KINE 3020 Readings 16-25

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York University
Kinesiology & Health Science
KINE 3020
Merv Mosher

Reading 16 Time to Contact Information • Our ability to alter the position of our body at a given point in space and to intercept a moving object ◦ Depends on our ability to process a number of movement variables during the early stages of execution • This early processing of visual information involves taking discrete retinal “snapshots” of the visual array that form the basis for predicting when the body or an object will arrive at a certain location • How accurately the performer is able to predict where an object or the body will be at a given time ◦ Determined by his or her existing knowledge of the Movement situation and by the Speed with which an appropriateAction plan can be retrieved from memory and then executed • Advocates of Direct Perception theories offer an alternative interpretation • They argue that Time- to- Contact information can be collected directly from the changing Optic array ◦ Eliminating the need for the performer to compute other flight-related variables that would appear to make the predictive process much more complex • Lee and Young believe that computing time to contact from such variables as Distance and Velocity introduces multiple sources of error that would not exist if contact point were directly perceived • Asingle optic variable provides us with an estimate of time to contact • This Optic variable, referred to as Tau, has been mathematically defined by Lee as ◦ The Inverse of the rate of dilation of an image on the retina ◦ The faster an approaching object fills the visual field, the faster the object will contact a particular point in space (eg. Ball contacting a bat) • Performers can therefore use Tau to time their actions simply by determining how quickly the size of an approaching object fills the visual field • Many experiment support this theory but many of the results can be explained just as well in terms of the performers using a Computational process to predict time to contact Grasping Tau • The strongest Empirical evidence supporting use of Optical variable Tau to predict time to contact information has been provided by a group of researchers at the Free University • In this experiment the size of the approaching ball could be altered ( changing in size) ◦ the deflation of this ball was so subtle that it was not perceptually noticed ◦ It was hypothesized that if performers rely on time to contact information to time their actions, they would be able to adjust their hand movements to accommodate the changing ball size ◦ Results showed that subjects adjusted the timing of their grasping movements right up to the moment that the deflating ball contacted the hand ◦ Conclusion was that subjects were using the optical expansion rate of the oncoming ball to time their grasping movements, particularly in the final 200ms before ball contact Reading 17- Hick Hyman Law • In the present discussion, our interest is in what occurs between the intention to act and the initiation of movement to perform the action itself ◦ Researchers sometimes use the term Movement Preparation to designate this activity ▪ We will use the termAction Preparation when referring to this process • Preparation in this context means to the specific preparation the Motor control system makes just prior to initiating movement • Two Preparation Issues ◦ How do different skill, performance-context, and personal factors influence the preparation process? ◦ Exactly what does the Motor control system prepare that makes preparation such a critical part of the performance of any skill? Action Preparation Requires Time • The principle that the Motor control system needs preparation before it can initiate an action has its roots in research carried out by Donders • This principle is derived from an inference based on the effects of various factors on observed differences in the amount of time between ◦ The production of a signal telling a person to begin performing a skill and the instant experimenters actually observe the beginning of movement ▪ We call this interval of time Reaction time • In the context ofAction preparation, RT is an Index of Preparation required to produce an action ◦ Sometimes this interval of time is called a Response Delay Interval • One of the things that RT tells us is that preparing to produce voluntary movement takes time ◦ Planned movement does not occur instantaneously ◦ Certain actions and circumstances require more preparation than others Task and Situation Characteristics Influencing Preparation • One set of factors that influenceAction preparation includes characteristics of both the task itself and the situation in which it must be performed The Number of Response Choices • An important characteristic of task and performance situations that influence preparation time is the number of response alternatives the performer has to choose from ◦ As the number of alternatives increases, the amount of time required to prepare the appropriate movement increases • RT increases according to the number of stimulus or response choices • The fastest RT's occur in simple RT situations which have only one stimulus and one response • RT slows down when more than one stimulus or response are possible • Hick's law predicts a person's TY when their SRT and the number of choices are known • Hick's law sometimes referred to as Hick- Hyman law ◦ States that RT will increase logarithmically as the number of stimulus response choices increases ◦ Choice RT=k [log2(N+1)] ◦ k is a constant, mostly SRT ◦ N is number of choices • Log2 function is the important component of the Law ◦ It designates that the RT increase is due to the information transmitted by possible choices, rather than to the actual number of choice alternatives • In Information theory, log2 specifies a “bit” of information ◦ a Bit is short for Binary Digit, is the smallest number of yes/no choices between two alternatives ▪ 1 Bit decision there are two alternatives, 2 Bits there are 4, etc • Hick's law also predicts the specific size of increase to expect The Predictability of the Correct Response Choice • RT decreases as the predictability of one of the possible choices increases • Precuing technique- researchers provide participants with differing amounts of advance information about which movement must be made in a choice situation ◦ As the number of Precued dimensions increased, the RT decreases, with the fastest RT occurring when all three dimensions were precued ◦ The benefit of the advance information was that participants would need to prepare only the remaining non-precued dimensions after the “go” signal • Eversheim & Bock showed that when a person's attention was diverted by some other activity between the precue and the signal to move, the person lost the RT benefit of the advance information The Influence of the Probability of Precue Correctness • The critical factor influencing preparation time in a situation where the advance information may or may not be correct is the probability of the advance information's correctness • Cost- Benefit Trade-Off ◦ the cost (slower RT) and benefit (faster RT) that occurs as a result of biasing the Preparation of an action in favour of one of several possible actions ◦ When receiving information that 80% correct the RT was faster ◦ When the information was wrong (in the 20% case) their RT was slower than the 50/50 condition Stimulus Response Compatibility • Another task characteristic that influences the movement preparation time is the physical relationship between the stimulus and response choices • Studies have shown consistently that RT will be faster as the relationship between the stimulus characteristics and their required response becomes more compatible ◦ RT will be slower as this relationship becomes less compatible Spatial Relationship Effects • The spatial relationship between the stimulus and response devices is the most common way of considering stimulus response compatibility ◦ Amore compatible relationship would lead to faster RT ( fewer errors) than a less compatible situation ◦ ex. Kitchen stovetop, having the controls for the burner in an organized layout would be more compatible as opposed to a less sensible one The Stroop Effect • Adifferent type of S-R compatibility situation occurs when the appearance of the stimulus suggests one type of response, but the situation requires a different response ◦ Best example is when you are trying to read the name of a colour but that word is in a different colour ▪ When reading the word BLUE people will read it faster if the word is in blue but if the word is RED and the colour of that word is blue then they will be slower • When SR compatibility is low, RT increases are due to response selection problems Foreperiod Length Regularity • Apart of the preparation process begins when a person detects a signal indicating that the signal to respond will occur shortly • Foreperiod- the interval between warning signal and the stimulus, or “go” signal • In SRT situations, the regularity of the length of this interval influences RT • If foreperiod is a constant length, the same amount for every trial, RT will be shorter than the amount of time that typically characterizes simple RT • We can attribute the short RT associated with constant foreperiods toAnticipation by the performer • In races, athletes can anticipate the signal and gain an advantage of when to start Movement Complexity • Is based on the number of parts to a movement • For a Ballistic task, which requires both fast RT and fast movement, RT increases as a function of the number of component parts of the required action • From a Preparation ofAction perspective, these results indicate that the complexity of the action to be performed influences the amount of time a person requires to prepare the motor control system • The amount of time to perform the action and the number of component parts of the action are confounded when actions of different complexity are compared ◦ Researchers support the conclusion that the number of component parts is the key in the RT increase The Classic Experiment of Henry and Rogers • Hypothesized that if people prepare movements in advance, a complex movement should take longer to prepare than a simple one ◦ Increased preparation time should be reflected in changes in RT • In their experiment they said the cause of the increase in RT was the increase in the amount of movement related information that had to be prepared • They proposed that the mechanism involved in this movement preparation was a Motor program ◦ which would control the details of the sequence of events required to perform the movement MovementAccuracy • As the accuracy demands for a movement increases, the amount of preparation time increases • In an experiment RT increased as the target size decreased when hitting a target • When the target was a constant size, the dispersion of the location of hits on that target was related to the size of the second target • An important aspect of this research is that it extends our understanding of Fitts' law • Fitts' law concerns the increase in movement time associated with the accuracy demands of a movement, regardless of movement complexity The Repetition of a Movement • a well known characteristic of human performance is that when the performance situation requires a person to repeat the same response on the next attempt, that person's RT for the next trial will be faster than it was for the previous attempt • As the number of trials increases, the influence of the repetitions on RT lessens The Time between Different Responses to Different Signals • There are some performance situations that require a person to respond to a signal with one action and then very quickly respond to another signal with a different action ◦ When a basketball player is against a defensive player he might fake a move in one direction (first signal) before moving in the opposite direction (second signal) • Each signal by the offensive player requires the defensive player to initiate a movement • In this situation, RT will be slower for the defensive player's second movement than for his or her first • The RT delay for the second movement is due to the Psychological refractory period (PRP) which can be thought of as a delay period during which a person cannot select the second movement until they select and initiate the first ◦ PRP reflects a distinct limitation in the action preparation process • General consensus that the delay in responding to the second stimulus is related to the Response selection demands of the two SR task that must be performed in rapid succession ◦ The response of the second stimulus waits for the completion of the response to the first stimulus Reading 18- Psychological Refractory Period • PRP is the delay in responding to the second of two closely spaced stimuli • There is a bottleneck in the response-programming stage, which can organize and initiate only one action at a time • Largest delay when the InterStimulus Interval is short because the response-programming stage has just begun to generate the first response; this response must be emitted before the stage can begin to generate the second • As the InterStimulus Interval increases more of the first response will have been prepared by the time Stimulus 2 arrives, so there is less delay before the response-programming stage is cleared • When the stimulus is VERY short (less than 40ms) the motor system responds to the Second stimulus in a different way ◦ It responds to the stimulus as if the first and second were one ◦ Termed Grouping • The delay in the second response depends on the ISI and is greatest when the ISI is slightly greater than 40ms • When the two stimuli are separated by only 40ms or less, the stimuli are perceived, and responded to as one • Delay occurs in the response-programming stage, where only one action can be organized and initiated at a time Movement-Output Chunking • PRP is important for understanding how movement is produced • Two separate actions each triggered by a separate stimulus cannot be produced very closely to each other in time • The movement control system must be putting out a movement into the environment as a chunk that exclusively occupies several hundred ms until the next one can be generated- some research show that these chunks are separated by approximately 200ms ◦ When numerous chunks have to be strung together, they are put out at a maximum rate of about three per second • The separation between the first and second signals should not be greater than 150ms or the second signal can be responded to normally Reading 19- Anticipation Anticipation to Minimize Delays • One way to cope with long reaction delays is toAnticipate • Skilled performers predict what is going to happen in the environment and when it will occur • Skilled know what stimuli are likely to be presented, where they will appear, and when they will occur • With this info performers can organize movements in advance, completing some of the information processing activities using conducted during the Response-selection or Response- programming stage ◦ This allows the performer to initiate the movement much earlier or at a time consonant with the movements of the environment ◦ Makes performers look like they had all the time they need Types of Anticipation • Two general types • Spatial anticipation- what will happen in the environment- allows performer to organize the movement in advance, so when the signal for action finally does occur, the movement can be initiated with a far shorter RT • Temporal anticipation-performer might or might not be able to predict when it will occur- not being able to predict what will occur prevents the performer from organizing the movement completely in advance Benefits fromAnticipation • If the performer can correctly anticipate both what will occur and when it will occur, the advantage becomes very large • Effective anticipation is not always easy because it requires the performer to have a great deal of knowledge about the opponent's tendencies in various circumstances • Opponents will do everything possible to prevent the performer from anticipating • Several factors affect the capability to predict effectively ◦ The regularity of the events-ex. If the opponent always serves left Costs ofAnticipating • The primary disadvantage for anticipation is when the anticipated movement is not the actual one • Anticipating allows various information processing activities to take place in advance so they do not have to be done after the stimulus ◦ If the anticipation was wrong then these processes would have to be inhibited or unprepared which takes time estimated to be 40ms, then the correct actions must be organized and initiated Strategies for Anticipating • One strategy is to do everything to prevent the opponent from anticipating correctly ◦ This can be done by being unpredictable, randomizing • An important principle for many rapid sports events is that, if you can organize your play so that your opponent must react to you using the slow, cumbersome RT methods then you have essentially won • You can allow your opponent to anticipate but then you make essentially the movement opposite Reading 20- Feedback Role of Feedback in Motor control • The CNS is continually receiving various sensory feedback Closed loop Control • Can be used to plan and initiate movements and also to adjust the progress of an ongoing movement ◦ ex. Threading a needle- while trying to thread, you may get the feedback that the thread is not moving on a trajectory to meet the eye and you correct your movements • AClosed loop system has feedback, error detection, and error correction • Closed loop control does not require detailed initial movement commands ◦ Adjustments based on response produced feedback are used to adjust the progress of the movement ◦ Movement control is regulated by an error nulling process and the movement is completed only when all perceptible error has been eliminated Evidence for Closed Loop Control • Under certain conditions, subjects utilize sensory information for the control of movement • If motor performance suffers when one or more sources of sensory information are reduced or eliminated, then it can be argued that the information was utilized in the control of movement • Anticipated visual information can influence responses with movement times as low as 130ms • Attempts to degrade or eliminate proprioceptive information in intact humans have not been totally successful • Sensory feedback has been experimentally reduced by injecting anesthesia to selectively deaden the nerves serving sets of sensory receptors or by applying blood pressure cuff to the arm to cut off O2 supply to the sensory nerves • The Compression block technique involves the application of a Sphygmomanometer (blood pressure cuff) to the upper arm, the pressure is maintained above that of Systolic BP ◦ The cuff selectively affects the sensory receptors and nerves, leaving the efferent fibres operational • Motor performance while the Block was applied, in general degraded ◦ However it is not clear whether performance suffered due to degraded feedback or if the efferent nerves were also affected by the cuff Advantages and Disadvantages • Closed loop has 3 advantages and 2 disadvantages • First advantage is that Closed loop can be utilized to produce unpracticed movements ◦ as long as the performer can determine the discrepancy between his or her current position and the desired position, a correction can be executed • Second a great deal of movement flexibility can be exhibited under closed loop control ◦ This is because movement control is not dependent on specifying in advance the exact movement path required to achieve a movement goal but rather involves nulling the error between a current movement state and a desired state • Third, it can be used to produce very accurate movement outcomes such as threading a needle, these movements require lots of precision • First disadvantage is the execution of corrections in Closed loop appears to be attention demanding • Alot of time is needed to execute successive corrections ◦ Keele and Posner says it takes 200ms to produce visually based corrections ◦ Others say can be more quickly than 200ms but no less than 100ms ◦ Thus Closed loop may be limited to relatively slow movements Open Loop Control • Motor program in 1968 was described as a set of muscle commands that are structured before a movement sequence begins, and allows the sequence to be carried out uninfluenced by peripheral feedback ◦ This definition suggested that a Motor program was the biological analog to a computer program ▪ This analogy may be unfortunate because the NS is quite different from a computer and a Motor program may be quite different from the simple computer programs with which most of us are familiar Evidence for Open Loop Control • There is really no direct human evidence of a Motor program; centralists reason that there is no other known means of producing movements; thus programs must be the explanation • Actually it should be shown either that feedback is present in movement but not used or that feedback is not present and movement can still occur ◦ neither of these possibilities has been shown experimentally • Three lines of research have resulted in finding ◦ If controlled movement is exhibited in the absence of feedback, some form of program must be responsible for the motor commands ◦ Second line uses a more behavioural approach-increasing the “complexity” of the movement should not affect reaction time if closed loop processes were responsible for the production of the movement ◦ If an initiated Motor program caries a movement sequence to completion without the aid of feedback, the program should not be influenced by demands introduced after the program was initiated and before the movement was completed Advantages and Disadvantages • Open loop control has two major advantages and two disadvantages • Open loop can produce very rapid movement or movements under conditions in which normal feedback sources have been eliminated or disrupted • Second, because Open loop is prestructured, feedback does not have to be processed during the movement, and attention normally allocated to making corrections is not tied up ◦ This lets the performer engage in other strategic processing that would not be possible if Closed loop were employed • Adisadvantage is that Open loop has no feedback or mechanism for error regulation • Open loop is not effective when the environmental conditions are constantly changing such that the demands of the movement cannot be determined in advance AClose/ Open loop Continuum • Researchers conducted Closed loop control experiments that used slow, self paced tasks that required subjects to compensate for changes • Open loop tended to use discrete, rapid tasks that could be preplanned • Later on researchers discussed motor control in terms of feedback contributions • Feedback was thought to be relatively more important for control purposes for continuous, slow, and unpracticed movements • Reliance on feedback was thought to diminish for discrete, rapid, and well- learned movements Reading 21- Open and Closed Loop Systems Open and Closed Loop Control Systems • Most theories of Motor control incorporate two basic systems of control, both these systems are based on mechanical engineering models of control • These two models are basic descriptions of different ways the Central and Peripheral nervous systems initiate and control action • Each system has a Control centre, sometimes referred to as an executive ◦ its role is to generate and issue movement instructions to the Effectors ◦ Both systems also have Movement instructions that come from the Control centre Difference Between the Systems • Differ in two ways • First a Closed loop control system has feedback ◦ Feedback isAfferent information sent by the various sensory receptors to the Control centre ◦ Feedback not only comes back from the effector but sensors like visual & auditory • Second is difference in movement instructions ◦ In Open loop because there is no feedback, the instructions contain all the information necessary for the Effectors to carry out the planned movement ◦ Closed loop-issues an initial instructions are quite different ▪ The control centre issues an initial instruction to the Effectors that is sufficient only to initiate the movement-output ▪ The actual execution and completion of the movement depend on feedback information that reaches the Control centre ▪ Feedback will tell the Control centre to continue the movement as instructed initially, provide additional instructions, or correct a movement error Examples of Open and Closed Loop • Open Loop mechanical ◦ Videocassette recorder- is open loop by being programmed to tape TV programs on specified dates and times • Open Loop Human ◦ Throwing a dart at a dashboard- when the person initiates the throw, the arm movement and dart release occur as specified by movement instructions developed before the initiation of the arm movement • Closed Loop Mechanical ◦ Thermostat in a house- controls theAC and heat, desired temperature is set andAC or heating turns on and off to reach that temperature based on feedback from the room • Closed Loop Human ◦ Driving a car- feedback to control the steering wheel to make the needed adjustments to keep the car from going outside the lane boundaries Two Theories of Motor Control • Motor program based theory and Dynamic Pattern theory Motor Program Based Theory • At the heart of central control oriented theories is the Motor program, a memory based
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