Lecture 3 - Sensation & Perception

8/3/2019 Lecture 3 - Sensation & Perception

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PL1101E INTRODUCTION TO PSYCHOLOGY

SEM. 2 AY2010/2011

WEEK 3

Lecturer: Dr. Travellia Tjokro.

E-mail: [email protected]
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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TODAYSAGENDA

Announcements.

Sensation & Perception.

Ch. 5 of your textbook.

Focus today:Sensation:

Some concepts of sensation.

Sensory system: Vision.

Perception.


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ANNOUNCEMENTS

Tutorial sessions start this week (Week 3).


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SENSATION & PERCEPTION

Sensation: the stimulus-detection process bywhich our sense organs respond to and translateenvironmental stimuli into nerve impulses thatare sent to the brain.

Perception: making sense of what our sensestell us.


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Psychophysics: the scientific area that studies

relations between the physical characteristics of

stimuli and sensory capabilities.


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STIMULUS DETECTION

Absolute Threshold: the lowest intensity at which

a stimulus can be detected 50% of the time.


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STIMULUS DETECTION

An individuals sensitivity can fluctuate.

Decision Criterion: a standard of how

certain they must be that a stimulus is

present before they will say they detect it.Signal Detection Theory: concerned with

the factors that influence sensory

judgments.

Depends on factors such as fatigue,

expectation, and significance of the stimulus.


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SIGNAL DETECTION


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SUBLIMINAL STIMULI

Subliminal Stimulus: one that is so weak or brief

that although it is received by the senses, it

cannot be perceived consciously.

Persuasive stimuli above the perceptual threshold

are far more influential.


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THE DIFFERENCE THRESHOLD

Difference Threshold: smallest difference

between two stimuli that people can perceive 50%

of the time.

Webers Law: the difference threshold is directly

proportional to the magnitude of the stimulus

with which the comparison is being made.


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SENSORYADAPTATION

Sensory Adaptation: the diminishing sensitivityto an unchanging stimulus.

Occurs in all senses.

Adaptive - allows our senses to pick up informative

changes in the environment that could be important

to our survival.


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SENSORYSYSTEMS: VISION

Transduction: the process whereby the

characteristics of a stimulus are converted into

nerve impulses.

Vision:

Stimulus is electromagnetic energy.

Sensitive to wavelengths from about 400 to 700

nanometers.


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THE EYE


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THE EYE: PARTS

Light waves enter the eye through the cornea.

Pupil: an adjustable opening behind the cornea that

controls the amount of light that enters the eye.

Dilates or constricts using muscles in the iris, the

colored part that surrounds the pupil. Lens: an elastic structure that becomes thinner to focus on

distant objects and thicker to focus on nearby objects.

Retina: a multilayered light-sensitive tissue at the rear of

the fluid-filled eyeball.

Contains two types of light-sensitive receptor cells.


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1. Rods - most abundant in the periphery of the eye and

respond to faint light.

2. Cones - most abundant in and around the fovea.

Essential for color vision & more useful in bright

light.


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Fovea: a small area in the center of the

retina that contains no rods but many

densely packed cones

Cones decrease in concentration the fartherthey are from the center of the retina.


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Rods and cones have synaptic connections withbipolar cells.

Bipolar cells are connected toganglion cells.

Axons of ganglion cells are collected into a bundle,

which forms the optic nerve.An absence of photoreceptors where the optic

nerve exits the eye creates a blind spot.


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THEVISUAL PROCESS

The Visual Process:

Lens reverses image from right to left, top to bottom

on retina.

Activity of photoreceptors and associated neurons

sends input into the brain. Brain reconstructs visual input in the correct

direction.


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HOW DO WE SEE COLORS?

Theories of color vision:

Young-Helmholtz Trichromatic Theory:

Cones are most sensitive to wavelengths

corresponding to blue, green, and red.

Opponent-Process Theory: Three types

of cones respond to two wavelengths

(opponents).

Red-greenBlue-yellow

Black-white


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Dual-Process Theory: combines trichromatic and

opponent-process theories to account for the

colour transduction process.

Trichromatic: cones are most sensitive to blue, green

and red. Opponent processes begin in ganglion cells and

beyond (not the cones).


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NOWLETS SWITCH TO

PERCEPTION


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PERCEPTION

Perception is an active, creative process in whichraw sensory data are organised and givenmeaning.

Bottom-up Processing: the system takes inindividual elements of the stimulus and thencombines them into a unified perception.

Top-down Processing: sensory information isinterpreted in light of existing knowledge,concepts, ideas, and expectations.


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TOP DOWN PROCESSING


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THE ROLE OFATTENTION

Attention involves two processes:

Focusing on certain stimuli

Filtering out other incoming information

Studied experimentally using shadowing (e.g.,

dichotic listening task).

Inattentional Blindness: the failure of

unattended stimuli to register in consciousness.


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Stimulus

characteristics that

affect attention:

Intensity

Novelty

Movement

Contrast

Repetition

Personal factors that

affect attention:

Threats to well-being

Participants are faster

at finding a singleangry face in a happy

crowd than a single

happy face in an angry

crowd


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PERCEPTION: ORGANIZATION &

STRUCTURE

Gestalt Principles: argues that the whole is more

than (and different from) the sum of its parts.

Figure-Ground Relations: our tendency to

organise stimuli into a central or foreground

figure and a background.


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FIGUREGROUND RELATIONS


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Gestalt Laws of Perceptual Organisation:

Law of Similarity: similar elements will be

perceived as belonging together

Law of Proximity: elements that are near eachother are likely to be perceived as part of the

same configuration

Law of Closure: people tend to fill in gaps in

incomplete figures

Law of Continuity: people link individual

elements together to form a pattern that

makes sense


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PERCEPTION NEEDS CONSTANCY

Allow us to recognize stimuli under different

circumstances.

Shape Constancy: allows us to recognize people

and other objects from many different angles.

Brightness Constancy: relative brightness of

objects remains the same under different

conditions of illumination.

Size Constancy: the size of objects remains

relatively constant even though images on ourretina change in size with variations in

distance.


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PERCEPTUAL ILLUSIONS

Illusions: compelling but incorrect perceptions.

Most can be attributed to perceptual constancies that

ordinarily help us perceive more accurately.


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PERCEPTUAL DEVELOPMENT

Results from

biological and

environmental factors.

What is the object

above the womanshead?


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PERCEPTUAL DEVELOPMENT

Critical Periods: certain kinds of experiences

must occur if perceptual abilities and the brain

mechanisms that underlie them are to develop

normally.

Kittens raised in completely vertical environmentswere unable to see horizontal objects, and vice-versa

(Blakemore & Cooper, 1970).

Lecture 3 - Sensation & Perception

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