CAFFEINE’S EFFECT ON VISUAL INPUT
Caffeine’s Effect on Certain Visual Sensory Input
CAFFEINE’S EFFECT ON VISUAL INPUT
This study will explore caffeine’s effect on the rate of eye movement while reading. To measure
rate of eye movement, one must examine rate of saccades, or small movements of the eye that
occur when a person reads, looks at a scene or searches for an object. Since caffeine is a
stimulant drug, the rate of saccades should increase while reading occurs. An individual will be
asked to read two paragraphs, one while not on caffeine and one after ingestion of about 160 mg.
of caffeine. Two EOGs will be taken while the participant performs the reading tasks and
comparison of the 2 EOG recordings will show how caffeine affected the rate of eye movement.
CAFFEINE’S EFFECT ON VISUAL INPUT
Caffeine’s Effect on Certain Visual Sensory Input
Caffeine is one of the most popular drugs used in the world today and caffeine
consumption is widely associated with increased energy and mental alertness. People’s reaction
times tend to improve with the presence of caffeine (Cheney, 1936). Caffeine in doses as small
as 12.5 milligrams even creates better reaction times than placebos (Smit & Rogers, 2000). Even
caffeinated gum has been shown to improve mood and performance efficiency (Smith, 2009).
While the drug stimulates the alertness of an individual, an interesting question is if the improved
cognitive function stems exclusively from an increase in brain activity or if certain sensory
systems also contribute to this phenomenon. For example, in a task such as reading a book, it is
beneficial to determine if the rate of eye movement increases with the amount of caffeine
because it helps us to further understand the effects of caffeine on the body.
While caffeine may stimulate reaction times, some studies have shown that it generally
decreases comprehension and recall. One study even went so far as to claim that caffeine may
induce psychosis in otherwise psychiatrically healthy people (Hedges, Woon, & Hoopes, 2009).
According to another study, caffeinated individuals scored consistently lower on the AVLT
(Auditory-Verbal Learning Test), a test of memory (Terry & Phifer, 1986). This goes against
common assumptions that caffeine increases your memory and improves your mood.
In order to study eye movement, background and techniques for studying the eye need to
be examined. According to Rayner (1998), saccades are eye movements continually made when
we read, look at a scene or search for an object. In between saccades, our eyes experience
fixations, where they remain relatively still for a fixed period of time. These fixations tend to
last differing amounts of time, depending on what task our eyes are trying to accomplish.
CAFFEINE’S EFFECT ON VISUAL INPUT
Rayner states that the average fixation interval for silent reading is 225 milliseconds, while the
average fixation interval for oral reading is 275 milliseconds.
Additional research on saccades has been conducted by other studies. Apparently, during
a saccade, at least one form of cognitive activity called mental rotation is stopped. If mental
rotation, which is the ability to rotate an object in your mind, ceases to function during a saccade,
possibly other mental processes also halt (Irwin & Carlson-Radvansky, 1996). If this was the
case, then an increase in eye movement would take the brain longer to comprehend a reading.
According to Irwin, the saccades are very good at picking up visual stimuli, which explains why
people’s reaction times could be quicker after ingestion of caffeine.
Current research in the field does not really touch on eye movement after caffeine
ingestion, but it does seem to further support the idea that it takes people on caffeine longer to
comprehend and recall material. One study measured the amount of lines read in a certain time
period and found that caffeine was associated with a higher average of lines read for impulsive
individuals, but the drug was also associated with a lower average of lines read for less impulsive
individuals. (Anderson & Revelle, 1982). Another study concluded that caffeine led to longer
reading times overall for specific stories (MacPherson et al., 1996). Apparently, while caffeine
does affect certain people differently, it generally seems to slow down the reading process.
One study actually did look at eye movement to detect various stimuli in participants’
visual field. The test results did not indicate increased visual activity while under the influence
of caffeine, however the team stated that this was probably due to a data-limited process that
resulted from the high-complexity of the experiment (Ruijter, Lorist, & Snel, 1999).
Based on the studies of reading times and the in-depth study on saccades, I believe that
caffeine does increase eye movement, which in turn slows down comprehension of reading
CAFFEINE’S EFFECT ON VISUAL INPUT
materials as your brain temporaily halts every time your eyes move. The increased reaction
times are explained by the ease with which visual stimuli are picked up by saccades. Since the
saccades, or eye movements, are more frequent while on caffeine, your eyes will detect stimuli in
the environment better, thus improving reaction times. My thesis for this research project,
however, only covers that people have a higher rate of side-to-side eye movement when reading
a book after consuming at least 15 milligrams of caffeine.
My hypothesis for this experiment is: If an individual consumes at least 15 milligrams of
caffeine and reads a book, they will experience an increase in the rate of saccades relative to
Participant
One individual from a general psychology class at Broome Community College will be
studied. The individual will be between 18 and 30 years of age.
Materials and Apparatus
One desk and one chair will be used to seat the test participant, while one Biopac MP40
device (with a built-in EOG monitor) will be used to record the test results. A computer will also
be required for the MP40 device to work properly. Two paragraphs from the book “Language
Development from Birth to Three,” a 1270L book on the Lexile scale, will be provided for
reading material. The 1270L measurement is consistent with a twelth grade reading level, to
ensure the reading material is not too easy and not too dificult for the participant to read. Finally,
one energy drink (about 160 mg. of caffeine) will be provided for test participant consumption.
Procedures
CAFFEINE’S EFFECT ON VISUAL INPUT
Before commencing the experiment, I will explain to the test participant the nature of my
test and obtain consent from the participant to test him or her. After approval, the participant will
be instructed to sit at the desk and chair provided while being hooked up to the Biopac MP40
device. The device will then be connected to a computer and the participant will be given one of
the two paragraphs as reading material. The participant will be instructed to read the passage at
their normal pace, while the MP40 device monitors their saccades. Afterwards, the individual
will be given an energy drink to consume within ten minutes. After consumption, the test
participant will be given a second paragraph to read and the MP40 device will record their
Method of Analysis
After the experiment, the two saccade recordings taken will be compared to see which
recording had the higher rate of saccades. The second recording should have the higher rate,
which should show that caffeine did increase the rate of saccades while reading. Some possible
error could be introduced into the test if the two paragraphs are not perfectly equal based on
CAFFEINE’S EFFECT ON VISUAL INPUT
References
Anderson, K. J., & Revelle, W. (1982). Impulsivity, caffeine, and proofreading: A test of the
Easterbrook hypothesis. Journal of Experimental Psychology: Human Perception and
Cheney, R. H. (1936). Reaction time behavior after caffeine and coffee consumption. Journal of Experimental Psychology, 19(3), 357-369.
Hedges, D. W., Woon, F. L., & Hoopes, S. P. (2009). Caffeine-induced psychosis. CNS
Irwin, D. E., & Carlson-Radvansky, L. A. (1996). Cognitive suppression during saccadic eye
movements. Psychological Science, 7(2), 83-88.
MacPherson, J., Sternhagen, S., Miller, T., Devitt, M., Petros, T. V., & Beckwith, B. (1996).
Effect of caffeine, impulsivity, and gender on the components of text processing and
recall. Experimental and Clinical Psychopharmacology, 4(4), 438-446.
Rayner, K. (1998). Eye movements in reading and information processing: 20 years of research.
Psychological Bulletin, 124(3), 372-422.
Ruijter, J., Lorist, M. M., & Snel, J. (1999). The influence of different doses of caffeine on
visual task performance. Journal of Psychophysiology, 13(1), 37-48.
Smit, H. J., & Rogers, P. J. (2000). Effects of low doses of caffeine on cognitive performance,
mood and thirst in low and higher caffeine consumers. Psychopharmacology, 152(2),
Smith, A. (2009). Effects of caffeine in chewing gum on mood and attention. Human Psychopharmacology: Clinical and Experimental, 24(3), 239-247.
CAFFEINE’S EFFECT ON VISUAL INPUT
Terry, W. S., & Phifer, B. (1986). Caffeine and memory performance on the AVLT. Journal of Clinical Psychology, 42(6), 860-863.
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