Name ______
Cognitive Science Fall 2008,
Midterm 2
80 minutes
Closed book
Total pts: 100.
Penn ID ______KEY______
______
Do not write below this line.
P2 ______
P3 ______
P4 ______
P5 ______
P6 ______
P7 ______
P8 ______
P9 ______
______TOTAL
1. True or False (2 pts each)
a. __T_____ Consider trials from an experiment in which the reaction time is measured for the letter “D” followed by the letters “GG” compared to “G” followed by “GG”. Reaction times are faster for a “G” followed by “GG” compared to “D” followed by “GG” regardless of whether or not the “G” or “D” provide informational about the subsequent trial. (Posner and Snyder).
b. ___F___ “Selective attention” is restricted to just spatial (auditory and visual) tasks.
c. ___ T__ P(x)+P(~x)=1.0
d. ___F___ In general, syntax is associated with brain sites posterior to those associated with semantics.
e. ____ T___ For most right-handed individuals, the right hemisphere contributes to the perception of prosody.
f. ____ F____ A hallmark of autism is the failure of individuals to develop a theory of mind.
g. ____T____ Observing people’s purchasing behavior during and after a sale can lead to a descriptive model of purchasing behavior.
h. ___T_____ People or animals with lesions to the amygdala tend not toexperience emotions as strongly as those with an intact amygdala.
i. _____T___ People with severe damage to the cortex often still exhibit P-consciousness.
j. ___T/ F__ Similar brain mechanisms seem to be involved in motor control and in syntax.
2. Fill in the blank. (3 pts each)
a) John has a lesion in his hippocampus. He can remember how to ride a bicycle; he can remember general facts, like who the first US president was; and he can remember things that he just heard a few seconds ago. However, he has trouble remembering what he did the day before or whether he had breakfast this morning. His __episodic______memory is impaired.
b) According to the stimulus-stimulus (Pavlovian) model of conditioning, __CS______and ____US______are associated.
3. Define THREE of the following: (3 pts each)
Hemineglect
Damage to parietal lobe (typically right hemisphere) leading to a deficit in attention to the contralateral portion of space (with potentially different reference frames). Vision and memory are not impaired.
Availability Heuristic
Estimates of frequency are generated by virtue of how readily examples can be generated.
Framing Effects
Human decision making is not invariant – the answer depends on the way in which the question is framed. For example risk-taking can be shifted to risk-averse if the example emphasizes “number to die” vs. “number to survive.”
Frequentist (in terms of probabilities)
The notion of probability of an event is the relative proportion of times that event occurs in a large number of trials.
4. The following are multiple choice. Select ALL that apply.(3 pts each)
a) Which of the following is NOT a basic emotion as proposed by Ekman:
i) fear
ii) hunger
iii) surprise
iv) disgust
v) all of the above are basic emotions
b) Frontal Lobe function is associated with which of the following:
i) perceptually-dominated behavior
ii) early attentional gating
iii) implicit emotional learning
iv) executive function
v) none of the above
c) ForBayes’ rule:
i)
ii) P(D) is called the prior
iii) P(H|D) is called the posterior
iv) P(H|D) is called the likelihood
5. Match the best descriptors / descriptions:(1 pt each)
1) _A__ Wernicke's aphasiaa) Word-salad or empty speech
2) _E__ Broca's aphasiab) Perception and manipulation of specific objects
3) _F__ Conduction aphasiac) Recognize agent and purpose in self and others
4) _D__ Motor neuronsd) General grasping, holding manipulating
5) __B_ Canonical neuronse) difficulty in producing fluent speech
6) _C__ Mirror neuronsf) difficulty in repeating and naming
6. Answer TWOof the following questions: (5 pts each)
What does it mean to say concepts are “embodied”?
Concepts are represented in the brain using the same neural mechanism originally used for perceptual/mortor/homeostasis, etc.
Why might Parkinson’s patients have more trouble with regular past tense words than Alzheimer’s patients do?
Syntax is required for regular past tense words, which might be associated with motor planning areas in the cortex, which are damaged in Parkinson’s patients. In contrast Alzheimer’s patients have temporal lobe damage, and difficulty with irregular verbs.
Describe the James-Lange-Schacter-Demasio theory (or extended James-Lange theory) of emotion/feeling.
The feeling of “I am xx” comes from the read-out of “emotional” response (heart pounding etc.), and a cognitive understanding of the situation modulates perceived feeling.
7. (5 pts) It is a well-established finding that taxi drivers, paradoxically, stay out trying to get passengers all day on slow business days, but go home pretty early on days when business is plentiful.Drawing from prospect theory, explain this behavior. (Hint: you might imagine that taxi drivers set for themselves a standard quota of how many passengers they ought to get each day.)
The slow business days are like a loss, and the good business days are like a gain. Because losses are more aversive than gains are positive, taxi drivers strive to reduce gains.
8. Consider the following conditioning experiment:
First, animals are exposed to a tone followed by a light: tone light.
Second, animals are trained with a light followed by a shock: light shock.
Third, animals tested using a presentation of only the tone.
(a) (5 pts) What does the stimulus-response theory predict;a fear response to the tone, or nofear response to the tone? Why?
The stimulus response theory predicts that there is no fear response because the tone is never associated with the shock.
(b) (2 pts) Circle the correct answer: What is observed – (i) fear response or (ii) no fear response?
9. Mickey, the mouse, is running through the “maze” below.
Value function of the states at the start:
A 0 / B 0 / C-Shock 0D 0 / E 0 / F 0
G 0 / H-Food
0 / I 0
Mickey's learning rate is c = 0.5.
The value of the reward function in the Food state is R(Food) = 1.0
The value of the reward function in the Shock state is R(Shock) = -0.5
All other values are currently 0 (i.e. V(s) = 0 where s is any state and R(s) = 0 where s is any state other than the Food or Shock state)
Assume Mickey uses reinforcement learning.
a) (4 pts) Please fill in the value of each state (V(s)) after the mouse runs ABCExit.
____0_A ___0___B __-0.25__C (or 0.5*-0.5)
___0__D __0____E __0____F
____0_G ___0___H _0_____I
b) (4 pts) Fill in the values after he runs the same path a second time.
__0___A ___-0.125___B __-0.375____C [or 0.5*-0.25; -.25 + 0.5*(-.5+0+.25)]
___0__D ___0___E ____0__F
__0___G ___0___H __0____I
c) (3 pts) Did he learn more about the Shock state on the first or second trial? What is the (brief) explanation for this?
The first, because the result is more surprising.
10. After taking CIS140, John wants to put all of his probability knowledge to good use in Atlantic City. (Sadly, John did not really do that well in the course). After studying the roulette table for three hours, he determines the following table of probabilities:
Next ColorLast Color / Red / Black / Green
Red / 0.3 / 0.5 / 0.2
Black / 0.6 / 0.3 / 0.1
Green / 0.4 / 0.5 / 0.1
That is, if on the last spin the ball landed on a red number, John believes the probability of the ball landing on a black number on the upcoming spin is P(c2=Black | c1=Red) = 0.5
a) (5 pts) The last color the ball landed on was Green. Jim is now going to bet on the sequence: Red, then Black, then Green. Using the Markovian simplification, what is the probability that the next three balls are red, black, and then green? Show your work.
P(R,B,G|G)~= P(R|G)P(B |R)P(G|B) = (0.4)(0.5)(0.1)= 0.02
b) (4 pts) Using the Markovian simplification, when John sees the sequence (Red, Green, Red, Black), what does he think will come next? Show your work.
P(x|R,G,R,B)~P(X|B)
Given black, red is the most likely (0.6 compared to 0.3 and 0.1)
11. (8 pts) You are reading through the internet cooking sites looking for something to cook over the winter break. In particular you are interested in baking either pumpkin pie (P) or fruit cake (F).
You’ve done this before, and the probability of recipe for pumpkin pie, p(P)=0.2, and the probability of an article being about fruit cake is p(F)=0.1.
It turns out that the likelihood of seeing various words depends on what kind of article you're reading:
p("eggs"|P) = 0.9
p("nutmeg"|P) = 0.4
p("pecans"|P) = 0.1
p("chopped"|P) = .05
p("eggs"|F) = 0.9
p("nutmeg"|F) = 0.2
p("pecans"|F) = 0.5
p("chopped"|F) = .01
Common words such as "add", "and", “stir”,etc, are equally likely in all recipe types.
Suppose you see the following sentence fragments:
"...add eggs, nutmeg, and stir pecans..”
According to a Naive Bayes classifier, is this more likely to be a pumpkin pie or a fruit cake recipe? Show your work.
Recall P(F|words)=P(words|F)P(F)/P(words).
By independence assumption –
Fruit cake : (0.9)(0.2)(0.5)P(F)= (0.9)(0.2)(0.5)(0.1)
Pumpkin Pie: (0.9)(0.4)(0.1)P(P)= (0.9)(0.4)(0.1)(0.2)
Sadly, the ratio of these two probabilities favors fruit cake.
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