NEUR1020 W8

• What is cell specialisation?

  Cells respond selectively to specific stimulus
• What is modularity?

  Cells that respond to similar stimulus characteristics are clustered into specific brain regions
• Where do signals from photoreceptors propagate to and via what?

  To retinal ganglion cells at the front of the eye, via bipolar and amacrine cells
• What is the receptive field?

  The region of retina to which a visual cell is responsive
• Where does processing of visual input begin?

  In the retinae
• What kind of receptive fields do retinal ganglion cells have?

  Circular receptive fields
• What are the 2 types of circular receptive fields?

  On centre/off surround --> respond positively to input from central region and respond negatively to surroundings.

  Off centre/on surround --> respond negatively to input from central region and respond positively to surroundings.
• What does receptive field size scale with?

  Distance from fixation. Due to this, visual acuity (sharpness) is much higher for input that project onto the fovea (centre of retinae)
• In retinae and LGN cells, how do visual cells have a simple response selectivity?

  They respond to circular blobs of contrast. In Hermann's Grid Illusion, if the entire receptive field is stimulated and the On/Off subregions are balanced, then no signal is produced
• Where do signals move to at the optic chiasma (crossing of optic nerves)?

  Signals from temporal sides of retinae project to the LEFT side of brain.

  Signals from nasal sides of retinae project to the RIGHT side of brain.

  This means that signals relating to one side of visual space, projects to the opposite side of the brain
• What must have been damaged if a person is blind to input from a given eye?

  Damage of the corresponding retina or an optic nerve before it moves to the optic chiasma
• What must have been damaged if a person is blind to input from the left or right visual field?

  Damage to a brain structure positioned after the optic chiasma
• Where do visual signals propagate from and to?

  Visual signals propagate from the optic chiasma to the LGN (lateral geniculate nucleus) and then to the primary visual cortex (V1) at the back of brain.
• Why is the primary visual cortex called V1?

  Because it's the first cortical brain structure to receive signals via primary visual pathway
• What do visual cells in V1 respond to, compared to just blobs of contrast?

  Complex properties such as stripes of contrast
• What do the different types of V1 cells respond to in oriented stripes of contrast?

  Simple V1 --> located in a specific subfield of its receptive field

  End-stopped V1 --> of a specific (limited) length

  Complex V1 --> located anywhere within its receptive field

  Complex direction-selective V1 --> located anywhere within its receptive field that move in a particular direction
• What is retinotopic mapping?

  Adjacent neurons in visual brain regions encode information from adjacent regions on the retinal surfaces
• Where is retinotopic mapping most apparent?

  In lower-level brain structures, where neurons are associated with small receptive fields (LGN, V1, V2 and V3)
• What does brain imaging show about V1?

  Each V1 contains a complete mapping of 1 side of visual space
• What inputs do cells in V1 respond to?

  Inputs you cannot see, hence this brain activity is sub-conscious
• What does blindsight imply?

  That there are multiple pathways by which information reaches your brain from your eyes. Monkeys and humans can display visual sensitivity even when they insist they cannot see
• The primary visual pathway travels to V1 via the LGN. How else can visual information be projected?

  From superior colliculus (SC) to pulvinar to medial temporal lobe (MT or V5). V5 is a brain region specialised for processing movement informations
• What is the dual visual streams hypothesis?

  Humans have 2 visual systems. One promotes perception (ventral stream, vision-for-perception) which is more important, and one guides our actions (dorsal stream, vision-for-action)
• What is the primary and secondary visual pathways?

  Primary --> enters cortex at V1, and damage to this pathway causes subjective blindness

  Secondary --> can support some visual sensitivity, but is insufficient to promote conscious perception of input
• What is functional modularity?

  Different regions of the visual brain seem to be specialised for processing different types of visual information
• What are the 3 selective deficits?

  Cerebral achromatopsia --> without colour vision

  Prosopagnosia --> inability to recognise face

  Cerebral akinetopsia --> without motion vision (cannot see smooth motion)
• What brain structure is responsible for akinetopsia?

  Bilateral (both hemispheres) damage to V5 structure. This can be localised with fMRI by contrasting the absence to the presence of motion. Almost all V5 cells are direction-selective, but not selective for colour
• What brain structure is responsible for achromatopsia?

  Unilateral V4 damage causes lateralised colour blindness while bilateral damage causes total colour blindness. This can be localised with fMRI by contrasting the absence the presence of colour. Many V4 cells are selective for specific colours, but only a few are direction-selective
• What brain structure is responsible for prosopagnosia?

  Correlates with Occipital Face Area (OFA), located ventrally/front from V1, usually in the right-hemisphere. OFA is adjacent to both V1 and V4
• What is the binding problem?

  The question of integration --> how can the brain tell when activity spread across the brain is related to a common object?
• What does colour-motion mis-binding depend on under the spatial binding problem?

  Poor resolution of peripheral vision. The perceptual combination of colour and motion in peripheral vision is guided by central vision
• What does the temporal binding problem tell us?

  We are all living in the recent past as visual brain activity lags the physical events. Also, the human brain is a predictive machine.
• What does the colour/motion perceptual asynchrony show?

  Brain can incorrectly bind visual features across time
• What were some of the suggestions to solving the binding problem?

  Solved by synchronous neural activity, but the binding problem had to be solved before neurons could decide to synchronise.

  Another way is that feedback might be involved (feed-forward must have feed-back connection).

  Another way was solved via attention, where there was a pre-attentive stage, then a focused attention stage, which led to the perception of the object
• What is the Feature Integration of Theory?

  Thought to be provided by instances of illusory conjunction (when you link an object with a certain colour)