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