lec 3 - visual perception

the where system

-Is concerned with determining the locations of objects and guiding our actions in response -Involves an occipital-parietal pathway -Damage to this system can result in problems with reaching for seen objects

the what system

-Is concerned with the identification of objects -Involves an occipital-temporal pathway -Damage to this system can result in visual agnosia (inability to recognize objects)

cones

-higher sensitivity -higher acuity -color sensitive -in the fovea (lots of light, detail, color)

rods

-lower sensitivity -lower acuity -color blind -periphery of the retina (low light, broad, black and white)

what neurons are in the eye

-photoreceptors -bipolar cells -ganglion cells and the optic nerve

how do those 3 come together to work

-rods and cones stimulate bipolar cells which excite ganglion cells -the ganglion cells converge to the optic nerve; this is the nerve that leaves the eye and carries info to the brain -the info travels to the thalamus to the LGN -from there the info is transmitted to the primary projection area for vision in the occipital lobe

what is the retina made up of?

3 layers: -rods / cones (which are the photoreceptors) -bipolar cells -ganglion cells

Linear Perspective

A monocular cue for perceiving depth; parallel lines seem to converge as they get farther and farther from the viewer -ex: looking on a straight road, and noticing the road narrows as it goes off in the distance.

monocular distance cues

Features of the visual stimulus that indicate distance even if the stimulus is viewed with only one eye.

edge enhancement

Lateral inhibition exaggerates the contrast at edges

size constancy

Perception of an object as the same size regardless of the distance from which it is viewed -If your far away from the object you're viewing, then the image cast onto your retinas by that object will be relatively small. If you approach the object, then the image size will increase. You manage to achieve size constancy — you correctly perceive the sizes of objects despite the changes in retinal-image size created by changes in viewing distance. -Helmholtz proposed that you achieve constancy through an unconscious inference—multiplying the image size by the distance.

lateral inhibition

The pattern of interaction among neurons in the visual system in which activity in one neuron inhibits neighboring neurons' responses.

what neurons are in the cortex

V1 = the primary visual area located in the occipital lobe

binding problem

With parallel processing, different aspects of a single object (e.g., shape, color, movement) are analyzed in different parts of the visual system. How the brain reunites these different features into a coherent, integrated perception of the objects in the visual scene is referred to as the binding problem.

shape constancy

a tendency to see an object as the same shape no matter what angle it is viewed from -ex: the door viewed straight on casts a rectangular image on your retina; the door viewed from an angle casts a trapezoidal image. but, you generally achieve shape constancy.

excitatory neurotransmitters

cause the neurons to fire more.

Pictorial cues

cues to depth perception that are used to convey depth in drawings and paintings -in pics it creates an impression of depth on a flat surface

Motion Parallax

depth cue where projected images of nearby objects move more than those of distant ones -ex: cars driving in the lane right next to me are going just about my speed. The cars on the opposite side of the high way appear to be moving slower because they are farther away in my visual field.

light entering eye....

enters through cornea and the cornea and lens refract the light rays to make a image on the retina -the iris opens or closes to control the amount of light that reaches the retina

magnocellular cells

have larger receptive fields and respond more strongly to changes in stimulation. -have very high temporal resolution but low spatial resolution so it can provide a blurry but moving image of an object

parvocellular cells

have smaller receptive fields and tend to continue firing as long as the stimulus is present. -shape is detected by them which have high color spatial resolution and permit us to see fine detail

Interposition

if one object partially blocks our view of another, we perceive it as closer

what neurons are in the thalamus

lateral geniculate nucleus (LGN)

inhibitory neurotransmitters

neurotransmitters cause the neurons to fire less

do Photoreceptors communicate directly with ganglion cells.

no

bottom-up processing

no prior knowledge, stimulus influences perception

serial processing

opposite of parallel processing, steps are carried out one at a time

How does object recognition work

parallel processing: -simple visual features -object recognition -knowledge all at same time

top-down processing

prior knowledge influences perception

single cell recording

procedure through which investigators can record, moment by moment, the pattern of electrical changes within a single neuron -neurons can vary in how often they fire, and when investigators record the activity of a single neuron, they're interested in the cell's firing rate

The ________ is the part of the eye involved in transducing light energy into neural energy

retina

how our mind creates objects:

similarity, proximity, good continuation, closure, simplicity

Optic Flow

the pattern of stimulation across the entire visual field changes as you move forward -ex: your sitting in a car and are looking out the window. You see trees appear to move backwards. This motion is optic flow.

blind spot

the point at which the optic nerve leaves the eye, creating a "blind" spot because no receptor cells are located there

texture gradient

the tendency for textured surfaces to appear to become smaller and finer as distance from the viewer increases

brightness constancy

the tendency to perceive the apparent brightness of an object as the same even when the light conditions change

spatial position

the visual areas processing features like shape, color, and motion each know the spatial position of the object.

neural syncrhony

the visual areas processing features of the same object fire in a synchronous rhythm with each other.

Ganglion cells are spread uniformly across the retina, and all of their axons converge to form the bundle of nerve fibers called the optic nerve.

true

Akinetopsia

unable to perceive motion

binocular disparity

your eyes look out on the world from slightly different positions so each eye has a slightly different view. This difference between the two eyes' views is called binocular disparity, and it provides important info about distance relationships in the world.