PSYC 200 Chapter 3

Materialism

Behavior and cognition can be explained by the working of the brain and rest of nervous system

• Mind is part of physical world

• Materialists believe that mental phenomena can be explained through physical processes

• Consciousness arises from complex interaction within brain

• Mind is an emergent property of brains physical structures

Dualism

Mind and body are distinct entities

• mind is not completely reducible to material body or brain

• Mind is partially independent of the body

• Mind functions in a way that cannot be fully explained by physical processes

How are the brain and behavior related

The brain affects behavior

• Hyperactivity in the dopamine system causes schizophrenia

Behavior affects the brain

• Learning can bring about long lasting changes in the brain

Evidence of Materialism

fMRI and EEG allow observations of brain activity in real time, correlating between specific mental states and pattern. Brain chemistry can alter mood, memory, and perception, and that physical processes in the brain are linked to consciousness

Neurons

Basic structural and functional units of the nervous systemG

Glial cells

Outnumber neurons by 10-1

make up 50% of the brain volume

Support, nourish neurons and remove waste

Unipolar Neuron

has 1 axon which extends into dendrites

Primary afferents of spinal and some cranial nerves in vertebrates

Most common neurons in the CNS of invertebrates

Pseudo unipolar neuron

1 axon that projects from the cell body for a short distance before splitting into 2 branches

Most sensory neurons are pseudo unipolar, dorsal root ganglia of spinal nerves

Bi polar neuron

2 independent structures extending from the cell body, 1 is an axon, other is a dendrite

• IE: Rod and cone cells of retina olfactory system

Multipolar neuron

only has 1 axon, but multiple dendrites, making transmitting information easier

Most common with multiple extensions from soma

A motor neuron

Majority of neurons of CNS and PNS as well as majority of interneurons

3 types of neurons

Sensory neurons

Interneuron

Motor neuron

Function of a neuron is to receive, integrate and transmit information

All neurons have:

A cell body/soma

Tree like dendrites to specialized to receive information

an axon

Axon

Long thin fiber that transmits signals away from the cell body to other neurons, muscles or glands

Direction of impulse in a sensory neuron

Direction of impulse in motor neuron

Interneuron signal direction

Myelin sheath

Many axons are wrapped in a myelin sheath

• is derived from glial cells

• speeds up signal transmission along an axon

Degeneration of myelin sheath

Leads to

ineffective signal transmission

• in MS

  • Loss of muscle control

  • Weakness and paralysis

  • Vision difficulties

End of an axon

Connection between 2 neurons or neuron and effector is called a synapse

(filled with neurotransmitters)

Neuron at rest

Cell membrane is semipermeable

Na and K are pumped back and forth across the membrane at different rates

Difference in flow rates leads to a significantly higher concentration of negatively charged ions inside

• Resting potential at -70mV

Action potential

When a neuron is stimulated, brief jump occurs in the neurons voltage

• change is called an action potential

  • AP travels along the axon like a spark along a trail of gunpowder

Action potential steps

Resting potential

• Na+/K+ pump

Depolarization

• Voltage gated Na+ channel

Repolarization

• Voltage gated K+ channel

Resting potential

• Na+/K+ pump

Depolarization

In myelinated neurons, AP occur only in nodes of Ranvier

When neuron is stimulated, voltage gated Na+ channels in its cell membrane open briefly, allowing Na+ to rush in

The negativity of the membrane potential is reduced

• Depolarization between -70 and 55 mV has no effect

• When membrane potential is reduced to less than -55, AP occurs

Repolarizartion

When transmembrane potential reaches 35+mV, the voltage gated Na+ channels close, and K+ channels open, allowing K+ to rush out of membrane

This causes the negativity of the cell membrane potential increases

Membrane is repolarized and membrane potential overshoots to -90 mV

Causes the K+ channels to close

Na/K pumps bring back to resting potential of -70mV

Absolute refractory period

After firing of an action potential, some time is needed to before firing another AP

Called the absolute refractory period

lasts 1-2 milliseconds

Relative refractory period

Neuron can fire but threshold for firing is elevated

• more intense stimulation is required to initiate AP

All or None law

Neural impulse either fires or does not fire

• when it fires, AP are all the same size

• Weaker stimuli does not equal smaller AP

• Stronger stimulus will cause faster rate of firing than weaker stimulus

• Thicker axons transmit neural impulse faster than thinner ones

3 possibilities of NTS during transmitters

Some are successful in making it to receptor

Some are destroyed in the synaptic cleft

Some are pumped back in via re-uptake pump

excitatory transmitters

Cause depolarization

• inside of receiving neuron becomes more positive

• Increases likelihood of AP

inhibitory transmitters

Cause hyperpolarization

• inside of receiving neuron becomes more negative

• decreases likelihood of an AP

Convergent/divergent synaptic transmission

Convergent = summation

• will produce a graded post synaptic potential

Post synaptic potential

When NT and a receptor molecule combine, reactions in the cell membrane cause a post synaptic potential (a voltage change at a receptor site on a post synaptic cell membrane)

PSP are graded because it is a summation of many signals from the presynaptic neurons

Size and direction of PSP will increase or decrease the probability of a neural impulse in the receiving cell

Excitatory PSP

Positive voltage shift

Increases the likelihood that the postsynaptic neuron will fire action potential

Inhibitory PSP

Negative voltage shift

Decreases the likelihood that the post synaptic neuron will fire action potentials

Dopamine

Influences movement, learning, attention, and emotion

Malfunctions:

• Excess dopamine = schizophrenia

• starved of dopamine = parkinson’s disease

Serotonin

Affects mood, hunger, sleep and arousal

Malfunctions:

• Undersupply linked to depression

Agonist drugs

Mimics a neurotransmitter, binding to NTs receptor and activating/increasing NT’s effects

Can also block reuptake sites of neurotransmitter or stimulate production

Antagonist drugs

Displace a particular NT, binding to the Nts receptor site to block neurotransmitter binding

Can destroy NT in synapse or block production

Dopamine hypothesis of schizophrenia

Some forms of schizophrenia caused by excessive dopamine activity

Amphetamine and cocaine create schizo symptoms by increasing dopamine activity at the dopamine synapses

Agonist:

• Drug that mimics or enhances effect of NT

• Amphetamine and cocaine

Antagonist

• Drug that blocks effect of NT

• Chlorpromazine (used to reduce symptoms of schizophrenia)

Corpus Callosum

Nerve fibers that enable communication between the 2 hemispheres

Michael Gazziniga

With teh corpus callosum severed, objects presented in the right visual field can be named but not the objects in the left

Transduction

Process by which sensory stimuli are converted to neural signals the brain can interpret

Sensation

Stimulation of sense organs

Involves absorption of energy by sensory organs

Perception

Selection, organization and interpretation of sensory information

Involves organization and translation of sensory information into something meaningful

Saturation

Purity of color

Brightness/value

Amplitude

Concentration of light energy

Hue/color

Wavelength/frequency

Timbre

Purity of sound: a pure tone that has only 1 frequency and 1 amplitude (sine wave produced by a tuning fork)

Timbre sets apart sound of piano from sound of flute

Loudness

Amplitude/ concentrationP

Pitch

Wavelength/frequency

Receptive field of ganglion cell

Responsible for seeing light/dark contrast

Has a property known as center-surround antagonism

Rate of firing decreases when light falls in the center of a receptive field

• Shading indicates area stimulated with light. Largest response occurs when the entire center is illuminated

Visual information processing

Thalamus

• perception of brightness

Primary visual cortex in the occipital lobe

• Perception of orientation

Inferior temporal lobe

• Perception of form and color

Parietal lobe

• perception of motion and depth

Cat experiment

Ventral stream

Leads to temporal lobe

Processes details of what objects are

Dorsal stream

Leads to the parietal lobe

Color sensation

Additive color mixing

Mixing light

• adding light so light gets lighter

Subtractive color mixing

Mixing pigments

• subtracting light so light gets darker

Color absorption

Yellow absorbs blue

Magenta absorbs green

Cyan absorbs red

Additive vs subtractive color mixing

Theories of color vision

Color blindness

Color-blind = born with only 1 or 2 cone receptors

Common deficiency is red or green receptor

If person is missing 2 types of receptors, person cannot create any colors

Opponent process theory

Trichromatic theory fails to explain complementary afterimage

Stimulus triggers excitatory reaction from 1 neuron, inhibitory from another

After repeated exposure to the same stimulus, both reactions weaken

When the stimulus is removed, inhibited neuron is released from the inhibition and becomes more active than its baseline

Blind spot

nerves that run from the retina to the brain coverage at a spot

There are no receptor cells on this spot

Each eye has a blindspot that is compensated for by the other eye

Receptor cells/photoreceptors

Are in the innermost layer to the retina

only 10% of light arriving at the cornea reaches the receptors

Rod to cone ratio

100-125million rods

5-6.4million cones

Fovea

Tiny spot in the center of retina that only contains cones

Cones

Responsible for color vision

Daylight vision

Visual acuity

Rods

Peripheral vision

Night vision

Convergent synaptic transmission

Multiple rod cells converge to one ganglion cell

• allows for low light conditions compared to cones

Rods vs cones

Both rods and cones have light absorbing pigments

Rods have the same pigment

Cones have three different pigments

Psychophysics

study of how physical stimuli are related or translated into psychological experience

Absolute threshold

minimum amount of stimulation that an organism can detect

No single stimulus intensity at which the subject jumps from no detection to accurate detection

Signal detection theory

Depends on the

• intensity of stimulus

  • If intensity of stimulus is low/ambiguous, decision outcome is affected by other factors

• psychological state of individual or context of situation

2 processes involved

• sensory process

• decision making process

4 possible decision outcomes

just noticeable difference

Smallest difference in the amount of stimulation that a specific sense can detect

Webers law

Size of a just noticeable difference is a constant proportion of the size of the initial stimulus

Fechner’s Law

Subjective sensation proportional to the logarithm of the intensity of the stimulation

S = K Log R

k=constant

S=sensation

R=Reiz(stimulus)

Sensation

Stimulation of sense organs

Involves absorption of energy by sensory organs

Perception

Selection, organization and interpretation of sensory information

Involves organization and translation of sensory information into something meaningful

Word superiority effect

People have better recognition of letters within words compared to isolated letters and to letters presented in nonword strings

Bottom up processing

Perception is based on the physical features of the stimulus

• Data-driven processing

  • Identify letters isolated from words or words isolated from sentences complete the stroop task without being affected by the meanings of the words

Top down processing

Interpretation of sensory information based on knowledge, expectations and past experience

• Concept driven processing

  • Context effect, word superiority effect, Stroop effect

Structuralism

Breaks down the whole into its parts/ a compound into its elements

Method: introspection

(experimental: systematically varied the stimulus and then recorded the subjects subjective feelings about the change)

Gestalt psychology

The whole is more than the sum of its parts

Integrating elementary components to form a whole - the opposite of structuralism

Humans have tendency to organize into a coherent whole

Organization is guided by general principles