Attention can be defined as a concentration of mental activity that allows you to take in limited portion of information available both of your sensory world and memory. Attention work as a gatekeeper. If certain information do not get attention, it has no existence in your cognitive system. This emphasises the view of attention as a limited resource.
The fact that attention is divided, explains why attention might be seen as a limited resource. In divided-attention task person is trying to pay attention to two kinds of simultaneous messages at the same time and tries to respond to these messages appropriately (for example teacher’s lecture and nearby conversation). In both tasks accuracy suffer. When tasks involve movement, speed can lower down (e.g. speaking in a phone when walking -> walking will get slower).
If person is multitasking, he is trying to concentrate on two tasks at the same time. It restricts the limits of attention and working and long-term memory. For example, when a person is driving a car and speaks on a phone (even when with hands-free), attention what happens in visual field is reduced.
Selective-attention task allows people to to pay attention to certain kinds of information, while ignoring other ongoing information. This makes our everyday life a bit easier. Selective attention also emphasise, that attention is seen as a limited resource. There are four kind of selective-attention tasks that clarify in which ways our attention is limited and selective. These are dichotic listening, the Stroop effect, visual search and saccadic eye movement. Next I am going to present these and show, how they support the fact that attention is limited.