Source: Laboratories of Sarah I. Gimbel and Jonas T. Kaplan— University of Southern California

Understanding language is one of the most complex cognitive tasks that humans are capable of. Given the incredible amount of possible choices when combining individual words to form meaning in sentences, it is crucial that the brain is able to identify when words form coherent combinations and when an anomaly appears that undermines meaning. Extensive research has shown that certain scalp-recorded electrical events are sensitive to deviations in this kind of expectation. Importantly, these electrical signatures of incongruity are specific to unexpected meanings, and are therefore different from the brain's general responses to other kinds of anomalies.

The neurophysiological correlates of semantic incongruity have been experimentally examined through the use of paradigms that present semantically congruent and incongruent ends to sentences. Originally introduced in 1980, the semantic incongruity task presents the participant with a series of sentences that end with either a congruent or incongruent word. To test that the response is from semantic incongruity and not more generally due to surprise, some sentences included words presented in a different size.¹ The semantically incongruent end to a sentence has been shown to elicit specific electrical events that are recordable at the scalp known as event-related potentials (ERPs). An ERP is the measured brain response resulting from a specific sensory, cognitive, or motor event. ERPs are measured using electroencephalography (EEG), a noninvasive means of evaluating brain function in patients with disease and normally functioning individuals. A specific ERP component found across the scalp, known as the N400, shows greater amplitude in response to semantically incongruent events. The N400 is a negative-going deflection in the EEG signal that occurs about between 250 and 400 ms after stimulus onset. In general, early potentials reflect sensory-motor processing, while later potentials like the N400 reflect cognitive processing.

In this video, we show how to administer a semantic incongruity task using EEG. The video will cover the setup and administration of EEG, and analysis of ERPs related to both control and target stimuli in the semantic incongruity. In this task, participants are set up with the EEG electrodes, then brain activity is recorded while they view control sentences and semantically incongruent sentences. The EEG procedure is similar to that of Habibi et al.,¹ and the task is modeled after Kutas and Hillyard.² When the ERPs are averaged across the congruous and incongruous sentences, the neural correlates of each event can be compared in a selected time window.