Beyond doubt, electroencephalography (EEG) is your means of choice when it comes to measuring brain activity associated with perception, cognitive behavior, and emotional processes. EEG can be considered as biometric sensor with the highest time resolution, revealing substantial insights into sub-second brain dynamics of engagement, motivation, frustration, cognitive workload, and further metrics associated with stimulus processing, action preparation, and execution (read our blog posts on EEG metrics and brain processes that can be measured with EEG).

Yet, in combination with other biosensors such as eye tracking, galvanic skin response (GSR) or facial recognition EEG can become even more powerful.

Here’s why.

EEG and eye tracking

Eye tracking provides immediate feedback on why specific brain activity emerged and which elements in the visual field induced the electrical activity. Taken by itself, EEG can convey merely a general idea as to why a person shows high workload or heightened emotional arousal at a certain point in time while being confronted with visual stimulus content. Without knowing where exactly the person is looking at in that very moment, it is patently impossible to identify clearly which particular visual stimulus triggered the increase in brain activity.

Complementing EEG with eye tracking can also reveal if a person missed to see a relevant cue that they were supposed to see. Even more, with synchronized eye tracking and EEG data at hand, you effectively can investigate if, for example, a stimulus in the periphery diverted the person’s attention without provoking a counteraction or movement that could have been picked up by the EEG.

Why you should combine EEG and eye tracking:

  1. Synchronizing eye tracking and EEG data allows you to detect the amount of workload or interest generated by a specific stimulus at a specific point in time. With eye tracking, you exactly know where, when, and what a person is looking at and which stimulus is driving the increased brain activity.
  2. Eye tracking delivers information about the exact orientation of the eyeball, thereby helping you to easily identify artifacts such as blinks, eye movements etc. and decontaminate your EEG data. Clean data allows clean responses to your research questions – in fact, there is no substitute for clean data (read our blog post on the basics of EEG data processing).
  3. Eye tracking delivers pupillometry arousal measures that you can combine with EEG-based intensity measures such as motivation and engagement in order to obtain comprehensive insights into cognitive processing.


EEG offers valuable information on the quality of an emotion, commonly referred to as valence, which can either be positive (“yay!”) or negative (“nay!”) – is a person drawn towards or rather drawn away by a certain stimulus? While EEG effectively measures the presence of an emotion, it reveals only little about the intensity of that emotion, which is generally referred to as arousal.

Why you should combine EEG and GSR:

One of the most sensitive markers for emotional arousal is galvanic skin response (GSR). GSR reflects the amount of sweat secretion from sweat glands triggered by emotional stimulation. To equally assess both the quality of an emotion and its intensity, it is worth combining EEG with skin conductance measures to link valence picked up by EEG with arousal derived from GSR.

EEG and facial expression analysis

Facial expression analysis impressively captures changes of facial features on a moment-to-moment basis, indicating which muscle groups are active during smiling, crying, being angry etc. While facial recognition certainly is a powerful measure to assess emotional valence based on facial movements, it doesn’t tell if the person truly is in a specific emotional state or mood – facial expression analysis can’t differentiate between a genuinely happy, hysterical or even phoney smile (click here for more details).

Why you should combine EEG and facial expression analysis:

Unlike facial recognition, EEG is able to monitor the global emotional state of a person, which cannot be controlled consciously (you can fake your smile, but you can’t trick your brain). Combining the two modalities allows you to get insights into both the moment-by-moment changes in emotional expression as well as variations in emotional states across a longer time span.

Whenever you synchronize EEG with other biometric sensors you can’t go wrong – you just add more specifics to the picture as every sensor contributes a valuable feature that you cannot get with any other. Who knows? You might even light upon a previously unknown, entirely new brain process driving exactly that specific emotion. Just think about it!

Get in touch with the team at iMotions and learn more about EEG and how to combine it with other biometric sensors to answer your research questions.