Flash suppression is a phenomenon of

visual perception Visual perception is the ability to interpret the surrounding environment through photopic vision (daytime vision), color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in the visible spectrum reflecte ...

in which an image presented to one eye is suppressed by a flash of another image presented to the other eye. To observe flash suppression, a small image is first presented to one eye for about a second while a blank field is presented to the other eye. Then a different, small image is abruptly shown, ''flashed'', to the other, second eye at the location corresponding to the image to the first eye. The image to the first eye disappears, even though it is still presented, and only the new image is perceived. The new image to the second eye ''suppresses'' perception of the image to the first. For example, if a vehicle is shown to the left eye for 1 second, and then a face is abruptly flashed to the right eye, the observer consciously sees first a vehicle and then a face. Note that the face is seen while the picture of the car is still present. If the order of presentation is reversed, the order of percept is reversed. The phenomenon of flash suppression seemed to have been known since the 19th century. The phenomena was described by McDougall in 1901 and utilized for an EEG experiment by Lansing in 1964. In 1984, Jeremy Wolfe characterized flash suppression in a systematic psychophysics study. Flash suppression is an example of

illusion An illusion is a distortion of the senses, which can reveal how the mind normally organizes and interprets sensory stimulation. Although illusions distort the human perception of reality, they are generally shared by most people. Illusions may o ...

s that render a highly visible image invisible and that are used to study the mechanisms of

conscious Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...

and non-conscious visual processing. Related perceptual illusions include

backward masking The concept of backward masking originated in psychoacoustics, referring to temporal masking of quiet sounds that occur moments before a louder sound. In cognitive psychology, visual backward masking involves presenting one visual stimulus (a "mask ...

binocular rivalry Binocular rivalry is a phenomenon of visual perception in which perception alternates between different images presented to each eye. When one image is presented to one eye and a very different image is presented to the other (also known as dich ...

motion induced blindness Motion Induced Blindness (MIB) is a phenomenon of visual disappearance or perceptual illusions observed in the lab, in which stationary visual stimuli disappear as if erased in front of an observer's eyes when masked with a moving background. Mo ...

and

motion-induced interocular suppression Motion-induced interocular suppression is a phenomenon in which when one eye is presented with a constantly moving visual pattern while the other eye is shown a stationary image, the stationary image is suppressed from awareness for long periods of ...

. The brain basis of flash suppression has been studied using microelectrode recordings in the visual brain of the macaque monkey and in the human medial temporal lobe.

Relationship with binocular rivalry

Flash suppression occurs due to the conflict between the inputs to the two eyes. When this conflict is sustained without any abrupt events, binocular rivalry occurs. In both flash suppression and binocular rivalry, perceptual conflict between the two eyes is required for the perceptual effect. If two similar images are used, fusion of the two images is experienced, rather than flash suppression or binocular rivalry. Despite some similarities in perceptual consequences, the neuronal mechanisms responsible for the two illusions can be different. For example, the strength (depth) of flash suppression seems much stronger than that of binocular rivalry. Comparative studies of the two methods are needed. Flash suppression has certain methodological advantages over binocular rivalry as a tool for probing conscious vision. Whereas the percept during binocular rivalry alternates stochastically, the percept during flash suppression is precisely controlled in time. Although flash suppression allows one to present an image to someone without his or her seeing it consciously, it requires a to-be-erased image to be presented for a fraction of second before introduction of a new image. This requirement limits the usage of flash suppression for the study of nonconscious visual processing.

Continuous flash suppression

A powerful variant of flash suppression is ''continuous flash suppression'', originally reported by Nao Tsuchiya and Christof Koch (2004) and Fang and He (2005). Here a small, fixed image in the first eye—say a gray-scale fearful face—is completely suppressed by a stream of constantly changing images flashed into the second eye (say a series of colorful Mondrian-scenes replaced every 0.1 sec by a new Mondrian pattern). This suppression can last for minutes, a remarkable testament to the fact that humans often do not see what is directly in front of their eyes. Continuous flash suppression is a useful method for psychologists and neuroscientists interested in studying the mechanisms of conscious and nonconscious visual processing. Whereas other visual illusions that render otherwise salient images invisible have their own shortcomings and advantages, continuous flash suppression has a number of advantages for wiping images from conscious vision. It can erase an image presented at the

fovea Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure. Human anatomy *Fovea centralis of the retina * Fovea buccalis or Dimple * Fovea of the femoral head * Trochlear fovea of the fr ...

(which usually is much more resistant to perceptual suppression, unlike, for example,

crowding Crowding (or visual crowding) is a perceptual phenomenon where the recognition of objects presented away from the fovea is impaired by the presence of other neighbouring objects (sometimes called "flankers"). It has been suggested that crowding ...

), in every trial (unlike

), for a longer duration (>1 sec, unlike

), with an excellent control of timing (unlike binocular rivalry). It has been widely exploited to tackle the scope and limits of unconscious processing.

Generalized flash suppression

The differences between flash suppression and

have been further emphasized by the finding that stimulus conflict between the two eyes is not a requirement to achieve visual suppression. The novel paradigm of generalized flash suppression (GFS) reported by Wilke, Logothetis and Leopold in 2003 demonstrates that any visual stimulus can be rendered invisible when presented outside the

for a certain amount of time, followed by the addition of a distracting second stimulus in its vicinity. This effect is strongest when the two stimuli are presented to (different regions in) opposite eyes, which suggests that it is somewhat related to binocular rivalry. At the same time, GFS shares similarities to

Troxler's fading Troxler's fading, also called Troxler fading or the Troxler effect, is an optical illusion affecting visual perception. When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point wi ...

and

. A recent study on the neuronal basis of GFS demonstrated that

neuronal A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. No ...

activity in early

visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...

was untouched by the perceptual effect, whereas

neurons A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

in higher areas altered their activity pattern during the

.Wilke, M., et al. (2006) Local field potential reflects perceptual suppression in monkey visual cortex. Proc Natl Acad Sci U S A 103, 17507-17512 Authors report that the disappearance of the stimulus triggered changes in the

local field potential Local field potentials (LFP) are transient electrical signals generated in nervous and other tissues by the summed and synchronous electrical activity of the individual cells (e.g. neurons) in that tissue. LFP are "extracellular" signals, meaning ...

s of all these areas, suggesting that the

perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...

during flash suppression is reflected in large parts of the brain.

References

Reviews
Lin, Z., He, S., Seeing the invisible: The scope and limits of unconscious processing in binocular rivalry, Progress in Neurobiology (2007)
{{doi, 10.1016/j.pneurobio.2008.09.002. Flash suppression *Sheinberg, D.L., and Logothetis, N.K. (1997) The role of temporal cortical areas in perceptual organization. Proc Natl Acad Sci U S A 94, 3408-3413 *Tsuchiya, N., et al. (2006) Depth of interocular suppression associated with continuous flash suppression, flash suppression, and binocular rivalry. J Vis 6, 1068-1078 Continuous Flash Suppression *Tsuchiya, N., and Koch, C. (2004) Continuous flash suppression. Vision Sciences Society, 4th annual meeting. Sarasota, FL. *Jiang, Y., et al. (2006) A gender- and sexual orientation-dependent spatial attentional effect of invisible images. Proc Natl Acad Sci U S A 103, 17048-17052 *Jiang, Y., and He, S. (2006) Cortical Responses to Invisible Faces: Dissociating Subsystems for Facial-Information Processing. Curr Biol 16, 2023-2029 *Kanai, R., et al. (2006) The scope and limits of top-down attention in unconscious visual processing. Curr Biol

External links

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