ScienceDaily has an item on research by M. Pessiglione investigating subliminal motivation. (here) In the experiment they gave the subject a subliminal look at the level of reward available for the strength of a hand squeeze. The size of reward affected the strength of the squeeze. In a second experiment the subliminal reward information was projected to only one eye (the therefore one hemisphere of the cortex) and the effect on the squeeze was only found for the one hand (controlled by the same hemisphere) and not the other.
The research shows that it’s possible for only one side of the brain, and thus one side of the body, to be motivated at a time, says Pessiglione. “It changes the conception we have about motivation. It’s a weird idea, that your left hand, for instance, could be more motivated than your right hand.” He says this basic research helps scientists understand how the two sides of the brain get along to drive our behavior.
The way I interpret this is that the size of the reward affects motivation. This is true even if the picture of the reward has too short a duration to reach consciousness. When the subliminal information is projected to only one side of the cortex, it remains only local knowledge. The other hemisphere would have knowledge of the reward only if it rose to consciousness and the short duration prevents this. Consciousness would seem to be very important for access and coordination between the two hemispheres at least in some situations.