Psych 104 unit4b

Dark adaptation

• Progressive improvement in light sensitivity in low light conditions

• Rod are slower to adapt than cones

• Red light maintains rods photopigments by preventing bleaching of rods

Trichromatic theory of colour

• By Young & hemholtz

• Vision is sensitive to primary colours

• 3 types of cones (blue, green, red)

Colour blindness

• Absence or reduced number of one or more cones

• Monochromats - no colour vision

• Dichromats - Missing 1 cone

• Most common in males bc on X chromosome

Opponent processing theory

• Phenomenon that trichromatic theory cant explain

• After images (seeing opposite colour when you look away bc opponent process cells fatigued)

• Why dichromates can see yellow with red or green cone

Dual process theory of perceiving colour

• 3 pairs of opponent cells (red-green, blue-yellow, white-black)

• After images show complement colours

• RGC & LGN have some cells respond to red but not green and vice vera

Visual perception pathway

Retina (RGCs) → visual thalmus (LGN) → V1

Different brain areas process different aspects

Size of fovea in visual cortex

Very big, but small in eye. Like motor cortex mapping

Feature detection

• By Husel & Wiesel

• In cats (similar to human visual system)

• Mapped V1

• Use minimal patterns to detect object features

V1 cells

• Respond to simple features of environment, simple and complex

• Higher complexity cells found in higher visual areas (visual association cortex)

Simple V1 cells

Respond best to lines of particular orientation, reduced activity when line id no their preference

Complex V1 cells

• Respond to bars over a range of positions

• Some only respond to bars in motion

• Detect lines and edges

Binding problem

• How does the brain bind diverse info to form whole?

• Hypotheses - rapid coordinated activity across multiple cortical association areas

Sound

Mechanical vibration. Pitch responds to frequency

Loudness

Determined by amplitude of sound wave. Measured in decibels

Outer ear

• Funnels sound waves into ear drum

• Pinna and ear canal

Middle ear

• Amplifies sound to inner ear

• Ossicle bones: malleus/hammer, incus/anvil and stapes/styrup

Inner ear

Has the cochlea to transduce sound

Cochlea

• Bony outer part, fluid filled inner part

• Has organ of corti and basilar membrane

Basilar membrane

Moves in response to fluid waves

Organ of corti

Embedded hair cells (transducing sound)

Pitch perception

Place theory: a specific place along basilar membrane & A1 match tone with specific pitch

High frequencies base of cochlea, low frequencies apex

Frequency theory

Neurons fire at the frequency of the pitch

100 hz → 100 nerve impulses

Volley principle

Groups of neurons fire in alternating bursts so that the combined firing rate matches higher frequencies

Localization of sound

• Locate with respect to body

• Brain stem

• Monaural cues (distinguish clarity of sound)

Auditory pathway

Cochlea → auditory nerve → brainstem → thalmus (MGN) → primary auditory cortex (A1)

Deafness

• Conductive (malfunctioning of ossicles)

• Nerve deafness (damage to auditory nerve)

• Noise induced (often with tinnitus)

• Aging (loss of hair cells & degeneration of auditory nerve)

Smell & taste

Chemical senses

Odours

Air borne chemicals detected by olfactory receptor cells in nasal passage transmit to olfactory bulb in brain

Pheromones

• Odourless chemicals for intraspecies communication

• Menstrual sync

Is the thalamus involved in olfaction?

No

Olfaction pathway

Odour molecules → receptors → olfactory bulb → limbic system → cortex

Taste buds

• Contained in papillae

• Separate taste receptors for each of the 5 tastes

• Taste happens through activity in neurons in combination of activity in taste receptor cells

• All regions of the tongue can detect all taste

Gustatory pathway

Chemical → taset receptor cell → cranial nerves → brainstem → thalamus → gustatory cortex

Somatosensory system

• Skin & body senses

• Skin (tactile) - touch, temp, pain

• Body - proprioception, vestibular

Specialized nerve endings

• Found at the end of sensory neurons

• Mechanoreceptors - light touch, deep pressure

• Pacinian corpuscle - specialized for pressure

Free nervings

• Touch, temp, pain

• Plentiful

• Distributed across skins surface

• Disproportionate representation in cortex (small nerve → big area in cortex)

Referred pain

Damage to internal organs caused pain elsewhere in the body

Pain

• Sharp, stabbing, aching, ect

• Each stimuli has a threshold for causing pain

• Harder to localize than touch

• Emotional component (S1 & limbic system)

Gate control model of pain

• Control pain by controlling thoughts & emotions in reaction to pain

• Pain blocked by consciousness - spinal cord acts as a gate

• Distractions & pressure effective

Endorphins

Decrease release of pain sensitive neurons

Proprioception sense

• How body is positioned, force we are applying, how much limbs are stretched

• Embedded in muscle (stretch) & tendon (force)

• Sensory neurons → spinal cord → brainstem → thalamus → M1 and S1

Vestibular sense

• Which way is up, how fast you’re moving, if you’re moving

• Semicircular canals

• Not cortically processed

• Respond to acceleration

Proprioceptors

• Embedded in muscle (stretch) & tendon (force)

• Sensory neurons → spinal cord → brainstem → thalamus → M1 and S1