Sensation and Perception

Electrical Activity of the Neuron

"Nothing is in the mind that did not first pass through the senses" (Aristotle)

Sensation stimulation of sense organs (Passive, Physiological)

Perceptionselection, organization, and interpretation of sensory

input (Active, Cognitive)

Psychophysical Relationship

Physical

Stimulus

Sensory

ExperienceTransduction

Not all physical stimuli result in sensory experience

EffectiveStimuli

IneffectiveStimuli

Threshold

Absolute Threshold (Absolute Limen)

The minimum intensity of a stimulus that will cause a perception to occur (Weber)

The Test Setting (Complete Darkness)

Absolute Threshold (Absolute Limen)

The 50% Detection

Level

Difference Threshold (Difference Limen)

The smallest degree of change in a stimulus which is detected by the subject (JND or Just Noticeable Difference)

The Test Setting (Dimly Lit Room)

Difference Threshold (Difference Limen)

Experiment #1 Required Transition from 60.0 to 61.0 to attain a JND

Experiment #2 Required Transition from 120.0 to 122.0 to attain a JND

Experiment #3 Required Transition from 600.0 to 610.0 to attain a JND

Size of the JND is not a constant amount but is rather a constant proportion of it initial value

Weber’s LawTo make a stimulus Just Noticeably Different you must

change it by a constant fraction of its initial value

ΔI

I= K

Weber’s Constants

Brightness 1/61 1.6%

Pitch 1/333 0.3%

Lifted Weights 1/51 2.0%

Saltiness 1/5 20.0%

Make it Saltier

Amount of Salt

10 12

JND = 2

14.4

JND = 2.4

17.3

JND = 2.9

20.8

JND = 3.5

25.0

JND = 4.2

The Sensory ModalitiesPhysical Stimulus

Transducer Perceptual Experience

Light Eye Vision

Sound Ear Audition

Chemical

(Atomized)

Nose Olfactory

Chemical

(Solution)

Tongue Gustation

Heat, Cold, Mechanical

Compression, Tissue Damage

Skin Tactile

VisionNeed to understand the nature of the physical stimulus (Light) as

well as the transducing system (the Eye)

Light - is a form of electromagnetic radiation that travels as a wave

Only a narrow band of electromagnetic wavelengths give rise to visual sensation

Light

VisionNeed to understand the nature of the physical stimulus (Light) as

well as the transducing system (the Eye)

Light - is a form of electromagnetic radiation that travels as a wave

Physical Properties Perceptual Properties

Wavelength Hue

Amplitude (Intensity) Brightness

VisionNeed to understand the nature of the physical stimulus (Light) as

well as the transducing system (the Eye)

Light - is a form of electromagnetic radiation that travels as a wave

Physical Properties Perceptual Properties

Wavelength Hue

Amplitude (Intensity) Brightness

Purity (Bandwidth) Saturation

Major Structures of the Eye

Retina – contains the light sensitive structures (rods and cones) that transduce light into neural activity

The Retina-contains the light sensitive structures (rods and cones) that

transduce light into neural activity

Rods - Very sensitive to light (Scotopic)Poor acuityNo color capability (monochromatic)Concentrated in peripheral visionMaximal sensitivity is at 511 nm

Cones - Daylight Vision (Photopic)Allow Color Perception (trichromatic)Great AcuityClustered at the FoveaMaximal sensitivity is at 555 nm

Dark AdaptationLight sensitive structures of the eye become more

sensitive to light when kept in the dark for a period of time

Cones – Dark adapt fully in approximately 7 minutes of darkness

Rods - Dark adaptation requires approximately 25 minutes of darkness

Dark AdaptationLight sensitive structures of the eye become more

sensitive to light when kept in the dark for a period of time

Cones – Dark adapt fully in approximately 7 minutes of darkness

Rods - Dark adaptation requires approximately 25 minutes of darkness

Red Lighting in the Cockpit to Protect

Rod Dark Adaptation

Organization of the light sensitive

structures of the Retina

Pathways of the Optic System

Pathways of the Optic System

AuditionAudition is the result of the Ear (Auditory System) transducing Sound

into neural activity.

Sound - Vibrations passed through an elastic medium (air, water, solids, anything but a vacuum). As an object vibrates it displaces molecules in the air around it, causing repetitive cycles of compression and rarefaction.

Physical Properties Perceptual Properties

Wavelength (Frequency) Pitch

Amplitude (Intensity) Loudness

Purity (Composition) Timbre

Range of Audible Frequencies - 20Hz to 20KHz - Ability to hear high frequencies goes away with age - Higher frequencies audible for smaller animals. smaller animals

The Major Structures of the Ear

• Sound waves vibrate the tympanic membrane

• These vibrations are passed on to the bones of the middle ear

• Stirrup hits against the oval window of cochlea

• Sets the fluid inside in motion

• Hair cells are stimulated with the movement of the basilar membrane

• Physical stimulation converted by the hair cells into neural impulses

• The axons of the hair cells form the auditory nerve

• The auditory nerve fibers synapse at the medial geniculate of the thalamus before continuing to the auditory cortex (temporal lobes)

The Auditory Process

Taste (Gustation)

Physical stimulus: soluble chemical substances

Receptor cells found in taste buds

Four primary tastes: sweet, sour, bitter, and salty

Taste: learned and social processes

Smell (Olfaction)

Physical stimuli: substances carried in the air dissolved in fluid, the mucus in the nose

Olfactory receptors = olfactory cilia

Synapse directly with cells in brain (only sensory input which is not routed through thalamus)

Tactile Senses

Physical stimuli = mechanical, thermal, and chemical energy coming in contact with the skin

Sensory receptors specialized to some degree for different

functions, such as pressure, heat, cold, etc.