Images in which one object is more salient than its surroundings lead to a ‘pop-out’ effect where subjects show very efficient behavioral responses to the salient object.  This pop-out effect is present for displays in which: 1) a single object is on a blank background, and 2) a single object is highly distinct from other surrounding objects. Thus it is generally assumed that this pop-out effect arise from the same neural computations for both of these types of displays, and it is thought that this effect is mediated by “bottom-up” attentional mechanisms. 

To directly examine whether these two types of displays are indeed processed the same way, we recorded neural activity in LIP and PFC which are two brain regions implicated in attentional processing. Using population decoding methods, in a population of 280 LIP and PFC neurons recorded from two monkeys we observed that when a single isolated object is displayed, information about the object’s location appeared ~10 ms earlier in LIP than in PFC, which is consistent with a feed-forward account for processing isolated objects. However, when a salient object is presented among multiple distractor objects, information about the location of the salient object was delayed by 60-90 ms in both brain regions, and information now first appeared in PFC. Despite the differences in the latency of information between the two display types, the latency of population firing rate activity was similar for both types of displays. Additionally, we see that pattern of neural activity is very similar for both types of displays (and across different color transformations of the stimuli) indicating that information about the object’s location is being coded in the same way regardless of display type. These results indicate that there is ‘top-down‘ neural component for processing pop-out displays, and that firing rate latencies can be quite distinct from the latency of when information first appear in a brain region.