Lecture 3 Notes: Action Preparation
Action Preparation
Performing voluntary, coordinated movement requires preparation of the motor control system; action preparation is influenced by multiple interacting factors related to task, performer, and environment.
Key idea: preparation helps determine the optimum motor response and reduces costly mistakes (e.g., an offensive player making a pass that is intercepted).
Important concept: processing information to determine the best future action is central to motor control.
Overview: Interaction of task, person and environment
Action preparation emerges from the interaction of task demands, the individual, and the environment.
Some responses require time to prepare before execution.
A standard way to study action preparation is by measuring Reaction Time (RT).
Practical implication: in sport, faster RT can confer advantages over slower RT.
Stages of information processing (Behavioural perspective)
INPUT: information selected from the environment that is
(a) Related to the nature of the task (e.g., visual info to judge distance when throwing, auditory cues for music timing in dance)
(b) Perceived as important by skilled performers who implicitly know what to attend to before moving
HUMAN: internal processing to convert input into action
OUTPUT: motor response generated and executed
STAGES OF PROCESSING (conceptual model):
Stimulus identification (perception)
Response selection (decision)
Response programming (action)
This leads to movement execution and eventual feedback for future corrections.
Reaction Time (RT): core idea
Definition: the interval between the presentation of a stimulus and the onset of the motor response.
Formal expression: ext{RT} = t{ ext{response}} - t{ ext{stimulus}}.
RT as an index of preparation required to produce an action; reflects information processing speed (decision-making).
RT is important in sport and daily activities for predicting performance and timing.
Types of Reaction Time
Simple RT (SRT): one stimulus, one response
Laboratory example: press a button when a single green light comes on.
Sport example: starting signal in a sprint.
Choice RT (CRT): more than one stimulus, each with its own response
Laboratory example: press one button for green, a different button for blue.
Sport example: responding to a bowler delivering different types of deliveries.
Discrimination RT (DRT): multiple stimuli but only one response to a specific stimulus; other stimuli require no response
Laboratory example: press a button for green light, ignore other lights.
Sport example: athlete decides to react only to a specific cue among several.
Conceptual takeaway: RT increases with task complexity (more possible responses or more decision options).
Stimulus types and cueing
Cues can be visual or auditory; the number of cues affects processing, requiring filtering of irrelevant cues to identify the appropriate stimulus.
Examples of cue relevance: skilled athletes know what to attend to (task-relevant cues) before moving.
Foreperiod: the interval between a warning signal and the stimulus; consistency of foreperiod speeds RT; too long or too short delays can increase RT.
Type of stimuli and their typical RTs
Auditory stimulus RT: roughly ext{RT}_{ ext{auditory}} \approx 140 ext{--}160 ext{ ms}
Visual stimulus RT: roughly ext{RT}_{ ext{visual}} \approx 180 ext{--}200 ext{ ms}
Tactile (touch) RT: roughly ext{RT}_{ ext{tactile}} \approx 155 ext{ ms}
Reasons: auditory signals reach the brain faster (ear-to-brain ~8–10 ms) than visual signals (eye-to-brain ~20–40 ms).
Discrepancies persist across simple vs complex responses.
Three main RT types (summary table)
Simple RT (SRT): one stimulus → one response.
Choice RT (CRT): multiple stimuli → specific responses for each.
Discrimination RT (DRT): multiple stimuli, but only one response to a specific stimulus (others ignored).
Real-world implication: different tasks recruit different processing loads and response strategies.
RT measurement and the components of response time
Response Time = RT + MT, where MT is Movement Time.
ext{Response Time} = ext{RT} + ext{MT}.
RT reflects pre-movement processing (premotor), while MT reflects execution after motor planning.
Electromechanical delay: the interval from EMG onset to observable movement.
Fractionated RT: premotor (cognitive/perceptual) processing vs motor execution can be distinguished via EMG timing.
How action preparation unfolds during RT
Postural preparation: anticipatory postural adjustments to stabilize before movement.
Sequences of movements: as movement complexity increases, RT tends to increase; complex actions can be pre-programmed as sequences.
Rhythmic preparation: pre-performance routines help stabilize motor control and promote rhythmic engagement; higher correspondence between ritual behaviors and performance success.
Relative time allocation in ritual behaviors correlates positively with successful performance (r ≈ 0.77).
Factors influencing RT
Task/situation characteristics
1) Number of stimulus–response (S–R) alternatives (Hick’s Law)
2) Predictability of response
3) Probability of precue correctness
4) Timing between stimuli for different responses
5) Stimulus–response compatibility
6) Foreperiod delay & consistency
7) Movement complexity/accuracyHicks’ Law: RT increases with more information to process; each additional S–R pair adds processing load.
Basic idea: with 1 S–R pair, RT is simpler; with 2+ S–R pairs, RT increases due to choice.
Practical form (commonly cited): ext{RT} = a + b \, ext{log}_2(n) where n is the number of S–R alternatives.
Illustrative examples: S-R tests and sport scenarios
Simple RT: respond to a single signal (e.g., fire at the starting light).
CRT (2+ options): choose the correct response to each of several signals (e.g., different ball trajectories requiring different catches).
DRT: respond to one cue while ignoring others (e.g., respond to a specific color light among distractors).
In sport, reaction time can reflect decisions under time pressure (e.g., starting a sprint, reacting to a bowler’s delivery).
Anticipation and precues
Anticipation advantages: faster RT if the stimulus is expected and correctly identified in advance; enables earlier processing for response selection and programming.
Risks: incorrect anticipation leads to wrong responses and large performance delays.
Precueing: advancing information about a forthcoming cue enhances RT when precue correctness probability is high.
Example: precue correctness probability = 80% for left vs 20% for right (vs a 50%/50% split).
End-of-play precue validity varies in-game depending on how consistent the cues are; sometimes effective, sometimes not.
Psychological refractory period (PRP)
PRP describes the delay in RT to a second stimulus following an initial stimulus; when a fake or fake move is used, the second RT is delayed due to processing bottlenecks.
Example: faking to left in a sport can lead to a delayed RT to the actual move on the right, as the defender processes the first cue.
Stimulus–Response compatibility
The degree of spatial congruence between the stimulus and the response affects RT.
More compatible mappings (e.g., lights and corresponding buttons on the same side) lead to faster RT.
Incompatible mappings slow RT because of misalignment between stimulus location and response execution.
Practical implication: align cues with natural body responses to enhance speed.
Stroop effect
Demonstrates the difference between automatic processing and controlled processing.
Task: say the ink color of a word that spells another color (e.g., the word RED printed in blue ink), which requires inhibiting the automatic reading response.
Illustrates the conflict between stimulus-driven and task-driven responses and how automatic processing can interfere with conscious control.
Foreperiod and warning/precue effects
Foreperiod is the interval between warning signal and stimulus.
More consistently timed foreperiods lead to faster RT.
RT tends to increase with longer foreperiods or if the foreperiod is too short or too long.
Practical takeaway: consistent foreperiods and well-timed cues improve response speed.
Movement complexity and accuracy effects
RT increases with greater movement complexity (e.g., using more digits, fine motor tasks vs gross movements).
RT also increases with higher accuracy demands (difficulties that require precise control).
Related concept: Fitts’ Law (not given as a formula in the transcript) links movement time to task difficulty and target size/distance; larger accuracy demands lead to longer preparation.
Action preparation in practice: coaching implications
To increase action preparation load: introduce more movement alternatives or increase unpredictability of the correct response.
Use incorrect pre-cues to challenge processing and adaptability.
Increase spatial incompatibility between cue and required movement to study how athletes adapt.
Increase foreperiod irregularity to require greater concentration.
Use tasks with little prior practice to examine planning under unfamiliar conditions.
Performer characteristics influencing RT
Age
Simple RT improves from infancy into the late 20s, then declines slowly into the 50s/60s, with faster deterioration in older ages.
Complex tasks show larger age effects; e.g., braking tasks in driving fall-prevention contexts benefit from RT training and physical/mental activity.
Practical focus: practice and lifestyle factors strongly influence RT in aging populations.
Key takeaway: age-related RT changes are modulated by training and activity.
Gender differences
Generally, males exhibit faster RT than females; practice has minimal impact on the female disadvantage (discrepancy small, ~0.02–0.20 ms).
Some studies suggest age-related deterioration in RT proceeds similarly in men and women.
Vigilance (alertness)
Warning signals used for speeded RT tasks (e.g., sprint starts) require optimal pre-movement alertness.
Maintaining alertness over long periods (e.g., fielding for hours) can degrade RT; sleep loss exacerbates this effect.
Sleep deprivation slows RT and increases missed stimuli; compensatory mental effort may increase with restricted sleep.
Sleep and alertness implications
Sleep deprivation effects on RT: slower RT, higher misses over time; recovery requires sleep.
Attentional focus
Directing attention to the start signal (sensory set) yields faster RT than focusing on the movement (motor set).
Attention and action preparation: practical implications
Where to direct attention can influence RT; sensory-set focus tends to yield faster responses than motor-set focus.
Training recommendations:
Practice to reduce RT through repetition and skill automation.
Improve stimulus–response compatibility by aligning cues with natural responses.
Use precues and predictable foreperiods to shorten RT where appropriate.
Manage cognitive load to prevent excessive processing time during decision-making.
What occurs during action preparation? (Key motor control events)
Postural preparation: prepare postural muscles prior to movement to maintain balance and stability; involves anticipatory postural adjustments.
Sequences of movements: break complex actions into components or chunks; practice sequences to speed up initiation.
Rhythmic preparation: pre-performance routines stabilize the motor system and promote rhythmic movement; strong correlation with successful performance.
EMG and RT relationship: RT can be fractionated into premotor (cognitive/perceptual) and motor (execution) components.
Premotor component shows no EMG activity change prior to perception; motor component shows EMG activity increase before movement begins.
Electromechanical delay exists between EMG onset and observable movement.
Key motor control events during action preparation (EMG perspective)
Postural preparation involves anterior deltoid and postural muscles activation in coordinated timing.
Sequences and rhythm preparation support faster and more reliable movement initiation.
EMG recording and RT can reveal distinct onset times for different muscle groups, illustrating the temporal structure of motor preparation.
Summary concepts and practical takeaways
Action preparation integrates task demands, individual capabilities, and environmental factors.
RT is a robust, practical measure of processing speed and preparation in both daily and athletic contexts.
Anticipation and precuing can improve RT but carry risks if incorrect.
Stimulus–response compatibility and foreperiod consistency are critical levers for optimizing RT in training and performance.
Age, vigilance, sleep, and attentional focus modulate RT; targeted training can mitigate some age- or fatigue-related RT declines.
Action preparation encompasses postural adjustments, sequencing, and rhythmic strategies; EMG-based analyses help parse the cognitive and motor components of RT.
Review questions (from transcript)
What are the different types of RT?
What are task factors that influence RT?
What are the performer factors that affect RT?
What occurs during action preparation?
Key references and numerical points mentioned
RT definition and calculation: ext{RT} = t{ ext{response}} - t{ ext{stimulus}}.
Response Time: ext{Response Time} = ext{RT} + ext{MT}.
Typical RTs by modality: ext{RT}{ ext{auditory}} \approx 140 ext{--}160 ext{ ms}, \, ext{RT}{ ext{visual}} \approx 180 ext{--}200 ext{ ms}, \, ext{RT}_{ ext{tactile}} \approx 155 ext{ ms}.
Hicks’ Law concept: RT increases with number of S–R alternatives; commonly summarized as ext{RT} = a + b \, ext{log}_2(n).
Foreperiod optimal range: approximately 1 \text{ s} \le T_{ ext{foreperiod}} \le 4 \text{ s}.
Correlation in ritual behaviors and performance: r ≈ 0.77.
Sleep deprivation effects: RT slows and misses stimuli after ~2 hours of testing; similar effects after ~2 days of restricted sleep; compensation via increased mental effort observed.
Attention focus finding: sensory-set focus yields faster RT than motor-set focus.
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