How does deciding whether to respond change reaction time? Compare your response to a green light with a task in which you respond to green and stay still for red. Measure the delay from the light to muscle activity, then examine what that comparison can tell you.
Reaction-time experiments use observable responses to investigate mental processing. Here, you compare a simple task with a go/no-go task. Subtracting their average times describes a difference between tasks; treating it as the time for one mental step assumes that other processing stays unchanged.
Be sure to complete the Visual-Motor Reaction Time experiment before attempting this test, as it provides the foundational skills you need and the data required for our calculations!
Connect the Human SpikerBox and Reaction Timer as before. Confirm that both the green and red buttons operate the green and red LEDs.
Attach the electrodes to the subject(s) exactly as in the previous experiment, using the same arm for consistency. Open the SpikeRecorder software and verify that inputs from both stimuli appear on-screen.
You’re ready to test your Choice Reaction Time! The subjects—already familiar with the reaction task—must react only when the green LED lights up. Ignore the red! If the red LED lights, the subject must remain still. (Strictly speaking, this is a go/no-go version of a choice task: you decide whether to move, not which way to move.)
The subject should flex their arm as quickly as possible for the green LED, just as before; that part is identical.
The experimenter will conduct 20–30 trials, 10 of which will use the green LED. Vary the timing and shuffle red LEDs randomly so the subject cannot predict when or which color will appear.
Record all reaction times in the SpikeRecorder App and note any incorrect responses.
Compare your data with classmates to see how adding a decision step affects speed.
Compare reaction times for valid green-light trials with your Visual-Motor results. Keep false starts, misses, and incorrect responses in a separate count, and state which trials you excluded from the timing comparison. Consider practice, anticipation, attention, and response preparation when explaining a difference. These measurements do not isolate the time taken by a single decision.
Add the respond-or-withhold task to your eye-to-muscle pathway drawing. Mark the stimulus and muscle-recording points, then identify which parts of the pathway these measurements cannot time separately.
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
Add the decision step to your eye-to-muscle pathway drawing and estimate how much time it adds.
3 Planning and Carrying Out Investigations
Run 20–30 trials in which only the green light calls for a flex.
4 Analyzing and Interpreting Data
Remove false starts and compare choice with simple reaction times.
5 Using Mathematics and Computational Thinking
Subtract simple from choice reaction time to estimate how long the decision takes.
Cause and Effect
Adding a decision step lengthens 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.
