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Reaction Times: Clock the Inner Workings of the Brain

Usain Bolt can blaze through 100 meters in under 9.64 seconds—a remarkable feat. But what is even more remarkable is the speed of reacting to the starting gun. Within 0.15s, his brain can process a sound and begin contracting his leg muscles. In this experiment, we delve into reaction times: the interval between the moment a stimulus (like a sound or light) is detected and the moment your muscles spring into action.

Brain Reaction Time Illustration

What Will You Learn?

  • How to measure and calculate your own reaction times using muscle electrical activity.
  • The difference between simple reaction time, and choice reaction time.
  • How long the nervous system takes to process various stimuli (sight or sound).
  • How to quantify and analyze data for scientific experiments.

Background

Humans have been fascinated by the speed of our bodies’ responses for centuries. French philosopher René Descartes proposed the idea of reflexes as a hydraulic mechanism driven by "animal spirits," a concept later disproven by the discovery of electrical conduction in nerves.

Today, we can measure our reaction times precisely using modern tools like the Human SpikerBox and the Reaction Timer.

Whether you’re leaping off starting blocks or catching a ball mid-air, your quick response is the result of rapid neural processing from your sensory systems to your motor pathways.

Procedure

Equipment Needed:
• Human SpikerBox
• Reaction Timer and orange expansion cable
• USB connection (iOS devices with a lightning connector require This Cable)
• Electrode stickers and cables
• Volunteers (lab partners) to serve as the “Subject” and “Controller”

1. Initial Setup

  1. Plug the Human SpikerBox into your computer or Android device via USB.
  2. Connect the Reaction Timer to the Human SpikerBox using the orange cable.
  3. Place electrode stickers on the forearm for recording, plus one on the back of the hand for ground. Attach red leads to the forearm stickers, black lead to the hand sticker.
  4. Open SpikeRecorder and confirm you can see clear EMG signals when flexing.
  5. Press the first button on the Reaction Timer. Check that a tick mark appears in your recording at stimulus onset.

1. Initial Setup

  1. Plug the Human SpikerBox into your computer or Android device via USB.
  2. Connect the Reaction Timer to the Human SpikerBox using the orange cable.
  3. Place electrode stickers on the forearm for recording, plus one on the back of the hand for ground. Attach red leads to the forearm stickers, black lead to the hand sticker.
  4. Open SpikeRecorder and confirm you can see clear EMG signals when flexing.
  5. Press the first button on the Reaction Timer. Check that a tick mark appears in your recording at stimulus onset.

2. Simple Reaction Time (SRT)

  1. Subject focuses on the Reaction Timer. Turn on Sound only (tone ON, light OFF, random OFF).
  2. Controller presses the left button at random intervals. Subject flexes quickly upon hearing the tone.
  3. Record ~10 trials. End the recording. Repeat with Light only, then with both Sound & Light.
  4. Measure reaction time from the tick mark (stimulus) to the start of muscle activity.

3. Recognition Reaction Time (Go/No Go)

  1. Subject flexes only when the red LED lights up. The green LED is a distraction—no movement required if green lights up.
  2. Observe how decision-making (red vs. green) affects reaction times compared to simple reaction tests.
  3. Record results and compare!

4. Choice Reaction Time

  1. Attach electrodes to both arms. Subject flexes left arm if light is green, right arm if light is red.
  2. Record multiple trials, measure reaction time, and compare to the other tests. Does multi-option decision-making slow down the response?

Results & Analysis

After each experiment, measure your data by selecting the time between the stimulus tick mark and the onset of muscle activity. Compare your average times across all conditions (sound only, light only, sound + light, recognition, choice). Look for trends: which scenario produces the quickest reactions? Which is slowest? Explore different variables—like changing which muscle you measure or adding random delays. Share your data with friends or classmates and see who has the fastest reaction time!

Further Explorations:
• Does using a different muscle (e.g., bicep vs. forearm) change reaction time?
• Are you faster when well-rested vs. tired?
• Does practice reduce your reaction time or help you adapt?

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