DefinitionsSensationThe detection of physical energy emitted or reflected by physical objects

Occurs when energy in the external environment or the body stimulates receptors in the sense organs

PerceptionThe process by which the brain organizes and interprets sensory information

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Sensation and perception

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Sensation

• What are the sensory systems?• Sight, sounds, touch, pain, smell, taste, sensation of

movement

• Why are the sensory systems important?

• Perception of external world• Maintains arousal, forms body image, regulates

movement

• Basis for our knowledge about the world and our

surroundings.

Psychophysics

• Correlates quantitative aspects of physical stimuli (energy) with the sensations they evoke

– 4 elementary attributes:1. Modality

2. Intensity

3. Duration

4. Location

Attributes of Sensation:Modality

• Quality of a sensation• Different forms of energy = Different sensations• 5 major: vision, hearing, touch, taste, smell

– Submodalities:» Touch – sweet, salty, bitter, sour» Vision – color, movement

• Law of Specific Energies• 1826 Johannes Muller• Each modality = activated by a specific stimulus = different

sensory nerve fiber

Sensory receptors are maximally sensitive to a specific energy

Modality Stimulus(energy)

Receptor Types

Receptor

Vision Light Photoreceptor Rods, Cones

Audition

(hearing)

Sound Mechanoreceptor Hair cells (cochlear)

Balance Head motion Mechanoreceptor Hair cells (semicircular canals)

Somatic

(touch)

Mechanical, thermal, noxious (chemical)

Mechanoreceptor, thermoreceptor, nociceptor, chemoreceptor

Dorsal root ganglion neurons

Taste Chemical Chemoreceptor Taste buds

Smell Chemical Chemoreceptor Olfactory sensory neurons

Adapted from Kandel, Schwartz, and Jessel, 1991

Attributes of Sensation:Intensity

• Strength of Energy Amount of sensation• Frequency of action potentials

– strong stimulus = more action potentials fired

• # of fibers activated– strong stimulus = more fiber stimulated

• Absolute Threshold• Smallest amount of energy/stimulation that can reliably

be detected• Variable

– Influenced by practice, fatigue, context

Absolute thresholds

VisionA single candle flame from 30 miles on a clear night

HearingThe tick of a watch from 20 feet in total quiet

SmellOne drop of perfume in a 6-room apartment

TouchThe wing of a bee on the cheek, dropped from 1 cm

TasteOne teaspoon of sugar in 2 gallons of water

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Attributes of Sensation:Intensity

• Strength of Energy Amount of sensation• Frequency of action potentials

– strong stimulus = more action potentials fired

• # of fibers activated– strong stimulus = more fiber stimulated

• Absolute Threshold• Smallest amount of energy/stimulation that can reliably

be detected• Variable

– Influenced by practice, fatigue, context

• Difference Threshold• Smallest difference that can be detected when 2 stimuli

are compared• Just Noticeable Difference (JND)

Signal-detection theory

A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process and quantifies the ability to distinguish between the stimuli and noise

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Drugs – Mechanism of Action on the sensation of pain

• Drugs that elevate the pain threshold– Morphine

» Reduces detectibility of painful stimuli = raises threshold

» Elevates criterion used to determine if a stimuli is painful = creates noise

– Marijuana» Elevates criterion used to determine if stimuli is

painful = makes noise

Attributes of Sensation:Duration

• Stimulus intensity and Perceived Intensity

• Adaptation– The reduction or disappearance of sensory responsiveness

when stimulation is unchanging or repetitious– Prevents us from having to respond continuously to

unimportant information

• Deprivation– The absence of normal levels of sensory stimulation

Attributes of Sensation:Location

• Spatial aspects of sensation:– Ability to locate origin of sensation– Ability to distinguish 2 closely spaced stimuli

• Two-Point Threshold– Minimum distance between 2 stimuli that allows

them to be perceived as distinct

• Function of receptive field of receptor and sensory neurons

Commonalities of the Senses• All extract same basic information

• Modality, intensity, duration, location

• Similar organization• Sensory receptors for specific type of energy• Receptor transforms energy into electrochemical

signal action potentials• Travel up afferent fibers to the brain• Relay information to Thalamus (except smell)• Continue on to specific regions in cortex

VisionStimuli (energy) = light waves

3 Psychological Aspects of Vision:HueRelated to the wavelength of light

BrightnessRelated to the amount of light emitted from or reflected by an object – amplitude of wavelength

SaturationRelated to the complexity of light waves - # of different wavelengths

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Vision

Adapted from Univ. Virginia, Dept of Astronomy

What we see

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Anatomy of the EyeCorneaProtects eye and bends light toward lens

LensFocuses on objects by changing shape

IrisControls amount of light that gets into eye

PupilAperture through which light reaches the retina

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Rods and Cones

RetinaNeural tissue lining the back of the eyeball’s interior containing the receptors for vision

RodsVisual receptors that respond to dim light

ConesVisual receptors involved in color vision

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Rods and Cones

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Structures of the retina

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Your turn

You have a hard time locating your red car at night, in the poorly lit mall parking lot. Why?1. Your rods are less sensitive to color in dim light.2. Your cones, which detect color, do not function well in dim light.3. Your ganglion cells receive insufficient overall stimulation to function.4. Your rods, which detect color, do not function well in dim light.

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The visual system is not a camera

Visual processing is done in the brain

The visual image that was reflected onto our retina is broken up into simple and complex features that the brain perceives, processes and interprets

Simple features - light and dark spots - Ganglion cells and neurons in Thalamus

Complex features – Lines with specific orientations, bulls-eyes, spirals, faces)

- Feature-detector cells in the Visual cortex- Sensitive to specific features in the environment

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Visual Cortex Neurons:Feature-Detector Cells Respond to lines oriented in a particular direction and in a particular space in the visual field

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Hubel & Wiesel Experiment

Hubel and Wiesel’s experiment

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Simple Cell in Visual Cortex

Hubel DH Sci Amer 209:54-62,1963

How do we see color?

• Two theories:– Trichromatic theory– Opponent-process theory

Trichromatic theory

Young-Helmholtz Theory:The eye detects 3 primary colorsRed, blue, and green

Retina has 3 basic cones detects the 3 primary colors

All other colors detected by the combined activity of these 3 cones

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Opponent-process theory

The visual system treats pairs of colors as opposing or antagonistic

• 3 opponent channels– Red-Green– Blue-Yellow– Black-White

If opponent-process cells are inhibited by a color then removal of the color results in a burst of activity

• Many respond in the opposite fashion to red and green, i.e. fire in response to red and turn off in response to green

• Negative afterimage

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Form Perception:Gestalt principles

ProximityThings close to one another are grouped together

ClosureThe brain tends to fill in gaps to perceive complete forms

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Form Perception:Gestalt principles cont.

SimilarityThings that are alike are perceived together

ContinuitySeeing continuity in lines that could be interpreted as either continuous or abruptly shifting in direction.

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Your turn

Which Gestalt principle is illustrated by the fact that we see columns of dots rather than rows in this diagram?1. Similarity2. Proximity3. Closure4. Continuity

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Depth and distance perception

Binocular cuesRequire both eyes working together

ConvergenceTurning inward of the eyes, which occurs when they focus on a nearby object

Retinal disparityThe slight difference in lateral separation between two objects as seen by the right and left eyes

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Depth and distance perception

Monocular cuesFor objects over 50 feet awayDoes not depend on both eyes

InterpositionLinear PerspectiveLight and ShadowMotion ParallaxRelative SizeRelative ClarityTexture Gradients

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Visual constancies

The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce

Shape constancy

Location constancy

Size constancy

Brightness constancy

Color constancy

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Last Class in Review• Sensation

The detection of physical energy emitted or reflected by physical objects

• PerceptionThe process by which the brain organizes and interprets sensory information

• Psychophysics – attributes of sensationModality, Intensity, Duration, Location

• Law of Specific Energies• Absolute Threshold vs. Difference Threshold (JND)• Adaption and Deprivation• Two-Point Threshold

• Vision– Psychological Attributes – hue, brightness, saturation– Anatomy – visual receptors = rods and cones; feature detector

cells– Depth and Distance perceptions: monocular and binocular cues– Gestalt Principles: proximity, closure, similarity, continuity

Sensation and Perceptionchapter 6

Learning Objectives:

1. What are the 3 main psychological dimensions of hearing?

2. What are the major structures of the inner ear that contribute to the sense of hearing?

3. Understand how the Gestalt principles may apply to other sensations, such as hearing.

4. What are the 5 major tastes? Why do people tastes things differently?

5. What are the basic senses of the skin? How is sensation organized? (hint: understand somatotopy)

6. How does gate-control theory account for our perception of pain?

7. Is there any evidence that some perceptual abilities are present from birth? What are these abilities and what is the evidence?

8. What 5 factors can influence our perception?

What we hear (audition)Stimulus (energy) = wave of pressure caused by vibrations

3 Psychological Aspects of Sound:

PitchFrequency of a pressure wave Measured in hertz (Hz)

LoudnessIntensity (amplitude) of a pressure wave Measured in decibels (dB)

TimbreComplexity of a pressure waveWhite noise – all frequencies of the sound spectrum

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Psychological Aspects of Sound

From Genetic Science Learning Center, University of Utah, http://gslc.genetics.utah.edu.

Example of differences in pitch and complexity

Anatomy of the Ear

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Gestalt Principles in Audition

• Proximity – Which sounds go together to form words

• Continuity– Helps you follow 1 persons voice in a room full of

background noise

• Similarity– Might also help you follow 1 persons voice in a room full of

background noise

• Closure– Helps you complete words when the speakers voice trails

off

Auditory localization

Sounds from different directions are not identical as they arrive at left and right ears.

Loudness

Timing

Phase

The brain calculates a sound’s location by using these differences.

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Taste (Gustation)

Taste buds =Bundles of taste receptor cells

Taste hairs (microvilli) contain taste receptors

Taste stimuli (energy) = chemical

Taste receptor cells send signals to sensory nerves (taste nerves)

Sensory nerves send action potential to the brain

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Five tastes

Five basic tastesSalty – keeps electrolytes (salt-balance) in checkSour – detects acidity = rancid foodBitter – allows sensing of natural poisonsSweet – energy rich nutrients, presence of sugarsUmami – taste of amino acids (glutamate) = protein rich foods

Why do people have different tastes?Genetics - supertastersCultureLearningFood attractiveness

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Smell (Olfaction)

Smell stimuli (energy) = chemicals Enter through the nose or mouth and pass into nasal cavity.

Receptors Olfactory nerve Olfactory bulb Pyriform cortex, hypothalamus, thalamus, frontal cortex, hippocampus

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Senses of the Skin

• Basic skin senses:• Tactition (touch) -

» stimuli is pressure » mechanoreceptor

• Thermoception (hot & cold) » stimuli is thermal » thermoreceptor

• Nociception (pain) » stimuli is noxious » nociceptor

Sensitivity to touch

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Somatotopy

Adapted from Sabes Lab - UCSF

The environment within

KinesthesisThe sense of body position and movement of body parts

EquilibriumThe sense of balance

- Semicircular canals Sense organs in the inner ear, which contribute to

equilibrium by responding to rotation of the head

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Critical period

An important period of time during development when the brain is capable of acquiring a specific ability

–Environmental stimulation needed to strengthen hard-wired innate connections

–If infants miss out on experiences during a crucial period of time, perception will be impaired.

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Zebra finches learn their adult song from a tutor during a critical period