Visual neuroscience
Retina: Lateral geniculate nucleus (LGN): Neuropsychology - impairments after brain
- Inverted image to eye - LGN cells have similar properties to ganglion injury/lesion (e.g. stroke)
- Cells specialised for receiving and processing light cells Case studies of patients that gave an insight into
in retina the 2 pathways (Milner & Goodale):
- Photoreceptors at back of retina so light has to go Primary visual cortex (V1): - DF:
through whole eye before it reaches photoreceptors - Right side of world is processed in left - Visual form agnosia (can’t recognise
- Initial response from rods and cones hemisphere, vice versa objects, though visually avoids obstacles)
- Electrical signal generated when light is absorbed - Orderly mapping of visual space onto V1 - Very poor form discrimination
- Bipolar cells pass signal along from photoreceptors - Disproportionate amount of cortex represents - Acuity and colour vision normal
to ganglion cells the centre (fovea) - Task - discriminate square from rectangle -
- Rods - night vision - 6 layers (striate) very poor even at ratio of 2:1 only 80%
- Cones - day vision and high detail vision - Dominance columns - each cell prefers either correct
- 3 types of cone: blue, green and red (how well they L or R input - Can’t visually recognise objects despite OK
absorb light - optimum wavelength) - Turned to orientation acuity and cognitive abilities
- Rods are sensitive in the blue-green wavelength - Orientation columns - Can see but not recognise
(500-550nm) - Simple and complex cells - E.g. shows spectacles and patient
- Photoreceptors not evenly distributed describes circle and cross bar and guesses
- Pit = blind spot V2: bicycle
- Cones - lots of receptors packed together in fovea - - Adjacent from V1 - DF doesn’t recognise objects but can draw
look straight at something to get good image as - Axons from V1 project to V2 them from memory
fovea is at front - Signals go from V2 to other areas - DF can “post” card in slot but can’t match
- Rods - no rods at fovea, specialisation is peripheral slots orientation to a picture
vision - Can’t see object properties such as
- Optic nerve - all nerve fibres from ganglion cells Vental stream (inferotemporal) - identify objects orientation
leave eye - no photoreceptors here (blind spot) as Dorsal stream (posterior parietal) - visual control - Can use vision to guide action
otherwise they would be in the way of the nerve of action - Perceptual recognition impaired,
fibres visuomotor performance OK
- Ganglion cells receive final output signal from all V4:
- Lesion in inferotemporal cortex
processing in retina - nerve fibres are called axons - Seems to be involved in colour processing - VK::
which take signal to brain - Our colour percept is loosely related to light - optic ataxia (can recognise objects but
- Can put electrode into optic nerve to measure firing wavelength; V1 cells response to wavelength can’t reach out for them)
rate - measures as the visual stimulus is changed - We don’t usually look at isolated coloured lights; we - Problems with visually guided action
- Receptive field - specific area where there is more see objects that selectively absorb and reflect
- Visual perception Ok
activity from the nerve wavelengths
- RV has provlems inserting hand into
- On cell - rate of firing increases if light is shone in - Humans, and V4 cells, achieve “colour constancy” orientation slot - orients hand wrong but
centre - Perceived colour not affected by changed can correctly report the orientation
- Off cell - rate of firing decreases if light is shone in illumination (fluorescent, LED, daylight)
- Doesn’t grasp objects properly
centre - Somehow our brains (V4) manage to see invariant - Perceptual recognition OK, visuomotor
- Ganglion cell has a network of dendrites looking for objects having some “colour” rather than a patch of performance impaired
signals and concentrate them into one spot mixed wavelengths
- Lesion in posterior parietal cortex
- Types of ganglion cells: magno (low resolution, - Somehow the object property (reflectance
transient - brief response to resolution) and parvo spectrum) is teased apart from illuminant spectrum
(high resolution, sustained response, colour)
Retina: Lateral geniculate nucleus (LGN): Neuropsychology - impairments after brain
- Inverted image to eye - LGN cells have similar properties to ganglion injury/lesion (e.g. stroke)
- Cells specialised for receiving and processing light cells Case studies of patients that gave an insight into
in retina the 2 pathways (Milner & Goodale):
- Photoreceptors at back of retina so light has to go Primary visual cortex (V1): - DF:
through whole eye before it reaches photoreceptors - Right side of world is processed in left - Visual form agnosia (can’t recognise
- Initial response from rods and cones hemisphere, vice versa objects, though visually avoids obstacles)
- Electrical signal generated when light is absorbed - Orderly mapping of visual space onto V1 - Very poor form discrimination
- Bipolar cells pass signal along from photoreceptors - Disproportionate amount of cortex represents - Acuity and colour vision normal
to ganglion cells the centre (fovea) - Task - discriminate square from rectangle -
- Rods - night vision - 6 layers (striate) very poor even at ratio of 2:1 only 80%
- Cones - day vision and high detail vision - Dominance columns - each cell prefers either correct
- 3 types of cone: blue, green and red (how well they L or R input - Can’t visually recognise objects despite OK
absorb light - optimum wavelength) - Turned to orientation acuity and cognitive abilities
- Rods are sensitive in the blue-green wavelength - Orientation columns - Can see but not recognise
(500-550nm) - Simple and complex cells - E.g. shows spectacles and patient
- Photoreceptors not evenly distributed describes circle and cross bar and guesses
- Pit = blind spot V2: bicycle
- Cones - lots of receptors packed together in fovea - - Adjacent from V1 - DF doesn’t recognise objects but can draw
look straight at something to get good image as - Axons from V1 project to V2 them from memory
fovea is at front - Signals go from V2 to other areas - DF can “post” card in slot but can’t match
- Rods - no rods at fovea, specialisation is peripheral slots orientation to a picture
vision - Can’t see object properties such as
- Optic nerve - all nerve fibres from ganglion cells Vental stream (inferotemporal) - identify objects orientation
leave eye - no photoreceptors here (blind spot) as Dorsal stream (posterior parietal) - visual control - Can use vision to guide action
otherwise they would be in the way of the nerve of action - Perceptual recognition impaired,
fibres visuomotor performance OK
- Ganglion cells receive final output signal from all V4:
- Lesion in inferotemporal cortex
processing in retina - nerve fibres are called axons - Seems to be involved in colour processing - VK::
which take signal to brain - Our colour percept is loosely related to light - optic ataxia (can recognise objects but
- Can put electrode into optic nerve to measure firing wavelength; V1 cells response to wavelength can’t reach out for them)
rate - measures as the visual stimulus is changed - We don’t usually look at isolated coloured lights; we - Problems with visually guided action
- Receptive field - specific area where there is more see objects that selectively absorb and reflect
- Visual perception Ok
activity from the nerve wavelengths
- RV has provlems inserting hand into
- On cell - rate of firing increases if light is shone in - Humans, and V4 cells, achieve “colour constancy” orientation slot - orients hand wrong but
centre - Perceived colour not affected by changed can correctly report the orientation
- Off cell - rate of firing decreases if light is shone in illumination (fluorescent, LED, daylight)
- Doesn’t grasp objects properly
centre - Somehow our brains (V4) manage to see invariant - Perceptual recognition OK, visuomotor
- Ganglion cell has a network of dendrites looking for objects having some “colour” rather than a patch of performance impaired
signals and concentrate them into one spot mixed wavelengths
- Lesion in posterior parietal cortex
- Types of ganglion cells: magno (low resolution, - Somehow the object property (reflectance
transient - brief response to resolution) and parvo spectrum) is teased apart from illuminant spectrum
(high resolution, sustained response, colour)
