Chapter 3 The Visual Brain Flashcards
Functional specialization
specialization of different neural pathways and different areas of the brain for representing different kinds of information
Retinotopic mapping
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
Optic chiasm
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
Optic tract
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
Contralateral organization
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
Lateral geniculate nucleus (LGN)
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
Magnocellular layers
Layers of lateral geniculate nucleus containing neurons with large cell bodies
- Dynamic visual properties (Motion)
- From parasol ganglion cells
Parvocellular layers
Layers of the lateral geniculate nucleus containing neurons with small cell bodies
- Static visual properties (color, form, stereo vision )
- From Midget ganglion cells
Koniocellular layers
Layers of lateral geniculate nucleus containing neurons with very small cell bodies
- Color
- From small bistratified ganglion cells
Parasol retinal ganglion cells
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
Midget retinal ganglion cells
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
Bistratified retinal ganglion cells
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
Superior colliculus (SC)
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
Multisensory integration
function of brain areas in which signals from different sensory systems are combined
Primary visual cortex (V1)
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
Simple cell
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
Preferred orientation
the stimulus orientation that tends to produce the strongest response from an orientation-tuned neuron such as a simple cell
Orientation tuning curve
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
Population code
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
Complex cells
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
Cortical column
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
Ocular dominance columns
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
Orientation columns
cortical columns consisting of neurons with the same (or very similar) orientation tuning
- Preferred orientations
- Neurons tuned to specific stimulus orientations
Cortical magnification
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
Dorsal pathway
from V1+V2 -> MT-> Parietal cortex
*Representing properties that relate to an object’s motion/location -> guide action (“where” pathway or “how” pathway)
Ventral pathway
V1+V2 -> V4 -> inferotemporal cortex
*Representing properties that relate to an object’s identity such as color and shape (“what” pathway)
Optic ataxia
deficit in ability to guide movements visually; can perceive objects
*Damage to dorsal pathway (“how”): coordinate perception and action; location and motion of objects
V4
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
Inferotemporal cortex (IT Cortex)
cortex in inferior/bottom part of the temporal lobe; one of the object-selective regions of visual system (faces)
Lateral occipital cortex
area of occipital lobe; one of object-selective regions of visual system (faces)
Fusiform face area (FFA)
area in the fusiform gyrus of the IT cortex; functional module that responds selectively to faces *Damages: prosopagnosia -> inability to recognize faces
Parahippocampal place area (PPA)
area of the parahippocampal gyrus of the IT cortex; functional module that responds selectively to large-scale spatial layouts such as landscapes and buildings
Middle temporal area (MT)
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
Lateral intraparietal (LIP)
Eye movements to visual targets, shifts of attention to locations in visual periphery
Medial intraparietal (MIP) and Antraparietal (AIP)
Visually guided reaching and grasping
Visual neuroprosthetic devices
devices designed to help the blind see; relay signals from a camera or photocells to implanted stimulators that activate visual system
Color-processing blobs
Neurons tuned to specific spectral light patterns
Size-selective neurons
Neurons tuned to specific stimulus sizes
