Abstract
The development of an emotion-based (or affect-based) apparel design system has become an important issue nowadays due to the customer’s increased demand for apparel products not only in the aspect of function but also of aesthetics or affect/emotion. This paper presents a study on developing a mapping from affective words to design parameters. The technique employed to develop this mapping is neural networks (NNs). Both linear NNs and higher-order NNs were applied. An example was taken to illustrate and validate the developed mapping. There are two main contributions from the study. The first is that this mapping is the first in the domain of apparel design, and with it, the computer-aided affect-based design for apparel becomes possible. The second one is the provision of some empirical knowledge for the evaluation of so-called higher-order NNs.
Designs need to be described in the form of parameters, that is, design parameters (DPs). In fact, the design description may not necessarily be represented by the parameter, but rather a drawing or image. Indeed, the design description in the form of a parameter can facilitate the computer processing and further computer-aided design (CAD) in the technology today.1–7 For whatever description, it follows a pattern called “type-instance”, 8 in which a description has a name that refers to a type of information or knowledge, for example, the “diameter of a cup” (with the unit being mm) and then an instance follows the name, for example, “0.5” under the name, “diameter of a cup”. Together, the type and instance formalism (i.e. diameter = 0.5) gives a clear description of the design – that is, the “diameter of a cup is 0.5”. In the apparel design domain, apparel design parameters (ADPs) have names such as “color”, “material” and “shape” (or “silhouette”).
The parameter is determined to meet the requirement of a product, apparel in this case. Generally, there are three types of requirements for apparel design, namely, function, comfort or usability and pleasure or affect. 9 Many studies have been conducted in the apparel domain to meet the requirements related to the function and comfort of apparel,10,11 while only a few studies have been made on design for affect or affective design – which is in essence about building the relationship between pleasure (or affect) and ADPs. For example, the relationship between the style of apparel (which falls into the category of ADP) and the mood, emotional, social or cultural factors have been discussed by Moody et al., 12 Na, 13 Khalid and Helander, 14 Cho and Lee 15 and Shishoo. 16 The main difference between these studies and the study presented in this paper lies in two aspects: (1) the completeness of affective words (AWs) and ADPs – in particular, these studies in the literature have a restricted scope of AWs and/or ADPs (e.g. only the style is considered by Moody et al., 12 Na, 13 Khalid and Helander 14 and Cho and Lee 15 ); and (2) the effectiveness of the way to develop the mapping between the AWs and the ADPs – in particular, these studies in the literature apply the statistic and linear regression technique, which has a limited capability to capture a highly subjective process (i.e. an affective design process). Nevertheless, these studies have laid the foundation for developing the emotion-based apparel design theory and methodology such that the quantitative relationship mapping from the affect (represented by AWs) to the design (represented by ADPs) could be built.
Three challenges are presented in developing the relationship between AWs and DPs in the domain of apparel. Challenge 1 is to represent a human’s affect that can be processed by a computer system; challenge 2 is to find ADPs that can describe apparel; and challenge 3 is to find a proper tool to build the mapping from AWs to ADPs.
Affective words
Summary of apparel design parameters (ADPs)
In order to address challenge 3, the selection of a proper mathematical modeling tool needs to be made. In the literature, statistical methods12,21–25 and intelligent computing technology26–33 have been used as a tool for this purpose. Statistical methods are used for simple and linear problems, such as regression (e.g. linear regression and logistic regression) and classification (e.g. factor analysis), while intelligent computing technology can tackle more complex and non-linear problems (e.g. artificial neural networks), and it can also deal with problems with imprecise information (e.g. fuzzy logic). 34 In fact, statistical methods can be viewed as a special case of the intelligent computing technology that contains more complex analysis.
In this paper, we present a work on building a model to represent the relationship from the AWs to the DPs for apparel design by applying the neural network (NN) technique. In this model, a human’s affect is the input, and DP is the output. The contributions of the work are as follows: (1) the model as developed enables affective design for apparel; and (2) a new experience of the efficacy of NNs, especially high-order NNs, is generated.
The rest of the paper is organized as follows: the second section presents the methodology for developing the mapping from AWs to ADPs. The third section is the architecture of the neural network. The fourth section is the results and discussion. The fifth section gives a validation of the developed model through an example. The sixth section is a conclusion with some further discussion.
Model development
There are two steps in applying the artificial NN model technique: (1) generation of training data and (2) determination of the weights for a particular NN architecture.
Acquisition of training data
The general methodology is to have a test-bed on which test samples with their ADPs and AWs are exposed to human subjects for them to express their opinions on the “strength” of the link between the ADPs and AWs. The test-bed includes two software systems: (1) Marvelous Designer, which is to simulate three-dimensional (3D) apparel in terms of ADPs; and (2) FluidSurvey, which is a platform for constructing a survey. The first was used in this study for constructing a test sample (apparel) described with ADPs, as shown in Table 2, and the second was used in this study to link the test sample to AWs, as shown in Table 1. The combination of these two systems results in a survey interface to the subject, as shown in Figure 1. The left part of Figure 1 shows a picture of apparel, generated by system (1), and the right part of Figure 1 shows all AWs with five-level Likert scales (1–5), generated by system (2). In the experiment, there were in total 27 test samples (which represent 27 combinations of ADPs) generated. A note is given regarding the 27 combinations. Each ADP was considered to have three levels (high, middle and low), and the orthogonal array technique
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was applied to result in 27 combinations. The duration of the survey was about two months. Each survey randomly displayed six scenarios (see https://fluidsurveys.usask.ca/s/rainzhao/) to the subject, and each scenario includes an apparel picture and 30 AWs (Figure 1 as a partial interface). There were, in total, 100 subjects recruited for this survey. The criteria for selection of subjects were as follows: (1) they must be Canadian residents and (2) their age must be in the range of 18–35.
A scenario from the survey.
The test procedure is as follows. Step 1: a survey with a test sample (i.e. apparel picture) and AWs were shown to the subject. The survey engine thus connects ADPs and AWs. Step 2: a subject ranks the appropriate AWs he or she feels while viewing the apparel picture by use of the subjective rating scale. Step 3: a pair of “values”, namely < ADP-level, AW-scale > (e.g. ADP-level: high; AW-scale: 5), was created, and subsequently, a number of such pairs was created. In total, 600 pairs of data (i.e. training data) were created as there were 100 subjects and each subject was given six pictures.
Before performing data analysis, the data collected required some cleaning and the outliers were removed from the data. The following data were removed: (1) the same Likert item is given to all or most of the AWs (e.g. “2” is given to all AWs); (2) the difference in the Likert items to all AWs is very small (e.g. “2” or “3” is given to all AWs); (3) the data is incomplete (i.e. some items are missing).
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As a result, 565 data out of 600 data were kept as the training data. The training data needs to be normalized to avoid disturbances due to different scales of data.
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The data in the training data were normalized to [0, 1] with the following equation
Neural network architecture
The NN method is a technique used to describe the multiple-input and multiple-output (MIMO) relation.38,39 NNs consist of a set of neurons (nodes) with a set of weighted edges that connect the neurons (nodes), a set of inputs and a set of outputs (Figure 2). The layer of neurons between the input and output layers is called the hidden layer. A neuron consists of two units connected in series: (1) the unit that aggregates the weighted (denoted by w) output of neurons in the preceding layer, plus a so-called bias (denoted by b); and (2) the activated unit in which there is a mathematical function called the activated function (more discussion about the activated function will be given later in this paper). For unit (1), if the aggregated function is linear, the NN is called the linear NN; if the aggregated function is with an order more than 1 (e.g. second order), the NN is called the higher-order NN.
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The general architecture of neural networks.
The design of a particular NN means to determine (i) the number of hidden layers, (ii) the number of neurons in each hidden layer, (iii) the activated function and (iv) the weight. Just like designing a product (e.g. apparel), the method of determining the foregoing components is empirical-based except for (iv) – determining the weight. The general principle of determining the weight is as follows: the weight is determined to make the behavior of a particular NN model under design match the known behavior of the application problem under modeling (e.g. the data pair < APA-value, AW-value>). Clearly, the known behavior of the application problem is the training data discussed previously. The process of determining the weight is called learning in the NN literature. 40 A commonly used method to determine the weight is called back-propagation (BP). 41 The algorithm called Levenberg–Marquardt (LM) was used for BP in this study. The LM algorithm is available in the MATLAB NNs tool box.
There are three main types of activated functions in NNs (Figure 2), namely, the Hyperbolic Tangent Sigmoid (HTS) (or Tansig function), the Log Sigmoid (LS) (or Logsig function) and the Purlin function (or Linear function; LF).33,42 It is noted that the rule of selecting the activated function in the output layer depends on the value range of the outputs of a particular NN architecture. If the value range of output is [0, 1], LS is chosen; if the value range is [–1, 1], HTS is chosen; and LF is suitable for both kinds of value range. In this study, we considered LS as the activated function for the output layer as the value range in the output layer in our problem is [0, 1], and considered both LS and HSL as the activated function for the hidden layers, as their value ranges are not restricted to [0, 1].
Structure for the neural network (NN) model and higher-order NN model (quadratic synaptic operation in particular)
BP: back-propogation; LS: Log Sigmoid; HTS: Hyperbolic Tangent Sigmoid; MSE: Mean Squared Error.
The higher-order NN model
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was also employed to develop the AW-to-ADP mapping in this study. In the higher-order NN model, the input to a particular neuron of a particular layer is not based on the linear weight sum but is rather the quadratic weighted function of all inputs from the preceding layer. Figure 3 shows such a NN model, which is also called Higher-order Synaptic Operation (HOSO).
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A neural unit (neuron) with the Higher-order Synaptic Operation.
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As shown in Figure 3, HOSO can be of numerous orders. The first order is the conventional linear correlation, which is the same as the conventional NNs. In this study, a second-order HOSO was considered, which is called the quadratic synaptic operation (QSO).44–47 The Nth-order HOSO is defined as
In this study, the structure of the QSO was quite similar to that of the conventional NNs (Table 3). The only difference between the structure of the LSO (linear synaptic operation) and the QSO is that the LSO considered one and two hidden layers, while only a single hidden layer was considered in the QSO. It is noted that, in theory, a single-layer QSO is able to deal with non-linear problems. The code for conducting the QSO can be accessed from http://homepage.usask.ca/∼yuz703/.
Results and discussion
Forty models were built through the LSO, and twenty models were built through the QSO. Figure 4 presents a comparison for all these models in terms of MSE, in which QSO-HTS refers to the QSO with HTS as the activated function in the hidden layer, QSO-LS refers to the QSO with LS as the activated function in the hidden layer, LSO-HTS-1 refers to the LSO with a single hidden layer and with HTS as the activated function in the hidden layer, LSO-LS-1 refers to the LSO with a single hidden layer and with LS as the activated function in the hidden layer, LSO-HTS-2 refers to the LSO with two hidden layers and with HTS as the activated function in the hidden layers, and LSO-LS-2 refers to LSO with two hidden layers and with LS as the activated function in the hidden layers.
Comparison of the neural network models in terms of Mean Squared Error (MSE).
It can be found from Figure 4 that the MSE of QSO-HTS and QSO-LS are more sensitive to varying numbers of neurons in the hidden layer(s) than any other LSO model. For example, the MSE of QSO-HTS dramatically changes from 10 neurons to 100 neurons. QSO-HTS hits the highest MSE (0.05664) at 20 neurons (in the hidden layer), while it hits the lowest MSE (0.03569) at 40 neurons (in the hidden layer). In general, the linear NN with two hidden layers has a better performance than the quadratic NN with one hidden layer. The smallest MSE is 0.03074 obtained from a linear NN (i.e. LSO-HTS-2 with 60 hidden neurons in the hidden layers (30 in each hidden layer, respectively)).
Figure 5 shows a comparison of the six NNs models in terms of test R. It can be found from Figure 5 that for the QSO (including both QSO-HTS and QSO-LS), the number of neurons is more sensitive than that for the LSO. For example, the test R of QSO-HTS dramatically changes from 10 neurons to 100 neurons. QSO-HTS hits the lowest test R (0.58339) at 30 neurons (in the hidden layer), while it hits the highest test R (0.71342) at 40 neurons. However, for the LSO, the number of neurons is less sensitive than that for the QSO in terms of test R. Among all the NN models, LSO-HTS-2 with 60 neurons in the hidden layers (30 neurons in each hidden layer, respectively) has the highest test R (with 0.74659) (i.e. the best prediction performance).
Comparison of the neural network models in terms of test R.
From Figures 4 and 5, it can be seen that the results based on the MSE and test R are consistent. The number of neurons in the hidden layer is more sensitive with test R than that with the MSE. This is reasonable, as according to the constructs of the MSE and test R, the MSE seems to be more robust than test R. It can also be found that the quadratic NN models are more sensitive to the number of neurons than the linear NN model. This is perhaps because the quadratic NN model is less robust due to its construction.
From both Figure 4 (in terms of the MSE) and Figure 5 (in terms of test R), the mapping of the linear NNs with two hidden layers (60 neurons in total) shows a better prediction performance than that of the quadratic NN with one hidden layer (40 neurons in total). There are two reasons for this outcome. Firstly, the suitability of a particular NN model inherently depends on the characteristic of an application problem – the linear NN model with two hidden layers of neurons and quadratic NN model with one hidden layer of neurons in particular. Secondly, the fitting or approximating power of the former is higher than that of the latter, as in the former, three layers (two hidden layers and the output layer) have an activated function that is non-linear and thus contributes to the fitting or approximating power significantly. Indeed, the result herein is significant in that it provides a counter-argument to the view that a higher-order NN model is promising in terms of fewer neurons in the model for achieving the same accuracy with its counterpart (i.e. the linear NN model). 40 It is noted that the number of neurons in total in the latter (40 neurons) is indeed less than that in the former (60 neurons), but the loss of accuracy with the latter seems to be significant (MSE = 0.03 for the former, MSE = 0.04 for the latter).
Model validation
In this section, an experiment was described to validate the developed model (i.e. the AW-to-ADP mapping). The general approach to do this validation was to develop a test-bed in which the customers will comment on a particular apparel. The customers will first specify their desired affects with the AWs (shown in Table 1) and then the AW-to-ADP mapping is applied to generate an apparel for the customers (respectively). Finally, the customers will comment on whether the designed apparel meets their desired affects.
In particular, in this test-bed, four nurses were invited to participate in the experiment. The criteria for recruiting the nurses are as follows: (1) the participating nurses must be working in a Canadian hospital; and (2) the age of the participating nurses is from 20 to 40. Each of them was asked to fill out a questionnaire regarding the nurse scrub (Figure 6). The questionnaire contained 30 AWs with the five-level Likert scale. The four nurses were asked to describe their desired affects of the nurse scrub under design. In total, there were four sets of data for AWs. Table 4 shows one set of AWs, and all four sets of AWs can be found from the following web site: http://homepage.usask.ca/∼yuz703/. The next step was to use each set of AWs as the input for the AW-to-ADP mapping to obtain the ADPs, respectively. At this point, the NN model of LSO-HST-2 with 60 neurons (30 neurons in each hidden layer) was used, as it the best model (see the previous discussion). Four sets of ADPs were generated from the LSO-HST-2 model, and four nursing scrubs based on the ADPs were created with the Marvelous Designer software. Figure 7 shows one of the four scrubs, and all four scrubs can be found on the web site: http://homepage.usask.ca/∼yuz703/. The four scrubs were then shown to the participating nurses for their feedback on whether the scrubs meet their affective requirements. The feedback on the scrubs includes the degree of satisfaction regarding color, material, shoulder design, waist design, hem design and overall design of scrubs.
Existing nursing scrubs in Canada.
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A set of affective words (AWs) and their rank by a nurse An example of a nursing scrub created by Marvelous Designer.

As a result of the experiment, all the nurses were satisfied with the color of the scrubs, 75% were satisfied with the material, 75% were satisfied with the shoulder design, 75% were satisfied with the waist design, 75% were satisfied with the hem design and all the nurses were satisfied with the overall design of the scrubs for their own desired affects.
Conclusions
In this paper, the development of the AW-to-ADP mapping, especially the mapping from AWs to ADPs, was presented. The mapping allows for affective design, namely given a set of desired AWs, one can find ADPs by use of the mapping. The technique used to develop the mapping was NNs. Both conventional NNs and higher-order NNs (in particular, linear NNs with one and two hidden layers and quadratic NNs with one hidden layer) were used to develop the mapping. A sufficient number of training data were acquired and the NNs were trained. The accuracy of the NN models was evaluated by the MSE and test R. The number of neurons for the hidden layers was determined with the tool available in the NN toolbox of MATLAB. A case study to show the validity of the mapping was also conducted. The following conclusions can be drawn from the results: (1) the mapping based on the architecture of the linear NN with two hidden layers is better than the mapping based on the architecture of the quadratic NN with one hidden layer in terms of both the MSE and test R; (2) the mapping makes sense for affective design for apparel products.
It is noted that in the literature, work closely relevant to the study presented in this paper may refer to the Kawabata evaluation system (KES). 16 However, there are two major differences between the KES and our work. Firstly, the KES only considered the comfort feeling of the customer given a fabric material property, while our work considered a list of 30 AWs, which is obtained through a comprehensive data mining technique. 17 Secondly, the KES can only be used for analysis (i.e. from ADPs to AWs), while our work targets design (i.e. from AWs to ADPs).
There are several limitations with the development described in this paper. The first limitation is that the number of training data is still restricted (about 600 in this case); ideally, 1000 training data may be better to test the number of neurons from 10 to 100. The second limitation is that the number of hidden layers for the quadratic NN model is only one; in the future, the quadratic NN with two hidden layers may be considered. Such a study will help us to understand further the characteristics of higher-order NNs in comparison with linear NNs to applications.
Footnotes
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
