the visual system: retinal processing (2.1) Flashcards
light (2 ways of thinking)
particles of energy (photons); waves of evergy
visible light (in humans)
waves of electromagnetic energy between 380-760 nm
wavelength vs intensity
wavelength: color; shorter = blue, longer = red
intensity: brightness; depends on perception
convex lens
bends light towards a focal point; slows down light rays (perception is 180 degree rotation)
iris
donut-shaped bands of contractile tissue that give the eye its color; a round muscle with a hole in the center of it (pupil is its absence); regulates the amount of light reaching the retinas
changes the size of the pupil
illumination
sensitivity vs acuity
sensitivity: the ability to detect the presence of dimly lit objects
acuity: the ability to see the details of objects
lens
focuses light on the retina
ciliary muscles
alter the shape of the lens as needed
accommodation
the process of adjusting the lens; allows us to see near and far objects simultaneously (lens flattens with distant objects)
convergence
eyes must turn slightly inward when viewing objects (where the light rays intersect, we are going to get an idea of how far away an object is)
binocular disparity
the difference in the position of the same image on the two retinas (greater for close objects than for distant objects)
retina (job, “inside-out”, layers (5))
retina: converts light to neural signals (after light passes through the pupil and lens); conducts the signals toward the CNS and participates in their processing
“inside-out”: light passes through several (4) cell layers before reaching its receptors
layers: receptors (capture light), horizontal cells (lateral communication), bipolar cells (pathway from rods and cones to ganglion cells), amacrine cells, retinal ganglion cells (have the axons,;take info in and send it to brain)
fovea
high-acuity area at the center of the retina; best vision; dominated by cones
blind spot
no receptors where the retinal ganglion cell axons exit the eye (optic nerve); cannot physically see any light; nasal part of retina; fixed by completion (filling in)
duplex theory of vision
rods and cones mediate different kinds of vision
rods (scotopic vision)
high sensitivity (nighttime vision) low-acuity (high convergence); black and white, no color
cones (photopic vision)
low sensitivity (daytime vision); high-acuity (low convergence); one-to-one; color
spectral sensitivity in rods vs cones
rods: sensitive to shorter wavelengths; most sensitive to blue light
cones: sensitive to longer wavelengths; most sensitive to yellowish light (i.e., the sun)
types of cones (3)
red: most sensitive to long wavelengths (L)
green: sensitive to the mid-range of wavelengths (M)
blue: sensitive to short wavelengths (S)
theories of color vision (2)
component (trichromatic) theory: color is encoded by the ratio of activity in the three kinds of receptors (cones)
opponent-process theory: color processed in an antagonistic manner (red/green, blue/yellow, white/black)
saccades
involuntary and quick eye movements (type of fixational eye movement)
temporal integration
bits of visual information are summated over time [to form a complete image]
visual transduction
conversion of light to neural signals by visual receptors (physical stimulus to PSP); indirect transduction where photon of light hits receptor then wanders over to the G protein which closes Na+ channel (depolarized in the dark and hyperpolarized in the light)
