-green, blue-yellow)
• Once an activated cell is fatigued (overstimulated), you see the opposite colour
• Later visual processing in the brain