Cognitive Science > Action and Cognition > Questions/1

[edit] Afferents from retina to V1

Describe the structure of afferents and major properties from the retina to primary visual cortex

[edit] General pathway

• Photoreceptor

  -> bipolar cells

  -> retinal ganglion cells

  -> optic nerve

  -> optic chiasm

  -> LGN

  -> cortex (V1, layer IV)

• Interconnections between bipolar and RGCs via horizontal cells
• Optic chiasm: Nasal part crosses to other side (nasal -> contralateral), outer part stays on same side (temporal part -> ipsilateral)

  Result: Right part of visual field of each eye in left hemisphere, left part in right hemisphere

• Neurons from LGN enter layer IV (stellate cells) of primary visual cortex, exit via layer vI, backprojection

  Color blobs (II, III), pyramidal cells (V)

[edit] Magnocellular pathway: "quick and dirty"

• Alpha-neurons
• Larger cell bodies
• Color insensitive
• Fast, transient, phasic
• Low resolution, large receptive fields
• High sensitivity to contrast
• Peripheral retinal areas
• Layers 1, 2 of LGN

[edit] Parvocellular pathway: "slow and detailed"

• Beta-neurons
• Smaller cell bodies
• Color sensitive
• Slow, sustained, tonic
• High resolution, small receptive fields
• Less sensitive to contrast
• Central retinal areas
• Layers 3-6 of LGN

[edit] Response properties of neurons in V1

Describe the response properties to visual stimulation of the two major types of neurons in primary visual cortex

[edit] Response properties of both

• Orientation selectivity: Stimulus to which they respond best is bar at certain angle of orientation
• Variations which respond best to bars at a certain length (end-stopped stimuli; for complex: "hypercomplex cells")

[edit] Response properties of simple cells

• Receptive field with either excitatory or inhibitory center and complementary surrounding
• Contrast-sensitive, i.e. important whether black on white or the other way round
• Stimulus must match center of receptive field, otherwise inhibitory influence from surround
• Linear

[edit] Response properties of complex cells

• Convergence of simple cells to complex cell
• No distinct excitatory/inhibitory areas, no center/surround inhibition
• Absolute position of stimulus does not matter
• Contrast (which color on which) does not matter
• Motion sensitive
• Nonlinear

[edit] Lateral view of human cortex

Make a rough sketch of a lateral view ofa human cortex and label the four major axes commonly used

• Rostral - caudal
• Anterior - posterior
• Ventral (inferior) - Dorsal (superior)
• Lateral - medial - lateral

[edit] Ways to define a cortical area

Give at least four ways to define a cortical area.

• Cytoarchitectonics (e.g. V1, M1)

  Brodmanns areas, microscopy

• Anatomical connectivity (e.g. MT)

  Define area through afferent connections

• Cellular response properties (e.g. XIP region)

  Single-cell recordings

• Regional response properties (e.g. fusiform face area)

  fMRI

• Gross anatomy (AIP, CIP: anterior/posterior area within intraparietal sulcus)

  lobes: frontal, parietal, temporal and occipital

[edit] Simple vs complex cells in V1

Explain the qualitative differences of simple and complex cells in primary visual cortex.

• See Q2