NeurAstra
S02 → Altanube Pando
S06 → Nimbus.Archives
S07 → N400
S08 → AofAP
S07 → N400
The Spike of Fascinating & Unexpected
“It’s not what you look at that matters, it’s what you see”. Henry David Thoreau was accustomed to thinking about the human condition and its relation with nature, thanks to his experience of living outside of civilisation for years. We can consequently believe him when he recommends seeing through the apparent banality of things to see all the fascinating and unexpected aspects of nature. And, indeed, once we start to see carefully, there is an infinity of events in our surroundings that deserve more than just a quick look.
Who could have thought that a dormant underground plant specialised in growing and flowering when triggered by the heat, smoke, and nutrients released after a fire in order to attract birds and other pollinators to rebuild the area? Who could have imagined that a question such as “Why does this cloud have this shape?” could be so complex that it required the knowledge of scattering theory, wave propagation models, cloud physics, statistical mechanics, and spatial statistics? N400 picks from other systems’ peregrinations some of those intriguing facts that trigger spikes of curiosity and release waves of genuine interest to document them.And why N400?
Discover the fascinating & unexpected answer with our first spike.
—
SPIKE 00
→ N400.
© 1. Amoruso, L. et al. (2013) — N400 brain activations for words and actions. / 2. Kutas, Lindamood & Hillyard (1984) — Lexical-semantic (meaning) processing.
-100
-400
“Every morning, I take my coffee with cream and dog.”
Do these sentences sound peculiar? Can you note an anomaly?
Once you finished reading them, something in your brain reflected this anomaly. This something was imperceptible to the naked eye, but if by chance someone was monitoring the electrical activity of your scalp at this moment, they could have observed a negative electrical potential response peaking. Several electrical potentials—called event-related potentials (ERPs)—are generated in the brain when external stimuli activate the neuronal network. The words "cry" and "dog" here, quite unexpected in these contexts, were the stimulus provoking this negative electrical response—the N400 wave.
Since its discovery by Marta Kutas and Steven A. Hillyard in the 1980s, the N400 effect—among other ERP responses—has been extensively studied in the context of language processing. Characterised as a broad negative deflection that starts 200-300 milliseconds (ms) after an unexpected word has been presented visually or auditorily, the wave peaks after approximately 400 ms—hence its name, N400. Its negative nature in response to semantic violations highlights the importance and influence of context in language processing. Indeed, the fit of a word to its sentence context significantly impacts the N400 amplitude. Kutas and Hillyard could observe reduced amplitudes to more predictable words and increased amplitudes to less predictable words.
The amplitude is determined by a measure named cloze probability. The cloze probability is the proportion of people giving a particular word as the most likely completion of a sentence fragment. The cloze probability of a word is typically determined through cloze tasks, where participants are asked to fill in the blank in a sentence. Thanks to that approach, N400s have been recorded for different types of linguistic stimuli, including spoken, written, and signed words, as well as word-like items, such as pseudowords and familiar acronyms.
Interestingly, N400s were also observed in non-linguistic stimuli, like line drawings, faces, movies, gestures, and environmental sounds. It is not rare for musicians to use this characteristic in their compositions by starting a melodic pattern and finishing it unexpectedly, playing with the need for meaningful completion.
The study of N400s is undoubtedly helpful in providing information about the timing, classification and interactions of the different cognitive processes involved in natural language comprehension. Used as a clinical tool, it is also thought to help evaluate reading impairment and language disorders in children.
—