Effects of examples on the results of a design activity

Effects of examples on the results O

of a design acfi ty

A T Purcell and J S Gero

The role of search processes and the knowledge used & the activity of designing has been receiving increasing attention in the areas of artificial intelligence, the study of design, and cognitive psychology. More recently, with the development of expert systems, considerable attention has been focused on the representation and retrieval of expert knowledge. What has not been addressed, however, is whether or not an expert represents, accesses and utilizes all knowledge equi- valently. The design-fixation effect, where pictures of design instances presented as part of a design problem result in the reproduction, by student and practising designers, of aspects of the presented instance, indicates that certain types of knowledge are more privileged in the design process than others. The results of a preliminary experiment, which exa- mined the role of pictures of different types of instances, verbal descriptions of those instances, and variations in the familiarity of instances in the fixation effect, are reported. Pictorial information was shown to have no effect if the instance was unfamiliar, and equally familiar pictures were found to produce both design fixation and increased variety in design. Verbal descriptions of two of the pictured designs also produced effects, although these were much reduced in comparison with those of the pictorial material that produced fixation effects. While preliminary, these results indicate a particularly important direction for research, the results of which could be important for artificial intelligence, the study of design, and the psychology of design processes.

Keywords: design fixation, design flexibility, cognitive processes in design, knowledge representation in design

The focus of the research reported in this paper is on the role of knowledge in the design of 3D artefacts. In common with what has been referred to as the second phase of work on problem solving in an artificial-intelligence context (see, for example, Reference 1), designing

Key Centre of Design Quality, University of Sydney, NSW 2006, Australia Paper presented at Artificial Intelligence in Design '91 Conf. Edinburgh, UK (25-27 Jun 1991). Revised paper received 5 September 1991. Accepted 24 October 1991

can be viewed as an activity in which expert knowledge is used to fill out an initial statement of a problem so that a solution can be developed. The initial statement of a problem that a designer works with contains two broad types of information: a statement of what is to be designed, and the constraints or requirements that the design has to meet. With the general conception of expertise that has been developed in a number of areas 2,3, expertise in design can be regarded as the use of knowledge that is relevant to the particular area to

• identify the implications of the stated constraints for the design,

• access a repertoire of potential part or whole physical solutions,

• identify, possibly through the process of designing, other constraints that are relevant to the design, but that were unidentified in the initial problem statement.

Given this general model of the design process, the question of knowledge in design involves issues concern- ing the representation of knowledge (knowledge about constraints and potential physical solutions or part solutions), and the processes involved in the use of that knowledge (the identification of implied constraints, and the development of design solutions).

Knowledge structures

Knowledge relevant to design comes from two sources. Because design is concerned with objects that do, or may, exist in the world, a designer generally has knowledge that is based on exposure to instances. This knowledge depends on the regularities in the world, and how frequently instances are encountered. In addition, the type and extent of the knowledge obtained in this way can depend on whether the knowledge accrues as a part of everyday, incidental experience, or as a result of intentional learning. In the latter case, knowledge can be the result of deliberately structured experiences that are relevant to the characteristics of particular domains, and the opera- tors that may be used to produce changes in a domain. Important issues, therefore, are the form that these differ-

82 0950-7051/92/010082-10 © 1992 Butterworth-Heinemann Ltd Knowledge-Based Systems

ent types of knowledge take, and the way that they enter into the design process.

Everyday, incidental experience is represented in knowledge structures such as schemas 4, scripts 5 and E-MOPS 6. These types of knowledge structure have prototypical default values at all levels of abstraction in the knowledge structure (see, for example, Reference 4). Prototypicality, in this context, refers to a representation of the most frequently occurring attributes and relationships, and the ranges of values that these attributes and relationships generally take in a set of instances from a particular domain. These knowledge structures represent generic knowledge about the world. Importantly, there is considerable evidence that a particular level of abstraction, the basic, is most frequently used in information processing and is easiest to access. Further, at this level, representation focuses on parts and the relationships between parts, rather than more abstract attributes, such as func- tions 7-1°, and this is the highest level at which an image of the objects in the category can be formed.

This type of knowledge about the world of designed artefacts is expected to be both similar and different for designers and nondesigners. The intentional learning that is associated with design involves exposure to a larger number, and a greater diversity, of instances within a domain. For this reason, expert designers' knowledge structures are expected to be more elaborated than those of nonexperts at the. more detailed levels within the structure. However, expert knowledge in general (see Reference 3) and design expertise involve the development of more abstract knowledge about principles. Further, expert knowledge in design involves knowledge about materials and parts of objects, and the relationships between these elements, that can be used to produce artefacts. Expert designers' knowledge structures at the detailed level can, as a result, be particularly rich in terms of the representation of visual material resulting from exposure to larger, more diverse sets, and because of the representation of materials, parts and relationships. It is these latter aspects of experts' knowledge structures that are different to the knowledge structures of nonexperts.

Design fixation

In terms of their processing, these various types of knowledge can be used in the ways described in the Simon ~1 model of search processes, and in the subsequent develop- ments in the area in relation to expert systems m3. How- ever, less attention has been paid to whether or not, or under what circumstances, the various types of knowledge will be accessed, an issue that is of some importance in relation to expert systems in design and in the education of designers. A possible indication that there is differential access to, and use of, the knowledge base in design comes from the work of Jansson and Smith L4. In a series of experiments, groups of mechanical-engineering student or professional designers were either presented with a statement of a design problem, or the statement of the problem and a picture of a possible design. The design problems used were the design of a bicycle rack for a car, a drinking cup for the blind, a spill-proof coffee cup, and a piece of apparatus for taking samples, and measuring speed and pressure at different points in the intestinal tract. In each case, the designers who were presented with a picture reproduced a number of aspects of the design, including

aspects that were inappropriate or incorrect. This effect is referred to as 'design fixation', and these authors relate it to the functional fixedness in a number of problem-solving situationslS, 16.

Jansson and Smith's results indicate that pictorial information can have a powerful effect on design, and they imply that access into relevant knowledge structures and processing of information may be at a corresponding level of specificity. This result is also consistent with the pre- viously demonstrated importance of the basic level in categorization discussed above. The impact of pictorial information may reflect the hypothesized elaboration of this material present in designers' knowledge structures. The effects of pictorial material on design may, therefore, reflect this preferred level of processing of information for designers. Given the role that pictorial material plays in much design education, and the implications of the fixation effect for the practice of design, particularly in terms of the replication of inappropriate aspects of the presented designs, the design-fixation effect, and the conditions that produce it, warrant careful investigation.

The Jansson and Smith 14 experiment does not, however, unequivocally demonstrate that it is the pictorial material that influences the designs produced. Their control group, against which the group who received the pictorial material was compared, only received a statement of the problem. The group who received the picture therefore received more information than the control group, in addition to pictorial information. To establish whether it is the pictorial form of the information that is important, it is necessary to equate the information presented with the form of the information that differed between the design groups. The first aim of the research reported in this paper was to attempt to replicate the design-fixation effect, and to examine this issue by repetition of the Jans- son and Smith experiment. One of their design problems was used, but a group that received a verbal description of the material presented pictorially and a control group that received only a statement of the problem were included. The use of a verbal-description group also addressed the issue of whether higher-level, semantic information can produce the same effects as pictorial material.

Familiarity and design

The use of verbal or pictorial information in this way can be thought of as being similar to the second type of design information discussed above: information derived from the presentation of specific design-related materials, as opposed to information derived from everyday experience with instances of different design types. In the context of the type of experiment proposed, the everyday knowledge could play a role in the designs that were produced, either independently of, or through, an interaction with the material presented in the context of the design problem.

On the basis of the work in category and concept for- marion, it is argued above that everyday knowledge is based on environmental regularities and repeated exposure to instances. Particular instances that are similar to the prototypical default values are experienced as familiar, and instances that depart from these default values are experienced as unfamiliar, depending on the extent of the difference from the existing knowledge structure. For design problems that involve the design of an everyday object, such as the bicycle-rack design of Jansson and

Vol 5 No 1 March 1992 83

Smith 14, it is expected that the participating designers will have reasonably well developed knowledge structures that relate to what is to be designed. The effects of the material presented as a part of the design problem can, as a result, depend on the relationship between this material and the default values in the existing knowledge structure. In Jans- son and Smith's work, a roof-mounted bicycle rack was used to produce the fixation effect. While no evidence is presented in relation to the familiarity of this type of design, an examination of available bicycle-rack designs indicates that the type of design that they used is reasonably common. An interesting and relevant question, therefore, is whether the same effects will be observed if pictorial and verbal-description material is used that varies in terms of its familiarity. The second aim of the experiment reported in this paper was to investigate the role of variations in the familiarity of the instances used as fixating material, with the familiarity being assessed by the frequency of purchase and use of various types of designs, and by judgments of the familiarity of these instances obtained from the participating designers at the completion of the design session. In relation to both aims of the experiment, it is stressed that the results obtained can in no way be considered to be definitive, but to be indica- tive of whether or not, and in what directions, empirical work may proceed in this potentially important area for design and artificial intelligence in design.

METHOD

Subjects

207 first-year design students participated in the experiment in the latter half of their first year. Participants were from the Architecture Departments of the University of Sydney, Australia, and the University of New South Wales, Australia, and from the Industrial Design Depart- ments of the University of Technology, Sydney, and the University of New South Wales.

Experimental material

Jansson and Smith's ~4 bicycle-rack design problem was used. Discussion with the local bicycle-riders association and retailers of bicycles and accessories indicated that five main types of bicycle rack were available. Two types were mounted on a tow ball at the rear of the car. One of these consisted of a single vertical tubular-steel post to which the bicycles were attached, and in the other, two similarly dimensioned steel posts were arranged to form an A frame. All the rack designs are shown in Figure 1. There were two roof-mounted designs, with the bicycle attached by the seat and frame in one design, and by the wheels and frame in the other design. Finally, there was a car-boot (trunk) mounted design, with the bicycles being supported by their frames. These discussions also indicated that the single-post design was the most frequently purchased design, with the A-frame and the frame-and-wheel roof designs being reasonably frequently purchased. The boot and seat-support roof designs were purchased much less frequently.

Three of these designs were used to create the required pictorial material: the single-post, A-frame and boot- mounted designs. These were chosen to give a range of frequency of purchase, and, hence,, frequency of occur-

rence in the environment. To investigate the effect of semantic information, verbal descriptions of the single- post and A-frame designs were developed. Two, rather than three, of the pictorial designs were represented in verbal form, in part because of limitations on the availabi- lity of participants in the experiment, and in part because of the complexity of the instructions required to describe the boot design. Further, it was considered that, as the experiment was a pilot experiment that was designed pri- marily to replicate the design-fixation effect, and explore some factors that might be related to it, two semantic conditions would indicate whether this issue was worth pursuing. The A-frame description and the simple description of the problem for the control group are both given below. The groups that received the pictorial and verbal descriptions also received the basic statement of the problem. The pictorial material was presented as an illus- tration of the way in which the designers were to present their designs.

Verbal instructions for A-frame design

The verbal instructions for the A-frame design were as follows. The aim of the design exercise is to come up with a sketch design(s) for a bicycle rack for three bicycles for a car. The bicycles have to be held securely, and without damage to either the bicycle or the car. The bicycles must not extend beyond the overall-width dimensions of the car to avoid potential damage to people or vehicles in passing.

There are a number of key issues to be considered in the design of a bicycle rack. The first is the way in which the rack is attached to the car. Then, there has to be a structural system that will support the bicycles. Third, there has to be a way of attaching the bicycles to the support system. Fourth, both the structural system and the way of attaching the bicycles have to have a correct relationship to the car to fulfil the other more general conditions of safety etc. To illustrate, the bicycle rack can be attached to the car at a number of locations: for example, at the rear of the car, to a tow-bar fitting, or directly to the chassis of the car. The bicycles can be supported structurally in a number of ways: for example, two steel posts in the shape of an A joined across the bottom of the A can be attached to the fitting fixed to the car. This has to be of a sufficient height to provide clearance above the ground.

Similarly, the bicycles can be attached to the rack in a number of ways: for example, they can be held by the top horizontal section of the bicycle frame in short half sections of pipe of a diameter that allows the bicycle-frame section to fit into the pipe with the other half section closing over the bike frame.

The bicycles then have to have an appropriate relationship to the car: for example, to the top of the A-frame, a short steel section can be attached at right angles in line with the length of the car. The fitting with the brackets attaching the bicycles can be placed at right angles to the length of the car on this section of the post, with the bicycles being placed parallel to, and clear of, the boot of the car.

Detailed and accurate drawings are not required; simple, rough, outline sketches are all that is needed. In addition to the sketches, you can write comments on the drawings to illustrate what you mean. You will be allowed 45 minutes in which to complete the sketch design. If you wish, you may complete more than one design.

84 Knowledge-Based Systems

8

b

i i

d

C e Figure 1. Five types of bicycle-rack design; (a) single-post, (b) A-frame, (c) boot, (d) upright, (e) seat-and-wheel

Control-group instructions

The instructions to the control group were as follows. The aim of the design exercise is to come up with a sketch design(s) for a bicycle rack for three bicycles for a car. The bicycles have to be held securely, and without damage to either the bicycle or the car. The bicycles must not extend beyond the overall-width dimensions of the car to avoid potential damage to people or vehicles in passing.

There are a number of key issues to be considered in the design of a bicycle rack. The first is the way in which the rack is attached to the car. Then, there has to be a structural system that will support the bicycles. Third, there has to be a way of attaching the bicycles to the support system. Fourth, both the structural system and the way of attaching the bicycles have to have a correct relationship to the car to fulfil the other more general conditions of safety etc.

Detailed and accurate drawings are not required; simple, rough, outline sketches are all that is needed. In addition to the sketches, you can make written comments on the drawings to illustrate what you mean. You will be allowed 45 minutes in which to complete the sketch design. If you wish, you may complete more than one design.

Measurement variables

On the basis of existing designs and an examination of the first set of 50 designs, four characteristics of each design were identified. At the most general level, the designs could be assessed in relation to the location of the bicycle rack on the car, as follows:

• rear, • roof,


• boot, • other locations.

The second characteristic related to how the rack was attached to the car, as follows:

• to the tow ball, • to the bumper bar, • to the roof, • to the boot.

Of particular importance was the third characteristic of the designs, which was the way in which the bicycles were supported. Seven supporting structures were identified:

• a single vertical post, • an A-frame post, • a single horizontal post, • roof racks, • multiple vertical posts, • multiple horizontal posts, • an angled post.

The fourth characteristic of the designs was the method of attaching the bicycle to the rack, i.e. by

• wheels, • frame, • bicycle enclosed.

Jansson and Smith 14 assessed the location of the bicycle rack, and the method of attachment of the rack to the car and of the bicycle to the rack; they did not assess the method of support of the bicycle by the rack. Each design was assessed in terms of these four aspects, and the analyses consisted of chi-square tests of significance. In addition, a count was made of how many designs each participant produced. Because of the classroom setting in which the experiment was conducted, and the use of design students from a number of sources, it was not possible to equate the numbers of participants in each of the experimental conditions. The numbers in each group were as follows: the control group: 30, the single-post picture group: 34, the single-post description group: 32, the A-frame picture group: 42, the A-frame description group: 38, and the boot picture group: 31. Because of these unequal numbers, the results are presented as percentages. Familiarity with each of the designs in Figure 1 was assessed using a 3-point scale of not at all familiar, quite familiar, or very familiar. Tables that show the details of the relationship between each aspect of the design and each group are given in the Appendix.

Procedure

The experiment was conducted as a class exercise. Each class was divided into groups, and each group received one of the six sets of instructions. Prior to the design activity, general instructions were given to the whole group. These introduced the general topic of the exercise to design a bicycle rack for a car. As in the Jansson and Smith 14 experiment, participants were told that the experi- menters were interested in the ideas that would be gener- ated, and they were encouraged to produce as many designs as they liked. It was stressed that the designs were

to be sketched and not finished designs. Drawings and verbal annotations could be used, with the aim being simply to provide enough information for the experi- menters to understand what was being proposed.

Each participant worked in a separate work area. Supervisors were present to answer questions and to ensure independent work. The instructions were provided when the participants were seated. 45 minutes were allowed for the design activity.

At the completion of the design period, participants were issued with a questionnaire. This collected information that related to demographic characteristics and the association with various aspects of bicycle riding, and it asked for a judgment of familiarity with the five types of bicycle designs presented as outline drawings. Finally, participants were asked to write a short description of how they went about designing the bicycle racks.

Analyses

The complete data set consisted of an assessment of each of the variables outlined above for each of the designs produced by each of the participants. However, there are particular combinations of the experimental treatments that are of interest, as opposed to overall analyses of each aspect of the bicycle design. Each pictorial or verbal- description treatment can be compared with the control for each aspect of the design, to determine whether the different types of information produce changes in the design. From Jansson and Smith's work in, design-fixation would be expected with each of the three types of pictorial representation. The comparison of the two sets of semantic descriptions with the control indicates whether it is the pictorial form of the information that is important in affecting the designs produced.

Five analyses were performed, which involved pairs of experimental treatments. These analyses were carried out for all the designs produced, and separately for only the first design produced by each participant. Where all of the designs were included in the analysis, the number of designs produced, and the location, the method of attachment to the car, the method of bicycle support, and the method of bicycle attachment, were analysed for each of the combinations of conditions discussed above. The analysis of the number of designs produced was necessary for two reasons. First, Jansson and Smith 14 found no difference in the number of designs using their single type of pictorial material relative to their control, and the analysis was necessary for comparative purposes. Second, because there are differing types of pictorial material and of equivalent semanti~ material, it was of interest to determine whether these variations, which were not present in the Jansson and Smith experiment, also resulted in no differences in the number of designs produced. Further, it is implicit in the Jansson and Smith result that the pictorial material simply affects the type of design produced. It is rather surprising that similar numbers of designs were produced by their experimental and control groups. If the presentation of pictorial material has the type of effect that is described by Jansson and Smith, it could be argued that this acts to limit the number of designs produced because it prevents changing to a different type of design, given that both groups were requested to construct as many designs as possible.

A different aspect of the same argument leads to an


Table 1. Freq~ncies with which one, two and three designs were produced by each experimental group

Group One Two Three p Average Total or more number

of designs

Control 28 5 2 1.3 35 Single-post picture 31 11 9 0.13 1.7 51 Single-post description 26 13 19 0.00 2.2 58 A-frame picture 32 21 34 0.00 2.6 87 A-frame description 31 14 9 0.08 1.7 54 Boot picture 27 7 3 0.78 1.4 37

analysis of the participants' first designs. For more than one design to be produced, two paths are open to the designer. Variations on the first design can be produced by, for example, change of one of the four aspects of the design assessed. Alternatively, the designer can switch to a different type of design, from a rear-mounted design to a roof-rack design, for example. If the second path is common, analysis of all the designs tends to mask any fixation effect, because the number of other types of designs is inflated. This possible effect can be overcome by analysis of only the first designs.

RESULTS

Differences in number of designs

Table 1 presents the frequencies with which one, two and three or more designs were produced by each of the groups, with the probability associated with the testing of the total number of designs for each experimental group against the control group. Significantly more designs were produced by the group who received a picture of an A- frame design and a description of a single-post design. The last column in the table shows the average number of designs for each group. It is apparent from the data that the A-frame picture group produced the most designs, with the single-post description group producing fewer designs than the A-frame picture group. There is also an indication of a trend in the data, with the control and the boot picture group being similar, and producing the low- est number of designs, the single-post picture and the A- frame description groups producing an increased number of designs, and the single-post description group and then the A-frame group producing the most designs.

This result contrasts with the absence of a difference in the number of designs in Jansson and Smith's work t4, in which the average numbers of designs were 4.5 and 4.3 in the control and fixation groups, respectively. It is also apparent that Jansson and Smith's designers produced many more designs. The most likely explanation of this difference is the difference in the amount of design experience between the two experiments; Jansson and Smith's participants were senior design students, while the participants in the experiment described in this paper were in the second part of their first year at university. This difference is the most likely cause of the effect, rather than the difference in design disciplines in the two experiments (mechanical engineering in the Jansson and Smith experiment, and industrial design and architecture in the experiment described in this paper), although the question of differences as a function of design background is an issue that should be investigated in future research.

Effects of pictorial information

Table 2 presents the probabilities associated with the chi- square values obtained for each of the five comparisons between the groups in the experiment for all the designs. Table 3 gives the probabilities associated with the same comparisons for the first designs. From Jansson and Smith's experiment t4, it would be predicted that each of the pictorial information conditions should result in, for each aspect of the bicycle-rack design, significantly more features associated with each particular picture relative to the control group. When all the designs are considered, there are no differences between the control group and the three picture groups for the location of the bicycle rack, the method of attachment to the car, the method of supporting the bicycle, and the method of attaching the bicycle to the rack. The only exception to this result is a significant effect that was associated with the A-frame picture group and the method of attaching the bicycle to the rack, where fewer wheel attachments and more frame and enclosure of the whole bicycle were used in the A- frame picture group.

For the first designs, there was a significant difference in the method of attaching the rack to the car for the single- post picture group, where 49% of designs in the picture group used a tow-ball attachment, in contrast to 13% in the control group (see Table 8 in Appendix). Significant differences were also found for the A-frame picture group for the method of attaching the bicycle to the rack, reflect- ing the same effect found for all the designs, and the probability associated with the bicycle-support comparison approaches significance. In this case, there are fewer single-post designs in the A-frame group, but more multiple vertical- and horizontal-post and angle-post designs than in the control group (see Table 11 in Appendix).

Effects of verbal descriptions

For all the designs, neither of the verbal-description conditions is significantly different from the control group for any aspects of the bicycle design. The one exception is associated with the method of attaching the bicycle to the rack for the single-post description group, where the effect approaches significance, and this effect is significant when only the first designs are considered. In both cases, the difference is similar to that found with the A-frame picture group, with the single-post description group having fewer wheel attachments and more frame attachments, or the whole bicycle enclosed (see Tables 12 and 13 in Appen- dix).

Familiarity of designs

Table 4 presents the levels of familiarity with each of the bicycle-rack designs presented in Figure 1. The level of familiarity is presented as a percentage of the respondents across all six of the experimental groups. Table 4 illus- trates clearly that there are differences in familiarity between existing bicycle-rack designs. It is apparent that a particularly high percentage of the participants were very, or quite, familiar with the single-post design (91%). A majority were very, or quite, familiar with the A-frame design (66%). In contrast, 7% of the participants were very, or quite, familiar with the boot-rack design. The roof-rack design, where the bicycle is carried on the roof


Table 2. Probabilities associated with chi-square obtained when all designs are considered for each of eight comparisons for number of designs and each aspect of design

Group Location of rack Car attachment Bicycle support Bicycle attachment

Control v e r s u s single-post picture Control v e r s u s single-post description Control v e r s u s A-frame picture Control v e r s u s A-frame description Control v e r s u s boot picture

0.36 0.38 0.53 0.17 0.83 0.88 0.72 0.06 0.79 0.64 0.21 0.02 0.30 0.13 0.61 0.12 0.89 0.99 0.86 0.26

Table 3. Probabilities associated with chi-square obtained for first designs for eight comparisons for each aspect of design

Group Location of rack Car attachment Bicycle support Bicycle attachment

Control v e r s u s single-post picture Control v e r s u s single-post description Control v e r s u s A-frame picture Control v e r s u s A-frame description Control v e r s u s boot picture

0.60 0.02 0.18 0.14 0.63 0.29 0.67 0.04 0.16 0.13 0.08 0.05 0.86 0.08 0.25 0.36 0.28 0.69 0.59 0.48

Table 4. Levels of familiarity with each bicycle-rack design

Rack design Levels of familiarity

Not at all familiar Quite familiar Very familiar

% % %

Single post 8 52 39 A frame 34 55 11 Roof I 65 3l 4 Roof 2 77 16 7 Boot 93 5 2

[Designs are designs a-e in Figure 1. n = 207.]

in a upright position, was very, or quite, familiar to 35% of the participants. The other roof-rack design, where the bicycle is carried in an upside-down position attached by the seat, was very, or quite, familiar to 23% of the participants. The judged familiarity of the various bicycle-rack designs therefore corresponds quite closely to the data on the frequency of use.

DISCUSSION

In their experiment that used a bicycle-rack design problem, Jansson and Smith la report the following percentage differences between their control group and the single experimental group given pictorial information. For top-mounted designs (the location variable of the experiment discussed in this paper), the figures were 59% for the control group, and 71% for the experimental group. For designs with suction cups (the experiment car- attachment variable), the figures were 6% for the control group, and 54% for the experimental group. For designs with tire railings (the experiment bicycle-attachment variable), the figures were 48% and 15%. Jansson and Smith did not score their designs for the method of supporting the bicycle on the rack. These figures show a consistent fixation effect across each aspect of the design.

In contrast, the results of the experiment described in this paper are quite different. For two of the pictured designs, the boot and the A-frame racks, their aspects are found very infrequently in the designs produced. For example, a specific A-frame used as the method of supporting the bicycle occurred in only 5% of the designs of the group shown a picture of this design. Boot-rack designs occurred infrequently. F6r example, 20% of parti-

cipants who were shown a picture of a boot-rack design located their design on the boot. In the specific comparisons between the experimental groups and the control group, statistically significant differences were only found for a limited number of the aspects of the design, rather than the differences that occurred for all the aspects of the design, as occurred in Jansson and Smith's work. While some of these differences are consistent with a design- fixation effect, for example the significantly higher percentage of tow-ball attachments in the single-post picture group, other differences appear to be related to design differences that did not occur either in the pictures presented or in the control-group description. For example, while the higher percentage of frame attachments of the bicycle to the rack for the A-frame picture group is consistent with a fixation effect, the higher percentage of designs that attached the bicycle by enclosing the whole bicycle represents a new aspect of the design. A similar situation exists with the verbal description of the designs, with there being very few significant differences between these groups and the control groups.

The authors' attempt to replicate the design-fixation effect was largely unsuccessful, and, as a result, the issue of differences in the effects of pictorial and semantic information could not be effectively addressed. Further, the largest effect in the data, the increase in the number of designs with the A-frame picture condition, is the reverse of the design-fixation effect. Very few of these designs reflected the particular characteristics of this design; rather, exposure to the picture appeared to result in more designs and more diverse designs. The important issues are, therefore, why design fixation did not occur, and why there was evidence of design diversity.

There are two types of factor that could have contri- buted to the results. First, there are the differences between the participants in the authors' experiments and the Jansson and Smith experiments, in terms of the amount of their design experience and the type of design discipline that they were studying, as commented on pre- viously. If the amount of design experience is the critical factor, this implies that, as designers become more experienced, the fixation effect increases, i.e. designers become more influenced by specific material that is related to what is to be designed than do relative novices. In contrast to this effect, novices are more affected by existing knowledge based on experience, i.e. knowledge that is based on


dran, M and Gero, J S Knowledge-Based Design Systems Addi son -Wes ley , U S A (1990)

13 Klahr , D and Kotovsky, K (Eds.) Complex Information Processing: The Impact of Herbert A. Simon Lawrence Erlbaum, USA (1989)

14 Jansson, D G and Smith, S M 'Design fixation' Proc. Engineering Design Research Conf. N a t i o n a l Science Foundation, USA (1989) pp 53-76

15 Weisberg, R W and Alba, J W ' A n e x a m i n a t i o n o f the al leged role o f ' f ixa t ion ' in the so lu t ion o f several ' ins ight ' p r o b l e m s ' J. Experim. Psychol. Vol 110 N o 2 (1981) pp 169-192

16 Weisberg , R W ' P r o b l e m solving and crea t iv i ty in Sternberg, R J (Ed.) The Nature of Creativity: Contem- porary Psychological Perspectives C a m b r i d g e Un ive r - sity Press, U S A (1988)

A P P E N D I X

Table 6. Percentages of a//designs for each experimental group and method of location of bicycle rack

Group Rear Boot and Roof Total number other

% % % %

Control 54 9 37 35 Single-post picture 69 4 27 51 Single-post description 55 12 33 58 A-frame picture 49 13 38 87 A-frame description 70 6 24 54 Boot picture 57 11 32 37

Table 7. Percentages of first designs for each experimental group and method of location of bicycle rack

Group Rear Boot and Roof Total number other

% % % %


Table 8. Percentages of all designs for each experimental group and method of attachment of bicycle rack to car

Group Tow Bumper Roof Total number ball bar

% % % %


Table 9. Percentages of first designs for each experimental group and method of attachment of bicycle rack to car

Group Tow Bumper Roof Total number ball bar

% % % %


Table 10. Percentages of all designs for each experimental group and method of support of bicycle rack

Group Single vertical post Single horizontal post Roof Multiple vertical, Angled post Total number horizontal posts

% % % % % % Control 32 11 23 17 17 35 Single-post picture 42 6 24 20 8 51 Single-post description 31 5 24 26 14 58 A-frame picture 17 8 21 37 l 7 87 A-frame description 28 9 13 28 22 54 Boot picture 32 5 30 14 19 37

Table 11. Percentages of first designs for each experimental group and method of support of bicycle rack

Group Single vertical post Single horizontal post Roof Multiple vertical, Angled post Total number horizontal posts

% % % % % % Control 34 13 27 13 13 31 Single-post picture 52 9 27 12 0 34 Single-post description 34 3 34 16 13 32 A-frame picture 15 8 17 37 23 40 A-frame description 19 10 23 37 11 37 Boot picture 32 3 39 16 10 30

90 K n o w l e d g e - B a s e d Sys t ems

Table 12. Percentages for all designs for each experimental group and Table 13. Percentages for first designs for each experimental group and method of attaching bicycle to rack method of attaching bicycle to rack

Group Wheels Frame Bicycle Total enclosed number

% % % % Control 40 49 11 35 Single-post picture 21 67 12 51 Single-post description 19 57 24 58 A-frame picture 17 61 22 87 A-frame description 20 69 11 54 Boot picture 24 68 8 37

Group Wheels Frame Bicycle Total enclosed number

% % % % Control 41 52 7 29 Single-post picture 19 75 6 32 Single-post description 14 65 21 28 A-frame picture 14 69 15 39 A-frame description 25 63 12 32 Boot picture 27 63 10 30

V o l 5 N o 1 M a r c h 1992 91

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Effects of examples on the results of a design activity