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Sensation & Perception

• Ch. 2: Physiology of Perception

© Takashi Yamauchi (Dept. of Psychology, Texas A&M University)

• Main topics– Neurons– Vision– Transforming light into electricity– Pigments and perception

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Key terms

• Staining• Doctrine of specific nerve energy• Modular organization• Primary receiving areas• Temporal, parietal, occipital lobe• Neurons (axon, dendrite, synapse, cell body)• Action potential, resting potential• Excitatory/inhibitory neurons (transmitters)

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Sample questions

• Describe the basic roles of “action potential,” “neurotransmitter,” and “synapse.”

• Describe the major differences between the rods and the cones.

• What is the “blind spot”?

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Anatomy Lesson by Dr. Nicholaes (painted by Rembrandt Harmenszoon van Rijn in 1632)

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Some brief history

• “Anatomy of the Brain” by Thomas Willis (1664)

• Oxford physician

• The first major work on the brain.

• Present the results of dissections of a human brain.

• Staining• By Gamillo Golgi (1873)

• Injecting dyes into the nervous system

• Enabled the visualization of neurons

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• A nerve cell (neuron) shown by the Golgi method.

http://en.wikipedia.org/wiki/Image:GolgiStainedPyramidalCell.jpg

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• Doctrine of specific nerve energy

– By Johannes Mueller (1842)

– Our perceptions depend on “nerve energies” reaching the brain and that the specific quality we experience depends on which nerves are stimulated.

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Basic structure of the brain

• Modular organization– Specific functions are served by specific areas of

the cortex.– Primary receiving areas:

• Occipital lobe (seeing)• Temporal lobe (hearing)• Parietal lobe (touching)

ch 2 9Source: Kandel et al., 1994

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Human brain

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Neuron

• Key components:– Cell body, dendrite, axon, and synapse

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Neuron I

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Neuron II

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Neuron III

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Neuron IV

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Neurons

Dendrites

Cell body

Axon

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Perception involves

• Transduction and neural processing

• And then behavior

Information

Behavior/action

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Transduction

–Different types of information (air vibration, light energy) is transformed into a common neural language in the brain neural information

this process is called “TRANSDUCTION.”

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Questions

(1) What is the mechanism of that process?

(2) What is “neural energy”?

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Transduction: Examples

– Touching a mouse, open a program, typing some words.– Driving a car

                  

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Neural energy

• What is neural energy?

– It is basically a conversation between neurons.

• Conversation? They talk to each other?

• Yap.

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How do neurons talk to each other?

• Neurons talk to each like a computer does.

• Neurons talk to each other by sending electrical signals.

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How so?

A neuron is immersed in liquid rich in ions (molecules that carry electrical charge).

This figure shows the high concentration of positively charged sodium (NA+) and the high concentration of positively charged potassium (K+).

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Ion?• An ion is an atom or group of bonded

atoms which have lost or gained one or more electrons, making them negatively or positively charged.

• A negatively charged ion has more electrons in its electron shells than it has protons in its nuclei.

• A positively-charged ion has fewer electrons than protons.

• An atom is the smallest particle still characterizing a chemical element; it is composed of various subatomic particles:

• Electrons have a negative charge; they are the least heavy (i.e., massive) of the three types of basic particles.

• Protons have a positive charge with a free mass about 1836 times more than electrons .

• Neutrons have no charge, have a free mass about 1839 times the mass of electrons.

• (Wikipedia.org)

Atom?

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Neurons talk to each other electronically by sending chemicals (neurotransmitters) from one neuron to other neurons.

Neurons are not directly attached but are connected indirectly at a juncture called “synapse.”

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Synapse

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Dendrite Axon

Synapse

Neurons (schematic Illustration)

When an electric signal reaches at the end of the axon of a neuron, that neuron releases “neurotransmitters”

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Dendrite Axon

Synapse

Synapse and neurotransmitter

The neurotransmitters reach a terminal of a dendrite of the other neuron, and change the neuron’s resting potential.

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Resting potential

The electrical charge when a neuron is at rest is called “resting potential.” -70millivolt

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Dendrites collect electrical signals from other neurons.

Dendrites forward these signals to the cell body.

axondendrites

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axon

dendrites

+

+

+

+

Firing (spike)

No Firing

Accumulation of signals

When the signals that gather at the cell body exceed a threshold, the axon triggers a new signal (i.e., spike).

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Dendrite Axon

Synapse

Neurotransmitters can sendpositive or negative signals.

Neurotransmitters can open positive or negative gates.

Some neurotransmitters open positive gates.

Other neurotransmitters open negative gates.

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axon

dendrites

Basically there are two types of neuro-transmitters.

One that sends excitatory (+) signals (transmitter), and the other that sends inhibitory (-) signals.

So, the excitatory neurons enhance the activity of other neurons; the inhibitory neurons suppress the activity of other neurons.

axon

dendrites

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Demonstration

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Activities of neurons can be schematically shown as

B

a1 a2 a3 a4The firing rate of neuron B is determined by the activation sent by neurons a1-a4.

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Summary

• A neuron consists of dendrites, a cell body and an axon.

• Neurons are not directly attached but are indirectly connected at synapses.

• One neuron sends an electrical signal to another neuron by releasing neurotransmitters.

• Some neurons send excitatory signals (+); others send inhibitory signals (-).

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What does this tell? (1)

• Perception can be examined by the activity of neurons.– When we are perceiving something, some neurons

are firing.

                           When we see a picture like this, neurons that respond to different colors, shapes, texture,… are firing together.

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Bridging the activity of neurons and behavior (perception)

• Single cell recording

• EEG / ERP (Event related potential/evoked potentials)

• PET (Positron Emission Tomography)

• fMRI (functional Magnetic Resonance Imaging)

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Single cell recording

• Deep brain stimulation (12 minutes)– http://www.youtube.com/watch?

v=ksjHNbb6NFQ&feature=related

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ERP

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ERP II

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Biofeedback

Neurofeedback for attention deficit disorderhttp://www.youtube.com/watch?v=2vUG6BDA8wI

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PET & fMRI

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fMRI

Source: Kandel et al., 1994

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fMRI

Source: Kandel et al., 1994

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fMRI Setup

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• Visit

• http://www.functionalmri.org/

• http://defiant.ssc.uwo.ca/Jody_web/fmri4dummies.htm

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fMRI Experiment Stages: Prep1) Prepare subject

• Consent form• Safety screening• Instructions

2) Shimming • putting body in magnetic field makes it non-uniform• adjust 3 orthogonal weak magnets to make magnetic field as homogenous as

possible

3) SagittalsTake images along the midline to use to plan slices

Note: That’s one g, two t’s

Source: Jody Culham’s fMRI for Dummies web site

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fMRI Experiment Stages: Anatomicals

4) Take anatomical (T1) images• high-resolution images (e.g., 1x1x2.5 mm)• 3D data: 3 spatial dimensions, sampled at one point in time• 64 anatomical slices takes ~5 minutes

Source: Jody Culham’s fMRI for Dummies web site

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MRI

Source: Kandel et al., 1994

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MRI

Source: Kandel et al., 1994

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fMRI

Source: Kandel et al., 1994

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fMRI

Source: Kandel et al., 1994

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PET (Normal resting pattern)

Source: Kandel et al., 1994

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PET (visual & auditory stimulation)

Source: Kandel et al., 1994

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• fMRI and a lie detector (10min)

• http://www.youtube.com/watch?v=Cwda7YWK0WQ

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TMS

• Transcranial magnetic stimulation

– Disrupt the electrical activity of neurons in a targeted area by a strong magnetic field (4:15)

– http://www.youtube.com/watch?v=XJtNPqCj-iA

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ERP, PET, &MRI

• Subjects carry out some psychological tasks (e.g., visual perception)

• Trace neural activities of the brain.

• Identify the brain location in which the psychological function takes place.

• Bridge psychological functions and their brain locations.

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Visual perception

• What is the difference between (a) & (b)?

• What is going on in your head when you see (a) versus when you see (b)?

(a)

(b)

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How about this?

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What’s going on?

• When you see the square, what’s going on?

• How do you find out?

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• In terms of the activity of neurons,

what is the difference between

A and B ?

Any guess?

A. B.

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Measuring the electrical activity of a neuron directly by inserting a thin needle into animal brains.

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Time0 t

The frequency of action potential

Time0 t

The number of action potential emitted by a neuron is correlated with the intensity of the stimulus.

Time0 t

5 units

10 units

20 units

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Physical quantities

Time

0 t

Time0 t

5 units

20 units

Perceived quantities

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Questions: What happens to B?

0 t

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Questions: What happens to B?

Excitatory Inhibitory

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Specificity coding vs. Distributed coding

• How are objects represented in the visual system?

• Think about human faces. Every face is different. So do we need an infinite number of neurons to represent individual faces?

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Specific coding?• A single neuron responds

to each face?

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Specific coding?• A single neuron responds to each face?

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Neurons in the hippocampus respond specifically to an individual person, such as Halle Berry, her face picture, her name, and pictures of her dressed as Catwoman from Batman.

But the hippocampus is a memory storage site. So, these specific neurons are responding to specific memory of a familiar person.

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Distributed coding

The same set of neurons respond to different faces but in different degrees.

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Combinations of neurons can express lots of different faces