Sensation and Perception

Perception

the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

Sensation

the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment

Physiological effect

The effect a sensation has on the body

proximal stimulus

In perception, it is the information our sensory receptors receive about the object.

Transduction

conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural impulses our brains can interpret.

Interpretation

The brain guessing what kind of distal stimulation created that pattern of sensory (proximal) stimulation

distal stimulus

In perception, it is the actual object or event out there in the world, as opposed to its perceived image.

nervous system

the network of nerve cells and fibers that transmits nerve impulses between parts of the body.

Neuron

a nerve cell, the basic building block of the nervous system

Neuron cell body

location of the nucleus with DNA

Dendrites

Branchlike parts of a neuron that are specialized to receive information.

Axons

a part of a neuron that carries impulses away from the cell body

axon terminal

The endpoint of a neuron where neurotransmitters are stored

Diameter of an axon

Determines communication speed in both vertebrates and invertebrates

Myelin

A layer of fatty tissue segmentally encasing the fibers of many neurons in vertebrates, enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next.

Nodes of Ranvier

gaps in the myelin sheath

Schwann cells

Supporting cells of the peripheral nervous system responsible for the formation of myelin.

Lack of myelin

Significantly impairs motor and cognitive function (eg. Multiple sclerosis)

Babies and myelin

People lack myelin on birth, it develops as we get older. Babies gain control of their bodies starting from the top and the core

Ions

positively and negatively charged atoms

Electricity

A form of energy caused by the movement of ions

Intracellular fluid

Fluid within cells: Lots of negative ions (amino acids), few positive ions (K+), creates negative charge

Extracellular fluid

fluid outside the cell: Mostly positive ions (Na+), overall positive charge

Voltmeter

A device used to measure voltage, or electrical potential energy difference

oscilloscope trace

A trace showing the change in electrical potential across the membrane of an axon at each stage of an action potential.

Resting potential

-70 mV, the state of the neuron when not firing a neural impulse

Axon membrane

has chemical gates that can open to allow electrically charged particles to enter or can close to keep out electrically charged particles

Action Potential (AP)

an electrical impulse changing the permeability of a membrane

depolarization phase

Na+ rush into axon, increasing charge from -70 to +40 very briefly

Hyperpolarization phase

-"Gates" close to Na+ and open to K+ -K+ rushes out of axon -Loss of positive ions causes charge to become negative, below -70

recovery phase

• Sodium-potassium pump

• Na+ leaves axon, K+ drawn back in

• Charge returns to -70

Refractory period

the time following an action potential during which a new action potential cannot be initiated

Action potential in unmyelinated axons

Ion exchange occurs at every point of the axon, one at a time (slower)

Action potential in myelinated axons

In myelinated axons, it creates saltatory conduction. Ion exchange occurs at Nodes of Ranvier, between bubbles of myelin, and then skips to the next node (faster)

Rate of spontaneous activity

Base rate of action potentials produced per second without stimulation in living beings

Transferring information between neurons

1. Electrical charge travels down axon to axon terminal

2. Synaptic vesicles release neurotransmitters into synaptic gap

3. Neurotransmitters are picked up by dendrites of receiver neuron

synaptic vesicles

Membrane-bounded compartments in which synthesized neurotransmitters are kept.

Excitatory neurotransmitters

chemicals released from the terminal buttons of a neuron that excite the next neuron into firing

Inhibitory neurotransmitters

chemicals released from the terminal buttons of a neuron that inhibit the next neuron from firing

Neuron notation

O

Axon notation

--------------

excitatory neurotransmitter notation

<

inhibitory neurotransmitter notation

|

linear circuit

Signal generated by each receptor travels straight to the next neuron, and no other neurons are involved.

converging circuit

postsynaptic neuron receives nerve impulses from several different sources

Imaging studies

Measures average activities in thousands of neurons

Psychophysics

the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them

Fechner

father of psychophysics

Absolute threshold

the minimum stimulation needed to detect a particular stimulus 50 percent of the time

high threshold

low sensitivity to stimulus (more stimulation needed for the observer to detect it)

low threshold

high sensitivity to stimulus (less stimulation needed for the observer to detect it)

Method of limits

A psychophysical method in which the particular dimension of a stimulus, or the difference between two stimuli, is varied incrementally until the participant responds differently.

Crossover point

the point at which a person changes from detecting to not detecting a stimulus or vice versa

method of adjustment

a psychophysical method in which the experimenter or the observer adjusts the stimulus intensity in a continuous manner until the observer detects the stimulus

method of constants

A psychophysical method in which a number of stimuli with different intensities are presented repeatedly in a random order for 100 trials

Difference threshold

the minimum difference between two stimuli required for detection 50 percent of the time

Pelli-Robinson contrast sensitivity chart

Lower contrast as the chart descends, measuring the lowest ability to discriminate the letters

Weber's law

the just noticeable difference of a stimulus is a constant proportion despite variations in intensity (K = JND/Standard)

Signal detection theory

a theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise). Assumes there is no single absolute threshold and that detection depends partly on a person's experience, expectations, motivation, and alertness.

Response criteria

how motivated we are to detect certain stimuli and what we expect to perceive

liberal response bias

high hit rate, high false alarm rate

• will readily report that the signal is present in ambiguous situations. These participants typically produce more hits and false alarms

conservative response bias

• respond "no" more than "yes"

• more misses and correct rejections

• Higher standard needed to claim they sensed the stimulus

sensory sensitivity

the extent to which a person registers sensory information. Measured by the difference of hits and false alarms

ROC curve

used to graphically summarize a subject's responses in a signal detection experiment. Points are plotted by trials in which participants are given incentives to respond more conservatively or liberally

Magnitude response compression

Perceived magnitude rises slower than physical intensity

Magnitude response expansion

Perceived magnitude rises quicker than physical intensity

Steven's Power Law

The perceived magnitude of a stimulus is equal to its actual physical intensity raised to some constant power. The constant power is different for each type of sensory judgement.

Acetylcholine

Excitatory neurotransmitter that causes muscle contractions. Black widow venom releases mass amounts of it, causing muscle spasms. Without acetylcholine, a person can be paralyzed

Curare

Blocks uptake of acetylcholine and causes paralysis. Used in stun darts

Glutamate

Common excitatory neurotransmitter in the brain

GABA

Inhibitory neurotransmitter. Sleeping pills increase the receptor’s access to GABA

Light

a form of electromagnetic radiation that is visible to the eye

Newton's view on light

Light is particles, called photons

Maxwell's view on light

Light is a wave created in the electromagnetic continuum

Amplitude of light

determines brightness

Wavelength of light

determines color (longer waves appear more red)

Cornea

the transparent layer forming the front of the eye.

Functions of the cornea

• responsible for refraction of light entering the eyes

• performs coarse focusing of light rays

• Keeps fluid inside of eye

• Protects eye from outside harm

Corneal disease

occurs when the cornea, the front surface of the eye, becomes clouded, scarred, or distorted by injury, disease, or hereditary defects. Creates a rainbow/halo effect around objects

corneal transplant

replacement of damaged cornea with donated tissue

Astigmatism

a condition in which the eye does not focus properly because of uneven curvatures of the cornea. Makes certain orientations of lines difficult to focus

Iris

a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

Pupil

the adjustable opening in the center of the eye through which light enters

Pupil and arousal

Pupil size can be controlled by autonomic nervous system. Adrenaline can cause pupils to dilate (eg. attraction- people find dilated pupils more attractive)

senile miosis

Normal with age Restriction of light entering the eye Decrease in resting diameter of the pupil Makes it harder to see in low light

Albinism

Absence of pigment in the skin, hair, and eyes. Eyes appear red because of reflection of blood vessels. Can create vision problems by clear irises not keeping light out

Lens

the transparent structure behind the pupil that changes shape to help focus images on the retina

Ciliary muscles

muscles which relax or contract and alter the shape of the lens. Bulge the lens for close objects and flatten for far away objects

Myopia

nearsightedness

Axial myopia

myopia in which the eyeball is too long. light rays from far objects converge in the front of the eye, making them appear out of focus

Refractive myopia

myopia (nearsightedness) in which the cornea and/or the lens bends the light too much

Hyperopia

A condition in which visual images come to a focus behind the retina of the eye and vision is better for distant than for near objects -- called also farsightedness.

axial hyperopia

eyeball is too short. light from objects focuses behind the retina

Refractive hyperopia

cornea/lens bends too little light

presbyopia

farsightedness caused by loss of elasticity of the lens of the eye, occurring typically in middle and old age.

Anomalies in colour vision with age

It gets harder to distinguish colours in the blue/green end of spectrum

Cataracts

Lens becomes milky-coloured which makes it hard to see through. Can be fixed through replacement with artificial lens