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Convergent evidence from single-cell recording studies in monkeys and functional brain imaging and event-related potential ( ERP ) studies in humans indicates that selective attention can modulate neural processing in visual cortex . Refinable Functions : A k-refinable function is a function f ( x ) that can be re-written in terms of the function f ( x ) . Among other things , this means that functions of instances ( e.g ., foo ( emp ) where emp is a class ) cannot be called anywhere in a rule . This protects the transaction from viewing inconsistent data that could be caused by ( other ) concurrent transaction updates on the same data rows , providing transaction isolation for each database session .