This ppt explains the cognitive psychological aspects about perception

1. PERCEPTION - LOCALIZATION
To know where the objects in our environment are

2. SEPARATION OF OBJECTS
• Figure and Ground
• Grouping of Objects – Grouping by proximity, Grouping by similarity,
Grouping by closure, Grouping by good continuation

3. PERCEIVING DISTANCE
BINOCULAR CUES
• Binocular Disparity refers to the difference in the views seen by each
eye.
• Beyond 10-12 feet the difference in views seen by each eye is so small
that Binocular disparity loses its effectiveness as a cue for depth.
• Visual part of the brain uses binocular disparity to assign objects to
various locations in space.
• Stereoscope – 3-D – fool the eye into seeing depth when none is
really present.

4. PERCEIVING DISTANCE
MONOCULAR CUES
When objects are farther away monocular cues must be used.
The visual system has to make use of a hodgepodge of available information
in the environment to come to a conclusion
1. Relative Size – If an image contains an array of similar objects that differ
in size, the viewer interprets the smaller objects as being farther away.
2. Interposition – If one object is positioned so that it obstructs the view of
the other, the viewer perceives the overlapping object as being nearer.
3. Relative Height – Among similar objects, those that appear closer to the
horizon are perceived as being farther away.

5. PERCEIVING DISTANCE
MONOCULAR CUES
4. Perspective – When parallel lines in a scene appear to converge in the image, they are perceived
as vanishing in the distance.
5. Shading and Shadows – The configuration of shading and shadows provides information about an
object’s depth;
Attached shadow/Shading – When shadow falls on a part of the same object that is blocking the
light;
Cast Shadow – If the shadow falls on another surface that does not belong to the object casting the
shadow;
Both give information about object shapes, distance between objects and the location of the light
source in a scene.
6. Relative motion – The different speeds of two objects can be a depth cue – when you are moving
quickly, nearby objects seem to move quickly in the opposite direction while more distant objects
move more slowly and extremely distant objects appear not to move at all; the difference in speeds
with which these objects appear to move – motion parallax – provides distance from us.

6. PERCEIVING MOTION
To move around – we need to know the locations of stationary objects and
the trajectories of moving ones.
STROBOSCOPIC MOTION –
We perceive that an object is in motion whenever its image moves across
the retina
We see motion even when nothing moves on the retina – Stroboscopic
motion (Wertheimer) – is produced most simply by flashing a light in
darkness and then, a few milliseconds later, flashing another light near the
location of the first light. The light will seem to move
Ex., Movie – is a series of still photographs (or Frames), each slightly
different from the preceding one.

7. PERCEIVING MOTION
REAL MOTION –
Visual system is also sensitive to the movement of an object through
all intermediate points in space – amazingly complex!!!
Some paths of motion – attributed to movements of the eye over a
stationary scene (ex., reading);
Other motion paths – attributed to moving objects (ex., Thrown Ball);
And some objects whose retinal images are moving must be seen as
stationary (ex., when the stationary background traces motion across
the retina because our eyes are pursuing a flying bird)

8. PERCEIVING MOTION
REAL MOTION –
Accordingly, our analysis of motion is highly relative –
We are better at detecting motion when we can see an object against a
structured background (relative motion) than when the background is a
uniform color and only the moving object can be seen (absolute motion)
SELECTIVE ADAPTATION – Loss in sensitivity to motion that occurs when we
view motion; the adaptation is selective in that we lose sensitivity to the
motion viewed and to similar motion, but not to motion that differs
significantly in direction or speed.
We do not loss sensitivity, but we notice the aftereffect produced by
adaptation (ex., waterfall – cliff - upward movement)

9. PERCEIVING MOTION
BRAIN - REAL MOTION
Some aspects of real motion are coded by specific cells in the visual
cortex.
These cells respond to some motions and not to others, and each cell
responds best to one direction and speed of motion; Evidence for
existence of such cells – studies with animals – records the responses
of single cells in the visual cortex while the animal is shown stimuli with
different patterns of motion.
Specialized motion cells provide possible explanation for selective
adaptation

10. PERCEIVING MOTION
NEURAL BASIS OF REAL MOTION
Is not limited to activation of specific cells
Ex., when we track a luminous object moving in darkness – our eyes
follow the object, the image is almost motionless on the retina, yet we
perceive a smooth, continuous motion.
Information about how our eyes are moving is sent from motor regions
in the front of the brain to the visual cortex and influences the motion
we see.