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# A compelling optical illusion called the illusion of

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A compelling optical illusion called the illusion of [#permalink]  22 Sep 2012, 14:02
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Question Stats:

70% (02:02) correct 30% (01:05) wrong based on 70 sessions
A compelling optical illusion called the illusion of velocity and size makes objects appear to be moving more
slowly the larger the objects are. Therefore, a motorist’s estimate of the time available for crossing a highway
with a small car approaching is bound to be lower than it would be with a large truck approaching.
The conclusion above would be more properly drawn if it were made clear that the
(A) truck’s speed is assumed to be lower than the car’s
(B) truck’s speed is assumed to be the same as the car’s
(C) truck’s speed is assumed to be higher than the car’s
(D) motorist’s estimate of time available is assumed to be more accurate with cars approaching than with trucks
approaching
(E) motorist’s estimate of time available is assumed to be more accurate with trucks approaching than with cars
approaching

(My only query - Read this after doing the Q why cannot the answer be D?. There are two things. First, either his estimate about cars is accurate (which should be if we have to prove that he has this optical illusion concerning large objects. Second, his estimate about cars is more accurate than trucks - which might mean that both his estimates are incorrect, hence he has optical illusion concerning large and small objects. Then this answer might not make sense??? --- please guide...
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Re: Optical illusion [#permalink]  23 Sep 2012, 20:22
talismaaniac wrote:
A compelling optical illusion called the illusion of velocity and size makes objects appear to be moving more
slowly the larger the objects are. Therefore, a motorist’s estimate of the time available for crossing a highway
with a small car approaching is bound to be lower than it would be with a large truck approaching.
The conclusion above would be more properly drawn if it were made clear that the
(A) truck’s speed is assumed to be lower than the car’s
(B) truck’s speed is assumed to be the same as the car’s
(C) truck’s speed is assumed to be higher than the car’s
(D) motorist’s estimate of time available is assumed to be more accurate with cars approaching than with trucks
approaching
(E) motorist’s estimate of time available is assumed to be more accurate with trucks approaching than with cars
approaching

(My only query - Read this after doing the Q why cannot the answer be D?. There are two things. First, either his estimate about cars is accurate (which should be if we have to prove that he has this optical illusion concerning large objects. Second, his estimate about cars is more accurate than trucks - which might mean that both his estimates are incorrect, hence he has optical illusion concerning large and small objects. Then this answer might not make sense??? --- please guide...

I could not really get your statement, however, I don't think the accuracy of time is really important in this question.

The premise already says that [b]larger objects tend to appear to be moving slowly.[/b] . You have to take this at Face value .

So if the truck and the car are moving at the same speed , only then will the motorist estimate that the truck is a large object and hence, he estimates it to be moving slowly.
That said, if they are at the same speed , the vehicles' weight then come into picture.

Larger objects -> slowly
Smaller objects -> faster .

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Re: A compelling optical illusion called the illusion of [#permalink]  24 Sep 2012, 22:00
I agree with Ankit.

The illusion is a function of two Variables
1 – Speed
2 – Size

We know that truck is bigger than the car but we do not about the speed. So, to arrive at a conclusion we need the second variable i.e. the Speed

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Re: A compelling optical illusion called the illusion of [#permalink]  20 Feb 2013, 23:28
This is classic example of Assumption question where we need not put Math knowledge in the POE.

we have to assume other things being equal , optical illusion is justified for the time(car) <time(truck)

Hope that helps !!
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Re: RE: A compelling optical illusion called the illusion of [#permalink]  21 Feb 2013, 01:12

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Re: A compelling optical illusion called the illusion of [#permalink]  21 Feb 2013, 03:34
I prethink an assumption before going to answer choices.

my prethinking: motorist is affected by ilusion.

clearly, this prethought assumption is different from the assumption in oa. but when I read b, I immediately realize this assumption.

the prethinking process help us better understand the argument because we already know one assumption. the point is that it is easier to realize a new assumption (in oa) when we already know an assumption which we prethink.

I think this point is important.

pls comment on my thinking.
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Re: A compelling optical illusion called the illusion of [#permalink]  21 Feb 2013, 03:43
thangvietnam wrote:
I prethink an assumption before going to answer choices.

my prethinking: motorist is affected by ilusion.

clearly, this prethought assumption is different from the assumption in oa. but when I read b, I immediately realize this assumption.

the prethinking process help us better understand the argument because we already know one assumption. the point is that it is easier to realize a new assumption (in oa) when we already know an assumption which we prethink.

I think this point is important.

pls comment on my thinking.

Hi thangvietnam,

Yes you are right, the importance of prethinking is to understand the argument before you jump into the answer choice. Even if you do not get the correct answer choice, you have a solid understanding of the argument before you attack the answer choices.

Vercules
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Re: A compelling optical illusion called the illusion of   [#permalink] 21 Feb 2013, 03:43
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