Binocular rivalry is a common laboratory paradigm for investigating how the brain integrates information from our two eyes.
During normal visual perception, our eyes receive roughly the same image on each of the two retina. The brain takes advantage of this redundancy to make sense of what is observed.
By presenting two different images to each eye separately, scientists can study how the brain coordinates and interprets their separate signals. Tricking the brain with two independent images is referred to as binocular rivalry.
This video demonstrates methods for using binocular rivalry, including how to design the stimulus, perform the experiment, and how to analyze and interpret data.
In this simple experiment, participants are asked to wear red-cyan glasses and report how a generated stimulus is interpreted.
In this case, the pair of glasses filter material to each eye, such that the red lens will filter out all but red light before it reaches the participant’s eye, and the cyan lens will filter out all but blue light.
The generated stimulus involves superimposing tinted words: a red, nonsense word, such as Cfbal, over a blue, meaningful word, like Hello.
When the filter glasses are worn by the participant, the blue tinted word Hello will not make it to the eye behind the red lens, and the red tinted non-word Cfbal will not make it to the eye behind the cyan lens.
During a period of 120 sec, participants are asked to report every 10 sec whether the meaningful word Hello or the nonsense word Cfbal is observed, or if it is too unclear, to say Unclear.
Along the time course of how each participant responds, the dependent variable is the number of times participants report observations among the three categories.
If binocular rivalry is produced, the participant’s responses will vary across time because the brain cannot easily perceive both words simultaneously.
Moreover, participants will report more observations of seeing the word Hello because of a tendency of the brain to perceive meaningful images over the nonsensical.
To demonstrate binocular rivalry, first gather a pair of red-cyan glasses and a stopwatch.
To conduct this study, create a stimulus slide with the word ‘Hello’ written in blue, and on top of it, write the letters ‘Cfbal’ written in red. Make the word on top 50% transparent.
After printing the stimulus slide on a white piece of paper, greet the participant.
Once the participant is seated, explain the instructions of the task, and then tell them to put on the filter glasses.
Before collecting data, set the stopwatch to countdown 120 sec. Inform each participant that they will be asked to report every 10 sec whether they see the word Hello or Cfbal, or the word appears Unclear.
Every 10 sec, ask the participant what they see and record each response across the 12 instances.
To analyze how each participant perceived the stimulus, plot every response as a function of time. Notice that the participant tends to only be aware of one of the words at a time.
However, over time the word that the participant is aware of at any given moment can change quickly and frequently. This suggests that the brain recognizes that something is not right. As a result, the brain tries to present a stable image to the participant but can’t decide what the right stable image is.
To examine the overall distribution of response types, average the percentages of each response type across participants. Notice that the observation of Hello dominated.
This suggests that the brain evaluates the contents of each image and prefers to bring to awareness things that make sense, are familiar, and have meaning.
Binocular rivalry forms the basis for most 3D movies and games. By wearing special glasses, the brain is tricked into seeing 3D when the screen it is looking at is actually 2D.
In addition, binocular rivalry lets researchers with neuroimaging tools, such as high-density EEG, know when the nature of a person’s conscious experience is changing suddenly—like the participant in this demonstration who went from seeing one word to the other.
Researchers can then map those changes in conscious experience onto events taking place in the brain at those moments. For example, different states of wakefulness—whether a person is asleep, relaxed, or wide awake and even on edge—each correlates with different brain waves, measured using EEG recordings
Current research is trying to determine whether changes between states of wakefulness correlate with changes in conscious perception, diagnosed using the binocular rivalry paradigm.
You’ve just watched JoVE’s introduction to Binocular Rivalry. Now you should have a good understanding of how to design and perform the experiment, as well as analyze results and apply the phenomenon of visual perception.
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