Task-specific change of unconscious neural priming in the cerebral language network

Abstract

We explored the impact of task context on subliminal neural priming using functional magnetic resonance imaging. The repetition of words during semantic categorization produced activation reduction in the left middle temporal gyrus previously associated with semantic-level representation and dorsal premotor cortex. By contrast, reading aloud produced repetition enhancement in the left inferior parietal lobe associated with print-to-sound conversion and ventral premotor cortex. Analyses of effective connectivity revealed that the task set for reading generated reciprocal excitatory connections between the left inferior parietal and superior temporal regions, reflecting the audiovisual integration required for vocalization, whereas categorization did not produce such backward projection to posterior regions. Thus, masked repetition priming involves two distinct components in the taskspecific neural streams, one in the parietotemporal cortex for task-specific word processing and the other in the premotor cortex for behavioral response preparation. The top-down influence of task sets further changes the directions of the unconscious priming in the entire cerebral circuitry for reading.effective connectivity ͉ masked priming ͉ reading ͉ repetition suppression and enhancement ͉ task set U nconscious exposure to written words facilitates the subsequent conscious processing of the same stimuli, a behavioral phenomenon known as subliminal priming (1). At the neural level, such response facilitation is mediated in part by the visual word recognition system in the left occipitotemporal cortex. By the use of functional magnetic resonance imaging (fMRI), the hierarchical architecture of this region has been demonstrated as a serial, posterior-to-anterior processing stream for increasingly abstract representations (2-4). For instance, a shape-invariant neural code for letter strings has been found at the left middle fusiform gyrus (FG) showing response attenuation to the repeated presentation of words and word roots, whereas a more anterolateral sector of the posterior temporal cortex exhibits sensitivity to semantic-level representations (5). For nonalphabetic languages, the repetition of logographic Kanji elicits a similar neural adaptation at the left middle temporal gyrus (MTG) associated with semantic knowledge (6).Importantly, most previous work measured the unconscious neural priming under a single word-recognition task tapping lexicosemantic representation (5-7). Thus, it remains open whether, and to what extent, the adoption of a voluntary task set modulates subliminal priming in the cerebral reading network. In fact, such an influence of intentional behavior on nonconscious cognitive processing has been proposed by neurocognitive models of consciousness (8, 9). Our transcranial magnetic stimulation study has further demonstrated a differential effect of task on subliminal priming (10). However, no previous work has examined the entire extent of the cerebral structures involved in unconscious word processing as a fu...

Unconscious Activation of the Prefrontal No-Go Network

“…Therefore, the instructed task set of the participant required a deep level of information processing (incorporating prefrontal cortex) of the unconscious stimulus. Recently, we (van Gaal et al, 2008) and others (Nakamura et al, 2006(Nakamura et al, , 2007 have shown that the instructed top-down task set strongly determines the processing routes taken by masked stimuli. The combination of both factors allowed us to tap more directly into the possible scope and depth of unconscious information processing than previous studies using the masking task (or related paradigms).…”

Frontal Cortex Mediates Unconsciously Triggered Inhibitory Control

“…Previous behavioral and imaging studies have shown that the way unconscious stimuli are processed is affected by top-down settings of the cognitive system, such as temporal/spatial atten-tion, task strategy and the task being performed (Naccache et al, 2002;Kunde et al, 2003;Sumner et al, 2006;Nakamura et al, 2007). To test whether the relevance of the masked No-Go signal influences the depth to which it is processed, we performed a control experiment, in which the physically identical masked stimulus was task irrelevant (see Fig.…”

Theories and methods in the scientific study of consciousness

“…Opinions however start to deviate when you ask where or when along the chain of processing unconscious sensory information becomes a conscious experience. Some theories make an even more subtle subdivision into unconscious/subliminal, pre-conscious and conscious stages (Dehaene, Changeux, Naccache, Sackur, & Sergent, 2006;Kouider & Dehaene, 2007) or, as mentioned before, into unconscious, phenomenally conscious and access conscious states (Block, 1995(Block, , 1996(Block, , 2005aLamme, 2003Lamme, , 2006Lamme, , 2010. Is this merely a matter of terminology (Block, 2005b)?…”

“…On the other hand, the nodes that are in principle active enough to communicate with the workspace neurons (the potential broadcasters) are called 'preconscious' . They are thought to require an attentional boost to become part of the network that involves the workspace neurons and constitutes (access) consciousness (Dehaene, Changeux, Naccache, Sackur, & Sergent, 2006;Kouider & Dehaene, 2007). As such, the preconscious nodes can perhaps be thought of as constituting phenomenal consciousness.…”

“…The depth of processing of the masked stimulus can also be inferred by subsequent priming effects. For example a masked word can prime observers on a sentence completion task, meaning that some semantic processing of the mask has occurred, even though the observer remains completely unaware of the masked prime Greenwald, Draine, & Abrams, 1996;Marcel, 1983;Nakamura, Dehaene, Jobert, Le Bihan, & Kouider, 2007).…”