You have a test next week!
Review Session Monday next week 4 – 5
Room Th 173
Parallel pathways in the visual
system
Dorsal and Ventral Pathways
• recall some details about visual pathways
Dorsal and Ventral Pathways
• Different visual cortex
regions contain cells with
different tuning properties
represent different features
in the visual field
– PET study by Zeki et al.
– Double dissociation of lesions
• V5/MT is selectively
responsive to motion
• V4 is selectively responsive
to color
What are the different roles of these
pathways?
• Ventral Stream
– Object identification
– Awareness?
• Dorsal stream
– Spatial representations
Dorsal and Ventral Pathways
• V4 and V5 are key parts of
two larger functional
pathways:
– Dorsal or “Where” pathway
– Ventral or “What” pathway
– Ungerleider and Mishkin (1982)
• Magno and Parvo dichotomy
arose at the retina and gives
rise to two distinct cortical
pathways
Fusiform Gyrus: Specialized for
perception of complex objects
• Ventral pathway has specialized regions for complex
object identification:
– Faces – Fusiform Face Area (FFA)
– Word Form – Visual Word Form Area (VWFA)
Visual Word Form Area
• fMRI contrasting
words with pictures
• Left inferior temporal
lobe
Deheane et al. (2009) NeuroImage
Visual Word Form Area
• Exhibits invariance
to surface structure
of words
– Table, TABLE, tAblE
are equivalent
Deheane et al. (2009) NeuroImage
Visual Word Form Area
•
Possibly mediates the critical skill of
overcoming mirror invariance for
objects during learning
Deheane et al. (2009) NeuroImage
Visual Word Form Area
• Lesions cause Pure
Alexia
– Inability to read
visual input efficiently
• Letter-by-letter
strategies are intact
but S – L – O – W
– Words traced on the
skin can be read!?
Deheane et al. (2009) NeuroImage