There is lots of discussion these days about dimensions and no. of dimensions. Lots of research are going on. Here is my idea,
The three dimensional objects cannot see three dimensional objects. Only two dimensions are visible for these 3d objects (human).The third dimension which is not visible for 3d objects can be if not is being assumed by human beings. They just assume the magnitude of the third dimension with their knowledge or experience. So hence all objects around us which are 3d in real are seen as 3d virtually. Nowadays the 3d movies are there . I think those are the mixture of 2d images which seems to be 3d for us. This shows the inability of human brain to see 3d objects. The great example for this is the sun which appears like a circle (circular region to be precise). But in actual it is a sphere.
In similar way, a 2d object can see one dimension. In similar fashion, we the 3d creatures cannot see 4d or even high dimensional objects, unless we assume extra dimensions with immense thinking ability or else wait for time to tell.
Whenever a human sees a circle, he cannot say that it is circle or cylinder if he see it along the centre of cylinder. For him the horizontal And vertical changes can be noticed but the changes on other dimension( the length of the cylinder) goes unnoticed. The third dimension is independent of his vision. It’s like intensity of sound in which after some decibels the human cannot be able distinguish the changes.