Smart Cupboard for Assessing Memory in
Franks González-Landero 1, Iván García-Magariño 2,* , Rebecca Amariglio 3,4 and
Raquel Lacuesta 5,6
1Edison Desarollos, 44002 Teruel, Spain; firstname.lastname@example.org
2Department of Software Engineering and Artiﬁcial Intelligence, Complutense University of Madrid,
28040 Madrid, Spain
3Harvard Medical School, Harvard University, Boston, MA 02115, USA; email@example.com
4Massachusetts General Hospital, Boston, MA 02114, USA
Department of Computer Science and Engineering of Systems, University of Zaragoza, 44003 Teruel, Spain;
6Instituto de Investigación Sanitaria Aragón, University of Zaragoza, 50009 Zaragoza, Spain
*Correspondence: firstname.lastname@example.org; Tel.: +34-913-947-643
Received: 26 April 2019; Accepted: 31 May 2019; Published: 4 June 2019
Sensor systems for the Internet of Things (IoT) make it possible to continuously monitor
people, gathering information without any extra effort from them. Thus, the IoT can be very helpful in
the context of early disease detection, which can improve peoples’ quality of life by applying the right
treatment and measures at an early stage. This paper presents a new use of IoT sensor systems—we
present a novel three-door smart cupboard that can measure the memory of a user, aiming at detecting
potential memory losses. The smart cupboard has three sensors connected to a Raspberry Pi, whose
aim is to detect which doors are opened. Inside of the Raspberry Pi, a Python script detects the
openings of the doors, and classiﬁes the events between attempts of ﬁnding something without
success and the events of actually ﬁnding it, in order to measure the user’s memory concerning the
objects’ locations (among the three compartments of the smart cupboard). The smart cupboard was
assessed with 23 different users in a controlled environment. This smart cupboard was powered
by an external battery. The memory assessments of the smart cupboard were compared with a
validated test of memory assessment about face–name associations and a self-reported test about
self-perceived memory. We found a signiﬁcant correlation between the smart cupboard results and
both memory measurement methods. Thus, we conclude that the proposed novel smart cupboard
successfully measured memory.
Keywords: IoT; memory loss; e-healthcare; Alzheimer’s; door sensors
Dementia is the progressive loss of cognitive functions due to brain damage or disorder.
Among dementia types, one of the most well-known and widespread diseases is Alzheimer’s disease,
and the number of people who will suffer from this disease is estimated to reach 131.5 million by
]. This disease hampers daily life activities such as recognizing faces and remembering names,
places, and positions [
]. Potentially 131.5 million people could put themselves at risk if they start
developing these symptoms without the proper cautionary measures and palliative treatments.
There is no cure for Alzheimer’s disease, but there are palliative treatments. Some of these are
medicines, but none of them has been proven to stop the progression of this disease [
]. Other examples
are psychosocial interventions, and these involve stimulation-oriented treatments with art, music,
Sensors 2019,19, 2552; doi:10.3390/s19112552 www.mdpi.com/journal/sensors
Sensors 2019,19, 2552 2 of 21
animals, or other recreational activities; however, the efﬁcacy of these treatments remains uncertain [
The last of the palliative treatments is caregiving, which is probably the safest one, but it has a great
impact in health economics for the necessary resources—mainly caregivers, but also measurement of
the state of the disease for suitable caregiving, tagging items in houses, and the maintenance of feeding
tubes in the case of eating problems.
On the other hand, the literature claims that Alzheimer’s disease represents the main cause of
neurodegenerative dementia in the population aged over 60 years old, with an estimated prevalence
of 5–7% [
]. People increase the probability of starting to suffer from Alzheimer’s disease when
getting older without noticing. If anyone suffers from Alzheimer’s disease, they need to receive some
treatment—the sooner the better.
At present, most people live surrounded by technology, including Internet of Things (IoT) sensor
objects that can collect, pre-process, and analyze continuous streams of data (e.g., weather, trafﬁc,
ﬁnance, and health data). One of the most common goals of the IoT is to enhance the quality of life.
IoT technology can track the interactions between quotidian objects and persons, or even among
objects, contributing to the digitalization of the physical world. Another goal of the IoT is to connect
and synchronize traditional utensils through the Internet in order to deliver a service more efﬁciently.
In this way, all elements that used to connect in a close circuit are now connected through a network,
increasing their utility [
]. IoT sensor systems now allow the connection of physical objects so that
remote services can be provided through the Internet by analyzing the data from these sensors.
Thus, once the hardware of the IoT sensors is installed, programmers can provide new functionalities
by developing new software based on different analyses.
In this paper we present a novel sensors system based on the IoT aimed at detecting memory
losses for the early detection of some neurodegenerative diseases, by continuously assessing the
memory of the user and notifying them when appropriate. Among other features of the system, we can
highlight that this measurement method does not require any additional effort from the user, and is
continuous. Users only need to go about their daily routine. The sensors system was installed in a
cupboard, converting it into an IoT smart cupboard (SC). We used a normal cupboard, such as one that
most readers could ﬁnd at their home or in their kitchen. The SC had some door sensors connected to
a Raspberry Pi, programmed to analyze the signals and measure the memory.
The main contribution of the current work over the related works of other authors is its
presentation of a low-cost solution that can monitor users in their daily lives for measuring memory
with the potential of detecting diseases with memory impairments, without needing qualiﬁed staff.
In addition, the mechanism is novel, as this is the ﬁrst work that presents a novel SC for this purpose,
and is based on magnetic door sensors with very low prices. This work extends our previous work
about IoT collaboration exempliﬁed with a SC prototype [
]. The contribution of the current work over
the previous one lies in the use of a more advanced three-door SC prototype that measures memory.
This wa proved with experimental results obtained from 23 participants in which the SC measurements
correlated with a validated memory test and another test about self-perceived memory.
The current work is organized as follows. The next section reviews the existing related works
considering the common technologies in this ﬁeld. Section 3describes the design of the proposed SC
to assess memory and all its features. Section 4describes the conducted experiments and the user tests
for validating the system. Section 5presents the main results. Finally, Section 6discusses the results,
draws conclusions, and depicts some future lines of research.
2. Related Work
The research community is actively involved in the topic of this work due to the consequences
of memory losses on the wellbeing of patients and their social environments. The goal is to reduce
their economic impact on the society due to treatment costs. IoT technology allows the interconnection
of small low-cost devices practically anywhere. These devices can monitor health indicators and the
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behaviors of people. There are many works and projects on this topic, and this section introduces the
most relevant ones.
Some projects present solutions involving Alzheimer’s disease and Raspberry Pi. For instance,
Nonavinakere et al. [
] developed a system that recognizes a person’s face and tells the user the name
of that person and the relationship they have with them. The tool was developed thinking about users
with Alzheimer’s disease. The system was tested using three different platforms; one of them was a
Raspberry Pi 3, and although it was not the fastest platform, it was the most accurate, since it was able
to detect a person within certain limits. Crema et al. [
] proposed an embedded platform-based system
for early detection of Alzheimer’s disease through transcranial magnetic stimulation (TMS). TMS is a
non-invasive way to stimulate the cerebral cortex in order to address Alzheimer’s disease. This system
was formed by a magnetic stimulus generator, an electric stimulus generator, a ﬁeld-programmable
gate array, and a Raspberry Pi. The goal was to introduce an alternative technique that supported
the early detection of Alzheimer’s with reduced costs, and provided results that were suitable for
medical interpretation. Narendiran et al. [
] developed a cognitive assistance system for smart
homes. The main aims of the project were (a) to simulate the progression of Alzheimer’s-type
dementia by evaluating performance in the execution of an activity of daily living and (b) to provide
support for impaired people who need help in daily activities such as preparing a cup of coffee.
The system used a camera connected to Raspberry Pi. The camera provided live images to the
Raspberry, whose contents were the patient inside the home environment. While the Raspberry was
receiving images, it assessed the performance of a task and provided feedback to the patient about
their performance. For instance, when a patient forgot some step of some task, the system reminded
the patient about this step. Ishii et al. [
] designed an early-detection system for dementia using
the Machine-to-Machine (M2M)/IoT platform. The system was formed by sound sensors, motion
sensors, pressure sensors, an Arduino board per sensor, a Raspberry Pi board, an M2M server, and the
corresponding analysis software. The authors assessed several activities and behaviors of a person
inside their home. Several sensors were set up in the home environment, including outdoors near the
home and inside some rooms (e.g., bedrooms, bathrooms). Each Arduino board connected to a sensor
sent information to the Raspberry Pi. This had two functions; the ﬁrst was to send information to the
M2M server, and the second was to analyze the collected information through the analysis software
in order to determine early symptoms of Alzheimer’s disease. It is worth highlighting the mixed
use of Arduino and Raspberry Pi boards. Kristalina et al. [
] kept in mind one of consequences of
memory impairment, which is that a certain person can forget where they are. In order to address
this handicap, they developed a system that involved a Raspberry Pi and an iBeacon. This was a
tracking system for patients with memory impairment. Each patient carried an iBeacon device that
was responsible for sending the ID and signal strength to the Raspberry Pi and then to the server in
order to convert the information to a distance. Due to the amount of noise, it was possible that the
obtained distance data did not match with current patient position, so the authors applied the Kalman
method in order to estimate the distance between devices. This system was assessed at the Dr. M.
Soewandhie hospital, and their tests showed an average percentage measurement error of 7.01% in the
actual patient position. Chavan and Chavan [
] proposed a novel system for fall detection in elderly
people. They beneﬁted from the new features of Raspberry Pi 3 with respect to the previous version
(i.e., Wi-Fi connection) for the creation of a new system with wearables. The system was formed by a
laptop, a Raspberry Pi 3, accelerometers, a heart rate sensor, and a temperature sensor. The sensors
sent information to the Raspberry, and this determined if there had been a fall. If so, a text message
was sent to a mobile device. Paul et al. [
] described a low-cost system for monitoring patients, which
was formed by several sensors, a Raspberry Pi, a database, and an application. The system’s aim was
to collect patient data (e.g., electrocardiogram signal, blood pressure signal, heart rate signal, blood
oxygenation, temperature) in order to send them to the patient’s doctor. The system was set up in
Bangladesh with success.
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Although they do not make use of a Raspberry Pi, the following projects addressed Alzheimer’s
disease with other IoT elements. Chong et al. [
] proposed a system in order to predict a potential
Alzheimer’s medical condition. They used a room with movement sensors inside it and analyzed
the data obtained from 20 elderly persons by means of ﬁve sensors over the course of six months.
The results provided three key factors in order to perform a prediction: excess activity levels, sleeping
patterns, and repetitive actions. These factors were useful for predicting the early warning signs
of Alzheimer’s, and allowed the authors to provide recommendations to caregivers based on the
prediction analyses. Navarro et al. [
] developed a fuzzy adaptive cognitive stimulation therapy
generation system for Alzheimer’s patients. The aim of the system was to reduce the cognitive
burden of care workers and therapists. The system assessed patient behavior through several activities
and even through their voice tone and their phrases. This system used the Mente Activa software,
whose aim was to provide computer-assisted cognitive therapy. The authors demonstrated the
enhancement of patients with the experiments with their system. Finally, Roopaei and Jane [
on another aspect related to memory loss, which was the ability to recognize familiar faces. The authors
developed a platform to support patients who suffered from face perception impairment with an
assistive intelligence device. The system included an algorithm that recognized a face among entries
in a face dataset. The algorithm used deep learning to recognize patterns in faces and match them.
Regarding IoT, the authors proposed to use glasses in order to let the user know who was in front of
them as well as their relationship.
Table 1depicts the main differences and similarities of the current work with the most related
ones. As one can observe, the current work is the only one that has all the following four features at
the same time: (a) it does not need qualiﬁed staff, and hence anybody can use it without previous
experience; (b) it has the potential to measure memory by just analyzing the daily activities of users;
(c) it is a low-cost solution for monitoring; and (d) it can detect symptoms of memory disease in early
stages. The most similar work is the one by Ishii et al. [
], as it also has the potential to measure
memory and conduct the early detection of memory-impairment related diseases by analyzing daily
activities without requiring qualiﬁed staff. Even though, the current work has all these features, it is
also low cost, thanks to the novel mechanism based on a SC with very low-cost magnetic door sensors.
Considering all the related works presented in this section, we also noticed a gap in the literature
about using pieces of IoT-enabled furniture for monitoring the memory of users for the early detection
of memory-impairment diseases. The current approach covers this gap in the literature by presenting
an IoT SC, built with low-cost magnetic door sensors, introduced in the next section.
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Table 1. Comparison between the current work and the most closely related ones.
et al. 
et al. 
Does this work use IoT? 3- - - 3
Does this work use
3 3 3 3 3 3
Does this work present a
low-cost solution for health
3 3 - - - 3
Does this system use
-3 3 - - 3
Can this solution be applied
without qualiﬁed staff?
3- - - 3
Does this solution measure
3- - - 3
Does this solution measure
cardiac measures? (heart rate,
heart rate variability)
- - - - - 3
Does this solution measure
- - - - - 3
Does this solution have
the potential to measure
any health indicator by just
analyzing the daily activities
3- - 3 3 3
Does this solution have the
potential to measure memory
by just analyzing the daily
activities of users?
3- - 3 3
Could this solution help to
diseases at an early stage?
3-3 3 3
3. Smart Cupboard for Assessing Memory
In Figure 1, the reader can observe a picture that depicts the overall experiment described in
this paper. This paper also presents the design of the SC, the assessment method of the SC, and the
experimentation with users. The core of the system is formed by a Raspberry Pi model 3 B+, with CPU
1.4 GHz 64-bit quad-core ARMv8, 1 GB Memory (SDRAM) (shared with GPU), 17x GPIO and HAT ID
bus, 5 V through MicroUSB or a GPIO header. A lithium-ion battery accompanies the Raspberry Pi,
which facilitated the setting up of the system inside the cupboard for the experiments, since a wire
connected to power was not necessary. This provided the possibility of installing the sensors system in
a cupboard without needing a nearby socket. The autonomy of the battery was 9 h, and we considered
that this was enough to assess our system in controlled environments with users. The SC also had
magnetic door sensors. The cupboard selection was made based on certain features. The requirements
that the furniture must have according to our controlled experiments were (a) to be placed in a
kitchen, (b) to have three compartments of the same size (to avoid memory techniques based on the
size of objects and compartments), and (c) that each compartment could hold 5 to 10 items without
overlapping (to facilitate the acquisition phase based on observation). We used an Excellway MC-38
wired magnetic alarm system door window sensor switch with screw provided by Banggood. Figure 2
shows this magnetic door sensor. Each sensor was composed of two parts; one was attached to the
cupboard structure and connected to the Raspberry Pi, and the other was attached to the door, such
that both parts were together when the door was closed and apart when it was open. Each sensor
closed the circuit when both parts were together (or very near to each other). For our system, we used
three pairs of sensors and these were set up in the three doors of the cupboard. A protoboard and
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jumper wires were used to connect the Raspberry Pi and door sensors, and the schematic design is
presented in Section 3.1. We wrote a Python script in order to manage the proposed SC. The script
assessed the memory of users based on the analysis of the signals of door sensors, with the algorithm
described in Section 3.2.
Figure 1. Overview of the smart cupboard and the experiments.
Figure 2. Door sensor.
3.1. Schematic Design of the Smart Cupboard
The door sensors and the Raspberry Pi were connected through jumper wires and a protoboard,
and this section explains in detail how these elements were connected. The Raspberry Pi had a pin
series placed on a side of the board, called GPIOs (general-purpose inputs/outputs). They performed
multiple input/output operations for different purposes. The Raspberry Pi model used in this work
had 40 pins. Figure 3depicts the schematic design of the SC, indicating the used pins. This schematic
design uses the following color notation to distinguish the different pin types:
•Red pins: power to 3.3 V and 5 V.
Green pins: Communication through Inter-Integrated Circuit (I2C) protocol in order to
communicate with peripherals that use this protocol.
Blue pins: Connection for the universal asynchronous receiver–transmitter (UART) for a
conventional serial port.
•Black pins: Connection to ground.
Orange pins: Communication through the Serial Peripheral Interface (SPI) protocol in order to
communicate with peripherals with this protocol.
•White pins: Reserved pins.
All GPIO pins: Apart from their particular function, all GPIO pins have general-purpose
Each door sensor had two wires and, due to their speciﬁcation, one of these wires needed to
be connected to ground and the other one needed to be connected to some input. Pins GPIO 18,
GPIO 12, and GPIO 25 were chosen as input pins; pins GPIO 14, GPIO 20, and GPIO 30 were selected
as ground pins. These choices were mainly arbitrary, and we only considered that chosen pins
with inputs/outputs had a ground pin next to them. Because wires of door sensors could not be
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directly connected to the Raspberry Pi, we connected these through a protoboard by means of jumper
wires. As one can observe in the schematic design, all ground pins were connected through jumper
wires to the positive power line of the protoboard (representing this connections with black lines).
Then, in order to ensure the connection continuity until the door sensors, a jumper wire was placed
from the power line to the central segment of the protoboard for each sensor. In the schematic design,
these connections are represented with black lines that go from the “+” column to the “A” column.
Finally, door sensors were connected to the circuit through column “E”. It was necessary to use one or
several jumper wires in this last step, depending on the distance from the protoboard to each door
sensor. Input GPIO pins were directly connected to the protoboard through the central segment,
then door sensors were connected with them through the same central segment (represented with
Figure 3. Schematic design of the smart cupboard. GPIO: general-purpose input/output.
3.2. Algorithm for Measuring Memory Based on the Door Sensor Signals
The algorithm was designed to determine when a user ﬁnds an item, and when the user searches
for an item without success. One research question was: how do we know that the user had success in
searching an item inside the SC? In order to answer this question, we had to explain all possible cases
in which a user can ﬁnd an object. The ﬁrst case is that the user ﬁnds a certain item in the ﬁrst attempt.
The second case is that the user ﬁnds a certain item in a certain number (denoted as
) of attempts,
assuming N≥2. The last case is the one in which the user did not ﬁnd the item.
Figure 4depicts the ﬁrst case. One of the rules that allows understanding this topic is that the
user usually has success in ﬁnding objects except in some cases. Nonetheless, we do not know how
many times the user has attempted to ﬁnd a certain object. In this ﬁrst case, the user is going to ﬁnd
a certain object at the ﬁrst attempt. With the open door of the SC, the user looks and searches for
the desired object. Once the user grabs the object, they close the door and at this moment, our script
takes note of one fail with the search. It seems illogical that our system would increase the fail counter,
but since we do not have another mechanism to determine exactly whether the user has grabbed the
desired item or to know whether the user has found the desired item (assuming this reduced set of
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low-cost sensors), our system marks one fail. However, we kept in mind that if the user does not open
another door or the same door in a reasonable amount of time, the most probable reason is that the
user found the item. We established 10 s as reasonable amount of time, and hence once the door of
the SC was closed and 10 s passed, we estimated with high probability that the user had the desired
item. When the door is closed, besides increasing the fail counter, the “closeDoor” signal is triggered,
which starts a time counter that allows us to know whether the user opens a SC door in a reasonable
time or not. Since we are explaining the case in which an object is found at the ﬁrst attempt, this time
the counter is not interrupted. In following cases we will explain what happens when this signal is
interrupted. So, when the system notices that after 10 s the user has not opened any door, it removes a
fail from the fail counter and increases a unit on the success counter.
Figure 4. Python script—First case.
The second case is more complex than the ﬁrst one. We will explain the same steps as above,
but with more signals and certain features. In the second case, the user ﬁnds a certain item after
attempts. The beginning is the same as the previous case, as one can see in Figure 5, which depicts
the diagram of the second case. The user opens the door, and before they search or ﬁnd anything,
the “openDoor” signal is triggered. The aim of this signal is to determine whether another door has
been opened before, and in the positive case our system cancels the count of 10 s in order to avoid
reducing the fail counter and to prevent increasing the success counter. In this way, our system counts
all fails during the process of searching for an item. Focusing again on this second case, we take for
granted that the “openDoor” signal has not been triggered, since it is the ﬁrst time that the user opened
the door. Nonetheless, the action of opening the door is the trigger of the “openDoor” signal. The same
signals as in the previous case are also triggered, but we have omitted them in this description in order
to ease comprehension.
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Figure 5. Python script—Second case.
When the “openDoor” signal is launched, the user starts searching for the item, then they close the
door. The fail counter increases and the “closeDoor” signal is triggered, and until this point, all steps
are the same as in the ﬁrst case. Now, the user knows whether they have the correct item. If so, it is
the ﬁrst case; if not, the “openDoor” signal must be interrupted. Empirical tests made by ourselves
and other users allowed us estimate that 10 s was enough time for someone to be able to open another
door of the SC; if not, again, it was assumed that the user found the correct item. Hence, in the second
case when the user thinks about what their next door choice will to be and opens it, the “openDoor”
signal is interrupted and the cycle starts again until the user opens the correct door. Until this moment
the user has always had success in searching for their object, regardless of whether it was found in
their ﬁrst attempt or in attempt
. However, in the following case the user does not have any success,
since according to our point of view the user does not reach to ﬁnd the required object. We kept the
third case in mind in order to manage two issues: the ﬁrst is that the user searches for an object but
forgets what they were searching for. This situation gives us information about the health of the user’s
memory. The second is that in this way we can avoid that someone cheated during the experimentation
phase (i.e., if we did not control the opening time of a door and a certain object was not inside the SC,
the user would have unlimited time to think about what other compartment the object may be in).
In the experimentation phase, this case did not appear at any moment, but it is important to check for
this issue because it makes the measurement of memory loss more accurate.
Figure 6depicts the third case. The beginning is the same as aforementioned cases, only with the
difference that another signal is triggered when the door is opened by the user; this signal is called
“countTimeDoor” (we have not mentioned the signal before in order to avoid over-long explanation,
but it was also present in the previous cases). The signal’s aim is to start to count the time that an SC
door is held open. This period of time matches with period of time the user is searching an object
inside of the SC. The assigned threshold for this signal was 10 s, that is, the user has 10 s to ﬁnd the
item, and if this time is surpassed the system increases the fail counter. We determined the threshold
of the “countTimeDoor” signal in the same way as we determined the 10 s in order to know whether
user was successful (i.e., through experiments made by ourselves and other users), until we were able
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to determine a proper threshold. We assume that the user overcame the signal threshold, so the fail
counter increases. Furthermore, the “openDoor” signal is canceled, since if it were not so, when the
user closed the door again, our system would increase the fail counter once again. Finally, it is worth
mentioning that if the user closes the door before 10 s, the “countTimeDoor” signal is canceled in order
to avoid increasing the fail counter twice.
Figure 6. Python script—Third case.
The algorithm was written in Python, and for the sake of reproducibility, we describe how the
implementation of this algorithm handled the pins. In order to manage pins inside the script, we used
the RPi.GPIO library. There were two options to enumerate the pins. The ﬁrst was GPIO mode,
in which each pin had the same number as their physical position, hence pins were enumerated
from 1 to 40. The second option was BCM (Broadcom mode), in which pins were numerated in
order to match with Broadcom chip, which was the CPU (central processing unit) of the Raspberry.
We used BCM for the implementation of the presented algorithm. The algorithm implementation
also needed to set up some pins as input pins, and this was achieved with the predeﬁned function
GPIO.setup. Finally, the GPIO.input function provided the current state of each door sensor, true when
the two pieces of a door sensor were separated (i.e., the door was open), and false otherwise. Figure 7
presents an excerpt of the Python implementation used in the SC, showing the aforementioned
implementation details about pins. Door sensor states were used as previously described when
presenting the algorithm.
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Figure 7. Implementation details about pins in the Python script of the smart cupboard.
We recruited 23 people for participation in this user study. Participants were 36.17 years old
on average (SD = 12.80) in a range from 18 to 60 years old, and had studied for 14.86 years on
average (SD = 2.88). Among the participants, only 8.69% were studying or work in computer science.
Males comprised 39.13% of participants. Participation in this experiment was voluntary and unpaid.
In order to evaluate whether the SC is able to measure memory, several tests were conducted.
In the ﬁrst test, a user was asked to observe the inside of the SC. The user had to memorize certain items
inside it in the acquisition phase. Then, the user was asked to ﬁnd certain items in the retrieval phase.
A test of face–name pairs [
] was used as a control method, since this kind of test has been proven
to measure memory. The test consists of showing a list of face–name pairs, so the user memorized
them in the acquisition phase, for later selection of the name associated with each face in the retrieval
phase. The main goal was to determine whether both results were correlated, besides performing other
analyses concerning the relation of the results with the participant features.
The test was conducted in a real kitchen so that participants were familiar with the scenario.
The Raspberry was set up inside a kitchen cupboard as shown in Figure 8. The size of this cupboard
was 130 cm width
71 cm height
29.5 cm depth, and it was 150 cm above the ground. In spite of
having ﬁve compartments, we only used the bottom three in order to avoid having compartments of
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Figure 8. Smart cupboard.
To assess the memory of participants with the SC, we selected 30 different items. All these items
were typical objects commonly found inside cupboards, and these objects were: a cup, a sweet corn can,
a chili can, an egg, a box of matches, an evaporated milk carton, a soda, a bag of breadcrumbs, a beer can,
a jar of chili peppers, a potato, a jar of lentils, a can of olives, a jar of mayonnaise, a carton of chocolate
milkshake, a can of grapes, a jar of soup cubes, a can of peaches in syrup, a can of condensed milk, salt,
a box of baking powder, a can of green peas, a milk bread, a jar of jam, a teaspoon, a jar of sausages,
honey, a can of tuna, a bag of tea, and a jar of oregano. In this experiment, each participant followed
the same process. The experimenter introduced the steps brieﬂy to each user. In the acquisition phase,
the experimenter asked each user to memorize all the items of each compartment, and they had 30 s
per compartment—1 min and 30 s in total.
In the retrieval phase, the experimenter told the participant that he would ask them to ﬁnd objects
selected in a random order from the ones inside the cupboard and previously memorized by them.
Thus, the participant had to open the compartment where they thought each required object was.
Furthermore, the experimenter indicated that only one door could be open at a time (i.e., before the
participant opened another door, they had to close the current door). Once the participant had found
the required object, grabbed it from the SC, and closed the door, the experimenter asked questions
about the item. The questions were varied and related to cooking or eating. For instance, what recipes
or dishes would you cook with this object? Or, what time of day do you usually eat this product?
Or, do you think this product is healthy and why or why not? And so on. The reasons for these
questions were to delay the retrieval phase and to increase the difﬁculty of the test. When users
opened the door in order to ﬁnd an object, they could re-memorize where each object was (reinforcing
the initial learning), since it was unavoidable to let them see the contents again. Thus, the goals
of these distracting questions were to compensate for this aspect and to be more similar to realistic
This process was repeated with ten different objects for each user. Due to the size of SC and
the amount of items, two rounds were required. In each round, each participant had an acquisition
phase in order to memorize the content of compartments concerning 15 objects, and had a retrieval
phase to sequentially ﬁnd 10 objects. When the ﬁrst round was ﬁnished, the experimenter asked the
user to leave the kitchen. While the participant was outside the kitchen, the experimenter set up the
second round, and then invited the participant to come into the kitchen again. Hence, users performed
20 memory retrievals about 20 different objects. In this way, this memory test had an accuracy error
margin of 5%, which is considered as appropriate in memory tests [
]. We decided that all participants
had the same conditions; hence, before starting this procedure, a list of items was selected for use by
Sensors 2019,19, 2552 13 of 21
The list had 15 items for the ﬁrst round and 15 items for the second one. The order of objects
was selected randomly, because we wanted to avoid the case where objects were organized by size or
semantic categories, in order to avoid bias in the memory measurement due to different memorization
techniques. Table 2indicates the order of objects in the SC, distributed in compartments per round.
Furthermore, another requirement of the experimentation phase was that objects could not be behind
others (i.e., all objects had to be visible from the participant’s position). The experimenter was always
with the participants, except when they were outside the kitchen. The experimenter made sure that
the participants properly followed the experimentation protocol. For instance, the experimenter was
advised to take note if any participant closed the door twice because it had not been closed with
enough strength the ﬁrst time. In this case, the system would register an additional fail, so then we
could revise the logs to know what had happened.
Table 2. Order of objects in the experimentation with the smart cupboard.
Object Compartment Round Object Compartment Round
Sweet Corn Soup cubes
Chili Peaches in syrup
Egg Condensed milk
Box of Matches Salt
Soda Green peas
Breadcrumb Milk bread
Chili peppers Teaspoon
Chocolate milkshake Oregano
The next step for participants was to take a control test based on face–name pairs in order to
statistically compare these results with the SC results and to determine whether our SC is able to
measure memory. This test was similar to the common memory tests about face–name pairs in the
], and we used a short-time version that did not require several days for acquisition
and retrieval phases. In this way, each participant could do all the experimentation in the same
day, facilitating the task of recruiting unpaid volunteer participants. In this experiment, the test of
face–name pairs consisted of showing a series of 30 face–name pairs to the participant such that they
memorized these associations in the acquisition phase. Each face–name pair was presented to the
user for 6 s, and consequently the whole acquisition phase took 3 min. In the retrieval phase, each
participant had to respond to 30 questions. Each question was composed of a face image and four
name options, and the participant had to ﬁll a form provided by the experimenter with the answers to
these questions. Figure 9shows an example of three questions. The face images have been blurred
in this article to protect the privacy of the models. The retrieval phase had no time limit, but the
experimenter instructed the participants to reply to the questions as accurately and quickly as possible,
and the reaction time was measured.
Furthermore, the participants engaged in a self-reported memory test. We performed this test
in order to compare the SC results with other memory-related variables. Since the self-assessment of
memory has proved to be relevant for evaluating memory despite other inﬂuencing factors such as
], we included this brief self-reported memory test as another control test. We selected
a short self-reported test available from the Psychology Today website (http://psychologytoday.
tests.psychtests.com/bin/transfer?req=MTF8MzM2MHw2NzI5MDI0fDB8MQ==) for its brevity and
its simplicity. In this test, participants replied to seven questions with a ﬁve-point Likert scale.
The questions of this test were: (1) Do you have difﬁculty in remembering people’s names or phone
Sensors 2019,19, 2552 14 of 21
numbers? (2) How often do you ﬁnd yourself trying to remember the location of everyday items (e.g.,
your keys, wallet, glasses, etc.)? (3) How often do you have to replace passwords (numerical or verbal)
because you’ve forgotten the original one? (4) How often do you ﬁnd yourself asking questions like,
“What was I about to do next?” (5) How often do you end up arranging overlapped plans because you
forgot you had made previous plans with someone else? (6) How often do you have to ask someone to
repeat instructions or a story because you can’t remember what was said the ﬁrst time? (7) How often
do you have difﬁculty in remembering where you parked your car? The last question was only replied
by participants who had a driving license.
The experimenter also asked participants to reply a brief demographic test to extract the
information presented in Section 4.1 when introducing the sample of participants. Once we ﬁnished
all the experimentation with all the participants, we analyzed the obtained data as described in the
Figure 9. Test of face–name pairs.
We performed several analyses considering the memory measurements in the different methods,
the reaction time, and the age of participants. Firstly, we compared the memory measurement
results between the SC test and the face–name test, reporting the accuracies of participants in the
In order to double-check that the sensors system of the SC was working properly, the experimenter
took notes about the fails and successes of participants during the experimentation phase, and then
the notes were contrasted against the system log. The notes and SC logs and results matched perfectly.
The accuracy percentage of each participant was calculated as shown in Equation
as a measurement
of their memory:
where ais the accuracy percentage, sis the number of successes, and fis the number of fails.
The accuracy of each participant in the retrieval of face–name pairs was calculated in a similar
way. The experimenter checked the ﬁnal test results, and the percentage was calculated as shown in
is the accuracy percentage,
is the number of successes, and
is the total number of questions.
Figure 10 compares the memory accuracies of the SC and face–name pairs, and one can observe
that both measurements methods followed similar trends and shapes. Thus, there may be a correlation
between these measurement methods. In order to statistically and reliably corroborate this correlation,
we conducted a Pearson’s correlation test between the results of the two memory measurement
methods. Table 3shows the results of this correlation test. According to the Pearson correlation
], both memory measurement methods had a signiﬁcant positive correlation. This positive
correlation was conﬁrmed with the Kendall’s tau coefﬁcient of 0.470 with a
-value of 0.003 and
Spearman’s rho coefﬁcient of 0.620 with a
-value of 0.002. The correlation between the SC test and the
Sensors 2019,19, 2552 15 of 21
test of face–name pairs proves that our SC sensors system is able to measure memory, since the control
memory measurement method has already been scientiﬁcally validated.
Comparison of memory measurements between the smart cupboard (SC) and the face–name
Table 3. Correlation between the accuracy of the SC and the accuracy of the face–name test.
Pearson Correlation 1 0.597 **
Accuracy Smart Cupboard Sig. (2-tailed) 0.003
Pearson Correlation 0.597 ** 1
Faces-Name Test Sig. (2-tailed) 0.003
**. Correlation is signiﬁcant at the 0.01 level (2-tailed).
Moreover, we analyzed the reaction time of participants in the SC and face–name pairs tests.
Figure 11 depicts the reaction time of each participant in both tests. The blue line represents the SC test
and the orange line represents the test of face–name pairs. In order to calculate the reaction time of the
SC test, the experimenter took note of the time spent by a participant to remember each item inside the
SC. Then, this was compared with the time in the system log in order to check that all times were correct.
Thus, 20 reaction time results were obtained for each participant. Finally, the reaction time of each
participant was calculated as the mean of all obtained times. In the face–name test, the experimenter
also measured the time spent by a participant in order to perform the test. The reaction time was
obtained from the division of the total time by the total number of questions by each participant.
According to the trend and direction of both lines in the graph, it is not easy to appreciate the similarity
in general. Nonetheless, a certain similar behavior is appreciated between participant 7 and participant
15. A similar correlation can be appreciated between these two tests, since both lines are almost parallel.
Because this observational analysis is not sufﬁcient to determine whether there was any signiﬁcant
relation between tests in reaction times, we performed another Pearson’s correlation test to statistically
determine whether there was a statistically signiﬁcant correlation. Table 4depicts the result of the
correlation test. It shows that both variables were not signiﬁcantly correlated. Neither Kendall’s tau
coefﬁcient nor Spearman’s rho coefﬁcient detected any signiﬁcant correlation with respective
of 0.597 and 0.428. Thus, in these experiments, the reaction time of our SC test did not correlate with
the reaction time of the control test of face–name pairs.
Sensors 2019,19, 2552 16 of 21
Figure 11. Comparison between the SC reaction time and the reaction time of the face–name test.
Table 4. Correlation between the SC reaction time and the reaction time of the face–name test.
Pearson Correlation 1 0.341
Reaction Time Smart Cupboard Sig. (2-tailed) 0.111
Pearson Correlation 0.341 1
Reaction Time Face-Name Test Sig. (2-tailed) 0.111
We also conducted an analysis of the relation between participant age and SC reaction times.
Figure 12 represents each participant considering these two aspects. It is worth highlighting that
we asked people to participate in these experiments, considering their age, to have both young and
aged people. In particular, there were six young participants in the 18–25 years old range and six
aged participants in the 55–60 years old range. In order to determine whether there was a statistically
signiﬁcant correlation, we performed three correlation tests between SC results and age. Table 5shows
the results of the Pearson’s correlation test. One can observe that these variables were not correlated
according to this test. In addition, neither Kendall’s tau coefﬁcient nor Spearman’s rho coefﬁcient
detected any signiﬁcant correlation, with respective
-values of 0.265 and 0.300. Thus, SC results and
age were not statistically signiﬁcantly correlated in these experiments.
Figure 12. Comparison between the reaction time in the smart cupboard test and participant age.
Sensors 2019,19, 2552 17 of 21
Table 5. Correlation between the reaction time and participant age in the smart cupboard test.
Age Reaction Time
Pearson Correlation 1 0.306
Age Sig. (2-tailed) 0.156
Pearson Correlation 0.306 1
Reaction Time Smart Cupboard Sig. (2-tailed) 0.156
We also performed an analysis comparing the accuracy of participants in the SC test and the
results of the self-reported memory test. Each possible answer of the self-reported memory test among
the options “almost always”, “often”, “sometimes”, “rarely”, and “almost never” were respectively
assigned the values 0, 1, 2, 3, and 4. The results of this test were standardized as a percentage calculated
with Equation (3):
Vmax , (3)
is the result of the self-reported test,
is the value of each answered question,
is the total
number of questions, and Vmax is the maximum value that a response can have (i.e., 4 in this case).
Figure 13 shows the accuracy of the SC test and this self-reported test. There were similarities
between both tests in some cases, as one can observe in the intervals between participants 1 to
4, participants 9 to 11, and participants 15 to 17. To determine the statistical signiﬁcance of this
relation, we conducted a Pearson’s correlation test, and Table 6presents the results. The test indicated
that the memory results between the SC test and the self-reported one were signiﬁcantly correlated.
This correlation was conﬁrmed with the Kendall’s tau coefﬁcient of 0.383 with a
-value of 0.014 and
Spearman’s rho coefﬁcient of 0.451 with a
-value of 0.031. The self-reported test is a subjective test,
and personality may cause bias in the results, since this test actually measures self-perceived memory
rather than actual memory (calculated as the accuracy retrieving information previously acquired).
According to these experiments, the SC results were correlated with self-perceived memory, despite
the possible bias because of personality.
Figure 13. Comparison between the accuracy of SC and that of self-reported tests.
Sensors 2019,19, 2552 18 of 21
Table 6. Correlation between the accuracy of SC and that of self-reported tests.
Smart Cupboard Accuracy Self-Reported Test
Pearson Correlation 1 0.443 *
Smart Cupboard Sig. (2-tailed) 0.034
Pearson Correlation 0.443 * 1
Accuracy Self-Reported Test Sig. (2-tailed) 0.034
*. Correlation is signiﬁcant at the 0.05 level (2-tailed).
6. Discussion and Conclusions
The article proposed a new mechanism of measuring memory with the SC as a novel IoT sensors
system. We presented the design of the SC as a cupboard with three sensorized doors with magnetic
door sensors connected to Internet via a Raspberry Pi 3B board with the corresponding software for
evaluating user memory.
The main goal was to have a device able to assess the memory in a familiar environment without
requiring additional effort from the user. Thus, we presented a solution in which the memory
measurement can be continuous and based on normal routine. The results based on 23 participants
in a wide age range (18 to 60 years old) showed that the accuracy of participants in ﬁnding objects
in the SC in a controlled environment was statistically signiﬁcantly correlated with the accuracy of
participants in retrieving face–name associations in a validated type of memory test. The accuracy of
the SC test was also statistically signiﬁcantly correlated with a self-reported memory test.
The current work attempted to ﬁnd a solution that was low-cost as possible, in order to propose a
step towards a solution that can get to the market with a proﬁtable margin, so that enterprises may
be interested and our solution can make a real impact on society. Note that the most fundamental
components of this solution were the magnetic door sensors, and in particular we used a door
sensor model that only cost $2.46. The Raspberry Pi 3B board could be easily replaced by any other
low-cost/green processing board in the market by using the same software and adapting the input
pins. Thus, a very cheap solution could potentially be developed for converting a cupboard into a
SC, so the user could install the sensor systems of their cupboard without needing to replace their
In the early detection of diseases, it can be difﬁcult to sell products to healthy people, even if
the product is cheap. We argue that as in the case of many other successful smart devices in the
market (e.g., smartphones, smartbands, and smart TVs), SCs could have multi-purpose functionalities
for successfully getting to the market. In this line, the SC could also be useful for detecting eating
patterns by classifying different kinds of food in different compartments. Eating patterns can be useful
for controlling dietary habits to reduce obesity, which is an issue for many people in countries like
the US [
]. Eating patterns could also be useful for tracking emotions by considering their known
The experiments showed that the reaction time measured by the SC test did not correlate with the
reaction of the control test about face–name pairs. However, these results are not conclusive, since
the number of participants (n= 23) was not sufﬁcient to detect medium effect sizes according to the
analysis based on statistical power performed by the G*Power 3 tool [
]. In addition, not all memory
tests need to have a correlation between reaction time and memory. In fact, strictly a memory test needs
to provide some measure that correlates with memory, which could be either accuracy or reaction time,
but not necessarily both. Thus, the proposed SC test is a reliable memory test according to the common
standards of memory tests .
In addition, the accuracy of the SC memory test correlated with self-perceived memory,
even though the literature supports that self-perceived memory is inﬂuenced by factors such as
personality , which could lead to differences between self-perceived memory and actual memory.
Sensors 2019,19, 2552 19 of 21
One limitation of the current version of the SC is that it is based on the assumption that there is
only one person using the SC to reliably measure their memory. We plan to overcome this limitation by
including an identiﬁcation mechanism, which could either be (1) facial identiﬁcation with a low-cost
camera following our previous work in facial authentication [
] or (2) radio-frequency identiﬁcation,
which would require the user to carry a card for the identiﬁcation. We will select one of these options
considering economic aspects, technological reliability, and user experience. In this manner, the SC
will determine who is using it and perform different measurements for the different family members.
In general, the inclusion of identiﬁcation will allow engineers to develop SC applications for providing
customized services to the user.
In the future, we plan to conduct a study with Alzheimer’s patients over a 10-month period to
detect memory losses during the evolution of this disease, by measuring the memory of the same
persons through the study with the proposed SC-based approach. If possible, we will also enroll
people considered to probably start having Alzheimer’s disease soon, known by the analysis of genetic
information in descendants of people with Alzheimer’s. As a control group, we also plan to track the
memory evolution of a group of healthy people, which may include some of the participants of the
presented study. In this way, we plan to detect improvement opportunities and further assess whether
it is possible to track memory losses and to detect Alzheimer’s at an early stage.
Another future work is the development of an app whose main aim will be to explain to users how
to turn a normal cupboard into an SC using gamiﬁcation to overcome the barrier of a possible difﬁcult
installation. Finally, our efforts will focus on improvement of energy efﬁciency, since cupboards are
not used very frequently. This could be achieved by lowering the checking frequency of sensors
when users do not usually use them, based on an initial training phase, following a similar approach
to our previous one in green communications with smartbands [
]. Another option that involves
the power system is to use some energy-harvesting techniques to overcome the limitation of the
long-term use of the SC powered by batteries. The aim of harvesting techniques is to accumulate
energy from several sources that capture energy from the environment. Once the energy is accumulated,
it can be used in the SC to track user memory. Several examples of energy harvesting can be
found in the literature [
], but techniques that involve components such as micro-photovoltaic
cells, micro-thermoelectric generators [
], or indoor ambient light [
] may be the most suitable for
SCs. Furthermore, we also plan to develop an app for remotely consulting memory measurement
results from any mobile device, and to provide notiﬁcations if a family member is starting to have
signiﬁcant memory losses.
Conceptualization, F.G.-L., I.G.-M. and R.A.; Data curation, F.G.-L. and I.G.-M.; Formal
analysis, F.G.-L. and I.G.-M.; Funding acquisition, I.G.-M. and R.L.; Investigation, F.G.-L., I.G.-M., R.A. and
R.L.; Methodology, F.G.-L., I.G.-M., R.A. and R.L.; Project administration, I.G.-M.; Software, F.G.-L.; Supervision,
I.G.-M., R.A. and R.L.
This work was mainly devised during the research stay of the second author in the Massachusetts
General Hospital and Harvard University, funded by “Dpto. de Innovación, Investigación y Universidad del
Gobierno de Aragón” through the program “FEDER Aragón 2014-2020 Construyendo Europa desde Aragón”
(Ref: T49_17R). This work has also been ﬁnanced by the Aragonese Government and the UE through the
FEDER 2014–2020 “Construyendo Europa desde Aragón” action (Group T25_17D). We also acknowledge the
support of the projects “Collaborative Ambient Assisted living Design” (TIN2014-57028-R), “Diseño colaborativo
para la promoción del bienestar en ciudades inteligentes inclusivas” (TIN2017-88327-R), and “Red Temática
de Investigación en Ciudades Inteligentes” (TIN2016-81766-REDT) funded by the Spanish council of Science,
Innovation and Universities from the Spanish Government.
Conﬂicts of Interest: The authors declare no conﬂict of interest.
Sensors 2019,19, 2552 20 of 21
The following abbreviations are used in this manuscript:
GPIO General-Purposes Input/Output
I2C Inter-Integrated Circuit
IoT Internet of Things
SD Standard Deviation
SPI Serial Peripheral Interface
SC Smart Cupboard
UART Universal Asynchronous Receiver-Transmitter
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