Lecture 4: Sensation & Perception Flashcards
The Senses
5 Common Senses:
Vision
Hearing
Taste
Touch
Smell
Also have:
Temperature
Pain
Hunger
Thirst
Full Bladder
Sensation vs Perception
SENSATION
process by which nervous system detects/ encodes information from environment & relays information to brain
ex. lightbulb shining and our eyes telling our brain what they see
PERCEPTION
how we interpret nerve sensations or give meaning to them
- what is it? how bright? what colour? where is it?
- unique to each of us but there are commonalities
- we don”t perceive everything in the world
- Perceptions are not true representations of the physical world
- reconstructions not reproductions
- imitation not carbon copy
Transduction
TRANSDUCTION
the process of converting an external energy or substance into electrical activity within neurons
- conversion of physical energy to nervous system activity
the light = physical energy → our sensory neurons transduce it → into nervous system activity
3 Themes of Perception
- Perception depends on… CONTEXT
- Perception is about OBJECTS
- Perception is MULTIMODAL - multiple senses involved
Visible Light Spectrum
Visible Light Spectrum:
- electromagnetic waves
- wavelengths between 400-700 nanometers
- can be a wave, and also consists of particles known as photons
- between ultraviolet and infrared
Light
(reflection, refraction, lenses)
REFLECTION:
when light bounces off of objects
REFRACTION:
when light passes through objects & bends
- ex. looking through glass and vision is distorted
LENSES:
work by refracting/ bending light
Key Parts of the Eye
CILIARY MUSCLE:
-changes shape of the lens
-controls accommodation
LENS:
- bends light so that it focuses/ projects on retina
- transparent disc behind pupil
RETINA
- has sensory cells that transduce light and turn it into action potentials
ACCOMMODATION:
when ciliary muscle contracts or relaxes to change shape of the lens
ACCOMMODATED:
- contracted, see close-up objects, thick
UNACCOMODATED:
- relaxed, see far away objects, thin
Corrective Measures
when the eyeball is too big relative to the size of it’s lens, it effects vision
- lenses work by bending/ refracting light
MYOPIA:
- Nearsightedness: can see close/ not far
- objects focus in front of the retina (instead of on it)
- can be fixed by a concave lens to bend light outwards to get focus properly on the retina
HYPEROPIA:
- Farsightedness: can see far/ not close
- objects focus behind the retina instead of on it
- can be fixed by **convex ** lens to bend light inwards so focus is properly on retina
Transduction Cells in the Retina
MACULA:
- centre of retina/vision** - sensory hub
- composed of an array of sensory cells: rods and cones (transduce light energy into neural signals)
SENSORY NEURONS:
RODS:
- dark vs light & motion
- located in the visual periphery
- more plentiful
- used for seeing in the dark
CONES:
- **colour** & **detail**
- 3 kinds; located in the **visual centre**
- mostly perceives what we are focusing on
- requires more light than rods
Cones: the Trichromatic Theory of Colour Vision
the combination of all cone activity influences colour vision, not the activity of a single cone type
- in order to see any colour, you need all three cones to be active/ operating at the same time
3 KINDS OF CONES:
BLUE CONES: long and low frequency
GREEN CONES: medium wavelengths
RED CONES: short and high frequency waves
- detect different wavelengths and our retina creates a code based on how much each kind of cone recognizes the wavelength
Colour Contrast vs Colour Constancy
COLOUR CONTRAST:
colours are more vivid when they contrast with their background
COLOUR CONSTANCY:
objects appear the same colour despite changes in the lighting conditions
- this is because our brain knew what it looked like before the change
ex. The Dress: looks different due to people conception of the illuminant (the lighting) emitting a warm or cool light
Perception is about Objects
the brain often “fills in” missing perceptual information to complete objects in your mind
- especially in blindspots in either retina that does not contain any sensory nerves to complete objects
- often based of what we experience in the past
Gestalt Principles of Perception:
4 Gestalt Laws of Organization: Combining and Grouping
we see the world as whole, organized objects, not individuals lines, curves, shapes, etc.
4 LAWS OF GESTALT ORGANIZATION:
1. LAW OF PROXIMITY:
we perceive objects near each other as being grouped together
- LAW OF SIMILARITY:
we perceive similar objects in groups - LAW OF CONTINUITY:
we perceive stimuli as single, uninterrupted objects - LAW OF CLOSURE
we perceive stimuli as a whole entity
- applies mostly to illusory contours and negative space
Depth: Seeing 3D
MONOCULAR DEPTH CUES:
visual depth perceived with only one eye
LINEAR PERSPECTIVE:
parallel lines converge in the distance and diverge closer to us
RELATIVE HEIGHT:
faraway objects are higher from our view than closer objects
RELATIVE SIZE:
nearby objects appear larger than objects at a greater distance
FAMILIAR SIZE:
prior knowledge about the size of the object and how it should appear relative to other objects
AERIAL PERSPECTIVE:
distant objects appear more hazy because light is scattered by atmosphere
MOTION PARRALAX:
distance estimated when viewing objects from two lines of sight
BINOCULAR DISPARITY:
image on the left retina is different from the image on the right retina
STEREOPSIS:
we see depth because of binocular disparity
Perception is Multimodal
- we perceive objects through more than one “more” or sense
- MCGURK EFFECT: speech that you hear is influenced by lip movement that you see
Sound
SOUND:
mechanical vibrations we detect with our ears, transduced by our brains
- a speaker or something else emitting sound uses compression and expansion of air molecules - sends it in a wave that we can pick up
NORMAL ATMOSPHERIC PRESSURE: the average between the peak and valley of a sound wave
AMPLITUDE:
the difference between the peak and valley of a sound wave - directly related to perceived loudness
1 CYCLE:
when the pressure raises, lowers, then returns to normal atmospheric pressure
CYCLES PER SECOND: frequency (units are Hertz, Hz); related to pitch
DECIBELS (dB):
how we describe how loud a sound is - not innately related to sound
dB Sound Pressure Level SPL:
ratio of measured sound pressure amplitude to weakest sound pressure humans can hear (1000Hz marked at 0dB))
- measuring the physical energy (not loudness - mental experience)
- 60 dB has 10x as much energy as 50 dB - this applies for each multiple of 10
Frequencies & Sound Levels we can hear
Regular Speech is ~60dB
Frequency: 20 - 20,000 Hz
Level: - 10 to ~140 dB SPL
Risky: 115 - 120 dB SPL
Pain: 135 - 140 dB SPL
Ear Anatomy
PINNA:
collects sound waves and force it into the ear canal; helps funnel air pressure vibrations into the ear canal
EAR CANAL:
connects with outside world into focusing air pressure wave in the ear drum
EAR DRUM:
detects wave vibrations, sound waves send ear drum Into motion
OSSICLES:
convert sound into vibration in liquid in our cochlea
- 3 smallest bones in body
- amplify different sounds/ frequencies
- makes you sensitive to different frequencies
- vibrate
- transfers vibrations of air into the cochlea
COCHLEA:
(snail shell) separates high and low pitches
- higher pitches near the opening (Base) 20,000 Hz
PIANO ANALOGY: at the top of the cochlea, we hear low pitches/ frequencies, at the base, we hear high pitches/ frequencies
- lower pitches near the middle/ end if it’s unraveled (Apex) 20 Hz
- analyzes/ breaks down sound by individual frequencies
- separates high and low pitch
- transduces sound vibrations into action potentials
- air pressure vibration come in and cause fluid vibrations in the cochlea
BASILAR MEMBRANE:
- between the Base and Apex
- has hairs that detect sound with sensory nerves
AUDITORY NERVE/ PATHWAY:
auditory cortex receives signals from the cochlea
- part of the temporal lobe
Audiovisual Speech Perception
Visual Cortex (V1 / V2) influence speech processing in auditory cortex (A1) through multisensory areas (posterior superior temporal sulcus, pSTS)
Visual Speech constrains the possible options for words that we hear
- visual information can constrain auditory perceptions
