A framework based on signal detection theory shows how visual attention influences tasks that require searching for a target among distractors. Data from physiology and psychophysics show that performance in a search task is largely determined by the discriminability of the target from the distractors. Attention acts by enhancing the response to the attended stimulus and by restricting the range and number of units responding to the distractors. Both processes improve performance by increasing the discriminability of the attended signal.
Verghese, P. (2004). Visual Search and Attention. Neuron, 31(4), 523–535. https://doi.org/10.1016/s0896-6273(01)00392-0