midterm Flashcards
myopia
axial: eyeball is too long = focus before the retina = cannot see far
refractive: too much refraction = focus before the retina = cannot see far
hyperopia
eyeball is too short = focus beyond the retina = cannot see close
astigmatism
irregular lens = cannot see close/far depending on where light falls on the retina
presbyopia
lens hardens with age and has difficulty accommodating = cannot see close
isomerization
light binds to opsin, retinal changes shape = electrical signals
- retinal detaches from opsin = visual pigment bleaching
- visual pigment regeneration = retinal must return to bent shape and re-attach to opsin to become light-sensitive again
detached retina
separated retinal and opsin cannot re-combine to become light sensitive = blindness in that area of the visual field
purkinje shift
rods are most sensitive to shorter wavelengths and have lower thresholds = during dark adaptation, we become more sensitive to shorter wavelengths (things appear more blue/green)
ratio of Na+ to K+ inside and outside the cell
Na+ is 10x more concentrated outside the cell
K+ is 20x more concentrated inside the cell
convergence
rods converge onto RGCs = compression of information, higher sensitivity
cones do not = visual acuity, less sensitivity
what does lateral inhibition explain?
- how RGCs are excitatory-enter inhibitory-surround using photoreceptors and horizontal/amacrine cells
- the Hermann Grid illusion (lateral inhibition on four sides in the periphery because of larger receptive fields)
- Mach bands/Chevreul illusion
describe how light reaches the retina and each hemisphere
- left side of left visual field - nasal retina of left eye - right area V1
- right side of left visual field - temporal retina of right eye - right area V1
- left side of right visual field - temporal retina of left eye - left area V1
- right side of right visual field - nasal retina of right eye - left area V1
feature detectors
- in area V1
simple cortical cells - orientation
complex cells - orientation-specific moving in a certain direction
end-stopped cells - angles/corners/lines of a particular length with a particular direction of movement
inverse projection problem
an image on the retina can correspond to many different stimuli (different shapes can project the same image)
so the brain has to guess, computer is bad at solving this
what can’t structuralism explain?
apparent movement (sensation not present)
illusory contours
Gestalt grouping principles
- similarity
- proximity
- good continuation
- closed forms
- common fate
- simplicity/pragnanz
- common region
- uniform connectedness
- symmetry
global image features
- naturalness
- roughness (small elements vs. smooth)
- openness
- expansion (convergence of lines)
- colour
Helmholtz’s Theory of Unconscious Inference
perceptions comes from unconscious assumptions (likelihood principle, Bayesian inference)
to solve the inverse projection problem
apparent motion
Phi phenomenon, movies
still activates area MT
motion aftereffects
waterfall effect, short-term selective adaptation
induced motion
clouds over moon = moon appears to move (larger object passes over a small object = small object appears to move
eyes following a moving object according to Gibson’s approach
local disturbance in optic array (background objects getting occluded, background stays stationary = object moving)
eyes stationary, object moves across field according to Gibson
local disturbance in optic array
eyes scan a scene according to Gibson
global optic flow (everything moves at once = no movement)
eyes following an object in movement according to corollary discharge
motor signal to eyes = corollary discharge signal to comparator (no image displacement signal) = movement perceived (receives only one signal)
object moves across field while eyes are stationary according to corollary discharge
image displacement signal to comparator (no motor signal to eyes = no corollary discharge signal) = movement perceived (one signal)
eyes scan a scene according to corollary discharge
motor signal to eyes = corollary discharge to comparator + image displacement signal to comparator = no movement perceived (receives two signals)
Reichardt detector
- direction-sensitive circuit
- output unit multiplies signals from A and B
- A has a delay unit (first cell in the circuit)
- signals must reach the output unit at the same time for movement to be perceived
- found in area MT
inferotemporal cortex
complex objects (end-point of ventral pathway)
fusiform face area (FFA)
part of area IT
faces/expertise hypothesis
lateral occipital complex (LOC)
part of area IT
any kind of object (not textures or scrambled parts)
parahippocampal place area (PPA)
part of area IT
spatial layout, navigation, locations, familiar places
extrastriate body area (EBA)
part of area IT
bodies and body parts
middle temporal area
part of the dorsal stream of visual processing (area V5)
motion
superior temporal sulcus
biological motion
medial temporal lobe (MTL)
memory (hippocampus, entorhinal cortex, parahippocampal cortex)
extensions from IT cortex reach MTL
anterior auditory cortex
most responsive to pitch (pitch neurons)
superior olivary nucleus
contains ITD detectors/coincidence detectors for the Jeffress model
ventrolateral/ventral posterior nucleus of the thalamus
touch relay area in the thalamus
contains centre-surround neurons
nucleus of the solitary tract
part of the brain stem for processing taste
