TYPICAL SERIES FOR THE MONTH
Key.
v = mean error.
R.H. = right hand.
R.F. = right foot.
E.O. = eyes open.
si. = simple motion
N = normal line.
Unit = 1 mm.
L.H. = left hand.
L.F. = left foot.
E.C. = eyes closed.
co. = compound motion.
M = mean line.
b = beats per minute.
c = constant error.
Table. 23 Huggins. c. N. 98 first column, '+55' changed to +'5.5'.
The records are averaged for nine subjects, three of them being left-handed. For the right hand we find, for mean error, a reduced error with visual control.
For constant errors, a similar result is apparent; when following the eyes-closed curve one may note a large negative error 20-50 beats, and a similar but larger positive error 70-160 beats, with a falling to a negative error again at 200 beats.
This may be interpreted to mean a groping for the correct length of line at the lower speeds when some time for reflective processes is allowed, and an inhibitory effect on the motor discharge; later the speed prevents this discrimination, and introspective testimony goes to show that a mental conception of a barrier, beyond which one cannot carry the pencil, is set up and kept more or less constant through the help of the joint and muscular sensations. It would follow, then, that this muscular stop is overestimated where reflection is not possible.
Finally, the falling-off of the length of the line is probably due to physical inability to rule a line of the full length of 140 mm. at 200 beats per minute and an examination of some individual cases confirms this opinion, for the lines may be started some distance away from the origin apparently in order to end them at the correct point.
Curve inclinations are upward, for mean errors, with visual control, while the eyes-closed records show no increase in error for the increased speeds.
For constant errors, with visual control, there is a similar inclination downward for both hands, with a 0 error at about 120 beats. It should be noted that this opposite tendency in mean and constant errors suggests that they should be kept separate in all computation.
The left-handed subjects have much better control of their left hand than have the right-handed subjects, and they may dispense with visual control to a large extent.
On the other hand, for right-hand records we find much the same increase in irregularity and error for both left- and right-handed subjects; they all must depend on visual control for reduction of errors.
It follows that the non-visual control exerted by the left-handed subjects on the right hand is as good or as great as for the right-handed subjects; while they have the hand in which they may be expected to excel under much better control.
It is not intended to present this as an argument for teaching left-handedness, but it is certainly suggestive when considering the question that ambidexterity be taught in early life.
It should be noted that two of the three left-handed subjects might be expected, because of special training, to show marked manual dexterity, while only one of the four right-handed subjects has had special training along this line.
No extended discussion is appropriate here as to the question of what portion of this extra ability of the left-handed subjects to react accurately is due to practice and habit, i. e., is automatic, and accomplished without reference to the sensory motor by-path to the cerebral cortex; and on the other hand, as to whether the direct sensory motor path via spinal cord or medulla is not cut off entirely.
For 140 mm. averages and free motion, we find in general
(1) a reduced error and greater uniformity of result at all speeds where visual control is added, in the case of both mean and constant errors and for all subjects;
(2) the mean errors for visual-control records show a rise along a line whose equation is approximately y = px, or the equation of a straight line, where p is an undetermined constant.
On the other hand,
(3) the eyes-closed mean errors show no increase or decrease in value during the entire series;
(4) the constant errors for visual-control records show a drop from positive errors to negative errors, along a line whose equation is approximately y = qx or the equation of a straight line, where q is an unknown constant, somewhat less in value than p in the case of mean errors; the constant error becomes 0 at about 120 beats;
(5) the eyes-closed constant errors follow the same equation for left-handed subjects, using the left hand, but all other cases suggest a curve of the parabolic form, having 0 constant errors at 60 and 180 beats and being convex upward.
Considering individual records for 14 cm.
A general survey of the charts suggests certain irregularities that call for explanation, for there will be sudden large increases in errors, that are explicable on the hypothesis that the subject has temporarily lost control of the moving hand, that is, that fatigue is to be noted.
While the purpose of the investigation has been to allow no lines to be ruled while the subject was conscious of any such feeling, there being a pause of any desired length to permit time for rest, it is to be noted that a considerable amount of recorded data as to fatigue shows that it is an unconscious or subconscious phenomena.
Further, the series of records have been arranged to occur from 20 to 200 beats and never in the reverse order, because of subjective limitations, so it is reasonable to expect that during the period of twenty minutes to one half an hour required for a series of records, there will be lapses of volitional control entirely beyond the ken of the subjects. It is to this cause rather than to pure chance that the results will be attributed. With this exception, the individual records show close agreement with their average.
The results obtained from a consideration of free hand-movements of 1, 10, and 14 cm. length are:
For 14 cm. lines
for the average of nine subjects:
The mean errors,
(1) increase with speed for eyes open;
(2) do not change in error with speed-change for eyes closed;
(3) visual control reduces errors for right hand, but does not for the left;
(4) right-handed subjects alone gain from visual control.
The constant errors,
(1) decrease with speed in visual cases;
(2) increase with speed to the middle and then reduce to 200 beats for eyes closed;
(3) left-handed subjects are more accurate for the left hand and can dispense with visual control;
(4) all subjects need visual control for the right hand;
(5) left-handed subjects show less error throughout for non-visual.
For the individual cases,
the mean errors
(1) show evidences of loss of control or fatigue for some speeds, and the average results are confirmed.
The constant errors show that the average deductions are confirmed.
Lines 10 cm. long:
Averages for seven subjects as regards mean errors have especial interest for l.h.e.c. records, which alone show a rise of error with speed-increase.
Noting that the records are overwhelmingly averages of right-handed subjects (six to one), it is of interest to examine this record.
We may say, then, that for right-handed subjects, the voluntary control for the right hand is not much improved by the introduction of visual assistance; it is more marked for speeds of 100 beats or less than for the high speeds. And in the latter case, it is under 10%; but when the left hand is considered, a marked gain or 40 or 50% is apparent, when the eyes are used except for the two lowest speeds.
As far as it is possible to offer any hypothesis from the few facts tabulated, it may be said that right-handedness implies a high development of muscular control, but slightly improved by the introduction of the visual element, as far as the right hand is concerned; but for the left hand muscular control comparable to the right-hand control can be obtained only with visual control; in short, I fail to find evidences of cross-education, where the visual element is absent, nearer than about 50% of the mean error.
No clearly marked gain through visual control can be pointed to in the case of constant errors; there is, to be sure, a slight gain in steadiness and error-reduction, where eyes help in the case of both hands, but not 5% in magnitude of the difference noted with mean errors.
Individual records show fatigue-points at 40 to 80 beats and again above 140 beats, but there is no perceptible loss of control during a series of lines ruled at only one speed.
It is apparent, when comparing with the 140 mm. records, that there is no physiological reason why the subjects may not rule the full length of a 10 cm. line at 200 beats, and the limit of movement for high speeds is probably between 10 and 14 cm.
The constant errors are in general positive and only Me. shows a tendency to underrule lines at high speeds.
For 10 cm. lines,
for the average record,
(1) the mean-error curve is horizontal for l.h.e.o., but otherwise rises with speed-increase;
(2) visual control is a 10% gain for right hand and 40 to 50% for the left, so right-handedness is prominent for the eyes-closed series;
(3) the constant-error curve for r.h.e.c. rises, but all others show reduction of error as rate increases;
(4) visual-control gains are not over 5%.
The individual curves show,
for mean errors,
(1) marked-fatigue points for l.h.e.o;
(2) r.h.e.o. curve is horizontal, but all others rise;
(3) l.h.e.o. curve is about the same as r.h.e.o., but there is more loss for non-visual series with left hand.
For constant errors,
(1) r.h.e.c. curve rises, but all others are horizontal;
(2) the eyes reduce errors especially for the left hand;
(3) overruling is prominent even at high speeds, for there is no evidence that the lines are shortened at high speeds.
Lines 1 cm. long:
Averages are made for nine subjects, three being left-handed.
The eyes are effective in reducing mean errors and to a less extent for constant errors.
A noteworthy feature of the constant-error record is that the errors are positive with one exception, that of 20 beats with l.h.e.c. and even this curve jumps rapidly above the 0 line.
In all cases the motor discharge is of sufficient magnitude to cause overruling in cases of normal lines of one cm. The assistance afforded by the eyes is not marked.
Certain evidence of an introspective character, that most of the subjects offer, is to the effect that, "when I would do good, evil is present with me"; that, where there is a decided feeling that the muscular limit, if such a term be permitted, is exceeded, yet the subject's will-power is not sufficient to inhibit the overruling; there is a more or less vivid conscious error in the 10 mm. series for the hands.
In regard to the relation of mean and constant errors, there is more close uniformity than with the 140 mm. lines, but it is to be noted that there is no comparison to be drawn between maximum or minimum points; for example, at 100 beats the minimum points for r.h.e.o. agree closely, but the maximum constant error matches the minimum mean error at 100 beats for r.h.e.c.
We cannot predict, then, that a subject capable of closely ruling to the normal will be able also to rule each line of the same length as the rest of the series, or vice versa.
As in the case of mean errors in general note that subjects show a less constant error and more regularity for their more dexterous member; it is not true for the left hand that for left-handed subjects visual control is a hindrance for accurate work; otherwise the same gain, by use of the eyes, is to be noted for the rest of the records.
Individual records show close correspondence with the average of results, and the latter may be considered fairly representative.
Almost the whole series shows the constant error positive, the most consistent example being for J. with l.h.e.o.; this tendency to overrun the 1 cm. lines is consistently uniform and has been elsewhere commented on, so it may be left with the observation that the log shows that the subjects were frequently conscious of this overruling, but confessed inability to correct it.
Only in the case of Y. for the three left-handed subjects and for W. among the six right-handed men does the left hand show less mean error than the right hand, and all other cases show such an interweaving of curves as to render it difficult to perceive any advantage that the more dexterous hand possesses on the score of accuracy.
For constant errors:
For individual cases it is to be noted that for the left-handed subjects J. is better for the right hand, Le. is indifferent, and Y. prefers the left hand; while three of the six right-handed subjects prefer the left hand and one is indifferent; thus giving still further proof that a more dexterous hand is a fiction on the score of the right or left-handed theory, when accuracy of straight-line movement is to be considered.
For 1 cm. lines,
for the average, note
for the mean errors:
(1) visual control reduces errors;
(2) errors increase for eyes open, but decrease for eyes closed, as speed increases when considering right hand, but left-hand errors are constant;
(3) as left-handed subjects are better for r.h.e.o. than right-handed subjects, but not for eyes closed, it is suggested that visual control equalizes differences in the subject's less trained hand.
For constant errors:
(1) visual control reduces errors;
(2) curves are horizontal in all cases;
(3) all errors are positive, showing consistent overruling;
(4) as visual control of the left hand is a gain for right-handed but a hindrance for the left-handed subjects, the more practised hand is probably able to dispense with visual control, and depend largely on the muscular sense.
Mean and constant errors are not comparable. For the individual cases we find a corroboration of the above and for mean errors: more dexterous hand does not excel, and evidence against ambidexterity is conflicting; for constant errors: overruling is consciously done.
Constrained hand-movements for lines 14 and 1 cm. long and for the weight, both accelerating and retarding the movement, are to be next considered.
Constrained motions are of two general types as examined by the writer. Series of the records for the hands were taken at 140 mm. and 10 mm. bases with a weight hung on the finger or fingers of the hand under investigation; in one series the weight acted as a pull or accelerating effect on the ruled line and in the other series the weight was imposed as a retarding effect, tending to restrain the movement of the hand.
This weight was in all cases 260 grams, this weight being chosen as of sufficient amount to have a perceptible effect, but not large enough to cause feelings of pain or fatigue in any case.
The average for seven subjects, three being left-handed, is as follows:
In general, the mean errors for the right hand are less, and less variable as compared with the left hand. The left-hand records are very close to the corresponding right-hand curves, especially the portions of the eyes-closed records 20 to 120 beats.
This may be said for both mean and constant errors. In general, mean errors are reduced, and curves are more nearly straight lines when the weight is added; also the weight reduces constant errors, and gains more regular records at all speeds. It is to be noted as a point of unusual interest that there is no apparent shortening of the line ruled when the weight is hung on the hand, for the negative errors are less, not more when the weight is applied.
In general, then, the imposition of a weight that will be small enough not to cause pain or fatigue shows that both mean and constant errors are reduced; that the amount of error is less variable over the range of speeds used; that the records show no retarding effect, but that the subject is both able to move the hand just as far as without the weight, and do it with much greater accuracy.
Individual records for 14 cm. and weight-retarding show a marked reduction in both mean and constant errors, and a less marked gain in uniformity in every case. This tends to confirm the introspective opinion of W. subject that the imposition of a retarding weight tends to reduce errors of both classes and to cause greater steadiness.
It should be added that there is evidence of an occasional letting-go of voluntary control, so to speak, resulting in a large increase in mean error, as already pointed out, or a large increase in negative constant error, as shown on all individual records, and it would seem then that the matter of cortical control is more vital and indispensable for the restricted movements.
The effect of weight-retardation on visual records is to reduce the error and steady the ruling of the less dexterous hand to a much more marked degree than for the well-trained hand.
In the l.h.e.c. records the lack of corrective effect of visual control is marked, as in the case of free movements, but the dip in the curve at 30 to 70 is not noted in the free ruling and should be considered as a distinct shortening due to weight-retardation before discriminative processes have oriented the subject.
Without considering the accelerating weight-records in detail note that:
The effect of weights (less than that necessary to cause pain or fatigue), either tending to accelerate or retard motions, is to reduce both mean and constant errors and to render more uniform or more uniformly increasing or decreasing such errors, except in the case of l.h.e.c., where constant errors are greater positively with the weight-pulling and greater negatively with the weight-retarding, than for free motions; that is, the effect of the weight is natural, and shows no signs of inhibition in this particular case.
There is no such marked fluctuation in error for the pull-records as was noted for the weighted curves, and it is further noted that the individual pull-records are more bunched or consolidated about some mean than are the free-movement curves. This suggests that the accelerating weight is a decided help for accuracy and regularity, and it would seem to call for less voluntary control than for either of the other movements.
Further, as the effect of pulling weights is to equalize the accuracy of movement of the hands, the hypothesis is proposed that weights either accelerating or retarding the movements of the hand tend to equalize their accuracy or to promote ambidexterity as far as accuracy of straight-line mean errors is concerned.
L.h.e.c. rise for Ha., are horizontal for J., W., and Y., and slope downward for the other subjects, the net effect being a slight downward slope. The loss of accuracy and regularity when the visual sense is inhibited is to be noted in every case, it being especially marked for Bo., Li., and W.
As compared with the r.h.e.c., there is not sufficient evidence to lead to the conclusion that the right hand is a more accurate member than the left, but on the contrary the left-hand record for non-visual control is lower for both weighted series than is the right-hand curve. Contrasting this with the eyes-open records for free and weighted movements, the visually aided results show a greater accuracy and regularity for the right hand.
This leads to a proposition that the greater dexterity on the line of accuracy, of one hand, that is the right hand for right-handed subjects, and the left hand for left-handed subjects, is a matter of visual control and is in no sense due to the muscular sense or to automatic action, for without eyes we are ambidextrous as far as accuracy of linear movements is concerned; the proposition needs careful scrutiny in application to the general question, but is held to be correct within the range of experiments.
We are tempted to extend this matter somewhat in the following way, by saying that there is no evidence deducible from this research that there is hereditary preponderance of activity or accuracy of one hand or one leg (as shown later) over its mate, and the baby is brought into the world with an equal capacity of accuracy of both members.
It is, then, an evolutionary matter, not racial but individualistic, and right-handedness or left-handedness is largely a development after birth. Our system of education is responsible for the over-development of one hand, and such a case as that of Dr. Anderson of the Yale University Gymnasium, who in class demonstration cannot instantly tell which hand is being used to actuate the chalk at the blackboard, is the normal symmetrically developed man.
The school reform for ambidextrous training is radical enough, but seems a logical conclusion of the argument. Apologies are appended for driving the argument beyond the limits of the investigation, but it is hoped that the enquiry is at least suggestive.
For 14 cm. lines,
weight-retarding movements:
For the average of nine subjects:
The weight reduces errors and promotes regularity in the case of both mean and constant errors, nor does it tend to cause underruling, save in the case of left-handed subjects for l.h.e.c. records. There is a gain, in general, when the visual factor is introduced.
For mean errors,
(1) right-hand curves are horizontal, while the visual records show increasing error and l.h.e.c. a reduction of errors;
(2) the right hand gives slightly better results;
(3) note that l.h.e.c. record is equally good for free or weighted movements.
For constant errors,
(1) r.h.e.o. and l.h.e.o. curve downward, while both non-visual curves slope upward;
(2) the left hand seems equally efficient, as compared with the right hand.
For individual cases,
note (1) fatigue-spots are more numerous than for free movements, especially for the left hand;
(2) weight reduces both mean and constant errors and to a less extent even records.
For mean errors,
(1) visual control reduces errors;
(2) the weight tends to equalize the accuracy of the right and left hands.
For constant errors,
(1) there is no general testimony showing shortening of lines at high speeds;
(2) the less trained hand is more helped by the weight, especially for non-visual work.
The evidence for right- and left-handed subjects is inconclusive, and we cannot finally say that the more trained hand is capable of greater accuracy.
Weight-accelerating movements:
The average of seven subjects:
The accelerating weight reduces mean and constant errors, and improves regularity of curves, except for l.h.e.c. constant-error record. There is some evidence that a pull causes overruling, while a retarding weight causes underruling, but there are exceptions enough to warrant care in finally accepting this statement. Visual control with accelerating weight reduces error more than the weight acting alone.
For mean errors,
(1) weight reduces errors for r.h.e.o. and l.h.e.c. as compared with free-movement records, while the other two curves are inconclusive;
(2) visual sense helps in accurate ruling;
(3) non-visual records are not reduced, as a rule, from the results of free motion.
For constant errors,
(1) the accelerating weight tends to greater accuracy, with an exception for the-non-visual records.
No testimony of marked importance is to be noted in comparison of right-handed and left-handed subjects; the more trained hand shows greater accuracy in some cases, but fails to excel in others; so the data is inconclusive.
For individual cases we find:
(1) the acceleration records are more accurate and regular, and present fewer lapses than the free or retardation results, suggesting greater ease with weight assisting;
(2) visual control is prominent throughout, and evidence shows that this sense is the greatest factor in the predominance of the more trained hand; the non-visual records should and do show no marked difference in the hands;
(3) a weight tends to equalize accuracy of hands;
(4) the overruling effect of weight is over-corrected in some cases for constant error of low rates.
Constrained movements of 1 cm.:
The average is of seven subjects, three of them being left-handed:
With weight-retarding movement, there is no reduction of mean error with visual control of right hand, but there is with the left. Constant errors show little reduction for either hand with eyes open.
The facts would seem to warrant the hypothesis that, for the left hand, a movement uncontrolled visually, whether restricted by a weight or not, can be made with greater accuracy, when time is permitted for discriminative and reflective processes and visual-control results in about the same error whatever the speed, while the right-hand motions show no such evening effect of visual control with the weight-records or even reduction of error; the free movement, however, does show a reduction of error.
A general statement may be deduced that, for lines of 10 mm. in length, there is no difference in either mean or constant errors, when a weight is imposed to cause retardation, provided the weight is not large enough to cause pain or fatigue.
By separating the averages for right- and left-handed subjects, it may be further said that:
Visual control is not efficient to reduce the error and no particular gain in regularity can be noted. The left-handed subjects show, for the left hand, much better results without visual control as far as the free motion is concerned.
While somewhat contradictory, it may be stated that constant errors are reduced by the weight addition, and there is some evidence leading to the belief that the ruled line is shorter when the weight acts as a retarding influence.
INDIVIDUAL RECORDS
Considering lines 10 mm. long with a retarding weight:
A glance over the seven individual records shows some considerable increase in both constant- and mean-error irregularities, as compared with the free-motion curves, as well as in actual errors; there are distinct losses of volitional control for both classes of errors, especially at or near the ends of the series.
There are cases of very low mean error to be found on all records, where the value is 1/4 mm. or less, and, while the same phenomenon is found with free motion, it is more marked here and occurs more frequently; in most cases it seems as a drop from errors of larger values rather than a gradual matter, as if the subject realized the large error and exerted unusual volitional control to correct and produce a very accurate record, but found that the attention needed was beyond his will-power, as shown by the immediate lapse of accuracy.
There is an indirect confirmation of this view from the introspective testimony of the subjects.
The visual element steadies but does not reduce mean errors when weight is retarding.
The general shape of curve for eyes closed is downward 20-40 beats, and rising for the rest of the series; it is less regular, but more accurate than the visual results.
The fact that constant errors are mostly positive leads to a denial of any inhibitory effect of the retarding weight.
For 1 cm. lines,
weight-retarding movements:
For the average of seven subjects we find:
(1) visual control does not improve accuracy or regularity as in free movements;
(2) a retarding weight tends to make errors constant whatever the speed-rate;
(3) the testimony goes to show that the free-movement records are more accurate than the retardation ones.
Mean errors are:
(1) no more accurate and perhaps less regular, when the weight is imposed;
(2) right- and left-handed subjects are equally accurate.
Constant errors:
(1) the more dexterous hand is superior for coördinations requiring accuracy;
(2) ruled lines are slightly shortened in some cases;
(3) weight-records do not give more accurate results as compared with free movements.
For individual records we find:
(1) retarding weights increase errors and irregularity;
(2) fatigue-points are more marked and frequent than for free movements.
Mean errors,
(1) the visual factor is of some value, but the testimony is varied; right hand for increased regularity only, and left hand for greater accuracy only;
(2) curves are horizontal or reducing with speed-increase.
Constant errors,
(1) the more dexterous hand coördinates better;
(2) all errors are positive;
(3) visual control helps only for regularity;
(4) curves are horizontal or rising.
With weight-accelerating movements, the average record shows a sudden rise in mean error at both ends, not in evidence with free or retardation results.
In general it is to be noted:
(1) that the visual element is of no value for reducing the error, and of little value for promoting regularity;
(2) that the pull-records are closely comparable to the free-motion records, and the accelerating influence of the weight is imperceptible;
(3) that the pull-records are more regular and closer to the free-motion curves than are the weighted records, especially at the ends of the left-hand curves.
For constant errors:
It is more in accord with the facts to say that the imposition of a weight tends to reduce the constant error, and this is more marked when the weight acts in pulling or to accelerate the motion.
Comparing with the weighted curve, we find the same general type of rising curve, similarly located, and the same is true when compared with the free-motion curve. Constant errors are reduced, but slightly, and visual control is rendered nil, when the weight acts either to accelerate or retard the movement, and of the two, the accelerating effect is more marked, as reducing errors and promoting regularity.
There is no appreciable tendency for the weight to reduce the ruled lines when retarding motion, nor is the weight as accelerating, able to extend the line beyond the point set in the free motion.
When contrasting averages from right- and left-handed subjects it may be said:
As compared with free motions there is a slight reduction of error and irregularity more marked with the left-handed subjects, but a general close correspondence of results.
The question is now appropriate, why should the right-handed men show a reduced error for speed-increase, while the left-handed subjects show the reverse? Bearing in mind that the right hand is the more dexterous or better trained in the former case, it may be suggested that the order of record from 20 toward 200 beats is such as to cause more accurate results at the upper limit, in spite of the fact that less time is allowed for discrimination and adjustments; on the other hand, left-handed subjects have much less advantage of practice and habit in their use of the right hand, and will show the predominance of error, when the ruling is too rapid for careful discrimination.
It becomes a struggle between automatism, or semi-automatism, on the one hand, and discriminative processes on the other.
Visual control is not an advantage in the case of accelerating weight, and the large reduction in error with visual control for the free movements is not evident with weighted motions.
For the left-handed subjects we find that the eyes-closed record shows closer work than does the eyes-open curve; it is lower and nearer the line of 0 error; in this respect, it shows the same effect as with the free-motion curve, and to a less extent as for the retardation weight-record. The accelerating record is, however, more accurate and regular than either of the other curves.
It will be clear, then, as observed, that for constant errors, visual control tends to reduce errors and steady records whatever the speed-increase, as far as right-handed subjects are concerned, but this effect is not noted for left-handed subjects using the right hand, and, with their left hand, visual control is a disturbing element.
Further this erratic effect of visual control is less marked but clear when the weight acts as a retarding factor, but is much more noticeable for the free-motion record.
Individual records show few lapses of control for either errors.
The bulk of the evidence is that the weight imposition, whether acting as a retarding or accelerating influence, is effective in rendering the results more accurate and regular, though at least one subject exhibits the opposite effect for the accelerating weight.
The left hand is better for J., Le., and W., but is less regular for all subjects, save Le. and W., showing again a somewhat complex mass of testimony, from which we may conclude that the right hand is the more accurate member for right-handed subjects, and to a much less extent the left hand is preferred by the left-handed subjects.
Visual control is to be noted as effective for accuracy and regularity, except for Ha., where the curves closely intertwine, and for J., where the eyes-closed record is much better.
Weight-accelerating movements:
For the average of seven subjects we find
visual control is of doubtful advantage, for left-handed subjects, but shows a clearly marked reduction of error for right-handed subjects.
Mean errors are:
(1) similar in all respects to free-movement results;
(2) acceleration-curves are closer to free-movement results than are retardation records;
(3) the more trained hand shows reducing error for speed-increase, while the other hand shows increasing errors, because of superiority of practice-effects over the native tendency to increase error as speed-rate rises, for the more dexterous hand alone.
Constant errors:
(1) there is no tendency to overrule, as compared with free movements, when weight acts to accelerate movements, for there are even cases of lines being shortened with accelerating weights;
(2) a weight seems to negate the results of visual control, as a rule.
For individual records we find:
(1) fatigue-points, for the right hand only, are to be found in a few cases;
(2) weight promotes regularity and accuracy;
(3) visual control is effective only for reducing variations of error;
(4) the better trained hand is the more accurate in the records, to a slight extent;
(5) there are evidences of semi-hypnotic or dreamy states in the non-visual series.
COMPOUND MOTIONS
Series of records were taken at 100 mm. and 10 mm. bases for the hands, with what is called compound motion. This consisted in an additional movement of the hand that was not ruling with the pencil, in a similar manner, as regards the amplitude and general character of the motion, but in an opposite direction.
For example, suppose the left hand is ruling a 100 mm. line outward, or to the left; coincident with this movement would be a similar motion of the right hand outward or to the right. The origin of both motions, or the starting-ends of actual and imaginary ruled lines, was optional, it being desired to bring out the effect of such additional motion, as little complicated as possible with restrictions, as to its position or extent. Actually this distance varied from about 10 mm. where both motions were outward to 600 mm. for inward motions.
A comparison of such compound motions with single-hand records shows in general the following:
For 10 cm. lines:
The case for mean errors may be summed up by saying:
(1) left-hand records are less accurate and regular than the right-hand curves;
(2) visual control reduces error and irregularity in all cases, but is more marked with the left hand;
(3) errors increase with speed-increase;
(4) compound-motion records show little increase in error or irregularity, as compared with the simple motions.
For constant errors:
No marked peculiarities are to be noted, but in general,
(1) left-hand records are less accurate and regular;
(2) visual control reduces errors and irregularity;
(3) errors reduce with increase of speed, except for compound motion uncontrolled visually;
(4) compound-motion errors are not much greater, nor is the irregularity increased.
INDIVIDUAL CASES
100 mm. hand with compound motions.
A glance at the charts shows for individual records a few examples of inhibition of voluntary control for both constant and mean errors, it being much more marked in the case of mean errors.
These lapses of control appear for constant errors for A. with l.h.e.c. at 160 and 180 beats, for mean errors for G. with l.h.e.c. at 200 and with r.h.e.c. at 180 beats; for Le. with l.h.e.c. at 50 and with r.h.e.c. at 160 beats; for A. with l.h.e.c. at 200 beats; thus giving evidence that the visual element has a steadying effect, and that the left hand is less reliable save for Le.
There seems reason for contending that the compound motion can be carried out, as arranged, without loss of accuracy or regularity on the part of the ruling hand, and further that the subjects are pretty generally apt to react to a given stimulus within certain rather narrow limits of accuracy.
The evidence is here pretty conclusive that the right-handed subjects, as a whole, show greater accuracy by about 25% for the more dexterous hand; but it will be wise to consider the individual cases on this point.
Greater regularity and accuracy for the right hand is attained by all right-handed subjects, while the preference of Le. for the left hand is clear but much less definite.
For individual cases:
The evidence again is fairly well marked that the more practised hand will give a better account of itself even when visual control is not called on.
The results for compound movements of the hand for 1 and 10 cm. lines are summarized as follows:
It should be kept in mind that the compound records were in all cases taken in connection with a duplicate series of lines for one hand, and called simple movements. These simple movements correspond with the free-movement records that have been considered already.
The purpose has been to bring out the modification of results that a compound movement introduces, rather than to bear heavily on intrinsic phenomena, i. e., comparison is deemed more important.
For lines 10 cm. long:
Average of seven subjects:
We find for mean and constant errors:
(1) left-hand records are less accurate and uniform;
(2) visual control increases accuracy and regularity, especially for the left hand;
(3) there is an increase as the speed increases for mean errors, and a decrease for constant errors;
(4) compound movements are practically as accurate and regular as the simple ones for constant errors.
For individual cases:
(1) a few lapses of control or fatigue-spots more marked for mean errors with the l.h.e.c., for the visual sense steadies ruling, and the left hand is less reliable;
(2) compound and simple records show close agreement;
(3) the more trained hand reacts more accurately, and with greater regularity;
(4) non-visual records show a cautionary shortening of line at low speeds, and another at the upper limit, the latter being due to physiological limitations.
For 1 cm. lines:
As far as averages are considered:
We may say, then, for mean errors:
(1) that visual control is effective for reducing errors, and increasing steadiness in both sets of records, being more marked with the less trained hand, the left;
(2) only in the case of the l.h.e.c. curves is the movement of the free hand noted as appreciably affecting the accuracy or steadiness of the record.
(3) eyes-closed records in general show a considerably greater error at 20 beats that practice rapidly reduces up to 40 to 60 beats.
We may note for constant errors:
(1) all errors are positive and confirm the earlier deductions on this point;
(2) visual control reduces error and improves steadiness of record;
(3) the free hand-movement does not affect either the accuracy or uniformity of results;
(4) errors do not increase with speed.
For individual records:
Comparing the individual cases of simple and compound movement, there is no particular reason for concluding that the compound movement is a disturbing influence as far as the records of all subjects are concerned, save possibly the lapse of G. at 20 beats, and on the other hand a case of greater accuracy and evenness for compound movements for Mo. with r.h.e.c. constant error.
It is, then, possible to extend the conclusion of the 10 cm. records, and say that both lengths of lines are ruled with a fairly constant limit of error, whether the movement be simple or complicated by movement of the free hand.
Individually there is testimony in favor of the gain in accuracy with visual control for Hu., Hy., and Le., while the crossing of curves for the other subjects shows that there is no difference in eyes-open and eyes-closed results, the general conclusion being in favor of the value of the eyes for accurate results.
For mean errors the right hand is more efficient in the case of A., Hu., Hy., and Me., while the reverse is the case for the rest, and the evidence goes to suggest that greater accuracy can be attained with the more practised hand.
For constant errors the right hand is more accurate in the case of A., G., Hy., only; Me. and Mo. are equally accurate with the hands, and the rest show a marked preference for the left hand, the evidence being thus conflicting, pointing to the theory of ambidextrous development on the lines of accuracy.
L.h.e.c. records are horizontal for all subjects except Hu., Me., and Mo., who show an upward slope to the curve. Evidences of visual control as giving greater accuracy are noted in general above 70 beats and individually for Hy. and Mo., only, the remaining records being so intertwined that no difference can be noted, all suggesting that the eyes are of but little assistance when the left hand is considered. The right hand is preferred with eyes closed by A., Hu., and Le., while four right-handed subjects testify that the less trained hand is more accurate.
The testimony here seems conclusive as pointing to a denial of the current notion as to the greater accuracy of the right hand for right-handed subjects, and of the left hand for left-handed subjects, and further suggests that visual control is a large factor in the supposed superior excellence of the hand mentioned.
SUMMARIZING
For lines 1 cm. long:
Average of seven subjects:
It may be said that:
(1) visual control reduces both mean and constant errors, especially for left hand;
(2) errors are constant whatever the speed;
(3) constant errors are positive showing overruling in all cases;
(4) there is no disturbance created by the second-hand movement, save for r.h.e.c. mean errors, where the accuracy is less for the compound records; this is probably due to the fact that this record shows the least evidence of voluntary control, and is thus most subject to disturbances;
(5) there is a marked reduction of mean error 20-50 beats, probably due to practice.
For individual cases note:
(1) fatigue-spots for non-visual mean errors only;
(2) the equality of result of both types of movements is noted for all cases;
(3) the non-visual right-hand records for some subjects are more accurate;
(4) the more trained hand is not, as a rule and subject to exceptions, the more accurate one, especially for the non-visual records; and
(5) there is evidence that the superior accuracy of the right hand for right-handed subjects is largely a matter of visual control.
HEAD-RECORDS
There was no attempt made to differentiate the visual element because the very movements of the head prevent the full use of the eyes; as a matter of fact, the subject's attempt to make use of the eyes and the aid is more marked at slow speeds and upon facing the apparatus. It is to be noted here that the visual element, as reducing the error at low speeds, is equally marked whether the eyes are directed toward the recording pencil or not. This raises an interesting question as to the direction the eyes must take for the optimal result; must the eyes be fixed on the moving pencil, on its immediate surroundings, or may they wander at will about the surrounding objects?
My own introspective testimony, corroborated by others, who have acted as subjects for this investigation, is that the eyes are most effective when gathering spatial relations in a gross way, and it may be expected that the effects of visual control as reducing errors will be equally efficient, whether the recording pencil be screened or visible, provided it be possible to bring on the retina objects that are grouped about the centre of attraction, the pencil, but not in its immediate neighborhood.
The records show that there is underruling at the higher speeds because of physiological limitations; but this shortening is greater for the backward movements, for the position of the subject is such as to lead to greater uncertainty as to the exact length of ruled line, and it is probable that a cautionary or inhibitory feeling is the cause of this shortening beyond what will be clearly due to inability to perform the desired movement.
Further, visual control is effective, in the case of constant errors, in lengthening the ruled lines at high speeds, and thus reducing the negative constant error.
While the muscular control of the head is a constant, whether the movement be forward or backward, it is less effective for constant error reduction when the head is moved backward. Consequently, while the backward and forward curves are fairly well in correspondence, there is some reason for offering the proposition that either the eyes are of assistance in forward movements to reduce mean errors at high speeds, and they are of no such value for backward movements, or the muscular control of the platysma myoides, trapezius and associated muscles of the neck group is more nearly perfect for movements of the head forward than for backward motions, the latter being to my mind the better hypothesis.
The results for head-movements for lines 1 and 10 cm. long are summarized:
For lines of 10 cm. length:
Average of six subjects:
For mean errors:
(1) the curve for head-forward and head-backward closely corresponds to l.h.e.c. record; the errors increase by 50% with increase of speed-rate, suggesting that
(a) visual control is negligible, as far as seeing the moving pencil is concerned;
(b) control of head for forward equals that for backward movements.
For constant errors:
(1) there is underruling at high speeds because of the usual physiological limitations, and this is more marked for head backward results, suggesting that
(a) spatial relations are obtained, when the apparatus is visible, that tend to correct underruling, or
(b) an extra inhibitory effect, due to lack of knowledge of spatial relations, is added to the normal physical shortening and the subject moves the head a less distance than is naturally possible; or
(c) the muscular control is less complete for movements of the head backward.
For individual cases we find:
(1) fatigue-lapses are less in magnitude than for the hands, because the head-movement can be only a fraction of the forearm-movement;
(2) mean errors increase and constant errors decrease with speed-rise;
(3) similarity of individual head-forward and head-backward curves is suggestive, taken with the fact that no typical form of curve is to be found;
(4) head-backward constant errors are greater and less regular in all cases, suggesting that the eyes, in head-forward records, by getting spatial relations, are more efficient.
For lines 1 cm. long:
Average of six subjects:
For mean errors note:
(1) the head-backward records are less regular than the head-forward ones, and rise a little with speed-increase, showing visual assistance for accuracy or better muscular control for the forward movements or both;
(2) the constant errors show shortening of ruled lines at high speeds a little more marked for the head-forward results;
(3) there is constant overruling.
Individual cases suggest:
(1) fatigue-spots are apparent, especially for head-backward movements;
(2) errors do not increase with speed;
(3) the movements of the head forward are under better control.
FOOT-RECORDS
10 cm. records show that
(1) the eyes are of no assistance as to increasing accuracy but help in promoting regularity of error;
(2) a shortening of ruled lines with speed-increase is noticeable, and is probably due to the usual physiological reason;
(3) the feet are capable of less accurate motion than the hands, but show better results than the head;
(4) mean errors increase but constant errors decrease with speed-increase.
Individual records show:
(1) less violent fluctuations of errors in all respects than do the results of head or hands, for vertical foot-movements are of less extreme extent than are arm- or head-motions;
(2) that for visual control with mean errors, no foot is the more accurate, and there is no reason to believe that the feet are unequally educated.
1 cm. records show, as far as mean errors are concerned, that:
(1) visual control is of no value as either reducing actual errors or as effecting greater regularity;
(2) Errors for foot-movements are no less, but considerably more regular than for head-motions;
(3) errors for hand-movements are more regular, and only 50% of the results for either head- or foot-movements;
(4) all curves are horizontal;
(5) there is no appreciable advantage as to accuracy or regularity that can be attributed to either foot. The evidence goes to show that the subjects are ambipedalous, if it be permitted to coin such a word.
In general, we find that, as far as constant errors are concerned,
(1) visual control does not help to reduce actual errors or promote uniformity;
(2) errors for foot-movements are less than the head records, and but little greater than the hand results, while the regularity for the feet is comparable to the hand, and much greater than for the head;
(3) all curves are horizontal;
(4) there is no particular advantage that either foot has over the other either as to accuracy or regularity.
The evidence is that the subjects were ambipedalous, as far as ability to reach a certain point equally well by either foot is concerned. The popular notion has been to the contrary, and it is a point of considerable importance to note the last point.
For example, in kicking, as developed by football trainers, it is commonly assumed that the right foot for right-handed subjects should be developed, and the opposite foot for left-handed men. Or again, in the case of a person lost in the woods and walking in a circle, it is observed that right-handed persons will turn to the left; probably because of the pace of the right foot being slightly longer than the left. My reply to this evidence will be that the data herein presented is for vertical movements of the foot, starting from the floor in every case, the subject being seated in a chair.
On the other hand, it is an entirely different movement, calling for a much different and greater muscular control in the case of kicking or walking that must be considered. For this reason the evidence, while conclusive within its range, is not offered as more than suggesting that the feet are equally well trained for the usual adjustments, and only an exhaustive investigation covering all possible foot-movements will settle the question.
The result for foot-movements for lines 1 and 10 cm. long is here summarized.
For lines 10 cm. in length:
Average of seven subjects:
Note in general that
(1) l.f.e.c. mean error is most erratic, while the same curve is the most accurate, as far as constant errors are concerned;
(2) the left foot mean and constant errors are slightly greater than those for the right foot, for visual records;
(3) mean errors increase and constant errors reduce with speed-increase;
(4) the visual sense improves regularity, but does not reduce errors;
(5) there is a physiological reason for the shortening of lines at high speeds;
(6) the feet are more under control than the head, but less than the hands.
For individual records:
(1) fatigue-lapses, all for non-visual, are less numerous and of less magnitude than for the hands and head, for the vertical movement of foot is likely to be of less extent than that of head and hands for the particular motion required here;
(2) there is no foot capable of being called more accurate than its mate;
(3) the eyes appear to be of no value for reducing or regulating errors for foot-movements.
For lines 1 cm. long:
Average of six subjects:
It may be said in general that
(1) the visual sense is valueless for promoting accuracy or regularity of curve;
(2) errors of foot-movements are more regular and, for the constant errors, more accurate than for the head-records;
(3) errors of foot-movements are less and less regular by 50% as compared with records for the hands;
(4) errors do not increase or decrease with speed-changes;
(5) the feet are equally accurate.
For individual results:
(1) fatigue-lapses and cases of large error-increases are noted in a number of subjects, both for visual and non-visual records;
(2) further, evidence is available as to the indifference to visual control;
(3) no preference for either foot is to be discovered.
The results for individual choice of rhythm.
In this series of records, the metronome was dispensed with, and the subject was permitted to react as he desired, taking the speed preferred because of ease, pleasure, or other reason.
Records were obtained for six subjects for feet, head, and hands, both single-hand and double-hand movements, all for lengths of line 1 and 10 cm. The charts for individual choice were plotted for a comparison of speeds rather than for accuracy.
It was noted for the hands:
(1) that every subject reacts more rapidly with the left hand;
(2) the eyes had little effect as to changing the speed-rate;
(3) single and double hand-movements were equally rapid.
Some subjects, as A., react more rapidly for the shorter lines, though no clearly marked evidence of this speed-increase is to be noted.
For the head, the results for both eyes opened and closed show the impossibility of separating the optimal or preferred rate of speed on the score of visual assistance or because of direction of head-movement.
There is a close agreement of the subject as to his best speed, and this is independent of special conditions; for example,
A. selects 50-57 beats per minute for 1 cm. and 48-68 for 10 cm.; G. has a preference for 61-66 and 56-71; Hu. rises to 103-125 for 10 cm. and selects 68-82 for 1 cm.; Le. 52-55 for 1 cm. and 45-52 for 10 cm., and so on.
We may say, then, that free rate-choice for head-movements results in a selection of some rate of speed that is not affected by the visual sense or direction of movement, and is strictly individualistic, covering a range of 50-130 beats per minute, and not increasing as the amplitude of movement is reduced.
Turning to individual choice of speed-rate, for the feet it will be seen that
(1) the non-visual records closely correspond as to chosen speed, and there is a less close correspondence of visual speeds;
(2) the visual records are ruled at a lower rate in some cases, but A., G., and Mo. show little difference;
(3) there is a tendency to speed up as the series progresses;
(4) the shorter lines are ruled with greater speed as a rule, though G. and Le. fail to show this phenomenon;
(5) The left-foot records show a higher speed-rate for all cases.
Among many interesting points that cannot be examined in this connection, such as relation of voluntary choice of rate to the main line of metronome records as regards accuracy, the fact of the higher rate of ruling for the left hand and foot stands most prominent.
Whether a record of head-movements to right or left, or other devices to compare the sides of the body or to contrast arm and leg speeds, will bear out this testimony is as yet unknown, so that the writer prefers to announce the result and not now fit theory to data. It may be said that the records were taken in reverse order and rearranged, as regards right and left foot or hand, and, in addition, the initial foot-movement varied with the subject, some being right and some left.
We ask finally: Is the time in which the greatest exactitude is produced, the same for every group of muscles; that is, has every motor apparatus the same natural rhythm? and: Is this natural rhythm a constant rapidity for all motor nerve-centres or does it depend upon the complexity and character of the movement?
The comparison will fall first on the averages and finally on the individual records.
The hand-movements show the following results:
Constant errors for 14 cm.:
For simple and weight accelerating and retarding motions, there is a close agreement about 120 beats for the minimum error for visual and right-hand non-visual records; left-hand non-visual records are spread more, but will also average the same.
For 10 cm. simple and compound movements the visual minimum errors are at 180-200 beats, while with the eyes closed the results are grouped about 60 beats; one record, that for l.h.e.c., has two minimum points at 60 and 180 beats, the latter being clearly a crossing of the 0 error-line, because of physiological limitations.
For 1 cm. simple and weighted minimum errors are grouped between 20 and 60 beats, while the simple and compound group show less regularity and a tendency to group minimum errors at 100 beats.
The head-movements show for both 1 and 10 cm. lines a minimum error at 180-200 beats, there being, however, one exception at 100 beats for 10 cm. head-backward movements.
The foot-movements show minimum errors at 80 beats for the right foot, and 180 and 100 beats for the left foot, visual and non-visual respectively.
Bearing in mind for a moment the individual choice records, there seems here a suggestion that the left foot is capable not merely of higher speeds, but of minimum errors at the higher rates as compared with the right foot.
No such differentiation of the hands can be discovered, however.
Mean errors:
For the hands:
For 14 cm. for simple and weighted results we find that the right-hand and left-hand eyes-open minimum errors are at 180 beats, but the non-visual left-hand minimums are at 30 beats.
For 10 cm. simple and compound records we find all minimum errors are between 160 and 200 beats.
For 1 cm. simple and weighted results there is a scattering of minimum errors from 20 to 200 beats, with a heavy preponderance at 200, and the same is true for the simple-compound series.
The head-movements minimum errors are at 40 beats without exception.
The foot minimum errors are distributed from 20-30 beats for the left foot to 160-180 for the right.
It is thus evident that each group of muscles and each motor centre has its own optimum, and that the conditions of complexity, resistance, etc., influence greatly the accuracy of the periodic movement impulse.
THE MOTOR POWER OF COMPLEXITY
BY C. L. VAUGHAN