A penalty kick is coming. You don’t have time to think—just to react. The ball moves, and in an instant, your brain processes the direction, sends signals to your muscles, and you dive. But what happens in those milliseconds before you move?
Reacting to a shot fired straight at you is one thing (block). But when the ball could go either way, your brain must do more than react—it must decide. How does having to choose between actions affect your reaction time?
This experiment shifts the focus from a simple go-no-go reaction to making a subtle motor decision. With electrodes now on both arms, a familiar green LED still signals the known response, but a red LED introduces a new challenge: use your opposite arm. This change adds an extra layer of complexity to your reaction-time measurement.
After completing the Visual-Motor Reaction Time experiment, prepare for this new challenge. Connect the Human SpikerBox and Reaction Timer as before, and attach electrodes to both arms. Ensure both the green and red LED systems are functioning properly.
This is a single-participant experiment. The green LED signals you to use the arm you’re familiar with, while the red LED instructs you to switch and move your other arm. Open the SpikeRecorder software and verify that both channels are active before beginning your randomized series of 10 trials.
It’s time to test your Motor Decision Reaction Time! With electrodes on both arms, you’re challenged to quickly choose which action to execute. When the green LED signals, use the familiar arm. When the red LED flashes, switch it up with your other arm. Each trial will reveal how well you adapt to this unexpected twist.
Examine your reaction times for both green- and red-LED trials. Did choosing which arm to move affect your speed? Compare the “green-light” results with your earlier Visual-Motor experiment and your Choice Reaction Time experiment to uncover insights into how adding a split-second motor decision impacts performance.
Draw both pathways, from your eyes to your left and right forearm muscles. Mark where your brain chooses which arm to move and where each EMG channel recorded.
The sensing–processing–responding loop, timed end to end.
MS-LS1-8 Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories.
HS-LS1-2 Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
2 Developing and Using Models
Draw both pathways, eye to left arm and eye to right arm, and mark where the choice is made.
3 Planning and Carrying Out Investigations
Record both arms while a green or red light picks which arm to move.
4 Analyzing and Interpreting Data
Compare green- and red-light reaction times with your earlier results.
Cause and Effect
Choosing which arm to move changes reaction time.
Systems and System Models
Timing the full loop.
LS1.D Information Processing
Receptor → brain → muscle information flow.
LS1.A Structure and Function
System organization.
Performance expectations, crosscutting concepts and core ideas from Hands-On Neuroscience Curriculum Overview, Unit 2, module 2.3, whose core lab this is. The practices are the ones this page asks students to do.
Can you measure the speed of cognitive processes with just your muscles? We will find out! In this experiment, we will measure how long it takes you to make a decision!
How fast can you react? Here we explore visual reaction time—the interval between seeing a stimulus and responding with movement.
