Lecture 4: sensation and perception

Question 1

Senses

Answer 1

the physiological capacities to provide input from the environment to our neurological system

Question 2

Sensation

Answer 2

the translation from information about the environment into patterns of neural activity

Question 3

perception

Answer 3

our sensory experience of the environment

Question 4

Although the senses work very differently, they have some anatomical and processing features in common.
Each sensory system:

Answer 4

Starts with an anatomical structure to collect, filter and amplify environmental information

has specializes receptors to transform the environment information in a neural signal that are passed along specific sensory nerve pathways

These nerves end up in the Thalamus and then go to a primary sensory region of the cortex (except olfactory nerve)

Question 5

Acuity

Answer 5

how good we can differentiate among stimuli within a sensory modality

acuity depends on:
the anatomical structure to collect the stimulus (dogs can move their ears independently to better capture sound waves)
The number and distribution of the receptors. acuity is best in the centre of the visual field because the fovea is packed with photoreceptors.

Question 6

our sensory systems (5)

Answer 6

olfaction: smell
gustation: taste
Somatosensation: touch
auditon: hearing
vision: sight

Question 7

Olfaction (smell)

The olfactory epithelium

Answer 7

odor molecules enter the nasal cavity
These molecules bind to bipolar receptors in the nasal mucosa (=The olfactory epithelium)

Question 8

Olfaction (smell) in the brain
glomeruli & olfactory cortex (pyriform cortex) & orbitofrontal cortex

Answer 8

The axons of the glomeruli from the olfactory nerve that projects to the primary olfactory cortex (pyriform cortex). from there the signal proceeds to the orbitofrontal cortex.

Question 9

Shape theory (docking theory) of olfaction

Answer 9

Odor molecules bind to some of the thousand different types of receptors because the shape of the molecule corresponds to the shape of the receptor (like a key fits a lock). The odor depends on which molecule binds to which receptor. however some molecules with similar shapes have very different odors

Question 10

Vibrational theory

Answer 10

Similarly shapes molecules have different molecular vibrations (at quantum level)

Question 11

olfaction and behavior

Answer 11

Men rated women as less attractive after smelling real tears:

Brain areas related to sexual arousal (hypothalamus & fusiform gyrus) showed a decreased BOLD response while watching emotionally evocative (erotic) clips after smelling real tears.

Question 12

Gustation (smell) way to the brain

papillae

Answer 12

on the tongue there are papillae and have taste buds.

food molecules (tastants) pass the tongue via the taste pores to the tase buds. each taste bud contains taste receptor cells.

molecules bind to receptor, the axons form the chorda tympani nerve. together with other nerves, this nerve forms the facial nerve VII and projects to the solitary tract nucleus in the brainstem.

from there the signal goes to the thalamus and the primary gustatory cortex in the insula.

Question 13

Gustotopic map

Answer 13

neurons in the gustatory cortex are organized meaning that their spatial organization follows a property of the environment or body

Question 14

gustation research in the thalamus showed:

Answer 14

when researchers recorded the thalamus they saw that neurons respond selectively to one taste (sour, sweet, bitter or umami)

Question 15

somatosensation (touch)

Answer 15

the perception of all mechanical stimuli that effect the body
- the interpretation of signals that indicate the position of the limbs and head (proprioception
- temperature
- pressure
-touch
-pain
-etc..

Question 16

somatosensation is caused by…

Answer 16

somatosensory receptors under the skin and at the musculoskeletal junctions (where all the muscle fibers meet)

Question 17

nociceptors

Answer 17

pain is sensed my the nociceptors (free nerve endings)

Question 18

somatosensation (touch) signal to brain

Answer 18

via the dorsal root ganglion, the signal travels through the spinal cord to the medulla and the contralateral side of the thalamus. the thalamus sends the signal to the primary somatonsensory cortex (the postcentral sulcus)

Question 19

somatotopic map

Answer 19

neurons in the primary somatosensory cortex are organized in a somatotopic map.

size of the representation is proportional to the sensitivity of the body part (hands are sensitive and have a relatively large representation in the brain)

Question 20

Audition (hearing

The peripheral auditory system: the external ear & the middle ear

Answer 20

The external ear: collect and focus sound energy

The middle ear: sound energy hits the eardrum (the tympanic membrane) that is connected to the three tiny bones: mallues, incus and stapes.

Stapes are connected to the cochlea via the oval window

Question 21

The internal ear

Answer 21

Cochlea consists of three chambers, all filles with fluid

Question 22

the basilar membrane

Answer 22

the basilar membrane inside the cochlea is embedded with hair cells (the tips of the hair cells are called sterocilia)

Question 23

tonotopic organization

Answer 23

depending on the frequency of the sound, different hair cells will move. the basilar membrane close to the oval window reacts to high frequencies; the membrane at the end of the cochlea (apex) react to low frequencies.

low tones travel far.

Question 24

The central auditory system

Answer 24

Signal from hair cells is propagated to the brain via the auditory nerve cell that first projects to the cochlear olivary complex. the signals from the left and right ear come together.

then to the inferior colliculus (orientation towards the sound) and medial geniculate complex.

Question 25

Localizing sounds:

interaural time difference

Answer 25

key idea: differences in length of path to neurons in the medial superior olive (MSO) create delay lines.

speed of sound is slow
neurons in the medial superior olive (MSO) function as coincidence detectors.

Question 26

Localizing sounds:

interaural intensity difference

Answer 26

head forms an obstacle for high frequencies. a stimulus is presented on the left will cause a higher activity in the left lateral superior olive (LSO). this activity will inhibit the activity coming from the right LSO
only activity from the left LSO is processed in higher centres

Question 27

Vision (sight)

photoreceptors

Answer 27

rods: primarily concerned with perception at very low levels of light
cones: perception at greater light intentsities. responsable for detail and colour percepts.

Question 28

rods and cones are not evenly distributed in the retina:

Answer 28

at fovea: mainly cones
away from the fovea: more rods

Question 29

Vision (sight)

acuity in vision

Answer 29

Acuity: how sharp your vision is (the discrimination ability)

is highest at the fovea and sharply decreases as a function of distance to the fovea.

example: it is easy to count the number of fingers if directly look at them, but impossible if you can only see them in the periphery.

Question 30

Vision (sight)

Fovea

Answer 30

your eyes five you a clear and color signal for what is present at the fovea. parafoveal: you only have fuzzy and no color information

Question 31

ipsilaterally

Answer 31

the optic fibers from the temporal half of the retina project ipsilaterally, and the nasal half crosses over the optic chiasm

Question 32

lateral geniculate nucleus (LGN)

Answer 32

90% of the retinogeniculate pathway projects to the lateral geniculate nucleus (LGN)

1% projects to the pulvinar, both the LGN and the pulvinar are involved in visual attention

Question 33

Geniculocortical pathway (optic radiation)

Answer 33

the LGN projects to the primary visual cortex V1

Question 34

primary visual cortex:
retinotopic organization

Answer 34

the spatial layout of the visual field that is projected on the retina is maintained in the thalamus and in V1

objects that are close to each other in the visual field (and hence the retina) are also represented close to each other in the primary sensory cortex.

Question 35

primary visual cortex:
cortical magnification

Answer 35

the size of each unit area of the retina is disproportionately represented in the visual cortex

visual information at the fovea occupies much larger area in the primary visual cortex compared to the parafoveal information.

Question 36

receptive field

Answer 36

visual neurons keep track of information about where objects are in space by their receptive fields

Question 37

Ganglion cells (retina) and LGN cells (thalamus)

Answer 37

respond to light going on and off in their receptive fields

Question 38

Receptive fields at the cortex

Answer 38

receptive fields at the cortex become more complex because a neuron in V1 receives input from multiple LGN cells. the receptive fields of neurons in V1 are edge detectors.

Question 39

Jennifer Aniston cells

Answer 39

The further you go in the visual stream the larger/more complex the receptive fields become

Jennifer Aniston cells: It activates when a person “sees, hears, or otherwise sensibly discriminates” a specific entity, such as their

Question 40

Functional organization of the visual cortex

hierarchical processing

Answer 40

simple cells (edge detectors) in V1 are combined to V2 to form complex cells. information in V2 is integrated in V3 to form hypercomplex cells.

the connections in the visual field cortex do not follow a nice hierarchy

Question 41

Functional organization of the visual cortex

analytic processing

Answer 41

Each visual area provides a map from the external environment, but each map represents different information (specialized processing)

Question 42

deficits in visual processing

Answer 42

achromotopsia: a condition characterized by a partial or total absence of color vision. People with complete achromatopsia cannot perceive any colors; they see only black, white, and shades of gray.
akinetopsia: “motion blindness”, which is a higher visual processing disorder from an extra-striate lesion, in which a patient has difficulty specifically perceiving objects in motion with variable severity and rarely complete.

Question 43

Flicker fusion

Answer 43

the frequency at which flikkering light can be perceived as continuous and is used to assess the processing of temporal vision.

Question 44

The enigma pattern

Answer 44

where in the brain does the activation correlate with our percept?

the illusion of motion activates the brain area related to motion processing V5!

Question 45

Multimodal perception

Answer 45

We use all availble information to converge to a coherent represention of the world. we integrate information from different sensory modalities to make sense of the world.

for multimodal integration to occur, the signals from different modalities need to be coincident in time and space

Question 46

Where in the brain does multimodal perception happen? animal

Answer 46

early studies on hamsters showed that neurons in the superior colliculus are very sensitive to the presentation of multimodal stimuli. (study of visual and auditory)

Question 47

Where in the brain does multimodal perception happen? human

Answer 47

The superior temporal sulcus (STS) is where different multimodal association has been found. related to the McGurk effect. (ba/ga)

Question 48

synseasthesia

Answer 48

when senses get mixed. when your brain routes sensory information through multiple unrelated senses, causing you to experience more than one sense simultaneously.

example: tasting words or linking colours to numbers and letters

Question 49

perceptual reorganization

Answer 49

The somatosensory cortex shows signs of plasticity

after removal of a finger, the brain area that used to represent that finger is now used to represent other nearby fingers.