Steady state topography
Encyclopedia
Steady State Topography is a methodology for observing and measuring human brain activity that was first described by Richard Silberstein and co-workers in 1990. While SST has been principally used as a cognitive neuroscience
research methodology it has also found commercial application in the field of neuromarketing
and consumer neuroscience
in such areas as brand communication, media research and entertainment. In a typical SST study, brain electrical activity (electroencephalogram or EEG
) is recorded while participants view audio visual material and/or perform a psychological task. Simultaneously, a dim sinusoidal visual flicker is presented in the visual periphery. The sinusoidal flicker elicits an oscillatory brain electrical response known as the Steady State Visually Evoked Potential
(SSVEP). Task related changes in brain activity in the vicinity of the recording site are then determined from SSVEP measurements at that site. One of the most important features of the SST methodology is the ability to measure variations in the delay (latency) between the stimulus and the SSVEP response over extended periods of time. This offers a unique window into brain function based on neural processing speed as opposed to the more common EEG amplitude indicators of brain activity.
Three specific features of the SST methodology make it a useful technique in cognitive neuroscience research as well as neuroscience-based communication research.
1. High temporal resolution: the SST methodology is able to continuously track rapid changes in brain activity over an extended period of time. This is an important feature as many changes in brain function associated with a cognitive task can occur in less than a second.
2. High signal-to-noise ratio
and resistance to interference and ‘noise’. The SST methodology is able to tolerate high levels of noise or interference due to such things as head movements, muscle tension, blinks and eye movements. This makes SST well suited to cognitive studies where eye, head and body movements occur as a matter of course.
3. The high signal-to-noise ratio
means that it is possible to work with data based on a single trial per individual as opposed to the typical situation encountered in event-related potential
(ERP) or event related fMRI studies where there is a need to average multiple trials recorded from each individual to achieve adequate signal-to-noise ratio levels.
techniques are used to extract the amplitude and the phase of the SSVEP at the stimulus frequency. When the stimulus frequency is in the alpha frequency range (8 Hz – 13 Hz), the SSVEP can be recorded from the occipital region and also from other ‘non-visual’ regions such as the frontal and prefrontal cortex and the temporal and parietal cortex.
Most SST studies use a visual stimulus in the upper alpha frequency range
(10 Hz – 13 Hz) or gamma frequency range
(30 Hz – 100 Hz) to elicit the SSVEP. Changes in the SSVEP amplitude and phase coinciding with a cognitive task or other material such as a television advertisement are then interpreted as changes in regional brain activity associated with the cognitive task. SSVEP amplitude changes are interpreted in a similar fashion to changes in upper alpha
EEG amplitude while changes in SSVEP phase are expressed as changes in SSVEP latency. An SSVEP latency reduction is interpreted physiologically as increased synaptic excitation in the neural networks generating the SSVEP implying increased regional brain activity and vice versa.
, emotional processes, as well as disturbed brain functions such as schizophrenia
and attention deficit hyperactivity disorder
, neuromarketing
, media and entertainment research. Neuro-Insight holds the exclusive world-wide rights to the SST methodology in the communication services field while Mediaplus has been licensed to offer SST based communication services in Germany, Austria and Switzerland. In this application area SST is used to measure second by second changes in brain activity associated with a wide range of communication media. By measuring brain activity at a number of scalp locations it is possible to estimate second by second changes in a number of relevant psychological parameters including, Long-term Memory Encoding, Engagement (sense of personal relevance), Motivational Valence (whether the material attracts or repels the viewer) as well as Emotional Intensity (arousal) and Visual Attention. Neuro-Insight research indicates that a major SST indicator of advertising effectiveness is the level of long-term memory encoding of the key message or the brand in the advertisement.
Cognitive neuroscience
Cognitive neuroscience is an academic field concerned with the scientific study of biological substrates underlying cognition, with a specific focus on the neural substrates of mental processes. It addresses the questions of how psychological/cognitive functions are produced by the brain...
research methodology it has also found commercial application in the field of neuromarketing
Neuromarketing
Neuromarketing is a new field of marketing that studies consumers' sensorimotor, cognitive, and affective response to marketing stimuli. Researchers use technologies such as functional magnetic resonance imaging to measure changes in activity in parts of the brain, electroencephalography and...
and consumer neuroscience
Consumer neuroscience
Consumer neuroscience is the combination of consumer research with modern neuroscience. The goal of the field is to find neural explanations for consumer behaviors in both normal and diseased individuals.-Consumer Research:...
in such areas as brand communication, media research and entertainment. In a typical SST study, brain electrical activity (electroencephalogram or EEG
EEG
EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...
) is recorded while participants view audio visual material and/or perform a psychological task. Simultaneously, a dim sinusoidal visual flicker is presented in the visual periphery. The sinusoidal flicker elicits an oscillatory brain electrical response known as the Steady State Visually Evoked Potential
Steady state visually evoked potential
Steady State Visually Evoked Potentials are signals that are natural responses to visual stimulation at specific frequencies. When the retina is excited by a visual stimulus ranging from 3.5 Hz to 75 Hz, the brain generates electrical activity at the same frequency of the visual stimulus.This...
(SSVEP). Task related changes in brain activity in the vicinity of the recording site are then determined from SSVEP measurements at that site. One of the most important features of the SST methodology is the ability to measure variations in the delay (latency) between the stimulus and the SSVEP response over extended periods of time. This offers a unique window into brain function based on neural processing speed as opposed to the more common EEG amplitude indicators of brain activity.
Three specific features of the SST methodology make it a useful technique in cognitive neuroscience research as well as neuroscience-based communication research.
1. High temporal resolution: the SST methodology is able to continuously track rapid changes in brain activity over an extended period of time. This is an important feature as many changes in brain function associated with a cognitive task can occur in less than a second.
2. High signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
and resistance to interference and ‘noise’. The SST methodology is able to tolerate high levels of noise or interference due to such things as head movements, muscle tension, blinks and eye movements. This makes SST well suited to cognitive studies where eye, head and body movements occur as a matter of course.
3. The high signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
means that it is possible to work with data based on a single trial per individual as opposed to the typical situation encountered in event-related potential
Event-related potential
An event-related potential is any measured brain response that is directly the result of a thought or perception. More formally, it is any stereotyped electrophysiological response to an internal or external stimulus....
(ERP) or event related fMRI studies where there is a need to average multiple trials recorded from each individual to achieve adequate signal-to-noise ratio levels.
Main Paradigm
In applying the SST methodology audio visual material is presented simultaneously with a peripheral, spatially diffuse visual flicker and FourierFourier
Fourier most commonly refers to Joseph Fourier , French mathematician and physicist, or the mathematics, physics, and engineering terms named in his honor for his work on the concepts underlying them:In mathematics:...
techniques are used to extract the amplitude and the phase of the SSVEP at the stimulus frequency. When the stimulus frequency is in the alpha frequency range (8 Hz – 13 Hz), the SSVEP can be recorded from the occipital region and also from other ‘non-visual’ regions such as the frontal and prefrontal cortex and the temporal and parietal cortex.
Most SST studies use a visual stimulus in the upper alpha frequency range
Electroencephalography
Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
(10 Hz – 13 Hz) or gamma frequency range
Gamma wave
A gamma wave is a pattern of neural oscillation in humans with a frequency between 25 to 100 Hz, though 40 Hz is prototypical.According to a popular theory, gamma waves may be implicated in creating the unity of conscious perception...
(30 Hz – 100 Hz) to elicit the SSVEP. Changes in the SSVEP amplitude and phase coinciding with a cognitive task or other material such as a television advertisement are then interpreted as changes in regional brain activity associated with the cognitive task. SSVEP amplitude changes are interpreted in a similar fashion to changes in upper alpha
Alpha wave
Alpha waves are neural oscillations in the frequency range of 8–12 Hz arising from synchronous and coherent electrical activity of thalamic pacemaker cells in humans...
EEG amplitude while changes in SSVEP phase are expressed as changes in SSVEP latency. An SSVEP latency reduction is interpreted physiologically as increased synaptic excitation in the neural networks generating the SSVEP implying increased regional brain activity and vice versa.
Scientific and Biomedical Applications
The SST methodology has been used to examine normal brain function associated with visual vigilance, working memory, long-term memoryLong-term memory
Long-term memory is memory in which associations among items are stored, as part of the theory of a dual-store memory model. According to the theory, long term memory differs structurally and functionally from working memory or short-term memory, which ostensibly stores items for only around 20–30...
, emotional processes, as well as disturbed brain functions such as schizophrenia
Schizophrenia
Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
and attention deficit hyperactivity disorder
Commercial Applications
The SST methodology has been applied commercially in areas such as consumer neuroscienceConsumer neuroscience
Consumer neuroscience is the combination of consumer research with modern neuroscience. The goal of the field is to find neural explanations for consumer behaviors in both normal and diseased individuals.-Consumer Research:...
, neuromarketing
Neuromarketing
Neuromarketing is a new field of marketing that studies consumers' sensorimotor, cognitive, and affective response to marketing stimuli. Researchers use technologies such as functional magnetic resonance imaging to measure changes in activity in parts of the brain, electroencephalography and...
, media and entertainment research. Neuro-Insight holds the exclusive world-wide rights to the SST methodology in the communication services field while Mediaplus has been licensed to offer SST based communication services in Germany, Austria and Switzerland. In this application area SST is used to measure second by second changes in brain activity associated with a wide range of communication media. By measuring brain activity at a number of scalp locations it is possible to estimate second by second changes in a number of relevant psychological parameters including, Long-term Memory Encoding, Engagement (sense of personal relevance), Motivational Valence (whether the material attracts or repels the viewer) as well as Emotional Intensity (arousal) and Visual Attention. Neuro-Insight research indicates that a major SST indicator of advertising effectiveness is the level of long-term memory encoding of the key message or the brand in the advertisement.