Elsie Dorman got habituated

[Tom Graves]

Background:

Elsie Dorman, filming the motorcade from a fourth-floor window with a camera that she had to hold a button down while filming, was only about 35 feet from Oswald's Carcano when it fired three shots about five seconds apart from the 6th floor Sniper's Nest, creating 135 dB muzzle blasts each time. When we synchronize her clip with the Zapruder film, we see that she was so startled by the sounds of the first and second shots, at "Z-124" and at Z-222, respectively, that she inadvertently removed her finger from the button both times, thereby creating two 3-second gaps in her clip. Interestingly, she was able to continue holding the button down after the third shot at Z-313.

ME: What is the probability that someone who is subjected to the 135 dB-sounds of three unexpected gunshots fired about five seconds apart would have a significantly smaller startle response to the third shot than to the first and second shots?

GROK: Very high—likely 70-90% or more for most people, depending on exact measurement and individual factors.

135 dB is well within (or above) the intensity range that reliably elicits a strong acoustic startle reflex in humans. Typical lab startle probes use 95–120 dB white noise bursts or tones (often 40–50 ms duration), and impulsive sounds like simulated gunshots at 135 dB would produce a clear, involuntary startle response (eye-blink, muscle contraction, etc.) in nearly everyone with normal hearing.

Habituation with repeated stimuli

The acoustic startle reflex shows rapid short-term habituation when the same (or highly similar) stimulus is repeated at intervals of a few seconds. This is a basic form of non-associative learning: the brain quickly recognizes the stimulus as non-threatening and reduces the reflexive response.

• With stimuli spaced ~5 seconds apart (as in your scenario), the response to the second shot is typically already noticeably smaller than the first.

• By the third shot, the reduction is often substantial—frequently described as “significantly smaller” or even approaching minimal levels in many studies and demonstrations. One clear summary: “The second time they hear the noise, they’ll startle significantly less; by the third time, they’ll barely startle at all.”

This pattern holds across humans and animals for loud acoustic stimuli. Habituation occurs within a session (short-term) and is driven by brainstem circuits, though modulated by higher factors like attention or context.

Factors that influence the chance

• Most people (majority): Expect a clear, measurable drop in startle magnitude (e.g., via EMG eye-blink response, whole-body movement, or self-report of flinch intensity) by the third shot.

• Variability: A minority may show slower habituation due to factors like high anxiety, certain disorders (e.g., PTSD can sometimes blunt habituation), fatigue, or individual differences in sensory processing. Unexpected real gunshots might add some sensitization (initial increase) in a few cases, but habituation still usually dominates quickly at short intervals.

• Measurement matters: “Significantly smaller” is robust in controlled EMG or accelerometer studies. In real life, it would feel noticeably less jarring.
In summary, for three unexpected 135 dB gunshot-like sounds ~5 seconds apart, the large majority of people would show a significantly diminished startle to the third one compared to the first. This is one of the most reliable and well-documented features of the startle reflex.


Click on "Carcano Sound Intensity and Startle" and scroll down to watch the videos showing the Dorman, Zapruder, and Secret Service films which have been synchronized and dubbed with gunshot sounds at different points.

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[Robin Unger]