design studies - uncertainty and sketching behaviour_impresso - s scrivener e linden ball

8/8/2019 Design Studies - Uncertainty and Sketching Behaviour_impresso - S Scrivener e Linden Ball

http://slidepdf.com/reader/full/design-studies-uncertainty-and-sketching-behaviourimpresso-s-scrivener 1/17

Design seems inconceivable without drawings. Produced drawings

are used at all stages of design for many different purposes.

Designers often distinguish between freehand drawings produced

in the early and late stages of design1,2, regarding the former as private

tools for thinking rather than public communication and presentation aids.

Vagueness, incompleteness and ambiguity are among the properties of

sketches taken as indicative of this function1,3–5. According to Goldsch-

midt2, design thinking is a dialectic between different forms of ‘seeing’,

seeing-as and seeing-that, that draw on different cognitive processes and

knowledge types. Translation between modes of seeing is thought to both

develop and stimulate new ideas through reinterpretation. Systematic stud-

ies are beginning to clarify the role of idea sketches in this cyclic pro-

cess2,4,6–11. It may be debatable whether sketches, via perception, are a

driving force for discovery or simply aid creative cognition (cf. Purcell

and Gero9), but it is becoming clear that sketching and cognition are closely

coupled. If these processes are closely coupled then cognitive processes

1 Herbert, D M ‘Study drawings

in architectural design: their

properties as a graphic medium’

Journal of Architectural Edu-

cation Vol 41 No 2 (19 88)

pp 26–38

2 Goldschmidt, G ‘The dialec-

tics of sketching’ Design Studies

Vol 4 No 2 (1991) pp 123–143

3 Scrivener, S A R ‘The inter-

active manipulation of unstruc-

tured images’ International Jour-

nal of Man-Machine Studies Vol

16 (1982) pp 301–313

4Goel, V Sketches of Thought

MIT Press, Cambridge MA

(1995)

5 Fish, J and Scrivener, SAR

‘Amplifying the minds eye:

sketching and visual cognition’

LEONARDO Vol 23 No 1 (1990)

pp 117–126

6 Goldschmidt, G ‘On visual

design thinking: the vis kids of

architecture’ Design Studies Vol

15 (1995) pp 158–174

www.elsevier.com/locate/destud

0142-694X/00 $ - see front matter Design Studies 21 (2000) 465–481

PII: S0142-694X(00)00019-3 465© 2000 Elsevier Science Ltd All rights reserved Printed in Great Britain

Uncertainty and sketching behaviour

Stephen A. R. Scrivener, Visual Information Design Research Centre,

Coventry University, Priory Street, Coventry, CV1 5FB, UK

Linden J. Ball, Institute of Behavioural Sciences, University of Derby,

Mickleover, Derby, DE3 5GX, UK

Winger Tseng, Visual Information Design Research Centre, Coventry

University, Priory Street, Coventry, CV1 5FB, UK

Evidence suggests that sketches of seen objects exhibit a structure

consistent with the volumetric parts of the recalled objects.

Occasionally, sketching structure does not match volumetric part

structure. Top-down cognitive factors, perception, or a combination of

both could trigger switching of drawing behaviour. From the evidence,

it is concluded that uncertainty is the primary factor triggering change

in drawing structure. Nevertheless, the data indicate that sketches can

engender uncertainty by revealing errors in recollection, through

recognition failures or by promoting reasoning about depicted objects,

and can facilitate the resolution of uncertainty by stimulating recall.

© 2000 Elsevier Science Ltd. All rights reserved

Keywords: conceptual design, design cognition, reasoning, uncertainty,

drawings



7 Schon, D A and Wiggins, G

‘Kinds of seeing and their func-

tion in designing’ Design Studies

Vol 13 No 2 (1992) pp 135–156

8 Suwa, M and Tversky, T

‘What do architects and students

perceive in their de sign

sketches? a protocol analysis’

Design Studies Vol 18 No 4

(1997) pp 385–403

9 Purcell, A T and Gero, J

‘Drawings and the design pro-

cess’ Design Studies Vol 19 No

4 (1998) pp 389–430

10 Suwa, M, Purcell, T and

Gero, J ‘Macroscopic analysis of

design processes based on a

scheme for coding designers’

cognitive actions’ Design Studies

Vol 19 No 4 (1998) pp 455–484

11 Verstijnen, I M, Van

Leeuwen, C, Goldschmidt, G,

Hamel, R and Hennessey, JM

‘Sketching and creative dis-

covery’ Design Studies Vol 19

No 4 (1998) pp 519–54612 van Summers, P Drawing

and Cognition Cambridge Uni-

versity Press, Cambridge, MA

(1994)

13 Novick, L R and Tversky,

B ‘Cognitive constraints on

ordering operations: the case of

geometric analogies’ Journal of

Experimental Psychology: Gen-

eral Vol 116 (1987) pp 50–67

14 Taylor, H A and Tversky, B

‘Descriptions and depictions of

environments’ Memory and Cog-

nition Vol 20 (1992) pp 483–496

15 Kavakli, M, Scrivener,

SAR and Ball, LJ ‘Structure in

and structures should be reflected in sketching structure, which indeed

seems the case12–15. We, too, are concerned with what sketching structure

reveals of cognitive processes and structures. We begin by reviewing data

supporting the hypothesis that drawings of recently seen objects are seg-

mented according to geometric components. However, our principal inter-

est are those data that go against the hypothesis. In particular, whataccounts for this unpredicted behaviour and what does it tell us about

underlying cognitive processes?

1 Structure in sketching behaviour Kavakli et al.15 conducted a study investigating whether sketching behav-

iour reflects the geometric structure of the objects represented. Novice

designers undertook five sketching tasks. Three required them to observe

and then draw from memory three chairs, called the Library, School and

Cafe chairs (Figure 1). The fourth required them to design a chair from

imagination and the last to overtrace their drawings.

The chairs were conceived as composed of volumetric components or parts

(Figure 2). The participants’ depicted chairs defined the geometric structure

to be analysed, i.e. this was not a memory test. If a designer drew one of

these parts completely, before moving on to draw the next part, they were

said to be drawing Part by Part. Consider Figure 5(c) where parts P5 and

P6 were coded Non Part by Part as they are clearly represented incom-

pletely. Had part P5 in Figure 5(c) been represented completely, like P5

in Figure 2(a), before drawing commenced on another part then it would

466 Design Studies Vol 21 No 5 September 2000

Figure 1 The Library, School and Cafe chairs



idea sketching behaviour’

Design Studies Vol 19 No 4

(1998) pp 485–518

have been coded Part by Part. Often participants began with ‘stick’ draw-

ings that were then elaborated (cf. Figure 6, drawing D1). The legs of

drawing D1 in Figure 6 were coded as Part by Part because, although

lacking geometrical detail, the full extent of the parts is represented. Thus

the judgement between Part by Part and Non Part by Part drawing is not

made on the basis of geometrical detail but on whether or not the represen-

tation captures the fundamental geometry of the part.

A significant proportion of drawn parts, whether from memory, imagin-

ation or by overtracing, were produced Part by Part15. Overall, sketching

behaviour corresponded with the volumetrical part structure of the objects

depicted. Nevertheless, some parts were represented Non Part by Part and

we analyse these data to throw further light on when and why designers

switch to Non Part by Part drawing. As the memory task required parti-

cipants to recall an actual chair, distinguishing between drawn parts was

straightforward using the actual chair and/or their recalled chairs for refer-

ence. The design task was problematic because one had to decide whether

a drawn part was a version of an existing part or a newly invented one,

and hence these data are less reliable. Overtracing data are excluded since

none are produced in the absence of other drawings. Hence, we only con-

sider data emerging from the memory tasks in subsequent sections.

2 Non part by part drawing in the memory tasksTable 1 presents the Part by Part and Non Part by Part drawing results for

the three memory tasks. Across participants and chairs the majority of parts

are drawn as complete representations of the volumetric components of

the recollected object. The data reveal sketching behaviour where typically

a complete part of a remembered chair is drawn before the next complete

part, and so on. Nevertheless, 19.3% of parts are represented Non Part by

Uncertainty and sketching behaviour 467

Figure 2 Parts of chairs (a) Library chair; (b) School char; (c) Cafe chair



Part and therefore occasionally drawing behaviour switches from Part by

Part to Non Part by Part, and back. Our goal is to examine possible causes

of this change in drawing behaviour.

In order to understand the determinants of changes in drawing behaviour

we assume that drawing reflects either high-level cognitive activity (e.g.

the manipulation of different knowledge representations), lower-level cog-

nitive activity (e.g. perceptually-driven recognition) or a mixture of both

types of activity (see Purcell and Gero9 for a relevant discussion of the

debate surrounding these possibilities). As such, we assume that changes

in drawing behaviour may be engendered by shifts in cognitive state arising

from: (i) top-down cognitive factors without any contribution from the

perception of drawing stimuli; (ii) top-down cognitive factors with a contri-

bution from the perception of drawing stimuli; (iii) purely perceptual fac-

tors, driven bottom-up by drawing stimuli.

3 Drawing stimuli as a determinant of cognitive shift

3.1 Non part by part drawing in session first parts, and first partsIf perception of drawing stimuli is the only cause of Non Part by Part

production, then we should expect the first part drawn in each session, the

Session First Part, to be Part by Part. In fact, 2 of these 12 parts are drawn

Non Part by Part, suggesting that a cognitive factor is involved in Non

Part by Part production, making Explanation (iii) (see previous section)

unlikely.

At the onset of a session participants must reproduce the remembered chair

onto a virgin sheet. As the session progresses each chair part is drawn out


Table 1 Part by Part and Non Part by Part drawing by task and participant

Library School Cafe´ Totals %

Participant Part by Non Part Part by Non Part Part by Non Part Part by Non Part Part by

Part by Part Part by Part Part by Part Part by Part Part

1 17 2 7 3 6 3 30 8 78.92 10 10 18 0 15 3 43 13 76.83 16 6 26 3 20 4 62 13 82.74 34 0 34 6 7 8 75 14 84.3Total 77 18 85 12 48 18 210 48%Part by 81.1 87.6 72.7 80.7 19.3Part



of memory. If pre-drawn parts determine those being produced for the first

time, then we might expect this to be reflected in changes in Non Part by

Part production. Of the 90 First parts produced 13.3% are drawn Non Part

by Part. While the percentage of Non Part by Part production in Session

First parts, 16.6%, is greater than that for other First parts, 12.8%, most

of the Non Part by Part production of First parts (75%) occurs in the firstdrawing in each session. The Non Part by Part: Part by Part ratio in Session

First parts is similar to that for other First parts in first drawings (i.e. 0.166

vs 0.179) suggesting performance in first drawings is unaffected by the

presence of other drawn parts. In contrast, the First part Non Part by Part:

Part by Part ratio is markedly different between the first drawings and later

session drawings (i.e. 0.214 vs 0.076).

Summarising, when parts are first externalised from memory they are

occasionally produced Non Part by Part. Of all First parts, 56.6% are pro-

duced in the Session First Drawings, with Non Part by Part productionapparently unaffected by the presence of parts drawn earlier, suggesting

this behaviour is cognitively determined. However, the proportion of First

parts produced Non Part by Part decreases markedly in later drawings com-

pared to Session First Drawings. Since Session First Drawings production

does not appear to benefit from drawing stimuli it is unlikely that reduction

in Non Part by Part in later drawings is principally due to drawing stimuli.

Rather, this variability in Non Part by Part production of First parts pro-

vides further support for top-down cognitively determined switching

involving factors that diminish in intensity as the task progresses.

3.2 Non part by part over drawingsOnly seven drawings are produced in Drawings 7–10, comprising only

8.5% of all parts (see Table 2), so subsequent discussion will focus on

Drawings 1–6. Table 2 shows that Non Part by Part production as a per-

centage of the total number of parts produced is relatively constant across


Table 2 Frequency of drawing number, parts and Non Part by Part percentages

Drawing 1 2 3 4 5 6 7 8 9 10number

Drawing 12 12 10 7 6 5 2 2 2 1frequencyPart 51 57 55 26 23 24 9 6 3 4frequency% Non 18 7 27 23 35 4 22 33 0 25Part byPart



drawing number except for Drawings 2 and 6 where Non Part by Part

production drops markedly. The total number of parts in second drawings

is 57, 22 being First parts and 35 Repeat parts, of which four are Non Part

by Part parts. In Drawing 3, 14 of 44 Repeat parts are Non Part by Part.

Hence, the proportion of Non Part by Part production of Repeat parts

increases markedly in Drawing 3 (31.8%) as compared to Drawing 2(11.4%). Overall, the proportion of Non Part by Part production increases

in Repeat parts compared to First parts (i.e. 22.4 vs 13.3%). Yet, Drawing

2 exhibits a lesser proportion of Non Part by Part First parts than Drawing

1 (i.e. 0 vs 17.6%), and a lesser proportion of Non Part by Part Repeat

parts than Drawing 3.

How can we explain the reduction in Non Part by Part production in Draw-

ing 2 vs Drawings 1 and 3? Thus far, the evidence suggests that changes

in drawing behaviour in First parts are determined by cognitive factors that

are less evident as the task progresses, hence the drop in Drawing 2. Letus assume, however, that drawing stimuli only become a driving force as

parts are repeated. Since the effect is weaker in Drawing 2 compared to

Drawing 3, we might expect Non Part by Part production to increase with

drawings. However, this does not appear to be the case from Table 2, and

Non Part by Part production decreases in Drawing 6. If drawing stimuli

are the primary determinants of cognitive shift then their effects are com-

plex. Again this suggests the involvement of top-down cognitive factors

in the variable proportion of Non Part by Part production over the first

three drawings.

Therefore, we conclude that the change in Non Part by Part production

over drawings reflects cognitive shifts determined by top-down cognitive

factors or these interacting with drawing stimuli. Given this interpretation,

the data suggest these factors arise less in Drawing 2 than other drawings

(apart from Drawing 6). This is of interest as there is an important qualitat-

ive difference between Drawings 1 and 3. As we have seen Drawing 1 are

comprised entirely of First parts, i.e. parts first realised entirely from mem-

ory, whereas Drawing 3 is comprised largely of redrawn parts (80%), i.e.

parts for which versions already exist in drawing stimuli. Given this quali-

tative difference it may be that the cognitive factors influencing Non Part

by Part production are also different between Drawing 1 and Drawing 3,

and beyond. However, the question remains as to what are the cognitive

factors that trigger the cognitive shifts evidenced by Non Part by Part

production and whether these cognitive shifts are influenced at all by draw-

ing stimuli.




16 Finke, R A Principles of

Mental Imagery MIT Press,

Cambridge, MA (1989)

17 Tversky, B and Hemen-

way, K ‘Objects parts and cate-

gories’ Journal of Experimental

Psychology: General Vol 113

(1984) pp 169–193

4 Cognitive synthesis and representational mode asdeterminants of cognitive shift

4.1 Cognitive synthesisKavakli et al.15 suggest that Non Part by Part production might be related

to cognitive synthesis, i.e. forming mental wholes from remembered sub-wholes that have been previously imaged16. Kavakli et al.15 argue that such

synthesis might require or be facilitated by functional knowledge of the

object, hence yielding Non Part by Part drawing. However, this does not

appear to be what happens. By the completion of Drawing 2, 81.1% of

first parts have been produced. Hence, Drawings 1 and 2 represent much

of the recalled chairs, suggesting that for this task objects are not mentally

synthesised in sub-wholes and then combined (i.e. this is not reflected in

the drawings).

4.2 Functional versus structural representationKavakli et al.15 argue that the predominance of Part by Part production

indicates that drawing production is driven by structural rather than func-

tional representations. They suggest that drawing behaviour might be tied

to these different kinds of representation, cognitive shift being a change

of one for the other (cf. Tversky and Hemenway17). However, each chair

is largely comprised of uni-functional components that do not enable a

distinction to be made between function or structure as Part by Part pro-

duction of these parts is consistent with either a functional or structural

representation. To explore this function/structure distinction further, we

focussed on the multi-functional components of the chairs. If these compo-nents are produced more often Non Part by Part than Part by Part then this

would suggest a functional representation.

Table 3 shows the multi-functional parts as recalled by the participants.

Three out of the four designers failed to remember the back-leg compo-

nents of the Library chairs. In each case, separate back and leg components

were produced. In the case of the School chair, all designers recalled the

back-seat component and the double leg components. However, two of the

four failed to recall the double leg components accurately. Participant 1

recalled all four legs as being connected to a single cross member, while

Participant 2 recalled the double leg component as comprising a front and

back leg. All participants accurately recalled the arm-leg component of the

Cafe chair apart from Participant 3 who failed to recall that the chair had

arms, producing a multi-functional component comprising a back frame

and rear legs. Multi-functional parts proved more difficult to remember

than uni-functional parts.




Table 3 shows which of these multi-functional parts were first produced

Non Part by Part (coded 0) or Part by Part (coded 1). Of these participant-

produced multi-functional parts, 27.7% were produced Non Part by Part,

which is a higher percentage than for all First parts (13.3%). Nevertheless,

72.3% of multi-functional parts are produced Part by Part supporting the

proposition that structure dominates function in drawing. Of course, these

parts are also geometrically more complex than uni-functional parts which

may also explain their poorer recall. However, it is unlikely that Non Part

by Part production of these parts is simply due to geometrical complexity

as multi-functional parts are often drawn in fragments terminating at func-

tional boundaries. Consequently, we cannot discount the possibility that

one effect of cognitive shift is selection between structural or functional

representations, reflected in Non Part by Part drawing.

5 Uncertainty as a determinant of cognitive shift Above we have suggested that variation in Non Part by Part production

over drawings reflects cognitive shifts. So far the analysis does not support

mental synthesis as a determinant of cognitive shift, while change in rep-

resentation with cognitive shift cannot be discounted. In this section, we

undertake a qualitative analysis of the Non Part by Part production in all

first, second, third and subsequent drawings to throw further light on the

cognitive determinants of Non Part by Part production. We will argue that

uncertainty is a primary determinant of the cognitive shifts giving rise to

Non Part by Part production.

Human memory, whilst often highly robust, is also known to be fallible

and liable to omissions, distortions, abstractions, and constructive influ-


Table 3 Multi-functional chair parts as recalled by participants (1 = Non Part by Part, 0 = Part by Part)

Library School Cafe´

Participant 1 – Back-seat 1 Arm-leg 0– Front legs 1

Back legs 1Participant 2 – Back-seat 0 Arm-leg 0

– Front-back left 1Front-back 1

right

Participant 3 Back-leg left 0 Back-seat 0 Back-leg 0Back-leg right 0 Front legs 0

Back legs 0Participant 4 – Back-seat 0 Arm-leg 0

– Front legs 0Back legs 0



18 Baddeley, A D Human

Memory: Theory an Practice

Revised edition, PsychologyPress, Hove (1997)

19 Cohen, G Memory in the

Real World Lawrence Erlbaum

Associates, Hove (1989)

20 Cavanaugh, J C ‘The place

of awareness in memory devel-

opment across adulthood’ in L W

Poon, D C Rubin and B A Wil-

son (eds) Everyday Cognition in

Adulthood and Later Life Cam-

bridge University Press, Cam-

bridge, MA (1988)

21 Roberts, M J and Erdos, G

‘Strategy selection and metacog-

nition’ Educational Psychology

Vol 13 (1993) pp 259–266

22 Ball, L J, Evans, J St B T,

Dennis, I and Ormerod, T C

‘Problem-solving strategies and

expertise in engineering design’

Thinking and Reasoning Vol 3

(1997) pp 247–270

ences such as those deriving from prior expectancies or stereotypical

beliefs18. Some memory retrieval difficulties also appear to be associated

with feelings of uncertainty. For example, tip-of-the-tongue states and feel-

ing-of-knowing states are examples of situations where people believe they

possess relevant information in memory but experience difficulty in

accessing it. An interesting aspect of such memory-engendered uncertaintyabout stored or partially-retrieved memories is that it may actually promote

strategic shifts in processing activity aimed at resolving the uncertainty.

This view has been supported by much evidence derived from studies of

strategy selection in memory and problem solving situations20,21. Generalis-

ing such ideas to design, Ball et al.22 have presented evidence that uncer-

tainties about current solution ideas cause major strategic switches in the

expert designer’s ongoing problem solving (e.g. changes from optimal bre-

adth-first design to novice-like depth-first or opportunistic design).

Here, we use the term uncertainty to refer to a cognitive state caused bythe lack of information in memory necessary to satisfy the needs of the

task, i.e. to enable a chair to be drawn to the complete satisfaction of the

participant. Recognition of this lack could be detected during visualisation

or during drawing. Additionally, data provided by perception may enable

detection of inadequacies in recollection. We suggest that these moments

of realisation are experienced as uncertainty because they impede the task

and, until they are resolved, what is to be done next is uncertain.

5.1 First drawingsAs noted earlier, Non Part by Part production occurs in two first drawings

(Figure 3). The general impression in both cases is that the participants

are uncertain about the components themselves and/or how they join

together. This is supported by the fact that both Participants 1 and 2 fail

to remember correctly the structure of the legs. Although Figure 3(a) indi-


Figure 3 Non Part by Part

first drawings (a) Partici-

pant 1’s School chair; (b)

Participant 2’s Library

chair



cates that Participant 1 has remembered correctly that the two front and

back legs are each created from single pieces of tubing that are then joined

together, when the drawing is overtraced the legs are shown in an arrange-

ment quite different from the actual chair. Similarly, although Participant

2 appears to remember that a component functions as both back support

and leg, when redrawn in Drawing 3 (see Figure 5(b)) the back supportand leg are shown as separate, therefore invented, components. Thus both

participants fail to correctly remember some aspects of the respective chairs

and must design their way out of this uncertainty, by determining the struc-

ture of components and their relationship to each other.

5.2 Second drawingsNon Part by Part production occurs in only one of the 12 second drawings,

i.e. Participant 4’s Cafe chair. In Drawing 1, the designer draws the com-

plete chair entirely Part by Part. Drawing 2 is also a complete drawing of

the chair although here it is seen in a rotated view showing the back (Figure

4). The designer partly draws the seat, followed by a partly drawn arm-

leg, left and right rear legs, and finally the back, which is the only part

drawn Part by Part. Comparing Figure 4 to Figure 1(c), it is clear that the

designer recalls the chair with a back-leg member that is not present in

the actual chair, i.e., the rear leg of the actual chair terminates at the seat.

Inspection of the near rear leg (Figure 4), suggests some uncertainty about

whether this invented component is a single multi-functional part or two

uni-functional components, i.e. leg and back support. Perhaps the designer

has a vague recollection that the back leg terminates at the seat that creates

doubts in his mind about the multi-functional part depicted in Drawing 1.

Drawing 3 (Figure 5(f)) supports the idea that this uncertainty exists as itclearly presents an alternative in which the rear components are shown as

leg and back.


Figure 4 Non Part by Part

second drawings; Partici-

pant 4’s Cafe chair



5.3 Third drawingsNon Part by Part drawing occurs in six of the ten third drawings (Figure

5). Considering Participant 1’s Library chair, Drawings 1 and 2 are ortho-

graphic front and side projections, whereas Drawing 3 is a perspective

drawing. Having first drawn the front near leg (Figure 5(a)), followed by

some construction lines, the designer then shows the depth of the seat at

the rear near leg before partially drawing the far front and far rear corners

of the seat. Here, then, Non Part by Part production seems to reflect the

needs of accurately reproducing the conjunction of parts. Like Participant

2, this designer recalls the back-leg component incorrectly as two compo-

nents. Given that this is an incorrect recollection, how the parts join at the

seat must also be undefined, or potentially in conflict with any recollection

of their actual alignment. Thus, although this Non Part by Part production

may be qualitatively different to that occurring in Drawing 1 described

above, as the conjunction of seat, legs and back supports has been pre-


Figure 5 Non Part by Part third drawings (a) Participant 1’s Library chair; (b) Participant 2’s Library chair; (c) Participant

3’s Library chair; (d) Participant 3’s School chair; (e) Participant 4’s School chair; (f) Participant 4’s Cafe chair



viously defined in Drawings 1 and 2, uncertainty may still play a part in

Non Part by Part production.

As noted above, Participant 2 appears confused as to whether or not the

back-leg component is one or two elements. In Drawing 3 (Figure 5(b)),

the designer first seems to settle on the correct recollection of a singleback-leg component, only to then redraw it as separate back and leg

components. Again, uncertainty appears to figure strongly in Non Part by

Part production. Later we shall return to consider what might cause a cor-

rect recollection to be discarded for an invention.

Participant 3’s first and second perspective drawings of the Library chair

are of single parts, the first showing the back-leg component, the second

the back. In Drawing 3 (Figure 5(c)), also in perspective, the designer first

draws the seat and near and far front legs completely before sketching only

the leg portions of the back-leg components, stopping in each case justabove the conjunction of seat and leg. Here the designer seems quite certain

about the back-leg component. However, the fact that he stops drawing at

the conjunction suggests some uncertainty, as otherwise why not complete

the entire legs? On the other hand, efficiency could account for Non Part

by Part production here.

When drawing the School chair (Figure 5(d)), Participant 3 draws the seat

completely, the hand hole in the seat and the leg-to-seat attachment bolts.

The designer then draws the back leg and then the front legs before adding

some detail to the seat. Given that it is a perspective drawing, at first only

the visible parts of the front and back legs are shown. However, having

embellished the seat the designer returns and draws in the occluded frag-

ments of the legs, correctly recalled in Drawing 1. Clearly, this disfigures

the chair’s mimetic realism. One reason for drawing in the occlusions

might be that the participant recognises that the bolts are inaccurately pos-

itioned with respect to their veridical mental model of the chair. In this

case Non Part by Part production would be in the service of accurate

description and is unlikely to register uncertainty. Alternatively, the partici-

pant might have realised that the bolts in the drawing (which in the actual

chair function to connect the seat to the legs) serve no proper function.

This realisation of a functional anomaly would produce uncertainty about

their conception of the chair.

When drawing an orthogonal projection of the School chair (Figure 5(e)),

Participant 4 draws the seat of the seat-back component and then the legs

before returning to complete the back part of the seat-back. This can either

be regarded simply as an artefact of the method of projection, or as a




function of depicting the conjunction of parts. Uncertainty does not seem

to figure here. Finally, when producing a rear perspective view of the Cafe

chair (Figure 5(f)), Participant 4 draws the seat, arm-leg, near and far back

legs incompletely. Here, again the designer seems to be exploring the

possibility that that which has been recalled as a back-leg component may

comprise several components. The rear view projection enables attentionto be focused on a local arrangement of parts that is not clearly visible in

the earlier drawings. This change of understanding is also evident in the

overtraced drawings where Drawing 2 is clearly traced as having a back-

leg component and Drawing 3 separate back and leg components.

We have noted above that Non Part by Part production in Drawings 1 and

2 appears to be connected with uncertainty. This may be uncertainty about

the structure of components and/or their conjunction. We are drawn to

conclude that Non Part by Part production in Drawing 1 is a feature of

the resolution of this uncertainty. A number of explanations for Non Partby Part production in Drawing 3 seem plausible (e.g. uncertainty, accuracy

and mode of representation). Nevertheless, uncertainty is again prominent

in our interpretations. Some Drawing 3 Non Part by Part production occurs

in the absence of component and conjunction information in earlier draw-

ings, but in most cases information about the parts drawn Non Part by Part

already exists. Since, typically, both parts and their conjunction have

already been outlined with some commitment, the impression is that Non

Part by Part production is related to uncertainty about the precise form and

arrangement of parts. Analysis of the 10 remaining drawings (8 of which

reproduce earlier drawings) that exhibit Non Part by Part production inDrawings 4–10 also reveals both instances of uncertainty (i.e. general

and particular).

5.4 DiscussionWe are now in a position to interpret the variations in Non Part by Part

production between Drawings 1 and 3. We have already concluded that

this is unlikely to be an effect of drawing stimuli. The qualitative analysis

of drawings above draws us to the conclusion that uncertainty is a primary

factor determining the cognitive shifts responsible for Non Part by Part

production. When a previously perceived object is recalled from memory

it is recalled part by volumetric part (e.g. Drawings 1 and 2). A cognitive

shift may be necessary to resolve uncertainty about the components them-

selves or how they are combined leading to Non Part by Part production

(e.g. Drawing 1). Once initial uncertainty is resolved, the remaining parts

can be extracted from memory Part by Part (e.g. hence the fall in Non Part

by Part production in Drawing 2). Having extracted First parts and their

organisation from memory in general terms, uncertainty, reflected in Non




by matching external depictions to memories). Mismatches may be experi-

enced without a clear sense initially of what is actually wrong, engendering

uncertainty to be resolved. This is like the situation where you recognise

a friend but also detect that he looks different—and you realise he has

shaved off his beard. Figure 5(f) is arguably an attempt to resolve uncer-

tainty arising from a mismatch between external representations and mem-ory. Initially the designer draws the entire chair Part by Part, but with a

back-leg component not present in the actual chair. The designer may

experience a mismatch between the way the back legs of the depicted chair

and remembered chair connect to the seat. In Figure 5(f) the designer cor-

rects this error, but only partially as he still retains a member that connects

the seat to the back.

The persistence of this back-member error perhaps reflects the outcome of

another kind of test in which designers appear to reason about the func-

tionality of their depictions. When describing Figure 5(b) above, we prom-ised to return to consider why the designer should have discarded what

was in fact a correct recollection for an incorrect invention. If we assume

that the participant was not deliberately designing the part, then it could

be that the designer reasoned that the chair, as recollected, would not func-

tion and therefore opted for a vaguer but more functional recollection.

Figure 6 provides clearer evidence for such reasoning processes and their

role in creating uncertainty. Figure 6 shows five depictions of the School

chair. In D1 all of the parts are externalised. However, the leg members

are wrong as they show front-back leg members. The designer then pro-

duces D2–D4, but seems to change his mind between D1 and D4 (D3

displaying Non Part by Part production) as the legs are now shown bending

toward the middle of the seat. Why might this change have occurred?

Considering D1, what is the function of the bolts? They appear to have

none as they are out of alignment with the legs. In D2 the relation between

bolts and legs is more salient than in D1. At this point the designer may

have realised that the legs would have to be positioned such as to bolt to

the seat, i.e. D4. Finally, in D5 the designer first draws the seat and the

legs, occluded by the seat. At this point the designer appears uncertain

about the legs and draws in the occluded parts, but this time showing them

correctly as a front and a back pair. Furthermore, although the front legs

(cf. Figure 1(b)) are shown incorrectly as bent into the horizontal plane,

this detail suggests that the change of mind reflects increased recollection

of the actual chair rather than simply an improved design. Thus, drawing

stimuli may engender uncertainty when compared to memory and when

used for reasoning about the functionality or logical coherence of depic-

tions.




6.2 Facilitating the resolution of uncertaintyWe have suggested that uncertainty arises when internal representations are

inadequate for the task in hand. Resolution of the problem would involve a

process in which the missing information is recovered or constructed from

prior knowledge. Resolution of uncertainty will depend on how success-fully memory and synthesis processes are stimulated. Along the lines sug-

gested by Fish and Scrivener5, it may be that representations of external

stimuli can be fused with internally generated representations around the

corresponding area of internal uncertainty. By stimulating recognition and

recall processes, these externally derived but incomplete data might facili-

tate a stream of mental images. Whatever the mechanism, the assumption

is that drawing stimuli facilitate the resolution of uncertainty by providing

cues or clues that stimulate the processes essential to it (i.e. additional

information). Whilst these data cannot shed further light on this proposition

it is notable that many decades of research on human memory have pro-

vided evidence for partial or incorrect memory productions stimulating cor-

rect recall (e.g. as in the tip-of-the-tongue phenomenon) and for external

cues similarly promoting improved recall19.

7 ConclusionBecause idea sketching is partially determined by underlying cognitive

structures and processes12,13,15 we can learn much about those processes


Figure 6 Reasoning with sketches



24 Visser, W ‘Use of episodic

knowledge an information in

design problem solving’ in N

Cross, H Christians and K

Dorst (eds) Analysing Design

Activity John Wiley and Sons,

Chichester (1996) pp 271–289

by studying its structure. It has been argued that uncertainty is the primary

determinant of the Non Part by Part sketching production reported by

Kavakli et al.15. If this descriptive analysis is confirmed experimentally,

Non Part by Part production may prove a useful metric of uncertainty in

form making. While it does not appear to determine Non Part by Part

production, perception of drawing stimuli may contribute both to engen-dering and resolving uncertainty and drawing stimuli probably facilitate

visual reasoning.

Drawing in design and recall may be different matters but their correspon-

dences are enough to suggest that the results may generalise. First, recalling

a previously seen object draws on episodic memory which is a feature of

design thinking6,24. Second, participants’ sketches are incomplete5, and like

idea sketches probably function to stimulate recall and inhibit premature

commitment5. However, here we are suggesting uncertainty is the cause

of incompleteness, i.e. its production is not a deliberate strategy exploitingperception to stimulate invention. The same is quite likely to be the case in

design also. Third, like design, sketches seem to support reinterpretation5–8

but here revealing weaknesses in conception that cause backward reflection

on the current conception rather than highlighting new conceptions that

move the task forward. Again reinterpretation may also contribute in this

way to design. Finally, the recall drawing task becomes a design task,

i.e. requiring invention, when episodic memory is insufficient for concrete

specification. This is probably the general case for any visual recall task

requiring the reification of recalled entities. Here, it is argued that uncer-

tainty drives invention and perhaps uncertainty also drives invention in

design.

AcknowledgmentsTo Dr Manolya Kavakli of the Faculty of Architecture, Istanbul Technical

University, Turkey, who worked with Scrivener and Ball on the design

and execution of the study on which this paper is based.


design studies - uncertainty and sketching behaviour_impresso - s scrivener e linden ball

Documents