I’ve been digging into the research on the focus of attention. Professor Wulf has done a great job of synthesising all the research every few years and publishing a review. One of the latest reviews is Attentional focus and motor learning: a review of 15 years. I particularly enjoyed the tables that listed all the studies and the tasks used. They allowed me to quickly find all the research that has used a stability platform for further investigation.

I still need to read about Professor Wulf’s 2016 Optimizing Performance through Intrinsic Motivation and Attention for Learning (OPTIMAL) theory of motor learning. I’ll post an update on that soon.

Clocking the mind

December 13, 2014

I just read Clocking the mind: mental chronometry and individual differences by Arthur R Jensen (2006). It is a wonderful tome of information that belongs in the same category as Response times by R Duncan Luce (1986) and Reaction times edited by WT Welford (1980). All three of these books delve into the use of mental chronometry (i.e. reaction times) in psychology. The books by Luce and Welford focus on cognitive psychology, whereas Jensen reviews mostly differential psychology. Clocking the mind, however, is still a great resource for cognitive psychologists as Jensen reviews a plethora of factors that are vital for any experiment measuring reaction time.

Below are my favourite excerpts from the book.

Simple and choice reaction time

I’m a sucker for tables that detail the processes that compose reaction time. Below is Jensen’s interpretation. (I’ve previously posted about the interpretations by R Duncan Luce and FC Donders.)

Jensen Table 10.1

The split-half reliability coefficients based on odd-even trials are high (around .90 with as few as 30 trials) for both RTm and MTm, and test-retest reliability for 15 trials measured on each of two days is about .80 for RTm and MTm… Several practice trials followed by 60 test trials are typically required for simple RT to attain a reliability coefficient of about .90.

As CRT tasks increase in information processing demands, there is a regular decrease in the correlation between CRT and SRT. SRT and 2-choice RT have about 80% of their true-score variance in common; SRT and 8-choice RT have only about 50% in common (Jensen, 1987a, p. 139).

In groups of college students, for example, there is an average difference of 40-50 ms even between SRT and two-CRT, when there is an optimal preparatory signal and the RT in each case is simply a bright green light going “on,” always in the same location (SRT), or randomly in one of two locations (CRT)… It is also important to note that the effect of increasing task complexity is to increase the slower RTs much more than the faster RTs.

…RT and MT. These measures are relatively independent, correlating with each other only about .30… It appears that CRT reflects mostly information processing whereas MT reflects mostly sensorimotor ability.

Masking the reaction stimulus

To make it difficult or impossible for participants to leave the home key before completely processing the precise location of the response stimulus, some researchers have all the lights go “on” the instant the participants release the home key, in order to lessen the possibility for participants to leave the home key prematurely and continue processing the location of the response stimulus while in transit (Smith & Correau 1987). This “masking” of the reaction stimulus at the instant of participants response is intended to discourage response strategies that interfere with conformity to Hick’s law.

Skewness

A simple but crude measure of skewness is Sk = 3(Mean – Median)/SD. A more precise and the preferred measure, included in most computerized statistical packages, is R. A. Fisher’s g1 = Σ(X – Xbar)3/N(SD)3.

Kurtosis, or the degree of peakedness (or flatness) of a distribution is measured by Fisher’s g2 statistic: g2 = [Σ(X – Xbar)4/N(SD)4] – 3.

The total distribution of a given individual’s RTs over n trials is not symmetrical but is necessarily skewed to the right (i.e., longer RT), because there is a lower physiological limit of RT and there is no naturally imposed upper limit of RT.

Jensen Fig 4.2

RT vs. RTSD

Also, the RT and RTSD behave quite differently in too many ways to make it seem likely that they are totally non-independent variables. In the Hick paradigm, for example, whereas RTm (or RTmd) shows a perfectly linear relationship to bits, or the binary logarithm of the number of RS alternative, RTSD shows a perfectly linear relationship to the number of alternatives per se and is exponentially related to bits.

Trials before and after errors

But the most interesting finding in this study is the nature of the RTs on the trials preceding and following an error response, which tend to average out in a subject’s mean RT based on many trials. Figure 5.12 shows the mean RTs of the 10 trials preceding and the 10 trials following an error response in each age group. At every age, subjects appear to be continually testing themselves for the fastest response speed they can get away with without risking an error, and when an error occurs they immediately go back to a more cautious speed of responding. The RTs for 5- and 7-year olds are markedly more erratic and the posterior effects of an error are much greater than in the older groups, indicating a less “fine-tuned” control of RT. Note also that it takes longer for the younger groups to recover to a faster RT after an error response; slower than average RTs occur for several trials following the error… Old adults resemble the 13 year-olds (Figure 6.13).

Jensen Fig 5.12 better

Jensen Fig 6.13

I’ll upload a better version of the first figure when I’m back in the lab.

Effects of practice

SRT to light, with maximum S-R compatibility shows virtually no practice effect (i.e., improvement) in RT after the first 10 trials. For CRTs, however, the practice effect persists over at least 10,000 trials and the CRT is a decreasing linear function of the logarithm (log10) of the number (N) of trials. The average slopes of the regression of CRT on log10N for 2-, 4-, and 8-choice RTs derived from a number of studies were -0.099, -0.169, and -0.217 s (Teichnet & Krebs, 1974, p. 82)… On a 2-choice RT task, for example, if the RT on the first trial is 0.725 s, it is 0.626 s on the 10th trial, 0.527 s on the 100th trial, and 0.428 on the 1000th trial… The investigator takes advantage of the fact that the largest practice effects occur in the early trials, and allows a fair number of discountable practice trials (e.g., 20 or so) before beginning the test trials.

I’ve been rereading Response times: their role in inferring elementary mental organization by R. Duncan Luce. It could be my choice of book to have if I was stuck on a deserted island with one book; there is so much information hiding within its covers! Chapter 3 begins with a description of the successive stages that contribute to reaction time. This reminded me of a similar section by Professor Donders that I shared in a previous post. Below is the except from Luce’s book (3.1 Independent, additive stage latencies, p 96).

It is widely, although by no means universally, believed that the total observed reaction time is the sum of a number of successive times. This idea dates to Donders’ (1868) classic paper, if not earlier. The times involved include, at least, the following:

  1. The time required for the physical signal to be transduced from the physical energy into the neural spike trains, which appear to be the information code of the nervous system
  2. The transit time for such pulses to pass from the output of the transducer to that part of the brain where the information arriving on the entire fiber bundle (the optic and auditory nerves being the most thoroughly studied) is processed and interpreted – the decision center
  3. The time required for that processing and for an order to be issued to the relevant muscle group – the decision latency
  4. The transit time between the issuing of an order and its arrival at the muscle group that effects a response
  5. The time for the muscles to complete the response

Any one of these stages may be subdivided further.

Aging-foreperiod effect

February 25, 2014

I’m currently a teaching assistant in an introductory course on motor control and learning. It is great to review the fundamentals of motor control and share them with a great group of students. We recently discussed temporal anticipation and the aging-foreperiod effect. This effect occurs in a reaction time task with a variable foreperiod and no catch trials. The classic finding is shorter reactions times with longer foreperiods. This is called the aging-foreperiod effect, and it is shown in the figure below from Schmidt and Lee (p 81, 5th edition).

schmidt_lee_fig_3-16

The explanation for this effect is that as the participant waits during the foreperiod (as the foreperiod “ages”), their anticipation of the imperative stimulus increases. Think of it this way, if the maximum foreperiod duration is 2.4 s (as in the figure above), then after a foreperiod of 2.2 s you will be pretty sure that the imperative stimulus is going to arrive soon. This ability to anticipate the imperative stimulus causes shorter reaction times as the foreperiod ages.

I decided to look for the aging-foreperiod effect in one of my experiments. It was a 4-choice reaction time task with 36 participants and ~360 trials per participant. That gave me a total of 12,967 trials, so lots of data to work with. The foreperiods were randomly selected to be between 1000 ms and 2000 ms, inclusive. The figure below shows a histogram of the foreperiod durations.

foreperiod_histogram

To calculate the effect of the foreperiod duration on reaction times, I grouped each participants reaction times into 50 ms foreperiod bins; for example, I calculated the mean reaction times for foreperiods from 1000 to 1049 ms, 1050 to 1099 ms, and up to 1955 to 2000 ms. This gave me 20 mean reaction times per participant and then I calculated the 20 grand means for all participants. The grand means +/- the standard errors are plotted below.

aging_foreperiod

It looks like a pretty good aging-foreperiod effect to me! You can see the fast decrease in reaction times for foreperiods from 1000 to 1500 ms and then an asymptotic decrease from 1500 to 2000 ms. I wonder if the increase in reaction times two means after 1500 ms is related to the relatively low probability of these foreperiod durations. These foreperiod, 1550 to 1599 ms, had the lowest frequency (by chance) with only 396 foreperiods. It is probably just noise, but it does make sense to have longer reaction times for a more unlikely foreperiod.

I just read Human motor actions: Bernstein reassessed and I only found one captivating section. Sorry Professor Bernstein! I’m sure the book was far more topical in 1984. Anyway, I’ve copied that section below. It discusses the stages of information processing, or more specifically, the stages of movement preparation. The excerpt is from chapter V, section III (Problems of the physiology of activity).

The sequence of the arousal and realization of any action of the class of so-called voluntary movements may be represented in the form of successive stages.

  1. Perception, and the necessary evaluation of the situation and of its bearing on the individual caught up in it.
  2. The individual determines in what way it is necessary to alter this situation; what, by means of his activity, the situation must become instead of what it is. The motor problem has already appeared at this stage. It is not difficult to guess that this motor problem must contain more information that is included in the bare perception of the situation, some of which is at least partially not present in the latter. Animals in a herd, or people in a crowd, may be confronted with the same situation, but the motor behaviour of each individual will be different. Examples of this may be readily found.
  3. The individual most next determine what must be done and
  4. How it must be done, and what are the available resources.

These two micro-stages already represent a program of the solution of the problem, and after these there follows the process of its actual solution in terms of motor activity. It is scarcely necessary to emphasize that the control and evaluation of successive moments of the actual activity, the variability of the situation itself, with the fact that it is, generally speaking, possible to program only rather roughtly movements which have some duration in time, all explain the adaptational variability of programs and of acts, permitting changes ranging form small corrections to widespread alterations in strategy.

It would be false to suppose that the micro-stages in the transition from the situation to the act which have been described above are found only in highly organized nervous systems. The same stages must also necessarily be found in such primitive acts as, for example, the pursuit of live prey be predatory fish. In this case we also have a situation which is perceived in the necessary form and measure, and a motor problem with a program for its solution. The precise way in which either of these aspects of the process is coded in the nervous system of a predatory fish is quite unknown to us, but it is beyond doubt that neither consciousness nor a particularly high level of nervous organization is necessary for them to take place.

Concerning the topic of higher information content of the problem in comparison with the actual perceived situation, we must add the following. From the point of view of the dependence of the actions of an organism on the stimuli which provoke them, or on the input in general, we may draw up an imaginary series in which we may rank all actions (confining ourselves here to the actions of human beings) according to their degree of dependence on such activating stimuli. At one end of the series we have movements which can be fully explained in terms of the stimuli which activates them. Among these we have all the so-called unconditioned or innate reflexes. We may also include all reflexes conditioned during life experience which are nevertheless dependent on the activating stimulus – reactions of the general class of conditioned reflexes found in humans and animals alike.

We may place next in our rank order, movements for which the stimulus or signal continues to play the role of an activator, but which have a meaningful content that is increasingly independent of the stimulus. For motor acts of this class the activating signal increasingly takes on the features of a trigger signal, analogous to the pressing of a button which sets in motion the whole complex process of firing a rocket, or to the interjections “hep” or “arch” after which follow sequences of activity which are very little related in significance to these interjections. Finally, at the other end of the series, we find acts for which the activating or triggering signal does not play a decisive role, and in which also the initiative, are entirely determined within the individual, and the term “voluntary movements” may properly be applied. It is not difficult to see that a progression along our scale coincides with the gradual shift from passive acts, to acts having an ever-increasing degree of active invovlement.

I’m a bit ashamed to say that I just read, for the first time, the foundational article on information processing by FC Donders (1868/1969. On the speed of mental processes. Acta Psychol, 30, 412-431). Donders followed-up the the research by Helmholtz in 1850 that measured the neural conduction time (more on that in a previous post, Origins of motor control research). The 1868 paper by Donders was translated and reprinted in 1969 for a special issue on mental chronometry. He compared the reaction times on a choice reaction time task to a simple reaction time task to determine the time required to discriminate between two or more responses. Donders also tested a go/no-go condition to determine the time required to recognise an imperative stimulus.

The paper holds up well, and I was amazed by how many foundational principles it touched on, which I’ve listed below.

  • Hick’s law: “…with the wider choice out of five, some more time is indeed required than with the choice of two…” (p 419)
  • Compatibility: “…when movement of the right hand was required with stimulation of the left side or the other way round, then the time lapse was longer and errors common” (p 421)
  • Imperative stimulus modality: sound < touch < vision “The reason may lie in the different stages of the complex process” (p 422), which he elaborated on
  • Preprogramming: “…the great influence of a predetermined conception on the recognition of forms became very clear to me” (p 425)

I also enjoyed the description of the events that occur between the imperative stimulus and the response. I’ve added my thoughts in brackets after some of these events.

  1. The action of the sensory elements in the sense-organs
  2. The communication with the peripheral ganglion cells and the increase required for discharge
  3. The conduction in the sensory nerves up to the ganglion cells of the medulla
  4. The increase in activity in these ganglion cells
  5. The conduction to the nerve cells of the organ of conception (stimulus identification?)
  6. The increase in activity of these nerve cells
  7. The increase in activity of the nerve cells of the organ of will (response selection?)
  8. The conduction to the nerve cells governing movement [response programming (?) by the motor areas of the frontal lobe, also likely involved in step 7]
  9. The increase in activity in these cells
  10. The conduction in the motor-nerves to the muscle (conduction velocity of the corticospinal tract)
  11. The latency in action of the muscle
  12. The increase in activity up to the moment of overcoming the resistance of the response (motor time)

If you are familiar with the neuromechanical research at the University of British Columbia, then you probably know that we are obsessed with the startle reflex. I recently stumbled on a book about startle entitled Neural mechanisms of startle behavior (1995) edited by Robert C Eaton. There is a great chapter (10) by Michael Davis on the mammalian startle response. It is a great review, and I recommend reading the entire chapter. Today, I’m going to focus on the section on the neural mediation of acoustic startle (4.1).

Davis and his colleagues have mapped the acoustic startle circuit from acoustic stimulus to muscular response (shown in the figure below). The acoustic stimulus travels the cochlear portion of the vestibulocochlear nerve (cranial nerve VIII) to the posteroventral cochlear nucleus (VCN, level C of the diagram). The next synapses are bilateral connections to the dorsal nucleus of the lateral lemniscus (DLL, level A) and the ventral nucleus of the lateral lemniscus (VLL, level A).

davis_1995_fig3

The startle reflex then travels bilaterally to the nucleus reticularis pontis caudalis (RPC, level B). This is the beginning of the reticulospinal tract (RST, levels B, C, and D) that descends to all levels of the spinal cord and result in the observable startle reflex.

An important note is that this is just the primary acoustic startle circuit. Davis notes that the startle response seen in EMG contains early (8-9 ms after the sound in the quadriceps of rats) and late responses (15-25 ms), and the later response likely involves a more complex circuit. I’m curious if there has been any research into these secondary startle circuits in the 18 years since this chapter was published (the original article with the figure was published 31 years ago in 1982). I’ll look into it and let you know if I find anything. If you know of any articles, then feel free to suggest them in the comments below (the first article I will read is a 2008 review by Davis, Acoustic startle reflex in rhesus monkeys).