"\Ne have assumed that it Is necessary to refer to the brain structure to understand mental functions". (Das et al 1979 p.31 )
The synthesis of the approaches of Luria and Das provides the final component of the 'nested' theories/models which constitute the theoretical framework for the current study. The Information Integration Model (Das et al 1979) takes as its starting point the assumption of a neural base to higher mental functions. The principal aim being to develop a "modern approach to intelligence" (Naglieri et al 1991). Das and colleagues believed that this was possible by extending the use of Luria's concept of cognitive processing through the development of psychometrically sound tasks which measure these processes. Language is of central importance in this model because of the ability of verbal instructions to control and influence the functional properties of the neural structures (Das et al 1979). Differences in language environment and in the socio-cultural context of the individual will determine the nature of the changes and the specific path of development experienced by the individual (Krywaniuk & Das 1976). Also central to the model is the view that neither the presence, nor the absence, nor the loss of any ability is immune to change. Thus deficits in performance can be reduced by educational programmes, which require detailed information about the cognitive "status" of the individual to be effective (Naglieri & Das 1990).
Initially studies carried out by Das and colleagues focused on the components of Unit 2 functioning (Luria 1973), which Das identified as being primarily concerned with information processing/coding (Das et al 1979).
The Coding Component
Das and Luria followed different methodological approaches to develop definitions of the processes involved. Luria's clinical method, syndrome analysis, defined individual deficiencies in cognitive processes by analysing the common demands in those tasks which are not completed optimally (Luria 1973). In contrast Das and colleagues used a statistical method to define, through factor
analysis, the common cognitive processes involved in the completion of a battery of tasks (Das et al 1979).
Luria's descriptions of the different forms of processing observed included details of the holistic, simultaneous, spatial sensations of visual perceptions; and the temporal, sequential input and retrieval of verbal/ auditory speech (Luria 1973). These descriptions were supported by Das' factor analytic method, and were developed into a model of Simultaneous versus Successive processing (Das et al 1979). Both of these forms of processing may take place in one of three levels of complexity (or variety of synthesis): the perceptual; memory (mnestic); or conceptual (Luria 1973, Naglieri et al 1990).
There are interesting parallels between the Das-Luria 'varieties of synthesis', U.S. Bruner's developmental model of information processing (Bruner 1964), and the stages of cognitive development as described in Piagetian theory (Bruner 1964, Luria 1973, Das et al 1979, Flavell 1977). The details of which help elucidate the differences between the three levels of complexity. In Bruner's model modes of representation become increasingly more powerful in the course of development. The first level of representation is the enactive level, where representation is through action. The second is the iconic, where representation is through imagery; and the third level is the symbolic, where language dominates as the preferred mode of representation (Bruner 1964).
In the Das-Luria 'varieties of synthesis' the simplest level is dependent upon direct perception. In the first of Piaget's stages, the Sensory-Motor, cognitive functioning is also dominated by direct perception. Even Bruner's enactive level requires direct action upon objects. Next in complexity, according to Das-Luria, is Mnestic synthesis, which is dependent upon the development of relevant memory traces, and thus requires a degree of imagery. Piaget's corresponding stage is the Concrete Operational, in which the manipulation of concrete objects can take place, even in the absence of the object itself, which is similar again to
the Bruner description of the iconic level. The most complex of the Das-Luria's levels of synthesis is referred to as Diagrammatic Representations, which, in common with Piaget's most complex level, is achieved with the development of abstract thought, similar again to the Brunerian symbolic level.
Whilst the Das-Luria descriptions refer more to differences in demands between tasks at any one time, Piaget's stages (in common with Bruner) refer to maturational changes within an individual in the approach to solving different tasks. This difference is probably accounted for by the differences in the techniques used to collect the data upon which these theories were based. Luria observed adult behaviour, from which an inference was made of the developmental progression (Gaddes & Edgell 1994), whilst Bruner and Piaget directly investigated the behaviour of children at different ages (Bruner 1964, Flavell 1977). However the coincidence of the frameworks which developed from these different sources lends support to Luria's deductions. This progression has also been observed in other investigations, for example in the development of classification strategies of real world objects (Rosch 1976), and in the development of memory strategies (Bruner & Kenny cited in Bruner 1964). Further examples will be provided below to illustrate these different levels.
Simultaneous processing
Simultaneous processing is employed when different items or sections of an item are related to each other to form an integrated whole, and is closely associated with spatial ability. It is postulated that it is the most successful strategy to apply in tasks such as the replication of designs, or the identification of pictures presented only section by section (Das et al 1979, Gaddes & Edgell 1994). Although regularly required for visual perception tasks, it is not confined to this modality, nor is visually presented material exclusively processed in this way. The following three tasks provide an example of each of the three levels at which simultaneous processing can operate. Task 1, Copvinq a design, is an example of the perceptual level. Task 2, drawing a design from memory, is at the mnestic level. An example at the conceptual level is Task 3, determining which design will
emerge from a particular transformation (see Ravens Matrices) (Naglieri et al 1990).
Successive processing
Successive processing is employed when the items, or sections of an item are related to each other in a series or chain, and where the relationship is temporal rather than spatial. Each section is a unit in itself, but the ordinal position of each section is important to the understanding of the whole. Successive processing is most often associated with tasks involving hearing and movement, although, as the examples below will show, visually presented material can also be processed successively. Memory is a common component of tasks where this is the predominant strategy (Luria 1973, Das et al 1979). Examples of successive processing at the perceptual level are activities requiring skilled movements, such as writing or driving a car (Naglieri et al 1990). Examples at the mnestic level include the repetition of a digit span, such as a telephone number. Much of speech is processed successively (Gaddes & Edgell 1994), and this activity provides an example of successive processing at the conceptual level. Constructions such as "the girl hit the boy" clearly illustrate the temporal sequence involved in processing the information presented (Naglieri et al 1990).
Determinants of the choice of processing strategy Assessment Materials
The following list gives examples of the sub-tests included in the studies which will be described below. Changes have occurred between studies, but essentially the tasks are predominately paper and pencil orientated, and thus more appropriate to older children (Ashman & Conway 1989). Included as examples of Simultaneous processing are: figure copying; memory of designs; matrices (adapted from Ravens’ Matrices); and design construction. In the selection of tasks designed to measure Successive processing are: digit span; sentence repetition; and word recall. Tests held to tap the other components of the model. Planning and Attention, have included: visual search; trial making; matching
common patterns/numbers, as planning tasks, and Stroop like tasks for selective attention.
Aae/Developmental Stage
The Das-Luria conceptualisation is not one where the measurement of intellectual performance is expected to provide a static picture of the individual's intellectual functioning. Rather it anticipates some changes in which form of processing will be applied to different tasks at different levels of maturity, as a consequence of different ranges of experience (Das et al 1979). Whilst the overall factorial structure has been found to be common to different ages groups (Naglieri et al 1990), some variation has been found in factor loadings for a range of different tasks (Molloy et al 1990). The Molloy study was designed to explore contention that the simultaneous and successive processing are not hierarchical, but develop in parrallel. The factor structure of sixty 6 year olds was compared to that of sixty 9 year olds, on tasks chosen to represent successive and simultaneous processing (see above). Although factor loadings were essentially the same, there were changes that were observed between age groups. These seemed to be attributable to two causes. Firstly, the younger group showed a pattern of performance suggestive of a degree of ambivalence in the selection of the mode of processing, with several tasks loading on more than one factor in this age group. One example was the Figure Copying task, whose factor loadings amongst the older age group placed it as a simultaneous task. In the younger age group this task also loaded, although to a lesser extent, on the successive factor (Molloy et al 1990).
Secondly, changes in the factor loadings of some tasks, led to alterations in the pattern of performance and suggested matu rational changes in the saliency of different elements within a task (Molloy et al 1990). Molloy refers to Bruner's developmental model of information processing (enactive, iconic, symbolic) to provide a more detailed explanation of this second type of change. The developmental progression in the ability to use and manipulate ever more powerful levels of representation could provide an explanation for the changes in
performance recorded between the two age groups studied (Bruner 1964). In the Molloy study Visual Short Term Memory for Digits, for example, loaded on separate factors for the two age groups. It was suggested that this difference arose because, whilst younger children used the iconic mode to code the numbers, the older children, more familiar with using and manipulating numbers, coded them at the more powerful symbolical level. Support for attributing the difference in performance pattern to the task content, rather than to differences in mental functions per se, was provided by the fact that in another very similar memory task, which used objects rather than numbers, the factor loadings were similar for both age groups (Molloy et al 1990).
The Influence Of The Socio-Cultural Environment.
A number of studies summarised in Das et al (1979) and Naglieri et al (1991) found the same basic factor structure in the performance of children from a variety of different cultural backgrounds. However, as with the developmental level studies, there were also some variations found between different cultural groups. One study, Krywaniuk & Das (1976) summarises the main variation found. This study compared the performance of Native and White Canadian children. It found that, where there were any differences in performance, these were predominantly in tests of successive processing. The efficacy of simultaneous processing over successive processing has been noted in other studies of children brought up in Native North -American culture (Cummings et al
1993).
Very similar differences to those described above have also been found between different groups of Brahmins in India, indicating that different socio-economic environments within the same culture also exert different influences upon the development of processing strategies (Das & Singha 1975). Here schooling effects were also found to be significant. It appears that differences in socio cultural experience, within which category the experience of formal education falls, not only effects the ability to apply a specific form of processing, but also the ability to select the optimal form of processing. The ability to select the optimal
form of processing was also an issue in the Krywaniuk and Das study (Krywaniuk & Das 1976). The group which demonstrated the weakest performance in successive processing, also, curiously, appeared to favour successive processing, in that it was applied even in tests, such as Raven's Matrices, where a more effective form of processing is simultaneous (Das et al 1979).
Information processing, achievement and schooling
The relationship between schooling and performance on information processing tasks appears to be two-way. Not only does school experience appear to affect the ability to process information, but the ability to process information also appears to have an affect upon school achievement itself (Das et al 1979, Dash & Das 1984, Watters & English 1995). Das claims studies have shown that: a) school achievement is related to both simultaneous and successive processing; b) achievement measures correlate with simultaneous and successive factor scores; and c) achievement tests load on a separate factor to those identified as simultaneous and successive factors. Furthermore the relationship between the two forms of processing and measures of achievement appears to vary across time. It was found that both reading and mathematics at the early stages was better predicted by variations in successive tests. Whilst at higher levels, simultaneous processing became more important (Merrit & McCallum 1984).
Application versus selection of processing strategies
As has already been alluded to, differences in performance can be caused by differences both in the ability to apply, and to select the appropriate strategy. In fact performance on tests which have been developed to assess processing strategies can be affected by both the ability to deploy the strategy, and by the ability to employ it optimally (Das et a 1979). The former ability is actually related to Luria's third functional unit of the brain (planning), rather than to his Unit 2 (coding). In order to understand in more detail the cause of failure, therefore, the model of assessment has been expanded to include more direct measures of Luria's other two functional units of the brain Unit 1 and Unit 3. This extends the original Simultaneous -Successive information processing model to include
Attention and Planning factors. Planning, Attention, Simultaneous and Successive processing were then combined into the PASS model of cognitive functioning (Naglieri et al 1990, 1991).
The Attention Component
Attention is associated with Unit 1 functioning, which;
"maintains a state of arousai or cortical ton e, which allows the individual to focus and specifically direct attention"(Naglieri et al 1990 p.426).
Initially studies identified an additional factor labelled Speed (Krywaniuk & Das 1976). This seemed to correlate with the length of exposure time required to apprehend the original task stimulus (Molloy et al 1990), and it could therefore be argued that this factor is part of selective attention or vigilance. In addition to speed, discrimination and accuracy are other important aspects of performance in selective attention. A broader Attention factor has therefore replaced the concept of Speed in later studies (Naglieri et al 1990). Both under and over arousal can have negative repercussions, through disrupting processes of attention, which in turn disrupt coding and planning activities (Naglieri et al 1990).
Examples of tasks which have loaded on the Attention factor, have included a variety of simple and more complex tasks, including signal detection and sustained attention (Naglieri et al 1991).
The Planning Component
The third functional unit is involved in developing
"plans of action, inspecting performance, and regulating behaviour so that it conforms to these plans." (Naglieri et al 1990 p.428).
Planning, as it is described in the PASS model, is therefore essential to the generation, selection, execution and monitoring of problem solving activity (Parrila et al 1994). Tasks which have been found to constitute a separate
planning factor have included simple tasks such as trail making and visual search; and complex ones such as writing a story (Naglieri et al 1990, 1991).
Validity Of The Model
A study conducted by Cowart and McCallum (1988), investigated the construct validity of a three factor model derived from the Simultaneous, Successive, Planning divide. The authors wrote that the investigation failed
"to produce conclusive evidence of convergent or discriminant vaiidity of the S-S-P constructs using an MTMM (multi-trait multi-method) matrix"
(Cowart & McCallum 1988 p.62).
Naglieri and Das (1990), focused their response on the selection of tasks which had been included (some previously unvalidated, and others whose reliability was reported to be questionable). They also criticised the changes in administration that were enacted, as the Cowart and McCallum battery, unlike those developed by Das and colleagues, was administered as a group test. Furthermore Cowart and McCallum provided no alternative model of performance, although it had been suggested that a verbal/visual dichotomy may underlie the simultaneous-successive factor structure (Cowart & McCallum 1988).
Taking another approach a number of studies have been carried out in order to assess whether the extended PASS Model provides a more informative
explanation of the pattern of performance than other theoretical models (reviewed in Naglieri et al 1990). The conclusions are summarised in the results of a further study carried out by Naglieri et al (1991). This compared the performance of 205 five to nineteen year olds against a hypothetical pattern of performance as predicted by different theoretical models of intellectual functioning. Confirmatory factor analyses were computed using the SIMPLIS programme (Joreskog & Sorbom cited in Naglieri et al 1991). Naglieri wrote that,
"this procedure provides a method for estimating the degree to which a hypothesised model describing the interrelationships of the variables corresponds to the observed patterns of covariances among the variables." (NagWen et al 1991 p.9)
Separate analyses were then carried out for each of the competing theoretical models which were being assessed. A number of criteria were applied to indicate goodness of fit. These were: a) non-significant chi-square results; b) a ratio of chi-square relative to its degrees of freedom of <2 (AIwin & Jackson cited in Naglieri et al 1991); c) values of the Tucker Lewis Index (TLI) of near .9 (Bentler & Bonett cited in Naglieri et al 1991). The results are presented in Table 5.1, and the description of the models given below.
Table 5.1 Results of Confirmatory Factor Analysis (Naglieri et al 1991)
Model Chi -sq Chi-sq/d.f. TLI
PASS .188 1.26 .77
G .001 2.15 ---
MR .001 2.04 .10
VNV .001 2.18 -.03
vss .037 1.58 .50
The theoretical models tested were:
a) Spearman's "g", or general intelligence (G). Within this model all tasks would be expected to load on one factor. In addition to the poor fit with the data the inherent generality of the model was criticised on other grounds. Not only because it ignores the observed complexity of human cognitive functioning, but also because it does not supply any information about the source of problems which might emerge.
b) The two factor model of memory versus reasoning (MR), described in Jensen's Level 1 and Level 2 abilities. This too was found to provide a poor fit with the results. The limitations of this model appear to be partly as a consequence of the isolation of memory as a unitary factor, as, in practice, memory tasks do not all load on the same factor. Another limitation is that this approach defines tasks by their content. This is criticised because it is seen as
limiting performance by that which a subject knows, not by how s/he can apply what s/he knows. Such tasks are consequently likely to be affected by prior experience and knowledge, and can therefore be said to be context specific.