Week 8- Sensation and Perception 1 Flashcards
Define sensation
The process by which the sense organs gather information about the environment and transmit the information to the brain for initial processing
Define perception
The process by which the brain selects, organises and interprets sensations
What are the three basic principles regarding sensation and perception?
- There is no one-to-one correspondence between physical and psychological reality; measuring this is the realm of psychophysics
- Sensation and perception are active processes
- Sensation and perception are adaptive (facilitation of survival and reproduction)
Outline the 5 features common to all sensory systems
- Each sensory system has sensory receptors that:
-Detect physical energy
-Translate physical stimulation into neural signals (transduction) - 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 - Sensation requires constant decision making
- Sensing the world requires the ability to detect changes in stimulation
- Efficient sensory processing requires “turning down the volume” or suppressing the redundant information
Define absolute thresholds
Sensory systems require a minimum amount of energy for activation
What affects the variation of thresholds between people and situations?
- External noise
- Internal noise- random firing of neurons
- Internal noise- psychological factors such as expectation, motivation, stress, fatigue
Define the just noticeable difference threshold
- The lowest level of stimulation required to sense that a change in stimulation has occurred
What is Weber’s law?
- 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
What is Fechner’s law?
The magnitude of a stimulus grows geometrically as the subjective experience of intensity grows arithmetically
What is Steven’s power law?
As the perceived intensity of a stimulus grows arithmetically, the actual magnitude of the stimulus grows exponentially (squared, cubed etc)
What do these laws tell us?
Sensation bears an orderly, predictable relation to physical stimulation, but psychological experience is not a photograph of external reality
What is signal detection theory?
How to make a decision when there are only two possible decisions to make
What are the four possible outcomes of signal detection theory?
- Hit- a correct identification of something you should say “yes” to
- Miss- you miss something you should have said “yes” to
- Correct rejection- properly say “no” to something you should say “no” to
- False alarm- you say “yes” to something you should have said “no” to
Define transduction
The process of converting physical energy or stimulus information into neural impulses
Outline light as a stimulus
- 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)
Outline pupillary response
- 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
What is the cornea?
A tough, transparent tissue covering the front of the eyeball and protecting it from damage
What is the aqueous humour?
A small area of clear fluid
What is the pupil?
An opening in the centre of the iris
Outline how light travels through the eye
- 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
Outline the structure of the retina
- 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
Outline the structure of rods
- More sensitive
- Good for dim light
- Not sensitive to wavelength and thus cannot distinguish colour
Outline the structure of cones
- Less sensitive, need strong light
- In the centre of the retina (the fovea)
- Detailed vision
- Respond to wavelength (colour)
Describe the layers of the retina and how light passes through them
- 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
