sensation and perception

sensory receptors

specialized cells that transduce sensory energy into neural activity

vision

light energy produces chemical energy

auditory

air pressure produces mechanical energy

somatosensory

mechanical energy

taste and olfaction

chemical molecules

receptive fields

region of sensory space in which a stimulus modifies a receptor’s activity

not evenly distributed

sensory receptors are ——————— across the body or its organs

receptor density

essential for determining the sensitivity of a sensory system

density example

more tactile receptors on the fingers than on the arm

neural relays

allow sensory systems to interact

cortex, intervening neurons

all receptors connect to the ————- through a sequence of ——————-

visual receptors

→ thalamus → cerebral cortex

auditory receptors

→ hindbrain → midbrain → thalamus → cerebral cortex

somatosensory receptors

→ spinal cord → brainstem → thalamus → cerebral cortex

how is sensory information encoded?

by action potentials traveling across the peripheral nerves to the CNS

neocortex

represents the sensory field of each modality as a spatially organized neural representation of the external world

homunculus

reflects the topographic map in the sensorimotor cortex, dispropotionately large areas control the body parts we use to make the most-skilled movements

sensation

registration of physical stimuli from the environment by the sensory organs

perception

subjective interpretation of sensations by the brain

cornea

clear outer covering

iris

opens and closes to allow more or less light, hole in it is the pupil

lens

focuses light, bends to accomodate near and far objects

retina

light-sensitive surface at the back of the eye; consists of neurons and photoreceptor cells

retina purpose

• translates light into action potential

• discriminates wavelengths (colors)

• works in a wide range of light intensities

fovea

region at the centre of the retina that is specialized for high acuity, receptive field at the centre of the eye’s visual field

acuity

vision is better in the center of the visual field than at the margins, or periphery

blindspot

includes region of the retina (optic disc) where axons forming the optic nerve leave the eye and where blood vessles enter and leave, has no photoreceptors

papilledema

swollen optic disc, may be due to high intracranial pressule or inflammation of the optic nerve, can cause loss of vision

rods

• more numerous than cones

• sensitive to low levels of light

• used mainly for night vision

• one type of pigment only

cones

• highly responsive to bright light

• specialized for color and high visual acuity

• in the fovea only

• three types of pigment

three types of cone pigments

absorb light over a range of frequencies

blue cones

• 419 nm

• short wavelength

• fewer cones

green cones

• 531 nm

• middle wavelength

• equal number as red

red cones

• 559 nm

• long wavelength

• equal number as green

the eye works correctly when ——————— passes through the ———— and is focused on the receptor surface

sufficient light, lens

bipolar cell

recieves input from photo receptors

horizontal cell

links photoreceptors and bipolar cellsa

amacrine cells

links bipolar cells and ganglion cells

retinal ganglion cells (RGC)

gives rise to the optic nerve

glaucoma

damages optic nerve, most common cause of irreversible blindness

two types of ganglion cells

m-cell & p-cell

magnocellular cell (m-cell)

• magno- large

• recieves input primarily from rods

• sensitive to light and moving stimulus

parvocellular cell (p-cell)

• parvo-small

• recieves input primarily from cones

• sensitive to color

optic chiasm

• junction from optic nerves from each eye

• axons from the nasal (inside) half of each retina cross over to the opposite side of the brain

• axons from the temporal (outer) hald od each retina remain on the same side of the brain

geniculostriate system

projections from the retina to the lateral geniculate to the visual cortex

tectopulvinar system

projections from the retina to the siperior colliculus to the pulvinar (thalamus) to the parietal and visual areas

retinohypothalamic tract

• synapses in the tinty superchiasmatic nucleus in the hypothalamus

• roles in regulating circadian rhythms and in the pupillary reflex

striate cortex

• primary visual cortex

• two visual paths emerge; one to parietal lobe and one to temporal lobe

dorsal visual stream

• pathway that originates in occipital cortex and projects in the parietal cortex

• the how pathway (how action is to be guided towards objects)

ventral visual stream

• pathway that originates in occipital cortex and projects in temporal cortex

• the what pathway (identifies object)

occipital cortex

composed of at least six visual regions

primary visual cortex (V1; striate cortex)

striate cortex recieves input from lateral geniculate nucleus

secondary visual cortex (V2-V5; extrastriate cortex)

visual cortex outside the striate cortex

extrastriate cortex

remaining occipital visual areas, each region processes specific features of visual information

blob (V1)

• region in the visual cortex that contains color-sensitive neurons

• revealed by staining for cytochrome oxidase

interblob (V1)

• region that separates blobs

• participates in the perception of form and motion

visual field

region of the visual world that is seen by the eyes

each responds to stimulatio on just a small circular patch of the retina

RGC

coding location

light falling on one place on the retina will activate one ganglion cell, and light falling on another place will activate a different ganglion cell

corpus callosum

connects the two hemispheres of the brain but only specific brain structures

seeing shape

neurons at each level of the visual system have distincltly different characteristics and functions

during neuronal representation, each —————————— is represented by a spike

action potential

retinal ganglion cells

• respond only to the presence or absence of light, not to shape

• concentric circle arrangement (periphery)

on-center cells

• excited when light falls on the center portion of the receptive field; inhibited when light falls on the surround of the receptive field

• light across while receptive fields produces weak excitation

off-centre cells

• excited when light falls on the surround of the receptive field; ihibited when light falls on the centre of the receptive field

• light across the whole receptive field produces weak inhibition

baseline

12 spikes per second

a small spot of light is likely to produce activity in both

on and off-centre ganglion cells

luminance contrast

the amount of light reflected by an object relative to its surroundings

what does luminance contrast do?

allows input from RGCs to tell the brain about shape

complex cells

are maximally excited by bars of light moving in a particular direction through the receptive field

hypercomplex cells

are like complex cells, maximally responsive to moving bars, have strong inhibitory area at one end of the receptive field

what are cells maximally excited by?

complex visual stimuli (e.g. faces or hands)

stimulus equivalence

recognizing that an object is the same across different viewing orientations

posterior parietal cortex

• involved in processing visual information for action: the how-to stream

  • neurons in this area are silent to visual stimulation when a person is under anesthesia

monocular blindness

destructon of the retina or optic nerve of one eye, producing loss of sight in that eye

homonymous hemianopia

blindness of an entire left or right visual field

quadrantanopia

blindness of one quadrant of the visual field

scotoma

small blind spot in the visual field caused by a small lesion or migraines of the visual cortex

agnosia

not knowing

visual-form agnosia

inability to recognize objects or drawings of objectsc

color agnosia (achromatopsia)

inability to recognize colours

face agnosia (prosopagnosia)

inability to recognize faces

injury to the what pathway

different types of agnosia

injury to the how pathway

optic ataxia

optic ataxia

• deficit in the visual control of reaching and other movements

• damage to the parietal cortex

• retention of the ability to recognize objects normally

simple cells

receptive field with a rectangular on-off arrangement