Before we get to the pathway itself, let's define a few of the major brain areas the study reports as being involved in conveying the information:
- Midbrain: The midbrain links the parts of the brain that control motor functions and voluntary ear and eye actions.
- Thalamus: The thalamus receives sensory information (coming in from the ears and eyes) and passes it on to the area of the brain that handles that particular sensory data. It also assists in the exchange of motor (movement) information between various parts of the brain.
- Motor cortex: The motor cortex is involved in controlling voluntary movements, like eye movements.
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The thalamus is located in the somatic sensory cortex, and the motor cortex is in the frontal lobe. The visual cortex delivers data to the sensory cortex telling it what our eyes are perceiving, and the sensory cortex interprets it.
What the study discovered is a pathway between the motor cortex and the visual cortex that activates visual neurons before the eye itself actually moves. According to one of the study's authors, Marc Sommer of the University of Pittsburgh, a signal from the motor cortex tells the visual cortex to shift its focus to where the eye is planning to move next. This neural pathway starts in the midbrain, which has access to data from the motor cortex related to eye movement.
This data indicates what the eye is about to do next -- it's a copy of the signal the motor cortex is sending to the visual cortex to tell the eye to move. Neurons in the midbrain pass that information on to the thalamus, which sends the information to neurons in the visual cortex, telling them to shift their "perception window" to match the upcoming command. The new, unperceived image from the shifted window arrives at the somatic sensory cortex, where it is soon joined by the visual image perceived by that same shift a moment later. When the somatic sensory cortex interprets the visual signal coming in from the primary visual cortex, it compares it to the prior view of the same scene. As long as both views are the same, it interprets "stability" and simply filters out any shakiness in the transition from one visual image to another.
The study's authors expect this finding to lead to further understanding of other uninterrupted sensory transitions, such as the constant perception of sound that occurs even as you turn your head in different directions.
For more information on the brain and sensory perception, take a look at the links on the next page.