7- Mechanisms of Perception: Hearing, Touch, Smell, Taste, and Attention

primary sensory cortex

a system is the area of sensory cortex that receives most of

its input directly from the thalamic relay nuclei of that system.

secondary sensory cortex

comprises the areas of the sensory cortex that receive most

of their input from the primary sensory cortex of that system

or from other areas of secondary sensory cortex of the

same system

Association cortex

any area of cortex that

receives input from more than one sensory system.

1. hierarchical organization

2. functional segregation

3. parallel processing

The interactions among these three types of sensory

cortex and among other sensory structures are characterized

by three major principles:

Sensation

process of detecting

the presence of stimuli,

Perception

higherorder

process of integrating, recognizing, and interpreting

complete patterns of sensations

Primary

input mainly from thalamic relay nuclei

Secondary

input mainly from primary and secondary cortex within the sensory system

Association

input from more than one sensory system, usually from secondary sensory cortex

Sensation

detecting a stimulus

Perception

understanding the stimulus

Functional segregation

distinct functional areas within a level 

Parallel processing

simultaneous analysis of signals along different pathways

Sounds

are vibrations

of air molecules that stimulate the

auditory system; humans hear only those

molecular vibrations between about 20

and 20,000 hertz

Pure tones

sine wave vibrations

Fourier analysis

mathematical procedure for breaking down complex waves

into their component sine waves

fundamental frequency

highest frequency

of which the various component frequencies of

a sound are multiples

missing fundamental

This important

aspect of pitch perception

tympanic membrane (the eardrum)

Sound waves enter the auditory canal of the ear and then cause the - to vibrate

Sound wave > eardrum > ossicles (hammer, anvil, stirrup) > oval window

soundwaves in the ear

oval window

Vibration of the - sets in motion the fluid of the cochlea

organ of Corti

The cochlea’s internal membrane, the -, is the auditory receptor organ

Basilar membrane

auditory receptors, hair cells, are mounted here

Tectorial membrane

rests on the hair cells

cranial nerve VIII (the auditory-vestibular nerve).

Stimulation of hair cells triggers action potentials in the auditory nerve, the -

round window

The vibrations of

the cochlear fluid are ultimately dissipated

by the -, an elastic membrane in

the cochlea wall.

tonotopic

the organization of the auditory system is

largely -

ipsilateral cochlear nuclei

The axons of each auditory nerve synapse in the -

semicircular canals

the receptive organs of the vestibular

system

vestibular system

carries

information about the direction and intensity

of head movements, which helps us

maintain our balance.

superior olives

From there, many projections lead to the - on both sides of the brain stem 

lateral lemniscus

From there, axons project via the - to the inferior colliculi

medial geniculate nuclei

Axons then project from the inferior colliculi to the - of the thalamus

primary auditory cortex

Thalamic neurons then project to the -

medial superior olives

Some neurons in the - respond to slight differences in the

time of arrival of signals from the two ears (

lateral superior olives

some neurons in the - respond

to slight differences in the amplitude of sounds from the

two ears

superior colliculus

The medial and lateral superior olives project to the

-

retinotopically

The superficial layers of the superior colliculi, which

receive visual input, are organized -

temporal lobe

Auditory cortex is located in the -

core region

  includes primary cortex

belt

surrounds the core region

parabelt areas

Secondary cortex outside the belt referred to as 

anterior auditory pathway

more involved in identifying

sounds (what

posterior auditory pathway

more involved in locating sounds (where)

rats

Lesions of auditory cortex in - results in few permanent hearing deficits

monkeys and humans

Lesions in - hinder sound localization and pitch discrimination

Conductive deafness

hearing impairments associated

with damage to the ossicles

nerve deafness

hearing impairments associated with damage to the cochlea or auditory nerve

Partial cochlear damage 

results in loss of hearing at particular frequencies

Cochlear implants

bypass damage

to the auditory hair cells by converting sounds picked up by

a microphone on the patient’s ear to electrical signals, which

are then carried into the cochlea by a bundle of electrodes.

Somatosensations

Sensations from your body are referred to as

1. exteroceptive system

2. proprioceptive system

3. interoceptive system

the somatosensory system—is three separate but interacting

systems:

exteroceptive system

which senses external

stimuli that are applied to the skin

proprioceptive system

which monitors information about the position of the

body that comes from receptors in the muscles, joints, and

organs of balance

interoceptive system

provides

general information about conditions within the body

(e.g., temperature and blood pressure).

free nerve endings

simplest cutaneous receptors

free nerve endings

neuron endings with no specialized

structures on them which are particularly sensitive

to temperature change and pain.

Pacinian corpuscles

Adapt rapidly, large and deep; onion-like

Pacinian corpuscles

Respond to sudden displacements of the skin

Merkel’s disks

gradual skin indentation

Ruffini endings

gradual skin stretch

stereognosis

identification

of objects by touch is called

dorsal roots

The neural fibers that carry information

from cutaneous receptors and other somatosensory

receptors gather together in nerves and enter the spinal cord via the-

dermatome

The area of the body that is innervated

by the left and right dorsal roots of a given segment

of the spinal cord is called a

dorsal-column medial-lemniscus system

carry information about touch and proprioception,

dorsal-column medial-lemniscus system

First synapse in the dorsal column nuclei of the medulla

Anterolateral system

tends to carry information about

pain and temperature.Anterolateral system

Anterolateral system

Synapse upon entering the spinal cord

1. spinothalamic

2. spinoreticular

3. spinotectal

The anterolateral

system comprises three different tracts:

postcentral gyrus

When stimulation was applied to the -, the patients reported somatosensory sensations in various parts of their bodies

somatotopic

the human primary somatosensory cortex (SI) is- — organized according to a map of the body

surface

somatosensory homunculus

This somatotopic map is

commonly referred to as the

SII

receives most of its

input from SI and is thus regarded as secondary

somatosensory cortex.

association cortex

Much of the output from SI and SII goes to - in posterior parietal lobe

bimodal neurons

Neurons that respond to activation of two different sensory systems

Astereognosis

inability to recognize objects by touch

Asomatognosia

the failure to recognize parts of one’s own body (the 

Anosognosia

the failure of neuropsychological

patients to recognize their own sympto

contralateral neglect

the tendency not to respond to stimuli

that are contralateral to a right-hemisphere injury.

rubber-hand illusion

the feeling that an extraneous object, in this case a

rubber hand, is actually part of one’s own body

Descending pain control

pain can be suppressed by cognitive and emotional factors

periaqueductal gray (PAG)

Electrical stimulation of the - has analgesic effects

anterior cingulate cortex

The cortical area that has been most frequently linked

to pain is the

Neuropathic pain

Severe chronic pain in the absence of a recognizable pain stimulus

Neuropathic pain

Likely from pathology of nervous system linked to an injury

Olfaction (smell)

Detects airborne chemicals

Gustation (taste)

Responds to chemicals in the mouth

Flavor

Molecules of food excite both smell and taste receptors

and produce an integrated sensory impression termed

Pheromones

chemicals that influence

the physiology and behavior of conspecifics

olfactory mucosa

Receptor cells embedded in the - of the nose

1,500;1,000

Rats and mice have about - receptors; Humans have almost

olfactory glomeruli

The axons of olfactory receptors terminate in discrete

clusters of neurons that lie near the surface of the olfactory

bulbs—these clusters are called the -

chemotopic

The poorly understood topographic

organization of the olfactory

bulbs has been termed a

- map

piriform cortex

The - is considered to be primary

olfactory cortex,

limbic pathway

The - is thought to mediate the

emotional response to odors;

thalamic- orbitofrontal

the -

pathway is thought to mediate the conscious perception

of odors.

taste buds

Taste receptor cells are found on the tongue

and in parts of the oral cavity; they typically

occur in clusters of 50 to 100 called -

papillae

taste buds are often located around

small protuberances called -

presynaptic cell

In each taste

bud, only one of the receptor cells, the

-, synapses onto the neuron

carrying signals away from the bud; communication

among the other cells of a taste

bud appears to occur via gap junctions

g-protein-linked receptor proteins

A major advance in the study of taste transduction

occurred with the discovery of various - embedded in the membranes of taste

receptor cells.