Color-matching, color-naming and color-memory in split-brain patients

Color-matching, color-naming and color-memory in split-brain patients

OOZS-3932/Sl/O40523 l%2.00/0 1981 Pergamon Press Ltd. Neurop~ycholog~a, Vol. 19. No. 4, pp. 523 541, 1981 Prmted in Great Bntam t> COLOR-MATCHING, ...

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OOZS-3932/Sl/O40523 l%2.00/0 1981 Pergamon Press Ltd.

Neurop~ycholog~a, Vol. 19. No. 4, pp. 523 541, 1981 Prmted in Great Bntam

t>

COLOR-MATCHING, COLOR-NAMING AND COLOR-MEMORY IN SPLIT-BRAIN PATIENTS JERRE LEVY* Department

of Behavioral

Sciences,

University

of Chicago,

Chicago,

Illinois, U.S.A

and COLWYN Department

of Psychology,

TREVARTHEN

University

of Edinburgh,

Edinburgh,

Scotland

(Rrcei~~d 19 Junuary 1981) Abstract-Bilateral chimeric stimuli were projected tachistoscopically to split-brain patients for the purpose of assessing hemispheric asymmetries in color-naming, color-matching and memory for colors ofwell-known objects. There was a strong bias for naming colors ofstimuli projected to the left hemisphere, but some patients were also above chance in naming colors of stimuli projected to the right hemisphere. In color-matching tasks, patients varied in the direction and degree of asymmetric control of responses, and asymmetry patterns varied within patients across different tasks, with symmetry of hemispheric control increasing as task complexity increased. Both hemispheres performed well above chance in memory for colors of objects depicted in line-drawings, and the right hemisphere appeared to perform somewhat better than the left.

of the left and right cerebral hemispheres in color perception has been a matter of debate for some years. Loss of the ability to name colors has been reported by a number of investigators [l, 23, and GESCHWIN~ and FUSILLO [3] described a case where color-naming disability was associated with a lesion of the left-hemisphere visual areas and of the splenium of the corpus callosum, suggesting that anomia for colors results from disconnection of visual from language regions. OXBURY et al. [4] have drawn a distinction between pure linguistic disruption as a cause of anomia for colors and the disconnection syndrome described by GESCHWINDand FUSILLO [3]. In both these disorders, however, a color-naming deficit results from a left-hemisphere lesion that either damages language regions directly or isolates them from visual processing regions. DE RENZI and SPINNLER [S] investigated subtle color discrimination not involving a verbal report, and found a significant inferiority in patients with right-hemisphere damage. SCOTTI and SPINNLER [6] observed that patients with right-hemisphere damage and visual field defects were inferior to others on the FarnsworthPMunsell 100 Hue Test, a finding consistent with CAPITANI et al.‘s [7] claim that patients with right parietal lesions have the highest error scores on this test. These studies of brain-damaged patients suggest that defects in color naming can be due either to a pure aphasia, to disconnection of visual from linguistic processing regions, or to THE ROLES

*Requests for reprints should Chicago, IL 60637. U.S.A.

be addressed

to: Jerre

523

Levy. 5848 S. University

Ave., University

of Chicago.

disorders in the color-perception system itself; the first two disabilities appear generally with left-hemisphere damage and the latter. with right-hemisphere damage. Investigations of normal people support the conclusion that the two hemispheres play differing roles in color perception and naming. PENNAL [S] presented one of 12 stimuli to the left or right field at a 30 msec duration, requiring subjects to press one of 24 colored buttons. arranged in a circle, to indicate their choice of a matching color. For both latency and error data, superior performance was observed for stimuli in the left visual field (LVF) as compared to stimuli in the right visual field (RVF). DIMOND and BEAUWNT 193 failed to find hemispheric differences in voice reaction time for naming tachistoscopically presented colors, but unlike the PENNAL study. the DIMONI> and BEACJMONTcolors were easily nameable and the dependent measure was a verbal response. Their results are consistent with the view that the hemispheres, though possibly using different strategies. are equally competent at discriminating and remembering nameable colors. Support for this possibility is provided in an investigation by S~HXWT and DAVIS [IO], who measured manual reaction times. Subjects were required to identify, as rapidly as possible, one of three color-words or one of three ink colors in which a word was printed. These stimuli were projected for 150 msec in the left or right field. For both word-reading and identification of ink color, words and ink colors were either congruent (e.g., the word BLUE printed in blue ink) or incongruent (e.g. the word BLUE printed in green ink). In the inkcolor identification task, no field difference appeared when words and ink colors were congruent. but incongruent stimuli induced a significantly greater increase in reaction time for the RVF than for the LVF. The field symmetry in the congruent task concurs with results of DIMOND and BEAUMWT 193 for nameable colors. The results for the incongruent task reflect, not a right-hemisphere perceptual superiority for nameable colors. but rather a greater right-hemisphere resistance to interference by color-words. The various studies reveal a right-hemisphere superiority for color discrimination when colors are difficult to name or describe, but equality of the hemispheres when colors come from an easily nameable set. Such a nameable/non-nameable distinction is similar to that pertaining to shapes. As MILNER [I l] and others have noted, studies of brain-damaged patients and of normal individuals indicate that the right hemisphere surpasses the left in shape discrimination and in memory for shapes that have no verbal labels or are resistant to verbal description. Many have suggested that processing strategies of the left hemisphere rely on language or language-related functions. whereas those of the right hemisphere depend on imagistic constructions closely representing the sensory experience. Thus. discrimination and memory for nameable stimuli or stimuli easy to describe would be equal for the two hemispheres, but via the use of different cognitive operations. There are, however. certain observations of neurological patients that. taken at face value. seem incongruent with inferences drawn from other studies regarding the roles of the left and right hemispheres in color discrimination and memory. COHFS and KFLTI-R [ 121found that aphasic patients. in selecting colors varying in hue. saturation, and brightness that represented the typical color of objects depicted in achromatic line-drawings. were equally disrupted for all three aspects of colors as compared to control subjects. confirming earliel investigations that showed poor performance of aphasics in associating colors with linedrawings [S. 13. 141 and also demonstrating that tho disability is beyond the perceptual level. at the le\-el of conceptual and abstract thinking. COW u and KF L.TI.Rsuggest that the deficit of aphasics is due to disruption of the abilit! to isolate and handle specific features of objects and L’onccpts. There ih much cmplrical support for the conclusion that chromatic qualities of

COLOR-MArCHING.

COLOK-NAMINti

AND COLOR-MEMORY

IN SPLIT-BKAIN

PATIENTS

525

objects are structured in the left hemisphere as specific feature characteristics, and that this structure is disordered with left-hemisphere lesions. A discrepancy arises because other findings, previously discussed, indicate that the right hemisphere has refined imagistic representations of colors, and it would be expected to have little difficulty in selecting colors of well-known objects. Either the right hemisphere is unable to use these representations for associating colors with line-drawings or left-hemisphere lesions resulting in aphasia entail a disordering of interhemispheric regulation, precluding the right hemisphere from bringing its skills to bear on the task. In particular, the deficits observed in aphasics may be due to a retention of processing control by the damaged left hemisphere, obscuring the abilities of the right, rather than being due to a real right-hemisphere incapacity. The possibility that, at least in some instances, the less competent hemisphere assumes control of processing and behavior, and that the tendency of a hemisphere to dominate behavioral control is not necessarily perfectly related to ability differences between the two sides of the brain has been confirmed in split-brain patients. In earlier studies, we found that the right hemisphere assumed control of behavior when a simple matching task was given, even when the left hemisphere was equally or more competent in terms of accuracy of performance [ 151, and the left hemisphere assumed control of processing when simple words had to be read for meaning, even when the right hemisphere showed perfect accuracy on the task [16]. Further, asymmetry ofcontrol can and does shift from one hemisphere to the other as a function of processing strategies that are employed even when stimulus items, choice items, and the motoric response remain invariant [17]. Thus, the deficit in aphasics at associating colors with line-drawings may imply abnormal control of processing by the damaged left hemisphere, or it may imply that the right hemisphere is simply incapable of performing the task. The goals of the present investigation were to determine first, which hemisphere actually dominates control of processing in any given task; second, the degree of unihemispheric or bihemispheric control as a function of task demands; and third, whether only the left hemisphere or both hemispheres is/are competent to derive the typical colors of objects depicted in line-drawings. We examined hemispheric asymmetry of control for the identification matching, or memory of nameable colors in split-brain patients.

METHOD SlrhifV’t Y The subjects were the five split-brain patients. A.A., C.C.. L.B.. N.G., and R.Y.: all are epileptics who have undergone total neocommissurotomy. A.A., although he suffered two convulsions at age 4 months associated with high fever. developed normally until age 51 when generaltzed convulsions appeared. These sometimes began in the right arm. suggesting a lefthemisphere focus. He was operated upon at age 14 in 1964. The surgery produced right cerebral swelling and a persistent spastic left leg with posittve Babinski sign. so that he prohably has significantly more right- than lefthemisphere damage. in spite of a possible left-hemisphere epileptic focus. C.C. experienced anoxia post-partum but developed normally until age X when his school work deteriorated. At age IO. spells of speechlessness occurred. associated with rightward head-turning and. occasionally. loss of consciousness. The hehavioral signs associated with the seizure suggest a left-hemisphere focus. The commissurotomy operation at age 13 in 1965 involved trauma to lhe left hemisphere and was followed hy muteness for 3 months. He is thought IO have greater left- than right-hemisphere damage. L.B. weighed 5 Ih at birth. was cyanotic and remained in an lsolette for 8 days. His first convulsion occurred at age 3;. becommg progt-esstvely worse unttl he was operated upon at age 13 in 1965. The surgery went smoothly. and L.B. showed a rapid recov cry : he \!‘a< able lo speak one day after sur-ger!. His performance 1.0. is aver-aec I 1001. ;tnd his verbal I Q ~~‘11above aver-age f I 151. The verbal I (_Iof I I5 I\ prohahly an undere\timatc of L.B.‘\ verbal rc;r~~ntng ~~pacit! \IIICC he u;c IOU on ho111 the Drgit Span and 12~-~~hrnet~c wbresr~ 01’ rhe bb4IS. hut \(;I\ tv,o \tandard

deviations above the population mean on the Similarities suhtest (equivalent to an 1.0. of 130). There IS no evidence of brain damage in either cerebral hemisphere. N.G. was premature. but developed normally until age IX when she began hacmg convulsions. She was operated upon at age 30 in 1963. Her EEG had shown left-temporal \lowing. and skull X-ray> revealed a mulberry calcificatmn, I cm in diameter. beneath the right central cortex. The postsurgical EEG WHS normal, and it has remained normal. except for a one-year period in 1972 when seizures recurred in association ulth a left tcmporallohc focus after a reduction III antI-se17ure medicatmn. N.G. manifesta no other sign\ of brain damage. R.Y. had a normal dellvery and de\elopcd normally until age 13 when he was struck by a car and wa\ stuporou\ for about half an hour. At age 16. hc began having what his family descrtbed as “cpells” (probably p~vir tntrl seizures), and generalized convulsions appeared one year Inter. HIS seizure> were associated with a visual aura, suggesting a right posterior focus. but preoperative and postoperatIve EEG’s were nonlocallring and neurological examinatlonh were normal. However. conslstent with possihlllty of a right postcrmr disorder. his postsurglcal verbal I.Q. ~35 99. whereas hi\ performance I.Q. was only 79. He was operated upon in 1966 at age 43. To summa-i/e, AA and C.C. probably have \ubstantlal asymmetric damage. /\.A. ulth more to the right hemisphere and C.C. *ith more to the left hemisphere. There I\ no evidence of damage to either side of the hraln in LB. and only Ehght local damage in N.G.; R Y. appears to habe a disorder of right posterior rcglons.

For all tests, sttmuh were exposed m a modllied Harvard 7-channel Tachlstoacopc for I SO myec. Each stmluluh card was seen as a 5 x 5 white square agamst a blue hackground, the whltc square having a luminance of 7.5 ft L. with stimuli centred in the middle of the square. A constantly illuminated tixation field of deep blue (0.2 ft L) way provided with a pin-pomt of red Ilght at the center that was allgned with the center of the stimult. Eye movements were monitored by electrooculography (EOG) during all tests. az described in a previous paper [IS]. Colored stimuli were fabricated of ‘%d-color” frosted acetate sheets chosen to obtain
C‘hlmeric stimuli in the form of butterllle\. each umg of a dlffercnt color. were constructed having a center gray body of 0.S of visual angle: each wing extended 2 into each visual field for the upper ulng and I.5 for the lower wing. On each trial. a chimeric butterlly was tachistoscopicnlly presented and subjects were asked either to (I) point to a nonchimeric hutterlly I” free cislon matching the color of the butterOy percaved or (2) name the color of the butterlly perceived. Three dlffcrent tcsta were gl\cn: In the first. vx chimera were constructed from the three colorc red, blue-green and orange ulth three nonchlmerlc hutterllies as choices. In the \econd. I2 chimeras acre constructed from the four color\ rcd.grecn. mustard yellou.and blur. with four nonchlmerlc butterRie\ as cholcc\. In the third.24chlmeras wereconstructed.Itlentlcal to tho\c III thcfout--color tc~t.ab~,ve.cvcept that corrtr;lstlng~p~,t\. different from either wing color. were added to each wing. Thel-c v.erc 12 spotted-wing huttertlie\ 111the choice \et Each spotted chimera. thus. contalncd all four color\ in wings and \pot\ (FIN. I )

2 ~‘oli,rccl-/o~fl1,\ I<‘\,,, A total of 36 chimcric

stimuh were constructed from outlmed triangles. square,. and circle5 The outline\ wcrc drawn in either red, blue-green. or orange ink; all chimerar differed on the left and rtght with respect to hoth COIOI and shape (Fig. 2). The sides of the square. equilateral triangle. and the diameter of the ctrcle were approximately 3 of visual angle when seen III the tachisto\cope Subject5 were asked either to (I) select from among three colored patches the color they UN. (7) select from among three black-outlmed drawing\ the form they WW. or (3) select from among nine color-outlined forms. the color and form of the qtimuluh they saw. or they ucre a\kcd to name the color. the form. or both the color and fol-m.

<‘hImeric stimuh were prepared ofthe words RED.GREEN. YELLOW and BLUE.cach word printed m an Ink color different from the color spelled on either half of the chzmcra (Fig. 3). Subject\ acre asked to (I) designate the mk color (Stroop test) or (2) designate the color-word (Reverse-Stroop test), their response\ bang either to (I )
Chlmerlc

stimuli of black-outllned

draulng\

of an elephant.

htrawhcrrleh.

an orange. pea\. honana\.

;\ fox, :I

COLOR-MAlCHING,

COLOR-NAMINti

AND

COLOR-MEMORY

EXAMPLE

IN SPLIT-BRAIN

527

PATIENTS

OF

CHIMERIC STIMULUS

PERCEPTUAL

COMPLETION IN THE TWO HEMISPHERES

YELLOW - 0 GREEN -

q

BLUE RED DARK GRAY _

q q

FK;. 1. An example of a chimeric stimulus from the Spotted-Wing Butterfly test, and representation perceptual completion by the two cerebral hemispheres.

of

flamingo and grapes were prepared. and presented by tachtstoscope (Fig. 4). Subjects were asked etther to (I) select from among erght colored patches the typical color of the object, (2) name the typical color of the object, (3) select from among eight pictures a matching object, or (4) name the object. When tachistoscopic testing was complete, pictures were shown tn free vision and subjects were asked to name them. Then. colors were named by the experimentor and stmjects were asked to point to the matching picture. These latter tests were run as a check that patients could. m fact. identify the ptctures and could recognize, when colors were named, which objects had these colors.

RESULTS 1. Butterfly

te.st.s

colors. Results for the naming portion of the Butterfly tests (Table 1) show that wing colors in the RVF were generally named with a high degree of accuracy, whereas, except in a few instances, colors seen in the LVF were not named more frequently than would be expected by chance. L.B. and A.A. were exceptions in displaying above-chance naming of colors in the LVF. For L.B., this was true on all three tests, and A.A. manifested LVF color-naming on the fourcolor test. Inspection of the EOG records showed that both these subjects were on fixation (a) Numing

528

JEKKE

LEVY

and

EXAMPLES

FORM CHOICES

VOLWYN

TKEVARIHEN

OF CHIMERIC

COLORED-FORM

STIMULI

COLOR

CHOICES

CHOICES

0 17 A FIG 2. Examples

of chimeric

stimuli

from

the Colored-Forms

test and

form.

colored-form.

and

color

choices.

GREEN

+

YELLOW

INK COLORS

FIG.

3. Examples

of

-

RED

-----

BLUE

chlmerlc stimuli from the Stroop and Reverse-Stroop

test

when LVF stimuli were named, but both displayed post-stimulus eye shifts towards the LVF when LVF colors were verbalized, consistent with CRWITZ and DAVIS’S finding [18] that post-stimulus eye shifts were significantly correlated with the region of a display correctly reported. (b) Matching colors. On the matching portion of the test (Table 2) patients fell into three groups with respect to asymmetry patterns. A.A. had either a RVF bias (on the three-color

COLOR-MATCHING.

COLOR-NAMING

AND

EXAMPLE

COLOR-MEMORY

IN SPLIl-BRAIN

529

PATIENTS

OF CHIMERIC

STIMULUS

ELEPHANT

FLAMINGO

ORANGE

GRAPES

FOX

PEAS

BANANAS

STRAWBERRIES

Fm. 4. An example of a chimeric stimulus from the Memory Colors test and the line-drawings which chimeric stimuli were constructed.

Table

1. Distribution

of color-naming

responses

on the Butterfly

tests

LVF* LVF

3-Color naming

A.A. L.B. N.G. C.C. R.Y.

4-Color naming

A.A. L.B. N.G. C.C.

Spottedwing names

A.A. L.B. N.G.

9

Error

RVF

Both

R:F
from

LVFt vs error

0

17

0 0 0 0

1 15 18 18

1 3 0 0 0

2 0 0 0

13 8 24 24

0 15 0 0

O.“o:O R
3 6 0

21 9 24

0 7 0

to.001 R 0.066 R
R: R R R

o.noso2 ns ns ns 0.002
RVFf “S

error < 0.001 0.063
*Either exact probability or x2 tests, as appropriate, were used for a two-tailed comparison of LVF and RVF response frequencies; the comparison was restricted to trials in which only one response was given. tSee Appendix for description of statistical techniques. The probabilities are one-tailed tests since the question of interest is whether correct responses exceed chance. Both single-response and double-response trials were counted in determining whether accuracy for a given visual field exceeded chance. $The letter R or L indicates an asymmetry of responses in favor of the RVF or the LVF, respectively.

JEKKF LFVY

530

Table 2. Distribution

LVF

and

COLWYN

of color matching

Error h 0 0

RVF

3-Color

N.G.

2 4x 47

matching

C.c‘.( LH)$ C.C.(RH) R.Y.(LH) R.Y (RH)

15 2 ‘1 0

0 0 0 0

A.A. L.B. N.G. <‘.C.( LH C.C.(RH)

2x 45 44 17 0

0 0

I

I 3

0 0

h 73 ‘0 4

I? 17 25 20

A.A. L.B.

4-C&r matching

Spotted wing makhing

A.A L.B. N.G. (‘.<‘

J

,-KEVAKrHtN

responses on the Butterfly tests

Both

40 0

0 0

I

0

3

6

IO

12

15 ‘4

0 0

19

LVFf vs RVF

iO.001 < 0.00

LVFt v’; error

R:

I L < 0.001L 0.00x L

0.03XR ns

Ilb rc 0.001 < 0.00 I < 0.001

< 0.001 0.002 II\

RVFt v’; error

Hand x field effect

< 0.001 ns ns

II\ II5 n\

0.00’

c 0.00

1

c: 0.001 < 0.001

i 0.00

I

i 0.001

I 0 ’

< 0.01R “S
i 0.001 i 0.001 cc0.00 I 0.037

7 74

0 0

c 0.001 1. O.OhX L < 0.00 I R

< 0.001 / 0.001 II\

n\ c 0.00 I s 0.001

30 7 ? 73

0

< 0.001 R

0.004

I

< 0.02 1.

c 0 001

I) 0


-: 0.001 II\

< 0.00 I O.DO4 II\ c-0 001

n\ II\ n ‘; < 0.00 I II \ ns II\ n\

IThe letter R or L designates an asymmetry in favor of RVF or LVF matches, rcqxctlvely. \‘The designation LH or RH stands for left-hand or right-hand pointing. respectively. Pointing hand ib not g~\cn when there was a complete absence of a hand hq field interaction.

and spotted-wing tests) or hemispheric symmetry (on the four-color test). with above-chance performance for both visual fields on the four-color and spotted-wing tests. L.B. and N.G. had a LVF bias, but L.B. was also above chance for RVF matching on the four-color and spotted-wing tests. Unihemispheric control was reduced for both A.A. and L.B. from the three-color test to the spotted-wing test. Both C.C. and R.Y. showed a significant hand x field interaction. the LVF dominating with left-hand pointing and the RVF dominating with right-hand pointing. R.Y., tested only on the three-color test, also had an overall RVF bias. summing across pointing hands. and C.C. had a RVF bias on both the four-color and the spotted-wing tests. The left-hemisphere bias for A.A. and for R.Y. may reHect asymmetric damage to their right hemispheres. However. AA. displayed no signiticant bias on the four-color test and had a predominance of responses to the LVF stimuli. Also, C.C. is likely to have more left- than right-hemisphere damage, but manifested a left-hemisphere bias on the four-color and spotted-wing tests. The direction of bias for C.C. and the variation across tasks in asymmetry patterns for A.A. are not easily interpretable on a brain-damage hypothesis. C.C.‘s responses on the three-color test, with both left-hand and right-hand pointing. indicated possible bilateral access to colors since he produced a substantial number of double responses. Since single responses to RVF stimuli with left-hand pointing and single responses to LVF stimuli with right-hand pointing did not exceed chance, the double responses are likely to have been mediated by the right hemisphere with left-hand pointing and the left hemisphere with right-hand pointing. If so, then the ipsilateral hemisphere had access to colors,consistent with inferences that can be drawn from A.A.‘s and L.B.‘s capacities to name colors projected in the LVF.

COLOR-MATC-HINC,.

2. Colored-Forms

COLOK-NAMING

AND COLOK-MEMORY

IN SPLll-BKAIN

531

PA I IEN IS

tests

(a) Naming ofcolors,forms, or color undfbrm. Color naming (Table 3) was similar to that on the Butterfly tests. Naming of RVF colors was well above chance in all subjects, but naming of LVF colors only exceeded chance for L.B. However, although LVF naming was not above chance in N.G., neither was there a significant difference in the frequency with which LVF and RVF colors were named, and the possibility that N.G., like L.B. and A.A., can occasionally name colors projected to the right hemisphere cannot be ruled out. For form naming, all subjects were above chance in the RVF, but neither A.A. nor N.G. had a significant asymmetry between visual fields, and particularly for A.A., the possibility must be entertained that he could name forms projected in the LVF. When both colors and forms had to be named, all patients showed a highly significant RVF naming ability, but L.B. had no asymmetry between fields and also was significantly and highly above chance at naming forms and colors projected in the LVF. Although he was not significantly above chance at LVF naming of forms when only the form had to be reported, an inspection of the distribution of L.B.‘s responses suggests the possibility that he might have been able to name LVF forms under this condition also. (b) Matching q/‘colors,fi,rms, or color and ,fi)rm. The most striking aspect of the colormatching data (Table 4) when the form dimension had to be ignored is the degree of symmetry of the two hemispheres in controlling responses, relative to the comparable (i.e. three-choice) Butterfly Matching Test. A.A., L.B., and N.G. all manifested significantly more bihemispheric participation for color matching of colored forms than for the three-choice Butterfly test [xzAA( 1) = 17.76. P < 0.001; x2,.8( 1) = 34.77. P < 0.001; Exact P,, = 0.0261. Since C.C. had a hand x field interaction on the three-choice Butterfly Matching test, responses for the two hands separately had to be compared. Table 4 collapses C.C.‘s responses over hands because the hand x field interaction for color matching here was not significant [x2( 1) = 2.98, P= 0.085] and went in the opposite direction from the hand x field interaction on other tests. Thus, for color matching on the Colored-Forms test, C.C. had five LVF matches and 12 RVF matches with left-hand pointing and 10 LVF matches and 7 RVF

Table 3. Distribution

Color naming

Form naming Colored-form naming

of naming

responses

LVF

Error

RVF

A.A. L.B. N.G. C.C.

2 7 6 3

4 0 2 0

I? 4

A.A. L.B. N.G. C.C.

6 2 4 4

L.B. N.G. C.C.

5 1

1

on the Colored-Forms

Both

test

LVF* vs RVF

LVFt “S error

RVFi “S WlOr

15

2 0 0

0.013 R: ns ns 0.008 R

0.002 ns “S

0.03x
1 2 3 3

II IO 9 II

0 4 I 0

ns 0.039 R ns 0.059 R

0.062 ns ns ns

0.003 0.002 0.046 0.029

0 4 3

6 14 I4

7 0 0

ns 0.001 R 0.001 R


*Comparisons as in Table I. tcomparisons as in Table I. fThe letter R or L indicates a RVF or LVF asymmetry.

I0

respectively.

0

“S


532

JERKF LEVY Table 4. Distribution

A.A. L.U. N.G.

CT.<‘. AA L.H N.G.
Colored-form matching

‘C‘ompwwn as tComparlwn as :The letter R or $The dwgnation given. there was an

A.,~ L.H. N.G.

and

(‘OLWYh

~KLVAKIHt.N

of matching response5 on the Colored-Forms LVFt vs error

LVF* vs RVF

LVF

Error

RVF

Roth

14 13 74 I5

5 6 7 2

I6 17 5 17

I 0 0 0

Ilb ns < 0.001 “S

30 24

2

4

I 0 I

I1 4 22

0 0 0 0

i 0.00 I L 0.02x L ~0.001 L ns

0 0 0 0 0

“S 0.001 L i 0.00 I L ns 0.006 R

32 13 7 24

7

4

h

21

I 5

7 I

3 6

I 7 II

testa

L:

RVFt “LI error

10.015 0.056 0.001 0.001

n\ i 0.001

-c 0.001 i 0.001 c 0.001 < 0.001

“h 0.003 n\ < 0.001

Hand x field effect

CI0.006 < 0 0 I‘?

0.039 < 0.001 n\ 8 0.001 c 0.001

m Table I. in Table I. L indicates an asymmetry in favor of the RVF or LVF. ~respect~ccly LH or RH indutes M-hand or right-hand pointing, respecllvely. When pointinp hand IS not absence of a hand x field effect.

matches with right-hand pointing. C.C., like the other three subjects, made significantly more matches for the visual field that had been relatively ignored on the Butterfly Matching test; for left-hand pointing, x2 c,-,,H( 1) = 10.36, P < 0.002. and for right-hand pointing, ~~,-c.~~,(1) = 5.17, P < 0.025. All four subjects, in other words, displayed more bihemispheric participation and less unihemispheric dominance over behavior when color matching necessitated the ignoring of an irrelevant, variable form dimension. On form matching, with an irrelevant, variable color dimension ignored, all subjects except C.C. had a significant asymmetry in favor of the LVF. Data were compared with a picturematching test given in an earlier study [IS], since picture matching, like form matching, involves a unified and nameable shape. The asymmetry distributions were not significantly different for A.A. and N.G., both having equally strong LVF biases on both tests. but the LVF bias for C.C. on the earlier picture-matching test was significantly stronger than the RVF bias on the form-matching test [~2~.c(l)= 11.44, P
COLOR-MAlCHING.

COLOR-NAMINti

AND

COLOR-MEMORY

IN SPLII-BRAIN

PATIENTS

533

[xzAA( 1) = 0.07, P > 0.803 nor for the left hand of CC. [x~,--,~~ (Ya,e’scorrec,ed, (1) = 1.56, P>O.20], but was significant for L.B. xzLs(l)= 7.00, P
tests

(a) Naming of co/or-words or ink colors. Only two patients, L.B. and N.G., were tested on the Stroop and Reverse-Stroop tests, and their results were practically identical and were combined (Table 5). For the naming of either color words, or for the naming of ink colors, there was a strong RVF bias, and naming of LVF stimuli occurred in only one instance on the color-word portion and in one instance on the ink-color portion, not more frequently than would be expected by chance. The ink-color naming task contrasts with L.B.‘s results for naming on the Butterfly tests and for naming of color and form on the Colored-Form test; in these latter cases, he showed above-chance naming of LVF colors. Possibly, naming of ink colors when an incongruent word was spelled required a greater allocation of attention by the left hemisphere than for other color tasks, precluding awareness of LVF colors. As KINSBOURNE [19] has suggested, perceptual biases for one or the other side of space may be magnified when a hemisphere is activated by task demands. (b) Matching of color-words or ink colors. When patients were required to read stimulus words for meaning or when they were required to read a choice word for designation of either a stimulus word or ink color, a strong RVF bias emerged. However, on the color-word task when choices were words printed in black ink, the LVF was also matched at an above-chance level, possibly because matching could be mediated by the form invariant between stimulus and choice, with the meaning of the word ignored. In an earlier study, L.B. and N.G. had a strong LVF bias for simple matching of words [16]. On the ink-color identification task where choices were words printed in black ink, the LVF stimuli were also matched at an above-chance level. Given the strong color-matching bias of L.B. and N.G. for the LVF, even the necessity to read choice words did not totally inhibit manifestation of LVF matching. A highly significant LVF bias appeared on the ink-color identification task when choices consisted of colored patches, but matches for the RVF were performed well above chance also. As for color matching on the Colored-Forms test, an irrelevant, variable form dimension was present, resulting in bihemispheric engagement. If the color-matching performance of L.B. and N.G. on the Colored-Forms test is used to derive a predicted distribution of LVF and RVF matches on the ink-color identification task with colored patches as choices, predicted and observed frequencies do not differ [x2( 1) = 2.05, P > 0.151. In contrast, if predicted frequencies are derived from the comparable (i.e. four-choice) Butterfly Matching test, predicted and observed frequencies differ significantly [Exact P
J~KK~ LI VY and C‘OIV+YN TKCVAKIHI r\,

534 Table

5. Distributions

of naming and matchmg

response\

on the Reverse-Stroop

LVF* Task

Color word identification Point-to-color Point-to-word Name color word Ink color identilication Point-to-color Point-to-word Name ink color

LVF

Error

RVF-

Both

4 x I

71 3:

hl 40 22

0 0 0

< 0.00 I R i 0.001 R < 0.00 I R

50

z

3

Y 0

IS 53 23

I** ,** 0

-c 0.001 L 4 0.001 R ( 0.00 I R

I

lb

R;\F

:md Stroop tests

LVlI\ error

“\ 0.009 11,

Hand x licld effect

i

0.001 c 0.00 I < 0.001

nh n\

‘. 0.00 I 0 045 11,

Data itre the comhincd results of L.B. ;md N.G. who did not differ m their pattern\ of rcyx,n\e\ *Statistical tests were performed :is described in Tahlc I : dcsignatlonj of R and L indlutc a\ynmetrle\ and LVF, respectively. tlnk color of LVF matched SIX times: RVF; once $Ink color of LVF matched twice; RVF once #Ink color of LVF named. Color word of LVF matched once; RVl- once. ’ Color word of LVF matched twice. **Double responses were produced by L.B Ofthe I I errorsmadeforcolor-word identilicatlon.nine werefor ink color\ofthc LVF:md only two of the RVF (Exact P = 0.033. one-talled).

ofthc RVI,

for inhcolor\

N.G. was comparable on the color-matching portion of the Colored-Forms test and on the ink-color-matching portion of the Stroop test, with colored patches as choices, and that on both tests, unihemispheric dominance over matching performance was diminished as compared to the Butterfly tests. (c) Nature rferrors. Too few errors were made on the ink-color identification task to permit a meaningful analysis, but of the 11 errors made on the color-word identification task, 9 were errors giving ink colors for the LVF and only two were errors giving ink colors for the RVF (Exact P =0.033, l-tailed), an outcome that is not unexpected given the strong LVF bias of L.B. and N.G. for color-matching. Evidently, this bias resulted in intrusion of the right hemisphere for the color-word identification task. The opposite intrusion, where words projected to the left hemisphere interfere with ink-color identification, was demonstrated by SCHMII)T and DAVIS [IO] in normal people, reflecting the well-known Stroop interference effect. In the present case, a Reverse-Stroop interference effect appeared in individuals having a strong right-hemisphere bias for the matching of nameable colors. Whether such a ReverseStroop interference would appear in people having no bias for the matching of nameable colors or a left-hemisphere bias is unknown.

(a) Naminy c$color.s urd ohjccts. When subjects were asked merely to name the object tachistoscopically flashed, all correct responses were for RVF stimuli, but error rates were high (Table 6). C.C. was totally incapable of providing object names, saying “I have a bad memory. I know what they are, but I can’t think of the names.” The anomia for C.C. and the

COLOR-MATCHING,

Table 6. Distributions

COLOR-NAMING

of selection

AND

COLOR-MEMORY

and naming

responses

IN SPLIl-BRAIN

on the Memory LVF*

Task

LVF

Error

RVF

Both

R:F

535

PATIENTS

Colors

test

LVF

RVF

“S

“S

error

error

Hand field effect

x

Selection color

of

L.B. N.G. C.C.

22 6 13

3 12 7

7 12 12

0 2 0


L



ns ns ns

Selection object

of

L.B. N.G.

16 15

0 0

0 0

0

I


< 0.001
ns js

ns

Name color of object

L.B. N.G. C.C.

8 I 3

18 13 7

22 18 6

0 0 0

<0.02 R
0.008 ns ns

c 0.001
Name the object

L.B. N.G. C.C.

0 0 0

8 6 32t

8 10 0

0 0 0

0.004 R
ns ns ns

< 0.001
“S

*Statistical tests were performed as in preceding tables; the letters R and L indicate asymmetry in favor ofthe RVF or LVF. respectively. tC.C. was unable to provide any object names at all, stating, “I have a bad memory. I know what they are, but I can’t think of the names”, a statement given support by C.C.‘s above-chance performance in selecting and naming object colors.

high error rates for L.B. and N.G. contrast strongly with chimeric picture naming in an earlier study [1.5], where all three patients were close to perfect accuracy. On the earlier test, there were three pictures (rose, eye, bee) instead of eight, as on the present test, and further, those three pictures were highly distinct in terms of meaning. In the present case, there were five fruits and vegetables and three animals. Quite often, L.B. and N.G. made errors that preserved the superordinate category, but not the specific exemplar. Thus, the flamingo elicited, “Wasn’t a stork, some kind of bird” on one occasion and “ostrich” on another occasion, the orange was called “squash”, “peach”, or “celery”, peas were called “corn”, strawberries were called “mushrooms”, the fox was called “cat”. When pictures were shown in free vision, the patients had no difficulty in correctly identifying them. Possibly, the rapid presentation, the chimeric nature of the stimuli, and the fact that only two superordinate categories were represented, placed a burden on the perceptual constructive abilities of the left hemisphere. All three patients, including C.C., were far above chance at naming the colors of objects seen in the RVF, and L.B. was also well above chance at naming colors of objects seen in the LVF. C.C. displayed no significant difference in color naming for objects in the two visual fields and, possibly, he was also able to name LVF object colors at an above-chance level, but this cannot be decided given the lack of significance for LVF naming tested separately. The ability of C.C. to provide the colors of objects, but not their names, indicates a dissociation between color-naming and object-naming functions. Additionally, A.A.‘s form-naming ability for LVF forms on the Colored-Forms test, L.B.‘s ability to provide names of forms in the LVF when both color and form had to be given on the Colored-Forms test, and L.B.‘s naming of colors of objects seen in the LVF on the present test, and his total lack of LVF naming of the objects themselves, suggests that the presence of color in a stimulus or the requirement to give a color response serves some form of activation function for speech processes. Overall error rates were high for L.B., N.G. and C.C., but were lower for L.B. than

536

JFKKF Lr VY and COL.HYN

TKFVAK~HFN

on the object-naming portion of the test. In free vision, patients identified colors of the eight objects correctly. (b) Motchirzg c~f‘colors trrld objects. Only L.B. and N.G. were tested for simple object matching; both showed a complete LVF bias, and no errors were made. The LVF bias is congruent with their performance in a previous study on a picture-matching task [lS]. The absence of errors shows that the high error rates observed when object naming was tested could not have been due to simple perceptual problems. At the least, we can conclude that patients could perceive the stimuli sufficiently well to produce errorless matching. It should be noted, also, that the object-matching portion of the test was given prior to the objectnaming portion for L.B. and N.G., so that by the time the naming task was presented, they had had the benefit of experience on object matching. All three patients showed highly significant above-chance performance with both hemispheres for matching colors to line-drawings, and only L.B. had a significant asymmetry (favoring the right hemisphere). Error rates were lower on the color-matching portion of the test than on the color-naming portion of the test. For matching, there were three errors out of 32 responses for L.B. (9”,,). 12 errors out of 34 responses for N.G. (35’Z,,), and seven errors out of 32 responses for C.C. (22”J, as compared to 38”,, errors for L.B., 41 “,, errors for N.G., and 44’,;, errors for C.C. when they named colors of line-drawings. The increase in errors for naming as compared to matching was significant for the group of three patients [x2(3)= 10.62, P
DISCUSSION All patients displayed good ability to name colors seen by the left hemisphere, confirming the results of studies in the introduction of this paper. L.B. and A.A. were also able to name colors projected to the right hemisphere, and on the color-naming portion of the ColoredForms test, N.G. may have been able at times to name LVF colors. In addition, form naming of LVF stimuli was achieved by A.A. in the form-naming portion of the Colored-Forms test, for L.B. when both color and form had to be named in this test, by L.B. when colors had to be provided for line-drawings, and possibly, by C.C. in this latter test. Verbalizations of LVF stimuli were confined to conditions when colors were present either in the stimulus or the response. No LVF naming was observed for object identification, a condition where no chromatic variable was present. The mechanisms whereby verbalization of LVF stimuli is accomplished in split-brain patients are unknown, but the data suggest that the presence of color in the stimulus or the necessity to name a color activates speech processes. The ability of C.C. to name colors of objects, while being unable to supply their names, also indicates a special association between chromatic qualities and speech. Conceivably, brainstem systems, capable of mediating information between hemispheres, and supplying arousal input to the brain, are activated selectively by color in stimuli or by the necessity to name colors. In simple color matching, with no other variable dimensions present, patients typically showed a strong asymmetry in favor of one hemisphere or the other, but the direction and

COLOR-MATCHING.

COLOR-NAMING

AND

COLOR-MEMORY

IN SPLIT-BRAIN

PATIENTS

537

degree of the asymmetry varied between patients and within patients across different conditions. Thus, for the simplest task (three-choice Butterfly test), A.A. had a strong RVF bias, and L.B. and N.G. had strong LVF biases. C.C. showed equally strong biases in opposite directions as a function of pointing hand, the left hemisphere dominating matching when the right hand was used, the right hemisphere dominating matching when the left hand was used. R.Y. had an overall RVF bias, but this was diminished with left-hand pointing. As task complexity increased, the magnitude of asymmetric control decreased. This was observed for A.A. and L.B. even on the spotted-wing test, where matches to LVF stimuli exceeded chance for A.A. and matches to RVF exceeded chance for L.B., in contrast to their performance on the three-choice Butterfly test. On the color-matching portion of the Colored-Forms test, where a variable, irrelevant form dimension was present, all patients showed bihemispheric engagement, in contrast to the results of the three-choice Butterfly test. This was also seen on the Stroop test when colored patches were provided as choices. The asymmetry in behavioral control of C.C. and L.B. was reduced on the form-matching portion of the Colored-Forms test, when the irrelevant, varying dimension was color, as compared to picture matching in an earlier study [ 151. When both color and form had to be matched., and neither dimension was irrelevant, A.A. and the left hand of CC. manifested as much bihemispheric engagement as when an irrelevant dimension had to be ignored, but L.B., N.G. and the right hand of C.C. showed a significant increase in asymmetry. For these latter, the presence of an irrelevant dimension that had to be ignored was, apparently, of importance in inducing both hemispheres to participate in the task. The change in hemispheric usage over tasks shows, first, the lability of the hemispheres for matching nameable colors. The hemisphere that dominates and controls behavior in one circumstance does not necessarily do so in other circumstances. It is not unreasonable to suppose that shifts in control between hemispheres reflect changes in strategies applied as task demands change. Second, the nature of changes observed shows that unihemispheric control is diminished with increases in task complexity, regardless of which hemisphere had dominated responding in the simpler task. We suggest that as task complexity increases, the capacity of a hemisphere to retain absolute control over processing decreases, and the other side of the brain is encouraged to collaborate in solving the problem at hand. If so, this could have implications for hemispheric cooperation in normal people. While either hemisphere alone in the normal brain might tend to assume control of well-practiced, habitual functions within its domain of specialization, both hemispheres might be called into play for cognitively complex, nonhabitual, and creative processes. The relative normality of split-brain patients in everyday life is likely to derive from the fact that most requirements of day-to-day living depend on overlearned responses where extensive, redundant contextual support is provided. The findings from the Stroop and Reverse-Stroop tests support inferences from other investigations. There was a strong left-hemisphere dominance over behavior whenever naming responses had to be given or words had to be read for meaning, either as the stimulus or as the choice. When the response entailed pointing to a colored patch, L.B. and N.G., the only patients tested on this task, manifested the same LVF bias for ink-color identification that they had shown on the color-matching portion of the Colored-Forms test and of less magnitude than produced on the Butterfly tests. Intrusion errors appeared when patients had to identify the color-word, reAecting intrusion of ink colors projected to the right hemisphere. This Reverse-Stroop interference effect seems analogous to the Stroop interference effect,

538

JFKKE LFVY and

COLWYIV

TKEVAKIHEN

where the word interferes with the identification of ink color. In the SCHMIT and DAVIS [ 101 study of normal people, there was a left-hemisphere asymmetry for Stroop interference, consistent with the left-hemisphere superiority for word identification that they observed. They found no evidence of hemispheric asymmetry for Reverse-Stroop interference: both hemispheres showed an increase in reaction time of equal magnitude for identification of color words printed in incongruent ink colors, as compared to the condition where they were printed in congruent ink colors. Given their observations, however, of equal reaction times for identification of ink colors when the carrier word was congruent (635 msec for the RVF and 634 msec for the LVF), one would not expect an asymmetry for Reverse-Stroop interference. In their sample of subjects, the hemispheres were symmetric for matching of nameable colors, in contrast to L.B. and N.G. who manifested a strong LVF bias. It would be of interest to determine whether normal individuals having an asymmetry for the matching of nameable colors display a correlated asymmetry in Reverse-Stroop interference. The results from the Memory Colors test show clearly that both hemispheres are capable of matching colors to line-drawings, and the lower error rates for the matching portion of the test as compared to the naming portion of the test, as well as the association between error rates and the degree of bias for right-hemisphere matching, suggest that the right hemisphere is somewhat more competent than the left. The difference in errors for matching vs naming cannot be due merely to the presence of a choice set in the former case since we counted as correct any naming response that could be an appropriate color for the object depicted in the line-drawing; naming responses, in other words, had more freedom for some objects than did matching responses with respect to what could be counted as correct. The evidence for better performance of the right hemisphere is consistent with what has been inferred regarding the nature ofcolor representations in the two hemispheres. If object colors are represented in the left hemisphere in terms of elaborate conceptual structures and in the right hemisphere in terms of sensory-rich images, almost any familiar object would provide access to its color by the right hemisphere, but depending on various experientially derived associations, the left hemisphere may or may not have object colors easily available. This interpretation would predict that color-matching performance by the right hemisphere should be less variable from person to person than color-matching performance by the left hemisphere. This was the case in the PEN:~AI. [X] study, both for colors presented in the lower half of the visual ticld [F( 124,124) = 1.53, P = 0.0251 and for colors presented in the upper half of the visual field [ E‘(124.124) = I .49. P < 0.051. Our data from the Memory Colors test arc consistent with studies showing that the right hemisphere has access to good imagistic representations and that the left hemisphere has a good ability to derive feature characteristics of objects from the conceptual structure it possesses. Our results arc also concordant with findings that color representation for the right hemisphere is at least as good as that of the left. and better for colors resistant to verbal description. The dcticits of aphasic patients with left-hemisphere lesions in matching colors with line-drawings [S. 12 141 can be interpreted as reflecting abnormal interhemispheric regulation, with processing control retained by the damaged left side of the brain, preventing the right hemisphere from manifesting its abilities in matching colors to objects. This interpretation could also explain why dcnsc receptive aphasias occasionally occur with lefthemisphere lesions when receptive disorders of such an extreme magnitude are not observed in the right hemisphere of split-brain patients. It is reasonable to infer. on the basis ofour data and those of others, that the approximately equal competence of the left and right hcmisphcres to discriminate and remember namcahle

COLOK-MArCHINti. COLOK-NAMtNcj AND COLOK-MEMORY

IN SPLIT-BKAIN

PATIEN

IS

539

colors is an equality of performance only, that the nature of color representations and of the strategies used in processing by the two sides of the brain differ. We suggest that variations observed among split-brain patients in asymmetry patterns reflect differences in the ways they integrate color information, differences that not only characterize different individuals, but that appear within the same person as task demands change. Both sides of the human brain appear to have an amazing aptitude for solving problems with which they are confronted in most circumstances. each using whatever strategies and processes that are incorporated in it. The differences between the hemispheres seem to reside predominantly in the nature of multipurpose processes used, and differences in performance are likely to occur only when special and rather artificial tasks are presented that are fundamentally insusceptible to solution by one or the other set of laterally differentiated functions.

Ack~~/edyemrnr.~~~ This research was conducted in the laboratory of Professor ROGER W. SPERRY at the California Institute of Technology with support from the Frank P. Hixon Fund and by the U.S. Public Health Service Grant MH 03372 01 to Professor SP~KRY. Preparation of this report was supported by a Spencer Foundation Grant and by a U.S. Public Health Service Biomedical Grant, PHS 5 SO7 RR 07029 13, to Jt RKI Lf v’v. The subjects were patients of Drs. pHtI.ff’ Vtxif f. of the California College of Medicine and JOSI PH &)(a \ of the Ross Loos Medical Group, Los Angeles. We are indebted to Professor SPERKY for the opportunity to carry out OUI studies in his laboratory and with-his support

REFERENCES I. 2. 3. 4. 5. 6. 7. x. 9. 10. 1 I. 12. 13. 14. 15. 16. 17. IX. 19.

KfNseotlRNf . M.

and WARRfNciToN, E. Observations on colour agnosia. J. Nrurd Nrurosurg. f?\ychiuf. 27, 296 299, 1964. Cancrtt.r:v, M. Acquired anomalies of colour perception of central origin. Bruin 88, 711 724. 1965. Gt:sc.tLwtNt), N. and Ft;stt.t o, M. Color-naming defects in association with alexia. Awh. Nrurol. 15, 137 146, 1966. Osetlav. J. M., OXWRY, S. M. and HtIMPffREY, N. K. Varieties of colour anomia. Bruin 92, 847 X60, 1969. DI- RtY(t, E. and SPINNLFK. H. Impaired performance on color tasks in patients with hemispheric damage. Cortrv 3, 194 217. 1967. Sr.orsr, G. and SPINNLI R, H. Colour imperception in unilateral hemisphere-damaged patients. J. Nertrol.. Ncwosury., P.$ychiut. 33, 22 28, 1970. CAIVIA\I, E., S(x)-rst, G., and StJthixt.f R. H. Color impairment in pattents with focal excisions of the cerebra1 hemispheres. Nr,urop.s~ch~~/f~~iu 16, 491 496, 197X. PI NUAI., B. E. Human cerebral asymmetry in color discrimination. Nruropsychok~~yiu 15, 563 568, 1977. DIMONI), S. and Bi AIIHOVT, G. Hemisphere function and color naming. J. r-up. P.qho/. %, X7 91. 1972. SCIIMIT, V. and DAVIS, R. The role of hemispheric specialization in the analysis of Stroop stimuli. Acru /?~~~ho/. 38, 149 15x, 1974. MII Nt-n, B. Brain mechanisms suggested by studtes of temporal lobes. In Bruin Mechanisms Un&r/yiny Spwch ud Lanquuye, F. L. DARI.I Y (editor). Grune & Stratton, New York, 1967. Cortru, R. and Kt l.Tl R, S. Cognitive impairment of aphasics in a colour-to-picture matching task. Corre\- 15, 235 245, 1979. DI Rt.N/t, E., F~AGIONI, P...%oI rr,G., and SIVNNI f K,H. Impairment in associating colour to form.concomitant with aphasia. Bruin 95, 293 304, 1972. BASSO, A., FA(,I IOUI. P., and SPIYNLfK. H. Non-verbal colour impairment of aphasics. Nrurop.\~c.ho/ogicr 14, 1X3 193, 1976. LI vt, J.. TKI.\ ,\K IIII h, C.. and St+ant. R. W. Perception of bilateral chimeric figures following hemispheric deconnexion. Bruin 95, 61 78, 1972. Lt VI. J. and TKI \AK~ ttt:N, C. Perceptual. semantic and phonetic aspects of elementary language processes in split-brain patients. Bruin 100, 105 118,1977. LI VY, J. and TKI vAKmf N. C. Metacontrol of hemispheric function in human split-brain patients. J. r.rp Psycho/.: Hum. Pcrcrpt. Prrlr,rtn. 2, 299 312, 1976. CKOLIT/, H. F. and DAVIS, W. Tendencies of eye movement and perceptual accuracy. J. cup. Psycho/. 63, 495 498, 1962. KtNsaot~aNt . M. The cerebral basis of lateral asymmetries m attention. .4cru t?syctrot. 33, 193 201, 1970.

540

JI:KKL LEVY and

COLWYN

TKEVAKIHEN

APPENDIX We considered three approaches for calcuiatmg whether performance is above chance for a given visual field. with the likelihood of falsely accepting the null hypothesis progreqslvely decreasmg through the three methods, A, B, and C. Method B was the procedure chosen for the analyses in this paper since It provides conservatism in acceptmg the null hypothesis without an unreasonably high likelihood of its being falsely rejected. As a simple example, consider a three-choice task where one choice conforms to the LVF stimulu?. one to the RVF stimulus, and one choice is erroneous. Suppose that in 24 trials, LVF responses are made IO times, RVF responses are made 12 times, and erroneous responses are made twice. The question, III this example. ohwhether LVF choices occur slgnlficantly more often than chance would allow. In method A, we absume that the right hemisphere always controls responses; thus. that any response other than one matching the LVF stimulus IS an error. Under this assumption,chance predicts that of 24 responses, eight would conform to the LVF stimuluh and I6 would represent other responses (eight RVF and eight errors). For the example. we calculate %‘(I) =0.75. P =0.3X44, two-talled, or :=().X7. P=O 1922. one-talled, and we conclude that LVF responses were not above chance. Method A was rejected because of the unreasonable assumption that the hemisphere under consideration always controls responding through all trials. regardless of whether “other” responses are true errors or responses conforming to the stimulus of the other hemisphere Method C allocates erroneous responses according to the proportion of LVF and RVF responses In the present example, the LVF contributes IO/22 = 45”,, of all correct responses. and we assume that (0.45)(2)=0.91 errors should be attributed to the right hemisphere. There are, therefore. IO.91 responses under consideration. and assuming that correct and erroneous responses are equlprobablc. chance predicts 5.45 LVF responses and 5.45 errors. Ciiven !O LVF and 0.91 erroneous responses. n’( I ) = 7.60, P = 0.005X. two-talled. or ; = 2.76, P = 0.0029, onetailed, and we conclude that LVF response% occurred more often than chance would allow. The allocation of error\ to the hemisphere5 In method C might be overly generous in that. at least theoretlcally. the hemisphere contributing fewer correct responses I\ more subject to error than the hemispherecontrihutlng morecorrect response\. Method C was rejected because the probabdlty of falsely rejcctlng the null hypothesis seemed too high. In method B, we reason that RVF responses. LVF- rc
COLOR-MATCHING.

COLOK-NAMING

Oesstimulus des

malades

dans On

la

B de

phke

un

biais

Dans

la

les et

varlaient

du

h6mlsph6rique

contr6le

de5

avaient

couleurs

des

de

les

dessines peu

&moire

des

PATIENTS

avec

bien au

les

la

que

les des

du

et

l'hQmisph6re

le

gauche.

au-dessus B

malades :

tbches. la

de

les

types

l'asymetrie

tache.

Les

chance

droit

du

l'hgmis-

diffkaient

r&ponses

de

niveau

stimulus

projet

diffkrentes

complexit

au-dessus

trait

meilleures

couleurs.

familiers.

des

aussi

stimulus

asym6trique selon

d'objets

couleurs

Btaient du

tachlstascope

h&misp!Sriques

couleurs des

malddes

de

au

asym6tries

des

cauleurs

contr5le

augmentant

projetes

les

denomination

quelques

malades

performances

quelque

la la

d'appariement

degr6

avec

d'objets

performances

et

mais

Qtaient

d'Qtablir

dBnomination

tkhes le

d'asymetrie

ph$i-es

but

dans

gauche

dans

direction

bilatkaux le

important

l'h8misphSre chance

droit. la

dans

l'appariement

dBnomination,

projstes niveau

chimeriques

split-brain

constatait

dans

IN SPLIT-BRAIN

:

RQsumi!

B

AND COLOR-MEMORY

pour

semblait

2 la

avair

hemism&moire des

Zusammenfassung

Bilaterale Patienten

chimsrische dargeboten

Farbenennen, trauten

einige

zeigten

wenn die Stimuli

variierten

Hemisphare

iiber unterschiedliche Komplexitat

Kontrolle

Beide

Farben

Es gab einen

die Leistungen

zunehmender zu.

van Objekten,

Hemisphlre

kamen.

Aufgaben

Effekt

beim

aber

Bei den Farbzuordnungsund die Muster

nahm die Symmetric

waren iiberzuf%llig

der

der Asymmetrie Patienten.

zu win.

Mit

hemisphtiischen

gut im GedLchtnis

dargeboten

der linken etwas iiberlegen

warden,

Farbbenennen,

bei ein und demselben

die als Strichzeichnungen

van ver-

fiir das Benennen

projiziert

Leistungen

beim

fiir Farben

starken

der Patienten,

der Aufgaben

Hemisphsren

schien

Split-BrainAsymmetrien

in die linke Hemisphlre

such iiberzufXllige

in die rechte

variierteh

tachistoskopisch

hemisphsrische

und fiir das GedZchtnis

herauszufinden.

wenn die Stimuli

Patienten

aufgaben

wurden

Farbenzuordnen

Objekten

van Farben,

Stimuli

mit dem Ziel,

wurden,

fiir die

die rechte

541