Chapter 4

Sensation & Perception

Sensation

• The process by which stimulation of a sensory receptor produces neural impulses that the brain interprets as sound, a visual image, an odor, a taste, a pain, or other sensory images.

• The registration of information.

Perception

• A process that makes sensory patterns meaningful.

How Do We Interpret Sensations?

• STIMULUS - energy that affects what we do.

• RECEPTORS – specialized cells that convert environmental energies into signals for the nervous system.

The brain senses the world indirectly because the sense

organs convert stimulation into the language of the nervous system: neural impulses.

How Does StimulationBecome Sensation?

Transduction

Transformation of one form of energy into another – especially the transformation of stimulus information into nerve impulses.

Sensory pathways – Bundles of neurons that carry information from the sense organs to the brain.

Sensory Adaptation• Loss of

responsiveness in receptor cells after stimulation has remained unchanged for a while.

Thresholds• Absolute threshold –

Amount of stimulation necessary for a stimulus to be detected.

• Difference threshold – Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND).

Approximate absolute thresholds for the 5 senses:

• Vision - Candle flame seen at 30 miles on a clear, dark night.

• Hearing - Tick of a watch under quiet conditions at 20 feet.

• Taste - 1 Teaspoon of sugar in 2 gallons of water.

• Smell - 1 Drop of perfume diffused into a three-room apartment.

• Touch - A bee's wing falling on your cheek from 1 centimeter above.

Thresholds

• Weber’s law – The JND is

always large when the stimulus intensity is high, and small when the stimulus intensity is low.

Signal Detection Theory• Signal detection theory –

Perceptual judgment as a combination of sensation and decision-making processes.

Stimulus eventStimulus event

Neural activityNeural activity

Comparison with Comparison with personal standardpersonal standard

Action (or no action)Action (or no action)

Subliminal Persuasion

• Studies have found that subliminal words flashed briefly on a screen can “prime” a person’s later responses.

• No controlled research has ever shown that subliminal messages delivered to a mass audience can influence people’s buying habits.

The Senses: Smell,

Taste, & Touch

Position and Movement

• Vestibular sense –Sense of body orientation with respect to gravity.– Tells us how our bodies

are positioned.– Movement and motion.

3 semicircular canals

Position and Movement

• Kinesthetic sense –Sense of body position and movement of body parts relative to each other.– Makes you aware when you are crossing your

legs.– Provides constant sensory

feedback.

Olfaction

• Sense of smell.

• Smell can influence mood, memory, emotions, mate choice, and the endocrine system (hormones).

Olfaction

• Olfactory bulbs –Brain sites of olfactory processing.

Olfaction

Olfaction

• Pheromones:

Chemical signals released by organisms to communicate with other members of the species.

• Sexual communication

Taste buds –Receptors for taste (primarily on the upper side of the tongue)

Taste

• Gustation – The sense of taste.

Taste Receptors

• Sweet• Salty• Sour• Bitter

– Umami• Savory

sensation

TASTE & SMELL• Our sense of smell is

responsible for about 80% of what we taste.

• All other flavors that we experience come from smell. This is why, when we have a cold, most foods seem bland or tasteless.

• Our sense of smell becomes stronger when we are hungry.

The Skin Senses

• Touch

• Warmth

• Cold

• Texture

• Pain

Review from Chapter 3!!!

Sensory information related to the skin senses

is processed within which part of the

brain???

Answer:

• SOMATOSENSORY CORTEX

Pain

Gate-control theory• An explanation for

pain control that proposes we have a neural “gate” that can, under circumstances, block incoming pain signals.

Decreasing Pain

• Endorphins – neurotransmitters that inhibit the release of substance P, and therefore weaken pain sensations.

Pain

• Placebos –Substances that appear to be drugs but are not.

• Placebo effect –A response to a placebo caused by subjects’ belief that they are taking real drugs.

Perception brings meaning to sensation, so perception produces an interpretation of the external world, not a perfect representation of it.

What is the RelationshipBetween Perception

and Sensation?

Perception and Sensation?

• Percept – Meaningful product of a perception.

• What we perceive.

The Machinery ofPerceptual Processing

• Feature detectors – Cells in the cortex that specialize in extracting certain features of a stimulus.

The Machinery ofPerceptual Processing

• Binding problem – A major unsolved mystery in cognitive psychology, concerning the physical processes used by the brain to combine many aspects of sensation to a single percept.

Bottom-Up andTop-Down Processing

• Bottom-up processing – Analysis that emphasizes characteristics of the stimulus, rather than internal concepts (stimulus-driven processing).

• Top-down processing – Emphasizes perceiver's expectations, memories, and other cognitive factors (conceptually-driven processing).

Perceptual Constancy

• Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location.

Color

Size

Shape

ILLUSIONS• An incorrect experience of a stimulus

pattern, shared by others in the same perceptual environment.

Muller-Lyer Illusion

Ponzo Illusion

Muller-Lyer Illusion

Ambiguous Figures

• Images that are capable of more than one interpretation.

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The Gestalt Approach• Gestalt psychology –

An approach to psychology that seeks to explain how we perceive overall patterns.

• Figure – Part of a pattern that commands attention.

• Ground – Part of a pattern that does not command attention; the background.

The Gestalt Approach

• Closure – Tendency to fill in gaps in figures and see incomplete figures as complete.

The Gestalt Laws of Perceptual Grouping

SimilaritySimilarity

ProximityProximity

ContinuityContinuity

Common fateCommon fate

PrägnanzPrägnanz

The Gestalt Approach

• Similarity – we tend to group similar objects together in our perceptions.

The Gestalt Approach

• Proximity – we tend to group objects together when they are near each other.

The Gestalt Approach

• Continuity – we prefer perceptions of connected and continuous figures to disconnected and disjointed ones.

The Gestalt Approach

• Common Fate – we tend to group similar objects together that share a common motion or destination.

The Gestalt Approach

• Law of Prägnanz– The simplest

organization, requiring the least amount of cognitive effort, will emerge as the figure.

ABIRD

IN THETHE HAND

Depth Perception

• Visual Cliff Experiment

• Develops around 6 months of age

Depth Perception

• Binocular cues – information taken in by both eyes that aids in depth perception, including convergence and retinal disparity.

Depth Perception

• Monocular Cues – information about depth that relies on just one eye; includes relative size, light and shadow, interposition, relative motion, and atmospheric perspective.

Theoretical Explanations for Perception

• Learning-based inference –View that perception is primarily shaped by learning, rather than innate factors.

• Perceptual set –Readiness to detect a particular stimulus in a given context.

The Hermann Grid

Do you see small gray squares between the black squares?

The Stroop Effect

End of Chapter 4