How does a predator within 4 seconds of scanning an environment map it, memorize it, and sort out all unnecessary information from the info needed to be able to survive? Many theories have to do with the difference between top down and bottom up visual processing. Top down processing refers to the slower, executive cognition behind vision while bottom up is fast and not consciously driven and heavily influenced by environmental cues. Those environmental cues have been studied as to their effect and also as to what exactly grants them salience, or the property that allows the stimulus to stand out against its backdrop. While many studies have already been done studying the effect of salience on such things as saccade movements in the eyes to fixation periods to mapping brain location, little to no experiments have been done trying to illuminate salience and its relationship to memory.
A simple task was devised consisting of having 12 participants focus on a scene for a brief period of time. The view is then removed from the participants and they are subjected to a wait period. Once that time is completed the participants are asked to recall the position of several figures in the scene to test their memory. They varied the difficulty of the scenes and the salience of the objects to see if there was any correlation between the two, and as it turns out there was indeed. The salience of the object was directly correlated with the performance of the participants meaning they were more successful at recalling the objects exhibiting greater degrees salience than they were recalling inconsequential items. Furthermore, they tested this with varying degrees of difficulty and found that the more difficult the recollection task was, the greater the positive effect of salience had on the performance of the participants. While one could argue that they perhaps were drawn to those items and they simply focused on those items more than the others thus increasing the chances of memorization, they mapped and timed their eye movements to measure any fixation times on the items and found no difference in the fixation times between the salient objects and the non-salient objects meaning that they spent the same amount of time memorizing each object.
To summarize the findings, they showed that human´┐Ż??s ability to recall objects within a certain space is positively dependent upon the salience of the object, and it is not due to any differences in memorization periods. A positive correlation between the increasing difficulty of the task and the positive effect of salience on memorization suggests that perhaps the brain may use salience to identify objects of value and omit objects deemed unimportant when the brain is forced to compromise.
They did make sure to mention another study with conflicting results. The study opted for a test involving people to assess whether a certain object was in a scene. They authors asserted that the difference in the findings could be attributed to the inherent difference in the tests, as one dealt with object identification and another with object location and spatial memory. They conclude that salience of an object and the effect it has on memory needs to be studied on a brain system to brain system basis, analyzing which systems are involved and what that would then imply.
This study provides more insight into the evolution of sight and how vision has been used and fine tuned throughout evolution. Recognition of the salience of an object is conserved throughout most species and clearly plays a pivotal role in the utility of vision as a whole. The ability to quickly asses an environment for all the information essential for survival is something that if without many animals would fall prey much more often due to lack of attention. This often taken-for-granted aspect of our vision that we are mostly unaware of is something that most certainly needs to be studied further and fully understood.
Original Article: http://www.jneurosci.org/content/29/25/8016.full