|PSY 101 Sensation & Perception: Vision II: Forms, Patterns, Objects, Depth, Distance|
Perceiving Forms, Patterns, and Objects
What do you see?
This is a reversible figure, that is, an image which has two equally likely interpretations of what it might be.
We can take the same stimulus and interpret it in different ways. Thus, perception has an interpretive, that is, subjective quality.
Our interpretation can be influenced by our "perceptual set" -- a readiness to perceive or see a stimulus in a particular kind of way.
The brain appears to go through a process of "hypothesis" testing when it perceives an ambiguous object. The hypothesis which is best supported by the visual evidence is then accepted as the perception.
Inattentional Blindness: The failure to see clearly visible objects if one's attention is directed or focused on something else
- Example: Selective attention test (Daniel Simons & Christopher Chabris, 1998, YouTube)
- How do we perceive forms of objects in the world? Evidence suggests that we use a process of detecting or extracting out specific elements in our visual input and assembling these into a more complex form = Feature Analysis (see diagram above on left)
- This is considered to be an example of a "bottom up processing" mechanism in which individual elements are assembled into a whole.
- However, top-down processing in which the whole is understood before the individual elements are deceiphered is also supported by research. Reading, for example, appears to be a highly "top down" behavior. Notice in the diagram above on the right how much easier it is to read the "upper letter" version. This may be due to our top-down processing abilities which come up with a solution to deciphering the words before all of the letters are identified.
Gestalt Principles: Looking at the Whole Picture
1912 German psychologist, Max Wertheimer (photo above), described the Phi Phenomenon, i.e., the tendency to see motion images are presented in rapid succession (see illustration on right).
In the 1920s and 1930s, a group of psychologists investigated our "perception of the whole" which they called Gestalt Psychology (Gestalt is the German word for "figure" or "form")
Their work led to a set of perceptual rules. These include:
A. Figure and Ground
In any whole scene, what we pay attention to is the figure and everything else is the ground. Usually a figure is scene as more fully defined, smaller, in front (closer), and often brighter:
What do you see? (1) A vase or (2) two profiles facing each other?
B. Proximity: That which is near is seen as belonging together
C. Closure: Gaps or missing elements in figures are filled in by the perceiver
D. Similarity: Objects which look alike are grouped together or seen as belonging to the same group
E. Continuity: We tend to see elements moving in the same direction as belonging together
F. Simplicity: The Gestalt "Law of Pragnanz" says that we group items together perceptually which make a good form. This is usually the simplest way of grouping. In Figure F below, do you see (1) one very complicated figure or (2) three overlapping rectangles? The Law of Pragnanz suggests you will see three rectangles.
B. C. D. E. F.
Perceiving Depth & Distance
- The eyes see slightly different views of the same object. The brain interprets these differences as "depth"
- Retinal Disparity: Objects within 25 feet actually project to slightly different locations on the retina of each eye. The disparity or difference between these views on the retina is used by the brain to create a sense of depth.
See the Autostereogram article in Wikipedia for a fascinating experience
of binocular cues and how the brain can be fooled into seeing
depth in a two-dimensional image
- Cues from Each Eye: As objects move closer, the eye itself must adjust to keep the object in focus. The brain uses the information about this muscular accommodation to determine distance
- Pictorial depth cues: cues for distance which can be deduced from a flat scene or picture. These include
- Linear perspective: Parallel lines grow closer together in the distance
- Textual gradient: A surface or texture is coarser for nearby objects and finer for distant objects
- Interposition: Objects which overlap or block another object from view are closer
- Relative size: Objects which are farther away are smaller than the same object which is nearby
- Height in plane: Objects which are low in the visual plane are nearby and objects which are higher are distant
- Light and shadow: We can use shadow and light to create a sense of depth
Use the following pictures to identify pictorial depth cues
Lake Winnipesaukee, NH (2002)
Lee Vining, California (Rt. 395, July, 1998)
Chapel of the Seven Lights
University of Seattle (Aug, 1998)
Reno, Nevada, July 4, 1998