Visual area V5, also known as visual area MT (middle temporal), is a region of extrastriate visual cortex that is thought to play a major role in the perception of motion, the integration of local motion signals into global percepts, and the guidance of some eye movements.

external image i_02_cr_vis_3b.jpg

Connections

MT is connected to a wide array of cortical and subcortical brain areas.

Inputs:
-Visual cortical areas V1, V2, and dorsal V3
-Koniocellular regions of the LGN
-Inferior pulvinar.
A standard view is that V1 provides the "most important" input to MT.

Outputs:
-FST
-MST
-V4t (middle temporal crescent).
Other projections of MT target the eye movement-related areas of the frontal and parietal lobes (frontal eye field and lateral intraparietal area).

Function

A large portion of the cells are tuned to the speed and direction of moving visual stimuli
These results suggested that MT plays a significant role in the processing of visual motion.

Damage/Lesions

-Unable to see motion
-Seeing the world in a series of static "frames" instead

-Deficits in perceiving motion and processing of complex stimuli (line ends, corners)

Notes

Since neurons in V1 are also tuned to the direction and speed of motion, these early results left open the question of precisely what MT could do that V1 could not. Much work has been carried out on this region, as it appears to integrate local visual motion signals into the global motion of complex objects.

There is still much controversy over the exact form of the computations carried out in area MT and some research suggests that feature motion is in fact already available at lower levels of the visual system such as V1.


Functional organization

MT was shown to be organized in direction columns.
It is argued that MT neurons were also organized based on their tuning for binocular disparity.