Chapter 4

Question 1

Optic chiasm

Answer 1

An x-shaped bundle of fibers on the underside of the brain, where nerve fibers activated by stimulation of one side of the visual field cross over to the opposite side of the brain.

Question 2

Visual field

Answer 2

The visual field is determined based on where the person is fixating; anything to right of the point of central focus is the right visual field (processed by the left hemisphere), and anything to the left is the left visual field (processed by the right hemisphere). Importantly, both eyes can see both visual fields.

Question 3

Lateral geniculate nucleus (LGN)

Answer 3

The nucleus in the thalamus (of each hemisphere) that receives inputs from the optic nerve and, in turn, communicates with the cortical receiving area for vision. Around 90% of the signals from the retina proceed to the LGN. Neurons in the LGN have center-surround receptive fields.

Question 4

Superior colliculus

Answer 4

An area in the brain that is involved in controlling eye movements and other visual behaviors. This area receives about 10% of the ganglion cell fibers that leave the eye in the optic nerve.

Question 5

Function of the LGN (theories)

Answer 5

• Regulate neural information as it flows from the retina to the cortex (comes from the observation that the signal sent from the LGN to the cortex is smaller than the input the LGN receives from the retina)
• The feedback information the LGN receives back from the brain may play a role in determining which information is sent up to the brain (the LGN is that it receives more signals from the cortex than from the retina)

Question 6

Visual receiving area

Answer 6

The area of the occipital lobe where signals from the retina and LGN first reach the cortex. The visual receiving area is also called the striate cortex, because it has a striped appearance when viewed in cross section, or area V1 to indicate that it is the first visual area in the cortex.

Question 7

Simple cortical cells

Answer 7

A neuron in the visual cortex that responds best to bars of a particular orientation. By flashing moving lines of light on different places in the retina, Hubel and Wiesel (1965) found cells in the striate cortex with receptive fields that, like center-surround receptive fields of neurons in the retina and LGN, have excitatory and inhibitory areas. However, these areas are arranged side by side rather than in the center-surround configuration. There are neurons that respond to all of the orientations that exist in the environment.

Question 8

Orientation tuning curve

Answer 8

A function relating the firing rate of a neuron to the orientation of the stimulus. It is determined by measuring the responses of a simple cortical cell to bars with different orientations.

Question 9

Complex cells

Answer 9

A neuron in the visual cortex that responds best to moving bars with a particular orientation. Further, many complex cells respond best to a particular direction of movement. Because these neurons don’t respond to stationary flashes of light, their receptive fields are indicated not by pluses and minuses but by outlining the area that, when stimulated, elicits a response in the neuron.

Question 10

End-stopped cells

Answer 10

A cortical neuron that responds best to lines of a specific length or to moving corners or angles (moving in a particular direction).

Question 11

Feature detectors

Answer 11

A neuron that responds selectively to a specific feature of the stimulus such as orientation or direction of motion.

Question 12

Selective adaptation

Answer 12

When we view a stimulus with a specific property, neurons tuned to that property fire. The idea behind selective adaptation is that this firing causes neurons to eventually become fatigued, or adapt. Typically, sensitivity to the exposed stimulus is decreased.

Question 13

Physiology of selective adaptation

Answer 13

The adaptation causes two physiological effects:
1. the neuron’s firing rate decreases,
2. the neuron fires less when that stimulus is immediately presented again.

Question 14

Selective adaptation explanation

Answer 14

According to this idea, presenting a vertical line causes neurons that respond to vertical lines to respond, but as these presentations continue, these neurons eventually begin to fire less to vertical lines. Adaptation is selective because only the neurons that were responding to verticals or near-verticals adapt, and neurons that were not firing do not adapt.

Question 15

Contrast threshold

Answer 15

The intensity difference between two areas that can just barely be seen. This is often measured using gratings with alternating light and dark bars.

Question 16

How to measure selective adaptation

Answer 16

1. Measure a person’s contrast threshold
2. Adapt the person to one orientation by having the person view a high-contrast adapting stimulus for a minute or two. In this example, the adapting stimulus is a vertical grating
3. Remeasure the contrast threshold of all the test stimuli presented in step 1

Question 17

Selective adaptation vs. orientation selectivity curve

Answer 17

Adaptation selectively affects only some orientations, just as neurons selectively respond to only some orientations. The selective adaptation curve and the orientation tuning curve for a simple cortical neuron are very similar. This similarity support the idea that feature detectors play a role in perception. The selective adaptation experiment is measuring how a physiological effect (adapting the feature detectors that respond to a specific orientation) causes a perceptual result (decrease in sensitivity to that orientation).

Question 18

Selective rearing

Answer 18

The idea behind selective rearing is that if an animal is reared in an environment that contains only certain types of stimuli, then neurons that respond to these stimuli will become more prevalent. According to this idea, rearing an animal in an environment that contains only vertical lines should result in the animal’s visual cortex having simple cells that respond predominantly to verticals.

Question 19

Neural plasticity or Experience-dependent plasticity

Answer 19

A process by which neurons adapt to the specific environment within which a person or animal lives. This is achieved when neurons change their response properties so they become tuned to respond best to stimuli that have been repeatedly experienced in the environment.

Question 20

Selective adaptation vs. selective rearing

Answer 20

• Adaptation is a short-term effect. Presenting the adapting orientation for a few minutes decreases responding to that orientation.
• Selective rearing is a longer-term effect. Presenting the rearing orientation over a period of days or even weeks keeps the neurons that respond to that orientation active. Meanwhile, neurons that respond to orientations that aren’t present are not active, so they lose their ability to respond to those orientations.

Question 21

Use it or lose it experiment (Blakemore and Cooper, 1970)

Answer 21

Kittens were placed into striped tubes, so that each kitten was exposed to only one orientation (horizontal or vertical). The kittens were kept in the dark from birth to 2 weeks of age, at which time they were placed in the tube for 5 hours a day; the rest of the time they remained in the dark. When the kittens’ behavior was tested after 5 months of selective rearing, they seemed blind to the orientations that they hadn’t seen in the tube (didn’t play with sticks in the other orientation).

Question 22

Neurons of cats from Blakemore + Cooper’s experiment

Answer 22

Cats brought up in the vertical-lines tube had many neurons that respond best to vertical or near-vertical stimuli, but none that respond to horizontal stimuli. The horizontally responding neurons were apparently lost because they hadn’t been used. The opposite result occurred for the horizontally reared cats.

Question 23

Retinotopic map

Answer 23

A map on a structure in the visual system, such as the LGN or the cortex, that indicates locations on the structure that correspond to locations on the retina. In retinotopic maps, locations adjacent to each other on the retina are usually represented by locations that are adjacent to each other on the structure. The spatial representation of the visual scene on the cortex is distorted, with more space being allotted to locations near the fovea than to locations in the peripheral retina.

Question 24

Cortical magnification

Answer 24

Occurs when a disproportionately large area on the cortex is activated by stimulation of a small area on the receptor surface. One example of cortical magnification is the relatively large area of visual cortex that is activated by stimulation of the fovea. An example in the somatosensory system is the large area of somatosensory cortex activated by stimulation of the lips and fingers.

Question 25

Cortical magnification factor

Answer 25

The size of the cortical magnification effect. For example, the fovea represents 0.01% of the retinal area but 8-10% of the cortical map’s area.

Question 26

Cortical magnification and reading

Answer 26

The letter near where the person is looking, is represented by a much larger area in the cortex than letters that are far from where the person is looking. The extra cortical space provides the extra neural processing needed to accomplish tasks such as reading that require high visual acuity. The letter doesn’t appear larger, but it is seen with more detail.

Question 27

Location columns

Answer 27

The visual cortex is organized into location columns that are perpendicular to the surface of the cortex, so that all of the neurons within a location column have their receptive fields at the same location on the retina. When an electrode penetrates the cortex perpendicularly, the receptive fields of the neurons encountered along this track overlap. Location columns are around 1mm long.

Question 28

Orientation columns

Answer 28

A column in the visual cortex that contains neurons with the same orientation preference. Adjacent orientation columns have cells with slightly different preferred orientations. 1mm (size of 1 location column) represents the entire range of orientations.

Question 29

Location column and orientation columns

Answer 29

One location column is large enough to contain orientation columns that cover all possible orientations. Thus, a location column serves one location on the retina (all the neurons in the column have their receptive fields at about the same place on the retina) and contains neurons that respond to all possible orientations.

Question 30

Hypercolumn

Answer 30

In the striate cortex, unit proposed by Hubel and Wiesel that combines location, orientation, and ocular dominance columns that serve a specific area on the retina. A hypercolumn receives information about all possible orientations that fall within a small area of the retina; it is therefore well suited for processing information from a small area in the visual field.

Question 31

Tiling

Answer 31

The adjacent (and often overlapping) location columns working together to cover the entire visual field (similar to covering a floor with tiles). The idea that each part of a scene is represented by activity in many location columns means that a scene containing many objects is represented in the striate cortex by an amazingly complex pattern of firing.

Question 32

Extrastriate cortex

Answer 32

Collective term for visual areas in the occipital lobe and beyond known as V2, V3, V4, and V5; where the visual signal goes after being processed by V1. As we move from V1 to higher-level extrastriate areas, the receptive field sizes gradually increase.

Question 33

Ablation

Answer 33

Removal of an area of the brain. This is usually done in experiments on animals to determine the function of a particular area. Also called lesioning.

Question 34

Object-discrimination problem

Answer 34

The behavioral task used in Ungerleider and Mishkin’s experiment in which they provided evidence for the ventral, or what, visual processing stream. Monkeys were required to respond to an object with a particular shape.

Question 35

Landmark discrimination problem

Answer 35

The behavioral task used in Ungerleider and Mishkin’s experiment in which they provided evidence for the dorsal, or where, visual processing stream. Monkeys were required to respond to a previously indicated location.

Question 36

Ungerleider and Mishkin pathways

Answer 36

• In monkeys with an ablated temporal lobe, the object discrimination problem was very difficult. Ungerleider and Mishkin therefore called the pathway leading from the striate cortex to the temporal lobe the “what” pathway.
• In monkeys with an ablated parietal lobe, the landmark discrimination problem was hard to solve. Ungerleider and Mishkin therefore called the pathway leading from the striate cortex to the parietal lobe the “where” pathway.

Question 37

What vs. where pathways

Answer 37

• Ventral: Pathway that conducts signals from the striate cortex to the temporal lobe. Also called the what pathway because it is involved in recognizing objects.
• Dorsal: Pathway that conducts signals from the striate cortex to the parietal lobe. The dorsal pathway has also been called the where, the how, or the action pathway by different investigators.

Question 38

Limitations of the pathways

Answer 38

• the pathways are not totally separated but have connections between them
• signals flow not only “up” the pathway from the occipital lobe toward the parietal and temporal lobes but “back” as well. The “backward” flow of information, called feedback, provides information from higher centers that can influence the signals flowing into the system (part of top-down processing)

Question 39

Pathways and the LGN

Answer 39

Using the techniques of both recording from neurons and ablation, researchers found that properties of the ventral and dorsal streams are established by two different types of ganglion cells in the retina, which transmit signals to different layers of the LGN. Thus, the cortical ventral and dorsal streams can actually be traced back to the retina and LGN.

Question 40

Dorsal stream as a “How” pathway

Answer 40

Milner and Goodale propose that the dorsal stream is for taking action, such as picking up an object. Taking this action would involve knowing the location of the object, consistent with the idea of where, but it goes beyond where to involve a physical interaction with the object. Evidence supporting this idea is provided by the discovery of neurons in the parietal cortex that respond when a monkey looks at an object and when it reaches toward the object-

Question 41

Double dissociation

Answer 41

In brain damage, when function A is present and function B is absent in one person, and function A is absent and function B is present in another. Presence of a double dissociation means that the two functions involve different mechanisms and operate independently of one another. Ungerleider and Mishkin’s monkeys provide an example of a double dissociation.

Question 42

Neuropsychology - patient D.F.

Answer 42

D.F. was a woman who had damage to her ventral pathway. One result of her brain damage was that she was not able to match the orientation of a card held in her hand to different orientations of a slot. But when D.F. was asked to “mail” the card through the slot, she could do it. Thus, D.F. performed poorly in the static orientation-matching task but did well as soon as action was involved. We can interpret this as showing that there is one mechanism for judging orientation and another for coordinating vision and action.

Question 43

D.F and double dissociation

Answer 43

These results for D.F. are part of a double dissociation because there are other patients whose symptoms are the opposite of D.F.’s. These people can judge visual orientation, but they can’t accomplish the task that combines vision and action. As we would expect, whereas D.F.’s ventral stream is damaged, these other people have damage to their dorsal streams.

Question 44

Testing the pathways in healthy people

Answer 44

Psychophysical experiments that measure how people perceive and react to visual illusions have demonstrated the dissociation between perception and action. Participants were given 2 tasks:
- a length estimation task in which they were asked to indicate how they perceived the lines’ length by spreading their thumb and index finger
- a grasping task in which they were asked to reach toward the lines and grasp each line by its ends
The experiment found that he illusion works for perception (the length estimation task), but not for action (the grasping task).

Question 45

Inferotemporal (IT) cortex

Answer 45

An area of the brain outside Area V1 (the striate cortex), involved in object perception and facial recognition. The neurons in the IT cortex are at the apex of the ventral stream, and have the largest receptive fields (arge enough to encompass whole objects in one’s visual field). There are some neurons that respond best to hands, to faces, etc.

Question 46

Hippocampus

Answer 46

Subcortical structure in the brain that is associated with forming and storing memories.

Question 47

Case of H.M., no hippocampus

Answer 47

H.M. had his hippocampus on both sides of his brain removed in an attempt to eliminate epileptic seizures. The seizures stopped, but H.M. also lost his ability to store experiences in his memory. The hippocampus is crucial for the formation of long-term memories.

Question 48

Medial temporal lobe (MTL)

Answer 48

Some of the signals leaving the IT cortex reach structures in the medial temporal lobe (MTL), such as the parahippocampal cortex, the entorhinal cortex, and the hippocampus. These MTL structures are extremely important for memory. MTL neurons respond not only to the visual perception of specific objects or concepts, but also the memories of those concepts.

Question 49

Testing importance of MTL in memory and perception

Answer 49

Researchers had epilepsy patients view a series of videos while recording from neurons in the MTL. The clips showed famous people, landmarks, and nonfamous people and animals engaged in various actions. As the person was viewing the clips, some neurons responded better to certain clips. They then asked the patients to think back to any of the film clips they had seen while the experimenter continued to record from the MTL neurons. They found that a neuron that was activated by a specific video is also activated by the memory of that video.

Question 50

Flexible receptive fields

Answer 50

The visual system is flexible and neurons can change depending on changing conditions (their response can be affected by what is happening outside its receptive field).

Question 51

Contextual modulation

Answer 51

Change in response to a stimulus presented within a neuron’s receptive field caused by stimulation outside of the receptive field. The response to stimulation within the receptive field of a neuron can be affected by what’s happening outside the receptive field.