Chapter 3 The Visual Brain

Question 1

Functional specialization

Answer 1

specialization of different neural pathways and different areas of the brain for representing different kinds of information

Question 2

Retinotopic mapping

Answer 2

Arrangement of neurons in the visual system whereby signals from retinal ganglion cells with receptive fields that are next to each other on the retina travel to neurons that are next to each other in each visual area of the brain

• Shows how retinal locations map onto a particular brain area
• Spatial relationships among retinal locations are preserved in the spatial pattern of processing areas
• Information from each location on the retina is processed in a specific location in each early brain area

Question 3

Optic chiasm

Answer 3

location where the optic nerves from the two eyes split in half, with half the axons from each eye crossing over to the other hemisphere of the brain

Question 4

Optic tract

Answer 4

continuation of the optic nerve past the optic chiasm; the right optic tract consists of axons from the retinal ganglion cells in the right half of each retina and the left optic tract consists of axons from the left half of each retina

Question 5

Contralateral organization

Answer 5

opposite side organization in which stimulation of neurons on one side of the body or sensory organ is represented by the activity of neurons in the opposite side of brain

Question 6

Lateral geniculate nucleus (LGN)

Answer 6

part of the thalamus (one in each hemisphere); receives visual signals via axons of retinal ganglion cells

• Layers 2, 3, and 5 receive signals from the ipsilateral eye (Left eye Left go to Left LGN 2,3,5; Right eye right go to Right LGN 2,3,5)
• Layers 1, 4, and 6 receive signals from the contralateral eye (Left eye right go to Right LGN 1,4,6; Right eye left go to Left LGN 1,4,6)
• Each eye sends signals to both LGNs and the information for each eye is kept separated

Question 7

Magnocellular layers

Answer 7

Layers of lateral geniculate nucleus containing neurons with large cell bodies

• Dynamic visual properties (Motion)
• From parasol ganglion cells

Question 8

Parvocellular layers

Answer 8

Layers of the lateral geniculate nucleus containing neurons with small cell bodies

• Static visual properties (color, form, stereo vision )
• From Midget ganglion cells

Question 9

Koniocellular layers

Answer 9

Layers of lateral geniculate nucleus containing neurons with very small cell bodies

• Color
• From small bistratified ganglion cells

Question 10

Parasol retinal ganglion cells

Answer 10

retinal ganglion cells that send signals to the magnocellular layers of the lateral geniculate nucleus

• Dynamic visual properties (Motion)
• Compute sum of L and M Cone (Brightness)
• Larger receptive fields
• Fast, transient response (motion)
• On and Off Center-surround receptive fields

Question 11

Midget retinal ganglion cells

Answer 11

retinal ganglion cells that send signals to the paravocellular layers of the lateral geniculate nucleus

• Static visual properties (color, form…)
• Compute difference in L vs. M cone signals (color)
• Smallest receptive fields (high acuity)
• On and Off Center-surround receptive fields

Question 12

Bistratified retinal ganglion cells

Answer 12

retinal ganglion cells that send signals to the koniocellular layers of the lateral geniculate nucleus

• Color
• Principle S cone pathway out of retina
• Compute difference in S vs L+M cone signals (color)
• S-on centered only, homogeneous receptive fields

Question 13

Superior colliculus (SC)

Answer 13

structure near top of the brain stem (one in each hemisphere); its principal function is to help control eye movements to visual targets

• Concerned with where things are than with what they are
• Receive signals from both auditory and somatosensory (touch) systems
• Respond to signals from 2 or more sensory systems -> reinforce others
• Sends signals it receives from retina to areas of visual cortex beyond area V1
• Center for reflex movements of the eyes, head, and neck and direction of gaze

Question 14

Multisensory integration

Answer 14

function of brain areas in which signals from different sensory systems are combined

Question 15

Primary visual cortex (V1)

Answer 15

Part of occipital lobe where signals flow from lateral geniculate nucleus

• Orient edges begin to tell the visual system what objects are at those locations
• 2/3 layer receive from koniocellular layers from bistratified retinal ganglion cells
• 4CX receive from magnocellular layers from parasol retinal ganglion cells (LGN 1-2)
• 4CB receive from parvocellular layers from midget retinal ganglion cells (LGN 3-6)
• Neurons in V1 respond best to bar stimuli of specific orientations, specific sizes, specific directions and velocities of motion
• Concentric center-surround cells

Question 16

Simple cell

Answer 16

type of neuron in area V1 that responds best to a stimulus with a particular orientation in the location of its receptive field

• also by the luminance contrast of the bar with its background
• Changing the contrast of stimulus doesn’t change the relative response of these two simple cells but changing the orientation does

Question 17

Preferred orientation

Answer 17

the stimulus orientation that tends to produce the strongest response from an orientation-tuned neuron such as a simple cell

Question 18

Orientation tuning curve

Answer 18

a curve on a graph that shows the average response of an orientation-tuned neuron such as a simple cell to stimulus with different orientations

Question 19

Population code

Answer 19

consistent difference in the patterning of the relative responses of a population of differently tuned neurons; used to compute perceptual features such as the orientation of a visual stimulus

Question 20

Complex cells

Answer 20

most numerous cell type in that area of visual cortex; bars within specific range of orientations

• Respond as well to light bar on dark background and dark bar on light background
• Respond equally well to bar at almost any location within their receptive field
• Larger receptive field

Question 21

Cortical column

Answer 21

small volume of neutral tissue running through the layers of the cortex perpendicular to its surface; consists of neurons that respond to similar types of stimuli and that have highly overlapping receptive fields; vertically through layers
*All information from a specific area of the visual field is processed in the same general location in V1. Within this location, there are groups of cells (columns) with specific response preferences that analyze different aspects of the visual stimulus

Question 22

Ocular dominance columns

Answer 22

cortical columns consisting of neurons that receive signals from left eye only or the right eye only

• Connection between layers of the LGN and layers 2/3 and 4C in cortical columns in V1
• Respond to input from both eyes, binocular disparity
• Neurons with left or right eye input

Question 23

Orientation columns

Answer 23

cortical columns consisting of neurons with the same (or very similar) orientation tuning

• Preferred orientations
• Neurons tuned to specific stimulus orientations

Question 24

Cortical magnification

Answer 24

nonuniform representation of visual space in the cortex; the amount of cortical territory devoted to the central part of the visual field is much greater than the amount of devoted to the periphery
*Many V1 neurons respond to stimulus at fovea than periphery; many more V1 neurons have receptive fields in fovea

Question 25

Dorsal pathway

Answer 25

from V1+V2 -> MT-> Parietal cortex

*Representing properties that relate to an object’s motion/location -> guide action (“where” pathway or “how” pathway)

Question 26

Ventral pathway

Answer 26

V1+V2 -> V4 -> inferotemporal cortex

*Representing properties that relate to an object’s identity such as color and shape (“what” pathway)

Question 27

Optic ataxia

Answer 27

deficit in ability to guide movements visually; can perceive objects
*Damage to dorsal pathway (“how”): coordinate perception and action; location and motion of objects

Question 28

V4

Answer 28

area in occipital lobe consisting of neurons that respond selectively to the color of stimuli and to the curvature of edges
*Lesion-> achromatopsia/cortical color blindness: inability to perceive colors despite having normal array cones in retina

Question 29

Inferotemporal cortex (IT Cortex)

Answer 29

cortex in inferior/bottom part of the temporal lobe; one of the object-selective regions of visual system (faces)

Question 30

Lateral occipital cortex

Answer 30

area of occipital lobe; one of object-selective regions of visual system (faces)

Question 31

Fusiform face area (FFA)

Answer 31

area in the fusiform gyrus of the IT cortex; functional module that responds selectively to faces
*Damages: prosopagnosia -> inability to recognize faces

Question 32

Parahippocampal place area (PPA)

Answer 32

area of the parahippocampal gyrus of the IT cortex; functional module that responds selectively to large-scale spatial layouts such as landscapes and buildings

Question 33

Middle temporal area (MT)

Answer 33

area in the middle temporal lobe consisting of neurons that respond selectively to the direction and speed of motion of stimuli
*Lesion: inability of detect and discriminate motion

Question 34

Lateral intraparietal (LIP)

Answer 34

Eye movements to visual targets, shifts of attention to locations in visual periphery

Question 35

Medial intraparietal (MIP) and Antraparietal (AIP)

Answer 35

Visually guided reaching and grasping

Question 36

Visual neuroprosthetic devices

Answer 36

devices designed to help the blind see; relay signals from a camera or photocells to implanted stimulators that activate visual system

Question 37

Color-processing blobs

Answer 37

Neurons tuned to specific spectral light patterns

Question 38

Size-selective neurons

Answer 38

Neurons tuned to specific stimulus sizes