Perception

PERCEPTION
Dr PS Deb
MD, DM Neurology

SENSATION AND PERCEPTION

•The process through which the senses pick up
visual, auditory, and other sensory stimuli and
Sensation transmit them to the brain; sensory information
that has registered in the brain but has not been
interpreted

Perception •The process by which sensory information is
actively organized and interpreted by the brain

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7/11/2010 Perception

NAÏVE REALISM

7/11/2010
1. There exists a world
of material objects.
2. Statements about these objects can
be known to be true through sense-

Perception
experience.
3. These objects exist not only when
they are being perceived but also
when they are not perceived.
4. The objects of perception are
largely perception-independent.
5. These objects are also able to retain
properties of the types we perceive
them as having, even when they are
not being perceived. Their properties
are perception-independent.
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INDIRECT/DIRECT (NAÏVE) REALISM

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 Hallucination and
illusions cannot be

Perception
explained by direct
realism
 Object of world lies
independent of
sensory image and
perception by brain
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EPISTEMOLOGICAL DUALISM

Whether the world • Representative realism claims
we see around us is that we are directly aware only of
the real world itself, internal representations of the
or merely an external world, as objects are
internal perceptual hidden behind a "veil of
copy of that world perception".
generated • Idealism asserts that no world
by neural processes exists apart from mind-dependent
in our brain ideas.
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EXTERNALISM AND INTERNALISM
• Externalists think that factors deemed
"external", meaning outside of the
Externalism psychological states of those who gain
knowledge, can be conditions of knowledge

• all knowledge-yielding conditions are
Internalism within the psychological states of those who
gain knowledge.
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SENSATION AND PERCEPTION

Sensation Input Processing Output

Perception Brain Sense Environment

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SENSATION -> PERCEPTION
• a) sensory organs absorb energy from a
physical stimulus in the environment.
Sensation • b) sensory receptors convert this energy
into neural impulses and send them to the
brain.

Perception • a) the brain organizes the information and
translates it into something meaningful.
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MEANINGFUL INFORMATION

Selective • Process of discriminating between
what is important & is irrelevant
Attention and is influenced by motivation.

Perceptual • How we perceive the world is a
function of our past experiences,
Expectancy culture, and biological makeup
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IN-ATTENTIONAL BLINDNESS

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Perception
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TYPES OF PERCEPTION

Sense perception

Mental Perception
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GESTALT PSYCHOLOGY

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Perception
The whole is different from the sum of its parts

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PHI PHENOMENON

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AMBIGUOUS PHI PHENOMENON

Which direction is
she revolving?

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GESTALT PRINCIPLE OF PERCEPTUAL
ORGANIZATION

1. Law of closure
2. Law of similarity
3. Law of proximity
4. Law of figure/ground
5. Law of good continuation
6. Law of simplicity
7. Law of common fate
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LAW OF CLOSURE
 Humans tend to enclose a space by completing a
contour and ignoring gaps in the figure

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LAW OF SIMILARITY
 Elements that look similar will be perceived as
part of the same form.

There seems to be a triangle in the square 17


LAW OF PROXIMITY
Elements that are closer together will be perceived as a
coherent object.

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LAW OF FIGURE/GROUND
 A stimulus will be perceived as separate from it's
ground

The above figure appears to the eye as a square inside a circle, or as a
donut shaped circle with a square hole 19


LAW OF GOOD CONTINUATION
 Humans tend to continue contours whenever the
elements of the pattern establish an implied
direction

People tend to draw a good continuous line 20


LAW OF SIMPLICITY (PRÄGNANZ)
 A stimulus will be organized into symmetrical,
simple, and regular.

The above figure appears to the eye as a square overlapping triangle, not
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a combination of several complicated shapes

LAW OF COMMON FATE
 Elements that move together tend to be grouped
together

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EMERGENCE

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 Emergence is the
process of complex

Perception
pattern formation
from simpler rules.
 a Dalmatian dog
sniffing the ground in
the shade of
overhanging trees.
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HOW DO YOU SEE THE GLASS?

Optimism Pessimism

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INFLUENCES ON PERCEPTION

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 Perceptual set What do you see?
 An expectation of

Perception
what will be
perceived, which
can affect what
actually is Now what do you see?
perceived

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SEAT OF MINDS EYE
 As humans, we have the ability to see with the mind's eye -to
have a perceptual experience in the absence of visual input.
 fMRI studies have shown that the lateral geniculate
nucleus and the V1 area of the visual cortex are activated
during mental imagery tasks
 The visual pathway is not a one-way street. Higher areas of
the brain can also send visual input back to neurons in lower
areas of the visual cortex...
 For example, PET scans have shown that when subjects,
seated in a room, imagine they are at their front door starting
to walk either to the left or right, activation begins in
the visual association cortex, the parietal cortex, and
the prefrontal cortex - all higher cognitive processing
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centers of the brain

VISUAL THINKING
 A phenomenon of thinking through visual
processing using the part of the brain that is
emotional and creative to organize information in
an intuitive and simultaneous way

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CONTROVERSY ABOUT VISUAL THINKING
 Eidetic Memory: (photographic memory) may
co-occur in visual thinkers as much as in any
type of thinking style as it is a memory function
associated with having vision rather than a
thinking style.
 Eidetic Memory can still occur in those with
visual agnosia, who, unlike visual thinkers, may
be limited in the use of visualization skills for
mental reasoning. 28


DYSLEXIA
 As dyslexia is believed to affect up to 17% percent
of the population and Visual thinking is
predominant in around 60%-65% of the
population, there is no clear indication of a link
between visual thinking and dyslexia.
 As visual thinking is the most common mode of
thought, it might be expected that the incidence
of visual thinking in the dyslexia community
would be reflective of that in the general
population, around 60%-65% of each population. 29


AUTISM
 Visual thinking has been argued by Temple
Grandin to be an origin for delayed speech in
people with autism.
 However, picture thinking itself is only one form
of "non-linguistic thinking" which includes
physical (kinaesthetic), aural (musical) and
logical (mathematical/systems) style of thought

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SPATIAL-TEMPORAL REASONING
 Acute spatial ability is also a trait of kinesthetic
learners (those who learn through movement,
physical patterning and doing) and logical
thinkers (mathematical thinkers who think in
patterns and systems) who may not be strong
visual thinkers at all.
 Similarly, visual thinking has been described as
seeing words as a series of pictures which, alone,
is not exactly the same phenomena spatial-
temporal reasoning. 31


PERCEPTUAL CONSTANCY

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 Perceptual constancy
 The tendency to perceive
objects as maintaining stable
properties (e.g., size, shape,

Perception
brightness, and color) despite
differences in distance, viewing
angle, and lighting
 Size constancy
 Perceiving objects as being about
the same size when they move
farther away
 Shape constancy
 Perceiving objects as having a
stable or unchanging shape
regardless of changes in the
retinal image resulting from
differences in viewing angle
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DEPTH PERCEPTION
 Depth perception
 The ability to see in three dimensions and to estimate
distance
 Binocular depth cues
 Depth cues that depend on two eyes working together
 Convergence
 Occurs when the eyes turn inward to focus on nearby objects
– the closer the object, the greater the convergence
 Binocular disparity (or retinal disparity)
 Difference between the two retinal images formed by the
eyes’ slightly different views of the objects focused on
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ERROR OF PERCEPTION

• Perception without
Hallucination
actual stimuli

• An incorrect perception
Illusion caused by a distortion of
visual sensations 34


MÜLLER-LYER ILLUSION

7/11/2010
The two lines above are
the same length, but

Perception
the diagonals
extending outward
from both ends of the
lower line make it look
longer than the upper
line

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AMBIGUOUS IMAGE

7/11/2010
 Ambiguous figures
 Can be seen in

Perception
different ways to
make different
images
 Best known
ambiguous figure is
“Old Woman/Young
Woman,” by E.
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IMPOSSIBLE FIGURES

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 Do not seem
unusual at first

Perception
 Figures that cannot
be build.

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ALICE IN WONDERLAND SYNDROME

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 The eyes themselves are
normal, but the sufferer
'sees' objects with the wrong

Perception
size or shape and/or finds
that perspective is incorrect.
 This can mean that people,
cars, buildings, etc. look
smaller or larger than they
should be, or that distances
look incorrect; for example a
corridor may appear to be
very long, or the ground
may appear too close.
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THE END
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Perception

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