Reflexes

This activity allows students to compare human reaction times to sound stimuli depending on whether the eyes are open or closed. It develops the understanding of sensory and motor mechanisms and the notion of measurement precision.

How fast can a human react? The answer depends on many factors: the type of stimulus, whether you are expecting it, and even whether your eyes are open or closed. A typical visual reaction time is about 250 milliseconds, while an auditory reaction time is faster at about 170 milliseconds. This difference arises because sound signals travel a shorter neural pathway to the brain's motor centers than visual signals do. Measuring reaction time precisely is surprisingly challenging because human reflexes are themselves involved in the measurement process: if you use a manual stopwatch, your reaction time in pressing the button adds to the measurement. This experiment elegantly solves this problem by using FizziQ's acoustic stopwatch, which triggers automatically on sound, to measure the time between two hand claps. By comparing this automatic timing with a manual stopwatch measurement, students can directly quantify their own reaction time and investigate how sensory conditions affect it.

Learning objectives:

The student compares a manual stopwatch and a FizziQ acoustic stopwatch to measure the time elapsed between two hand claps. By starting the manual stopwatch at the first clap and stopping it at the second (while the acoustic stopwatch is triggered automatically) the student can evaluate their reaction time and then repeat the experiment with their eyes closed to compare the influence of visual and auditory stimuli on their reflexes.

Level:

Middle school

FizziQ

Author:

Duration (minutes) :

30

What students will do :

- Measure the time between two acoustic events using both a manual stopwatch and an automatic acoustic stopwatch
- Determine personal reaction time by comparing the two measurements
- Investigate how visual conditions (eyes open vs. closed) affect reaction time
- Understand the neural pathway for auditory and visual reflexes
- Develop skills in measurement precision and systematic error analysis

Scientific concepts:

- Reaction time
- Auditory and visual reflexes
- Sensory integration
- Measurement accuracy
- Human nervous system

Sensors:

- Microphone (acoustic trigger / sound stopwatch)
- Manual stopwatch (for comparison)

What is required:

- Two smartphones including at least one with the FizziQ application
- Manual stopwatch on one of the smartphones
- A calm environment
- A partner to perform the snaps
- FizziQ experience notebook

Experimental procedure:

Set up two smartphones: one with FizziQ's acoustic stopwatch (which starts and stops automatically when it detects a loud sound), and one with a manual stopwatch app.
Work with a partner. The partner will make two hand claps, separated by a few seconds.
The student holds the manual stopwatch and positions the FizziQ acoustic stopwatch nearby (within 1 meter of the clapping).
The partner claps once. The student starts the manual stopwatch at the clap. The FizziQ acoustic stopwatch starts automatically.
After 3-5 seconds, the partner claps again. The student stops the manual stopwatch at the second clap. The acoustic stopwatch stops automatically.
Record both times: the manual time and the acoustic time. The difference (manual minus acoustic) is approximately your reaction time.
Repeat this measurement 10 times with eyes open and calculate the average reaction time.
Now repeat 10 times with eyes closed. The student must rely entirely on hearing to react to the claps.
Compare the average reaction times for eyes-open and eyes-closed conditions.
Create a table of all 20 measurements and calculate the mean and standard deviation for each condition.
Discuss: does closing your eyes improve auditory reaction time? What does this tell you about sensory processing?
Investigate the effect of fatigue or distraction: repeat while counting backward from 100, or after physical exercise.

Expected results:

Typical auditory reaction times (from the manual-acoustic difference) range from 150-300 ms, with an average around 200-250 ms for most students. With eyes open, the reaction time is often slightly longer (by 20-50 ms) because the visual system may partially interfere with auditory processing. With eyes closed, auditory attention may be enhanced, reducing the reaction time by 10-30 ms in some individuals. The standard deviation of reaction times is typically 30-80 ms, reflecting natural variability. Fatigue and distraction increase reaction times by 20-50 ms on average. The acoustic stopwatch should be consistent to within ±1 ms (limited by the phone's audio sampling rate), making it far more precise than the manual measurement.

Scientific questions:

- Why is auditory reaction time faster than visual reaction time?
- What are the steps in the neural pathway from hearing a sound to pressing a button?
- Why does the standard deviation of reaction times give useful information about the measurement?
- How do athletes train to minimize their reaction time (e.g., sprinters at the starting blocks)?
- What factors other than the stimulus type can affect reaction time?
- Why is the acoustic stopwatch more precise than a manual stopwatch for this experiment?

Scientific explanations:

Human reaction time is the delay between a stimulus and the onset of a voluntary response. This delay includes several stages: detection of the stimulus by sensory receptors, transmission of the nerve signal to the brain, processing of information, decision-making, and transmission of the motor command to the muscles concerned.

Reaction times vary considerably depending on several factors: the type of stimulus (visual, auditory, tactile), age, fatigue, attention, and even the complexity of the required response. Typically, auditory reflexes (150-180 ms) are faster than visual reflexes (180-200 ms), because the processing of sound signals involves fewer neurological steps than that of visual signals.

The comparison between the manual stopwatch and the FizziQ acoustic stopwatch makes it possible to precisely measure this reaction time. The acoustic stopwatch, triggered automatically by sound, represents "perfect" measurement with no reaction time, while the manual stopwatch includes human processing time.

The difference between the two measurements therefore corresponds to the user's reaction time. By repeating the experiment with eyes closed, we can observe whether the deprivation of visual information modifies performance.

Paradoxically, some people react more quickly with their eyes closed, because the absence of visual distractions allows better concentration on the auditory stimulus. This experiment also illustrates the notion of multimodal processing of sensory information: the brain simultaneously integrates information from different senses to optimize its responses.

In emergency situations, this integration is crucial to minimize reaction time and can make the difference between avoiding or suffering an accident.

Extension activities:

Frequently asked questions:

Q: The manual and acoustic times are sometimes very close, giving a near-zero reaction time. Is this reliable?
R: Occasionally, you may anticipate the second clap and react almost simultaneously. These measurements are biased by anticipation and should be noted as outliers. Use the median of 10 measurements to reduce the effect of outliers.

Q: My reaction time seems very slow (>400 ms). Is this normal?
R: Reaction times vary widely between individuals and depend on attention, fatigue, and practice. Values up to 400 ms are within the normal range, especially for unpracticed subjects. Consistent practice over several trials usually brings the average down.

Q: The acoustic stopwatch sometimes does not trigger on the clap. Why?
R: The sound threshold may be set too high, or the phone may be too far from the clapper. Move the phone closer to the sound source and check the sensitivity settings in FizziQ.

Q: Does it matter which hand I use for the stopwatch?
R: The dominant hand typically has slightly faster motor response (by about 5-10 ms). For consistency, use the same hand for all measurements in a session.