Neuroscience of Visuo-Motor Control

• Phototaxis


  Orientation of an organism in response to light
• Evolution of the Visual Eye

  • Type of thing
• Visual Neglect


  Not seeing what's left
• Visual Neglect


  • Damage to the right parietal cortex (e.g., stroke or accident)
  • Patient may have no deficit in perception, movement, cognitive skills, arousal/wakefulness, orientation, motivation, etc.
  • But may consistently ignore the left half of the world: read only the right half of a page, wash, dress, shave, or apply make-up to only the right side of the body, eat only what's on the right side of the plate
• Formal test 1: Line Bisection


  Explicit task
• Formal test 2: Object Comparison

  Explicit task
• Formal test 3: Implicit Knowledge Task

  Implicit task
• Selective 'disinterest' in the left side, but intact ability to make implicit selective choices based on unacknowledged information
• Conscious awareness of the left side is impaired, processing of left-side stimuli as such is not impaired
• Blindsight


  Vision in a blind spot
• Blindsight


  • Lesion to primary visual cortex causes scotoma (blindness in part of the visual field)
  • Patients report not seeing anything in that area (subjective blindness)
  • Patients do not respond to stimuli presented in that area (objective blindness)
  • Yet some residual visual processing exists in the blind area
• Localization task


  1. Patients only react to blind-field stimuli when prompted

  2. Insist that they do not see these stimuli
• Other examples of blindsight: Correct 'guessing' of orientation, shape, direction of movement, etc.; in all of these no subjective sense of 'seeing' anything and no spontaneous (unprompted) reaction towards these stimuli
• Spontaneous, voluntary responses (to something else) can be affected by these stimuli
• Subliminal Perception


  Below the threshold where we can still reliably make an explicit, voluntary judgement
• Subliminal Prime Paradigm


  1. Task: make an explicit judgement about the clearly visible stimuli (e.g., did the arrows in stimulus 2 point to the left or to the right?)

  2. If stimulus 1 is really invisible (if we don't process it at all), then its identity shouldn't make a difference... but it does!

  
• Subliminal Free Choice Priming Task

  1. Following >>, people should be more likely to choose a right-hand than a left-hand response (and should be faster to execute it)

  2. Following <<, people should be more likely to choose a left-hand than a right-hand response (and should be faster to execute it)
• Subliminal primes do trigger their corresponding motor response (hypothesis 2 supported)
• Subjectively 'free choices can be subliminally manipulated
• Subliminal arrow primes do not trigger a motor response when participants are not already prepared for them to do so
• Subliminal arrows only affect our choices when we already want to respond to arrows and in line with our normal response to arrows
• Functional Magnetic Resonance Imaging (fMRI)


  Measures oxygen levels through the different magnetic properties of oxygen-rich versus oxygen-poor blood
• Electroencephalogram (EEG)


  Uses electrodes on the scalp to measure changes in the electrical currents produced by large groups of synchronized neurons
• Event-Related Potential (ERP)


  The pattern of activity that remains the same for each occurrence of an event
• Lateralized Readiness Potential (LRP)


  Shows the differences between left and right motor cortex activity during left and right manual responses, and how a manual response develops over time