Vision

Vision

1. The Eye

   • Light / electromagnetic energy as stimulus
     • 3 Spectra of light perception
       • Brightness - intensity
       • Saturation - purity
       • Hue - dominant wavelength
   • Retina - photoreceptive cells and neural tissue
     • Rods - low intensity light (b/w)
       • Rhodopsin - splits when exposed to light (retinal & rodopsin
       • Light -> hyperpolarization
     • Cones - maximally sensitive (color)
     • Other Cells:
       • Bipolar - middleman; passes info between photoreceptors and ganglions
       • Ganglion - receives visual info from ganglions; comprises optic nerve
       • Horizontal - adjacent photorecepters; bipolar outer processes
       • Amacrine - connects adjacent ganglions; bipolar inner process
   • Fovea - spot controlling acute vision; full of cones
   • Optic Disk - blind spot; exit point for optic nerve fibers
   • Central/peripheral vision
     • Receptive field - area within visual stimulus must be located to fire a particular neuron
     • Fovea acuity is higher bc smaller receptive field
     • Eye movements
       • Vergence - focused on same item in same retinal spot
       • Saccadic - jerky
       • Pursuit - following a target

2. Brain Regions Involved in Visual Processing

   • Path:
     • Retina
       • Optic Nerve
         • Optic chiasm
           • LGN
             • Optic radiations
               • Visual cortex
             • 6 layers of neurons: 1/4/6 contralateral eye, 2/3/5 ipsilateral eye
   • Visual cortex
     • Striate cortex - V1 / primary
       • CO blobs - color sensitive info
         • Inter-blob areas - orientation, spatial freq, movement, retinal disp
       • Purpose: detect particular features
     • Extrastriate cortex
       • Combines info to produce perception of objects / scenes; responds to features
       • Regions V2 - V5
       • Dorsal stream: where/how
         • Posterior parietal cortex
       • Ventral stream: what
         • Inferior temporal cortex

3. Perception - interpretation of stimuli

   • Color
     • Retina has 3 different types of photoreceptors for color
     • Each cone type has different opsin
       • Blue - short waves | Green - med | Red - long waves
     • x-color blind means that certain receptors are filled with the wrong opsin or lack cones entirely
   • Form
     • Analysis begins in striate cortex neurons
       • V2A
         • Extrastriate's ventral stream
     • Larger neuronal receptive fields: V1 - temp cortex
     • Prosopagnosia - disorder where can't recognize faces; caused by damage to the FFA
     • Extrastriate body area - responds to body shapes
     • Parahippocampal place area - PPA - scenes, places
   • Spatial location
     • Stereopsis
     • Depth perception factors: perspective, relative retinal size, atmo haze (less detail), apparent movement of retinal images with head movement
     • Optic flow - visually perceive yourself and stimuli location in relation to self
     • Akinetopsia - can't perceive movement

4. Sensation - raw stimuli

   • Sensory receptors - detect stimulus
     • Changed into receptor potentials (slow/graded) by sensory transduction