Bottom-up attention is typically not guided by observers' goals or knowledge, only by the physical properties of the stimuli.
[3] Many studies employ various methods involving intertrial priming to assess the contribution of top down versus bottom up processes in guiding attention in visual search tasks.
[4] Studies that have found that stimuli that are equally salient and are connected with rewards and can draw a participants' attention, even if this choice doesn't match their selection goals.
An alternative framework has been proposed where past selection history, current goals and physical salience are integrated in a model of attentional control.
Different trial designs and visual search tasks can be employed to measure intertrial priming.
Studies often compare blocked and mixed visual search trials to measure intertrial priming.
[6] Reaction times may be faster in blocked trials because participants are required to respond to targets that differ in only one dimension from non-targets.
A cue is a presentation of a stimulus prior to a trial to inform the participant of an upcoming target feature.
Pop-out search tasks include a target that differs in one dimension from a group of homogeneous non-target items.
[10] The "dimension-weighting account" of visual selection states that there is a limit to the attentional weight that can be allocated to a particular dimension of an object at any one time.
The dimensions of stimuli perceived as important to an observer are allocated more attentional weight (i.e. a target in a visual search), resulting in faster detection times.
When target dimensions remain the same across trials there is no change in attentional weight required, resulting in faster reaction times (intertrial facilitation).
[10] However, the repetition of target defining features cannot be excluded as a contributor to the priming effect found in conjunctive searches.