On columns and pathways

Question 1

optic chiasm

Answer 1

visual signals from both eyes leave the back of the eye in the optic nerve and meet at the optic chiasm - an x-shaped bundle of fibers on the ventral surface of the brain, inferior to the hypothalamus. at the optic chiasm, some of the fibers cross to the contralateral brain hemisphere

Question 2

double dissocation

Answer 2

in one person, damage to one areas of the brain causes function A to be absent while function B is present. In another person, damage to another area of the brain causes function B to be absent while function A is present. The conclusion is that the 2 functions can be disrupted and operate independently of one another

Question 3

Visual agnosia

Answer 3

inability to recognize/describe common objects, faces or pictures, even though the ability to navigate through the world persists. Caused by damage to the occipitotemporal region.

Question 4

Optic ataxia

Answer 4

inability to reach accurately towards visual targets or adjust their grasp to reflect the size of the target object, even though the ability to recognize them persists. Caused by damage to the posterior parietal region.

Question 5

Visual prosopagnosia

Answer 5

inability to recognize faces. Different features of the faces can be perceived, but the person whose face this is cannot be indetified. Developmental prosopagnosia is something that is present from birth

Question 6

inferotemporal (IT) cortex

Answer 6

receptive fields of neurons in the IT cortex are large enough to encompass whole objects in the visual field. evidence for faces and hands and face selectivity

Question 7

medial temporal lobe (MTL)

Answer 7

some of the signals leaving the IT cortex reach the medial temporal lobe (MTL), more specifically the parahippocampal cortex, the entorhinal cortex and the hippocampus. also respond to memories of concepts.

Question 8

Extrastriate cortex

Answer 8

areas outside the striate cortex to which the visual signals travels from V1. They are also separately known as V2, V3, V4, and V5.

Question 9

What (ventral) pathway

Answer 9

The signal from the occipital lobe continues through the what pathway and the how pathway. A pathway leading from V1 to the temporal lobe. Important for determining an object’s identity. Sensitive to form, pattern and color.

Question 10

How (dorsal) pathway

Answer 10

a pathway leading from V1 to the parietal lobe. Important for directing an action with regard to a visual stimulus (e.g., pick up an object). Is faster, but colorblind.

Question 11

selective adaptation

Answer 11

constantly viewing a stimulus with a specific feature causes neurons that respond to that feature to adapt, decreasing their firing rate if the stimulus is presented again immediately

Question 12

selective rearing experiments

Answer 12

animals are raised in an environment that contains only certain types of stimuli with the expectation that neurons that respond to these stimuli will become more prevalent

Question 13

location columns

Answer 13

the striate cortex is organized into location columns, which are perpendicular to the cortical surface. All neurons within a location column have their receptive fields at approximately the same location in the retina.

Question 14

orientation columns

Answer 14

the striate cortex is also organized into orientation columns. All neurons within an orientation column respond best to approximately the same orientation. Adjacent orientation columns have cells with slightly different preferred orientations.

Question 15

Ocular dominance

Answer 15

V1 neurons have a preference for stimuli presented in one eye rather than the other eye.

Question 16

ocular dominance columns

Answer 16

the striate cortex is also organized into ocular dominance columns, again perpendicular to the cortical surface. 1mm in the cortex contains oriention columns that represent the entire range of orientations. One location columns i large enough to contain orientation columns that cover all possible orientations

Question 17

Hypercolumn

Answer 17

a location column with all of its orientation columns. There are 2 ocular dominance columns within each hypercolumn, one of the left eye and one for the right.

Question 18

Simple cortical cells

Answer 18

neurons in the striate cortex, whose receptive fields have a side by side excitatory and inhibitory areas. These cells respond best to bars of lights, edges and lines of particular orientations

Question 19

Orientation tuning curve

Answer 19

a graphical representation of the relationship between line orientation and firing of a neuron.

Question 20

2 proposed mechanisms for how the circular receptive fields in the LGN are transformed to elongated receptive fields in the striate cortex

Answer 20

1) LGN cells that feed into a cortical cell are all in a row
2) neural interactions (e.g., lateral inhibition) between the cortex also play an important role for this

Question 21

complex cells

Answer 21

neurons in the striate cortex, which do not have clearly defined excitatory & inhibitory regions. Some of them respond best to moving bar-like stimuli with specific orientations. Respond best to a particular direction of movement.

Question 22

End-stopped cells

Answer 22

neurons in the striate cortex, which respond to moving lines of a specific length or to moving corners or angles

Question 23

feature detectors

Answer 23

Simple, complex and end-stopped cells are called feature detectors, because they fire in response to specific features of a stimulus (e.g., orientation, direction of movement)

Question 24

Primary visual (striate) cortex

Answer 24

from the LGN, the visual signal travels to the Primary visual cortex. Locatioons on the striate cortex correspond to location on the retina and the visual world

Question 25

Retinotopic/topographical map

Answer 25

the orderly mapping of the world and the retina on the visual cortex and the LGN

Question 26

Cortical magnification

Answer 26

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 27

Eccentricity

Answer 27

distance from the fovea (in degrees)

Question 28

lateral geniculate nuclei (LGN)

Answer 28

After the optic chiasm, 90% of the tracts proceed to the LGN - thalamic nuclei in each cerebral hemisphere. Neurons in the LGN have center-surround receptive fields, just like the retinal ganglion cells. LGN output to the cortex is smaller than the input from the retina. LGN receives more feedback from the cortex than input from the retina. Each LGN has 6 layers and looks like a stack of pancakes that is bent in the middle. Layer 1,4 & 6 receive input from the contralateral eye. Layers 2,3, &5 receive input from the ipsilateral eye

Question 29

magnocellular layers

Answer 29

the bottom layers are called magocellular layers. Receive input from M ganglion cells. Respond to large, fast-moving objects.

Question 30

parvocellular layers

Answer 30

receive input from P ganglion cells. responsible for processing the details of stationary stimuli

Question 31

Koniocellular cells

Answer 31

a neuron located between the magnocellular and parvocellular layers of the LGN. The layer is known as the koniocellular layer.

Question 32

superior colliculus

Answer 32

plays a role in controlling eye movements