Chapter 1 Neuron Methods Neuron Huxley and Hodgkins o Worked out details of electrical properties of axons o Shared Nobel prize in 1963 with Eccles Creating potentials in neurons o Neural membranes separate ionic charges Charges differ inside to outside called the resting potential o Separation is a high energy state Certain conditions cause a rapid reversal of that state The signal produced is called the action potential AP The lipid bi layer o Impermeable to many molecules o Do any materials pass through Placed throughout the lipid bi layer are ionic channels Allow for the passage of certain ions but not others o What is allowed through Allows for the passage of some ions Potassium K o Potassium movement K moves somewhat freely across the cell membrane Due to the inside of the cell being negative K moves into the cell but then exits diffusion An equilibrium is eventually reached corresponds to the resting potential 70 mV But not others Proteins Sodium Na2 Action Potential o Moment of liberty o Sodium channels in the membrane briefly become permeable Causes of massive current ion flow o Resting potential vanishes and is even slightly reversed o Hyperpolarization inside of the neuron becomes more negative o Steps Resting potential is established Action potential is created when voltage dependent or gated ion channels are triggered Triggers when the membrane becomes slightly depolarized sodium channels open allowing a rapid influx of these ions which momentarily reverses the resting potential Postsynaptic ion channels o Transmitter gated o Channels stay open for as long as the transmitter molecules are present o The more transmitter present in synapses the more ion channels opened Thus the signal received at postsynaptic membranes is graded in contrast to all or none APs o The postsynaptic membrane passively conducts potentials Does not produce APs o Excitatory postsynaptic potentials EPSPs o Inhibitory postsynaptic potentials IPSPs Summation of potentials o Postsynaptic potentials decay relatively slowly o Multiple synaptic inputs are summed spatial summation Special summation depends on multiple inputs action more or less o Rapid presynaptic inputs are also summed temporal summation Temporal summation depends on rapid release of neurotransmitter by simultaneously fewer inputs o EPSPs and IPSPs cancel o If sufficient depolarization reaches the cell s axon an AP is generated at the axon hillock Electroencephalography EEG Hans Berger 1929 o Placed electrode on scalp and plotted electrical activity o Results were controversial at the time o However EEG was eventually accepted into the scientific community EEG o Electrodes are placed on the scalp to measure electrical activity o Postsynaptic potentials Event related potential ERP o Electrical brain activity measured from the scalp and evoked by a stimulus event Pros Cons of EEG o Advantages great temporal resolution relatively inexpensive o Disadvantages poor spatial resolution participants must go through many trials Transcranial Magnetic Stimulation TMS A technique whereby a brief intense pulse of magnetic energy is applied to the scalp to temporarily disrupt normal processing Functional Magnetic Resonance Imaging fMRI Neuroimaging technique that capitalizes on the fact that neural activity triggers a temporary increase in metabolic demand at the site of activation o Oxygenated blood has different properties than deoxygenated blood Pros Cons o Advantages great spatial resolution o Disadvantages poor temporal resolution loud expensive Positron Emission Tomography PET Imaging technique capitalizing on the brain s need for glucose and oxygen o A safe radioactive substance is injected that tags glucose or oxygen atoms Pros Cons o Advantages quit o Disadvantages radioactive substance poor spatial resolution relative to fMRI Methods for Understanding Perception Thresholds Ernst Weber 1795 1878 o Weber found that the just noticeable difference JND smallest detectable difference between two stimuli depends upon the referent Gustav Fechner 1801 1887 o Developed psychophysics specifying quantitative relations between physical stimuli and how they are perceived o Used Weber s findings to establish Weber s law K Change in I I o Extended law to create Fechner s law S k log R Assumes that all JND s are the same Thresholds o Absolute threshold the minimum amount of stimulus that a person can detect o Difference threshold same as the JND o Different methods for measuring thresholds Method of constant stimuli Psychophysical procedure in which each of a fixed set of stimuli is presented in a random order After completing all possible comparisons a JND can be computed that is noticeably stronger and noticeably weaker Method of Limits Similar to the method of constant stimuli Comparison stimuli start at a level of intensity either higher or lower than the standard and decrease or increase for descending and ascending respectively Ascending series start with a stimulus that is initially weaker than Descending series start with a stimulus that is initially stronger the standard than the standard Pro efficient Con expectations Staircase procedure Variant of the method of limits Stimulus presentations governed by the person s responses are made to bracket the threshold Alternating between 2 different staircases can reduce expectations o Ratings in gymnastics and ice skating are examples of scaling methods o Magnitude Estimation A psychophysical procedure in which people assign numbers to stimuli in proportion to the perceived intensity of those stimuli Scaling Scaling Methods S aI b Signal Detection Theory SDT Method used to quantify the ability to detect signal from noise Assumes an active part on the perceiver decision must be made Criterion internal threshold set by the observer Possible states of the world in SDT o Signal response yes HIT o Signal no response yes FALSE ALARM o Signal yes response no MISS o Signal response no CORRECT REJECTION o Based on this info we can calculate a measure of sensitivity quantify how well signal is detected from noise Receiver Operating Characteristic ROC curves o ROC curve a plot of the hits and false alarms SDT applied to memory paradigms used to examine recognition memory Theoretical Approaches Computation Ideal Observer IO o Specify operations performed in order to accomplish a goal Chapter 2 Early Vision Light Emission Theory o Empedocles eye made with Earth vision fire o Plato agreed Aristotle didn t o