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