Br. J . PsychZ. (1976), 67, 1, p p . 89-100
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Printed in Great Brituin
CONSTRAINTS ON CLASSIFICATORY SKILLS I N YOUNG CHILDREN BY ROBIN CAMPBELL University of Stirling MARGARET DONALDSON University of Edinburgh AND
BRIAN YOUNG
University of Hong Kong On three occasions over a one-year period 23 children aged 3-4 were asked to match target objects with other objects which were similar to the target in shape or in colour but not in both. A sequence of matches to each target waa asked for. The structure of these sequences is examined for evidence of classificatory abilities. Many subjecta appear to be attempting (not always successfully) to follow a strategy of ‘holding fast’ to their original choice of matching criterion (colour or shape) on subsequent trials. The striking differences between performance after a first-trial colour-match and after a first-trial shape-match are described. It is argued that development during this period involves an increasing ability to ignore the more salient attribute (shape) when matching by colour. The general developmental significance is discussed.
If a person gives evidence of ability to discriminate between objects on some basis of likeness and difference is this enough to warrant the conclusion that he is able to classify? Most writers on the subject - including Inhelder & Piaget (1964), Werner (1948) and Vygotsky (1962), who have contributed perhaps more than any others to our understanding of classificatory skills - would agree that it is not. When a child selects all the red objects then all the white objects and so on from a pile of different colours we can no more be sure that he is classifying than we are justified in ascribing classificatory skill to a bee which systematically discriminates between one type of flower and another. In the definition of classification more than the discrimination of attributes is involved. Inhelder & Piaget, Werner and Vygotsky have somewhat different ways of stating what more is necessary for true classification and of testing for its presence. Yet they would all agree on this point: that classification is marked at one and the same time by the ability to hold consistently to a criterion of grouping, once chosen, and by the ability to abandon this criterion by a deliberate act of decision and reclassify on a basis that is entirely new. This amounts to saying that, for all three writers, the critical issue is whether the overall behaviour is under the control of an active plan. Is the subject passively noting resemblances or is he actively constructing a classificatory system? We are concerned in this paper with the development of classificatory skills in children. However, it has often been suggested that there exist parallels between early behaviour patterns and those that are characteristic of pathological mental states in adults. It is therefore interesting to note that Werner (1948) argues strongly
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for such parallels in the w e of classification. He refers to the work of Gelb & Goldstein (1925) who, in speaking of their brain-damaged patients, make very clear the distinction between passive registration and active construction. Gelb & Goldstein say: ‘If in sorting they put particular colours together, this procedure is forced upon them passively by the experience of coherence of the moment. Furthermore, even when a particular aspect of the sensory impression has forced this procedure on them, the patients are unable to hold fast to this aspect in their subsequent procedure. They cannot make it into a principle of classification.. .’ The question we shall now consider is whether our subjects (children between the ages of three and five) are at the mercy of some such momentary ‘experience of coherence’ when they respond to likenesses and differences in the materials that we present to them, or whether the evidence justifies us in saying that ‘principles of classification’ already guide the patterns of their responding. It should be noted now that most previous studies of the classifictt&oryskills of children in this age range have tended to the conclusion that true classification is beyond their powers. On this point, too, Inhelder & Piaget, Werner and Vygotsky are at one. Traditionally, methods of investigating classificatory skills have involved sorting tasks and matching tasks. In the former a collection of objects differing in shape, size, colour, etc., is placed before the subject who is invited to ‘put the ones that are the same together’ or some such. This is sometimes followed by a second invitation to ‘do it another way’. Consistent sorting in both phases of such a task can probably be regarded as a suflicient condition for the existence of classificatory powers. The subject is clearly capable of sorting the material in alternative ways and the consistency of his performance makes it unlikely that his treatment of each object is under the control of whatever property he happens to notice at the time. Unlike Gelb & Goldstein’s patients he is able to ‘hold fast’ to a particular aspect. Matching tasks constitute a less severe, possibly minimal, test of classificatory abilities. They do not call for the sustained concentration and motor control demanded by sorting tasks and are therefore valuable for studying the early stages of the development of classificatory skills, since pre-school children are often hyperactive, easily distractable, and impatient with lengthy manipulative tasks, the point of which no doubt escapes them. In matching tasks the subject is required to select an object which matches (‘is the same as’) some target object. If he is encouraged to pick a number of objects, one after the other, as matches to the same target object in a situation where matches according to more than one criterion are possible, then the nature of the chosen sequence gives evidence about whether he ‘holds fast’ to one criterion and whether, when the set of objects that satisfy this criterion is exhausted, he is able to recognize that an alternative basis for matching remains. In this paper we report the results of a longitudinal study using matching tasks as the basis for an assessment of clctssiGcatory skill.
METHOD MderiaES Two sorts of stimulusmaterial were used: common objects and formal shapes. The formerwere pencils, toothbrushes, eggcups and miniature plastic roses, sll in a a g e of coloure; the latter
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were squares, circles, triangles and narrow rectangles, all cut from coloured perspex so that the biggest dimension of each figure was approximately 1 in. The common objects were thus familiar and readily nameable and differed among themselves by many attributes other than the two (shape and colour) which were systematically varied. By contrast the formal shapes - and their names -were likely to be relatively unfamiliar to the children and differed only in shape and colour. From these materials two sets of objects were constructed as follows: Task 1: one red, one white and one yellow toothbrush; and similarly for eggcups, pencils and roses. Task 2: one red, one white and one black square; and similarly for circles, triangles and rectangles. Thus in each task there were five objects similar in shape or in colour to any given object but no objects similar in both. T w o other matching tasks in which the only objects similar to a given object were similar in both shape and colour were also used; but repeated matching was not studied in their case for obvious reasons, and results from them will not be reported in this paper. Subjecta The subjects were 23 children who were taking part in a larger longitudinal study of the development of cognitive skills. In socio-economic background, the children represented the middle range of the population. They came neither from culturally deprived homes, nor from homes that were specially intellectually stimulating. They were tested on three occasions, at mean ages of 3 years 7 months, 4 years 2 months and 4 years 6 months. The age range of the group was 9 months. The range of IQs on the Stanford-Binet Intelligence Scale before the first test was from 88 to 127 and the mean was 100. The results obtained from one subject have been discarded because it came to seem probable that he waa colour-blind.
Prdure On each of the three occasions of testing, referred to below aa Times 1, 2 and 3, the two matching tasks were administered in the same order: task 1 before task 2.* On eaoh task, several matching trials were allowed. The procedure for the first trial was as follows. The set of objects was plaoed haphazardly on a table with the subject facing the experimenter. A target object (task 1 -the red toothbrush; task 2 -the white square) was held up by the experimenter and the subject was asked ‘Give me one that’s the same as this one in some way’. On second and later trials the subject was asked, ‘Now give me another one that’s the same as this one in some way’. After each trial the selected object waa removed from sight. The target object remained the same throughout the series of trials. Repeated-matching trials ended when the subject failed to fhd a matahing object or when he shifted his criterion. That is, if the first two objects selected in task 1 were toothbrushes, they were presumed to be matches on the basis of shape (referred to below as shape-matches); if now the third object waa a red eggcup this waa presumed to be a match on the basis of colour (a colour-match). The subject waa asked to give a reason for each of his choices.
RESULTSAND DISCUSSION In the analysis that follows, S stands for a match on the basis of shape, C for a match on the basis of colour and 0 either for choice of an object which did not match (according t o our prejudices) or, much more commonly, for a statement that there were no matching objects.
* This study was not carried out in isolation but formed part of a much larger one, so some of the features of the present design were determined by the objectives of the wider study. For example, the precise choice of materials was influenced by consideration of certain other taaks which were to be given to the children. And the absence of counterbalanoingin the order of task presentation is attributable to the faot that we wanted to be able to make strict comparisons between individual children in the course of longitudinal analysis of the findings.
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R. CAMPBELL,M. DON~LDSON AND B. YOTJNGI Table 1. Sequential matching padtern overall frequenoy of ooourrenoe
Response pattern 1 0 2 s0 3 sc 4 c0 6 CS 6 SS0 7 ssc 8 ccs
8 7
3 9 16 26 13 8 6 7 31
cc0 cccs ccc0
9
10 11
Table 2. Distribution of types of response pattern Type of response p8ttern *
f
\
No Typeofmateriel
response
P,
P,
El
E,
Common objeota Formal shapes
6
3
12 10
13 13
28 28
8 12
Table 1 gives the 11 different patterns of response and their frequencies over all trials and on all occasions of testing. That is, it shows how often, overall, a given sequence of choices occurred. Thus, for instance, the choice of a single object that matched on the basis of shape followed by no further matching choice (pattern 2) occurred seven times. In the light of the question asked in the introduction, two features of Table 1 are of particular interest: (1) whether the set of objects satisfying the initial matching criterion is exhausted; and (2) whether the criterion ever changes. If the patterns in Table 1 are grouped according to whether or not they possess these two features, then we have the following four types of pattern (excluding pattern 1 in which no matching choice at all is made). (1) Partial single-criterion matching, in whioh there is no oriterion shift but the single category used is not exhausted. This type is exemplified by patterns 2 , 4 and 9 in Table 1. We refer to it in future aa type P, - that is, partial and involving only one criterion. (2) Partial double-criterion matching (P,) in which both criteria are used but neither category is exhausted. This is exemplified by patterns 3,6 and 8. (3) Exhaustive single-criterion matching (El), in which there is no criterion shift but the single category used is exhausted: patterns 6 and 11. (4) Exhaustive double-criterion matching (E,) in which the fist category used is exhausted and then there is a shift of criterion to the second category: patterns 7 and 10. (It should be noted that we did not persist in ctsking for more choices after this point to avoid undue lengthening of the task (cf. Procedure), so the reference to exhaustive matching is a reference to exhaustion of the first category only.) Table 2 gives the frequencies of these four types of pattern and of the residual
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category of no response for the two kinds of material - common objects and formal shapes. A 22 test reveals no evidence of association between type of material and type of response (x2= 1.66; d.f. = 4; P > 0.76). So in the report which follows we present results for the two kinds of material combined. Single-criterion matching (types P, and El) occurred in 63 per cent of all cases (excluding, once again, those where no matching choice was made, i.e. pattern 1, Table 1). A notable feature of single-criterion matching is that type El was more common than type P, (72 and 28 per cent, respectively) - that is, more often than not, all objects which matched according to the criterion in question were selected. So there is some evidence of a tendency to hold to a criterion once chosen. And it should be noted that there are no grounds for believing that this tendency is due to some enduring preference for shape or colour on the child’s part. Colour-matching was slightly more common than shape-matclung on initial trials (60 per cent of choices); but at Trial 1 there were always three colour-matches available in the pool and only two shape-matches (see Method). Moreover, our data were not produced by so many individuals who always chose colour and so many who always chose shape. Each child performed this task six times (two types of material by three times of testing) so that there were seven different possible categories of performance (initial match by shape six times, by colour no times; initial match by shape five times, by colour one time, etc.). The distribution of children over these categories is approximately binomial with equal probabilities, as we would expect if the choice of a basis for matching depended on the whim of the moment. Again, those few children who did show an extreme preference for a colour or shape-match on the initial trials were only slightly more prone than the group as a whole to singlecriterion matching (68 per cent of caaes). So the ‘modal’ type of response in our sample is exhaustive single-criterion
94 R. CAMPBELL,M. DONALDSON AND B. Yoma matching (type El) which is characterized by: (1)apparently unsystematic selection of the initial matching criterion; (2) adherence to this criterion once chosen; (3) exhaustion of the relevant category of objects; (4) failure to shift to another matching criterion when the first criterion yields no more choices. Fig. 1 gives the proportions of the four different types of response at the three times of testing. The suffix ‘ a y appended to a pattern category indicatm that the first match was based on shape; and the results for cases where this occurred are shown in Fig. 1B. Similarly the results when the first match was baaed on colour are shown in Fig. 1C and marked by the suffix ‘c’. Fig. 1A gives the two combined. The symbol 0 indicates that no matching choice was made. The numbers below abscissa marks indicate the number of cases on which the proportions are based. Figs. 1 B and 1 C obviously do not include subjects whose response pattern waa pattern 1, i.e. subjects who did not provide either a shape-match or a colour-match at all. Fig. 1A shows that the frequencies of PI and P, decline with age while those of El and E, increaae. Figs. 1B and 1C make it clear, however, that there is considerable interaction between the age trends and the nature of the initial match, for the increase in E, is found only when the first match is a shape-match and the increase in Elis found only when the firat match is a colour-match. Moreover, there is a considerable disparity between the level of P, responses and that of P,. These differences might be thought to be explicable on the general ground that more colour choices than shape choices are available and therefore exhaustion of the colour category might be expected to be slower to appear on some assumption that the ability to sustain interest in the tmk would increase with age. However the disparity between P, and P, is maintained over all three occasions of testing so that does not seem to be a particularly helpful explanation. Moreover, it is the level of initial shape responses which is the lower, though initial colour, on average, involves more matches. Comparison of P, with Elgives a clue to where a better explanation may be found. When the initial match is a shape-match subjects are more likely to hold to and and less likely to shift to the other criterion without exhaust a single criterion (El) exhausting the first category (PB) than when the initial match is a colour-match. One way to try to account for this is simply to suppose that the children attended more readily to the shape of an object than to its colour, which at first appears perfectly plausible. However, this notion runs into difficulties with two other aspects of the data: (1) the roughly equivalent levels of choice of a fht match by colour and by shape (colour being, if anything, slightly more common); and (2) the increase in E, from Time 1 to Time 3 while E, remains low throughout. The latter objection is particularly damning since, if shape is the more likely to attract attention, the probability of shifting to shape after exhausting colour should be greater than the probability of shifting to colour after exhausting shape. A somewhat Merent explanation is therefore proposed. This alternative explanation is like the first in supposing that shape tends to be in some way a more salient attribute than colour; but it emphasizes not so much attention to a salient attribute as the ability t o ignore one. Let us postulate that in order to ca,rry out a successful single-criterion matching process the child has not only to attend to the attribute which forms the basis of the match but also to w e in some positive manner any more salient attribute which does not. The notion
Clmsi$catory skills
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is that some attributes are more intrusive than others and must be positively kept out if adherence to a less intrusive one is to be achieved. This notion is not introduced here as a novel idea. It has a considerable ancestry, though it has not always received the attention it deserves. Kiilpe (1904) distinguished two perceptual processes of set: positive abstraction in which a crucial aspect of the stimulus is accentuated; and negative abstraction in which the perception of incidental aspects of the stimulus is actively inhibited. What we propose is that processes of negative abstraction are important in the business of ‘holding fast’ to a criterion m e chosen, and resisting the temptation to switch to another. It is important to stress that we are not talking here about the initial attractiveness of the different attributes. It is only after an initial choice has been made that it makes sense to speak of the ‘intrusion’ of some feature of the stimulus - a feature which would have to be ignored if a particular strategy were to be followed consistently. We propose, then, that the initial choices are largely fortuitous, dependent perhaps on where the child‘s glance happens to fall as he looks at the array but that differences arise when it is a question of a whole sequence of responses, i.e. of deliberately redirecting attention if the glance happens to fall in the wrong direction. The following two suggestions seem to fit a number of aspects of our data: first, that the shape of an object is more difficult to ignore in this deliberate and sustained way than its colour;* and second that, with increasing age, subjects become more competent at ignoring. Then El, responses will require a deliberate attempt to ignore shape, whereas E, will call for the less difficult ignoring of colour (which can account for the differences between these two pattern in Fig. 1). If the attempt to ignore shape fails then an differences). (involuntary) shape-match will result (accounting for the P,-P, Lastly, even if the attempt to ignore shape is successful, the E , m a t c h pattern will still be difficult since it calls first for an effort to ignore shape and then for enough flexibility to start attendmg to it. E,, on the other hand, looks like a shift in an easier direction. We may now postulate two ways in which a single-criterion matching process might fail to lead to exhaustion of the category. Either there is failure of some process not specific to the matching task itself (some inadequacy of search of the array perhaps) so that a response of type P, results; or else the attempt to ignore one attribute fails, yielding a response of type P, - and this is more likely when the attribute to be ignored is shape, with the result that P , responses are more numerous than P,. Consideration of the curves for P, and P, in Fig. 1 makes it seem likely that failures due to the first of these causes are soon eradicated, whereas failures due to the second are still present to some extent even at the third time of testing. These remarks suggest the following developmental pattern. Type P , has been omitted from Fig. 2 because the place it should occupy is unclear. In fact, there are only three instances of this response (out of 132 responses) so that, as far m our data can indicate, it matters little where we put it.
* Blum & Porter (1973) report work with adult subjects in which active inhibition of attention waa triggered by a post-hypnotic cue. They found attention to form harder to inhibit than attention to colour; and they stress the importance of Kiilpe’s distinction.
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R. CAMPBELL,M. DONALDSON AND B. Yoma
Fig. 2. Developmental relationehipa between typea of m8bhhg pattern. (crOsS-seCtiOD8l analysis.)
We now conclude by examining the longitudinal sequences to see how they relate to the scheme shown in Fig. 2. The usual technique for investigating longitudinal trends where the data can be ranked is to use Kendall’s S as a descriptive statistic and employ, for instance, Jonckheere’s test for trend (1967) to test hypotheses of no trend. Since we are dealing with nominal data this cannot be done. Kendall’s S compares the rank of items early in a longitudinal sequence with the rank of those that come later, working from early to late through the sequence and summing the differences (positive or negative) in ranks. A comparable approach with nominal data seems to be to take the firsf item in the sequence and note those which come after it, logging an entry in the appropriate row of an r z x n matrix for each such subsequent item (where rz is the number of nominal categories). The next item is then treated in the same way and so on until the end of the sequence is reached. Given a pair of categories, A and By we can then find in our sample how many times A occurs before B and how many times B occurs before A and compare the two. If this is done for our nine categorim 0, PI,,Pie, .. ., E, with the Task 1 data and again with the Task 2 data then in many cams the number of before-after comparisons is exceedingly small. If the distribution is 4: 0 in favour of our hypothesis, four such comparisoas are suflEicient to yield a one-tailed P of 0.06 on an exact test of no longitudinal priority, so we w i l l report only those cases where we have four or more such before-after comparisons. With these provisions, we get the results shown in Table 3. In Table 3, z/y means that of the z+y comparisons, z were ‘befores’ and y were ‘afters’. In brackets, P values on an exact test of no priority are given. These tests are one- or two-tailed dependmg on the cross-sectional indication. Clearly from the results shown in Table 3 for Tasks 1 and 2 separately, little can be inferred beyond perhaps that P,, and P, are developmentally prior to Ele. However, the agreement between the results from the two tasks is sufEciently good to justify pooling them. The pooled results in Table 3 yield the information about developmental priority shown in Fig. 3. (In the diagram, an arrow indicates priority.) If one takes all the priorities suggested by our analysis of the cross-sectional results (cf. Fig. 2) and counts the number of ‘befores ’ consistent with these priorities and the number inconsistent with them, it turas out that 86 per cent of the relevant comparisons are consistent with the cross-sectionalanalysis, which seems reasonably good agreement. In an attempt to resolve some of the remaining issues of developmental priority, we now present the data from Tasks 1 and 2, having combined them directly, i.e. before making any analysis of before-after comparisons. This manoeuvre yields for each child a structure consisting of a sequence of three paira of responses. From each such structure, three coincidences, 12 ‘befores’ and 12 ‘ai’bm’ are
97
Clussi$icatory skills Table 3. Before-after comparisons Task 1 PI, before El,: 4/0; P,, before El: 2/4; Pp,before Elo: 6/0; ( P = 0.06)* ( P = 049)t ( P = 0.01). El, before El,: 6/1; El, before Ez0:0/4 ( P = O.ll)* ( P = 0.13)t PI, before El,: 4/0; ( P = 0.06)*
Task 2 P,, before El,: 9/1; E, before El,: 4/1 ( P = 0.01)* ( P = 0.19)* El, before E,: 4/l ( P = 0.38)t
Tasks 1 and 2 combined PI, before Pzo:4/0 ( P = 0.06)* PI, before El,: 8/0; PI; before El,: 4/0; P1,before E2,: 6/0 ( P < 0.01)* ( P = 0.06)’ ( P = 0.03)* P,, before El”:2 / 6 ; P,, before El,: 16/1; P,, before Ez,: 3/0 ( P = 0.46)t ( P < 0.01)* ( P = 0.31)* E, before El,:9/2; El ‘before E,,: 3/1; E,, before E?,: 3/1 ( P = 0.03)* ( P = 0.31)* ( P = 0.31)* El, before E,,: 4/6 ( P = l.OO)t * One-tailed. t Two-tailed.
Fig. 3. Developmental relationshipsbetween types of matching pattern. (Longitudinalanalysis.)
obtained. The results of the analysis will not be presented in full since the matrix is massive and many of the cells still contain small numbers. The omission of such cells yields the half-matrix shown in Table 4. Inside each cell is the distribution of ‘befores’, coincidences and ‘afters’ and the goodness of fit x2 value for the null expectation of 12: 6: 12. It is evident that we have substantial confirmation of the results obtained from the tasks considered singly and we are therefore justified in making further inferences from the pooled data. Also we can, with some confidence, argue that there is no developmental priority of PZcwith respect to El,and of El, with respect to E,, an important point in connexion with our presentation of the cross-sectional data relating to these categories given earlier. The indications of these longitudinal results are summarized in Fig. 4. The horizontal axis represents level of development, the two sequences of categories represent longitudinal priority aa assessed by the above analyses, and the bell-shaped curves represent the distribution of cases with respect to level of development and with respect to the response categories (as shown in Fig. 1).It is important to stress 7
PSY
67
98
R. CAMPBELL,M. DONALDSON AND B. Yoma Table 4. Before-coincident+fter comparisons for Tmks 1 and 2 combined PI, pl#
4:2:0
(4.00) P*O
p*,
El0
E, p, 7:o:o 3:l:O (10.60) (2.88) 4:6:2 8:O:O (4.91) (12.00) 6:6:8 (1.31)
EP. El0 3:O:O 4:O:O (4.60) (6.00) 18:3:2 1l:l:O (14.61) (1342) 28:3:3 6:3:1 (25.63) (3.22) 19:1:4 6:2:2 (16.48) (1.28) 6:2: 10 (2.00)
Fig. 4. Schematic model relating level of development to favoured type of mmtching p8ttern.
that this is a mere indication - we are unable to find an inferential technique which would allow us t o express the degree of support for this model formally. Perhaps the best that can be said for it is that it is maximally consistent with the data obtained. As a final substantive point about these longitudinal results we would like to draw attention to the fact that, in the model just illustrated, double-criterion matching (Pzand E,) occurs at two different levels of development separated by a level at which only single-criterion matching is found. (This kind of developmental pattern is discussed in Donaldson, 1971.) On the other hand, the tendency to exhaust whatever category of objects is selected in Trial 1 of the matching task (El and E,) becomes steadily stronger as development proceeds. The main finding, then, is that, even at Time 1, there is a clear tendency for later choices in the sequence to be constrained by the initial one, though the initial choice itself may be largely fortuitous. If a child begins by matching on a given attribute he will tend t o hold to that attribute, and, increasingly as he grows older, he will tend to hold to it until no exemplars of it remain.
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A fundamental question about the nature of the constraint exercised by the first choice then arises. When a child holds to a single attribute is he following a planned strategy or is he merely ‘drawn’ to the objects which most resemble the one he has first chosen? Here a first point to note is that the objects which a child selected were removed from his sight before another choice was made. This, of itself, reduces the likelihood that anything like what Gelb & Goldstein (1925) call ‘the experience of coherence’ could explain our results. However, the fact of central significance is that there tend t o be different outcomes according t o whether the first choice is a colour-match or a shape-match. The detailed evidence which we have presented suggests that it is necessary t o introduce the notion that different attributes have different ‘saliency’ or ‘pull’, yet at the same time that the notion of increase in the capacity for voluntary - or planned - resistance to that pull has also t o be invoked to explain the developmental data. If a child begins by matching on the basis of shape it is easier for him to hold to this criterion than if he begins by matching on the basis of colour. And this is not so much a matter of being more or less prone t o attend t o a given attribute as of being more or less able t o ignore it. We have then a developmental lag of the kind shown in Figs. 2, 3 and 4 with the same sequence being followed for shape and colour but with colour showing systematic delay. To this general statement, however, it is necessary t o add a word of qualification. It would be unsafe to conclude that shape is easier t o hold to than colour for all shapes and for all colours. There is a growing amount of evidence for the existence of certain kinds of natural perceptual dominance; and among the evidence is a report by Rosch (1973) of findings that there are colours which are more perceptually salient than others; and likewise for forms. If this is so, then our results could perhaps be reversed by constructing the sets of objects from forms of low salience and from colours of high salience. (Both were probably highly salient in the sets we used.) However this may turn out, if the developmental disparity between shape and colour that we observed is indeed to be explained by postulating that some attributes are harder t o ignore than others and that the ability to ignore the more intrusive of them increases over the age-range we studied, then the bulk of our data can be accounted for in terms of successful and unsuccessful attempts to follow a strategy. Most earlier studies of the classificatory skills of young children have not led to a conclusion of this kind. Notably, the work of Vygotsky (1962) and of Inhelder &, Piaget (1964) has been taken to show that children of the age-range we have studied typically do not have a plan that they are attempting to follow. We are therefore in disagreement with them at this point; though, of course, i t is crucial not t o lose sight of the distinction between matching and sorting. It looks as if three main types of matching process occur in our sample. I n the first of these, there is a single-criterion strategy which, for one or another reason, fails; and this yields a matching pattern of either type P, or type P,. I n the second, the single-criterion strategy is successfully carried out; and this is the ‘modal’ process in our sample, yielding patterns of type El. I n the third, there is a doublecriterion strategy, i.e. the child carries out a single-criterion strategy successfully, then shifts t o the other category. This strategy produces response patterns of type E,, 7-2
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R. CAMPBELL,M. DONALDSON AND B. Yoma
which are rare in our group of subjects unless the fht choice is a match on the bash of shape. It must be noted that responses of type P, would readily be produced if no strategy of any kind were being followed (and so, of come, fortuitously, would some instances of the other types). No doubt there were a certain number of cases requiring an explanation of this kind. However, once again, the differencebetween the sequenoes beginning with shape and those beginning with colour helps one to see what is happening; for if there were no strategy a t all, the frequencies of P,, and of P,, would presumably be quite similar. The fact that P,, occurred very rarely (three instances out of 132 responses) argues strongly that, even at time 1 when the children were around 3 years 7 month old, a matching strategy, however unsuccessful, was usually there. We can therefore conclude that the children’s responses are not on the whole Iike those of Gelb & Goldstein’spatients. The procedures they follow are not forced upon them passively. On the contrary they already have some capacity to ‘hold fast’; and, at least towards the end of our study, they show signs of an ability to recognize that possible alternative bases for classification can exist. The limitation is that neither of these abilities is as yet free from circumstantial constraints. This is to say that the constraints which the formal classificatory taak imposes are still interacting with constraints of a very different kind. The latter-the circumstantial constraints - derive from a kind of force of circumstance that has no relevance for the task. Specifically, they derive in this instance from the child’s predispositions (‘natural’ predispositions perhaps) to respond in various ways to the nature of the material to be classified. The question of whether the matching sequence starts with shape or colour exerts an effect upon the outcome, though it is strictly irrelevant to the requirements of the classificatory endeavour. Until this ceases to be true, it obviously cannot be claimed that the children are, in the fullest sense, capable of classifying. This study waa supported by a grant from the Social Science Research Council. Roger Wales waa one of the investigators, and we gratefully acknowledge his contribution to the research.
REFERENCES BLTJM, G. S. & PORTER, M. L. (1973). The capacity for selective concentration on colour versus form of consonants. Cogn. Psychol. 5, 47-70. DONALDSON, M. (1971). Preconditions of inference. In J. K. Cole (ed.), N e b w k u Symposium on Motivation. Lincoln: University of Nebreska Press. GELB,A. & GOLDSTEIN, R. (1926). tfber Farbennahmenamnesie. P s y c b l . Formh. 6, 127-199. INHELDER, B. & PIAQET, J. (1964). The Early Qrowth of Logic in the ChiEd. London: Routledge & Kegan Paul. JONCKEEERE, A. R. & BOWER, G. H. (1967). Non-parametric trend tests for learning data. Br. J . math. statbt. Psychol. 20, 163-186. K W E , 0. (1904). Versuche uber Abstraktion. Berlin International Ccmgre-38 of Expet%me& Psychology, 66-68. ROSCH,E. H. (1973). Natural categories. Cogn. Psychol. 4, 328-360. WERNER,H. (1948). The Comparative Psychology of Mental Dev-nt. New York: International Universities Press. VYQOTSKY, L. S. (1962). Th~.qhtand L a m e . Cambridge, Mass:M.I.T. Prees~.
(Manuscript received 25 April 1974; revised manuscript 4 February 1978)
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Printed in Great Brituin
CONSTRAINTS ON CLASSIFICATORY SKILLS I N YOUNG CHILDREN BY ROBIN CAMPBELL University of Stirling MARGARET DONALDSON University of Edinburgh AND
BRIAN YOUNG
University of Hong Kong On three occasions over a one-year period 23 children aged 3-4 were asked to match target objects with other objects which were similar to the target in shape or in colour but not in both. A sequence of matches to each target waa asked for. The structure of these sequences is examined for evidence of classificatory abilities. Many subjecta appear to be attempting (not always successfully) to follow a strategy of ‘holding fast’ to their original choice of matching criterion (colour or shape) on subsequent trials. The striking differences between performance after a first-trial colour-match and after a first-trial shape-match are described. It is argued that development during this period involves an increasing ability to ignore the more salient attribute (shape) when matching by colour. The general developmental significance is discussed.
If a person gives evidence of ability to discriminate between objects on some basis of likeness and difference is this enough to warrant the conclusion that he is able to classify? Most writers on the subject - including Inhelder & Piaget (1964), Werner (1948) and Vygotsky (1962), who have contributed perhaps more than any others to our understanding of classificatory skills - would agree that it is not. When a child selects all the red objects then all the white objects and so on from a pile of different colours we can no more be sure that he is classifying than we are justified in ascribing classificatory skill to a bee which systematically discriminates between one type of flower and another. In the definition of classification more than the discrimination of attributes is involved. Inhelder & Piaget, Werner and Vygotsky have somewhat different ways of stating what more is necessary for true classification and of testing for its presence. Yet they would all agree on this point: that classification is marked at one and the same time by the ability to hold consistently to a criterion of grouping, once chosen, and by the ability to abandon this criterion by a deliberate act of decision and reclassify on a basis that is entirely new. This amounts to saying that, for all three writers, the critical issue is whether the overall behaviour is under the control of an active plan. Is the subject passively noting resemblances or is he actively constructing a classificatory system? We are concerned in this paper with the development of classificatory skills in children. However, it has often been suggested that there exist parallels between early behaviour patterns and those that are characteristic of pathological mental states in adults. It is therefore interesting to note that Werner (1948) argues strongly
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for such parallels in the w e of classification. He refers to the work of Gelb & Goldstein (1925) who, in speaking of their brain-damaged patients, make very clear the distinction between passive registration and active construction. Gelb & Goldstein say: ‘If in sorting they put particular colours together, this procedure is forced upon them passively by the experience of coherence of the moment. Furthermore, even when a particular aspect of the sensory impression has forced this procedure on them, the patients are unable to hold fast to this aspect in their subsequent procedure. They cannot make it into a principle of classification.. .’ The question we shall now consider is whether our subjects (children between the ages of three and five) are at the mercy of some such momentary ‘experience of coherence’ when they respond to likenesses and differences in the materials that we present to them, or whether the evidence justifies us in saying that ‘principles of classification’ already guide the patterns of their responding. It should be noted now that most previous studies of the classifictt&oryskills of children in this age range have tended to the conclusion that true classification is beyond their powers. On this point, too, Inhelder & Piaget, Werner and Vygotsky are at one. Traditionally, methods of investigating classificatory skills have involved sorting tasks and matching tasks. In the former a collection of objects differing in shape, size, colour, etc., is placed before the subject who is invited to ‘put the ones that are the same together’ or some such. This is sometimes followed by a second invitation to ‘do it another way’. Consistent sorting in both phases of such a task can probably be regarded as a suflicient condition for the existence of classificatory powers. The subject is clearly capable of sorting the material in alternative ways and the consistency of his performance makes it unlikely that his treatment of each object is under the control of whatever property he happens to notice at the time. Unlike Gelb & Goldstein’s patients he is able to ‘hold fast’ to a particular aspect. Matching tasks constitute a less severe, possibly minimal, test of classificatory abilities. They do not call for the sustained concentration and motor control demanded by sorting tasks and are therefore valuable for studying the early stages of the development of classificatory skills, since pre-school children are often hyperactive, easily distractable, and impatient with lengthy manipulative tasks, the point of which no doubt escapes them. In matching tasks the subject is required to select an object which matches (‘is the same as’) some target object. If he is encouraged to pick a number of objects, one after the other, as matches to the same target object in a situation where matches according to more than one criterion are possible, then the nature of the chosen sequence gives evidence about whether he ‘holds fast’ to one criterion and whether, when the set of objects that satisfy this criterion is exhausted, he is able to recognize that an alternative basis for matching remains. In this paper we report the results of a longitudinal study using matching tasks as the basis for an assessment of clctssiGcatory skill.
METHOD MderiaES Two sorts of stimulusmaterial were used: common objects and formal shapes. The formerwere pencils, toothbrushes, eggcups and miniature plastic roses, sll in a a g e of coloure; the latter
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were squares, circles, triangles and narrow rectangles, all cut from coloured perspex so that the biggest dimension of each figure was approximately 1 in. The common objects were thus familiar and readily nameable and differed among themselves by many attributes other than the two (shape and colour) which were systematically varied. By contrast the formal shapes - and their names -were likely to be relatively unfamiliar to the children and differed only in shape and colour. From these materials two sets of objects were constructed as follows: Task 1: one red, one white and one yellow toothbrush; and similarly for eggcups, pencils and roses. Task 2: one red, one white and one black square; and similarly for circles, triangles and rectangles. Thus in each task there were five objects similar in shape or in colour to any given object but no objects similar in both. T w o other matching tasks in which the only objects similar to a given object were similar in both shape and colour were also used; but repeated matching was not studied in their case for obvious reasons, and results from them will not be reported in this paper. Subjecta The subjects were 23 children who were taking part in a larger longitudinal study of the development of cognitive skills. In socio-economic background, the children represented the middle range of the population. They came neither from culturally deprived homes, nor from homes that were specially intellectually stimulating. They were tested on three occasions, at mean ages of 3 years 7 months, 4 years 2 months and 4 years 6 months. The age range of the group was 9 months. The range of IQs on the Stanford-Binet Intelligence Scale before the first test was from 88 to 127 and the mean was 100. The results obtained from one subject have been discarded because it came to seem probable that he waa colour-blind.
Prdure On each of the three occasions of testing, referred to below aa Times 1, 2 and 3, the two matching tasks were administered in the same order: task 1 before task 2.* On eaoh task, several matching trials were allowed. The procedure for the first trial was as follows. The set of objects was plaoed haphazardly on a table with the subject facing the experimenter. A target object (task 1 -the red toothbrush; task 2 -the white square) was held up by the experimenter and the subject was asked ‘Give me one that’s the same as this one in some way’. On second and later trials the subject was asked, ‘Now give me another one that’s the same as this one in some way’. After each trial the selected object waa removed from sight. The target object remained the same throughout the series of trials. Repeated-matching trials ended when the subject failed to fhd a matahing object or when he shifted his criterion. That is, if the first two objects selected in task 1 were toothbrushes, they were presumed to be matches on the basis of shape (referred to below as shape-matches); if now the third object waa a red eggcup this waa presumed to be a match on the basis of colour (a colour-match). The subject waa asked to give a reason for each of his choices.
RESULTSAND DISCUSSION In the analysis that follows, S stands for a match on the basis of shape, C for a match on the basis of colour and 0 either for choice of an object which did not match (according t o our prejudices) or, much more commonly, for a statement that there were no matching objects.
* This study was not carried out in isolation but formed part of a much larger one, so some of the features of the present design were determined by the objectives of the wider study. For example, the precise choice of materials was influenced by consideration of certain other taaks which were to be given to the children. And the absence of counterbalanoingin the order of task presentation is attributable to the faot that we wanted to be able to make strict comparisons between individual children in the course of longitudinal analysis of the findings.
92
R. CAMPBELL,M. DON~LDSON AND B. YOTJNGI Table 1. Sequential matching padtern overall frequenoy of ooourrenoe
Response pattern 1 0 2 s0 3 sc 4 c0 6 CS 6 SS0 7 ssc 8 ccs
8 7
3 9 16 26 13 8 6 7 31
cc0 cccs ccc0
9
10 11
Table 2. Distribution of types of response pattern Type of response p8ttern *
f
\
No Typeofmateriel
response
P,
P,
El
E,
Common objeota Formal shapes
6
3
12 10
13 13
28 28
8 12
Table 1 gives the 11 different patterns of response and their frequencies over all trials and on all occasions of testing. That is, it shows how often, overall, a given sequence of choices occurred. Thus, for instance, the choice of a single object that matched on the basis of shape followed by no further matching choice (pattern 2) occurred seven times. In the light of the question asked in the introduction, two features of Table 1 are of particular interest: (1) whether the set of objects satisfying the initial matching criterion is exhausted; and (2) whether the criterion ever changes. If the patterns in Table 1 are grouped according to whether or not they possess these two features, then we have the following four types of pattern (excluding pattern 1 in which no matching choice at all is made). (1) Partial single-criterion matching, in whioh there is no oriterion shift but the single category used is not exhausted. This type is exemplified by patterns 2 , 4 and 9 in Table 1. We refer to it in future aa type P, - that is, partial and involving only one criterion. (2) Partial double-criterion matching (P,) in which both criteria are used but neither category is exhausted. This is exemplified by patterns 3,6 and 8. (3) Exhaustive single-criterion matching (El), in which there is no criterion shift but the single category used is exhausted: patterns 6 and 11. (4) Exhaustive double-criterion matching (E,) in which the fist category used is exhausted and then there is a shift of criterion to the second category: patterns 7 and 10. (It should be noted that we did not persist in ctsking for more choices after this point to avoid undue lengthening of the task (cf. Procedure), so the reference to exhaustive matching is a reference to exhaustion of the first category only.) Table 2 gives the frequencies of these four types of pattern and of the residual
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category of no response for the two kinds of material - common objects and formal shapes. A 22 test reveals no evidence of association between type of material and type of response (x2= 1.66; d.f. = 4; P > 0.76). So in the report which follows we present results for the two kinds of material combined. Single-criterion matching (types P, and El) occurred in 63 per cent of all cases (excluding, once again, those where no matching choice was made, i.e. pattern 1, Table 1). A notable feature of single-criterion matching is that type El was more common than type P, (72 and 28 per cent, respectively) - that is, more often than not, all objects which matched according to the criterion in question were selected. So there is some evidence of a tendency to hold to a criterion once chosen. And it should be noted that there are no grounds for believing that this tendency is due to some enduring preference for shape or colour on the child’s part. Colour-matching was slightly more common than shape-matclung on initial trials (60 per cent of choices); but at Trial 1 there were always three colour-matches available in the pool and only two shape-matches (see Method). Moreover, our data were not produced by so many individuals who always chose colour and so many who always chose shape. Each child performed this task six times (two types of material by three times of testing) so that there were seven different possible categories of performance (initial match by shape six times, by colour no times; initial match by shape five times, by colour one time, etc.). The distribution of children over these categories is approximately binomial with equal probabilities, as we would expect if the choice of a basis for matching depended on the whim of the moment. Again, those few children who did show an extreme preference for a colour or shape-match on the initial trials were only slightly more prone than the group as a whole to singlecriterion matching (68 per cent of caaes). So the ‘modal’ type of response in our sample is exhaustive single-criterion
94 R. CAMPBELL,M. DONALDSON AND B. Yoma matching (type El) which is characterized by: (1)apparently unsystematic selection of the initial matching criterion; (2) adherence to this criterion once chosen; (3) exhaustion of the relevant category of objects; (4) failure to shift to another matching criterion when the first criterion yields no more choices. Fig. 1 gives the proportions of the four different types of response at the three times of testing. The suffix ‘ a y appended to a pattern category indicatm that the first match was based on shape; and the results for cases where this occurred are shown in Fig. 1B. Similarly the results when the first match was baaed on colour are shown in Fig. 1C and marked by the suffix ‘c’. Fig. 1A gives the two combined. The symbol 0 indicates that no matching choice was made. The numbers below abscissa marks indicate the number of cases on which the proportions are based. Figs. 1 B and 1 C obviously do not include subjects whose response pattern waa pattern 1, i.e. subjects who did not provide either a shape-match or a colour-match at all. Fig. 1A shows that the frequencies of PI and P, decline with age while those of El and E, increaae. Figs. 1B and 1C make it clear, however, that there is considerable interaction between the age trends and the nature of the initial match, for the increase in E, is found only when the first match is a shape-match and the increase in Elis found only when the firat match is a colour-match. Moreover, there is a considerable disparity between the level of P, responses and that of P,. These differences might be thought to be explicable on the general ground that more colour choices than shape choices are available and therefore exhaustion of the colour category might be expected to be slower to appear on some assumption that the ability to sustain interest in the tmk would increase with age. However the disparity between P, and P, is maintained over all three occasions of testing so that does not seem to be a particularly helpful explanation. Moreover, it is the level of initial shape responses which is the lower, though initial colour, on average, involves more matches. Comparison of P, with Elgives a clue to where a better explanation may be found. When the initial match is a shape-match subjects are more likely to hold to and and less likely to shift to the other criterion without exhaust a single criterion (El) exhausting the first category (PB) than when the initial match is a colour-match. One way to try to account for this is simply to suppose that the children attended more readily to the shape of an object than to its colour, which at first appears perfectly plausible. However, this notion runs into difficulties with two other aspects of the data: (1) the roughly equivalent levels of choice of a fht match by colour and by shape (colour being, if anything, slightly more common); and (2) the increase in E, from Time 1 to Time 3 while E, remains low throughout. The latter objection is particularly damning since, if shape is the more likely to attract attention, the probability of shifting to shape after exhausting colour should be greater than the probability of shifting to colour after exhausting shape. A somewhat Merent explanation is therefore proposed. This alternative explanation is like the first in supposing that shape tends to be in some way a more salient attribute than colour; but it emphasizes not so much attention to a salient attribute as the ability t o ignore one. Let us postulate that in order to ca,rry out a successful single-criterion matching process the child has not only to attend to the attribute which forms the basis of the match but also to w e in some positive manner any more salient attribute which does not. The notion
Clmsi$catory skills
95
is that some attributes are more intrusive than others and must be positively kept out if adherence to a less intrusive one is to be achieved. This notion is not introduced here as a novel idea. It has a considerable ancestry, though it has not always received the attention it deserves. Kiilpe (1904) distinguished two perceptual processes of set: positive abstraction in which a crucial aspect of the stimulus is accentuated; and negative abstraction in which the perception of incidental aspects of the stimulus is actively inhibited. What we propose is that processes of negative abstraction are important in the business of ‘holding fast’ to a criterion m e chosen, and resisting the temptation to switch to another. It is important to stress that we are not talking here about the initial attractiveness of the different attributes. It is only after an initial choice has been made that it makes sense to speak of the ‘intrusion’ of some feature of the stimulus - a feature which would have to be ignored if a particular strategy were to be followed consistently. We propose, then, that the initial choices are largely fortuitous, dependent perhaps on where the child‘s glance happens to fall as he looks at the array but that differences arise when it is a question of a whole sequence of responses, i.e. of deliberately redirecting attention if the glance happens to fall in the wrong direction. The following two suggestions seem to fit a number of aspects of our data: first, that the shape of an object is more difficult to ignore in this deliberate and sustained way than its colour;* and second that, with increasing age, subjects become more competent at ignoring. Then El, responses will require a deliberate attempt to ignore shape, whereas E, will call for the less difficult ignoring of colour (which can account for the differences between these two pattern in Fig. 1). If the attempt to ignore shape fails then an differences). (involuntary) shape-match will result (accounting for the P,-P, Lastly, even if the attempt to ignore shape is successful, the E , m a t c h pattern will still be difficult since it calls first for an effort to ignore shape and then for enough flexibility to start attendmg to it. E,, on the other hand, looks like a shift in an easier direction. We may now postulate two ways in which a single-criterion matching process might fail to lead to exhaustion of the category. Either there is failure of some process not specific to the matching task itself (some inadequacy of search of the array perhaps) so that a response of type P, results; or else the attempt to ignore one attribute fails, yielding a response of type P, - and this is more likely when the attribute to be ignored is shape, with the result that P , responses are more numerous than P,. Consideration of the curves for P, and P, in Fig. 1 makes it seem likely that failures due to the first of these causes are soon eradicated, whereas failures due to the second are still present to some extent even at the third time of testing. These remarks suggest the following developmental pattern. Type P , has been omitted from Fig. 2 because the place it should occupy is unclear. In fact, there are only three instances of this response (out of 132 responses) so that, as far m our data can indicate, it matters little where we put it.
* Blum & Porter (1973) report work with adult subjects in which active inhibition of attention waa triggered by a post-hypnotic cue. They found attention to form harder to inhibit than attention to colour; and they stress the importance of Kiilpe’s distinction.
96
R. CAMPBELL,M. DONALDSON AND B. Yoma
Fig. 2. Developmental relationehipa between typea of m8bhhg pattern. (crOsS-seCtiOD8l analysis.)
We now conclude by examining the longitudinal sequences to see how they relate to the scheme shown in Fig. 2. The usual technique for investigating longitudinal trends where the data can be ranked is to use Kendall’s S as a descriptive statistic and employ, for instance, Jonckheere’s test for trend (1967) to test hypotheses of no trend. Since we are dealing with nominal data this cannot be done. Kendall’s S compares the rank of items early in a longitudinal sequence with the rank of those that come later, working from early to late through the sequence and summing the differences (positive or negative) in ranks. A comparable approach with nominal data seems to be to take the firsf item in the sequence and note those which come after it, logging an entry in the appropriate row of an r z x n matrix for each such subsequent item (where rz is the number of nominal categories). The next item is then treated in the same way and so on until the end of the sequence is reached. Given a pair of categories, A and By we can then find in our sample how many times A occurs before B and how many times B occurs before A and compare the two. If this is done for our nine categorim 0, PI,,Pie, .. ., E, with the Task 1 data and again with the Task 2 data then in many cams the number of before-after comparisons is exceedingly small. If the distribution is 4: 0 in favour of our hypothesis, four such comparisoas are suflEicient to yield a one-tailed P of 0.06 on an exact test of no longitudinal priority, so we w i l l report only those cases where we have four or more such before-after comparisons. With these provisions, we get the results shown in Table 3. In Table 3, z/y means that of the z+y comparisons, z were ‘befores’ and y were ‘afters’. In brackets, P values on an exact test of no priority are given. These tests are one- or two-tailed dependmg on the cross-sectional indication. Clearly from the results shown in Table 3 for Tasks 1 and 2 separately, little can be inferred beyond perhaps that P,, and P, are developmentally prior to Ele. However, the agreement between the results from the two tasks is sufEciently good to justify pooling them. The pooled results in Table 3 yield the information about developmental priority shown in Fig. 3. (In the diagram, an arrow indicates priority.) If one takes all the priorities suggested by our analysis of the cross-sectional results (cf. Fig. 2) and counts the number of ‘befores ’ consistent with these priorities and the number inconsistent with them, it turas out that 86 per cent of the relevant comparisons are consistent with the cross-sectionalanalysis, which seems reasonably good agreement. In an attempt to resolve some of the remaining issues of developmental priority, we now present the data from Tasks 1 and 2, having combined them directly, i.e. before making any analysis of before-after comparisons. This manoeuvre yields for each child a structure consisting of a sequence of three paira of responses. From each such structure, three coincidences, 12 ‘befores’ and 12 ‘ai’bm’ are
97
Clussi$icatory skills Table 3. Before-after comparisons Task 1 PI, before El,: 4/0; P,, before El: 2/4; Pp,before Elo: 6/0; ( P = 0.06)* ( P = 049)t ( P = 0.01). El, before El,: 6/1; El, before Ez0:0/4 ( P = O.ll)* ( P = 0.13)t PI, before El,: 4/0; ( P = 0.06)*
Task 2 P,, before El,: 9/1; E, before El,: 4/1 ( P = 0.01)* ( P = 0.19)* El, before E,: 4/l ( P = 0.38)t
Tasks 1 and 2 combined PI, before Pzo:4/0 ( P = 0.06)* PI, before El,: 8/0; PI; before El,: 4/0; P1,before E2,: 6/0 ( P < 0.01)* ( P = 0.06)’ ( P = 0.03)* P,, before El”:2 / 6 ; P,, before El,: 16/1; P,, before Ez,: 3/0 ( P = 0.46)t ( P < 0.01)* ( P = 0.31)* E, before El,:9/2; El ‘before E,,: 3/1; E,, before E?,: 3/1 ( P = 0.03)* ( P = 0.31)* ( P = 0.31)* El, before E,,: 4/6 ( P = l.OO)t * One-tailed. t Two-tailed.
Fig. 3. Developmental relationshipsbetween types of matching pattern. (Longitudinalanalysis.)
obtained. The results of the analysis will not be presented in full since the matrix is massive and many of the cells still contain small numbers. The omission of such cells yields the half-matrix shown in Table 4. Inside each cell is the distribution of ‘befores’, coincidences and ‘afters’ and the goodness of fit x2 value for the null expectation of 12: 6: 12. It is evident that we have substantial confirmation of the results obtained from the tasks considered singly and we are therefore justified in making further inferences from the pooled data. Also we can, with some confidence, argue that there is no developmental priority of PZcwith respect to El,and of El, with respect to E,, an important point in connexion with our presentation of the cross-sectional data relating to these categories given earlier. The indications of these longitudinal results are summarized in Fig. 4. The horizontal axis represents level of development, the two sequences of categories represent longitudinal priority aa assessed by the above analyses, and the bell-shaped curves represent the distribution of cases with respect to level of development and with respect to the response categories (as shown in Fig. 1).It is important to stress 7
PSY
67
98
R. CAMPBELL,M. DONALDSON AND B. Yoma Table 4. Before-coincident+fter comparisons for Tmks 1 and 2 combined PI, pl#
4:2:0
(4.00) P*O
p*,
El0
E, p, 7:o:o 3:l:O (10.60) (2.88) 4:6:2 8:O:O (4.91) (12.00) 6:6:8 (1.31)
EP. El0 3:O:O 4:O:O (4.60) (6.00) 18:3:2 1l:l:O (14.61) (1342) 28:3:3 6:3:1 (25.63) (3.22) 19:1:4 6:2:2 (16.48) (1.28) 6:2: 10 (2.00)
Fig. 4. Schematic model relating level of development to favoured type of mmtching p8ttern.
that this is a mere indication - we are unable to find an inferential technique which would allow us t o express the degree of support for this model formally. Perhaps the best that can be said for it is that it is maximally consistent with the data obtained. As a final substantive point about these longitudinal results we would like to draw attention to the fact that, in the model just illustrated, double-criterion matching (Pzand E,) occurs at two different levels of development separated by a level at which only single-criterion matching is found. (This kind of developmental pattern is discussed in Donaldson, 1971.) On the other hand, the tendency to exhaust whatever category of objects is selected in Trial 1 of the matching task (El and E,) becomes steadily stronger as development proceeds. The main finding, then, is that, even at Time 1, there is a clear tendency for later choices in the sequence to be constrained by the initial one, though the initial choice itself may be largely fortuitous. If a child begins by matching on a given attribute he will tend t o hold to that attribute, and, increasingly as he grows older, he will tend to hold to it until no exemplars of it remain.
Classi$catmy skills
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A fundamental question about the nature of the constraint exercised by the first choice then arises. When a child holds to a single attribute is he following a planned strategy or is he merely ‘drawn’ to the objects which most resemble the one he has first chosen? Here a first point to note is that the objects which a child selected were removed from his sight before another choice was made. This, of itself, reduces the likelihood that anything like what Gelb & Goldstein (1925) call ‘the experience of coherence’ could explain our results. However, the fact of central significance is that there tend t o be different outcomes according t o whether the first choice is a colour-match or a shape-match. The detailed evidence which we have presented suggests that it is necessary t o introduce the notion that different attributes have different ‘saliency’ or ‘pull’, yet at the same time that the notion of increase in the capacity for voluntary - or planned - resistance to that pull has also t o be invoked to explain the developmental data. If a child begins by matching on the basis of shape it is easier for him to hold to this criterion than if he begins by matching on the basis of colour. And this is not so much a matter of being more or less prone t o attend t o a given attribute as of being more or less able t o ignore it. We have then a developmental lag of the kind shown in Figs. 2, 3 and 4 with the same sequence being followed for shape and colour but with colour showing systematic delay. To this general statement, however, it is necessary t o add a word of qualification. It would be unsafe to conclude that shape is easier t o hold to than colour for all shapes and for all colours. There is a growing amount of evidence for the existence of certain kinds of natural perceptual dominance; and among the evidence is a report by Rosch (1973) of findings that there are colours which are more perceptually salient than others; and likewise for forms. If this is so, then our results could perhaps be reversed by constructing the sets of objects from forms of low salience and from colours of high salience. (Both were probably highly salient in the sets we used.) However this may turn out, if the developmental disparity between shape and colour that we observed is indeed to be explained by postulating that some attributes are harder t o ignore than others and that the ability to ignore the more intrusive of them increases over the age-range we studied, then the bulk of our data can be accounted for in terms of successful and unsuccessful attempts to follow a strategy. Most earlier studies of the classificatory skills of young children have not led to a conclusion of this kind. Notably, the work of Vygotsky (1962) and of Inhelder &, Piaget (1964) has been taken to show that children of the age-range we have studied typically do not have a plan that they are attempting to follow. We are therefore in disagreement with them at this point; though, of course, i t is crucial not t o lose sight of the distinction between matching and sorting. It looks as if three main types of matching process occur in our sample. I n the first of these, there is a single-criterion strategy which, for one or another reason, fails; and this yields a matching pattern of either type P, or type P,. I n the second, the single-criterion strategy is successfully carried out; and this is the ‘modal’ process in our sample, yielding patterns of type El. I n the third, there is a doublecriterion strategy, i.e. the child carries out a single-criterion strategy successfully, then shifts t o the other category. This strategy produces response patterns of type E,, 7-2
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which are rare in our group of subjects unless the fht choice is a match on the bash of shape. It must be noted that responses of type P, would readily be produced if no strategy of any kind were being followed (and so, of come, fortuitously, would some instances of the other types). No doubt there were a certain number of cases requiring an explanation of this kind. However, once again, the differencebetween the sequenoes beginning with shape and those beginning with colour helps one to see what is happening; for if there were no strategy a t all, the frequencies of P,, and of P,, would presumably be quite similar. The fact that P,, occurred very rarely (three instances out of 132 responses) argues strongly that, even at time 1 when the children were around 3 years 7 month old, a matching strategy, however unsuccessful, was usually there. We can therefore conclude that the children’s responses are not on the whole Iike those of Gelb & Goldstein’spatients. The procedures they follow are not forced upon them passively. On the contrary they already have some capacity to ‘hold fast’; and, at least towards the end of our study, they show signs of an ability to recognize that possible alternative bases for classification can exist. The limitation is that neither of these abilities is as yet free from circumstantial constraints. This is to say that the constraints which the formal classificatory taak imposes are still interacting with constraints of a very different kind. The latter-the circumstantial constraints - derive from a kind of force of circumstance that has no relevance for the task. Specifically, they derive in this instance from the child’s predispositions (‘natural’ predispositions perhaps) to respond in various ways to the nature of the material to be classified. The question of whether the matching sequence starts with shape or colour exerts an effect upon the outcome, though it is strictly irrelevant to the requirements of the classificatory endeavour. Until this ceases to be true, it obviously cannot be claimed that the children are, in the fullest sense, capable of classifying. This study waa supported by a grant from the Social Science Research Council. Roger Wales waa one of the investigators, and we gratefully acknowledge his contribution to the research.
REFERENCES BLTJM, G. S. & PORTER, M. L. (1973). The capacity for selective concentration on colour versus form of consonants. Cogn. Psychol. 5, 47-70. DONALDSON, M. (1971). Preconditions of inference. In J. K. Cole (ed.), N e b w k u Symposium on Motivation. Lincoln: University of Nebreska Press. GELB,A. & GOLDSTEIN, R. (1926). tfber Farbennahmenamnesie. P s y c b l . Formh. 6, 127-199. INHELDER, B. & PIAQET, J. (1964). The Early Qrowth of Logic in the ChiEd. London: Routledge & Kegan Paul. JONCKEEERE, A. R. & BOWER, G. H. (1967). Non-parametric trend tests for learning data. Br. J . math. statbt. Psychol. 20, 163-186. K W E , 0. (1904). Versuche uber Abstraktion. Berlin International Ccmgre-38 of Expet%me& Psychology, 66-68. ROSCH,E. H. (1973). Natural categories. Cogn. Psychol. 4, 328-360. WERNER,H. (1948). The Comparative Psychology of Mental Dev-nt. New York: International Universities Press. VYQOTSKY, L. S. (1962). Th~.qhtand L a m e . Cambridge, Mass:M.I.T. Prees~.
(Manuscript received 25 April 1974; revised manuscript 4 February 1978)
