Short Answer 
Divided attention negatively impacts cognitive performance due to the finite capacity of our brains to process multiple tasks simultaneously, resulting in decreased accuracy and efficiency. Research demonstrates that both the accumulation of cognitive load from multiple tasks and the demands of switching tasks lead to errors and reduced productivity.
Step 1: Understanding Divided Attention
Divided attention refers to the phenomenon where cognitive performance declines when individuals engage in multiple tasks at once. This occurs because our brain has a finite capacity for processing information, and when we attempt to manage various tasks, it leads to a strain on our cognitive resources. As a result, individuals often experience decreased accuracy and efficiency in their performance.
Step 2: Evidence of Performance Decline
Research supports the impact of divided attention on performance. For instance, studies such as those by Spelke, Hirst, and Neisser (1976) reveal that trying to take dictation while comprehending unrelated material significantly impairs participants’ performance. This indicates that:
- Cognitive load increases as more tasks are added, stretching the brain’s ability to focus.
- Errors and slower performance emerge from the inability to adequately allocate cognitive resources across tasks.
Step 3: Effects of Task Switching
Another critical aspect of divided attention is task switching, which has been shown to have detrimental effects on performance. Research by Monsell (2003) highlights the cognitive demands involved in switching between tasks, leading to a drop in efficiency. The implications of this are that:
- Reallocating cognitive resources during task switching requires mental effort, which reduces overall productivity.
- Our attentional flexibility is limited, meaning that frequent task switching can lead to additional errors and decreased efficiency.