Understanding Reaction Time and Information Processing

Posted on Dec 9, 2025 in Physical Activity and Sports Sciences

Information Processing & Reaction Time Revision Sheet

1. Core Concept
The human brain processes information like a computer, in a series of stages from receiving a stimulus to producing a response. The speed of this processing can be measured by Reaction Time (RT).

2. The Information-Processing Model
A three-stage model explaining how sensory input is transformed into motor output.

• Input: Information from the environment received via the senses.

• Stimulus Identification Stage: Deciding if a stimulus is present and what it is.

• Response Selection Stage: Deciding what response to make.

• Movement Programming Stage: Preparing the motor systems to execute the chosen response.

• Output: The observable movement or action.

3. Key Researcher & Method

• Franciscus Donders (1818-1898): Used Mental Chronometry to measure the duration of mental processes.

  • Subtraction Method: By comparing RTs from different tasks, the time for specific stages can be estimated.

    • Stimulus Identification Time ≈ Go/No-Go RT – Simple RT

    • Response Selection Time ≈ Choice RT – Go/No-Go RT

4. Types of Reaction Time (RT)
RT is the period from the presentation of a stimulus to the start of the movement response.

5. Limitations of Donders’ Method

• Assumes strictly serial processing (stages happen one after another), not parallel.

• Assumes adding a stage doesn’t change the duration of previous stages.

• Neglects the effects of practice; experts can restructure or automate stages, making them faster.

6. Applications & Examples

• Sport: A goalkeeper facing a penalty kick is in a high-choice RT situation, slowed by the need to identify the ball’s direction and select a dive.

• Skill Training: Practicing a “Go/No-Go” drill in baseball batting improves a batter’s ability to quickly identify and react to pitch types.

• User Interface (UI) Design: Simplifying choices and making buttons distinct reduces users’ response selection time.

7. Summary Table

Factors Affecting Reaction Time (RT) Revision Sheet

1. Core Concept
Reaction Time (RT) is not fixed; it is systematically influenced by factors like the number of choices, how naturally a stimulus links to a response, and our level of anticipation. Understanding these factors allows us to predict and optimize human performance.

2. Key Principles & Laws

• Hick’s Law: RT increases linearly as the logarithm of the number of Stimulus-Response (S-R) alternatives increases.

  • Formula: RT = a + b·log₂(N)

  • a = Baseline RT (intercept)

  • b = Slope (rate of increase per bit of information)

  • N = Number of S-R alternatives

  • Interpretation: Each doubling of choices adds a constant amount of decision time.

• Stimulus-Response (S-R) Compatibility: How “naturally” a stimulus maps to a response.

  • High Compatibility: Natural mapping = Faster RT & fewer errors (e.g., left light → left key).

  • Low Compatibility: Unnatural mapping = Slower RT & more errors (e.g., left light → right key).

  • Incompatibility Cost: The additional time (often 30-100 ms) added due to an unnatural mapping.

3. Types of S-R Compatibility

4. Other Critical Factors

• Practice & Remapping:

  • Practice reduces RT for a specific mapping, making it more automatic.

  • Remapping Cost: Switching between different S-R mappings causes a temporary increase in RT and errors, even for well-practiced tasks.

• Expectancy & Foreperiod:

  • Expectancy: Being prepared for a specific stimulus speeds RT.

  • Foreperiod: The time interval between a warning signal and the stimulus.

    • A predictable foreperiod leads to faster RT.

    • A variable foreperiod leads to slower RT due to uncertainty.

• Modality & Intensity:

  • Modality: The sensory channel of the stimulus (e.g., auditory, visual, tactile). Auditory RT is typically faster than visual RT.

  • Intensity: A stronger or more intense stimulus (e.g., brighter light, louder sound) leads to a faster RT.

5. Components of Reaction Time (Lab Context)
RT can be broken down into physiological components measured in a lab:

• Foreperiod: The variable time between “Set” and the start signal.

• Premotor Time: Time from stimulus to the onset of muscle electrical activity (EMG). Reflects central brain processes.

• Motor Time: Time from muscle activation (EMG) to the actual onset of movement. Reflects neuromuscular execution.

• Response Time = Premotor Time + Motor Time

6. Applications & Examples

• Sport: A football goalkeeper facing a penalty (high N per Hick’s Law) must anticipate, as waiting to see the ball’s trajectory results in a RT that is too slow to make a save.

• Interface Design: Cockpit controls and computer interfaces use high S-R compatibility (e.g., moving a control stick right to move the aircraft right) to minimize errors and RT under pressure.

• Training: Practicing under variable conditions (e.g., different foreperiods, S-R mappings) helps athletes cope with unpredictability and reduces the cost of remapping.

7. Summary Table

Stimulus-Response Compatibility & Anticipation Revision Sheet

1. Core Concept
The speed of our reactions is heavily influenced by how naturally a stimulus links to its response (“compatibility”) and our ability to predict future events (“anticipation”). While beneficial, anticipation is a double-edged sword that can be exploited by deception.

2. Key Principles & Effects

• Stimulus-Response (S-R) Compatibility: The “naturalness” of the link between a stimulus and its response.

  • High Compatibility: Intuitive mapping = Faster Reaction Time (RT) & fewer errors.

  • Low Compatibility: Unintuitive mapping = Slower RT & more errors.

  • Incompatibility Cost (ΔRT): The additional time (often 30–100 ms) added by an unnatural mapping. This affects the Response Selection stage.

• The Simon Effect: A specific type of interference where an irrelevant stimulus location (e.g., a left-pointing arrow appearing on the right side) affects RT, even when location is not part of the task instruction. Responses are faster when the stimulus location and response location correspond, even if the mapping is technically incompatible.

• Psychological Refractory Period (PRP): A bottleneck in central processing that causes a delay in responding to a second stimulus when it appears very soon (~100-500 ms) after a first. Deception in sport exploits this.

3. Types of S-R Compatibility

4. Anticipation: Benefits vs. Costs

• Correct Anticipation:

  • Benefit: Can reduce effective RT to near zero, providing a significant performance advantage (e.g., a sprinter anticipating the gun).

• Incorrect Anticipation:

  • Cost: The performer must inhibit the pre-planned response and then go through the full response selection process again. This often results in a response that is slower than if no anticipation had occurred.

5. Deception & The PRP Bottleneck
Deception works by exploiting the central processing bottleneck:

1. Fake (Stimulus 1): The deceiver presents a false cue (e.g., a dummy pass).

2. Short SOA: The real action (Stimulus 2) follows very shortly after (~100-200 ms).

3. Bottleneck: The opponent’s brain is still processing the fake, causing a delay (PRP) in processing the real action.

4. Delayed Reaction (RT2): The opponent’s reaction to the real move is significantly slowed, creating an advantage for the deceiver.

6. Applications & Examples

• Sport – Deception: A rugby player using a dummy pass or a footballer using a step-over to delay the defender’s reaction via the PRP effect.

• Design: Placing a “stop” button at the bottom of a touchscreen interface aligns with the population stereotype that “down” means “stop” or “less,” improving compatibility.

• Coaching & Training:

  • Teach Attention: Train athletes on which specific cues to focus on.

  • Randomise Practice: Use variable timing and options in drills to reduce an opponent’s ability to anticipate.

  • Drill Inhibition: Practice “late commitment” to prevent athletes from falling for fakes.

7. Summary Table