Visual pathway & Spatial vision

Question 1

Cornea

Answer 1

the first tissue that light will encounter is the cornea, it is transparent meaning it is made of a highly ordered arrangement of fibers and contains no blood vessels or blood which would absorb light

Question 2

Ciliary muscles

Answer 2

responsible for stretching and compressing the zonules of zinn

Question 3

Zonules of zinn

Answer 3

responsible for changing the lens to intake the light

Question 4

Iris

Answer 4

the colored part of the eye , consisting of a muscular diaphragm surrounding the pupil and regulating the light entering the eye by expanding and contracting the pupil

Question 5

Fovea

Answer 5

A small pit located near the center of the macula and containing the highest concentration of cones and no rods. It is the portion of the retina that produces the highest visual acuity and serves as the point of fixation

Question 6

How images are projected onto the retina

Answer 6

REVERSED TO RIGHT -> LEFT AND UPSIDE DOWN!!

Question 7

photoreceptors

Answer 7

light sensitive receptor in retina

Question 8

Rods

Answer 8

a photoreceptor specialized for night vision

Question 9

Cones

Answer 9

a photoreceptor specialized for daylight vision, fine visual acuity and color

Question 10

Bipolar cells

Answer 10

Bipolar cells are the ones spoken about in class when discussing convergence and are primarily thought of as the connection between rods/cones and ganglion cells- furthermore they are distinct as midget/ non midget cells where the former receive information from a single cone rather than multiple receptors.

Question 11

Horizontal cells

Answer 11

Squeezed between rods/cones and bipolar cells these cells are important for creation of center-surround receptive fields

Question 12

Visual angle

Answer 12

the angle that would be formed by lines going from the top and bottom of a cycle on the page, passing through the center of the lens and ending on the retina

Question 13

Fovea

Answer 13

~2º diameter of central vision; no rods, only cones; 1% retina but ~50% of visual cortex!!!

Question 14

Para-fovea

Answer 14

area immediately surrounding fovea (~4-5º around the center)

Question 15

Periphery

Answer 15

the area beyond fovea

Question 16

Blind spot

Answer 16

location of optic nerve that leaves the retina about 3 degrees diameter.

Question 17

Eccentricity

Answer 17

the distance between the retinal image and the fovea many functions depend on the eccentricity of the stimulus, such a acuity, color, and motion

Question 18

Distribution of rods and cones in terms of retinal location

Answer 18

Rods are in the periphery and cones are primarily in the fovea

Question 19

Pupil size

Answer 19

the diameter of the pupil can vary by about a factor of 4; pupil size accounts for only a small part of the visual system’s overall ability to adapt to light/dark conditions

Question 20

Photopigment regeneration

Answer 20

Second mechanism for achieving a large sensitivity range is provided by the way photopigments are used up and replaced in receptor cells

Question 21

Dim Lighting

Answer 21

As the overall light level inc the number of photons starts to overwhelm the system: photopigment molecules can’t be regenerated fast enough to detect all the photons hitting the photoreceptors ties into opposite neurons

Question 22

Difference between rods and cones

Answer 22

responses to different wavelengths (cones can detect different colors [S,M,L]; rods only have one kind of photopigment called rhodopsin)
In their distribution across retina (rods in periphery, cones in fovea)

Question 23

Retinal ganglion cells

Answer 23

These cells are responsible for telling the brain what the eye sees; this is accomplished through two pathways: the M absorb information from multiple converging bipolar cells whereas those in the P pathway synapse with single bipolar cells which lead to individuals cones and less information.

Question 24

Visual acuity

Answer 24

the smallest spatial detail that can be resolved at 100% contrast

Question 25

Difference in acuity between foveal and peripheral vision

Answer 25

Rods and cones in the periphery are packed together less tightly than in the fovea and her many receptors converge on each ganglion cell making acuity much poorer in the periphery than the fovea!

Question 26

The acuity-sensitivity trade-off

Answer 26

Cones have higher acuity because of their ability to see detail and color whereas rods are more sensitive as they can see in the dark, recover faster in the dark and allow you to see movement in dim lighting (this may have evo psych implications)

Question 27

Sine-wave gratings

Answer 27

a grating with a sinusoidal luminance profile as shown in figure

Question 28

Sensitivity of retinal ganglion cells to:

Answer 28

responds (ON to light on-center and OFF to dark on-center) greatly to 0 degrees (upward sine wave) and 180 degrees (downward sine wave). Flat line response at 90 degrees and 270 degrees (responding to half light/dark in center).

Question 29

phase

Answer 29

the relative position of a grating

Question 30

spatial frequencies

Answer 30

the number of grating cycles (i.e., dark and bright bars) in given unit of a space.

Question 31

Lateral Geniculate Nuclei (LGN)

Answer 31

a structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex.

Question 32

Topographical mapping

Answer 32

the orderly mapping of the world in the lateral geniculate nucleus and the visual cortex

Question 33

Magnocellular layers

Answer 33

either of the bottom tow neuron-containing layers of the lateral geniculate nucleus, the cells of which are physically larger than those in the top four layers.

Question 34

Parvocellular layers

Answer 34

any of the top fou neuron-containing layers of the lateral geniculate nucleus, the cells of which are physically larger than those in the top four layers

Question 35

Primary visual cortex (V1)

Answer 35

the area of the cerebral cortex of the brain that receives direct inputs from the lateral geniculate nucleus, as well as feedback from other brain areas, named because it has white stripes.

Question 36

Topographical mapping

Answer 36

Adjacent things are adjacent. Systematic mapping of visual field. It is not just a bigger version of the LGN. A major and complex transformation fo visual information takes place in the striate cortex.

Question 37

Cortical magnification factor

Answer 37

Foveal representations are ‘expanded’ relative to peripheral representations. The amount of cortical area devoted to a specific region

Question 38

Receptive field

Answer 38

The region in space in which stimuli will activate a neuron.

Question 39

Cells in V1

Answer 39

a cortical neuron whose receptive field has clearly defined excitatory and inhibitory regions

Question 40

Simple cells

Answer 40

Respond to edges/bars of specific orientations • This is a different receptive field structure than the center/surround structure of cells in LGN - orientation

•   spatial frequency (related to scale)
•   phase sensitive

Question 41

Complex cells

Answer 41

Orientation specific (like simple cells). But, they are most active when the oriented stimuli is moving. Some cells respond to motion in any direction, some respond to motion only in very specific directions -  orientation

•   spatial frequency
•   phase insensitive
• motion direction

Question 42

End-stopped cells

Answer 42

Like complex cells but respond to lines of only a certain length - Orientation specific

• Motion specific
• Length specific
• corners
• motion direction

Question 43

V1 Organization

Answer 43

The cortex is organized into ‘columns’ that represent specific values of a feature. A column is a vertical arrangement of neurons. Neurons within a single column tend to have similar receptive fields and similar orientation preference.

Question 44

location columns

Answer 44

Columns of neurons that all have their receptive field on roughly the same location on the retina. Run perpendicular to the cortex

Question 45

orientation columns

Answer 45

Column of cells that all prefer the same orientation

• Aligned perpendicular to cortex (like location columns

Question 46

ocular dominance columns

Answer 46

property of receptive fields of striate cortex neurons by which they demonstrate a preference, responding somewhat more rapidly when a stimulus is presented in one eye than when it is presented in the other.

Question 47

Hypercolumns

Answer 47

Complete set of orientation and ocular-dominance columns for a given retinal location. Like a ‘super-column’ that contains all the column types
A 1-millimeter block of striate c degrees, w/one sets of columns, each covering every possible orientation (0-180 degrees), with one set preferring input from the left eye and one set preferring input from the right eye.

Question 48

Spatial frequency

Answer 48

essentially, the amount of ‘stuff’ present per unit length • V1 cells are also tuned to spatial frequency
• Similar to orientation tuning

Question 49

Contrast sensitivity function

Answer 49

The psychophysical contrast threshold is a function of spatial frequency

Question 50

Ventral stream (the “What” pathway)

Answer 50

Processes shape/form

Question 51

Dorsal stream (the “Where” pathway)

Answer 51

Parietal lobe. Processes location, and HOW to interact with it based on location (used to plan action). • Location (e.g. left vs. right)

Question 52

Extrastriate cortex

Answer 52

V2, V3, V4, MT & IT

Question 53

V2

Answer 53

Illusory contours

Question 54

V3

Answer 54

Maybe combining info for 3D percepts

Question 55

V4

Answer 55

Color

Question 56

MT

Answer 56

Motion

Question 57

IT

Answer 57

Shapes, form, faces