Reaction Time Notes

Motor Control and Reaction Time

Introduction to Reaction Time (RT)

  • Reaction time (RT) is a commonly used variable in experimental psychology because it is easily measurable.

  • Historically, RT studies began with astronomers investigating personal differences in sensory transmission speed.

  • The personal equation, addressing individual differences in astronomical observations, spurred the development of experimental psychology in the 19th century.

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

  • RT can reflect proficiency or complexity of inner processes.

Types of Reaction Time Experiments

  • Simple Reaction Time (Type A): One stimulus and one response. Examples include reacting to a light or sound.

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

  • Choice Reaction Time (Type B): Multiple possible signals, each requiring a different response. Requires signal discrimination and response selection.

    • Hick's Law: RT is proportional to log2(N)log_2(N), where N is the number of possible stimuli.

    • Formula: RT=a+blog⁡2(N+1)RT = a + b \log_2(N+1), where a and b are constants.

    • 'a' is the irreducible minimum RT, and 'b' determines the slope.

  • Recognition Reaction Time (Type C): Multiple stimuli, but only one correct response (go, no-go paradigm). Slower than simple RT.

    • Sternberg (1969): RT increases proportionally with the number of items in the memory set (proportional to N, not log N).

    • Laming (1968): Simple RT averaged 220 ms, recognition RT averaged 384 ms.

Reaction Time Components

  • RT is not a homogeneous process; it can be broken down into components:

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

    • Afferent (neural transmission from receptor to brain): 8-9 ms.

    • Central (brain processing time): 70-90 ms.

    • Efferent (neural transmission from brain to muscles): 10-15 ms.

    • Muscle time: 30-40 ms.

Mental Processing Time Sub-Stages

  • Sensation: detecting sensory input.

    • RT decreases with greater signal intensity, foveal viewing, and better visibility conditions.

  • Perception/Recognition: recognizing the meaning of the sensation by applying information from memory.

    • Novel input, low signal probability, uncertainty and surprise slows the response.

  • Situational Awareness: Recognizing the meaning and possibility extrapolate into the future.

  • Response Selection and Programming: Deciding on a response and mentally programming the movement.

    • Practice decreases required time.

  • Movement (or Muscle) Time: Time to perform the muscle movement.

    • More complex movements take longer; practice reduces movement times.

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

  • Device Response Time: Time for mechanical devices to actuate.

Factors Affecting Reaction Time

  • Type of Stimulus: Reaction to sound is generally faster than reaction to light.

    • Auditory RT: 140-160 ms; Visual RT: 180-200 ms; Touch: 155 ms; Pain (with touch): 268 ms; Pain (without touch): 889 ms.

  • Stimulus Intensity: Stronger stimuli lead to faster RT, up to a certain point.

  • Arousal: Intermediate arousal levels result in the fastest RT.

  • Age: RT shortens from infancy to late 20s, then increases with age, especially for complex tasks.

  • Gender: Males generally have faster RTs than females.

  • Handedness: The preferred hand is generally faster. Hemispheric specialization may give left-handed people an advantage in spatial tasks.

  • Vision: Direct vision (cones) results in faster RT than peripheral vision (rods).

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

  • Fatigue: Fatigue slows RT, especially mental fatigue and sleepiness.

  • Fasting: Does not decrease reaction time, although it does impair capacity to do work.

  • Distraction: Increases reaction time.

  • Warnings: RT is faster when subjects are warned of an impending stimulus.

  • Alcohol: The effect of alcohol is biphasic where small doses initially shorten RT, but then lengthen it and high doses only lengthen RT.

  • Urgency: People brake faster when there is great urgency, when the time to collision is briefer.

  • Cognitive Load: When other driving or nondriving matters consume the driver’s attention, then brake time becomes longer. For example, on a winding road, the driver must attend more to steering the car through the turns.

Alcohol and Reaction Time

  • Blood Alcohol Concentration (BAC) affects abilities.

  • BAC is measured as weight of alcohol per volume of blood (e.g., grams per liter).

  • Factors affecting BAC: amount of alcohol consumed, eating while drinking, body fat percentage.

  • Alcohol is eliminated by the liver at 7-10 g/h.

  • Alcohol impairs executive cognitive functioning (ECF).

  • Fitts’ Law: MT=a+blog⁡2(2A/W+c)MT = a + b \log_2(2A/W + c)

    • MT = movement time

    • A = distance to target center

    • W = width of the target

    • a and b = empirically determined constants

    • c = constant (0, 0.5, or 1)

  • The term log2(2A/W+c)log_2(2A/W + c) is called the index of difficulty (ID). The ID increases by one unit for each doubling of amplitude and halving of width.

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