I seem to have found an answer to the amount of time required for a
startle response which is the final piece of the calculation I am using to
determine from the jiggles when each shot was fired. Luis Alvarez proposed
over 50 years ago that a cameraman will be unable to hold the camera
steady when startled by a noise as loud as a rifle shot. CBS tested this
during their 1967 documentary on the WCR and found that to be true. Since
the distance from Zapruder to the rifle was constant, about 270 feet
according to an HSCA document, the time required for the sound to reach
his ears would be the same for all three shots. It seems likely his
reaction time would be about the same for all three so we should expect
the same time lag between shot and jiggle for all three shots. Once that
figure is calculated, we can work backwards from the observed jiggles to
determine when the shots were fired.
I had read several years ago that a startle response requires about 200
milliseconds. It
appears that is an oversimplification. This is what I have discovered:
"There are many various reflexes that can occur simultaneously during a
startle response. The fastest reflex recorded in humans happens within the
masseter muscle or jaw muscle. The reflex was measured by electromyography
which records the electrical activity during movement of the muscles. This
also showed the latency response or the delay between the stimulus and the
response recorded was found to be about 14 milliseconds. The blink of the
eye which is the reflex of the orbicularis oculi muscle was found to have
a latency of about 20 to 40 milliseconds. Out of larger body parts, the
head is quickest in a movement latency in a range from 60 to 120
milliseconds. The neck then moves almost simultaneously with a latency of
75 to 121 milliseconds. Next, the shoulder jerks at 100 to 121
milliseconds along with the arms at 125 to 195 milliseconds. Lastly the
legs responds with a latency of 145 to 395 milliseconds. This type of
cascading response correlates to how the synapses travel from the brain
and down the spinal cord to activate each motor neuron."
From this layman's reading, it seems like the response time is different for different parts
of the body. That makes sense since the sound impulse must travel to the brain which will
then send the signal to the muscles throughout the bod. The response time for the arms is
in the range of 125 to 195 milliseconds. I am going to take an educated guess that the
longer time is for the extremities, i.e. than hands. Since the camera was in Zapruder's hands,
the higher figure seems the most pertinent one but if the upper arm began to move before the
hands, that could shorten the time for the jiggle to occur slightly. I am going to arbitrarily use
190 milliseconds as the lag time between the sound reaching Zapruder and the jiggle to begin.
That I believe is sufficiently close for this exercise.
I also learned in researching this that the speed of sound will vary slightly due to temperature.
I am using a speed of 1120 fps which is also close enough for this exercise. It would have
required .241 seconds for the sound of the muzzle blast to reach Zapruders ears. add to that
.190 (190 milliseconds) for his startle response gives a total lag time of .431 seconds from
muzzle blast to jiggle. At 18.3 frames per second, that indicates 7.89 frames would elapse
from the time the shot was fired until we observe a camera jiggle. Not quite 8 full frames but
very close.
Keep in mind that a jiggle could begin early during a frames exposure, late in the exposure, or
in the gap between exposures so we cannot pinpoint the shot any closer than that. Following
the two shots that struck JFK, we see camera jiggles at frames 227 and 318. Working back
7.89 seconds means it is likely those shots were fired at frames 219 and 310 or in the gap
just preceding them. This is about a frame earlier than my previous calculations. The hard
part is deciding when the missed shot was fired because we have no definitive evidence of
that, only clues. All jiggles are not associated with gunshots so finding those jiggles doesn't
tell us with certainty which one is due to a gunshot. We have to use other clues to make that
judgement. I believe the jiggle at 158 is due to the first shot that missed. This syncs up the
best with Connally's 164 head snap and Rosemary Willis slowing to a stop and turning back
toward the TSBD. I am aware others have differing opinions about when that shot was fired.
For the two shots that struck, we can calculate which frame they struck at by starting from
when the calculation indicates those shots were fired, estimating the average velocity of the
bullet and determining JFK's distance from the rifle at the moment those shots were fired.
The limo would move a negligible distance while the bullet is in the air but that would be
unlikely to change which frame the bullet struck at. At 11mph, the limo would be moving
about .88 feet per frame. JFK was estimated to be 190.8 feet from the rifle at frame 225
but I'm estimating about 187 feet at the time the bullet struck a few frames earlier. A
bullet traveling at an average velocity of 2000 fps would cover that distance in .0935
seconds or 1.71 frames. If the shot were fired at 219, it likely would have struck at frame
221. This is a frame earlier than my previous calculations. JFK's and JBC's simultaneous
reaction at frame 226 would seem to fit with that calculation. For the head shot, the
distance to the rifle was 288 feet. That would require .144 seconds or 2.64 frames for
the bullet to reach JFK. If fired at 310 it would strike either late in the exposure of 312
or in the 312-313 gap. I think the latter is more likely since we see no visible evidence of
a strike in frame 312.
I seem to have developed an obsessive compulsion to determine as precisely as possible
when the various shots were fired and when they likely struck. Precision is limited by the
fact we have to estimate things like bullet velocity, the relatively slow speed of the camera,
and the fact that we don't know when during the cycle of each frame each event occurred.
I think the above calculations give us an answer accurate to within a frame. If anyone can
see any errors I made in my calculations or factors I omitted, I welcome your comments.
Or you can tell me I'm full of shit. You won't hurt my feelings.