Vision

• What are the main components of the visual processing pathway discussed in the lecture overview?

  • Retina
  • Lateral Geniculate Nucleus (LGN) – part of the thalamus
  • Striate Cortex
• What does the term "ambiguity" refer to in the context of visual signals?

  It refers to the inherent uncertainty in the visual signals our eyes receive.
• What is an example of visual ambiguity mentioned in the study material?

  The "Spinning Dancer" illusion.
• What are the key features of retinal ganglion cells?

  • Last stage in retinal processing
  • Large Parasol ganglion cells
  • Small Midget ganglion cells
  • Have 'Receptive Fields' from which they receive input
• How do ciliary muscles contribute to vision?

  They change the shape of the lens to bring objects into focus at different distances.
• What are the types of photoreceptors in the retina and their functions?

  • Rods: contain rhodopsin, respond in dim light, none in fovea
  • Cones: three types with photopigments sensitive to different wavebands (long, medium, short) for daytime vision
• What is the last stage in retinal processing?

  Retinal Ganglion Cells.
• What is the significance of receptive fields in retinal ganglion cells?

  They define the part of the retina from which the ganglion cell receives input.
• What are the types of cells in the Lateral Geniculate Nucleus (LGN) and their functions?

  • Koniocellular cells: in between layers
  • Magnocellular cells: respond to movement & flicker
  • Parvocellular cells: respond to color & detail
• What is the significance of retinotopy in the visual cortex?

  • It refers to the spatial mapping of visual information in the cortex.
  • Each part of the visual field is represented in a corresponding area of the cortex.
• What is the concept of neural plasticity as demonstrated by the kittens raised in striped tubes?

  • Kittens raised in striped tubes showed no response to orientations absent in the tube.
  • This illustrates the role of development and critical periods in visual processing.
• What are the two streams of processing beyond V1 in the visual system?

  • Dorsal stream: "where" pathway- down a road
  • Ventral stream: "what" pathway- opposite of vertical
• The sclera (white part of eye) is not common in animals and is used in humans sociaslly to see where people are looking
• Fovea has the densest population of photoreceptors- only cones
• Cones process daytime vision and rods process dim light
• the light has to go through the neural machinery to get to the photoreceptors due to the receptors needing high amounts of nutrients from the adjacent cells
• Midget ganglion cells connect to the parvocellular system as just a small part
• Parasol cells connect to the magnocellular cells as they are large
• Midget cells have small receptive fields which is useful for small details
• on-centre off-surround retinal ganglion cells increase activity when light in centre and decrease when light is in the outer area (lateral inhibition)

  
• Retinal ganglion cells are good at detecting edges due to on-centre off-surround cells but bad at gradual changes
• The lateral geniculate nucleus has 3 types of cells:

  1. Magnocellular
  2. Parvocellular
  3. Koniocellular

  
• Magnocellurar/parasol cells detect movement and flickerin light
• Colour wise parvocellular cells detect red and green and koniocellular does blue and yellow
• what is retinotopy?


  the mapping of sections of the retina to the visual cortex to organise the process
• hubel and wiesel cat study showed cells were tuned for specific orientations
• the instrinsic optical imaging shows pinwheel organised cells with specific orientations and this is based on the retinal ganglion cells in the area
• Kittens raised in vertical striped tubes could not respond to horizontal orientation 5 months later due to neurons not responding