Lecture 12: Vision Flashcards
Where are the first stages of visual processing?
Retina
What are the first stages of visual processing handled by the retina?
Edge detection in visual scenes, edge enhancement in patterns, filtering of spatial, wavelength, movement and directional information
What is responsible for edge enhancement (and the Matchband effect)?
Lateral inhibition in retinal cells
How do edges and shadows contribute to visual perception?
They provide context about the spatial structure of objects and their relationships
How are receptive fields formed in bipolar and ganglion cells?
Cones/rods converging on a bipolar cell form its receptive field.
Cones/rods and bipolar cells converging on a ganglion cell form the ganglion cell’s receptive field.
Larger in the periphery (blurrier vision, lower acuity).
Smaller in the fovea (highest acuity).
What are the two types of centre-surround receptive fields?
ON-centre/OFF-surround: Lateral inhibition from receptors in the surround.
OFF-centre/ON-surround: Lateral inhibition from photoreceptors in the centre.
How do ganglion cells respond to light and dark stimuli?
They respond to light/ dark rations (e.g., a small dot of light), but not to uniform illumination
What are the key differences between P and M ganglion cells?
Project to different layers in LGN and V1.
Differ in receptive field size, conduction speed, acuity, and colour sensitivity.
How do P and M ganglion cells project to the LGN?
They project retinotopically to segregated layers in the LGN
What is the columnar structure of V1?
Organized in hypercolumns.
Each hypercolumn contains orientation columns and ocular dominance columns.
Orientation columns: Neurons share the same orientation preference.
Ocular dominance columns: Separate input from the left and right eye.
What do simple cortical cells (bar/ edge detectors) respond to?
They respond best to an edge or bar of specific width, orientation, and location
How do complex cortical cells respond to stimuli?
They respond best to a bar of specific size and orientation anywhere in a certain area
