Exhibit 15.11 Electrode locations of for EEG recording according to the international 10-20 system. (Source: Wikipedia).
The roughly 100 billion interconnected neurons in
our brain constantly emit electric signals. These signals comprise a mixture of several
underlying base frequencies, lying between 1 to 80 Hz that vary in magnitude (voltage).
They are classified into frequency bands associated with different cognitive-affective
states of mind.
Of the different ways that these synaptic waves are analysed by EEG devices,
frequency-based analysis is of greatest relevance to consumer research. It is better
suited for detecting emotions, thoughts, and motivations in relation to the testing of
advertising and packaging, product testing, and the design and navigation of websites. By
analysing the different frequency bands of the brain's electrical activity, EEG can provide
insights into the cognitive and emotional responses of consumers to marketing stimuli.
The frequencies are classified into these five bands:
- Delta (1 – 4 Hz): These slow, high amplitude brainwaves are present only when the subject is in deep sleep, i.e.,
technically speaking, stage 3 or non-REM (non-rapid eye movement) sleep. The stronger
the delta rhythm, the deeper the sleep. Since memory consolidation occurs while we sleep, delta
frequencies are associated with the formation of long-term memories, including
biographic memory and procedural memory.
- Theta (4 – 8 Hz): Oscillations in the theta range relate to mental workload and working memory.
They correlate with the level of difficulty of the mental task, with theta power
increasing as the task becomes more challenging. Theta activity is also associated
with cognitive processing, attention, and memory retrieval. In consumer research,
theta rhythms can be used to assess the level of cognitive effort required to process
marketing stimuli such as product information, pricing, and promotional offers.
- Alpha (8 – 12 Hz): These frequencies correlate with mental and
physical relaxation with eyes closed. When alpha activity is prominent, the
brain is in a state of rest and is not processing any specific information.
Conversely, alpha blocking or suppression relates to activities with eyes open when the brain is focussed and ready
to absorb information. When alpha waves decrease, it indicates that the brain is
engaged in active mental processing. Alpha rhythms are commonly used in consumer
research to assess the level of attention and engagement with marketing stimuli such
as advertisements, product packaging, and website designs.
- Beta (12 – 25 Hz): Frequencies in this range correlate with active or anxious thinking that requires
concentration. Beta activity is associated with cognitive functions such as attention,
focus, and working memory. It is also observed when the subject is thinking about
executing movements demanding motor skills. In consumer research, beta rhythms can be
used to assess the level of mental effort and engagement required to process marketing
stimuli such as advertisements, product packaging, and website designs.
- Gamma (above 25 Hz): This is a relatively grey area. There is lack of consensus among researchers as
to what mental activities these frequencies relate to.
The analysis can be broken down in the following stages:
- Clean and prepare the data.
- Breakdown the total duration of the analysis into smaller time periods or
epochs. For instance, a one-minute advertisement is broken into 60 two-second epochs, each
overlapping by 1 second.
Exhibit 15.13 Example of the EEG rhythms in frequency domain.
- Fast Fourier Transformation (FFT) is applied to transform the EEG signals
for the epochs into their frequency domain, which can be represented by frequency-amplitude
charts similar to one in Exhibit 15.12. This data is captured across epochs, across
electrodes and across respondents. By analysing the frequency distribution of the EEG signals,
researchers can gain insights into the cognitive and emotional responses of consumers to
marketing stimuli.
- Compute the metrics. Some of the better-known metrics include:
- frontal asymmetry index for approach-avoidance behaviour,
- cognitive state for engagement and distraction,
- cognitive workload.
More information about these metrics is provided in the next section.
- Plot the metrics across the epochs (time periods) to visualize how the state of mind varies over the
duration of the stimulus. The data is usually averaged across respondents, and for an overall index, it is averaged
over the epochs.
As can be seen from the findings of the studies on
Coca-Cola and
Carls Jr TVCs
(shown in exhibits 15.14 and 15.15), the research combines EEG with eye tracking
in order to determine which visuals are eliciting a higher degree of cognitive engagement and
arousal. The EEG signals from the electrodes are aggregated into emotional states, such as
arousal, motivation, and cognitive load, for the Carls Jr TVC. These emotional states are then
tracked over the course of the advertisements, providing analysts with valuable insights into
how viewers are responding to the content.