Mod 2 - Liana Flashcards
Transcranial Magnetic Stimulation (TMS) over Primary Visual Cortex- effect?
Artificial V1 activation
- flash of white light
= phosphene
ecstasy user V1 excitability
negative correlation between frequency of use and threshold –> suggests ecstacy users have more excitable visual cortex
Sensory Integration
- combination of incoming info from multiple senses
- e.g. visual + hearing
- superior colliculus
- contains retinotopic map
- but also get incoming info from medial colliculus re auditory info
ventriloquist illusion
The ventriloquist illusion occurs due to the sound source being mislocalised towards a synchronous but spatially discrepant visual event (in this case, the puppets mouth moving).
- if a good puppeteer, we experience it as if sound is coming from the puppet, not the puppeteer
- visual system is very spatial acute, but auditory is not
- brain might decide based on visual, bc knows its more accurate
- same for movie, speakers on the side
MT (non-human primates) = V5 (humans), neurons have preference for:
- direction of motion
- speed of motion
What do the cortical Visual Pathways - dorsal and ventral - code for
- The dorsal stream codes motion and location = “where” pathway
- The ventral stream processes detailed stimulus features and object identity = “what” pathway?
V4
= colour and form = what (ventral stream)
cortical vs subcortical vision in humans
cortical = 90% of neurons project here (V1) - really important for humans,
conscious, phylogenetically newer
subcortical = 10% of neurons project here (superior colliculus), some is unconscious, phylogenetically older
in what layer of the superior colliculus are the neurons that receive information from the retinal ganglion cells located?
superficial layers
mapping on superior colliculus
- retinotopic
- y axis stretch across the top
- distorted, with more neurons for analysis of central vision
knockout cortical visual area on one side =
contralateral cortical blindness/neglect
sprague effect
lesioned subcortical visual area on opposite side to cortical visual area knockout
= started responding to both sides again
explanation of sprague effects
release of inhibition (cut inhibitory fibres) to subcortical area on same side as cortical damage = hyperactive = restored orientation
Visual cortex vs. superior colliculus damage - localisation (orient to sunflower seed) and discrimination tasks (maze to find hidden seed) - RESULTS AND CONCLUSION
- Cortical damage could do localisation task but not discrimination
- Subcortical damage could do discrimination but not localisation
= double dissociation = opposite results
Conclude: cortical for more complex tasks, subcortical for basic visual orienting
blindsight
- no conscious awareness of seeing a light but eyes moved towards where light was
- response was there, visual system working, so retinotectal pathway (subcortical)
blindsight experiment with distractor
- slower reaction time when distractor in blind hemifield
- this distraction effect would also increase reaction time for people with normal vision
Conclude: the subcortical visual pathway in humans may play an important role in orienting toward visual stimuli.
Unilateral damage to primary auditory cortex (A1) (compared to V1)
not nearly as devastating as damage to V1 bc neurons from ears project to both sides of the brain (bilateral projections)
EMG vs EOG
- Electromyography (EMG) records muscle activity
- Electrooculography (EOG) records movement of the eyes
where in SC are neurons for reflexive eye movement?
Deeper into the superior colliculus
types of cells/preferences for reflex movements in SC
Some cells are just visual or just motor, some are responsive/fire with both - important for integration of motor and visual systems
neurons have preferences for direction and distance of movement (amplitude) within the field
which way will eyes move if you stimulate cells deep in the R SC
left
mapping of occularmotor in SC
movement fields tend to code for eye movements into the same area of the visual field represented by the retinotopically organised visual receptive field of the neurons just above them in the superficial layers
smallest saccades = [central vision] = rostral SC
largest saccades = caudal SC
retinotopic map (superficial layer of SC) is info about central vision at top/rostral SC and info from peripheral vision at caudal SC
Effects of unilateral SC damage on reflexive saccades
- ipsi = moving towards hemi on same size as damage = same reaction time as control
- contra = movement opposite direction to damage = much slower, but could still move eyes