PY 262 Sensation & Perception

Introduction to the senses

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George Berkeley (1710) “A Treatise Concerning the Principles of Human Knowledge”

• “If a tree falls in the woods, and there’s no one around to hear it… does it make a sound?”

• Is there “objective” reality or only “subjective” perspective?

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Do we all see the same color, shape, size?

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• Some species sense energies that humans cannot:– Bees see ultraviolet lights– Rattlesnakes sense

infrared energy– Dogs and cats can sense

sounds with higher frequencies

– Birds, turtles, and amphibians use magnetic fields to navigate

– Elephants can hear very low-frequency sounds, which are used to communicate

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Which view is real?

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Which view is real? They both are.

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3rdQtr

North

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What is Real?http://www.youtube.com/watch?v=Dseb1Y1GBx8

( @ 0:00 to 2:00, then 3:34 to 7:40 )

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From The Matrix:

Morpheus says to Neo….

“If you’re talking about what you can feel, what you can smell, what you can taste and see, then real is simply electrical signals interpreted by your brain. This is the world that you know.”

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Is the “Matrix” simply science fictions?

• http://www.cbsnews.com/video/watch/?id=5228109n

• Recognizing the “Brain Power” of sensation, perception and thought

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Wilhelm Wundt (1879):

Our PERCEPTION is constructed from the combinations of our SENSATIONS

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What is this object?

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Can you “reverse frame?”

1. Cube floating over dark circles? (hint, first see how the white lines connect; seeing “white box”)

2. Cube seen through (or behind) holes or perforations? (hint, seeing “black box”)

3. Cube pointed “up” or “down?”

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Wilhelm Wundt (1879) had some things WRONG!

Our PERCEPTION is NOT constructed from JUST the combinations of our SENSATIONS, but involves “interpretations” of the mind

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Sensation -the reception of stimulus energy by the nervous system-conversion or transformation

Perception -interpretation of the barrage of stimulus events-a conscious sensory experience

Recognition -ability to categorize objects, to give them meaning

Action -motor activity-the outcome of the perceptual process-ultimately changes perception

Knowledge-memories, information-processing, reasoning, problem solving, etc-important for determining perception, recognition and action

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•EnvironmentalStimuli

AttendedStimulus

Stimulus on Receptors

Transduction

Processing

Perception

•Recognition

•Action

Knowledge

Central Nervous System (CNS)

Sensation & Perception

External World: “environment”

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Synaptogenesis• Form in large numbers quickly in early infancy• “Use it or lose it” processes• Synaptic pruning – over-produced number of

synapses are reduced over time & experience

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The importance of experience (Greenough & Black, 1992)

• Experience-Expectant Plasticity – typical brain development occurs as a result of general species-typical experience– Vision is processed in the occipital lobe– Occipital lobe development is atypical when

lacking typical visual experience• Infants’ vision is progressively more impaired the

longer it takes to remove a cataract

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The importance of experience (Greenough & Black, 1992)

• Experience-Dependent Plasticity – Unique neural connections occur from an individual’s personal experiences– How we recognize what is familiar to us

(mom’s face; home telephone number)– Relative sophistication of CNS connections as

a function of experience• Musician’s finger tips have a larger region of the

Somatosensory cortex processing touch than do non-musicians

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Brain plasticity is the norm not the exception – the example of “selective rearing”

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EnvironmentalStimuli

NervousSystem Activity

SENSATION & PERCEPTION

Stimulus-Physiological question: How are the properties of objects represented by the activity of neurons?

Stimulus Environment question: What information do we use from the environment to create perceptions?

Sensation & Perception question: How does the brain mediate perception & action, and extract the gestalt (the “big picture”) interpretation? 20

EnvironmentalStimuli

NervousSystem Activity

SENSATION & PERCEPTION

Stimulus-Physiological question: Neurophysiology

Stimulus Environment question: Psychophysics

Sensation & Perception question: Psychophysiology

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The Dawn of Psychophysics• Fechner (1801–1887) invented

“psychophysics,” thought to be the true founder of experimental psychology– Pioneering work relating changes in the

physical world to changes in our psychological (perceptual/subjective) experiences

Psychophysics: The science of defining quantitative relationships between physical and psychological (subjective) events

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The Dawn of Psychophysics (cont’d)

• Two-point threshold: The minimum distance at which two stimuli (e.g., two simultaneous touches) can be distinguished

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The Dawn of Psychophysics (cont’d)

• Just Noticeable Difference (JND)

– The smallest detectable difference between two stimuli

– The minimum change in a stimulus that can be correctly judged as different from a reference stimulus

– Also known as “difference threshold”– Weber’s Law – JND is proportional to the

magnitude change of the physical stimuli24

The Dawn of Psychophysics (cont’d)

• Absolute threshold: Minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time

• “Common” examples of Absolute Threshold:– Vision: Stars at night

– Hearing: A ticking clock at 20 feet

– Vestibular: Tilt of less than ½-minute on a clock

– Taste: A teaspoon of sugar in 2 gallons of water

– A drop of perfume in a 3-room apartment

– The wing of a fly falling on your check from 3-inches25

The Dawn of Psychophysics (cont’d)

• Fechner’s (Weber-Fechner) Law– A principle describing the relationship

between stimulus magnitude and resulting sensation magnitude

– The magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity

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Fechner’s Law(L

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(Sound Pressure Level (Decibels dB)) 27

Perceived magnitude: understanding response expansion vs. response compression

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The Structure of a Neuron

Stimulus-Physiological question: How are the properties of objects represented by the activity of neurons?

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Stimulus-Physiological question: How are the properties of objects represented by the activity of neurons?

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- synapses involve an electrical to chemical to electrical process

Stimulus-Physiological question: How are the properties of objects represented by the activity of neurons?

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Crossing the Synapse

Vesicles contain neurotransmitters

Stimulus-Physiological question: How are the properties of objects represented by the activity of neurons?

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Neural Communication

Whether a neuron fires depends upon the inputs it gets from multiple sources.

Some connections are excitatory (systematic neural activation) and others are inhibitory (systematic neural quieting).

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Neurons have a resting potential of about –70mv

outside – positively charged Sodium (Na+) ions, negatively charged Chloride (Cl-) ions

inside – positively charged Potassium (K+) ions.

Stimulus-Physiological question: How are the properties of objects represented by the activity of neurons?

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The physics & chemistry of membrane permeability:

Ionic “current” is created by the change in positive and negative charges

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Excitation causes Na+ ion channels to open – cell becomes less negatively charged = DEPOLARIZATION

Stimulus-Physiological question: How are the properties of objects represented by the activity of neurons?

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inhibition causes chloride ion channels to open – cell becomes more negatively charged = HYPERPOLARIZATION

Stimulus-Physiological question: How are the properties of objects represented by the activity of neurons?

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How does a neuron propagates an electrical signal down the axon?

[Alan] Hodgkin – [Andrew] Huxley cycle

Sodium (Na+) in = depolarization; Potassium (K+) out = hyperpolarization

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Centre-Surround Receptive Field In the Lateral Geniculate Nucleus: neurons act together as a group

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Stimulus-Physiological question: How are the properties of objects represented by the activity of neurons?

Physiological-Perception question: This is your brain during perception

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EnvironmentalStimuli

NervousSystem Activity

SENSATION & PERCEPTION

Stimulus-Physiological question: Neurophysiology

Stimulus Environment question: Psychophysics

Sensation & Perception question: Psychophysiology

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Herman Grid

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"Throwing cast nets"

Circles appear to expand.

Copyright A.Kitaoka 2004 (February 12, 2004)44

"Rotating snakes"

Circular snakes appear to rotate 'spontaneously'.

Copyright A.Kitaoka 2003 (September 2, 2003)

Explanation (PDF file)45

"Dongururin"*

*Rotation of donguri (acorns). "Gururin" means rotation.

Rings of donguri appear to rotate.

Copyright A.Kitaoka 2003 (July 3, 2003) 46

"Light of chrysanthemums"

The center of a flower appears to be bright.

Copyright Aiyoshi Kitaoka 2005 (April 5)47

From The Matrix:

Morpheus says to Neo….

“If you’re talking about what you can feel, what you can smell, what you can taste and see, then real is simply electrical signals interpreted by your brain. This is the world that you know.”

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