Age differences in the effects of stimulus complexity and symmetrical form on choice reaction and visual search performance

Age

Differences

in the Effects

and Symmetrical and Visual

Form Search

of Stimulus

Complexity

on Choice Reaction Performance’

CHOICE

REACTION

AiVD

VISUAL

SEARCH

407

also poorly understood, partly because stimulus properties have not always been defined objectively in research with children, and researchers have typically not used a sufficiently wide age range (Cantor, 1963). A furtlwr limitat~ion of the research with children stems from the frequent use of a prefercncc measure as the criterion of rcsponsc to complexity. The relation of prcfcrcncc to information prowssing is obscure. This invest~igation cxamincd thkx cffcct~ of pattern complexity and form On the speed of pat tern ~liscriniination in two kinds of tasks~ :i fourchoice classification problem am1 :k visinil starch task. The chief intcrcst of the study was the Lxtcnt to which such cfl’ects are ckpcndent upon the age of the iii(lividu:~l. +(>-corrclatc~l amount of cxpcricnce with stimulus propertieS, such as complexity am1 ~yn~x~l~t~~~~-:~sy~l~~~l~~tr~, was cxpectcd to result, in markedly diffwcnt lcvcls of diwrimin:~tioii pcrformanw by sub.iects varying in :igc. Such diffcrenccs, cxaminc(l in the conkxt, of the ~liffcring demands rcprwcntcd in dissimilar tasks, wcrc expcctcd to yield evi~l~~nccconccining the import:uicc of some lwimary form properties for the dcvclopincnt of :Lbility. 130th Experiment I ( four-choice classification) aiid Experiment II (viwal scarch1 u~cd random shapes which wcrc lnlatcr:~lly symmetrical or asymmetrical in form! and which variwl in conil)lexity, the latter variable being clcfined as the numtwr of “turns” or angles iti each shape (Munsingcr and Kcswn, 1964) .: -\ttncave (1957 I lw ~ho~w that the number of in~lcpcndcnt turn<, oi ‘*complexity of the patkin,” in each random ~hapc accounts for 78% of the variance of ratings by college stu(lents. W~er invwtigators (c.g.. Ikcw, 19.56; Munsingcr a~~1 Forsman, 1966; Alunsingcr, Kcssen, and IGwwn~ 19641 have demonstratecl in a variety of tasks that st~imulus complexity, ,~ knilarly varied, exerts considcrable control owr %’ discrimination pwi’or~~x~nce :LIJ(~ stimulus prefercncw. The prcscnt study usc~l sh:~lws having .5 I 6’) , 10, 2O, md 40 turns.

The timed dis,junctivc reaction, or choice rcspon~e, has a long history of use as a sensitive and accurat.c indicator of stimulus discriminability (Garner, 1962’), appropriate for use with young children (Morin and Forrin, 196.51 as well as with adults. ‘The research reported herein has been influenced considerably by information theoretic issues, and therefore the results have potential bearing upon information theory in psychological applications. In the report, the terms &jor~~ak’on and COWL$c.r&?/ are used interchangeably. When the complexity of a pattern is increased, its stimulus uncertainty and therefore its information value, are also mcreased (cf. Garner. 1962). I&xise, when the constraint of bilateral ,s~wrrne~q/ is introduced into the procedure by which random shapes are generated, such shapes are re&wZu& in comparison to asymmetrical shapes. irrespective of level of complexity.

408

CHOICE

REACTIOX

AND

VISUAL

SEARCH

409

t.here in front of you. Your task is simply this. When the window lights up, like this (demonstrate), look at t’hc shape and decide whether it has 5 angles, or 10 angles, or 20 angles, or 40 angles. An angle is any place where the outside edge of the shape changes direction. Each shape you see will have tither 5, or 10, or 20, or 40 angles. When you have decided which one of these groups of shapes a particular one belongs in, you press down t,hc correct button there in front. of you. You’ll notice that they arc m:arkcd ,5, 10> 90, and 40. Thc~ window will remain lighted, and t.hus you may look at thtl shalx~, until you praxesone of the buttons. When any button is press~~d,tlits light will go out. “Try to decide which group the shape belongs in as q~(ickLu as you possibly can, but, at t,he same time, bc c~cc~L~&. That is, you shoulcl be fairly surt’ of your choice before you prthss one of t’hc buttons. If you should make an error and wish to change it, that will be fink. *Just tell me. .4ny questions? (Uncorrected error t.rials wcrc rqxxtcd svveral trials later. Spontaiieously corrertcd errors were trcatfxl as correct, rcsponscs. ) “Thcrr is one minor exception to one thing I’ve told you. Some of the simplest shapes, that is, some of the &angle shapes, actually hav exact,ly 6 anglcbs in them. If you notice this, just ignore it and call them fives, okay? Now, before we start with the shapcy, I’m going to give you some practice to get used to where the diffcr(>ut buttons are. I’ll do thi,q l)y calling out. the (liffcivnt numbvrv, and you press thv bilt~totl that corresponds t,o each number.” Approximately tight to ten such practice trials were sufficient for the IS to 1Parn the dis~rimin:~ti~e respotiscs , so that he did not need to look at the arrangement, of buttons when responding. The practice trials were followed by 48 experimental trials. (The children were shown an IXample of each class of shapes during atlministration of the instructions.) Earh of t)hc two age samples was subclivided into three groups of ten Ss. 011~ of thcsp three groups CA-S) was given 24 trials of asymmetrical shape: followed by 24 trials of symmetrical shapes. A second group (S-A) was shown t’hc two stimulus sets in rcvcrsc order. A third group 0!Iixcd~ was gilyen 48 trials of both forms of shapes intermixed randomly, within the requirement that symmetrical and asymmc$rical shapes of each class ocrurrccl qually often within successive blocks of eight t.rial,s. For the :~symmct,rical and symmetrical se& presented int,act, equal nunib~r~ of 5-> IO-, 20-, and 40-turn shapes appeared within blocks of Piglit, tri:il?.

410

RODl?RIC!K

FORShlAYi

Illumination of the stimulus ~1~1 :tctixxt,ion of the electric timer were controlled simultaneously by a single switch. Thwe operations were stopped by a rwpoiw from S. A holding thircuit kept. tSlie timer inactivated and the stimulus compartment darkcnvd following tlw S’s rcleasc of a rcsponx hutton. The l:atcncy of the IYJ~~WIW~ for that. trial was then recorded, am1 :L new stimulus was pl:~c~~din tlic compartmriit accor(ling tSo a prcarrangwl o&r. The :Ludil)lc click mxlc by wch wetting of the t,imcr sigixalccl to the S that. another t~rial woul~l begiti within a few sw0~1s. The swsion proc~~l~~l at :ln av~~r:~g~pact’ of four to fixxb trials 1~1 minute.

The 24 presentations of :qmnlctrical ~hapcs, and those of hymmetrical shape, wrc scparatoly divicdcd illto three blocks of eight trials. Within each block, the two RTs oht~aincd for cwh class of shape were summed. For t#lw Mixed groql, the latw(~ics wrc sorted xcording to asymmctrial and synimctriwl wt’s prior to summing. These sum scores wow entvrpd into :a l,(,l~(,:~t~~l-~ilc~~surcs analysis of variance in which age ~1~1 or~lcr of ~l~l~lil~i~t~,:~tioiiwere lwtwcn-group factors, while stimulus complexity, form, :~n(l l~lo~ks of kials were repeated-mcasurw fartow. -111 main effects rxcept order OPINEAgliifirxntly rcsl:ited to RT. Adults wsponded faster than rhildrcn (P = 16.68, elf = 1 and 54, p < ,001). The mow complex shalw s wrrc (*l:wsifkd 1~~s ixpidly than the simpler ones (j’ = 49.58, fij = 3 and 162, p < .OOl 1. RT incrcaw(l liwarly with rcwhiiig x71 zsymptotc for 20- and 40-t,urn 5-, lo-, :mcl 20-turn shpw, shapes. Figuw I shows t,lw interaction of :[~csa1111voml)lcxity Cl+’= 5.83, clj = 3 and 162, p < ,001 ) . Tlw children wxrc slowr to rwpon(l than the adults for :a11clasws of shapes, hut the :igc diffctwcc is greatest’ for loand 20-t,urn figures. With respect] to the latter finding, one may note a possible sourc(x of addit,ional task uncertainty for the 8 in the fact that thwc t,wo cla~sw of intcrmediak complexity could hr w~srl:wsifie~l in eit,hw of two directions, whereas a S-turn shape could errowously be 0zxvwtimated, and a 4O-t,ilrn shalx~ crroncously z~~~~~~~~~ti~~l:~t,(,(l in romplwity. The children’s disproportionately blower classification of loand 20-turn shapes, :w coniparc(d with xlults? swnis to rcflwt this additional uncertainty. The classes of wymmctrical shapes wrr~~ mow quickly classifi~~d t#han t,hosr of symm&riral ones (F = 18.54, (lj = 1 and 54, p < ,001 J. As Fig. 2 indicates! the diffcrencc was largwt, in the case of tlw synnnvtrical and asymmetrical shapw administ~ererl first, (A-S and S-*41 This intcract,ion of orckr IqJ form (Zp = 20.52, Cl! = 2 :and 54, ‘p < .Wl) suggests

CHOICE

RFlACTION

AND

1

,

5

N”M:ER

FIG. 1. Mean of 5,10,20, and

reaction 40 turns.

time

I

of

adults

VISUAL

411

SEARCH

I

,

20

40

OF TURNS

and

children

for

classifying

random

shapes

!

1 MIXEO

FIRST

ORDER

OF

FOLLOWING OPPOSITE FORM

ADMINISTRATION

FIG. 2. Mean reaction time for classifying shapes administered in three different orders

symmctriral to separate

and groups

asymmetrical of ASS.

random

412

RODERICK

FORYM 5

L4S

that the within-trials experience in discriminating classes of complexity in as~ynmctrical shapes had greater transfer value for the subsequent discrimim~tion of Plasses of complexity in symmetrical shapes than did t,he re~rse order ( SA4’). The Mixe(l voudition effectively controlled for qerific transfer of experi~~n~(~with eitll(Br form, on sul)s(~(~uvnt performancv with the :tltPrnate forni, t)y intermixing the two forms r:domly across trials. The interaction illustrated in Fig. 2 differed with age. This :Lgc (litierencc is indicated by the inter:iction of age, or&r, and form (~b’= 5.56, dj = 2 :md ,54! 71< .Ol), Ivliirh is pr(~~ctite(l graphidly in Fig. 3. AUults

L

’

1

FIRST

MIXED

ORDER 3~. 3. Mean symrnc-trical (S)

rwckiou time or asymmetrical

for

FOLLOWING OPPOSITE FORM

OF ADMINISTRATION classifying (A) form,

random and order

shprs, as :i function of administration.

of

foun(l initiaZly encountered bymmetry rvlativcly more difficult (as compared with asymmetry) than did the children. This comparison suggests :i possible age Mfcrcntial in sensitivity to symmetry and ;Lsymmetry. In the classification of shapes in the form-set, the children wcw hcndited more th:m were the dults hy t~h~~irprior task experielice, irrcspectivc of form. Curiously, Lidults W+OS~ initial experience was in classifying asvmmdrical . shapes tended not to hive shorter R.Ts in the ~eco~i~l-~~~lnli~listcrc~lset of tBrids of symmetrical shapes. Tll~ slight il~vrease in RT! seen in Fig. 3, W:W ~lu~a:Llmost esclusively to cliffi~~ulty itI ~lisfl~illii~l:~ti~~g20-turn and 40-turn symmetrical

BLOCKS OF TRIALS e

CHILDREN

ADULTS

1

5

FIG. 4. Mean reaction as a function of complexity

IO NUMBER

time of adults and successive

OF

20 TURNS

40

and children for blocks of trials.

classifying

random

sha~ws

CHOICE

cognitive maturity, tive of his age.

REACTIOK

and is relatively

,1X1)

VISCAL

SE.kRCH

easy for the 8 to perform

415 irrcspec-

5l3ast Lawn Elementary School and -J. W. Eater Junior High School, Rmtoul, Illinois. The intpwst and cooperation of their respm+iw principals, Mr, Joseph (2, F’ilan~l and Mr. Gmald Obrwht, and tlwir teachers, arc gratefully xknowkdgrd, ’ T11e data of two additional Ss, a third-gradm and an adult, wxe diwardcd bevx~w~ of lligh error scores.

Following quwtion~, t,hc instructioiis for speed, wcuracy, and systematic left-right scanning were rwmph:wizcd. Three a~lditional practice trials were given to acquaint the S further with t,hc task. Each class of complexity occurred oliw in the practiw trials. Bcforc each trial, the E inxrtc(l the next card into the reader, and indicated a “go ahead” to the S by the re11 signal light. The S’s subsequent press of his switch rcwltcld in the offset of the signal light ancl the onset of the target shape. The target was displayc(l alone for 2 seconds prior to the owct of the field. An electronic clock was actix~ted at the same time as the field onset. The trial was terminated by a second prws of the S’s switch, which darkened the display ancl stopped the clock. The S reportecl the ~UVL?E~ of the ficlrl stimulus which matched thr target. If S was correct, the warch time for that t8rial was recorded (in 0.01 swond). If the rcportcd match was ineorrwt, the error was rword~~l anal the trial was rqxatcd following the fifth subsequ(Jnt, trial.

CHOICE

REACTION

AiXD

TABLE

*p < .OOl. ** p < .ot.

VISUAL

1

SEARCH

419

CHOICE

IUUCTIOK

AND

VISLAL

421

SEARCH

the brief span of a single experimental session (see Table 2 for all mean search time scores averaged across target posit8ion). The expected interaction of age and complexity showed that younger children did find the more complcs shapes disproportionately more difficult to locate rapidly than dkd the older children and adults. Form also intcractc(1 with complexity (WC Fig. 5). The retarding effect of asymmetry, rclativc to symmct,ry, on s~!arch 5pe~Ylwas progressively greater for the 20-turn anI1 40-turn shapes. 6 GRADE

0’

’

I

’

2

’

3

TARGET

’

4

’

5

’

6

’

7

’

0

3

’

9

POSITION

Target position was treated statistically as a factor not 0nLy to providc information about possible differential age, form, complexity, and trial-blocks effects, but also to provide evidence concerning the extent to which Ss followed the instructions to scan systematically from left to right in each display trial. The linear increase of search time with increasing displacement, of the target to the right in the field indicates that, considered as a group, the S’S(iid exccutc their searches in a regular left-right direction. -411 interesting age difference was indicated in the age by target position interaction, shown in Fig. 6. L411three age groups showed regular increments of search time associated with the successiy(l ordinal positions of the hrgct patterns in the displays, up to and including t8hc seventh

422

RODERICK

FORSMAX

target poGtion. However, t’lic search times for both okkr groups asymptote, whereas t,ho>c for the young~t SS decrease, over ordinal target positions 7, 8, and 9. The al~ncc of direct informat,ion about eye movements limits interpretation of this age differcncc. 0nc suggested hypot’hcsis is that t’hc sixth-grad(xrs and adults ~-crc more Fystemat,i(x iii their scarch(+ through th(l CU~~Wdisl)l:ty t8h:iil wvw th
ASYMMETRICAL

&is

0:

I23456789 TARGET

POSITION

(i.e., on trials wheu the t.argct matj(~h LV:LSi~unll~r 7, 8, or 9 1. Cousidei what the scanner must bc doing in each starch trial. I’art of each cumulative search time may be apportioned to the Ss glancing lx~ck to “IX>fresh his memory” about what. the target, pattern looks like, :m~l~‘or to compare the located match with the target for confirmation. If t,h(l carrect match is in the far right of the display on a given trixl, possibly several review glances have already occurred by the last third of the display, each review having rcsult’ed in a more stable image of the target. One could interpret the asymptotic search times of the two ohlcr groups for the final three target positions in terms of rapid scanmug facilitated by the nonoccurrence of addit,ional reviewing of the t,arget. on the other hand, may have tended t,o skip to the The third-graders, final display pattern if the target hacl not bun found by the sixth ot seventh pat,tern. Figure 7 shows tb(x interaction of form anI target, position. In view of the previously described main effect, of form, which associatccl sym-

metry with a facilitating effect on search speed7 the interaction demonstrates the .sume facilitation on a time-per-item basis. (The slope of any scar~h t,ime by target-position function denotes sranning time per item, :md an interaction such as that depictcad in Fig. 7 in~li(~at(~sa difference twtwwn slopes.) The slower search associated with pattcrlls of grc:tkr complcxit~ would also be cxpectecl to interact statistically with t:qkLt po,Ation. Slop? (tifYerencc+ were predickd, i.e., that search time ~oul~l iiicrcase more fol 20- and 40-turn shapes than for 5- and lo-turn sh:~p~+. u :L function of the higher ordinal posit’ion of the target p:xtt(‘rn in thy ~liq)lay. Figure 8 shows the obtained interaction of (*oniplvxitJ :ui~l txrg(lt IGtiotk. NUMBER OF TURNS

5

01 FIG.

of

the

S. Mean starch target pattern

and

’

’

’

123456789 TARGET

time scores complexity.

’

’

’

’

’

’

POSITION

of S as a ,ioint

function

of the

ordin;

lktion

A significant three-way interaction of form, complcxityJ and target position inclicated t,hat the relations shown in Fig. S :W Ilot identical for the two types of form. Inspect~ion of this interaction suggests that ~~.synmetricaZ 20-turn and 40-turn shapes led to ~lisl)rol~~Jrtioiiately .qlower search t,han did sy~mnaetriml 20-turn and 40-turn shap(~. as a fmlction of target position, but that the slop(n diffcrcnre for the two t’orms did not obtain when the sc:arrhes involve{1 the simpler 5- and loturn patterns. In short, the interaction of form, complexity, am1 target l)osition demonstrates t,he form by complexity interaction tl?ig. 5~1on :I time-per-item basis.

asymmetrical forms because the majority ul’ ol)~ivcts in our (~~~~~i~~(~tl~~l~l~t, we symmetrical. Perhaps the most notable finding of both cxpcriments was the consistently superior performance of the older Ss. An (q3lanation Of t,he :Lg(J variance in search speed, for example, by an hypothesis of :tgc-correlat(~~l diffcrenccs in task motivation would fail t,o accouiit for the obscrwd interactions between age and the form and complexity wri:~blw. Marcover, if the older Ss scanned fast,er because Ul(!y ww mow moi,ivat(t(l, an interaction of age by trial blocks shoul(l liaw bwn obscrwd. IIow:~~~~r, the younger 23simprowd their pcrformancc (Turin-0 the II38 trials 3s much as did the older 8s. Only in the RT cxperimcnt Idid :qe intwact with t,rials, and there the interaction shoxwl that the c~~&/w~‘,s Iwrfwtn:~nw improved more than the adults’ across trial?. :Ll)ilit,y is A more plausible account of thts age wriancc iii wwning offered by perceptual and cognitiw factors. ExIwricllw wil.11 pattern complexity must lead to the formation of cocling rules which, onc(’ format-1 and integrated into the cognitive strucWc of the il~~lividual, allow him to process and to order progrcssivcly greater :miounts of informat~ion cxtractccl from the environment. The possession tq chil~lr(w of fewer and Icss adqua& coding rules than adults is con&tcnt wit11 the fillcling in Uie visual search study that the general adwnt3ge of ~yni~ii(atry xvas wen greater among the younger 3s. Conwrwly, increaws in tlw complexity of patterns cwrtcd a ~lisI)ro~ort’ioii:ltcl~ l:lrgct~ i~ct:li~(lingt$fw~ on t,Iie search speed of the younger 8s. JYliat might tlicw “coding rules,” which li:t\.tx 1~~3 :wignc(l Llw t~lir(1ct~ of q~lanation, bc like? Their formal status is fr:mkly :wsu~t~I)tivt~, an(l worse, their (1cIinwtion is wguc. But, cwn xvith only q~arw knowlc~lg~ of the mechanisms of human inforniatiou prow+ing, likely c:in(lirlat,cs arc available. Some rulw arc un~loubtc~lly :attcntion:tl, invol~?ng mechanisms for classifying impinging information into 3 r~~l~~~xnt, :li1(1~‘iwfi11” portSion, the remainder being irrclcvant. 13ro:xltwnt (19.58 1 11:~ po,+latc(l :l “filter” mechanism sewing .such a scltxtivc function. In th(l raw of random shapes, such :L mechanism would I~i~~suni~bl~ ii~herc in I):lrtiwl:ir contour features as suggested by the fincling that Ss ~:unplo~l only :i part, of the contour of some patterns for the twgct of ~~:wli. (~)thcr cotliiig l,lllcs must consist of Icarncd factors! for (x~lliplc. t,llc :~~ail:~l)ility of tlamcs, labels, am1 meaningful associations to the in(lix-i(luaI patterns, or otherwise knowing what stimulus xttributc ELI ~nco~lc fir,.