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PSYC 2390
Lana Trick

1. The neuropsychology of perception. a). Describe the process in which a neural impulse travel down one axon, making sure to specify chemical substances involved and how that affects the charge within the cell at each stage. Use a graph to show how the membrane potential changes as a function during the different stages of the process. Answer: neural impulses, or action potentials travel down an axon when stimulated enough and there is a transfer of ions; the neuron goes up to 40 positive millivolts and let in sodium ions and boots out potassium ions, it will then go down to below 70 negative millivolts which is the recovery phase during which the sodium ions are booted out and the potassium ions are taken back in; it will then return to its resting potential of -70 millivolts b). What are neurotransmitters? Describe the difference between neurotransmitters that have excitatory and inhibitory effects, using examples of neurotransmitters of each type to clarify your description. Answer: neurotransmitters are different types of chemicals that travel through neurons to send information; excitatory neurotransmitters increase the probability that the receiver will have an action potential (they increase the positivity, or in other words depolarize), acetylcholine, curare and glutamate are exctitatory. Inhibitory neurotransmitters reduce the probability that a neuron will have an action potential; gaba and serotonin are examples c). What does it mean to say that cells have a rate of spontaneous activity? Why is this important to understanding the way that neurons send messages and communicate? Answer: spontaneous activity means that neurotransmitters are released through the synaptic gap to other neurons (action potential) without any stimulation; this is important to know because a neuron that is stimulated is already firing off action potentials from its spontaneous activity and neurons will be affected differently depending on whether it is being stimulated by an excitatory or inhibitory neurotransmitter d). Draw the following neural circuits (using the notation taught in class) and then say what would happen if they were stimulated as specified. i). A simple excitatory linear circuit between neurons A and B and C. What would happen to the activity of B if A were stimulated?
 A B C Answer: A would receive an action potential and since it is an excitatory neuron, B would therefore be stimulated ii). A circuit that shows convergence between neurons that send excitatory neurotransmitters. Neurons A, B, and C each lead into neuron D (and no other neuron). What would happen to the activity of neuron C if A and B were stimulated? Answer: Nothing would happen to C because they are attached to neuron D and therefore wouldn’t stimulate eachother, only neuron D iii). A circuit that shows convergence between neurons that have excitatory and inhibitory neurotransmitters. Neurons A and B each lead into neuron C (and no other neuron). What would happen to the activity of neuron C if neurons A and B were stimulated at the same time (and to an equal extent). Assume that all axons are the same length and there is no difference in the effectiveness of neurotransmitters. Answer: Since neurons A and B are an excitatory and inhibitory neurotransmitter, if both were stimulating neuron C to an equal extent, they would cancel each other out and neuron C would receive no stimulation. 2. Psychophysics I.
 a). Describe the *3* major psychological methods for measuring the absolute threshold, making use of the example of your own creation to illustrate how each would work. Answer: method of limits involves the experimenter presenting the stimulus in ascending order and then descending order, after which the two results are averaged out to give you the participants absolute threshold; the method of adjustments involves the participant manually adjusting the stimulus intensity until they cant just barely detect it and then that is their absolute threshold; the constant stimuli method involves the experimenter presenting 5-9 stimuli with different intensities in random order many times and the absolute threshold is determined by which intensity is detected 50% of the time b). What is a difference threshold and how is it measured? What is a JND? (Use an example of your own creation to clarify these ideas.) Answer: the difference limens is the smallest difference detectable between two stimuli, it is measured by the method of limits, method of adjustment or method of constants; the JND is just noticeable difference c). Describe Weber's Law using an example of your own creation to clarify your ideas. Answer: Webers Law: K = JND/S; K is a constant called the Weber fraction, S is the value of the standard stimulus and JND is the just noticeable difference or difference threshold (or differenze limenz) d) A researcher was interested in measuring the faintest sound that people could detect. Sound intensities range from 1 to 10 in this study (with 10 being the most intense or loudest sound). What is the absolute threshold in this study? Y= subject says that they sense it. N = subject says no they do not sense it. Intensity Trial 1 Trial 2 Trial 3 Trial 4 23 Y Y Y Y Y Y 22 Y Y 21 Y Y Y Y 20 Y N Y Y 19 Y N N N 18 N N N N 17 N N N N 16 N N N N N N 15 N N Answer: Trial 1 is 18.5, Trial 2 is 20.5, Trial 3 is 19.5 and Trial 4 is 19.5; (18.5+20.5+19.5+19.5)/4=19.5 THEREFORE the absolute threshold for the participant is 19.5 i. What type of study is this?
 Answer: This is a method of limits study ii. ii. Calculate the absolute threshold in this study. (I'm looking for a numerical answer.) Answer: 19.5 iii. What is the difference between how absolute and difference thresholds are calculated in method of constants studies? Illustrate the difference using an example of your own creation involving absolute and difference taste thresholds for substance X. [The physical intensity of a tasted substance can be measured in terms of the number of mg of the substance (substance X in this case) per 1000 liters of water.] You should be getting numerical answers her
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