Design_Principles

=**What is Depth Perception?**=

//Depth perception// is the sensory ability to perceive the visual world in three dimensions. (1) Using depth perception techniques, a person can guage the distance between the eye and an object.

Depth can be perceived in a number of ways. As humans with binocular vision (two visual fields merging into one), we perceive depth in a different way from lower ended animals.

There are two cues to Depth Perception: Primary and Secondary.

=**Primary Depth Cues**=


 * Retinal Disparity** - having our eyes about 7 centimeters apart allows us to see objects in a three-dimensional perspective (Benyon, 2006). The sizes of our heads vary; small heads may have their eyes closer together and larger heads may have their eyes further apart (Benyon, 2006).




 * Stereopsis** - As mentioned above, humans have binocular vision. This allows two seperated images to be filtered in through each of our eyes to be fused together allowing one visual depth image to be produced.




 * Accomodation** - the lenses in our eyes change shape as they try to focus on objects far away or closer to us. Usually, images or objects further away from us require sharp focus and thus, a contraction of the lens. Objects closer to us require us to focus less sharply, thus allowing in the decontraction of the lenses. In both cases, the objects components can be seen clearly (Benyon, 2006).
 * Convergence** - similar to accomodation, this depth cue requires our eyes to adjust to objects further away by moving our eyes closer together for objects close by and back to normal position by focusing our lenses on objects far away.

=**Secondary Depth Cues**=


 * Light and Shade** - objects with a shadow create greater depth cues as it helps give an object at three dimensional appearance.


 * Linear Perspective -** this is where objects drawn on paper or by computer that have multiple lines trying to prtray it as an object with depth.
 * Height in Horizontal Plane** - makes lines which are further away from the eye to look smaller than lines that are closer to the eye.


 * Motion Parallax** - The depth cue illusion of movement which states that closer objects appear to be moving faster (causing it to blur) than objects in the same scene that are farther away and moving slower in the background.




 * Overlap -** overlapping objects show content which lays over other content with shaded corners, appearing closer to the viewer and vice versa. For example, having open multiple MSN windows.


 * Relative size -** objects that are further away tend to look smaller than similar or larger sized objects closerby


 * Texture Gradient** - Rough texture makes visual images look as though it is close-by, whereas smoothened out textured images appear distant.

= = =**References**=

Benyon, David and Phil Turner, and Susan Turner. "Designing Interactive Systems (People, Activities, Contexts, Technologies)". 2005. Spain. Pearson Education Limited.

Depth Perception Definition image - http://en.wikipedia.org/wiki/Depth_perception Shading image - http://www.quia.com/files/quia/users/rachael%20jaster/Art_I/Shading.jpg Linear image - http://www.thehypertexts.com/Mysterious_Ways/Images/Richard%20Moore%20The%20Self%203D%20Box.gif Motion Parallax image - http://www.employmentscreeninginc.com/customers/104101109382899/images/Driving.jpg relative size image- http://www.msnbc.com/news/2027856.jpg overlap image - http://www.43folders.com/images/Drag_Into_Dialog_Boxes.jpg Retinal Disparity image - [|http://alpha.furman.edu/~einstein/general/sandpdemo/98.jpg]
 * Stereopsis image - http://users.ntua.gr/thanny/stereopsis/bimbo.jpg**
 * Accomodation image - http://intropsych.mcmaster.ca/intropsych/1a3/S_P/sp2j.gif**