4) SENSATION AND PERCEPTION

Sensation

Detection of external stimuli, responding and sending that response to the brain

From the world → Brain

Transduction

Sensory receptors receive stimulation and pass the information to connection neurons

Eg. Skin when touch

Sensory thresholds

Absolute and difference

Absolute threshold

Minimum intensity to experience the sensation

Difference threshold

Noticeable difference between 2 stimuli

Sensory adaptation

Adapting to stimuli → eg. Adapting to cold water

Perception

Processing, organizing and interpreting sensory signals → conscious experience

Main sensing chemicals

Taste and smell

Taste Basic qualities

1. Sour

2. Sweet

3. Salty

4. Bitter

5. Umami

Smell

Mucosa it’s a thin layer of tissue with smell receptors that sends the information to the olfactory bulb (in the brain)

Orbitofrontal cortex

Receives the information from the smell, taste and visual systems to create flavour perception

Vestibular system

Eyes follow the vision although head is moving

Contralateral organization

Left hemisphere processing right side

Right hemisphere processing left side

Nociceptors

Pain receptors activated by damaging stimuli

Main nociceptors

Myelinated fibres and lightly or non-myelinated

Myelinated nociceptors

For protection of immediate pain

Lightly or non-myelinated nociceptors

Recuperation of steady pain

Gate control theory

“Gate” in the spinal cord that must be open to experience the pain

Somatosenses

Touch:

1. Tempture

2. Pain

3. Pressure

Cornea

Surface of eye → focuses light as it enters

Pupil

Controls how much light enters the eye

Lens

Focuses light onto the retina → see things near and far

Retina

Back of the eye → contains special cells that detect light (rods and cones)

Optic nerve

Carries visual information from the eye to the brain

Visual fields

Everything you can see without moving your eyes → left and right fields processed by opposite side of the brain

Fovea

At the back of the eye → processing incoming light on what we are focusing on

Eg. Following letter when reading

Optic disk

Blind spot without photoreceptors

Accommodation

Muscles changing based on what we are trying to focus on

• something far, close is blurry

• Something close, far is blurry

Photoreceptors

Convert energy form photons into chemical reactions to produce electrical signal

Rods

Retina cells that respond to low light levels → black and white

Cones

Retina cells respond tot high levels of light → colour perception

S cones

Short wavelengths → blue

M cones

Medium wavelengths → green

L cones

Long wavelengths → red

Trichromatic theory

Perception of colour based on the ratio of activity of the 3 cones → rainbow

Opponent process theory

One colour in the pairs is stimulated, the other one is inhibited

• blue/yellow

• Green/red

• Black/white

Motion perception

Fatigue of motion sensitive neurons leads to motion after-effects → waterfall illusion

Visual transmission

Visual areas beyond the primary visual cortex (occipital lobe) form parallel processing steams:

1. Dorsal

2. Ventral

Dorsal processing steam

“Where” = spatial perception → where objects are

Ventral processing steam

“What’ = perception and recognition of objects → shape and colour

Gestaltism principles of perceptual organization

Explain how we perceive objects in our environment and then organize them into groups:

• figure ground

• Illusory contours

• Proximity

• Similarity

• Continuation

• Closure

Retinal disparity

Caused by the gap between eyes that compute distances

Monocular depth cues

Include occlusion, relative size, familiar size, linear perspective, texture gradient, and position relative to horizon

Muller-layer illusion

Vertical lines that seem larger/shorter but are the same size

Ponzu illusion

Horizontal lines seem larger/shorter but are the same

Motion cues

Objects far away seem to move slower

Bottom up processing

Information sent from lower to higher level processing areas

Top down processing

Information from higher levels processing areas influence in lower levels

Fusiform face area FFA

Area of the brain that actives when looking at people’s faces