Dear Hoover,
I would be most grateful if you would consider posting this on CVnet.
Cheers,
Robert.
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Dear Colleague,
Happy Holidays! Here is some light reading for the holidays: some
howlers made in response to three essay questions during a recent,
final examination by the 1995, University-of-Otago, undergraduate,
PSYC-201 class. I regret to say that I did actually lecture these
students. I hope you will get some joy out of their efforts, if only
to balance my suffering when marking them. You will need to scroll 137
lines.
Cheers,
Robert.
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Robert P. O'Shea phone: +64 (3) 479 7617 (w)
Department of Psychology fax: +64 (3) 479 8335
University of Otago e-mail: r_oshea@rivendellotago.ac.nz
P.O. Box 56
Dunedin
New Zealand
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Howlers for 1995 from the PSYC-201 Examination: Perception section
7. Purkinje (1825) watched a cavalry procession pass down a street.
After the procession had passed, he noticed that the houses appeared
to move up the street. Outline an explanation of this movement
aftereffect. (Attempted by 59 students.)
The movement aftereffect that Purkinje (1882) noticed has also been
documented in other parts of the world. A famous waterfall in Loch
Ness also displays the movement aftereffect.
Movement disparity causes the brain to facilitate a movement
parallelity.
The movement aftereffect is a common phenomena which is not readily
defined in definite terms.... [The MAE] is the result of the inhibited
processing pair releasing its supressed energy and sufforcating
temporially the exhausted other processing pair.
Assumptions are always made when [the MAE] is viewed that one might
need glasses or perhaps even just a good nights sleep. This however is
a scientific phenomenon.
The eyes will be tricked into jump starting the U cells at a fast
rate.
After the parade has passed this cell is (in a word) tired. So it
stops firing. Now it next door neighbour is a cell which going the
other way to the just used cell. The cell now stops firing at 20 and
ends up going into negatives which stimulates the next cell to fire
now since this cell normally rests at the same 10 because the other
cell hits negative it triggers a response from resting of the other
cell (which at this point in time I can not remember if that would
make it eg +15 or -5) either way the mind now fires the other cell so
instead of being even as one cell is tired out the brain perceives the
rest of the world moving in the opposite direction.
.... In order to watch the procession, Purkinje joined the rest of the
onlookers on the street. He settled himself into a good vantage point
in the crowd, that is he didn't place himself at the very front of
everyone because he feared that he wouldn't be able to see the whole
procession, but only those procession members right in front of him
who would have been very close (and he didn't want to block the view
of the children who were standing in the front). He ended up standing
quite far back in the crowd, but behind short people so that his
visual field was large.
As the procession came down the street Purkinje was intrigued. He
focussed intently on the procession members, admiring their outfits
amongst other things. [This goes on for another two pages.].... the
houses on the other side of the street clearly appeared to be moving
in the opposite direction! ``Are my eyes playing tricks on me? Am I
going mad?'' pondered Purkinje. Being a psychophysicist, Purkinje
didnt go to the optometrist for a check-up, but instead went home to
outline his observations.
For simplistic reasons he described his vision phenomena in a
linear perspective.... Hence, when the procession had passed, the
houses, in a fashion, `overcorrected' that on which he had been
concentrating and, thus appeared to move up the street. ``What a
breakthrough!'', claimed Purkinje excitedly, ``I shall go down in
history as the man who defined the movement aftereffect in
psychophysics. Wow!!''
Purkinje called this [MAE] the `Purkinje Shift'.
8. Explain how the Theory of Signal Detection helps us to understand
human performance in detecting stimuli under conditions of
uncertainty. Illustrate your answer with at least one example.
(Attempted by 95 students.)
One consilation is that the invaders appear as larger dots amongst the
noise blips on the screen. The test is, if a bomber is detected, the
fighter piolets must be administered to destroy the bomber. However
this exercise is extremely expensive for the nation, to absolute
certianty must be confirmed before confirming an invader. A second
condition is added when survival of the civilised world is lying in
the controlers hand, so here even if remote invader look alikes are
detected, fighter piolets must be administered, expense does not
matter in the second senoria.
The signal when presented especially of the stage of just noticeable
differences or absolute lumens can be confused with noise.... There is
always noise on the Radar scope that is sent from the Politically
assigned enemy of this day and age (PAE).
OBSERVER
PRESENT ABSENT
PRESENT Hit Miss
STIMULUS
False Correct
ABSENT Alarm Rejection
For example if we are at home with our flatmate who likes to walk
around with a sharp needle in his hand and poke you with it when we
will be biased to registering any random firing in our bodies which
feels like a prick as a poke from our flatmate. If however we are
sitting in a psychology exam and our flatmate is on holiday in the
Bahamas then our bias will be to say that any random firing or indeed
prick will not be from a needle, but will be random firing.
Sensitivity of the situation has to do with how one is sensitive to
the situation at hand.
blipps, blobs, and blops
The brain may get confused also.
We can have an example of a student trying to decide whether or not to
study a certain lecture, say "Theory of Signal Detection". To have
either a hit or a miss is O.K. ie to think there will be a question so
to study the lecture & find it is in [the examination], or to decide
to study it and it insn't in. However, it is far better to study the
lecture and not have it come up than to not study it and have the
question come up. We see in this situation a False Alarm is much
better than a miss, so obviously we will be more inclined to say "yes"
(I will study it) than "no" (I won't study it).
--looks like I got a hit!
9. Describe the similarities and differences in colour vision from a
retina containing two cone types versus a retina containing three cone
types. (Attempted by 26 students.)
Helmzt versus Hersel [Hering]
`Normal' individual have 3 varying cone types in their retina for
detecting high, medium & low intensity light.
Young-Heimholtz trichromatic theory [versus] Heron's theory of
opponents.
Two cone system .... requires two eyes
[Dichromats] are just not able to distinguish between 2 different
light intensities.
trichotic [versus] dichotic