EMIT: A Reflection of Your Time

Project Video

Idea/Vision

Although phones have become ubiquitous, and they are marginally more effective in keeping time, we still wear stylish watches and keep analog timepieces in our office to glance at every once in awhile.  Taking this into account, we have designed and produced EMIT.  EMIT is a clock that shows you your perception of time based on your emotional and cognitive state. We show the rate at which time flows for an individual by varying the speed of an extra clock hand through strobe lights. We also show the individual’s current perceived emotion by using different hues of RGB LED lights.
Time perception is complex as it is dependent on the different ways in which our brain experiences perceptions (Van Wassenhove 2008) and reconstructs those experiences in different parts of the brain (Rao, Mayer, Harrington 2001). Our goal in this project is not to find a holistic way of measuring one’s time perception, but to put together the different pieces that are known to influence time perception and to represent people’s distorted time perception to them in a meaningful and informative way. The hope is that increased awareness of time perception would trigger behavior change, e.g. take a break to reduce anxiety and slow down time perception.

Motivation

Humans are obsessed with the concept of time. We are always running after time, and there never seems to be enough of it to do everything we want. Our daily lives are scheduled metrically, governed by this unseen force that we always keep close to us.  We define this unseen force, time, as a duration/interval of one type or another. It is interesting to see that although our clocks tick at a fixed rate, our perception of time is not constant (Fraisse 1984; Joubert 1984; Gibbon 1986; Zakay 1990). Clocks show us objective time, but our subjective or mind time is what we interpret to be the duration of an interval between two events. Our subjective time is intimately tied to our emotional and cognitive (Droit-Volet, Meck  2007; Droit-Volet, Gil 2016) states.  For example, if we are happy or busy, we perceive time as going fast.  The opposite is also true if we are sad or free, time will seem to go by slow.  We wanted to build a device that could display people’s perception of time.  Through this representation, we hope to make people more conscious of their emotional and cognitive state.  We also hope that this device can serve as an indicator for other people in order to give a quick insight into a user’s state.

Background Research 

There is a lot of literature on the relationship between our emotional/cognitive state and our time perception. In the 80s researchers demonstrated that time seems to go by faster when you are expecting something positive to happen rather than when you are expecting something negative to happen (Edmonds, Cahoon, Bridges 1981).  This was one of the first clues that emotions were linked to the perception of time.  Later on in the early 2000s S. Droit-Volet, et al. (2007) went on to test this in more detail by evaluating the perceived duration of time intervals when one is staring at a smiling rather than a frowning person.  He found that positive emotions (smiling) make the intervals go faster and vice versa.  Around this time researchers also found that time appears to move faster during positive experiences and it slows down during negative emotional states, e.g. when we are sad, depressed (Gil, Droit-Volet 2009), afraid (Stetson, Fiesta, Eagleman 2007; Buetti, Lleras 2012), or lonely (Twenge, Catanese, Baumeister 2009).  These results show a clear correlation between emotions and the perception of time.   

 

Time perception is also affected by how engaged or attentive we are (Burnside 1971; Curton, Lordahl 1974; Tse, et al. 2004).  Researchers found that people who keep track of time perceive it as going slower rather than those who do not, they also found that people give shorter estimates of time when they are under a load rather than when they are not (Brown 1985).  These results also show that there is a strong correlation between the perceived and mind time and the cognitive state of the user.

 

Time perception is also tied to psychological conditions such as ADHD (Levy, Swanson 2001), schizophrenia (Franck, Pichon, Haggard 2005), impulsivity and borderline personality disorder (Berlin, Edmund 2004), and anxiety disorders (Bar-Haim, et al. 2010).  Time perception also affects our decision-making as impulsive decisions are highly correlated with an overestimation of time, i.e. a speedy perception of time (Wittmann 2008).    

 

Time perception is also a key consideration in areas of consciousness. The specious present is the time duration wherein one’s perceptions are considered to be in the present (James 1893).  Researchers have also found that mindfulness meditation lead to slower perception of time (Kramer, et al. 2013).   Chronesthesia (Tulving 2002), or the ability to go back and forth in time within your mind,  is also interpreted to be the navigation or manipulation of the subjective perception of time.
Because of all the research done on the field, we are able see that there are various factors that affect the perception of time amongst human beings.  Put together, there are 2 large areas that surface: emotion and cognition.  There is also a promising application area with regards to the modification of the perception of time to take more rational decisions.  We intend to take exploit these topics in our design of EMIT to try and conscientize users of their current perception of time and what it could be due to.  

Using the aforementioned relationships between emotional/cognitive states and time perception, we were able to create a mapping between our narrow set of emotional/cognitive state and time perception.

Related Work

In the following section we present related work regarding clocks that present new ways of visualizing time. To the best of our knowledge, there have been no other implementations of a an emotion-aware timepiece that includes the dimension of time perception embedded in a clock hand. Therefore, we focus on relevant projects that focus on representing or adjusting our perception of time.

In 1999, Mark Weiser wrote “The Computer for the 21st Century” and proposed devices that would “weave themselves in the fabric of everyday life until they are indistinguishable from it”.  There are several examples of such ‘calm’/ubiquitous computing devices. For example Breakaway – a desk sculpture that nudges users to take a break when they have been sitting too long (Jafarinaimi, et al. 2005), or PlantDisplay, which is an ambient display on plants (Kuribayashi, Wakita 2006). EMIT is a context- and emotion-aware ‘calm’/ubiquitous computing device that has an ambient display of user’s emotional and cognitive state. Nimio (Brewer, Williams, Dourish 2005) is an example of a tangible device that represents user activity using different light hues, and Tea Place (Lee, et al. 2007) is a an example which uses light to alter user’s moods.

The Durr watch is a device which tries to present the objective perception of time using a method different than clock hands: vibration.  The Durr watch vibrates every five minutes of objective time.  (Durr: http://skrekkogle.com/projects/durr/).   Durr sought to explore how a user’s perception of time varies when the only queue that they have is a consistent vibration.  However, the Durr watch was a prototype and the idea was put on hold.  Later on, a Media Lab Alumni called Che-Wei Wang made a vibration watch similar to Durr but with customizable intervals.  He explored how this would affect users.

Slow Dance is a Kickstarter project in which Jeff Lieberman tries to alter the perception of time using strobe lights.  At 80Hz, a strobing light is perceived by human eyes as constant, however, when a moving object is placed within the range of the light, the object will appear to move slower as if it were in slow motion.  We decided to exploit this behavior in our project to make objects seem slower or faster than they appear to be moving at.  (Slow Dance: https://www.kickstarter.com/projects/xercyn/slow-dance-a-frame-that-slows-down-time)


Hidden time is a clock which tries to conscientize a person of the passing hours.  The most recent hour is the clearest, and the oldest one is the least visible.  The effect that it creates is that a person should focus on the most recent hours rather than the oldest ones.  (https://www.indiegogo.com/projects/hidden-time-watch-design-fashion#/)  Similar to this is the Circadian clock, which presents a simpler interface to the regular clock.  As night time comes, the watch face becomes black and vice versa in daytime it becomes light (Circadian clock: http://abduzeedo.com/circadian-clock)

Design

 

In this section, we present the design process of the EMIT system. There were 3 main guidelines for our design:

  1. Normal clock: It would ‘look’ as close to a normal clock as possible so that people may be aware of their subjective time as they look at the clock’s objective time. Most people are familiar with the concept of objective time on clocks, and clocks are a common object in people’s homes/offices. This way, we are augmenting an already acceptable and used product.
  2. Extra hand and strobe light: We would add an extra hand to the clock and the speed of this extra hand would represent our subjective time. As time slows down for a person, the extra hand would go in slow motion, and vice versa. We decided to use the strobe light effect here as it allows us to change the perception of an object moving at a constant rate. Using strobe lights, we could show the hand completely frozen or moving in slow motion (forward and backward) or quickly jumping between positions (again, forward and backward).
  3. Colors: People can perceive time as slowed down for different reasons, e.g. when they are afraid or sad or relaxed, etc. Similarly, time may speed up when we are happy or focused. To disambiguate the different states during which time slows down or speeds up, we decided to use colors to guide the users. For example, when a user is sad, the extra hand would slow down, but the clock would be purple colored. Whereas when the user is afraid, the extra hand would still slow down, but the clock would be blue colored.


The initial concept design accounted for the aforementioned guidelines. The EMIT timepiece would consist of a set of mechanical hands that present objective time in the innermost layer. When the clock is not enabled by a user in the near vicinity, the time perception and emotional cues are inactive. When a user desires to broadcast his/her emotional and time perceptual markers, he/she can use a smartphone to connect to the device and initiate a session. It is important to note that emotional and time perceptual displays are independent. Since the clock is designed to be a piece that might be on public display, the user can select which components he/she is comfortable sharing with the world.

Color Theory and Emotions

People’s emotional and cognitive states are intertwined with their time perception. For our clock, we decided to recognize five of Ekman’s six basic emotions (Ekman 2016) – Fear, Anger, Sadness, Joy, and Disgust. Ekman’s six emotions are commonly understood in the literature for affective computing, but the five emotions we chose out of the six basic emotions were depicted in the Disney movie Inside Out and are more likely to be understood by people outside academia. Our color theme is based on the colors associated with these emotions in Ekman’s Atlas of Emotions website (http://atlasofemotions.org/) as well as the colors used in Inside Out.

Inside Out Emotion Representations

Ekman’s Color Atlas

Strobe Lights

An important design decision that impacted the implementation of EMIT was whether to use mechanical or strobe light control for the time perception clock hand. Although mechanical control of a servo or stepper motor would allow use to implement a traditional clock hand effect of which we could adjust speed and direction, we include some advantages of choosing strobe lights over a more traditional, mechanical approach:

  1. Ability to Disappear: A mechanical hand would always be there. Even if the hand was disabled, it would be constantly visible to the user. In our design, we strived to create a device for which the user could opt in or out for different markers. For instance, a user might not want to display time perception at some point during their day, in which case a mechanical display of time perception is unnecessary. With the strobe lights, the mechanical time perception hand is spinning so fast that it is practically invisible to the naked eye. Whenever the user wants to opt out of the time perception display, the strobe lights can be turned off, making the time perception hand invisible.
  2. Multiple Hand Illusion: A mechanical hand would only allow use to display increases in speed and direction through the usage of the EMIT system. In the case of a strobe display, different frequencies can be used to achieve effects that would normally be impossible for a traditional mechanical hand. For instance, strobing at multiples of the rotating frequency of the motor can make it seems like there are multiple hands. Moreover, other effects can be implemented to create more complex interactions.
  3. Multiple User Support: A mechanical hand would only support the display for the perception of a single user. In order to show the perception of more users, multiple hands would need to be included in the system to show differing perceptions of time.  Different sets of strobe lights can be programmed to strobe at different frequencies to create the illusion of multiple hands moving at different speeds, which would allow multiple users to concurrently interact with the system.
  4. Subliminal Interface: Studies (Chebat, et al. 1993) have shown that visual cues can have an impact on the perception of time. Hanus, Kang, Ricker (N.d.), showed that using strobe lighting at different frequencies can slow down our speed up the time perception of a person. Although our project seeks to visualize and allow for a reflective experience, in the future we would like our platform to help align a user’s perception of time with their ideal mind time. For this, strobe light controls might prove a suitable alternative to subliminally alter a user who is looking at the clock.

 

CAD model

The Emit timepiece was modeled in the Fusion 360 CAD software. The model is available online in the following link:  http://a360.co/2paAYyA

Components

Based on our design concept, there are three main electronic components:

  1. Rotation motor to spin the extra hand
    • This component will consist of a simple switch that will turn on and off the motor.  In a future iteration, the switch will be controlled by a microcontroller that detects the presence in order to conserve energy.
  2. Strobe lights to create the strobe effect
    • This component consists of a simple transistor which controls whether a LED strip is powered on or off.    In future iterations this component will be improved to give more power to the LED strip.
  3. Status lights to indicate change in user’s emotional state
    • This component consists of a Neopixel ring driven by an Arduino.

Implementation

Failure-First Prototype (V1)

The biggest concern we had about the clock was about the strobe effect. This was because we had never used strobe lights before and we were not sure how to create the effect.  We figured out that there were two big considerations in strobe effect:

  1. Rotational motor
  2. Consistent strobe light frequency and brightness

Initially, we used servo motors as a rotational motor because they allow control over the motors rotations. But servo motors have low rotations per minute (RPM), and even at the max speed, the rotating hand was visible to the naked eye and slow.  For the strobe effect to be useful, we wanted a very fast rotating hand so we switched to DC motors that have ~8000 RPM. The constraint with DC motor is that DC motors do not allow fine control over the motor speed.

In order to test the strobe effect, we used an iPhone app that created the strobe effect with the device’s  flash. This allowed us to test the motor and strobe light effect without having to make our own strobe effect and thus, made sure that our tests were independent of any errors in our strobe lights.

We ended up putting a motor with a Lego brick to simulate the rotating hand in a holder.  We placed this system inside a cardboard box.  We painted the brick with glow in the dark paint and used an Ultra Violet (UV) LED strip with strobing to make the hand appear.  We used UV light because we wanted the hand to only be visible/prominent when the strobing was on. With the UV-glow paint on the hand, the hand was only visible when the UV LEDs were strobing. However, the LEDs were not bright enough while strobing and we decided that our next step was to figure out a brighter light source to create the strobe effect.

Lessons learned from the first motor and iPhone strobe light test:

  1. The motor and the hand needed to be relatively stable. Extra vibrations in either the motor or the hand prevented us from creating a smooth slow motion strobe effect.
  2. The rotating hand had to be balanced about the center. If most of the weight was just on one side, the rotational frequency varied slightly, but that was enough to break the smooth frozen effect of the strobe light. To freeze motion using strobe light, we need the strobe frequency to be an integer multiple of the rotational frequency. If the hand was not balanced, the rotational frequency varied and thus, it was difficult to freeze motion using the strobe light.

Component-Complete Prototype (V2)

Strobe lights

We carried forward two issues/lessons from our failure first prototype:

  1. Pick brighter strobe lights
  2. Stabilize the motor and rotating hand

Our initial choice for a strobe light was this: https://www.amazon.com/gp/product/B013OIT17W/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1.

This was a very bright light (850 lumens) and we were able to control the frequency to strobe the light, and when we were testing it in front of the hand, it worked really well, i.e. it was bright enough to illuminate the hand as it was strobing. However, when we placed it in front of the hand inside the clock, it needed to be at least 7 inches away from the hand to illuminate completely the portion of the hand that was sticking out behind the light and henceforth be visible to the user.  Also, due to the internal LED driver of the light, we couldn’t strobe it accurately with a frequency larger than 30 Hz and that was a limiting factor for our rotational motor. Therefore, we decided to abandon this light because of its form factor, limited illumination, and small strobing frequency range.
Our next choice was these LED strips: https://www.amazon.com/gp/product/B00HSF65MC/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1. These LEDs turned out to be very bright and the flexibility of the strip allowed us to wrap the lights around the edges of the clock (facing the LEDs inwards so that they were focused on the rotating hand). We were able to strobe the lights at a very wide range of frequencies.

 

Status lights

We used Neopixel lights to show the emotion colors. We used a translucent white sticker to diffuse the light from the Neopixels.

Clock

We used real clock hands: https://www.amazon.com/gp/product/B01LXWJFPW/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1.

We stuck the clock mechanism behind the translucent screen so that only the clock hands were visible and the clock system itself was hidden.

Redbear Blend

Redbear Blend is an Arduino-based board with BLE communication. We use this board to control the status and strobe lights using commands from the Android phone.

Circuits

Pretty Final Prototype (V3)

We had two main goals for this prototype:

  1. Replace the cardboard with wood
  2. Make the inside circular rim of the clock slanted so that the strobe LEDs were more directed towards the extra hand. The sketch shows the sides are slanted instead of at an angle.

For this prototype, we incorporated the lighting, the clock, the strobing and a wood body.  We also incorporated the strobe control using a microcontroller with BLE.

Woodworking

We wanted to construct a solid base for the clock and opted to make it out of wood.  We designed three inner rings to be able to separate the large wooden base into makeable cuts.  We also opted to make the rings with a slanted inner wall to be able to shine the strobe lights into the clock.  After various troubled attempts, we were finally able to get a successful cut.  We then proceeded to sand these cuts and paste them together with wood glue.   

 

PHYSIOLOGICAL SENSORS

EMPATICA

Empatica provides heart rate, body temperature and galvanic skin response (GSR). We retrieved data from Empatica in an Android app using Bluetooth Low Energy (BLE). We use GSR to try to detect the arousal of a person, as changes in arousal are related to the perception of time.

MUSE

Muse provides electroencephalogram (EEG) data, i.e. alpha, beta, gamma, etc brain wave signals. We receive EEG data from Muse in our mobile app.  Based on this data, we then calculate the cognitive states of the user such as mellow, concentrated, etc.

AFFECTIVA

Affectiva API recognized basic emotions, such as happiness, fear, anger, sadness, etc..  We integrated the Affectiva API in our Android app and used the phone camera to take a picture of the user and pass it to the Affectiva API to recognize basic emotions

The complete system workflow diagram is as follows:

  

Usage Scenario

The EMIT system was designed with four use case scenarios in mind: time perception awareness, social indicator, reflection, and time bending. In this section, we describe how a user would make use of the prototype to achieve each of these goals, which are not necessarily independent of each other.

  • Time Perception Awareness: The most basic usage scenario for EMIT is that of a tool to visualize your perception of time as a reflection of your inner emotional and cognitive states. In this case, the clock acts as a passive timepiece which can be positioned in a visible location where the user spends time. The EMIT clock system acts as an aesthetically pleasing piece of art and functions like any other normal clock. If and when the user wants it to, the user can connect his phone to the clock, which then processes all available biological data to add additional dimensions: time perception and emotion display.

  • Public Indicator: Linked to the previous time perception awareness scenario, the EMIT also displays your cognitive and emotional states to those around you. As a result, the device acts as a public indicator, which allows others around you to make informed decisions about whether or not to approach you. For instance, the device can be placed in a visible spot in your office, where others who pass by can see whether or not you are busy or idle with a simple glance.

  • Reflection: EMIT can also be used actively, as opposed to a passive timepiece that merely displays your perception of time. The EMIT application visualizes all incoming physiological data before aggregation. As a result, any user is able to sit in front of the clock and reflect on their inner state, both cognitive and emotional. Because the clock aggregates this information and visualizes it in an easily understandable format, the system affords dedicated sessions of reflection and meditation throughout the day.

  • Time Bending: In this work, we refer to time bending as the ability to control, through practice, your cognitive and emotional state in order to change your perception of time. Moving a step beyond reflection, a user may train to modulate their biosignals using the EMIT system to slow down or speed up their perception of time. The biofeedback loop created by the system affords this kind of interaction which could come in handy in many cases. For instance, a user enduring a particularly boring presentation may use this honed skill to speed up his perception of time and feel better. Similarly, feeling like a week of vacation lasted really long can be a healthy experience for a weary mind.

Conclusion

In this work, we presented EMIT, a smart timepiece that portrays both objective and perceived time passing for its user. The implemented prototype used the MUSE sensing headband, the Empatica E4, and the Affectiva API to effectively become aware of its user’s inner cognitive and emotional state. This data is aggregated and portrayed in two ways. A Neopixel LED display portrays five emotional states(anger, fear, joy, sadness, and disgust) by changing color. Strobe Light frequency is subsequently adjusted to show a rotating outer hand moving at different speeds to represent the user’s perception of time. We discussed how such a system can be used as a tool for visualization, reflection, and training, as it allows a user to become aware of his current state, reflect upon it, and even train himself/herself to modulate his biosignals to achieve a conscious “bending” of time perception itself.

Future Work

We propose three different venues for future improvements for our EMIT timepiece. First, a more robust metric should be devised in order to aggregate the different biological data points. In order to achieve a more precise metric, it would be ideal to carry out data collection from MUSE and Empatica E4 and correlate it to time reproduction exercise. This could then be fed to a neural network that would learn the intricacies and patterns (if any) of how these biosignals alter time perception for a user, as opposed to naively aggregating these signals. A second, perhaps more interesting direction for this work, is to delve into the use case scenario of time bending. How can the clock enable users to train and change their perception of time? One possibility is to enable mechanisms to engage the user in active meditation over periods of time, vibrating or beeping to remind its user to engage in a training session. The second possibility is to capitalize on strobe light patterns and see if different frequencies can stimulate the brain and induce time distortions subliminally. Finally, we highlight that the EMIT timepiece currently works when the user is near the system. As a result, a lot of emotional and cognitive data that can be useful is lost when the user is on the move. The narrative clip, a device that takes pictures throughout the day at a specified interval to keep track of your life, can be used to further enhance the timepiece in a way that reflects more about your ongoing day.

Citations/Bibliography

Chebat, Jean-Charles, Claire Gelinas-Chebat, and Pierre Filiatrault. “Interactive effects of musical and visual cues on time perception: An application to waiting lines in banks.” Perceptual and Motor skills 77.3 (1993): 995-1020.

Hanus, Deborah, Christina Kang, and Elizabeth Ricker. “Time Perception: Audio Perception with Visual Cues.”

Lee, Kyudong, et al. “Ambient Lamp Display in the Active Home Ubiquitous Computing Environment for Relaxing and Mediation.” Future Generation Communication and Networking (FGCN 2007). Vol. 2. IEEE, 2007.

Brewer, Johanna, Amanda Williams, and Paul Dourish. “Nimio: an ambient awareness device.” Proc. of ECSCW 2005. 2005.

Rao SM, Mayer AR, Harrington DL (March 2001). “The evolution of brain activation during temporal processing”. Nature Neuroscience. 4 (3): 317–23. doi:10.1038/85191. PMID 11224550. Lay summaryNature Neuroscience.

Kramer, Robin SS, Ulrich W. Weger, and Dinkar Sharma. “The effect of mindfulness meditation on time perception.” Consciousness and cognition 22.3 (2013): 846-852.

Wittmann, Marc, and Stefan Schmidt. “Mindfulness meditation and the experience of time.” Meditation–Neuroscientific Approaches and Philosophical Implications. Springer International Publishing, 2014. 199-209.

Bar-Haim, Yair, et al. “When time slows down: The influence of threat on time perception in anxiety.” Cognition and Emotion 24.2 (2010): 255-263.

Fraisse, Paul. “Perception and estimation of time.” Annual review of psychology 35.1 (1984): 1-37.

Joubert, C. E. (1984). Structured time and subjective acceleration of time. Perceptual and Motor Skills, 59, 335-336.

Zakay, D. (1990). The evasive art of subjective time measurement: Some methodological dilemmas. In R. A. Block (Ed.), Cognitive models of psychological time, (pp. 59-84). Hillsdale, NJ: Erlbaum.

Gibbon, John. “The structure of subjective time: How time flies.” Psychology of Learning and Motivation 20 (1986): 105-135.

Droit-Volet, Sylvie, and Warren H. Meck. “How emotions colour our perception of time.” Trends in cognitive sciences 11.12 (2007): 504-513.

Gil S, Droit-Volet S (February 2009). “Time perception, depression and sadness” (PDF). Behavioural Processes. 80 (2): 169–76. doi:10.1016/j.beproc.2008.11.012. PMID 19073237.

Droit-Volet, Sylvie, and Sandrine Gil. “The emotional body and time perception.” Cognition and Emotion 30.4 (2016): 687-699.

Edmonds, E. M., Cahoon, D., & Bridges, B. (1981). The estimation of time as a function of positive, neutral, or negative expectancies. Bulletin of the Psychonomic Society, 17, 259-260.

Stetson C, Fiesta MP, Eagleman DM (December 2007). “Does time really slow down during a frightening event?”.

Buetti, Simona, and Alejandro Lleras. “Perceiving control over aversive and fearful events can alter how we experience those events: an investigation of time perception in spider-fearful individuals.” (2012).

Twenge, Jean M., Kathleen R. Catanese, and Roy F. Baumeister. “Social exclusion and the deconstructed state: time perception, meaninglessness, lethargy, lack of emotion, and self-awareness.” Journal of personality and social psychology 85.3 (2003): 409.

Brown, Scott W. “Time perception and attention: The effects of prospective versus retrospective paradigms and task demands on perceived duration.” Perception & Psychophysics 38.2 (1985): 115-124.

Wittmann, Marc, and Martin P. Paulus. “Decision making, impulsivity and time perception.” Trends in cognitive sciences 12.1 (2008): 7-12.

Levy F, Swanson JM (August 2001). “Timing, space and ADHD: the dopamine theory revisited”. The Australian and New Zealand Journal of Psychiatry. 35 (4): 504–11. doi:10.1046/j.1440-1614.2001.00923.x. PMID 11531733.

Jafarinaimi, Nassim, et al. “Breakaway: an ambient display designed to change human behavior.” CHI’05 extended abstracts on Human factors in computing systems. ACM, 2005

Kuribayashi, Satoshi, and Akira Wakita. “PlantDisplay: turning houseplants into ambient display.” Proceedings of the 2006 ACM SIGCHI international conference on Advances in computer entertainment technology. ACM, 2006.

Van Wassenhove, Virginie, et al. “Distortions of subjective time perception within and across senses.” PloS one 3.1 (2008): e1437.

Berlin, Heather A., and Edmund T. Rolls. “Time perception, impulsivity, emotionality, and personality in self-harming borderline personality disorder patients.” Journal of personality disorders 18.4 (2004): 358-378.

Curton, Eric D., and Daniel S. Lordahl. “Effects of attentional focus and arousal on time estimation.” Journal of experimental psychology 103.5 (1974): 861.

Burnside, W. (1971). Judgment of short time intervals while performing mathematical tasks,Perception & Psychophysics,9, 404–406.

Franck N, Posada A, Pichon S, Haggard P (May 2005). “Altered subjective time of events in schizophrenia”. The Journal of Nervous and Mental Disease. 193 (5): 350–3. doi:10.1097/01.nmd.0000161699.76032.09. PMID 15870620.

Tse, Peter Ulric, et al. “Attention and the subjective expansion of time.” Attention, Perception, & Psychophysics 66.7 (2004): 1171-1189

Ekman, Paul “What Scientists Who Study Emotion Agree About“, Perspectives on Psychological Science (2016): 31-34

James, W. (1893). The principles of psychology. New York: H. Holt and Company. Page 609

Tulving, Endel. “Chronesthesia: Conscious awareness of subjective time.” (2002).