introduction: early philosophies of perception

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1Introduction: Early

Philosophies of Perception

Chapter 1

1 Senseless Person

Think of a person without senses. What would her world like? What would she know?

Helen Keller (1880-1968)

1 Sensibility and Reality

“What is real? How do you define real? 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.”—Morpheus’ answer to Neo in The Matrix, 1999

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1 Introduction

• Early Philosophy of Perception• Nativism and Empiricism• The Dawn of Psychophysics• Biology of Perception

1 Early Philosophy of Perception

Plato’s “The Allegory of the Cave” (380 BCE) and reality.


Perception and your sense of reality are the products of evolution:

– Survival,– Importance of type of energy in the

environment determines which senses have developed.

– Five human senses

Seeing Hearing Smelling Tasting Feeling

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1 Animal Senses

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


Heraclitus (540–480 BCE): “You can never step into the same river twice.”

– Everything is always changing– Idea that perceiver cannot perceive the

same event in exactly the same manner each time

– Adaptation: A reduction in response caused by prior or continuing stimulation


Democritus (460–370 BCE): The world is made up of atoms that collide with one another, and the sensations are caused by these when they make contact with our sense organs:

– Perception is the result of the physical interaction between the world and our bodies

– Idea of primary qualities and secondary qualities

Sensory transducer: A receptor that converts physical energy from the environment to neural activity.

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1 Nativism and Empiricism

• Nativism: The idea that the mind produces ideas that are not derived from external sources.

• Descartes’ (1596–1650) dualist view of the world: both mind and body exist.

• Mind–body dualism: Originated by Descartes, the idea positing the existence of two distinct principles of being in the universe: spirit/soul and matter/body.


• Monism: The idea that the mind and matter are formed from, or reducible to, a single ultimate substance or principle of being.

• Materialism: The idea that physical matter is the only reality, and everything including the mind can be explained in terms of matter and physical phenomena. Materialism is a type of monism.


• Empiricism: The idea that experience from the senses is the only source of knowledge

• Hobbes (1588–1678) believed that everything that could ever be known or even imagined had to be learned through the senses

• Locke (1632–1704) sought to explain how all thoughts, even complex ones, could be constructed from experience with a collection of sensations

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Berkeley (1685–1753) studied ways in which perception is limited by the information available to us through our eyes.

Concluded that all of our knowledge about the world must come from experience, no matter how limited perception may be.

1 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 experiences

– Panpsychism: The idea that all matter has consciousness (Fechner).


Psychophysical Methods:– Method of constant stimuli– Method of limits– Method of adjustment– Magnitude estimation

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1 Method of Constant Stimuli

Yes8No2No6No8

Yes7Yes21Yes10Yes34

No7No9

109

5310

Sound (db)

YesYes10Yes

NoYesNo

Response ResponseSound (db)

Yes8

No5No10No2

1 Method of Limits

1 Method of Adjustment

0 5 10 15 20 25 30Trials

YesNo

Stim

ulus

Inte

nsity

1 2

3

4

5 6

7

8

9 1

0 1

1

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

1 Common Thresholds


Fechner’s Law: A principle describing the relationship between stimulus magnitude and resulting sensation magnitude such that the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity.

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Weber (1795–1878) discovered that the smallest change in a stimulus, such as the weight of an object, that can be detected is a constant proportion of the stimulus level—“Weber’s Law”

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


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

• JND (Just Noticeable Difference): The smallest detectable difference between two stimuli, or the minimum change in a stimulus that can be correctly judged as different from a reference stimulus. Also known as difference threshold.


Signal Detection Theory: A psychophysical theory that quantifies the response of an observer to the presentation of a signal in the presence of noise.

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1 Signal Detection Theory (Part 1)


1 SDT Matrix (Part 2)

Correct Rejection

FalseAlarmAbsent

MissHitPresent

Signal

NoYes

Response

On each trial either the signal is presented or not.The observer has to decide, whether she hears the toneor not. This translates into four outcomes based on the

observer’s responses.

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1 Receiver Operating Characteristics (ROC)

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Stevens’ Power Law: A principle describing the relationship between stimulus magnitude and resulting sensation magnitude, such that the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent.

1 Biology of Perception

Doctrine of specific nerve energies (Müller, 1801–1858): A doctrine stating that the nature of a sensation depends on which sensory fibers are stimulated, not on how fibers are stimulated.


Helmholtz (1821–1894): Studied activity of neurons; how fast they transmit signals

– Resonators, ophthalmoscope

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Cranial nerves: Twelve pairs of nerves that originate in the brain stem and reach the periphery through openings in the skull.


Synapse: The junction between neurons that permits information transfer.

CahalSherrington


Neurotransmitter: A chemical substance used in neuronal communication at synapses.

Lowei

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1 Sir Alan Hodgkin and Sir Andrew Huxley

Action potential: Conduction of nerve electrical message through the axon.

1 The Action Potential

Na+ ions enter the axons increasing the positive charge inside it. This positive charge moves towards the axon terminals.

introduction: early philosophies of perception

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