biopsych ch 6: vision & chemoreception

transduction

process of converting outside stimuli into neural activity

electromagnetic spectrum

range of frequencies of electromagnetic radiation often denoted as different wavelengths

cornea

light enters first through here

clear outer surface of eye that bends light

responsible for 80% of focusing images

lens

responsible for controlling 20-30% of eye’s focusing power

retina

3 layers of cells at the back of the eye

PIG: photoreceptor cells, intermediate cells, ganglion cells

ganglion cells

light hits these cells first

get info from intermediate & photoreceptor

intermediate cells

transmit info from photoreceptor to ganglion

bipolar, amacrine, horizontal cells

none can transduce light to APs

rods

black & white photoreceptor cells; found in periphery of retina

responsible for scotopic vision (low-light)

cones

color photoreceptor cells; found with greatest density in fovea of retina

photopic vision (well-lit)

fovea

small portion of center of retina

highly populated with cones

trichromatic theory

color vision theory that assumes there are 3 types of cones: red, green, blue

sensitive to different wavelengths of light

opponent process theory

color vision theory that assumes cells in retina & thalamus send 2 different signals if excited/inhibited

lateral inhibition

process in retina where intermediate cells accentuate transitions between light & dark by inhibiting neurons next to them

receptive field

refers to all cells in visual system that influence another cell

center-surround

type of receptive field; looks like a donut (circle within circle)

on-center

type of ganglion cell; responds most when light strikes center of receptive field

inhibited when light strikes periphery

off-center

type of ganglion; responds most when light strikes periphery

inhibited when light strikes center

lgn

lateral geniculate nucleus; on either side of thalamus that gets info from ganglion, sends info to primary visual cortex (PVC)

map of retina

retinotopic map

location of cells in LGN & PVC correspond to map of retina

simplified: LGN = map of retina

P cells

parvocellular; type of ganglion cell. gets info from fovea, sends info to parvocellular layer in LGN

sends projections to layers 3, 4, 5, 6

process color, shape, details

M cells

magnocellular; type of ganglion. gets info from rods in periphery, sends signals to magnocellular

projects to layers 1 & 2

movement, low-intensity light

PVC

primary visual cortex; area of occipital lobe that first gets info from LGN

also called V1/striate cortex

more complex than LGN

orientation, movement, angles, size

neuronal tuning

hypothesis that individual brain cells are tuned to specific stimuli

simple cells

cells of PVC; have rectangular receptive fields, sensitive to lines of specific orientations

complex cells

PVC cells that get info from simple cells

respond selectively to lines of specific orientations that move in specific directions

hypercomplex cell

PVC cells that receive info from simple + complex

also called ‘end-stop cells’

respond to lines w/ specific orientations, angles, lengths

dorsal stream

visual pathway that starts in M layer of LGN

travels through V1, V2, V3, V5, then to parietal lobe

perception of movement

akinetopsia

motion blindness

result of damage to dorsal stream; V5

ventral stream

visual pathway that starts in P layer of LGN then to V1, V2, V4, then to inferior temporal lobe

perception of color & object recognition

cerebral achromatopsia

inability to perceive color

damage to ventral, V4

inferior temporal lobe

(IT) area of TL w/ cells that are “tuned” to responding to complex shapes & faces

medial temporal lobe

(MT) area of TL that is V5 in dorsal

perception, memory, motion

fusiform gyrus

area of IT that contains cells that respond to shapes, textures, faces

prosopagnosia

face blindness

damage to fusiform gyrus

linear process

theory that visual perception goes from simple (line) to complex (shape) in 1 direction

parallel processing

theory that visual perception is the product of many areas of visual system working & affecting each other

odorant

chemical signals found in air that affect olfactory receptor neurons in nose

ORN

olfactory receptor neurons; bipolar neurons that have cell bodies within olfactory epithelium & signal up into olfactory bulb through olfactory nerve

glomeruli

round structures in olfactory bulb where connections are formed between terminal end of ORN & dendrites from mitral cells

mitral cells

cells in olfactory system that get info from ORN & send axons to entorhinal cortex, pyriform regions, & amygdala

tastant

chemical molecules found in food that dissolve in saliva & affect chemoreceptors on tongue, initiating perception of flavors

taste papillae

bumps on surface of tongue, esophagus, & palate

taste receptor cells

clusters of cells on tastebuds that detect tastants in saliva

supertasters

people that are sensitive to bitter flavors