Vision : part 2

Question 1

How vision scientists measure visual acuity

Answer 1

Smallest visual angle of a cycle of grating.

Question 2

visual angle

Answer 2

Unit used to measure the size of an object in your visual field (regardless of its absolute distance or size).
- Since there is a direct one-to-one correspondance between the size of the object in your visual field and on your retina, the visual angle is the unit used to measure the size of an object on the retina.

Question 3

Cycle

Answer 3

If you consider a grating of alternating black and white stripes, a cycle is one black and one white stripe

Question 4

Better vision = ____smaller/larger visual angle required to identify a grating cycle.

Answer 4

Smaller

Question 5

For most people, visual acuity corresponds to…

Answer 5

One minute of arc, or 1/60 of one degree of visual angle.

Question 6

The visual angle is _____dependent/independent of the actual size of the object in the world.

Answer 6

Independent

Question 7

A large object in the distance, may take up the same degree of visual angle as a _____ small object

Answer 7

Close

Question 8

~10% of retinal outputs bypass the LGN and project to the …

Answer 8

Superior colliculus (SC)

Question 9

The superior colliculus (SC) has a _______ layout of the contralateral visual field.

Answer 9

Retinotopic

Question 10

Blindsight Phenomenon

Answer 10

• proves you need cortical processing for conscious vision
• Seen in patients with damage to the primary visual cortex.

Question 11

Unconscious visual perception in blindsight

Answer 11

• Patients respond to visual stimuli without conscious awareness
• Can accurately guess line orientation, object movement, and spatial location.

Question 12

Blindsight is due to…

Answer 12

SC projections bypassing the primary visual cortex.

Question 13

Primary visual cortex / Area V1/ Striate cortex

Answer 13

• Essential for conscious vision
• In occipital lobe

Question 14

Secondary visual cortex is also called…

Answer 14

• Area V2
• Extrastriate cortex

Question 15

Retinotopic Mapping

Answer 15

The spatial organization of the visual field is preserved in the LGN, with neighboring areas of the retina mapping onto neighboring areas of the primary visual cortex (V1) in a point-by-point manner.

Question 16

More cortical space in V1 is dedicated to ____central/peripheral vision compared

Answer 16

Central

Question 17

The fovea has a higher density of _____ cells than the peripheral retina.

Answer 17

Ganglion

Question 18

The LGN has twice as many ______ layers as magnocellular layers.

Answer 18

Parvocellular

Question 19

Cortical Magnification

Answer 19

V1 further amplifies the total number of neurons devoted to central vs. peripheral vision where the central 10° of the visual field (~1% of the total visual field) occupies 50% of V1’s surface

Question 20

Retinal ganglion cells are very good at extracting the spatial frequency of the visual input, but not the ______

Answer 20

Orientation

Question 21

By combining information from several _____ cells, it is possible to detect the orientation of lines

Answer 21

retinal ganglion cells

Question 22

Retinal ganglion cells with a ON center OFF surround receptive field diagonal line organization

Answer 22

If they are presented with a line that touches all the on centers of all the retinal ganglion cells : they will fire at the same time, transmit the info to the LGN then the V1 neurons

Question 23

Neurons in the V1 have a preferred ______ .

Answer 23

Orientation. They will respond less and less as it gets farther from this preferred orientation

Question 24

The response to stimulus is ______ if only one retinal ganglion receptive field is touched in its on-center

Answer 24

Moderate

Question 25

Adaptation

Answer 25

Looking at a pattern of stripes for a certain time will “tire” the V1 neurons and shift the balance in the opposite direction

Question 26

Tilt after-effect

Answer 26

1. Habituate a diagonal line 2. Present vertical lines again. 3. The pattern of a population of V1 neurons activity that are preferentially tuned to 45° will exhibit a decreased firing rate compared to before the habituation occurred. 4. The ones that are not close to the 45 degree pattern won't change their response pattern because they haven't habituated. As a result, the whole pattern of activity across the population of V1 neurons is tilted to the right.

Question 27

Hypercolumn

Answer 27

Contains cells responding to 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 28

In an area of __mm, you will have columns that have a preferential response for all possible orientations, that preferentially respond to input from the left eye and other columns that preferentially respond to input from the right eye

Answer 28

1

Question 29

Each hyper column as all of the tools necessary, to perceive all ___ and ______ in any area of your visual field

Answer 29

Lines and orientations

Question 30

Simple Cells

Answer 30

- Respond to light with increasing intensity when the orientation matches their receptive field. - Orientation selectivity represented by tuning curves(firing rate vs. line orientation).

Question 31

Complex cells

Answer 31

- Detect motion in their receptive fields. - Selective for line orientation and often for movement direction.

Question 32

Receptive Field Properties of complex cells

Answer 32

- Larger and less well-defined than simple cells - Some span a whole hemifield, responding to specific orientations/movements across this area.

Question 33

End-Stopped Cells (specializied complex cells)

Answer 33

- Respond best to moving bars of a specific length - Do not fire if bars exceed their receptive field. - Involved in detecting angles, corners, and boundaries.

Question 34

the visual information reaching our retina is __2D/3D

Answer 34

2D

Question 35

We do not get depth directly from our ____ : the visual system is prearranged for this

Answer 35

Senses

Question 36

Pictorial Cues

Answer 36

Depth cues that can be inferred from a 2D static image, using monocular vision. - occlusion, relative size, familiar size, linear perspective, texture gradient, aerial perspective and shading

Question 37

Occlusion

Answer 37

A depth cue where one object partially blocks another, indicating that the blocked object is farther away. - one of the most reliable depth cues.

Question 38

Accidental Viewpoint

Answer 38

A specific line of sight that creates an ambiguous or misleading depth interpretation

Question 39

Relative size

Answer 39

A comparison of size between items without knowing the absolute size of either one. All things being equal, we assume that smaller objects are farther away from us than larger objects.

Question 40

Familiar size

Answer 40

A comparison of size between items when knowing the absolute size one of the items. In this case, we can infer the absolute distance because we know the exact size of one of the objects.

Question 41

Relative height

Answer 41

For objects touching the ground, those higher in the visual field appear to be farther away.

Question 42

Shadows

Answer 42

For objects that are floating in the air, shadows can help infer their relative heights.

Question 43

Objects that are further away are seen with a ____ angle relative to our body

Answer 43

Wider

Question 44

It is when our sight is parallel to the ground, i.e. perpendicular to our body, that we experience the greatest feeling of ______.

Answer 44

Distance

Question 45

Texture gradient

Answer 45

A depth cue based on the geometric fact that items of the same size form smaller, closer spaced images the farther away they get.

Question 46

Linear perspective

Answer 46

Lines that are parallel in the three-dimensional world will appear to converge in a two-dimensional image as they extend into the distance

Question 47

Vanishing point

Answer 47

Apparent point at which parallel lines receding in depth converge.

Question 48

Aerial perspective

Answer 48

Implicit understanding that light is scattered by the atmosphere. More light is scattered when we look through more atmosphere. Thus, more distant objects appear fainter, bluer, and less distinct.

Question 49

Shading

Answer 49

Variations in light and shadow on a surface provide information about its shape, depth, and orientation. Objects with gradual shading changes appear curved, while sharp contrasts suggest edges or discontinuities in depth. The brain assumes light comes from above, influencing depth perception.

Question 50

Dynamic cues of depth

Answer 50

Depth information can be extracted from the movement of images on the retina.

Question 51

Kinetic depth effect

Answer 51

When the observer is stationary, depth is perceived through the relative movement of objects at different depths , particularly strong for rotating spheres, where luminance variations further enhance depth perception

Question 52

Motion parallax

Answer 52

Images closer to the observer move faster across the visual field than images farther away.The brain uses this information to calculate the distances of objects in the environment

Question 53

When we move our eyes to track a particular object, it seems that objects beyond the fixation point are moving in the ____ direction

Answer 53

Same

Question 54

Optic flow

Answer 54

Apparent motion of objects in a visual scene produced by the relative motion between the observer and the scene.

Question 55

Objects in the _____ ___ ______ won’t move when we look at them

Answer 55

focus of expansion (right in front, parallel to our eyes)