Chapter 3- Spatial Vision: From Spots to Stripes

Question 1

Contrast

Answer 1

The difference in luminance between an object and the background, or between lighter and darker parts of the same object.

Question 2

Acuity

Answer 2

The smallest spatial detail that can be resolved at 100% contrast.

Question 3

Cycle

Answer 3

For a grating, a pair consisting of one dark bar and one bright bar.

Question 4

Visual Angle

Answer 4

The angle subtended by an object at the retina.

Question 5

Sine Wave Grating

Answer 5

A grating with a sinusoidal luminance profile.
- The light intensity in such gratings varies smoothly and continuously across each cycle.

Question 6

Vertical Meridian Asymmetry

Answer 6

Visual acuity in peripheral vision is not uniform- it falls off more rapidly along the vertical midline of the visual field than along the horizonal midline. We also have better acuity a fixed distance below the midline of the visual field than above.

Question 7

Visual Acuity

Answer 7

Distance at which a person can just identify the letters/ Distance at which a person with “normal” vision can just identify the letters.

Question 8

Amblyopia

Answer 8

A developmental disorder characterized by reduced spatial vision in an otherwise healthy eye, even with proper correction for refractive error. Also known as lazy eye.

Question 9

Minimum Visible Acuity

Answer 9

Refers to the smallest object that one can detect.

Question 10

What are the types of acuity?

Answer 10

1) Minimum Visible Acuity
2) Minimum Resolvable Acuity
3) Minimum Recognizable Acuity
4) Minimum Discriminable Acuity

Question 11

Minimum Resolvable Acuity

Answer 11

Refers to the smallest angular separation between neighboring objects that one can resolve.

Question 12

Minimum Recognizable Acuity

Answer 12

Refers to the angular size of the smallest feature that one can recognize or identify.

Question 13

Minimum Discriminable Acuity

Answer 13

Refers to the angular size of the smallest change in a feature (e.g., a change in size, position, or orientation) that one can discriminate.

Question 14

Spatial Frequency

Answer 14

The number of grating cycles (e.g., changes in light and dark) per unit of visual angle (usually specified in degree) in a given unit of space.

Question 15

Cycles per Degree

Answer 15

The number of grating cycles per degree of visual angle.

Question 16

Contrast Sensitivity Function (CSF)

Answer 16

A function describing how the sensitivity to contrast (defined as the reciprocal of the contrast threshold) depends on the spatial frequency (size) of the stimulus.

Question 17

Contrast Threshold

Answer 17

The smallest amount of contrast required to direct a pattern.

Question 18

Fourier Analysis

Answer 18

A mathematical procedure by which any signal can be separated into component sine waves at different frequencies. Combining the sine waves (Fourier synthesis) will reproduce the original signal.

Question 19

Phase

Answer 19

The position of grating relative to a fixed position measured in degrees, where one complete cycle is 360 degrees.

Question 20

Filter

Answer 20

An acoustic, electric, electronic, or optical device, instrument, computer program, or neuron that allows the passage of some range of parameters (e.g., orientations, frequencies( and blocks the passage of others.

Question 21

Lateral Geniculate Nucleus (LGN)

Answer 21

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 22

Magnocellular Layer

Answer 22

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

Question 23

Parvocellular Layer

Answer 23

Any of the top four neuron-containing layers of the lateral geniculate nucleus, the cells of which are physically smaller than those in the bottom two layers.

Question 24

Koniocellular Layer

Answer 24

A neuron located between the magnocellular and parvocellular layers of the lateral geniculate nucleus. This layer is known as the koniocellular layer.

Question 25

Contralateral

Answer 25

Referring to the opposite side of the body or brain.

Question 26

Ipsilateral

Answer 26

Referring to the same side of the body or brain.

Question 27

Topographical Mapping

Answer 27

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

Question 28

Primary Visual Cortex, (VI), Area 17, or Striate Cortex

Answer 28

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.

Question 29

Cortical Magnification

Answer 29

The amount of cortical area (usually specified in millimeters) developed to a specific region (e.g., 1 degree) in the visual field.

Question 30

Eccentricity

Answer 30

The angular distance from the fovea (the region of highest visual acuity).

Question 31

Perceptual Consequences of Cortical Magnification

Answer 31

1) Visual acuity declines in an orderly fashion with eccentricity.

Question 32

Why is the foveal representation in the cortex so highly magnified?

Answer 32

The visual system must make a trade-off. High resolution requires a great number of resources: a dense array of photoreceptors, one-to-one lines from photoreceptors to retinal ganglion cells, and a large chunk of striate cortex. Thus, we have evolved a visual system that provides high resolution in the center and lower resolution in the periphery.

Question 33

Visual Crowding

Answer 33

The deleterious effect of clutter on peripheral object recognition.

Question 34

What was Hubel and Wiesel’s most fundamental discovery?

Answer 34

Discovered that the receptive fields of striate cortex neurons are not circular, as they are in the retina and LGN. Rather, they are elongated. As a result, they respond much more vigorously to bars, lines, edges, and gratings than to round spots of light.

Question 35

Orientation Tuning

Answer 35

The tendency of neurons in striate cortex to respond optimally to certain orientations and less to others.

Question 36

How are the circular receptive fields in the LGN transformed into the elongated receptive fields in the striate cortex?

Answer 36

… studies have shown that the arrangement of LGN inputs is indeed crucial for establishing the orientation selectivity of striate cortex cells. However, other evidence suggests that neural interactions (e.g., lateral inhabitation) within the cortex also play an important role in the dynamics of orientation tuning.

Question 37

Ocular Dominance

Answer 37

The property of the 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 38

Simple Cells

Answer 38

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

Question 39

Complex Cells

Answer 39

A cortical neuron whose receptive field does not have clearly defined excitatory and inhibitory regions.

Question 40

End-Stopping

Answer 40

The process by which a cell in the cortex increases its firing rate as the length of a bar increases until the bar fills up its receptive field, and then it decreases its firing rate as the bar is lengthened further.

Question 41

Columns

Answer 41

A vertical arrangement of neurons. Neurons within a single column tend to have similar receptive fields and similar orientation preferences.

Question 42

Hypercolumn

Answer 42

A 1-millimeter block of striate cortex containing two sets of columns, each covering every possible orientation (0-180 degrees), with one set preferring input form the left eye and one set preferring input from the right eye.

Question 43

CO Blobs

Answer 43

Regular arrays of “blobs” spaced about 0.5 millimeter apart in the striate cortex (VI), so named because their presence is visualized by staining with the enzyme cytochrome oxidase (CO). They may function in color perception.

Question 44

Adaptation

Answer 44

A reduction in response caused by prior or continuing stimulation.

Question 45

Tilt Aftereffect

Answer 45

The perceptual illusion of tilt, produced by adaptation to a pattern of given orientation.

Question 46

What does the transfer effect of adaptation effects imply?

Answer 46

Implies that selective adaptation occurs in cortical neurons…

Question 47

Spatial-Frequency Channels

Answer 47

A pattern analyzer, implemented by an ensemble of cortical neurons, in which each set of neurons is tuned to a limited range of spatial frequencies.

Question 48

What does the multiple spatial-frequency model of vision imply?

Answer 48

Implies that spatial frequencies that stimulate different pattern analyzers will be detected independently, even if the different frequencies are combined in the same image.

Question 49

Why would the visual system use spatial frequency filters to analyze images?

Answer 49

One important reason may be that different spatial frequencies emphasize different types of information.

Question 50

Critical Period

Answer 50

A phase in the life span during which abnormal early experience can alter normal neuronal development.

Question 51

Strabismus

Answer 51

A misalignment of the two eyes such that a single object in space is imaged on the fovea of one eye and on a nonfoveal area of the other (turned) eye.

Question 52

Anisometropia

Answer 52

A condition in which the two eyes have different refractive errors (e.g., one eye is farsighted and the other not).

Question 53

What limits the development of acuity and contrast sensitivity?

Answer 53

The primary postnatal changes in the retina concern differentiation of the macular region. (See page 90)