Sinistral inverters do not possess an anomalous visuomotor organization

NOTE SINISTRAL

INVERTERS

DO NOT POSSESS AN ANOMALOUS ORGANIZATION

VISUOMOTOR

JOHN L. BRADSHA~.’ NORXIAN NETTLETOS and KAREN SPEHR Department

of Psychology,

Monash

University,

(Receiued

2 February

Clayton,

Victoria

3168, Australia

1982)

Abstract-MoscovtTcH and SMITH (Science 205, 7 10-713, 1979, and Nertrops);choloyin 17. 637644, 1979). while failing to confirm Levy and Reid’s general hypothesis that sinistrals writing with an inverted posture have predominantly uncrossed or ipsilateral motor pathways, nevertheless reported that they may possess an unusual visuomotor organization. We incorporated an extra (arm-acrossthe-midline) condition into a version of their study. Not only could we not replicate their original findings, but we believe that their data may have been contaminated by spatial compatibility effects which require the crossed-arm condition for elimination. Sinistral inverters in fact appear to have exactly thesame motor and visuomotor organization as noninverters and dextrals. A value of4 msec for transcommissural transmission times was obtained, which corresponds well with other electrophysiological and behavioral esti_mates.

LEVY and REID [I. 21 published a study which has exerted a strong influence on experimental and educational psychology and neuropsychology. They claimed to have shown that the hemisphere which is dominant for verbal and spatial functions in a given individual can be reliably predicted by a knowledge of that person’s hand preference (left or right) and hand posture (inverted or normal) for writing. Thus in normal writers language dominance occurs in the hemisphere contralateral to the writing hand, while inverted writers are supposed to exhibit the reverse (ipsilateral) organization, with in both cases spatial processing occurring in the opposite hemisphere. LEVY and REID [Z] further proposed that both writing postures are directly controlled by the language-dominant hemisphere via pyramidal libres; these they claimed are predominantly contralateral in normals and ipsilateral in inverters, the phenomenon of inverted posture being attributed to this ipsilateral pyramidal control and to partial agenesis of the corpus callosum. We have recently shown [3] that Levy and Reid’s general neurological model fails to receive empirical support, and is moreover probably based on certain misapprehensions and false premises. However, the specific postulate that hemispheric motor projections are primarily contralateral in noninverted writers and ipsilateral in inverted writers has been tested and partially supported by MOSCOVITCHand SMITH [4] and SMITH and MOSCOVITCH[S], the two reports covering essentially one and the same experimental study. These authors employed a reaction time experiment with lateralized visual, tactual and auditory stimulation. Subjects depressed a response key with the left or right index finger when they detected a stimulus in either sensory field (left or right). Noninverters were faster to stimuli on the same (ipsilateral) side as the responding hand in all sensory modalities. Inverters also showed this pattern in all but the visual modality, where they responded more quickly to stimuli on the side opposite (contralateral) to the responding hand. Moscovitch and Smith, while concluding that the bulk of their results challenge the Levy-Reid hypothesis (since it predicts the visual effect in all three modalities for inverters), nevertheless suggest that inverters may indeed possess anomalous visuomotor organization. So far there have been no reported attempts at validating such a conclusion. It is moreover possible that Moscovitch and Smith’s findings may have been contaminated by unwanted stimulusresponse spatial compatibility effects, despite their attempts to avoid this, and that even their weak support (in respect to possible visuomotor anomalies in sinistral inverters) for certain aspects of the Levy-Reid hypothesis is unwarranted. Thus it is very difficult to assess the effects of anatomical connectivity (e.g. the effects of a longer interhemispheric pathway when stimulus and responding limb are on opposite sides of the body in noninverters,

*Author

to whom requests

for reprints

should

be addressed. 605

606

NOTE

and, putatively.

on thesamestdetn invertsrst.uncontaminated is to emplo) ZI rumple reactton

bysp~tt~lcompattbtlitysffects ume paradigm with hlvcks

of untlsterall~

sttmult (and, consequently. controls to ensure central tixatton) so that there is no posiriuu uncrrrainr.v these conditions a pure interhemisphrrtc transmission time of around 4 msec has been reported.

presented

[6-g]. L’nder a value whtch

corresponds well to the number of synapses known to be involved [IO]. H owevcr. this procedure of blocked presen:stton was not adopted by hloscovitch and Smtth. whose obtained values (around IO msec) are in any case rather too htgh and perhaps further indicate the confoundin, 0 effects of spatial compattbtltty. The other way to unconfound these variables IS to subtract the spatial compatibility effect. This can be done with .m additional arm-across-the-body (i.e. crossed-arm) condition. such that in addition to the ortginal uncrossed condition employed by Moscovitch and Smith and Smith and Moscovttch, the ri,ght hand now presses a key on the left side of the body for a block of trials. and vice versa. In the crossed-arm condttton the confrolofrru/ relationship (where. e.g. the left hand responds to a right light with a key on the right) should be the faster. though by a smaller amount than the ipsilateral superiority in the uncrossed-arm condition. since now the effects of anatomical connectivity and spatial compatibility go in opposite directions. Indeed the above”smaller amount” (the difference between the mean of the crossed and uncrossed ipsilateral condtttons and the mean of the corresponding two contralateral condttions) will represent the effect due to anatomical connectivity. We report such an experiment to test this hypothesis.

METHOD There were 12 dextral subjects, 12 sinistrals who wrote wtth an inverted hand posture. and 12 sinistrals who normally adopted a non-mvcrted writing posture. In each of the three groups there were six males and six females. Noneofthedextrals had asinistral in theimmediatefamily, and all ofthesinistrals hadat least onesinistralsibhngor parent. Handedness was carefully ascertained by our usual pegboard, questionnaire and object manipulation procedures [ I I]; thus all dextrals demonstrated a preference for using their right hand in each of the following tasks: writing, throwing a ball, using a racquet. striking a match. ustng a hammer, using a toothbrush, and brushing fingernails. Manual speed was measured over eight trials with a stopwatch to time the rate at which subjects could move IO dowelling pegs from a row of holes 1.3 cm in diameter to another row of holes separated from the first by 20.3 cm. All experimental dextrals exhibited a faster mean tome for the right hand. Analogous criteria for acceptance were employed for the two sinistrai groups of subjects. We followed the procedures of LEVY and RFII) [I, 21 and MCISUJVITC~I and SVITH [4, S] in determining hand posture. All subjects had normal or corrected viston. To control for any confounding effects ofeye dominance on visual field differences, each subject was given an acuity test using a Bausch and Lomb Orthorater for near and fAr vision for each eye tested independently. None ofthe selected subjects had more than two points difference between eyes for near and far vision. All subjects were paid volunteer undergraduate or postgraduate students at Monash University.

Apparurus

and procedure

Subjects sat with chin in a chin rest and fixated upon a red light-emitting diode placed as a fixation point at a distance of 80 cm at one end of a wooden cabin, The cabin enclosed the subject’s upper body and the stimulus lights and response buttons. Four stimulus lights were arranged in two pairs, with one pair placed on either side of the fixation light. The two members of a pair were placed so that one was 5.5 cm directly above the other, and both were 15.5 cm either to the left or the right ofthe central fixation light. The latter lay on the axis running between the upper and lower lights on either side. There were four vertically-disposed response microswitches arranged to correspond spatially to the four stimulus lights, two (one above the other) on the left, and two on the right at a corresponding position. Each pair was situated 21 cm from the subject’s midline, as this was found to be the most comfortable distance for the two response positions, arm crossed and uncrossed. Since the crossed-arm condition enabled us to subtract the effect of spatial compatibility. we employed a design incorporating a untmanual two-finger choice response; the hand rested sideways, thumb downwards, palm out, the fore and middle finger each touching a microswitch. The left hand was employed on either the left set (uncrossed condition) or the right set (crossed-arm condition, the left arm crossing the body). Likewise in other blocks of trials the right hand was employed on either the right set (uncrossed) or the left (crossed). Subjects pressed the lower switch (wtth the forefinger ofthe responding hand) ifthe lower light flashed on either side, and the upper switch (with the middle finger) for the higher light. This unimanual choice design avoided the need either for catch trials [4] or for variable foreperiods [9] to prevent anticipatory responses. Each trial was preceded by a warning tone of 1 kHz which lasted for SO0 msec, after which the central fixation light flashed on and offin 100 msec cycles for I sec. This was followed by a stimulus presentation of 100 msec duration. Trials were presented in blocks of 64, within which stimuli to the left or right were presented in a pseudorandom sequence. There were eight experimental blocks per subject, one quarter requiring an uncrossed response with the left hand, one quarter a crossed response with the left hand, and the rest involving similar conditions with the right

607

NOTE

hand. ;\ different counterbalanced sequence of blocks was employed for each subject. and the expertmental series was preceded by practice blocks from each type of condition until performance stabilized. Any reaction time was excluded which exceeded by 200 msec the subject’s overall experimental mean. No subject had more than five such long response times. and most had none. The presentation ofstimuli and the recording ofresponse time was under thecontrol ofa National Semiconductor RMC SO/l-( micro-computer.

RESULTS AND DISCUSSION The latency data were subjected to Analysis of Variance by Group (Dextrals, Inverted and Noninverted Sinistrals). Sex. Hand, Visual Field. Finger and Position (arm across or out from the body midline), with nonrepeated measures on the first two factors. Only two main effects reached significance, Finger [F (I, 15)= 16.0. P <0.005]. whereby not unexpectedly the forefinger proved to be 13 msec laster than the middle, and Position. The latter effect demonstrated that. again not surprisingly, the crossed-arm posture (410 msec) was 12 msec slower than the uncrossed (398 msec). F (1. 15)= 17.4. P
I. Reaction

times in msec by visual field (LVF-left visual field. RVF-right visual field) hand and hand position (arm across or out from the midline), for the three groups of subjects

Dextrals Left hand, crossed, LVF Left hand, crossed, RVF Right hand. crossed, LVF Right hand, crossed, RVF Left hand, uncrossed. LVF Left hand, uncrossed, RVF Right hand, uncrossed, LVF Right hand, uncrossed. RVF

-

397 317 390 396 385 402 387 369

Sinistral Noninverters 421 407 415 415 400 411 406 389

Sinistral Inverters 422 419 428 430 394 408 419 403

procedure adopted by Moscovitch and Smith) the ipsilateral relationship (left hand-left field, right hand-right field) was indeed I6 msec laster than the contralateral relationship (left hand-right field, right hand-left field). in the crossed-arm condition (which we introduced as an innovation) the mean of the ipsilateral relationships (left hand-left field and right hand-right field, 414 msec) was 8 msec slower than the mean of the contralateral relationships (left hand-right field and right hand-left field. 406 msec). Consequently averaging across the crossed and uncrossed conditions, and thus subtracting the effect of spatial incompatibility, the ipsilateral relationship (402 msec) proved to be 4 msec faster than the contralateral (406 msec), a value which is in remarkably close agreement with other empirically [6-91 and theoretically [lo] derived values for “pure” transcommissural transmission times. Moreover this value did not differ significantly between any of the three handedness groups (indeed contrary to the prediction of Moscovitch and Smith it proved to be fractionally greater for Sinistral Inverters), as the appropriate interactions involving Group were all nonsignificant. In our uncrossed condition we were also quite unable to confirm the original finding of Moscovitch and Smith of anomalous performance by Sinistral Inverters, since we found that these subjects gave exactly the same (15 msec) ipsilateral superiority (over contralateral) as did the Sinistral Noninverters (15 msec) and the Dextrals (17 msec). These values probably represent two components, approximately 4 msec for interhemispheric transmission time, and the balance for spatial compatibility effects. We cannot therefore concur with Moscovitch and Smith on either theoretical or empirical grounds that sinistrals writing with an inverted hand posture have a peculiar visuomotor organization, though we do indeed agree with them in disputing the general hypothesis of Levy and Reid. While the interaction of Group, Position, Hand and Visual Field was nonsignificant, F (2. 15)= 1.04, and there was in fact absolutely no evidence in the uncrossed condition of differential ipsilateral/contralateral effects between the three subjects groups, there appeared to be a trend in our data for the contralateral superiority in the crossed-arm condition to be greatest for dextrals (14 msec), intermediate for sinistral noninverters (8 msec) and smallest for sinistral inverters (2 msec). However, when these data were subjected to a post hoc ANOVA by Group and Ipsilateral/Contralateral sensorimotor relationship, the interaction was nonsignificant_ F (2, 1 I)= 1.58. Such an effect, had it been significant, could have reflected weaker lateralization with respect to spatial relationships and

608

SOTF

compattbllit>; effects m simstral mierters. cf. [I. 121. and could perhaps somehow anomalous hndings reported bq Mosco\itch and Smith m the visual modalit!.

have

been related

IO the

.~~kno,~/r~lyrmmt.~-This Hark was supported b> the Australian Research Grants Committee. We Hlsh to thank JOHV DICK and Boa Wtwm for their help in desqnin_e and constructing apparatus and for progammtng Hark.

REFERENCES I. LE\~. J. and Rt~t>. 51. Variations in v+riting posture and cerebral organization. Sciencr 194. 337 339. 1976. 7. LEE). J. and REID, M. Variations in cerebral organization as a function of handedness. hand posture in wrmng. and sex. .I. e.~p. Ps~chol. Gen. 107, 119-144, 1978. 3. WEIIER, A. M. and BRADSH~~~, J. L. Levy and Reid’s neurological model in relation to writing hand/posture: An evaluation. Psycho/. Bull. 90, 74-88, 1981. 4. MOWWITCH, M. and SLIITH. L. C. DilTerences in neural organization between individuals Hith mberted and noninverted handwrtting postures. Scirwr 205, 710.-713. 1979. 5. SVITH. L. C. and MOXO~IT~H, M. Writing posture. hemispheric control of movement and cerebral dominance in individuals with inverted and noninverted hand postures during writrng. Newop~ychologia 17, 637444. 1979. 6. BERLLCCHL G. Interhemispheric integration of simple visuomotor responses. In Crrebrc~/ Corrrk~tes oj Conscious Exprrir~e, P. A. BUSER and A. ROU(;I.CL-BISEK (Editors), Elsevier/North-Holland Biomedical Press, Amsterdam, 1978. 7. BERI.UCCHI.G..CRE~. F.. DI STEFANO, M.~~~TA\sINARI.G. Innuencrofspatialstimulus-responsecompatlbillty on reaction time of ipsilateral and contralateral hand to lateralized light stimuli. J. rxp. Psycho/. Hum. Prrcrpr. Per/brtf~ 3, 505-S 17, 1977. 8. RIZZOL,ZTTI, G. Interlield diNerewes in reaction times to laterallzed visual stimuli in normal subjects. In Srr~crwr ant! Funcrion ofCerebra Commissures. I. SwEt.E Rvsst~~.. M. W. HOF and C. BERLCU-HI (Editors). Macmillan. London, 1979. 9. AVZOLA, G. P., BERTOLOVI. G., BtIr’HTEL, H. A. and RIZZOLATTI, G. Spatial compatibility and anatomical factors in simple and choice reactiontime. Nruropsycholo~gicz 15, 295-302. 1977. IO. S~AI)LOW, H. A., GESCH\~INII, N. and WAXYAN, S. G. Commissural transmissionin humans. Science 204. 530-531, 1979. I I. PATTI~RSOX., K. and BKADSHAW, J. L. Differential hemispheric mediation of nonverbal visual sttmuli. J. e.rp. Psycho/. Hum. Percept. Prrjbrm. I, 246-252, 1975. 12. W,\RSHAL, D. and SPIRIXSO, W. W. Concurrent verbal-manual performance in inverted and non-inverted writers. Prrcrpr. Nor. Skills 53. 123-126, 1981.

RESUME Moscovftch et Smith (Science, 205, 710-713, 1979 et Neuropsycholoqia, 17, 637-644. 1979), tout en ne pouvant confirmer l'hypothke globale de Levy et Reid que chez les gauchers icri;ant avec une posture inverse les vofes matrices non-crofsQes ou IpsilatPrales oridominent, ont cependant rapports qu'ils pourrafent posseder une organfsatfon visuomotrfce inhabituelle. Nous avons ajouth dans une rsolique de leur travail une condition suool6mentaire (le bras croise la liqne Nous n'avons pu reproduire leurs observations o;iddiane). ginales. En outre, nonuspensons que leurs don&es ont pu itre contam!n&s par des effets de compatibilitg spatiale qui ne peuvent etre ilfmfnis que par une condition 0; le bras croise la lfgne kdiane. Les gauchers avec posture d'kriture inversie semblent en fait avoir exactement la m&e organisation motrfce et visuomotrfce que les gauchers sans posture inversee et que les droitfers. linevaleur de 4 msec pour le temp5 de transmission Vans-comnissural a ht.6obtenue, ce qui correspond bfen aux autres estimations Blectrophysioloqiqueset comportementales.

609

NOTE

Zusammenfassung: Moskovitch nicht

und Smith

bestktlgen,

schreiben,

vorwlegend

Dennoch

die

Bedingung

van Levy der

durch

welche

durch

eliminiert

werden.

tats2ichlich als

Wert

4 msec

was

gut mit

iibereinstimmt.

iiber

die

nicht

experimentelle

gleiche

anderen

die

Linkshsnder Wir

haben

Mittellinie)

mit

invertierter

motor&he

ijbertragung

elektrophysiologischen

eine

besondere

Version

ferner,

des

das

waren,

Uberkreuzenden

Handposition

und Rechtshsnder. fiir

der

da8 ihre

beeinflui3t

Armes

scheinen

und visuo-motorische

Schreiber

haben.

ungewijhnliche

die ursprUngllchen

glauben

Bedingung

Bahnen

eine

in eine

konnten wir

Handstellung

motorische

ijbereinstimmungseffekte

invertierte fiir

Wir

Hypothese

invertierten

ipsilaterale

kdnnten. die

wiederholen.

Linkshdnder

genau

zu haben van

nicht

allgemeine

einer

da0 dlese

eingebaut.

rlumliche die

oder

haben

(Arm

und Reids

Autoren

Ergebnisse nur

und Reids die mit

Autoren.

Organisation

experimentelle

Befunde

Levy

ungekreuzte

berichteten

visuo-motorische

Studie

konnten

dafl Linkshander,

Organisation Es wurde

Kommissurensystem und verhaltensm33igen

ein

gemessen, Schstzungen