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Chapter 1: Foundations (neurons in the brain and perception (general…
Chapter 1: Foundations
the process of perception
perception vs sensation
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
apply term 'perception' to organisms with nervous systems in which specialized sensory cells convert physical features of environment into electrical signals that motivate physiological, behavioral, emotional, and cognitive responses and can give rise to awareness
form mental representations of the objects and events in a sense to they can be recognized, stored in memory, used in thought/action
representations
:
information in the mind and brain used to identify objects and events, to score them in memory, and to support thought and action
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
senses evolve in response to the physical properties of objects and events in the world that organisms need to sense in order to survive
in addition to vision, audition, tactile perception, olfaction, gustation, there are proprioception (body perception), pain perception, thermoreception (temperature perception), balance, and body movement
can also include information about body states such as hunger (blood glucose level), thirst (body fluid levels), internal body temperature, and muscle fatigue
biological structure and function of every organism on earth is a result of billions of years of evolution driven by the mechanisms of natural selection
natural selection
:
the basic mechanism of biological evolution, whereby advantageous traits are more likely to be passed on to offspring through genetic inheritance and to become increasingly prevalent in a population
three core ideas at most general level of the modern theory of evolution
organisms have observable characteristics/traits called phenotypes that result from genetic code called a genotype, carried in DNA, that uses the machinery of a cell to produce the organism’s phenotypical structures and functions
genetic code transmitted in DNA via reproduction; can undergo mutations that might produce new phenotypes, occasionally yielding a new trait that is advantageous and can be passed on
organisms what that adaptive new trait compete more effectively for resource and are more likely to survive/reproduce and through natural selection, an increasing proportion of individual organisms in a population will come to possess those traits
starting point of process of perception is the world itself
objects and events in world give rise to physical phenomena that can be sensed
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
proximal stimulus
:
a physical phenomenon evoked by a distal stimulus that impinges on the specialized cells of a sense
neurons
:
cells of the nervous system that produce and transmit information-carrying signals
neural signals
:
information-carrying electrochemical signals produced and transmitted by neurons
brain combines signals into integrated conscious experience of the message, an experience that you can store in memory
sensory receptors
:
specialized neurons that convert proximal stimuli into neural signals
speed and accuracy of perception often enhanced by perceiver's knowledge about current scene and expectations about what kinds of things are likely to be present/occur
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
the study of perception
ask three kinds of questions
how does the proximal stimulus carry information about the thing that is perceived?
how does light projected into the eyes carry information about the position, shape, and color of an object in the world?
how is the proximal stimulus transformed into neural signals- a process called transduction
transduction
:
the transformation of a physical stimulus into neural signals
how do neural signals form a neural code?
neural code
:
a pattern of neural signals that carries information about a stimulus and can serve as a representation of that stimulus
how is the information in the neural code processed in the brain?
what is the relationship between perceptual experience and distal stimulus?
psychophysics
:
a field of study concerned with relating psychological experience to physical stimuli
assesses perceptual experience on the basis of simple behavioral responses, such as reporting whether a stimulus was detected or whether two stimuli appear to be the same or different
requires that investigator precisely controls the physical attributes of the perceptual stimuli
by analyzing responses, can develop theories of how perceptual systems encode these attributes
investigates the relationship between stimuli and experience in two ways
absolute threshold
:
the minimum intensity of a physical stimulus that can just be detect by an observer
reveal which stimuli are more detectable than others which can provide important hints about how the brain processes those stimuli
measuring an absolute threshold involves presenting stimuli that vary in physical intensity and having participants respond to each stimulus by indicating whether they detected it; involves three methods
method of adjustment
:
a behavioral method used in psychophysical experiments; when used to measure the absolute threshold, the participant observes a stimulus and manipulates a control that directly adjusts the intensity of the stimulus
starts with extreme detectable or undetectable tone and participant changes intensity until they can just barely not sense it or just barely sense it
repeated several times and average of the threshold estimates is taken as the final estimate of the absolute threshold
gives quick results but tend to vary quite a bit; can't tell if respondent being honest or not
method of constant stimuli
:
a behavioral method used in psychophysical experiments; when used to measure the absolute threshold, the participant is repeatedly presented with a fixed set of stimuli, in random order, covering a range of intensities, and the participant must indicate whether or not each stimulus was detected
each intensity of stimuli predetermined beforehand; presented multiple times throughout experiment and participants either responds that they can or cannot sense it
frequency that participant reported sensing stimulus at each intensity calculated; resulting curve used to estimate absolute threshold for given stimulus
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more reliable results than method of adjustment and easier to tell if subject lying, but not especially effective because involves retesting extreme values multiple times
staircase method
:
a behavioral method used in psychophysical experiments; when used to measure the absolute threshold, 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
can vary size of steps as experiment continues, allowing for the absolute threshold to be approached with increasing accuracy
advantage of not wasting much time on testing extreme intensities
difference threshold
:
aka just noticeable difference (JND); the minimum difference between two stimuli that allows an observer to perceive that the two stimuli are different
experiments designed to find this involve comparing two stimuli called the standard stimulus (intensity remains constant) and the comparison stimulus (intensity varies from one trial to the next)
method of adjustment- start with stimuli at same intensity and then increase/decrease intensity of one until they are noticeably different
method of constant stimuli- present two stimuli and ask whether comparison stimulus is more or less intense than standard stimulus in each trial
JND determined by finding the point on the psychometric function where 25% of the responses were yes and the point where 75% of the responses were yes and halving the difference between these two values of intensity
JND reflected in steepness of psychometric function
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staircase method- ask if comparison stimulus is more/less intense and change comparison stimulus based on response to approach JND
Weber’s law
:
a statement of the relationship between the intensity of a standard stimulus and the size of the just noticeable difference (JND = kI, where I is the intensity of the standard stimulus and k is a constant that depends on the perceptual dimension being measured)
the size of the JND tends to increase as the intensity of the standard stimulus (or background) increases)
Weber fraction
:
the constant k in Weber’s law (JND = kI)
psychophysical scaling
:
the process of measuring how changes in stimulus intensity relate to changes in the perceived intensity
two different approaches
Fechner’s law
:
a statement of how the perceived intensity of a stimulus changes as its physical intensity changes (S = k ln I/Io, where S is the perceived intensity, k is the Weber fraction, and I/Io is the natural logarithm of the ratio of the stimulus intensity, I, to the intensity, Io, of the same stimulus at the absolute threshold
wanted to use Weber's law to quantify how people perceive stimulus intensity in general; supposed that 1 JND is equal to 1 unit difference in the perceived intensity
means that validity of Fechner's law depends on validity of Weber's law
curve is steep for low-intensity stimulus but then flattens out as the physical intensity of the stimuli increases
means that for low-intensity, a 1 JND increase in perceived intensity is achieved by just a small increase in physical intensity, but for higher-intensity stimuli, a much larger increase in physical intensity is needed to produce the same 1 JND increase in perceived intensity
Steven’s power law
:
a statement of the relationship between the physical intensity of a stimulus and its perceived intensity (S = cIn, where S is the perceived intensity of the stimulus, I is its physical intensity, the exponent is different for each perpetual dimension, and c is a constant that depends on which units are being used for S and I)
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
selects wide range is stimulus with varying intensities, begins by presenting one in the middle and asks participant to assign number to it; following intensities are presented and participants assign numbers to them in reference to standard
line length is a straight line, indicating that relationship between perceived magnitude and physical magnitude are nearly constant for perceiving length of line
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brightness starts out steep and then flattens, indicating that as magnitude of physical stimulus increases, perceived magnitude increases more and more gradually
electric shock produces accelerating curve- starts out rather flat and then gets rather steep
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when exponent less than 1 (as for brightness), produces decelerating curve
neurons in the brain and perception
general principles
perception relies on activity of neurons, beginning with the activity of receptors that transduce proximal stimuli into neural signals that are propagates through vast networks of other neurons in the brain
‘law of specific nerve energies’ articulated by Müller in 1826, states that kinds of perceptions we have depend on which neurons are activated, not on what’s activating those neurons
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
specific aspects of stimulus are called trigger features
the construction of a neuron
characteristics similar to other cells
cell membrane
:
a cell structure that separates what’s inside the cell from what’s outside the cell
cell body
:
the part of a cell that contains the nucleus
characteristics unique to neurons
main characteristic that distinguishes neurons from other cells is the ability to receive and transmit neural signals
are also extensively interconnected- any one neuron sends signals to and receives signals from as many as several thousand other neurons
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
any given axon may branch into as many as several thousand axon terminals, each of which ends immediately adjacent to a dendrite or the cell body of another neuron
nerve
:
a bundle of axons that travel together from one location in the nervous system to another
action potential
:
an electromechanical signal that begins in the dendrites of a neuron and travels down the axon to the axon terminals
properties of action potentials
stimulated by a signal from another neuron
action potentials are all-or-none, magnitude and duration of change in membrane potential are almost always exactly the same
speed of action potential also the same, but can differ in different neurons depending on various factors
large-dimension axons propagate action potentials faster than small-diameter axons and those with myelin have faster speed
firing rate
:
the rate at which a neuron produces action potentials; usually expressed in terms of actions potentials (spikes) per second
usually between 0-few hundred times per second
baseline firing rate
:
a neuron’s low rate of spontaneous firing at fairly random intervals in the absence of any stimulus
changes in firing rates can result from wide variety of changes in proximal stimuli
firing rate functions as neural code, convening useful information about stimulus that evoked the neural activity
every atom contains one or more positively charged particles called protons in its nucleus, surrounded by cloud of negatively charged particles called electrons
in neutral state, atom contains the same number of electrons and protons
ion
:
an atom that has an imbalance in the number of protons and electrons and that therefore has an electric charge
difference in concentration of ions in fluid around neuron give rise to electrical potential (voltage) across the cell membrane
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
single-cell recording
:
a technique used to measure the membrane potential
cell membrane is semipermeable- certain ions can cross the membrane through ion channels
ion channels
:
small pores in the cell membrane of neurons through which certain ions can flow into or out of the cell
channels are voltage-gated- only open when membrane potential changes sufficiently
when neuron receives signal from another neuron, receiving one undergoes abrupt change in membrane potential which causes voltage-gated sodium channels to open at the base of the axon
allows extracellular Na+ atoms to flow into axon because concentration is much greater outside than inside
influx of positive ions causes membrane potential to become more positive
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resting potential
:
the membrane potential when a neuron is at rest (about -70mV)
higher concentration of negatively charged ions inside the cell than outside
transmitting signals between neurons
the arrival of an action potential at an axon terminal causes synaptic vesicles to merge with the presynaptic membrane, releasing neurotransmitter molecules into the synapse
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 involves 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
some molecules flow across the synapse and come into contact with the postsynaptic membrane, which contains proteins called receptors
neurotransmitter molecules fit into, or bind, to receptors
binding causes certain ligand-gated ion channels in the postsynaptic membrane to open (ligand is molecule such as a neurotransmitter), leading to change of membrane potential through process of ion flow
postsynaptic neuron’s firing rate depends on balance between EPSPs and IPSPs; if sum exceeds threshold, neuron will fire
if enough neurotransmitter binding events result in opening of enough ion channels, change in membrane potential in postsynaptic neuron can reach threshold at which action potential is initiated by opening of voltage-gated ion channels
excitatory neurotransmitters
:
neurotransmitters that have an excitatory effect on the postsynaptic neuron, increasing 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
work by depolarizing membrane potential
increase the probability that an action potential will be initiated in the postsynaptic neuron
inhibitory neurotransmitters
:
neurotransmitters that have an inhibitory effect on the postsynaptic neuron, decreasing the probability that an action potential will be initiated
work by hyperpolarizing membrane potential
at inhibitory synapse, inhibitory neurotransmitter is released and binds, causing Cl- ion channels to open in postsynaptic neuron’s membrane, letting Cl- neurons enter the cell, making membrane potential more negative
inhibitory postsynaptic potential (IPSP)
:
the effect of an inhibitory neurotransmitter, making the postsynaptic neuron’s membrane potential more negative
decreases the probability that an action potential will be initiated in the postsynaptic neuron
the brain
structure of the brain
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
cerebral cortex
:
the outermost layer of the cerebral hemispheres; about 2-4mm 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
left cerebral cortex and right cerebral cortex each divided into four lobes
frontal lobe
:
one of the four lobes of each cerebral cortex (left and right); 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 cortex (left and right); separated from the frontal lobe and the parietal lobe by the lateral sulcus
parietal lobe
:
one of the four lobes of each cerebral cortex (left and right); 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 cortex (left and right); separated from the parietal lobe by the parieto-occipital sulcus
thalamus
:
the most important subcortical structure involved in perception; most neural signals originating in the sensory organs pass through the thalamus on their paths 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
module processes only specific types of information, making it domain specific
idea of functional modularity often accompanied by assumption of anatomical modularity- idea that a functional module resides in a specific region of the brain
sometimes particular function carried out by neurons in several different brain regions working in concert
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 to 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
provides strong evidence that two functions are carried out by separate modules that can be separately damaged
assumption of cognitive uniformity
:
the assumption that the functional organization of human cognition and of the brain is essential the same in everyone
there are individual differences in perpetual functions that can have both genetic and experiential causes
functional neuroimaging
:
an array of techniques for measuring brain activity in healthy volunteers carrying out carefully designed tasks
divided into two broad types
techniques for measuring the electrical or magnetic fields produced by populations of active neurons (electroencephalography and magnetoencephalography)
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
use the fact that when many neurons are simultaneously active, activity produces weak electrical and magnetic fields
are good at tracking changes many times per second, but only approximate locations in the brain of neural activity being measured
techniques for measuring the changes in blood flow and blood oxygenation that accompany brain activity (positron emission tomography, functional magnetic resonance imaging, and diffuse optical tomography)
position emission tomography (PET)
:
a functional neuroimaging technique based on the changes in blood flow associated with brain activity; relies on the introduction of a radioactive substance into the blood
use the fact that when neurons in part of brain become more active, more blood flows to that area to supply it with oxygen and other metabolites
when blood flow to certain area changes, strength of radioactive signal emitted from that location also changes
functional magnetic resonance imaging (fMRI)
:
a functional neuroimaging technique based on measurement of the changes in blood oxygenation associated with brain activity; relies on production of magnetic fields in the brain
magnetic resonance imagine (MRI) invented in early 1970s, takes advantage of magnetic properties of molecules that occur naturally in body to produce high resolution 3-D images of bodily structures and their internal features
diffuse optical tomography (DOT)
:
a functional neuroimaging technique based on measurement of the changes in blood oxygenation associated with brain activity; relies on measurement of light absorbed and reflected by the brain
has similar temporal resolution to fMRI, but lower spatial resolution