Neural capacity limits during unconscious semantic processing

Abstract

A growing body of neuroimaging data suggests that direct measurements of brain activity can reveal subliminal effects that remain invisible with behavior measures alone. We examined whether sentence comprehension processes could be triggered by a sequence of masked words. On each trial, participants viewed a rapid sequence of masked or unmasked words, including a subject noun, three adverbs and followed by a visible target verb. To probe the capacity limits of unconscious processing, we measured event-related potentials associated with the semantic congruency between the noun and the verb, while varying the subject position in each sentence. Unmasked sentences produced significant behavioral effects of congruency, paralleled by robust N400 effects, independently of subject-verb distance. By contrast, masked sentences produced no behavioral effect and elicited N400 effects only when subjects and verbs were separated by 0 or 1 word. The present results suggest that semantic integration of multiple words can occur unconsciously only if the distance between the words to be integrated does not exceed two words. Although the possibility remains that even longer sequence of invisible words may produce similar neural effects in different experimental settings, our ERP data show that only conscious perception gives access to a buffer that enables robust sentence-level processing independently of temporal distance.

Probing the limits of activity-silent non-conscious working memory

“…It has proven difficult to put upper bounds on the depth of non-conscious processing. Non-conscious signals tend to affect a wide range of behaviors and trigger activity in many different brain areas, including the prefrontal cortex (27,28). Recent work on non-conscious WM has even called into question basic assumptions regarding the nature of non-conscious processes, suggesting that non-conscious stimuli may be maintained much longer than previously thought (7)(8)(9)(10)26).…”

No language unification without neural feedback: How awareness affects sentence processing

“…Still, in our paradigm, single words could occur in different prime positions. Previous studies have shown that the Stimulus Onset Asynchrony (SOA) between prime and target affects the strength of semantic priming (Greenwald et al, 1996;Kiefer, 2002;Kiefer and Brendel, 2006;Nakamura et al, 2018). Therefore, we investigated whether prime position affected N400 amplitude.…”

“…not good), can be performed under masked processing van Gaal et al, 2014), although only after considerable training of the negation process (van Gaal et al, 2014). Some authors have suggested that masked combinatorial processing occurs for entire sentences Nakamura et al, 2018;Sklar et al, 2012), even though evidence is mixed (Rabagliati et al, 2018;Yang et al, 2017).…”

Probing the limits of activity-silent non-conscious working memory

“…It has proven notoriously difficult to put clear upper bounds on the depth of nonconscious processing. Non-conscious signals tend to affect a wide range of behaviors and trigger activity in many different brain areas, including the prefrontal cortex (van Gaal et al, 2010;Naccache and Dehaene, 2001;Nakamura et al, 2018;van Vugt et al, 2018). Recent work on non-conscious WM has even called into question some of the most basic assumptions regarding the nature of non-conscious processes, suggesting that non-conscious signals may be maintained much longer than previously thought (Bergström and Eriksson, 2017;King et al, 2016;Soto et al, 2011;Trübutschek et al, 2017).…”