The visual brain Flashcards
Refractive structures of the eye
Cornea and lens
Problems with focusing the light through the cornea and lens
Cataract, myopia, presbyopia
Myopia
Near-sightedness
Presbyopia
Age-related far-sightedness
Anatomy of an eye
Pupil, Macula lutea, Fovea centralis, Optic disc, Optic nerve
Macula lutea
Yellow spot, central area of the retina where the light rays are focused
Fovea centralis
The center of the macula, responsible for the highest visual acuity and colour
Optic disc
Axons of retinal ganglion cells leave the eye at the optic disc and form the optic nerve
Retinal organization - neurons
Retinal ganglion cells, interneurons, photoreceptors
Retinal ganglion cells
Receive information from the photoreceptors via the interneurons, the only retinal neurons whose axons leave the brain
Photoreceptors
Rods and cones, respond to reflected light and convert it into a neural signal
Rods
Ca. 120 million, very sensitive to light (night vision), multiple rods converge on the same interneuron
Cones
Ca. 6 million, less sensitive to light (day vision), 3 types of cones (red, green, blue), one-to-one convergence with an interneuron
Saccades
Rapid eye movement to shift visual fixation from one point to another
Microsaccades
A type of fixational eye movement produced during visual fixation
Left visual hemifield
Seen by the nasal left retina and temporal right retina
Right visual hemifield
Seen by the nasal right retina and temporal left retina
Visual pathways
Optic nerve, optic chiasm, optic tract, thalamus (LGN) and optic radiaton (Geniculocortical pathway)
Optic nerve
Splits into temporal and nasal branch
Optic chiasm
Crossover of optic nerve branches
Optic tract
Information from the left visual field travels in the right optic tract and information from the right visual field travels in the left optic tract
Thalamus (LGN)
Is the major target of the retinal ganglion cells, receives information from both eyes and sends it to V1
Lateral geniculate nucleus
6 layers, 2 types of cells
Midget (parvocellular)
Receives small details from cones, makes up 4 layers of the LGN
Parasol (magnocellular)
Receives information from a bigger area via rods, makes up 2 layers of the LGN
V1
Elementary features of objects
Hubbel and Wiesel
Single cell recordings in the cat visual cortex
Neurons in V1 are selective for?
Position and orientation of edges and direction of movement of edges (bars)
Magnocellular pathway
Movement and direction
Parvocellular pathway
Colour and orientation
V2 and V3
Relay of information, integration of elementary features and motion (especially V3)
V4
Colour perception
V5/MT
Motion perception
Inferior temporal cortex (IT)
Stronger responses to objects than non-objects
Fusiform face area (FFA)
Responds to faces
Extrastriate body area (EBA)
Responds to bodies
Parahippocampal place are (PPA)
Responds to places
ERPs
A method of measuring brain activity during cognitive processing, using EEG
Dorsal “WHERE” pathway
Magnocellular, carries information about motion and localization, towards parietal cortex
Ventral “WHAT” pathway
Parvocellular, carries information about form discrimination and object identification, towards temporal cortex
Blindsight
“When the blind can see”, Lawrence Weiskrantz
Explanations for blindsight
Subcortical visual pathway (superior colliculus), geniculo-extrastriaste pathway, residual V1 function
Akinetopsia
Lesion in V5/MT, loss of motion perception
Cerebral achromatopsia
Lesion in V4, loss of color perception
Visual agnosia
Lesion in the occipito-temporal cortex, results in poor object recognition
Apperceptive agnosia
When a person cannot name, copy, match or discriminate visual objects
Integrative agnosia
When a person is unable to “put the pieces together”
Associative agnosia
When a person is unable to access knowledge of an object’s functions and associations
Prosopagnosia
Lesion in FFA, loss of face recognition
Optic ataxia
Lesion in parietal cortex, person can identify but not grab object