Motion-induced Blindness
Source: Laboratory of Jonathan Flombaum—Johns Hopkins University
One thing becomes very salient after basic exposure to the science of visual percepti…
1. Stimulus
- Doing a motion-induced blindness experiment requires software or a programming environment that can make simple animations and collect keypress responses.
- The basic motion-induced blindness stimulus involves three features: a square made up of bright blue crosses on a black background, a bright yellow disc towards one of the corners of the space occupied by the square, and a white disc in the centre of the screen to serve as a fixation point. Figure 1 shows a single frame of basic motion-induced blindness stimulus.
- Set the square of blue crosses to rotate continuously in one direction, as though the square is pegged down by a fixation point.
Figure 1: A single frame containing the motion-induced blindness stimulus. In the dynamic version, the square of blue crosses rotates around the central fixation point, while the yellow dot remains stationary.
2. Producing the illusion
- To experience the illusion, fixate the white disc in the center of the stimulus, but also attend to the yellow disc as you watch the motion of the blue crosses. The yellow disc should disappear from awareness, even though it never actually disappears from the screen.
3. Running an experiment
- To run a basic experiment, create a slightly different version of the stimulus. Rather than the one yellow disc in the upper left corner of the stimulus, include a yellow disc in the right corner and one on the bottom as well, for a total of three yellow discs. Figure 2 shows a single frame from such a stimulus.
Figure 2: A single frame of a simple motion-induced blindness experiment. Participants are asked to report the number of yellow discs absent from their awareness at each moment.
- Instruct a participant to fixate on the center point while attending to the stimulus widely.
- Tell the participant that the experiment will involve 5, 30-s trials. In each trial they should fixate and attend to the stimulus, and they should report when discs disappear from awareness as follows:
- If one disc is absent, hold down the 'J' key. If two are absent, hold down the 'K' key, and if three are absent, hold down the 'L' key. Adjust which keys are held down as discs enter and disappear from awareness. And when all the discs are perceived, be sure to release all the keys.
- The experiment program should record the participant's key presses.
What we see in our surroundings does not always match the reality of the physical world. Sometimes, our brains actually erase sensory information.
In certain situations, like driving on a busy and narrow highway at night, a driver might find himself staring into oncoming headlights. When this happens, the taillights of the car immediately in front of him can temporarily disappear.
This phenomenon is an example of motion-induced blindness, a perceptual illusion in which the brain discards part of the visual field when motion occurs simultaneously.
In this video, we describe the elements used to create the illusion in a laboratory setting based on the methods of Bonneh and colleagues. We will also determine the frequency at which stimuli disappear and provide additional scenarios where the brain alters awareness of the world.
In this experiment, participants observe a simple animation with three basic features: a square containing bright blue crosses on a black background, bright yellow discs within the orderly pattern, and a centered fixation point.
For every 30-s trial, participants are asked to fixate their eyes on the center point and attend to the stimuli as a whole while the background rotates in continuous motion.
During this time, they?ll report how many of the yellow discs vanish, which serves as the dependent variable. If one or more disappear, motion-induced blindness is expressed.
In this case, the yellow circles are invariant and don?t rotate as they should if they were on the same surface with the moving squares. Consequently, the brain concludes that they must not be real and removes them from awareness, thereby distorting physical reality.
As the first step, verify that stimuli have been accurately animated.
Then, greet a participant in the lab and have them sit comfortably in front of a monitor and keyboard.
To begin, explain that the participant should fixate on the white dot and attend to the yellow discs, while the square of blue crosses rotates. Indicate that the 'J' key should be held down when one yellow disc disappears, 'K' if two are absent, and 'L' for all three. If all objects are perceived, completely release keys.
Go ahead and turn off the room lights to reduce glare and start the program. Note that every participant should complete a total of five trials, each one lasting 30 s, with the yellow discs in a shifted location every time; during these instances, perception may change and the computer will record all responses behind the scenes.
When the participant has finished, thank them for taking part in the experiment.
To analyze the data, compute the percent of time that one, two, or all three yellow discs were not perceived by the participant and graph the results.
Notice that participants saw one disappear more often than two or three. If the brain believes that the dots may not really be there?but is also uncertain?then it makes sense that one will be deleted more frequently than all.
Now that you are familiar with the motion-induced blindness illusion, let?s look at a recent theory of why the brain deletes items from awareness, as well as insights into the functioning of the parietal cortex.
In 2008, researchers New and Scholl developed the Perceptual Scotoma theory to explain why motion-induced blindness happens. They suggested that the human brain mistakes the yellow dots on the screen for scotomas, which are injuries to the retina. People with scotomas should experience an empty space in their visual perceptions, but they do not.
The reason is that the brain learns to discount the empty space caused by the scotoma because it is invariant with respect to the rest of the outside world. That is, it must originate from inside the eye, and as a result, the brain removes the blank space from awareness.
This is also why an individual who wears glasses is not always aware that they are dirty; the brain removes the dirt specks!
In another study assessing conscious perception, Funk and Pettigrew used transcranial magnetic stimulation, or TMS, to investigate where motion-induced blindness is induced in the brain. They found that the disappearance and appearance of stimuli can be modified with TMS pulses to the parietal cortex, an area implicated in visuospatial attention.
By combining motion-induced blindness and TMS in patients with parietal cortex damage, especially those that experience visual extinction, it is possible that a therapeutic procedure could be found to alleviate symptoms.
You?ve just watched JoVE?s video on the motion-induced blindness illusion. Now you should have a good understanding of how to incorporate the elements and run the experiment, as well as how to analyze and assess the results.
Thanks for watching!
View the full transcript and gain access to JoVE Science Education videos
Q1: What is motion-induced blindness and when does it occur?
Motion-induced blindness is a perceptual illusion where the brain discards part of the visual field when motion occurs simultaneously. For example, a driver staring at oncoming headlights may temporarily fail to see the taillights of the car ahead. This phenomenon demonstrates that what we perceive does not always match physical reality, as the brain actively constructs our visual experience.
Q2: How does the Perceptual Scotoma theory explain motion-induced blindness?
The Perceptual Scotoma theory, developed by New and Scholl in 2008, suggests the brain mistakes moving yellow dots for scotomas, which are retinal injuries. Since scotomas remain stationary relative to the eye, the brain learns to discount them from awareness. Similarly, people wearing dirty glasses often don't notice the dirt because the brain removes these invariant visual elements from conscious perception.
Q3: What stimuli and setup are used in a motion-induced blindness experiment?
The experiment uses a square containing bright blue crosses on a black background, bright yellow discs arranged in an orderly pattern, and a centered fixation point. Participants fixate on the center point while the background rotates continuously for 30-second trials. The yellow discs remain stationary and invariant, creating the illusion that they disappear as the brain discards them from awareness.
Q4: How do participants report their observations during motion-induced blindness trials?
Participants hold down the 'J' key when one yellow disc disappears, 'K' for two absent discs, and 'L' when all three vanish. If all objects remain visible, they completely release the keys. Each participant completes five 30-second trials with the yellow discs in shifted locations each time, allowing researchers to measure how perception changes and record responses automatically.
Q5: What does the frequency of disappearing stimuli reveal about brain perception?
Data typically shows participants perceive one yellow disc disappearing more often than two or three. This pattern suggests that when the brain is uncertain whether stimuli are real, it deletes individual items more frequently than all objects simultaneously. This selective deletion reveals how the brain makes probabilistic judgments about visual awareness and constructs conscious perception.
Q6: What role does the parietal cortex play in motion-induced blindness?
Funk and Pettigrew used transcranial magnetic stimulation to investigate motion-induced blindness in the brain. They found that TMS pulses to the parietal cortex, an area involved in visuospatial attention, can modify the disappearance and appearance of stimuli. This research suggests potential therapeutic applications for patients with parietal cortex damage and visual extinction symptoms.
Q7: Why is motion-induced blindness useful for studying visual awareness?
Motion-induced blindness is a powerful tool for studying visual awareness because it reveals how the brain constructs experience rather than passively recording reality. By observing when and why stimuli disappear from conscious perception, researchers gain insights into the mechanisms underlying awareness. This illusion demonstrates that investigating visual awareness and inattentional blindness helps distinguish between physical reality and subjective perception.