Keywords

1 Introduction

Packaging materials are consumer products which have interfaces with everyday life that are frequently used. However, many such materials do not satisfy aspects related to usability and safety. For this reason the design of packaging must provide the user with safety, comfort, efficiency and aesthetic satisfaction. In addition, the user’s capabilities should be taken into consideration especially in relation to usability and accessibility when opening the product. This question, when it involves seniors and children, should be a priority for the designer.

In this case, the interface problems harm users when accidents occur, which, among other causes, can be due to improper sizing of the strength needed while handling product packaging [1, 2]. Thus, individuals considered strong as well as those considered weak may suffer adverse effects in the motor performance of this task. Furthermore, the difficulty of opening a PET bottle may lead to waste and even the ruin of the product.

Thus, studies related to measuring user satisfaction with PET bottles for soft drinks are still scarce, especially when related to the user´s actual performance at the moment when he/she opens screw caps.

Bevan [3] explains that even though usability is a tool used to improve the development of products and interfaces, this is still not enough for optimizing the human-product interface. Tullis and Albert [4] explain that usability uses metrics to measure a user’s experience and that this takes place during the design and evaluation process which helps to identify possible usability problems. Moreover, some measures are taken to facilitate the analysis and the conduct of usability tests, such as by applying usability models.

However, the researcher does not always have factual knowledge about whether or not the experience reported by the user at the time of the experiment is fully consistent with the actual experience that the user feels. The difference between what is reported and, in fact, felt becomes an unknown to the researcher.

In this perspective, ergonomics studies associated with neuroscience have given rise to Neuroergonomics which studies the brain and its behavior in various work activities [5, 6]. This area enables cognition and human behavior in various activity sites to be analyzed. This research set out to conduct a usability evaluation of a sample of users when they were manually handling soft drink PET bottles by comparing the experience the user reported and the real experience felt by measuring them using the techniques of eye tracking and electroencephalography (EEG).

2 Methodology

The methodology of this study was of a quantitative character, consisting of a field study, comprising 12 participants for the usability study who are from different age groups and are higher education students. As for the Electroencephalogram (EEG) study, initially seven volunteers were recruited.

To select the sample for the usability study, the inclusion criteria were: individuals about whom no pathological condition of the upper limbs had been reported in the previous year and the exclusion criteria were patients who had a reported pathological condition of the upper limbs in the previous year. This exclusion criterion was justified since, for this study, those having limitations in their upper limbs cannot manipulate the PET bottles.

For the neuroergonomics study, the inclusion criteria were: no fluid intake, the intention being to cause the volunteers to feel thirsty when they first saw the soft drinks packaging. In addition, the volunteers were asked not to use alcohol or illicit drugs, caffeine, colas for 24 h before the experiment.

As to the exclusion criteria, these were: not to present any kind of neurological lesion or dysfunction, such as traumatic brain injury, epilepsy, stroke or psychiatric symptom, such as bipolar disorder, schizophrenia and cyclothymia. Also excluded were those who had artifacts or unusual changes in their pattern of electrical activity, as well as participants who did not match up to the inclusion criteria.

The results of the steps of the experiment were analyzed using software corresponding to each technique and compared with each other by conducting usability analysis to investigate whether the opinion reported by means of the questionnaire that evaluated usability was similar to the experience felt and measured on using eye-tracking techniques and EEG.

3 Field Study on Usability

For the first step of the experiment, PET bottles packaging were selected in accordance with the study by Silva [7]. In this study, the author assessed the level of difficulty of opening five types of soft drinks PET bottle. For this, the Likert scale was used to assess the level of user satisfaction. According to the results of this research, PET bottle 1 (Fig. 1a) and PT bottle 2 (Fig. 1b) were selected because these were considered easy and difficult to open, respectively.

Fig. 1.
figure 1

(Source: Authors)

PET bottles considered easy (a) and hard (b) to open.

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Thus, 12 users were asked to open the top of the two PET bottle models for soft drinks (Fig. 2). Then, a usability evaluation was conducted to analyze the user’s satisfaction level as to the level of difficulty of opening them based on the Likert scale by Tullis and Albert [4].

Fig. 2.
figure 2

(Source: Authors)

Participants in the act of opening the soft drinks PET bottles.

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The choice of this scale enables an analysis of the user’s satisfaction regarding the opening of the two models of PET bottle to be made. This scale has extremes corresponding to the degree of positive or negative affirmation to which respondents assess their level of agreement or disagreement with what was requested. Five options were presented: very satisfied, satisfied, moderately satisfied, dissatisfied and very dissatisfied.

Thus, this scale let the participants express their satisfaction in degrees of agreement with a positive affirmation or in disagreement with a negative affirmation, thereby enabling them to compare and define which of the PET bottles was the most or least difficult to use.

Analysis and Results of the Experiment.

The responses to the usability evaluation were organized according to the participants’ level of satisfaction and presented the following results: as to PET bottle 1, seven respondents reported being very satisfied and satisfied four. As for PET bottle 2, one respondent reported being very satisfied, three were satisfied, five stated that they were indifferent (moderately satisfied), two were dissatisfied and one was very dissatisfied.

Thus, it can be seen that as to PET bottle 1, the responses were clustered at two levels of positive satisfaction, thus indicating that it was less difficult to open, while as for PET bottle 2, the responses were more spread out among the alternatives presented. Thus, we can conclude that in this study, most respondents preferred PT bottle 1 as this was easier to open.

4 Eye-Tracking Field Study

We used the Tobii Pro TX 300 equipment was used to record the position and the fixations of the patients’ eyes in accordance with what PE bottle the user chose as having “liked” and “disliked”, at a sampling rate of 300 Hz.

The experiment used two sets of stimuli for cognitive activity. The first set consisted of an image with both PET bottles against a white background (Fig. 3) and the second set was represented by the same content of image and background. The images had a resolution of 648 × 1080 and were established with average luminance and equal sizes.

Fig. 3.
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(Source: Authors)

Image of the PET bottles displayed in Tobii.

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In the second phase, the volunteers were asked verbally by the moderator to initially close their eyes for one minute. Soon after, the record of cognitive activity was started when they opened their eyes and this was followed by a fixed gaze activity, for five seconds, at the PET bottle that “you did not like” the photo with the PET bottles 2 and 1.

The presentation of this image was interspersed with neutral 20 images for 20 s, followed by displaying the photo with PET bottles 1 and 2 and asking the participant to gaze fixedly at the PET bottle that “you liked” for five seconds. Finally, 20 neutral images were shown again for 20 s. The total time of this experiment was 50 s.

Five seconds was considered as the time needed to make a decision and so was chosen as the time needed to analyze the PET bottles the user “liked” and “did not like”. This would define the user’s preference for PET bottle 1 or 2.

Analysis and Results of the Experiment.

By using Tobii® Studio 3.2.1 software, the exact moment that the user made a decision was identified as being the moment at which the fixed gaze was longest on the PET bottle that he/she “liked” and “did not like”, namely, long periods of fixed gazing at PET bottles 1 or 2 shown in red.

Identifying the length of time (start and end) of fixed gaze and glances in the area that represents the PET bottle image that the user “did not like” and “liked” is the means by which the user´s preference between these two options is determined.

With respect to PET bottle 1, 11 participants were identified as casting long fixed stares at it. As to PET bottle 2, only one volunteer had the longest fixed stare at it. Therefore, in accordance with the highest total number of fixed stares, it was PET bottle 1 which individuals “least liked” and PET bottle 2 that they most “liked”.

5 EEG Field Study

In the second stage of the experiment, the recording of electrical brain activity with EEG (Fig. 4) was carried out at the same time as capturing the Eye Tracking with 12 participants.

Fig. 4.
figure 4

(Source: www.neuroup.com.br)

Image of EEG cap produced by NeuroUp Company.

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The EEG analysis aimed to record the electrical oscillations of the brain while the PET bottles were being displayed when this was associated with the command to fix a stare at the bottle that the volunteer did not like, and then following the same pattern analysis, the stare at the bottle liked.

The electrical signals of the brain were obtained by placing a cap with 64 gold chloride channels. The size of the cap was based on the measurement of the circumference of the brain. Placing the electrodes followed the 10-10 international system and the reference electrodes are sited in the linked-mastoids of the temporal bones, and earthed in the AFz position. A conductive gel was applied to each of the 64 electrodes.

For analysis of the EEG offline data, first of all, a visual inspection was made to identify the artifacts, and then the automatic removal using Neuroup/Matlab software aided by Independent Component Analysis - ICA and the Multiple Artifact Rejection Algorithm - MARA.

After removing the artifacts, the record of the following regions was selected and sent in ASCII format to sLORETA software in order to analyze the current density in the time domain of the cognitive tasks: FC6, FC4, F8, F4, F6, AF8, O2, P8, PO 4, PO8, FT8, C6, T8, CP4, CP6, TP8, P4, P6, Oz, C4, FC2, FCz, FC1, F2, Fz, F1, AF4, Fp2, Fpz, Fp1, Iz, C1, C2, CP1, CPZ, CP2, P1, Pz, P2, AF3, Cz, C3, C5, T7, FC3, FC5, FT7, F3, F7, AF7, PO3, TP7, CP3, P7, P5, P3, PO7, POZ, O1, F5, CP5.

The EEG recording began with the volunteer resting for one minute with his/her eyes closed and then open for one minute to capture the basal electrical activity. Immediately thereafter the activity of choosing the bottle they “did not like” and “liked” was recorded in accordance with what was obtained from applying the eye tracker.

Results of the Experiment.

Using sLORETA software, 61 electrodes were selected, with 250 times, a 512 Hz sampling rate. The 10-10 system was used as coordinates to create the transformed matrix. Thus, in accordance with the intensity of the current, only values greater than 2.5 (MaxLor) were selected.

In accordance with the software, the records of the individuals corresponding to the two classes of those who “liked” and “disliked” what PET bottles were analyzed. Thus, in Class 3, the Brodmann areas (BA) that were activated were 18, this being located in the occipital lobe and median occiptal gyrus and AB 7 which is located in the parietal lobe and median occipital gyrus. Class 4 activity activated Brodmann areas 5 (parietal lobe and post-central gyrus), 6 (frontal lobe and medial frontal gyrus), 7 (parietal lobe and post-central gyrus), 11 (frontal lobe and median frontal gyrus) and 47 (frontal lobe and lower front gyrus).

In addition an analysis was performed on the record of a volunteer per individual in order to investigate more specific results on the satisfaction of the activity of choosing the PET bottle in the two classes of “liked” and “disliked” (Fig. 5a and b). As to Class 3, the areas of the brain activated were 1 (post-central gyrus) and 7 (precuneus and superior parietal lobes) both in the parietal lobe. Class 4 activated Brodmann areas 5 and 07 both located in the parietal lobe and post-central gyrus (Fig. 6).

Fig. 5.
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Images from sLORETA with the 3D representation of classes 3(a) and 4(b) and the respective transversal sections of the brain.

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Fig. 6.
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sLORETA image of individual 01 of the class that did not like (a) (AB 7) and the class that liked (b) (AB 1) schematized in the 3D map, and in the displays of anatomical sections of the brain.

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Results of the Experiment.

We believe that the EEG records of Classes 3 and 4 do not show significant results in the brain areas activated by choosing the sections of the times that had been analyzed after the process for selecting the PET bottles (decision making) had taken place which is when we synchronized the EEG with the activity of the eye tracker.

Therefore, according to [8], we can say that the area of the precuneus and the parietal lobe that were activated in both classes are related to the voluntary control of staring, the task of spatial visual attention and saccadic movements when tracking the accompanying oculomotor movements. However, the objective of this study was not to check staring in itself or to see if the individual managed to plan and perform the activity requested.

To do so, an additional analysis was conducted to understand the process by which users select PET bottles. During this further analysis, it was observed that individual 01 of the (disliked) class had activated the primary somatosensory cortex, which is formed by the post-central gyrus in the parietal lobe and its operation of Brodmann area 1. This system is involved in the central processing of tactile stimuli and of noxious (aversive or aggressive) stimuli [9].

Thus, we can suggest that the somatosensory cortex, especially in Brodmann area 1 was activated at the time when an individual is likely to have associated the activity of opening the bottle with an aggressive stimulus, as mentioned by [9]. In this reasoning, the nociceptive stimuli found may be related to the difficulty of opening PET bottle 1, this being perhaps what causes less satisfaction in using it. This suggests that the user preferred PET bottle 2.

As to individual 01, in class 4, what was activated was his tertiary somatosensory cortex that consists of the superior parietal lobe and relates to the posterior parietal association area which corresponded to the workings of Brodmann Areas 5 and 7.

Area 5 is related to the tactile information from mechanoreceptors of the skin, muscles and joints. This area also integrates information for both hands [10, 11]. The authors cited add that area 7 is related to receiving visual, tactile and proprioceptive stimuli that let visual and stereognostic information to be identified.

According to neurologists, the property known as stereognosis has the capacity to perceive/recognize or identify shapes and objects with one´s hands and is also responsible for processing cognitive information in the brain [10].

Therefore, we can suggest that as a result of activating Brodmann area 5, the individual obtained tactile information while performing the activity with the PET bottles. As to activating area 7, what was received was visual and tactile stimuli for the process of identifying and probably selecting the PET bottles. In this case, no activities in the brain related to this user’s preference for PET bottle were observed.

Attention should be drawn to the need to carry out new randomized experiments with displaying images with the PET bottles so as to clarify or confirm these results.

6 Conclusions

The findings were obtained arising from the two hypotheses that underpinned this research study. The first put forward the possibility that “The experience reported by the users of the soft drink PET bottles can be analyzed by means of the score for satisfaction obtained from the Likert scale (usability assessment) and compared with the experiences felt by the users (eye tracking and EEG).”

Given this hypothesis, the field study of usability evaluation succeeded in proving that it is possible to analyze the experience reported by users. Likewise, it was also possible to analyze the experience felt by the user on using ET and EEG techniques which were compared with the usability evaluation. Thus, this hypothesis was confirmed.

The second hypothesis stated that “The results obtained by the eye-tracking techniques and EEG are effective for measuring the satisfaction (felt experience) of the users of the soft drinks PET bottles.”

In eye-tracking we obtained a response that was in line with our objective. The volunteers, by fixing their gaze, selected the bottle that they preferred. The objective of this technique, which captures the participant’s attention, is to filter the individual’s oculomotor behavior while performing a given cognitive activity (selecting a PET bottle that he or she liked or did not like).

When choosing which bottle he/she liked, the volunteer had fixed his/her gaze on this one and developed a cognitive activity. This procedure reinforces our hypothesis that this technique reveals the experience felt by the volunteer.

It was also possible to identify the experience felt while the PET bottles were being opened by using Electroencephalography (EEG) techniques. In this case, the user’s mental performance was captured by the EEG during his/her cognitive and physical work. In the eye tracking activity, the EEG recording was associated with the volunteer choosing the PET bottle that he/she liked. This choice, at the mental (cognitive) level, with subsequent selection at the visual (physical) level characterizes an activity related to the experience that the user feltfelt by the user, confirming the hypothesis presented.

Thus, the tools used confirmed the hypotheses that (1) the reported experience can be compared to the experience that the user felt and (2) that the tools used are appropriate to measure the experience felt and consequent satisfaction of the user.

Attention should be drawn to the fact that the Usability Field Study presented a result that is contrary to other studies. In this field study, volunteers said they liked PET bottle 1 best, while in other field studies, PET bottle 2 was chosen.

These results may suggest that the opinion reported by the user at the time of a usability evaluation by using a questionnaire, can be totally different from his/her thoughts/feelings or impressions regarding the use of a product.

Therefore, what our brain perceives and remembers may be different from the things that we say we understand and record when we are asked about this [12]. Thus, it is extremely important to use techniques that can compare the experience felt and the experience reported by the user. Another point of interest is that users can carry out correlations with their own unconscious processes with the meaning of their answers, the reasons for their preferences, their beliefs, and the analysis of their experiences [13].