Sensation and Perception, Chapter 1

Sensation

The initial steps in the perceptual process, whereby physical features of the environment are converted into electrochemical signals that are sent to the brain for processing

Senses

Physiological functions for converting particular environmental features into electrochemical signals

Perception

The later steps in the perceptual process, whereby the initial sensory signals are used to represent objects and events so they can be identified, stored in memory, and used in thought and action

Representations

Information in the mind and brain used to identify objects and events, to store them in memory, and to support thought and action

Stimuli

The objects and events that are perceived (distal stimuli) and the physical phenomena they produce (proximal stimuli)

Distal stimulus

A perceived object or event in the world (ex: a slamming door)

Proximal stimulus

A physical phenomenon evoked by a distal stimulus (ex: sound waves from a slamming door)

Neurons

The cells of the nervous system that produce and transmit information-carrying electrochemical signals

Neural signals

Electrochemical signals carried by neurons

Sensory receptors

Specialized neurons that convert proximal stimuli into neural signals

Photoreceptors

Neurons in the eye that convert light into neural signals

Mechanoreceptors

Neurons in fingertips that convert pressure on your skin into neural signals

Top-down information

An observer's knowledge, expectations, and goals, which can affect perception

Bottom-up information

The information contained in neural signals from receptors

Transduction

The transformation of a physical stimulus into neural signals

Neural code

A pattern of neural signals that carries information about a stimulus and can serve as a representation of that stimulus

Psychophysics

A field of study concerned with relating psychological experience to physical stimuli

Body senses

Senses that include the ability to sense body and limb position, pain, skin temperature, balance, and body movement

Natural Selection

The basic mechanism of biological evolution, whereby adaptive traits are more likely to be passed on to offspring through genetic inheritance and to become increasingly prevalent in a population

Phenotypes

Observable characteristics, or traits, of an organism

Genotypes

The genetic makeup of an organism

Proprioception

Body perception

Nociception

Pain perception

Fitness

The ability of an organism to survive and reproduce in its environment

Johannes Müller

German scientist who stated the "law of specific nerve energies" in 1826

Law of Specific Nerve Energies

Law that states that the kinds of perceptions we have depend on which neurons are activated, not on what's activating those neurons

Charles Sherrington

British scientist who, in 1906, articulated the fundamental principles of brain function, including how neurons communicate with one another in networks

Wilder Penfield

Canadian neurosurgeon who found that when he directly stimulated neurons in certain areas of the brain of awake patients, the patients would report the sensation of being touched at certain places on their body; created a complete "touch map" of the body

Neuron doctrine

The principle that perception depends on the combined activity of many specialized neurons, each of which responds to specific aspects of a stimulus

Trigger features

Specific aspects of a stimulus

Cell membrane

A cell structure that separates what is inside the cell from what is outside the cell

Cell body

The part of a cell that contains the nucleus

Dendrites

Projections that emanate from the cell body of a neuron and that receive signals from other neurons

Axon

A projection that emanates from the cell body of a neuron and that conducts neural signals to the axon terminals, for transmission to other neurons

Axon terminals

Endings of an axon, where neural signals are transmitted to other neurons

Nerve

A bundle of axons that travel together from one location in the nervous system to another

Tract

The term for a nerve found in the brain

Action potential

An electrochemical signal that begins in the dendrites of a neuron and travels down the axon to the axon terminals

Protons

Positively charged particles in an atom

Electrons

Negatively charged particles in an atom

Ion

An atom that has an imbalance in the number of protons and electrons and that therefore has an electric charge

Sodium (Na+) and Potassium (K+)

The two main types of positively charged ions that are found in the fluid within and around neurons

Membrane potential

A difference in electrical potential across the cell membrane, due to a difference in the concentrations of positive and negative ions inside and outside the cell; measured in millivolts (mV)

Resting potential

The membrane potential when a neuron is at rest (about -70 mV due to the higher concentration of negative ions inside the cell than outside)

Single-cell recording

A technique used to measure the membrane potential that involves placing insulated wires inside and outside of the cell membrane

Ion channels

Small pores in the cell membrane of neurons through which certain ions can flow into or out of the cell

Voltage-gated

Term describing ion channels that open only when the membrane potential changes sufficiently

Depolarization

Part of the sequence of evens of an action potential, during which an inflow of positively charged ions causes the membrane potential to become markedly more positive

Repolarization

Process by which potassium channels open in response to the depolarization of the membrane, allowing positively charged K+ ions to flow out of the axon

Hyperpolarization

A change in a cell's membrane potential such that the inside of the membrane becomes more negative relative to the outside

Refractory period

A brief period following an action potential during which a new action potential cannot be initiated

Firing rate

The rate at which a neuron produces action potentials; usually expressed in terms of spikes per second

Baseline firing rate

A neuron's low rate of spontaneous firing at fairly random intervals in the absence of any stimulus

Threshold

Level of stimulation needed to trigger a neural impulse

Synapse

A tiny gap between the axon terminal of one neuron and the dendrite or cell body of another neuron

Presynaptic membrane

The membrane at the axon terminal of a neuron producing an action potential

Postsynaptic membrane

The membrane of the dendrite or cell body receiving a neural signal

Synaptic vesicles

Within axon terminals, tiny sacs that contain neurotransmitter molecules

Neurotransmitters

Chemical substances involved in the transmission of signals between neurons; neurotransmitter molecules released into a synapse by the neuron sending a signal bind to receptors on the neuron receiving the signal

Ligand-gated

Term describing ion channels that open in response to a chemical signal, allowing or blocking the flow of specific ions

Excitatory neurotransmitters

Neurotransmitters that have an excitatory effect on the postsynaptic neuron, increasing the probability that an action potential will be initiated

Inhibitory neurotransmitters

Neurotransmitters that have an inhibitory effect on the postsynaptic neuron, decreasing the probability that an action potential will be initiated

Excitatory postsynaptic potential (EPSP)

The effect of an excitatory neurotransmitter, making the postsynaptic neuron's membrane potential more positive

Inhibitory postsynaptic potential (IPSP)

The effect of an inhibitory neurotransmitter, making the postsynaptic neuron's membrane potential more negative

Cerebral hemispheres

The two most important divisions of the brain; separated by the longitudinal fissure

Corpus callosum

A large bundle of axons that constitutes the major connection between the two cerebral hemispheres

Gyrus

An elongated bump on the surface of the cerebral hemispheres

Sulcus

An indentation between two gyri on the surface of the cerebral hemispheres

Frontal lobe

One of the four lobes of each cerebral hemisphere; separated from the temporal lobe by the lateral sulcus and from the parietal lobe by the central sulcus

Temporal lobe

One of the four lobes of each cerebral hemisphere; separated from the frontal lobe and the parietal lobe by the lateral sulcus

Parietal lobe

One of the four lobes of each cerebral hemisphere; separated from the frontal lobe by the central sulcus, from the temporal lobe by the lateral sulcus, and from the occipital lobe by the parieto-occipital sulcus

Occipital lobe

One of the four lobes of each cerebral hemisphere; separated from the parietal lobe by the parietal-occipital sulcus

Cerebral cortex

The outermost layer of the cerebral hemisphere; about 2-4 mm thick and consisting mostly of gray matter (neural cell bodies)

Gray matter

The cell bodies of neurons making up the cerebral cortex

White matter

The myelin-covered axons of cortical neurons, making up the interior parts of the cerebral hemispheres; these axons connect neurons located in different parts of the cerebral cortex

Thalamus

The most important subcortical structure involved in perception; most neural signals pass through here on their paths from the sensory organs to the cortex

Cognitive neuropsychology

The investigation of perceptual and cognitive deficits in individuals with brain damage in order to discover how perception and cognition are carried out in the normal, undamaged brain

Modularity

The idea that the human mind and brain consist of a set of distinct modules, each of which carries out one or more specific functions

Dissociation

In cognitive neuropsychology, a pattern of brain damage and impaired function in which damage to some specific brain region is associated with impairment of some specific function but not with impairment of another function

Double dissociation

In cognitive neuropsychology, a pattern of brain damage and impaired function in which damage to some specific brain region is associated with impairment of some specific function A but not with impairment of another function B, along with a pattern (in a different patient) in which damage to a different region is associated with impairment of function B but not with impairment of function A

Assumption of cognitive uniformity

The assumption that the functional organization of human cognition and of the brain is essentially the same in everyone

Functional neuroimaging

An array of techniques for measuring brain activity in healthy volunteers carrying out carefully designed tasks

Electroencephalography (EEG)

A functional neuroimaging technique based on measurement of the electrical fields associated with brain activity

Magnetoencephalography (MEG)

A functional neuroimaging technique based on measurement of the magnetic fields associated with brain activity

Positron emission tomography (PET)

A functional neuroimaging technique based on measurement of the changes in blood flow associated with brain activity, using a radioactive substance introduced into the blood

Functional magnetic resonance imaging (fMRI)

A functional neuroimaging technique based on measurement of the changes in blood oxygenation associated with brain activity

Absolute threshold

The minimum intensity of a physical stimulus that can just be detected by an observer

Method of adjustment

A behavioral method used in psychophysical experiments; the participant observes a stimulus and adjusts a knob that directly controls the intensity of the stimulus

Method of constant stimuli

A behavioral method used in psychophysical; the participant is presented with a fixed set of stimuli covering a range of intensities that are presented repeatedly in random order, and the participant must indicate whether or not each stimulus was detected

Psychometric function

A curve that relates a measure of perceptual experience to the intensity of a physical stimulus

Staircase method

A behavioral method used in psychophysical experiments; the participant is presented with a stimulus and indicates whether it was detected, and based on that response, the next stimulus is either one step up or one step down in intensity

Difference threshold

The minimum difference between two stimuli that allows an observer to perceive that the two stimuli are different

Ernst Weber

German physician who developed Weber's law

Weber's law

A statement of the relationship between the intensity of a standard stimulus and the size of the just noticeable

Weber fraction

The constant "k" in Weber's law (JND=kl)

Psychophysical scaling

The process of measuring how changes in stimulus intensity relate to changes in the perceived intensity

Fechner's law

A statement of how the perceived intensity of a stimulus changes as its physical intensity changes (S=k ln I/Io)

Magnitude estimation

A behavioral method used in psychophysical experiments to estimate perceived intensity directly; the experimenter assigns an arbitrary number to represent the intensity of a standard stimulus, and then the participant assigns numbers to other stimuli to indicate their perceived intensity relative to the standard

Stevens power law

A statement of the relationship between the physical intensity of a stimulus and its perceived intensity

Noise

In the study of neural activity, slight random variation in the number of action potentials produced by neurons in response to a fixed sensory stimulus