BIO302_Study_Guide_Exam2_2009

BIO302_Study_Guide_Exam2_2009 -...

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Unformatted text preview: STUDY
GUIDE
FOR
NBIO
302
EXAM
2,
2009.
 
 Topics
and
questions
on
Electric
Fish.
This
list
should
not
be
considered
 comprehensive
for
the
material
included
in
Exam
II.
 
 Electrosensory
system
in
e‐fish
and
sensory
systems
in
mammals
(e.g.,
visual
 system)
share
a
number
of
similarities
both
in
functional
organization
and
 behavioral

capabilities.
 
 Electroreceptors
and
their
properties.
 
 




Ampullary
organs
 
 




Tuberous
organs
 
 Electrical
image
 
 Role
of
electric
organ
discharge
(EOD)
and
Sequence
of
pulse
interval
(SPI)
in
 communication.
 
 What
signals
the
presence
of
a
female
to
a
male?
EOD
or
SPI?
 
 Playback
experiment



 
 Mechanisms
of
JAR.
 
 Interaction
of
S1
and
S2
creates
beat
pattern.
What
is
a
beat
pattern?
 
 The
interaction
of
S1
and
S2
should
yield
differential
geometry
(some
areas
more
 contaminated
by
S2
than
others)
for
JAR
to
occur.

 
 Contamination
of
S1
by
S2
must
differ
across
different
body
areas.
 
 Calculations
of
differential
phase
between
body
areas
may
yield
contradictory
 results
for
Df.
 
 Solution
fro
this
problem:
Computations
from
the
body
area
with
the
greatest
 amplitude
“wins”.
 
 This
hypothesis
was
supported
by
the
Titration
Experiment
(see
figure
below):

 
 Figures
A,B,C
below
show
stimulus
conditions
in
two
body
areas
(A,
B)
of
a
e‐fish
 that
encounters
stimulus
S2
from
another
fish.
Contamination
of
S1
(not
shown)
by
 S2
is
different
at
A
and
B.

Amplitude‐phase
plots
shown
in
figure
B
were
computed
 at
each
area
with
reference
to
S1.
Because
the
contamination
is
different
at
areas
A
 and
B,
the
amplitude
modulation
of
each
beat
pattern
at
each
point
differs
 (remember
that
a
different
beat
pattern
forms
at
each
area,
resulting
from
the
 interaction
of
S1
and
S2
at
each
area).
However,
the
sign
of
the
phase
differences
for
 each
beat
pattern
with
respect
to
S1
is
the
same
for
both
areas
A
and
B
(simply
 because
both
phases
are
derived
from
comparing
the
frequencies
(zero
crossings)
of
 S1
and
S2.
Because
the
amplitude
modulation
of
the
beat
patterns
is
different
in
A
 and
B,
the
amount
of
phase
changes
varies
in
A
and
B.
This
results
in
amplitude‐ phase
circles
of
different
diameter
for
areas
A
and
B
(Figure
B).
 
 However,
the
fish
cannot
use
S1.
All
it
can
use
are
the
beat
patterns
present
at
A
and
 B
(different
combinations
of
S1
and
S2,
depending
on
the
degree
of
contamination).
 Therefore
the
fish
will
compare
beat
patterns
at
A
and
B.
Two
comparisons
are
 possible:
A
with
respect
to
B,
and
B
with
respect
to
A
(Figure
C).
The
amplitude
 modulation
will
not
change,
but
because
both
waves
are
not
identical,
there
will
be
 phase
differences
between
A
and
B.
In
the
case
illustrated
in
C,
A
shows
a
delay
 when
amplitude
increases,
etc,
resulting
in
counterclockwise
rotation.
But
if
there
is
 a
delay
when
one
compares
A
with
respect
to
B,
there
must
be
a
phase
advance
(the
 opposite)
when
one
compares
B
with
respect
to
A
(if
A
goes
after
B,
then
B
goes
 before
A).
This
explains
why
the
rotation
reverses
in
the
two
plots
in
C.
This
results
 in
conflicting
Df’s.

The
hypothesis
was
advanced
that
the
area
with
greater
 amplitude
modulation
would
win.
How
to
test
this?

 
 One
possibility
would
be
to
increase
the
amplitude
modulation
in
area
B
in
the
 figure.
But
since
there
is
not
separation
between
A
and
B,
electrical
changes
in
one
 of
the
areas
would
also
modify
the
other
area.
It
was
necessary
to
electrically
 separate
A
from
B.
This
is
represented
in
D
(titration
experiment).

 
 Study
figure
C
and
note
that
separate
stimulators
(SA
and
SB)
are
used
for
 compartments
A
and
B
(head
and
body).
Moreover,
there
is
no
differential
geometry
 in
each
compartment
because
one
of
the
electrodes
(the
+)
is
applied
at
both
sides
of
 the
body
and
head.
Only
differences
between
head
and
body
can
exist.
The
 experiment
requires
that
SA
and
SB
deliver
the
same
sinusoidal
wave
at
both
head
 and
body
(simulating
S2).
BUT
EACH
STIMULATOR
CAN
MODULATE
THIS
BASIC
 WAVE
(ALSO
CALLED
CARRIER)
IN
BOTH
AMPLITUDE
AND
PHASE
SEPARATELY
 IN
EACH
COMPARTMENT.
In
other
words,
the
stimulators
can
deliver
waves
that
 resemble
beat
patterns,
and
these
can
be
different
in
both
amplitude
and
phase
in
 each
compartment.

Because
S1
does
not
reach
the
head
because
of
the
pectoral
seal,
 the
stimulus
at
the
head
is
a
beat
pattern
generated
by
SA.
In
the
body
however,
 where
S1
can
act,
the
wave
generated
by
SB
does
not
have
to
be
a
beat
pattern
 because
a
constant
wave
produced
by
SB
would
generate
a
beat
pattern
interacting
 with
S1
just
as
any
S2
does.

 
 It
is
important
to
note
that
this
experiment
can
also
be
done
in
curarized
fish,
but
in
 this
case,
the
stimuli
delivered
by
both
SA
and
SB
would
be
beat
pattern‐like.
 
 At
this
point,
all
we
need
to
do
is
manipulate
SA
and
SB
(changing
amplitude
and
 phase,
but
not
changing
the
carrier
wave)
to
generate
conditions
shown
in
C.
When
 this
is
done,
we
increase
amplitude
modulation
in
B
(the
smallest
of
the
two),
 WITHOUT
CHANGING
PHASE,
and
see
what
happens:
JAR
responses
vanishes
when
 amplitude
reaches
a
certain
point,
called
the
titration
point:
the
fish
can
no
longer
 discriminate
between
contradicting
signals
because
both
are
equally
strong.
But
if
 amplitude
continues
to
rise,
then
the
JAR
response
reverses.
This
supports
the
idea
 that
the
areas
with
greater
amplitude
modulation
win.
The
titration
point
is
not
 necessarily
reached
when
the
amplitude
modulation
is
the
same
at
both
 compartments.
If
there
are
more
electroreceptors
in
one
of
the
areas,
such
as
the
 head,
the
titration
point
will
be
reached
sooner
in
the
head
because
it
is
more
 sensitive
to
electrical
stimuli.
 
 
 
 
 
 
 
 
 Neural
pathway
for
JAR.
 Electroreceptors,
Elctrosensory
Lateral
Line
Lobe
(ELL),
Torus
semicircularis
(TS),
 nE
(up
and
down
regions),

Prepacemaker
Nucleus
(PPn),
Pacemaker
Nucleus
(Pn),
 electromotor
neurons
in
spinal
cord,
electrocytes
of
electric
organ.
 
 Cells
in
JAR
pathway

 
 ELL:
Spherical
cells
(phase
information),
basilar
pyramidal
(E‐unit)
and
nonbasilar
 pyramidal
(I‐unit)
cells
(amplitude
information).
 
 TS:
Small
cells,
Giant
cells,
Sign
selective
cells
(Df
<0,
Df
>0)
 
 Emergence
of
Phase
Advance
and
Phase
Delay
Small
cells
by
convergent
input
from
 Spherical
cells
and
Giant
cells.
Giant
cells
have
widespread
projections.
 
 Possible
mechanisms
for
differential
phase
sensitivity
for
small
cell
in
TS.
Delay
 lines,
coincidence
detection.
 
 What
are
possible
ways
for
delaying
signals?
What
are
possible
places
for
signal



 delay?
 
 Emergence
of
Sign
selective
cells
by
convergent
input
from
Small
cells
and
from
E‐
 and
I‐units.
There
are
four
types
of
sign‐selective
neurons
in
the
TS.
 
 Sign
selective
cells
in
the
TS
are
sensitive
to
orientation
of
the
jamming
stimulus
 
 Possible
mechanism
for
sensitivity
to
orientation
of
jamming
stimulus
at
the
 level
of
sign
selective
cells
in
the
TS:
orientation
of
long‐range
projections
of
 Giant
cell
making
synaptic
contact
onto
Small
cells
in
the
TS
 
 
 Nucleus
Electrosensorius
(nE).
True
Sign
Sensitive
cells,
i.e,
not
sensitive
to
 orientation
of
jamming
stimulus.
Two
types:
Df
<
0,
Df
>
0.

 Somatotopy
is
lost
by
the
convergence
from
the
Sign
Sensitive
cells
in
the
TS.

 
 
 Depth
perception.
 
 Parameters
that
could
potentially
be
useful
for
depth
perception
by
e‐fish.

 
 Combination
of
parameters
that
have
been
shown
to
provide
unambiguous
cues
for
 depth:
ratio
between
rostral
slope
of
electric
image
and
maximum
amplitude
of
 electric
image.
 
 Observation
that
spheres
yield
slope/amplitude
ratios
that
are
smaller
than
those
of
 other
objects
placed
at
identical
distance.
 
 Electrical
illusion:
The
observation
that
spheres
yield
slope/amplitude
ratios
that
 are
smaller
than
those
of
other
objects
placed
at
identical
distance
led
to
the
 prediction
that
e‐fish
perceive
spheres
to
be
farther
away
than
other
objects
located
 at
the
same
distance.
 
 This
prediction
was
tested
and
confirmed
experimentally.

This
result
provided
 strong
support
for
the
hypothesis
that
depth
perception
depends
on
the
 slope/amplitude
ratio.
 
 Perception
of
object
shape.
 
 It
was
discovered
that
e
fish
might be able to compensate for distance measurement errors, which occur when natural objects resembling spheres are electrolocated. This suggests that they identify the shape of spheres prior to compensating for distance. 
 Review
experiments
described
in
class,
which
provided
evidence
that
G. petersii can determine the shape of an object by using only its electrical sense. These experiments also showed that there is response invariance to changes in size and composition, indicating the shape was the main parameter recognized by the fish. Mechanisms of object recognition during active electrolocation. In order to determine the impedance of an object, the fish has to measure the waveform (capacitance) and the amplitude (resistance) of the locally perceived signal within the electric image. However, the amounts of waveform distortions and the amounts of amplitude changes do not depend on the capacitance of the object alone, but in addition on its size and on its distance from the fish. The fish have to measure at least four parameters of the electric image (peak amplitude, maximal slope, image width, and EOD waveform distortions) to determine an object’s location, its distance, size, and complex impedance. In order to determine the shape of an object, some additional parameters might be necessary, such as dynamic parameters arising from swimming around the object and scanning it from different sides and angles (viewpoint changes). It appears that an accurate distance measurement is a crucial factor for determining all other object parameters. END 
 
 
 
 
 
 
 
 
 
 

 
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