Chapter 5 Sensation and Perception

Question 1

What is a percept?

Answer 1

Mental representation of the original stimulus. The stimulus has been processed and interpreted by the brain

Question 2

Which 4 things are common across the senses?

Answer 2

1) Collect information from environment
2) Receptor cells transduce stimuli into neuronal signals
3) Have specific sensory nerve pathway
4) Travel through thalamus to primary sensory regions (except olfaction)

Question 3

What is adaptation and acuity of senses?

Answer 3

Adaptation: adjustment of sensory sensitivity

Acuity: how well we can distinguish among stimuli within a sense

Question 4

What are the neural pathways of olfaction?

Answer 4

1) Odorants enter nasal cavity
2) Odorants bind to receptors in olfactory epithelium
3) Bipolar neurons send signals to glomeruli in olfactory bulb
4) Axons from glomeruli form olfactory nerve
5) Olfactory nerve projects to primary olfactory cortex/pyriform cortex
6) Signal proceeds to orbitofrontal cortex and other regions

Question 5

How are olfactory receptors activated? Discuss the two theories

Answer 5

Shape/docking theory = odor molecules bind to receptor that corresponds to shape of molecule

Vibrational theory = similar shaped molecules have different molecular vibrations

Question 6

Name 3 reasons why olfaction is an unique sense

Answer 6

1) Doesn’t project to thalamus
2) Most axons olfactory nerve project to ipsilateral cortex
3) Connections to amygdala and therefore can affect emotions, autonomic behavior and memory

Question 7

What are respectively the roles of the primary vs. the secondary olfactory cortex?

Answer 7

1: detecting odor changes
2: identifying odor

Question 8

What is the neural pathway of gustation?

Answer 8

1) Papillae on tongue contain taste buds with receptor cells (more in back of tongue)
2) Molecule stimulates taste receptor and causes depolarization
3) Receptor cells synapse with bipolar neurons
4) Axons form chorda tympani nerve
5) Projection to gustatory nucleus in brainstem
6) Integration of information can produce rapid reaction if input from gastrointestinal tract is bad
7) Projection to VPM Thalamus
8) Projection to primary gustatory cortex in insula
9) Secondary processing in orbitofrontal cortex

Question 9

Why are gustation and olfaction so related?

Answer 9

Both secondary processing units are in orbitofrontal cortex

Question 10

What are the neural pathways for somatosensation?

Answer 10

1) Different types of receptors in skin/musculoskeletal junctions that respond to different types of touch
2) Dorsal root ganglia contain cell bodies
3) Sometimes reflexes, otherwise up in spinal cord
4) Crossing-over in medulla
5) Projection to VPN in thalamus
6) Projection S1, cerebellum and other subcortical structures

Question 11

What is the difference between S1 and S2?

Answer 11

S1: Simple representation of body (sensory homunculus). Face and fingers have larger area, which corresponds to higher acuity

S2: Complex representations where information from both sides of the body are integrated

Question 12

What is proprioception?

Answer 12

The sensation of the position of the limbs and head

Question 13

What is the neural pathway of audition?

Answer 13

1) Sound collected by pina
2) Sound hits tympanic membrane
3) Tympanic membrane moves malleus, incus and stapes
4) Stapes move liquid in cochlea through oval window
5) Hair cells on basilar membrane depolarize when moving
6) Signals from haircells into auditory nerve
7) Projection to cochlear nucleus in Medulla
8) Cochlear nucleus projects to superior olivary nucleus
9) Projection to inferior colliculus, where the signals can trigger motor structures
10) Projection to MGN in thalamus
11) Projection to A1 in superior temporal lobe

Question 14

Describe the topographic organization of the cochlea

Answer 14

Hair cells for high frequencies are located close to the oval window and lower frequencies are located toward the end of the cochlea

Question 15

What is tonotopic organization?

Answer 15

The organization of the A1 is tonotopic. The rostral part responds to lower frequencies and the caudal part to higher frequencies.

Question 16

How can we locate the sounds we hear? Name two ways.

Answer 16

1) interaural time difference: coincidence detectors in medial superior olive must receive input simultaneously to be activated

2) Interaural intensity difference = head causes acoustic shadow. Louder sound on left triggers more activity in left superior olive and only this signal will be processed

Question 17

What are the neural pathways for vision?

Answer 17

1) Cornea/pupil/lens focus and filter light
2) Retina contains rods and cones photoreceptors that transform light into neuronal signals
3) Receptors to bipolar cells to ganglion cells
4) Ganglion cells form optic nerve in blind spot
5) Optic nerve half crosses in optic chiasm
6) Projection to LGN and pulvinar in thalamus
7) LGN projects to V1 (left visual field ends up on the right)

Question 18

What is the difference between rods and cones photoreceptors?

Answer 18

Cones allow high intensity color view, highest amount in fovea
Rods allow low levels of light

Few cones per bipolar cell but many rods per bipolar cell

Question 19

What do the following areas respond to: LGN-V1-V2-V4-V5/MT?

Answer 19

LGN: light
V1: simple forms, edges
V2: more complex forms
V4: color
V5: movement

Question 20

What happens to the receptive fields when going up in the visual system?

Answer 20

Receptive fields become larger across visual systems

Question 21

What is cortical magnification?

Answer 21

The size of each unit area is disproportionately represented in visual cortex, where the fovea has the largest area

Question 22

What happens when you have damage in rods/cones?

Answer 22

Decreased sharpness in vision, increased sensitivity to light, impaired color vision, blind spots in visual field, partial loss of peripheral vision

Question 23

What is hemianopia?

Answer 23

Lesion in optic chiasm that causes blindness of an entire side of the visual field

Question 24

What happens when there is a lesion in V1?

Answer 24

It causes blindness in the part of the visual field that projects to damaged area. No entire blindness because of retinotopic mapping

Question 25

What happens when there is a lesion in V4?

Answer 25

This leads to achromatopsia, where everything is seen in greyscale

Question 26

What happens when there is a lesion in V5?

Answer 26

This leads to akinetopsia, where everything is seen as a series of pictures

Question 27

What does the flicker fusion experiment point out?

Answer 27

Perception is not always reality. When presented with fast flickering of red and green, the circle is perceived to be yellow

Question 28

What is multimodal perception and how does the McGurk effect relate to this?

Answer 28

Multimodal perception is the integration of information from all sensory modalities.

McGurk effect = perception of speech is severely influenced by what you see. Visual is the dominant sense

Question 29

Where does multimodal perception take place?

Answer 29

Superior colliculus in midbrain combines visual+auditory input.
Superior temporal lobe (STS) is responsible for McGurk effect

Question 30

What is synesthesia?

Answer 30

Abnormal activation and connectivity patterns where senses get mixed (smelling color)

Question 31

What is cortical plasticity and what is cross-modal plasticity?

Answer 31

Cortical plasticity = functional reorganization due to experiences. Violin player has more cortical representation of left hand

Cross-modal plasticity = if sensory system is absent, inputs from other sensory systems expand their cortical recruitment. The other senses then get better at sensing

Question 32

What happens if GABA level is low and what are the consequences for cortical plasticity if that is the case?

Answer 32

If GABA is low, neurons will respond to a wider range of stimuli
If that is the case, there can be more cortical plasticity