Reaction Time Notes

Motor Control and Reaction Time

Introduction to Reaction Time (RT)

• Reaction time is a readily measurable variable in experimental psychology.

• Historically, RT studies aimed to understand sensory transmission speed and individual differences.

• The 'personal equation' in astronomy spurred the development of experimental psychology.

• Exner (1973) coined 'reaction time' and emphasized the importance of preparatory set.

• RT reflects performance and inner process complexity.

Types of Reaction Time

• Donders (1868) classified RT into Simple (Type A), Choice (Type B), and Recognition (Type C).

• Simple RT is shortest, followed by Recognition, with Choice RT being the longest.

Simple Reaction Time

• Involves one stimulus and one response.

• Mean simple RT for college-age individuals: ~190 ms for light, ~160 ms for sound.

Choice Reaction Time

• Requires a response corresponding to the stimulus.

• Involves signal discrimination and response selection.

• Hick's Law: Response time is proportional to log_2(N), where N is the number of stimuli.

• Hick's Law formula: H = log2(N + 1), RT = a + b log2(N+1).

  • a = irreducible minimum RT.

  • b = slope, varies by task.

Recognition Reaction Time

• Involves responding to some stimuli ('Memory set') and not others ('Distractor set').

• Also known as the 'go, no-go' paradigm.

• Reaction times are longer than simple RT.

• Sternberg (1969): RT increases proportionally to the number of items in the memory set (N).

• Laming (1968): Simple RT ~220 msec, Recognition RT ~384 msec

Reaction Time Components

• RT is not a homogeneous process; it comprises several components:

  • Sensory (receptor) time: 1-2 (to 20-30) msec.

  • Afferent (neural transmission): 8-9 msec.

  • Central (brain processing): 70-90 msec.

  • Efferent (neural transmission): 10-15 msec.

  • Muscle time: 30-40 msec.

Mental Processing Time

• Time to perceive a signal and decide on a response.

• Substages:

  • Sensation: Detect sensory input.

  • Perception/recognition: Recognize meaning.

  • Situational awareness: Recognize scene, meaning, extrapolate.

  • Response selection: Decide and program movement.

Movement (or Muscle) Time

• Time to perform the muscle movement.

• Affected by movement complexity/practice.

• Yerkes-Dodson Law: High arousal speeds gross motor movements but impairs fine movements.

Device Response Time

• Time for mechanical devices to actuate.

Factors Affecting Reaction Time

• Stimulus Type: Sound faster than light (auditory ~140-160 msec, visual ~180-200 msec).

• Stimulus Intensity: Stronger stimuli elicit faster RTs, up to a point.

• Arousal: Intermediate arousal levels yield fastest RTs.

• Age: RT shortens until late 20s, then increases, especially for complex tasks.

• Gender: Males generally have faster RTs than females.

• Handedness & Vision: Task-specific differences exist between hands and central/peripheral vision.

• Practice/Errors: Practice improves consistency; errors lead to slower subsequent RTs.

• Fatigue: Fatigue slows RT, particularly mental fatigue; muscular fatigue has no effect.

• Fasting: Does not decrease reaction time

• Distraction: Increases RT.

• Warnings: Warnings of impending stimuli decrease RT.

• Alcohol Warnings: Warned subjects react faster

• Order of Presentation: Runs of identical stimuli are faster.

• Breathing Cycle: Expiration faster than inspiration.

• Finger Tremors: Downswing tremors faster.

• Personality: Extroverted and anxious types faster.

• Exercise: Exercise can affect reaction time.

• Punishment: Shocking slow reactors decreases RT.

• Stimulant Drugs: Caffeine often decreases RT.

• Intelligence: Slightly faster RTs for more intelligent people, especially on complex tasks.

• Brain Injury: Slows RT.

• Illness: Minor infections slow reaction time

• Expectation: Reaction times are greatly affected by whether the responder is alert to the need to react

Driver Alertness Classes

• Expected: 0.7 seconds

• Unexpected: 1.25 seconds

• Surprise: 1.5 seconds

• Cognitive Load: Consumes the drivers attention, increasing reaction time from 0.3 to 1 second.

• Stimulus-Response Compatibility: Can make accidents common if a driver cannot observe the car's trajectory.

• Psychological Refractory Period: Steering right becomes slower after immediately steering left.

• Nature of the Signal: Braking cues being subtler and more difficult to detect, causing slower braking times.

• Estimating Time-To-Collision (TTC): Tougher to judge than motion that cuts across your path.

• Visibility: Increases in poor visibility

• Response Complexity: More complex muscular responses take longer than those that are not as complex.

• Contrat: People see contrast not light

Alcohol and Reaction Time

• Blood Alcohol Concentration (BAC) affects abilities; higher BAC impairs judgment and motor skills.

• Alcohol is eliminated at a rate of 7-10 g/h.

• The upper limit of BAC for drivers is regulated by almost all countries from Zero (e.g. Hungary) through 0.5 mg/ml (most EU-countries) to 0.8 mg/ml (e.g. UK, USA).

• Kraepelin described a biphasic effect: small doses initially shorten RT, then lengthen it; high doses only lengthen it.

• Straub (1938): 0.35mg/ml BAC increases RT by 10%.

• Executive cognitive functioning (ECF) are impaired during the descending limb of the blood alcohol concentration curve.

Fitts's Law

• Models speed/accuracy tradeoffs in rapid, aimed movement.

• MT = a + b log_2(2A/W + c)

  • MT = movement time.

  • A = movement amplitude.

  • W = target width.

  • ID (Index of Difficulty) = log_2(2A/W + c)

  • IP (Index of Performance) = 1/b

• Big targets at close distance are acquired faster than small targets at long range.