Attentional shift (or shift of attention) occurs when directing attention to a point increases the efficiency of processing of that point and includes inhibition to decrease attentional resources to unwanted or irrelevant inputs. Shifting of attention is needed to allocate attentional resources to more efficiently process information from a stimulus. Research has shown that when an object or area is attended, processing operates more efficiently. Task switching costs occur when performance on a task suffers due to the increased effort added in shifting attention. There are competing theories that attempt to explain why and how attention is shifted as well as how attention is moved through space. Unitary resource and multiple resource models According to the unitary resource model of attention, there is a single resource of attention divided among different tasks in different amounts, and attention is voluntarily shifted when demands on attention needed exceeds the limited supply of attentional resource available. In contrast, there are also multiple resource models of attention that propose that different attentional resources exist for different sensory and response modalities, which would mean that tasks requiring different senses or different kinds of responses should be easier to switch attention to and from, and that switching costs would be less for similar tasks than tasks that involve different resources. The spotlight and gradient theories In attention research, one prominent theory attempting to explain how visual attention is shifted is the moving-spotlight theory. The primary idea being that attention is like a movable spotlight that is directed towards intended targets, focusing on each target in a serial manner. When information is illuminated by the spotlight, hence attended, processing proceeds in a more efficient manner, directing attention to a particular point and inhibiting input from any stimuli outside of the spotlight. However, when a shift of spatial attention occurs, the spotlight is, in effect, turned off while attention shifts to the next attended location. Attention, however, has also been proposed to adhere to a gradient theory in which attentional resources are given to a region in space rather than a spotlight, so that attentional resources are most concentrated at the center of attentional focus and then decrease the further a stimuli is from the center. Attention in this theory reflects both current and previous attentional allocation, so that attention can build up and decay across more than one attentional fixation over time. This means that time to