This document provides an overview of sensation and perception. It defines sensation as the basic process of receiving sensory information, while perception involves interpreting that information. It discusses the sensory receptors and pathways for different senses. Key aspects of perception covered include thresholds, adaptation, attention, form perception, depth perception, movement perception, constancy, plasticity, and individual differences. Factors that can influence perception like the stimulus characteristics, context, and the individual are also summarized. The document is presented by Dr. Subodh Kumar Sharma on sensation and perception.

1. SENSATION
AND
PERCEPTION
Presenter: Dr. Subodh Kumar Sharma (Resident Ist year)
Moderator: Assoc. Prof. Sandesh Sawant, (Clinical Psychology)
Department of Psychiatry
National Medical College, Birgunj

2. Overview:
• Sensation and its psychophysics aspect
• Sense organs and their pathways
• Perception
• Various Perceptual Process
• Factors affecting Perception

3. Sensation
• The process of receiving information through the senses (organs), which
can later be interpreted by the brain.
• Is a general biological process.
• The source is stimuli received by the senses.
• Results in raw information.

4. Psychophysics:
Thresholds and Stimulus Change
• Threshold: minimum amount of any given sensation that has to be present
for us to notice.
• Absolute threshold: minimum amount of stimulus that is necessary for us to
notice it 50% of the time.
• Difference threshold: difference between two stimuli to be detected.
• Weber’s law: The law states that the change in a stimulus that will be just
noticeable is a constant ratio of the original stimulus.
• Sensory adaptation: reduction in sensitivity to a stimulus after constant
exposure to it.
• Helps free up our attention and resources to attend to other stimuli in the
environment around us.

5. Physical energy
From the
environment
Transduction
at receptor
Receptor
potentials
Generator
potentials
Nerve
Impulses
SENSATION
(Sensory
Cortex)

6. Sensory Receptors:
• Detect stimuli and convert energy into neural impulses.
• Receptors are special cells designed to serve very specific functions.
• Rods and Cones cells
• Pacinian , Meissner's, Ruffini’s corpuscle, Merkle's disc, free nerve endings,
hair receptors
• Taste Buds
• Hair cells in Ear
• Olfactory Epithelium (Bulb)

9. VISION

10. Visual Pathway

11. Hearing Pathway

13. OLFACTORY PATHWAY

15. Skin and Sensations

17. Cutaneous Sensory Pathway

18. Sensation to Perception
• Perception is the process of interpreting the information received by the
sensation process.
• Results in meaning of that information.
• More of a psychological process as it is affected by the prestored information
in the brain.
• Perception thus is whatever is experienced by the person. The way world
looks, sound, feels, tastes or smells.

19. Perception
• Arrived from Latin word “percepio”…..
• Meaning action of taking possession and apprehension from mind and
senses.

20. Perception
• “part of what we perceive comes through the senses of the object before
us; another part… always comes…out of our own head”
-William James
Father of American Psychology

21. Perceptual Process
• Attention
• Form perception
• Visual Depth Perception
• Constancy
• Movement Perception
• Plasticity
• Individual Differences

22. Perceptual Process: Attention
• Attention is the term given to the perceptual process that select
certain inputs for inclusion in our conscious experience, or
awareness, at any given time.
• Characteristics of attention:
• Selective
• Shiftable

23. BottleneckTheory: filtration

24. Early vs Late Bottleneck
• Specially two Theories regarding filtration:
• Broadbent ,1958: the filter or information bottleneck is at sensory organ or at
least at the very early stage of information processing.
• Shiffrin and Schneider, 1977 argue that filtering take place at later stages of
information flow (at the stages where input is interpreted as meaningful)

25. Filtration: Processing Capacity
• Kahneman 1973,
• We have limited mental capacity for processing all the information so
allocation of processing capacity to one set of input or another.
• Inputs which take up most of our processing capacity takes the focus of our
attention.

26. Determinants of Attention
• Depends upon different character of stimuli:
• Nature
• Reality
• Familiarity
• Proximity
• Novelty
• Suspense
• Conflict
• Humor
• Vitality
• Activity
• Intensity

27. Perceptual Process: Form Perception
• Ability to distinguish an object from its general background
Form perception is the recognition of visual elements of objects, specifically
those to do with shapes, patterns and previously identified important
characteristics.
Components of form perceptions:
• Contour
• Organization

28. Contour in Form Perception:
Figure Ground Relationship
• An outline representing or bounding the shape or form of something,
separates figure with ground
• Formed whenever a marked difference occurs in the brightness or color of the
background..
• Contours are determinant of the shape but they are shapeless.

30. Break in the contour results in Camouflage!

31. Organization in Form Perception:
• Refers to systematic, orderly , regular or patterned arrangement
• In perception refers to the pattern of the stimuli
• Was studied by GESTALT psychologists.
• Emerged in early 20th century, Germany
• Refers to the essence or complete form of a entity

32. The whole is more important the sum of its parts..
• Mental experience depends upon the patterning and organization of
elements and is not due simply to the compounding of the elements.
• Mind is best understood in terms of the way elements are organized.

33. Gestalt Principles of Perceptual Organization

34. Law of Proximity
Items which are close together in space or
time tend to be perceived as belonging
together or forming an organized group.

35. Law of Similarity
Items that are similar in shape size or color
are perceived as being grouped or related.

36. Law of Good Figure (Symmetry)
There is tendency to organize things to make
a balanced or symmetrical figure that
includes all the parts.

37. Law of Continuation
There is tendency to perceive a line that
starts in one way as continuing in the same
way.

38. Law of Closure
Tendency to organize the perceived world by
filling the gaps in stimulation, and perceive a
whole form rather than disjointed parts.

39. Perceptual Process:Visual Depth Perception
Depth perception is the ability of the human eye to see in three dimensions.
It is often demonstrated with the measurements of length, width and height.
Perceiving the three dimensional world is attributed to:
• Monocular Cues
• Binocular Cues

40. Monocular Cues:
• Linear Perspective
• Clearness
• Interposition
• Shadows
• Gradients of texture
• Movement

41. Binocular Cues:
• Stereopsis:
Retinal disparity, or binocular parallax
the difference in images between the
two eyes, which is greater for objects
that are close and smaller for distant
objects.
• Convergence:
The rotation of the two eyes in their
sockets to focus on a single object,
resulting in greater convergence for
closer objects and lesser convergence
if objects are distant.

42. Perceptual Process: Constancy
• Size Constancy:
• The tendency to interpret an object as always being the same actual size,
regardless of its distance.

43. Perceptual Process: Constancy
• Brightness Constancy:
• The tendency to perceive the apparent brightness of an object as the same
even when the light conditions change

44. Perceptual Process: Constancy
• Shape Constancy:
• the tendency to interpret the shape of an object as being constant, even
when its shape changes on the retina

45. Perceptual Process: Movement Perception
• Constancy of real motion perception:
• Independent of the real motion of the image across the retina, perception
depends upon the motion relative to the background of the image.
• Brain Comparator and Real motion Perception:
• The brain comparator is the system which compares information about the
muscle movements with the information about the movement of retinal
image.
• Apparent Motion: Movement perceived in the absence of physical
movement of an image across the retina.
• Stroboscopic Motion
• Induced movement

46. Perceptual Process: Plasticity
• Visual Deprivation: restriction of visual impulses during the sensitive period
results in impaired visual perception even after correction of restraints.
• Nature VS Nurture: inborn, innate vs learning and effect of environment
Refers to the moldability or modifiability of perception.
Prolonged changes in sensory input can modify the ways information is processed.

47. Perceptual Process: Individual Differences
• Perceptual Learning:
• Learning, experience and practice in past makes the difference in ability to
extract information from the stimuli, Practical and adaptive value
• Example: Bird expert (Ornithologists) can separate more sounds of birds.
• Set:
• Refers to the readiness or condition we are primed for.
• Set (mind set) may determine the difference in perception

48. Perceptual Process: Individual Differences
• Motives and Needs:
• Physiological > safety > Social > Esteem
> Self Actualization -Abraham Maslow
• Perceptual Cognitive Styles:
• Flexibility of perception: Flexible
wider focus of attention and less influence
• Field dependance: unify and organize
inputs making it difficult to break

49. Parrot
High heeled boot
Screw driver
Kangaroo
Horse shoe
Mitten
Squirrel
Cap
Shark
Eel
Sunglasses
moon

50. Factors Influencing Perception:
• Character of Stimulation
• Character Of Context
• Character of Individual

51. Summary
Stimulation
Received via Sense
Organ and
Receptors
Filtration
of
Stimulati
ons
Informati
on
Processin
g
Perception
Workin
g
Memor
y

52. References:
• Introduction to Psychology, Seventh Edition, CliffordT. Morgan Et. all
• A text book of General Psychology, First Edition, Grishbala Mohanty
• General Psychology

53. THANKYOU!!