Seeing is all about attention
Perceiving is a skilled active process. Whenever we see any mobile app or website there are frequent eye movements, so that any critical information present can be scanned at first. These eye movements are done to satisfy our need for information. Each time the eye briefly comes to rest, the pattern-processing machinery goes to work sorting out what is most likely to be relevant to our current cognitive task. Almost everything else is either not seen at all or retained for only a fraction of a second. A few fragments are held for a second or two, and a tiny percentage forms part of our long-term memory.
e.g. When I am searching for my car keys in a drawer, I am scanning the drawer to look for something in key shape. Once I find the car keys, I can recall only a few items that were present in the drawer but I will remember them for a long time and I can recall those items maybe after 10 days also.
Similarly, when we are designing websites or mobile applications, we need to understand that the user has come to our platform for a purpose. They are scanning the content till they find any resourceful information. The rest of the information present, the user may not recall them except in fragments.
What users perceive of the website or app is strongly biased according to what they are attempting to accomplish.
We make visual queries every time we search for some visual information that we need to carry out our cognitive task of the moment. Understanding what visual queries are easily executed is a critical skill for the designer. Effective design should start with a visual task analysis, determine the set of visual queries to be supported by a design, and then use color, form, and space to efficiently serve those queries.
When using images, illustrations, colors and copywriting in our digital products, these elements may make a long lasting memory for user subconsciously.