Our eyes are one of our sense receptors that register impressions coming from outside our bodies and through them we see and perceive the world around us. But in order to know what we register with our receptors, like eyes and ears, we must let the impressions pass through a “filter” in our brain. Filter by definition is a piece of equipment or a substance that you pass gas or liquid through to remove unwanted substances1. Like the definition this filter in the brain select which of the impressions are necessary for forming an opinion about the surrounding world – those who stay left in the filter are the unwanted substances and those who get through are the “wanted substances” used for perception. Another way to put it is that we must cook the raw sensation before we can digest it2, i.e. we have to filter our sense data before we can perceive.
For new born babies the surrounding environment is often apprehended as chaotic with many new impressions. They have difficulties keeping up with the information given to them through their receptors that has to be registered, categorized and excluded. The difficulty for a baby is to select which impressions are important and which are not in order to perceive an accurate image of the world around him/her.
Learning how to see, as in the case of the infant, is really learning how to associate certain sense data (e.g. sound and colour) with objects and through this learning we develop a filter through which all our impressions go through. This filter is built up of experiences based on everything we have done and everything that has happened to us, emotionally and so on. So to understand how our filters are working we have to be familiar with all experience we have gained throughout our life.
If I go on vacation to Spain and there meet some Spaniards which are really impolite and unfriendly these experiences will be saved in my “filters”. Next time I meet a Spaniard, or someone who looks like or seems like it, the impressions will be go through my filters and since I from experience registered them as impolite and unfriendly I will regard them as that now as well even if they might not be like that.
For a grown-up person the process of perception is automatic, he/she has learned how to filter the sense data, i.e. selecting which impressions are relevant or not, to see the thing perceived by the sense receptors.
Each and every person have different filters, this is why we perceive the exact same thing/event differently. If two persons saw a car accident on a street and where to retell the story for a policeman, the two stories received would not be alike. This since the information received to the two individual persons
But the things we perceive might not always bee correct since we often see what we expect, or want, or are used to see – so forth the filters in this case do not fulfil their function of giving a picture of how things really are and even if we know that this is the case of the perception it is hard to identify when we use our filters in this way, i.e. we can not understand our filters.
To say that the grass is green is not a fair statement, this because the statement is subjective and relative – it varies with many conditions which are extrinsic to the object perceived4.So when you look at the grass at night it does not look green, but since we know that grass normally has a greenish colour, from experience, we will see it as green and therefore we ignore the impressions filtered because we are used to it as being green.