---
# System prepended metadata

title: Eink psych - Literature review
tags: [literature review, psychology, psych-ux]

---

# Eink psych - Literature review

The aim of this document is to compile existing research that has been conducted comparing eink and LCDs/OLEDs on areas such as visual fatigue, reading ability/anything that seems important for productivity and wellbeing!

Getting together the existing research will help us work out exactly where the knowledge gap is!

Anyone and everyone is welcome and invited to contribute!

###### tags: `psych-ux` `psychology` `literature review`

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## Benedetto et al (2013)
 

#### Research Question:
Do eink vs LCD vs Book trigger different levels of visual fatigue over a prolonged reading period (70 mins)?


#### Method:

<br/>

* Number of participants = 12, all had normal vision
* Each participant came into the lab 3 times over the course of 10 days

* Each time they came into the lab, they had to read for 70 mins on one of the devices
* Each participant read on each of the different devices
* Analysis was conducted “within participant” (i.e. comparing each participants’ visual fatigue against only their own visual fatigue after each different device



* Participants’ visual fatigue was measured in three ways
    * (1) Critical Flicker Frequency
        * A flickering stimulus was presented. 
        * There is a visual illusion in which this flickering stimulus appears not to flicker, but as a single continuous stimulus
        * Participants required to indicate whether an actually stationary stimulus had started flickering
        * The idea being that if they were slower/less good at doing that then they were more visually fatigued
    
    * Eye blinks
        * Less frequent eye blinks indicate visual fatigue
        * Eye tracking cameras were used to record rate of eye blinks
    * Visual fatigue questionnaire
        * Participants indicated level of agreement with statements (e.g. I have difficulties seeing, My eyes feel tired) on a 7-point scale

* Before and after the reading session, participants performed measures (1) and (3). (2) was measured during reading.

<br/>

#### Findings:
* No difference between eink, LCD, book on the critical flicker frequency score (measure (1))
* Significantly fewer blinks during LCD than during both eink and book reading (which were not significantly different)
* Visual fatigue questionnaire ratings were highest following LCD, followed by eink followed by book

#### Limitations

#### Take aways
* According to eye blink and self-report questionnaire, LCD causes more visual fatigue than eink
* Could be worthwhile to explore other potential visual fatigue measures
    * E.g. attention lapsing?

* Key aspect of the study was the reading session length – sessions were 70 minutes
    * Nonetheless, average time staring at laptop screen probably much greater than this >>> key area for research to target.

* The researchers thought further research should investigate: how does luminance level modulate their findings?






<br/>

## Kim, Lim, Gu, Yong Park (2017)

#### Research Question:
* To what extent does prolonged viewing of a high-resolution display (iPad Air), which presents bright and clear images, induce visual fatigue?

#### Method:
* num participants = 59, all participants said that they viewed a screen for at least 2 hours every day and had healthy vision
* Participants watched a film or played a computer game for 1 hour on an iPad (viewing distance > 40cm)
* Visual fatigue and discomfort was assessed before and after using the device:
    1. An asthenopia questionnaire (self-report)
        * rate on a 0-6 scale (from none to severe): 
            * tired eye, sore/aching eye, irritated eye, watery eye, dry eye, eye strain, hot/burning eye, blurred vision, difficulty in focusing, visual discomfort
    2. tear-film break up time (TBUT)
        * the time it takes for the first dry spot to appear on the surface of the eye after a full blink
    3. total ocular wavefront aberration
        * not clear why exactly they included this measure
        * total ocular wavefront aberration is essentially a measure of the impairment in visual ability caused by physical imperfection in the eye - not affected by glasses (an analogy: one persons eye might be a zeiss lens, anothers might be plastic - this method helps you detect whether a person is zeiss or plastic)
        * however you wouldnt expect this to change after a brief period of time, unless you were firing a laser at them


<br/>

#### Findings:
* Asthenopia score went up significantly after the ipad session - specifically, "tired eyes", "sore/aching eyes", "irritated eyes" "watery eyes", "hot/burning eye" all increased
* Tear film break-up time significantly decreased (lower score is worse; is a sign of a poor tear film)
    * >> increased tear evaporation may be linked to asthenopia 
* Total ocular wavefront abberation was unchanged (not surprising)

#### Limitations
* No control group or comparison... hence not clear whether the same would be true for someone staring at a piece of paper or an eink device
* Study and discussion was essentially based on a subjective questionnaire, the two objective measures (TBUT and Ocular wavefront were not really discussed by the authors)
* 

#### Take aways
* KEY point: Staring at an ipad noticeably fatigues the eyes; it is not clear from this study whether this would also occur for reading a piece of paper.
* Long-term visual effects of intense and chronic smart mobile device use have not been extensively investigated
* Health impacts may not be limited to ocular surface problems (as investigated here), but extend further up into neuronal networks of the retina
* Worth mentioning:
    * although exact mechanism of Computer vision syndrome is unclear, decreased blink rate (Portello, Rosenfield & Chu, 2013) + increased accomodative effort (keeping the eye focused at a certain distance)(Bababekova, Rosenfield, Hue, Huang, 2011) could contribute to it
    * Also blue light exposure, which has been shown to cause eye fatigue 
        * Lee, Kim, Lee, 2014
        * Niwano, Kanno, Iwasawam 2014 
        * Jaadane, Boulenguez, Chahory, 2015
            * retinal damage induced by commerically available LEDs
        * Ide, Toda, Miki, Tsubota (2015)
            * blocking blue light with a special lens significantly reduced critical flicker frequency



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## Benedetto, Carbone, Drai-Zerbib, Pedrotti, Baccino (2014)

#### Research Question:
* How does screen luminance, and general ambient illuminance effect visual fatigue and arousal

#### Method:

<br/>

* num participants = 48
* each participant was randomly assigned to one of 4 experimental groups; [bright environment, bright screen], [dim environment, bright screen], [bright environment, dim screen], [dim environment, dim screen]
    * environment brightness was measured with the computer screen off, with a digital light meter placed 5cm above the participant's head
    * screen brightness was measured with a digital luminance meter
* Screen was kept black and white throughout

<br/>

* Participants had to read text from a novel for 60 minutes


<br/> 

* Measures:
    * Subjective Visual Fatigue scale survey
        * performed before and after reading passage
        * Taken from Heuer et al (1989)
    * Eye Blinks
        * measured blink rate: total number of blinks over the 60 minute reading period
        * blinks are a well known indicator of both visual fatigue and drowsiness - blinks decrease when luminance increases; such a reduction contributes to a poor tear film quality, temporarily stresses the cornea causing dry eye
    * Microsleep
        * measured microsleep episodes (eyelid closures longer than 500ms) - indicating drowsiness
    * Fixations (the maintaining of gaze on a single location)
        * measured number of fixations that took place in each experimental run
        * measured average fixation duration
            * (longer fixations thought to indicate issues in extracting information, more fixations indicate higher arousal?)
    * Saccades (fast eye movements which occur between fixations)
        * Saccade velocity
            * average velocity of saccades during the 60min reading period
            * indexes arousal - faster saccades indicated increased arousal (Di Stasi, Catena, Cañas et al., 2013)
        * Regressive saccade rate
            * regressive saccade is a saccade that goes backwards through the text, performed in order to reread material that was not fully understood
            * usually an increase in regressive saccades indicates a lower ability to comprehend the text/reduced legibility
            * regressive saccade rate = number of regressive saccades that took place in the 60min reading period
        * Microsaccades
            * involuntary, saccade-like fixational eye movements of very short distances, occurring within fixations
            * lower microsaccade rates are usually associated with increased levels of arousal
            * Microsaccades can only occur during fixations, therefore Microsaccade rate = (total number of microsaccades)/(time spent fixating)
        * Pupil diammeter
            * pupil gets smaller as light intensity increases
            * pupil gets wider as arousal increases
            * The mean pupil diammeter for the whole 60min reading period was calculated (to assess differences between lighting conditions), as well as pupil diammeter over 12 time blocks of 5 min (to assess change over time - possibly reduction in arousal over course of reading)
        * Reading speed
            * number of words read per minute
        * Reaction time beep task
            * while reading, participants were told to respond by pressing a button every time they heard a beep
            * the beep would appear every ~3min
            * Kind of measuring how well they are focusing, the better their focus, the slower to respond on the task
        * Memory Awareness (remember/know test - see Tulving (1985))
            * after finishing the 60min reading, participants were asked to complete a memory test
                * list of 30 words, 15 of them had appeared in the text
                * participants had to say whether they rememembered from the text or just knew the words presented
                    * remembered = episodic memory
                    * know = semantic memoru
                * Garland & Noyes (2004) suggested that the cognitive processing taking place while learning from EVDs and paper is different, mainly because the characteristics of the computer screen might interfere with cognitive processing for long-term memory resulting in greater use of episodic memory




<br/>

#### Findings:
* Reading from a bright screen is related to a reduced blink rate (in line with many other studies)
* Subjective visual fatigue increased after reading, but this did not significantly differ based on screen brightness or environment brightness (in line with Lee et al., 2011)
    * dim environment, dim screen led to biggest drop in visual fatigue
* Dim screen seemed to reduce arousal:
    * had slower saccade velocities, lower microsaccade rate
* Dim environment:
    * more regressive saccades (rereading previous material)
    * slower reactions to beep task
        * possibly less peripheral processing going on >> less aware of environment outside of the locus of attention
* Dim environment, Dim screen:
    * fixations are longer, and more frequent
* Pupil diammeter
    * was more influenced by screen brightness than by environment brightness, though was influenced by both
    * got smaller and smaller over time, but steeper decrease when screen was low brightness
* Memory awareness
    * no effect on recall scores
    * Difference was small but more episodic remembering during bright screen than dim screen



#### Limitations
* visual fatigue measures were perhaps inadequate? subjective scale and eye blinks, how else could you measure it - perhaps with attention lapsing?
* Only measured visual fatigue, no attempt to see how this might affect other task performance

#### Take aways
* reading speed increased for brighter screen, eye blinks decreased
* brighter screen increases arousal, not clear whether it is more tiring (eye blinks data might suggest this, but participants did not self-report feeling more tired)
* possibility that different level of processing occurs on paper vs LCD screen





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## Write up template (YYYY)

#### Research Question:
*

#### Method:

<br/>

* 

<br/>

#### Findings:
* 

#### Limitations
*

#### Take aways
* 





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## Up next:
 
* Kang, Wang, Lin (2009)
* Benedetto et al. (2014)
* Siegenthaler et al (2011)
* Garland & Noyes (2004)
* Lee, Ko, Shen, Chao (2011)

### Computer vision syndrome
* Gowrisankaran & Sheedy (2015)
* Rosenfield (2011)
* Klamm & Tarnow (2015)


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## Research Ideas

* investigating the difference between using e-ink vs LCD over a long period of time (e.g. a full 8 hour working day rather than 30 min sessions)

    * Would be relevant to also see about using a mix, as I can imagine many/most wouldn't be able to use e-ink exclusively.
    * Areas where anecdotally one might possibly expect some interesting findings:
decreased rate of mental fatigue over a full days work for an e-ink user, which perhaps translates to more available cognitive resources for e.g. thinking about hard maths problems, writing etc.  

* maybe some stuff to do with screen addiction
