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Brain and behaviour > Lecture 9 > Flashcards

Lecture 9 Flashcards

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1
Q

Sensation

A

Registration of physical stimuli from the environment by the sensory organs.

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2
Q

Reception and transduction (conversion to neural activity)

A
  • Electromagnetic (vision)
  • Air pressure, mechanical (audition)
  • Thermal, mechanical, electrical (somatosensory)
  • Chemical (taste and olfaction)
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3
Q

Encoding (differentiation between sensations)

A
  • Activity (action potentials) > frequency, modulation, rhythm
  • Spatial (topographic map) > neutral-spatial representation of the body or of the areas of the sensory world perceived by a sensory organ.
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4
Q

Perception

A

Subjective experience of sensation – influenced by context, emotional state, past experiences.

  • An organism’s perception of the world depends on its nervous systems complexity and organisations.
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5
Q

Visual information may alter perception in other senses

A
  • Visual-auditory (e.g., speech-in-noise, McGurk effect)
  • Visual-tactile (e.g., thermal perception, rubber hand illusion)
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6
Q

Structure of the eye

A
  • Pupil
  • Lens
  • Iris
  • Retina
  • Cornea
  • Optic disc
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7
Q

Iris

A

The colour iris opens and closes to allow more or less light through a hole (the pupil)

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8
Q

Lens

A

Lens focuses the light that passed through from the iris through the pupil
The lens focuses light rays to project a backward, inverted image on a light receptive surface.
Small muscles adjust the curvature of the lens to focus nearby or far away

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9
Q

Cornea

A

As light enters the eye, it is bent first by the cornea
The curvature of the cornea is fixed.

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10
Q

Retina

A

Light energy initiates neural activity. At the centre of the retina, the fovea is the region of the sharpest vision and has the densest distribution of photoreceptors specialised for colour

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11
Q

Optic disc/nerve

A

Where blood vessels enter the eye and the axons that form the optic nerve leave the eye, has no receptors and thus forms a blood spot. The optic nerve conveys information from the eye to the brain.

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12
Q

Hyperopia

A

People with hyperopia cannot focus on nearby objects because the focal point of light falls beyond the retina. Whereas the myopic eyeball may be too long, the hyper-optic eyeball may be too short. Farsightedness may also be since the lends to flat and refract light adequately.

  • Hyperopia = farsightedness
  • Converging/convex corrective lens (+)
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12
Q

Myopia

A

People with myopia cannot bring distant objects into clear focus because the focal point of light falls short of the retina. Most caused by the normally round eyeball being elongated, near-sightedness can always be caused by excessive curvature of the front of the cornea.

  • Myopia = near-sightedness
  • Diverging/concave corrective lens (-)
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12
Q

Receptive field

A

Part of the visual space that activates a certain cell.
What the cell ‘sees’.

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12
Q

Visual field

A

Part of the visual space seen by the eyes.
What a person sees.

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13
Q

3 types of photoreceptor cells

A
  1. rods
  2. cones
  3. photosensitive retinal ganglion cells
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14
Q

Rods

A

Sensitive to dim light
Black/white and night vision

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15
Q

Cones

A

Three types of cones: blue (419), green (531), red (559)
Sensitive to bright light
Colour vision and fine detail

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16
Q

Photosensitive retinal ganglion cells

A

Synchronised circadian rhythms, regulate pupil size
Regulate melatonin release by pineal gland

17
Q

Fovea

A

Centre of the retina, densely packed with cones, no rods.
Fine detail/sharp, colour vision

18
Q

Retinal neurons - layers

A

Layer 1:

  • Horizontal cells
  • Bipolar cells
  • Amacrine cells

Layer 2: Retinal ganglion cells (two types)

  • Parvocellular (small, mostly in fovea, input from cones)
  • Magnocellular (large, throughout retina, input from rods)

NB: the axons of the retinal ganglion cell form the optic nerve

19
Q

Optic chiasm

A

Just before entering the brain, the optic nerves partly cross, forming the optic chiasm.
Medial (nasal) parts of the optic nerves cross to other side (contralateral).
Lateral (temporal) parts of the optic nerves travel back to the same side (ipsilateral).

  • The left half of each optic nerve goes to the left hemisphere.
  • The right half of the optic nerve goes to the right hemisphere.
20
Q

3 routes to the visual brain

A
  1. Geniculostraite system
  2. Tectopulvinar system (where)
  3. Retinohypothalamic tract
21
Q

Geniculostraite system

A
  • From retina to lateral geniculate nucleus (LGN, in thalamus), to layer IV of the primary visual cortex (V1, striate cortex), and then to other visual areas.
  • All parvocellular retinal ganglion cell (RGC) axons + some magnocellular

Layers 2,3,5 > ipsilateral.
Layers 1,4,6 > contralateral.
Layers 3-6 are parvocellular > colour and form (cones).
Layers 1 and 2 are magnocellular > movement (rods).

22
Q

Tectopulvinar system (where system)

A
  • From retina to superior colliculi (in tectum, midbrain), to pulvinar nuclei in the thalamus, and then to other visual areas (i.e., bypasses the primary visual cortex).
  • Only magnocellular RGC axons.
23
Q

Retinohypothalamic tract

A
  • From photosensitive RGC axons to suprachiasmatic nucleus (SCN) in thalamus.
  • Circadian rhythms and pupillary reflex.
24
Q

Occipital cortex

A

6 different areas, primar y projection area is called:

  • V1 for animals
  • Brodmann area 17 for humans
  • Striate cortex
25
Q

Occipital cortex patterns in V1 & 2

A

V1: blob patter - colour; interblobs = form, motion
V2: striped pattern - thick tripes = motion; thin stripes = colour; interstripes = form

26
Q

Receptive field hierarchy

A

The receptive fields of neurons become larger as the cell is located further in the processing stream.

The receptive field of many retinal ganglion cells combine to form the receptive field of a single LGN cell. The receptive fields of many LGN cells combine to form the receptive field of a single V1 Cell.

NB: sensory areas that have more cortical representation provide a more detailed construct of the external world (e.g., fovea).

27
Q

Luminance

A

Amount of visible light reflected to the eye from a surface

28
Q

Contrast

A

Difference in luminance between adjacent parts of the surface

29
Q

2 types of receptive ganglion cells (RGCs)

A

ON-centre OFF-surround
OFF-centre ON-surround

30
Q

ON centre, OFF surround

A
  • Increase firing rate when light falls on its centre.
  • Decrease firing rate when light falls in periphery.
31
Q

Simple V1 cells

A
  • Have an on-off receptive field
  • Respond to line segments (rectangular).
  • With a specific orientation.

NB: receptive field of simple V1 cells ~RGCs (but rectangular instead of circular).

32
Q

Complex V1 cells

A
  • Respond to moving line segments.
  • With a specific orientation.
33
Q

Hyper complex V1 cells

A
  • Respond to moving line segments (like complex cells).
  • Also have a strong inhibitory area in the end of their receptive field (on-off receptive field).
34
Q

Orientation columns

A

Host neurons that respond to the same line orientation

  • Adjacent columns house neurons that are responsive to slightly different line orientations, forming an array of 180 degrees
  • Every neyron in the same column has the same orientation bias
35
Q

Ocular dominance columns

A

Receive input from the left or the right eye

36
Q

Stimulus equivalence

A

Recognising an object as remaining the same despite being viewed from different orientations

37
Q

Theories for seeing colour

A

Trichromatic theory: explains colour vision by photoreceptors - does not explain paired colours

Opponent processing theory: explains colour vision at neural level.

38
Q

Trichromatic theory

A
  • We see 3 primary colours because we habe 3 types of cones.
  • If all primary colours are equally active we see white.
  • Can explain colour blindness
39
Q

Opponent processes theory

A
  • ON/OFF, centre/surround organisation in retinal ganglion cells creates colour opponent cells.
  • Three opposing colour pairs: black-white, green-red, blue-yellow
40
Q

2 visual streams after the occipital lobe

A

Ventral > temporal lobe: what functions
Dorsal > parietal lobe: how functions

  • NB: both the geniculostriate and techopulvinar (where) system contribute to the dorsal and ventral streams.
41
Q

Visual agnosia - temporal lobe (what)

A
  • Object recognition disorder.
  • Patients can see normally, but do not recognise objects.

e.g., visual form agnosia, prosopagnosia = inability to recognise faces due to lesion in fusiform face area.

42
Q

Optic ataxia - temporal lobe (what)

A
  • Executive disorder.
  • Patients see and recognise normally but cannot translate visual information into actions.

e.g., patients with dorsal stream lesions cannot appropriately grasp objects.

43
Q

Blindsight

A
  • Complete loss of striate cortex in geniculostriate system.
  • Intact tectopulvinar system

Brain and behaviour (14 decks)

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