Top-Down Effects on Perception

For much of the history of neuroscience, perception was viewed as a rigidly hierarchical process. A bottom-up network beginning with the transduction of different sensory modalities into action potentials, relay distribution through the thalamus and finally cortical processing from early sensory areas to the frontal lobe.  Once thought to fully explain perception, evidence from the last few decades suggests that is an incomplete view. Expectation, attention, memories, tasks and emotions can affect perception and sensory processing even in early cortical stages. These top-down effects suggest that the subjective reality each one of us experience is not determined solely by the shapes of objects, frequency of air vibrations or structure of odorant molecules. Reality is built at the intersection between the physical attributes of the world and  our brains’ internal processes.