PROBABILITY LEARNING IN STEP-INPUT TRACKING*

A Neural System for Error Detection and Compensation

Humans can monitor actions and compensate for errors. Analysis of the human event-related brain potentials (ERPs) accompanying errors provides evidence for a neural process whose activity is specifically associated with monitoring and compensating for erroneous behavior. This error-related activity is enhanced when subjects strive for accurate performance but is diminished when response speed is emphasized at the expense of accuracy. The activity is also related to attempts to compensate for the erroneous behavior.

Small perturbations in a finger-tapping task reveal inherent nonlinearities of the underlying error correction mechanism

Time processing in the few hundred milliseconds range is involved in the human skill of sensorimotor synchronization, like playing music in an ensemble or finger tapping to an external beat. In finger tapping, a mechanistic explanation in biologically plausible terms of how the brain achieves synchronization is still missing despite considerable research. In this work we show that nonlinear effects are important for the recovery of synchronization following a perturbation (a step change in stimulus period), even for perturbation magnitudes smaller than 10% of the period, which is well below the amount of perturbation needed to evoke other nonlinear effects like saturation. We build a nonlinear mathematical model for the error correction mechanism and test its predictions, and further propose a framework that allows us to unify the description of the three common types of perturbations. While previous authors have used two different model mechanisms for fitting different perturbation types, or have fitted different parameter value sets for different perturbation magnitudes, we propose the first unified description of the behavior following all perturbation types and magnitudes as the dynamical response of a compound model with fixed terms and a single set of parameter values.

Effect of Contrast on the Active Control of a Moving Line

In many passive visual tasks, human perceptual judgments are contrast dependent. To explore whether these contrast dependencies of visual perception also affect closed-loop manual control tasks, we examined visuomotor performance as humans actively controlled a moving luminance-defined line over a range of contrasts. Four subjects were asked to use a joystick to keep a horizontal line centered on a display as its vertical position was perturbed by a sum of sinusoids under two control regimes. The total root mean square (RMS) position error decreased quasi-linearly with increasing log contrast across the tested range (mean slope across subjects: −8.0 and −7.7% per log2 contrast, for the two control regimes, respectively). Frequency–response (Bode) plots showed a systematic increase in open-loop gain (mean slope: 1.44 and 1.30 dB per log2 contrast, respectively), and decrease in phase lag with increasing contrast, which can be accounted for by a decrease in response time delay (mean slope: 32 and 40 ms per log2 contrast, respectively). The performance data are well fit by a Crossover Model proposed by McRuer and Krendel, which allowed us to identify both visual position and motion cues driving performance. This analysis revealed that the position and motion cues used to support manual control under both control regimes appear equally sensitive to changes in stimulus contrast. In conclusion, our data show that active control of a moving visual stimulus is as dependent on contrast as passive perception and suggest that this effect is attributed to a shared contrast sensitivity early in the visual pathway, before any specialization for motion processing.

Directional errors of movement and their correction in a discrete tracking task

Many studies have shown that subjects can correct their own errors of movement more quickly than they can react to external stimuli. In the control of movements, three general categories of feedback have been defined as follows: (a) knowledge of results, primarily visually mediated, (b) proprioceptive or kinesthetic, such as from muscle spindles and joint receptors, and (c) corollary discharge or efference copy within the central nervous system. Experiments were conducted on eight normal human subjects to study the effects of these feedbacks on simple RT, choice RT, and error correction time. The movement used was plantarflexion and dorsiflexion of the ankle joint. The feedback loops were modified (a) by inverting the visual display to alter the subject's perception of results and (b) by applying a 100-Hz vibration simultaneously to both flexor and extensor muscles of the ankle joint. Central processing was altered by giving the subjects moderated doses of alcohol (blood-alcohol concentration levels of up to.10%). Vibration and alcohol increased both simple and choice RT but not the error correction time. These data reinforce the concept that there is a central pathway which can mediate error correcting responses.

Is it possible to prepare the second component of a movement before the first one?

Experiment 1 utilized a choice reaction time paradigm to examine whether advance information about the second component of a movement has similar effects upon movement initiation and execution as advance information about the first component. Four stimuli were assigned to four goal keys. Subjects responded with the index finger of their preferred hand. They had to press on of two intermediate keys before pressing the assigned stimulus goal key. Advance information signaled one pair of goal keys in such a way that either the first or the second movement component was unequivocally specified before the response signal appeared. Shorter reaction times resulted when the first component was precued. Further control conditions showed that advance information about the second movement component could not be utilized for movement preparation. Experiment 2 ruled out a perceptual interpretation of this effect. Experiment 3 showed that preparation time for two-component movements are longer than for one-component movements. The study permits the conclusions that speeded two-component movements are controlled by motor programs and that advance information about the first movement component is required before the second movement component can be programmed.

N200 in the flanker task as a neurobehavioral tool for investigating executive control

Event-related potentials were recorded in a flanker task using arrowheads pointing to the left or to the right as targets and as congruent or incongruent flanker stimuli using squares as neutral flanker stimuli. The onset of the flanker stimuli preceded that of the target stimuli by 100 ms. Lateralized readiness potentials showed response activation below execution threshold in correspondence to the information conveyed by the flanker stimuli. Exclusively, the incongruent flanker condition provoked a N2c, which evolved closely synchronized to the erroneous response. Graded response analyses separating incongruent trials with weak, medium, and strong incorrect response activation revealed that the N2c amplitude covaried with the magnitude of the erroneous response. The N2c in the incongruent compatibility condition of the flanker task thus corresponds to the avoidance of inappropriate responses, possibly reflecting the inhibition of automatically but erroneously primed responses. The results are compatible with studies of error correction, suggesting that efference monitoring is a constituent of executive control.

Observations on the microstructure of response conflict

Three experiments are detailed which indicate the usefulness of the frequency of double responses (DRs) as an indicant of response conflict, in addition to the usual RT measures. DRs are responses on which an initial (often partial) error response is made that is rapidly amended to a correct response. Such responses occur most frequently in stimulus conditions where response conflict is expected by theory to be present and is indicated by changes in RT. Partial activation of competing responses has been demonstrated before using physiological measures (Coles, Gratton, Bashore, C. W. Eriksen, & Donchin, 1985; C. W. Eriksen, Coles, Morris, & O'Hara, 1985) when both responses could physically be made at the same time. DRs seem to be an equivalent type of movement when the subject cannot physically make but one movement at a time. The usefulness of this index of response conflict lies in its ease of implementation.

Measuring impaired performance with the NRC "stressalyser"

The NRC 'stressalyser' is a step-input subject-paced pursuit tracking task used to detect the effects of various extrinsic factors on skilled performance. It gives measures of reaction time, movement time, error score and overshoot score, each at four levels of the relevant within-task variable (directional probability, target distance or boundary distance). Several investigations have shown how these measures vary with such factors as sleep loss, time of day, alcohol, insulin-induced hypoglycaemia and diazepam, and thus demonstrate the applicability of the device to many applied problems of performance impairment.

Memory overload or expectancy effect? 'Hysteresis' revisited

The effects of expectancy and variation in task demand on the rate of human information transmission were studied. Subjects performed an eight-choice key-pressing task, attempting to match characters presented singly under both increasing and decreasing demand. The results support previous research indicating that the relationship between the rate of information an individual is able to transmit and task demand depends, at least in part, upon the temporal history of demand. When a relatively high level of demand was imposed, performance failed to recover at the expected rate as demand was reduced. However, this 'hysteresis' effect occurred even when a cue was provided to indicate clearly that a reduction in task demand was imminent, suggesting that an overload of short-term memory, rather than an individual's erroneous expectations regarding demand, is primarily responsible for the effect.

The control of movement in the preferred and non-preferred hands

The nature of the difference in skill between the preferred and non-preferred hands was investigated using a peg-board task. The first experiment examined the effects of varying movement amplitude and target tolerance on performance. The difference between hands was found to be related to tolerance rather than movement amplitude. The second study analysed a film record of well-practised subjects, confirming the hypothesis that most of the difference between hands is due to relative slowness of the non-preferred hand in the positioning phase involving small corrective movements. Analysis of the type and number of errors further suggested that this result is not due to differences in duration of movements but to their increased frequency, implying greater accuracy of aiming with the preferred hand. Thus whilst the initial gross analysis implicated feedback processing in skill differences the more detailed analysis suggests that motor output of the nonpreferred hand is simply more variable.

Minimum visual feedback processing time for amendment of an incorrect movement

The average minimum time required by a performer to amend an incorrect movement based upon his ability to process visual feedback is discussed. Further, a decremental effect of the psychological refractory period on minimal visual feedback processing time is suggested.

Alcohol and amitriptyline effects on skills related to driving behavior

Three motor-skill tests related to driving ability were given to 21 healthy young volunteers after administration of various combinations of amitriptyline, placebo, and alcohol. It was found that the tricylic antidepressant added to the deleterious effects of alcohol.