Binocular Rivalry
Source: Laboratory of Jonathan Flombaum—Johns Hopkins University
Why do people have two forward-facing eyes? By presenting the brain with two ever so…
1. Equipment
- To easily produce binocular rivalry, use a pair of red-cyan glasses (Figure 1).
Figure 1. A pair of red-cyan rivalry glasses. The glasses make it possible to present two overlaid images such that only one arrives to each eye. The red lens will filter out all but red light before it reaches a viewer’s eye, and the cyan lens will filter out all but blue light. This means that a blue tinted image won’t make it to the eye with the red lens, and a red tinted image won’t make it to the eye behind the blue lens - A stopwatch will also be necessary.
2. Stimulus
- An easy demonstration having to do with rivalry involves nonsense words superimposed on something meaningful.
- In PowerPoint©, create a 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. It will look like this (Figure 2).
Figure 2. Sample stimulus for a demonstration of binocular rivalry. The word ‘Hello’ is written in blue, and in a 50% transparent red, the nonsense letters ‘Cfbal’ are written on top.
3. Running the Experiment
- Print the slide on a piece of white paper. Seat a participant in front of the paper and ask them to put on the glasses.
- Set the stopwatch to countdown 120 seconds.
- Instruct the participant that every ten seconds they will be asked to report what they see, and that they should answer in one of three ways, ‘Hello,’ ‘Cfbal,’ or ‘Mixed / Unclear’.
- Begin the count, and every ten seconds, ask the participant what they see. Mark down the responses.
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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Q1: What is binocular rivalry and why do researchers use it?
Binocular rivalry is a laboratory paradigm where two different images are presented to each eye separately to investigate how the brain integrates information from both eyes. Researchers use it to study visual perception, conscious experience, and the mechanisms underlying 3D vision. It reveals how the brain coordinates conflicting signals and determines which image reaches awareness.
Q2: How does the red-cyan glasses method create binocular rivalry?
Red-cyan glasses use color filters to direct different images to each eye. The red lens filters out blue light, allowing only red wavelengths through, while the cyan lens filters out red light. When a red nonsense word and blue meaningful word are superimposed, each eye receives only one word, creating the rivalry effect that prevents simultaneous perception of both images.
Q3: What do participants report during a binocular rivalry experiment?
During a 120-second trial, participants report every 10 seconds which image they perceive: the meaningful word, the nonsense word, or neither if unclear. Their responses vary across time because the brain cannot easily maintain awareness of both conflicting images simultaneously. This switching between percepts is recorded as the dependent variable across 12 reporting intervals.
Q4: Why do participants report seeing meaningful words more often in binocular rivalry?
The brain evaluates the contents of each image and preferentially brings meaningful, familiar, and sensible information to conscious awareness. In the experiment, participants report seeing the word "Hello" more frequently than the nonsense word "Cfbal" because the brain prioritizes meaningful stimuli. This demonstrates that conscious perception is influenced by semantic content and familiarity.
Q5: How does binocular rivalry relate to 3D movies and games?
Binocular rivalry forms the basis for 3D visual technology. Special glasses trick the brain into perceiving three-dimensional depth by presenting slightly different images to each eye, similar to how the brain naturally processes depth from two forward-facing eyes. Although the screen displays only 2D images, the brain integrates the separate signals to create the illusion of three dimensions.
Q6: What can neuroimaging reveal about consciousness using binocular rivalry?
Neuroimaging tools like high-density EEG can detect sudden changes in conscious experience when participants switch between perceiving different images during binocular rivalry. Researchers map these perceptual shifts onto brain activity, correlating different states of wakefulness—such as sleep, relaxation, or alertness—with corresponding brain wave patterns. This helps determine whether changes in consciousness relate to specific neural events.
Q7: What does the switching pattern in binocular rivalry responses reveal about brain function?
The rapid switching between perceived images indicates the brain recognizes conflicting information and attempts to construct a stable, coherent visual experience. However, because both images are equally valid, the brain cannot settle on one stable interpretation. This oscillation demonstrates the brain's active role in organizing sensory input and maintaining conscious perception rather than passively receiving visual information.