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
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
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
22 Y Y
21 Y Y Y Y
20 Y N Y Y
19 Y N N N
18 N N
17 N N N N
16 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
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
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