V4 lesions in macaques and ventral cortex lesions in humans also cause dramatic losses of noise masked contrast sensitivity, but only small losses of unmasked contrast sensitivity. This finding may reflect a disruption of feedback or top down processing in the ventral pathway, whose normal function is to identify interesting visual stimuli in cluttered environments. Independent movements of different fingers commonly are assumed to be generated by different muscles, and controlled from different parts of the primary motor cortex, not unlike the separate fingers, motors and software channels used for a robotic hand. But in fact, real fingers do not move independently. Passive mechanical linkages account for only part of the interactions between the digits.
Additional interaction results from the multitendoned muscles that flex and extend the fingers.
These muscles act simultaneously on multiple fingers, requiring contraction of additional muscles to check unintended movements of other digits when a given digit is moved. Rather than groups of physiologically similar neurons being organized somatotopically to control particular muscles or fingers, control of any finger movement thus involves a physiologically diverse subpopulation of neurons distributed throughout the M1 hand area. The subpopulation controlling a particular finger movement shares members with, and spatially overlaps, the subpopulation controlling any other movement. These findings suggest that individuated finger movements are controlled by a spatially distributed network of highly diverse neuronal elements in the M1 hand area. Research addressing how combinations are interpreted have implications for theories of knowledge representation and language comprehension because it provides insight into how noun phrases are interpreted, how new concepts are built up from existing concepts, and how individual concepts are represented in memory.