Early top-down modulation in visual word form processing: Evidence from an intracranial SEEG study

Visual word recognition, at a minimum, involves the processing of word form and lexical information. Opinions diverge on the spatiotemporal distribution of and interaction between the two types of information. Feedforward theory argues that they are processed sequentially, while interactive theory advocates that lexical information is processed fast and modulates early word form processing. To distinguish the two theories, we applied stereoelectroencephalography (SEEG) to 33 human adults with epilepsy (25 males and 8 females) during visual lexical decisions. The stimuli included real words (RWs), pseudowords (PWs) with legal radical positions, nonwords (NWs) with illegal radical positions, and stroked-changed words (SWs) in Chinese. Word form and lexical processing were measured by the word form effect (PW vs. NW) and lexical effect (RW vs. PW), respectively. Gamma-band (60 similar to 140 Hz) SEEG activity was treated as an electrophysiological measure. A word form effect was found in eight left brain regions (i.e., the inferior parietal lobe, insula, fusiform, inferior temporal, middle temporal, middle occipital, precentral and postcentral gyri) from 50 ms poststimulus onset, while a lexical effect was observed in five left brain regions (i.e., the calcarine, middle temporal, superior temporal, precentral and postcentral gyri) from 100 ms poststimulus onset. The two effects overlapped in the precentral (300 similar to 500 ms) and postcentral (100 similar to 200 ms and 250 similar to 600 ms) gyri. Moreover, high-level regions provide early feedback to word form regions. These results demonstrate that lexical processing occurs early and modulates word form recognition, providing vital supportive evidence for interactive theory.

Automated summary

In a study utilizing stereoelectroencephalography on 33 epilepsy patients during visual lexical decisions, it was found that lexical processing occurs early and modulates word form recognition, providing supportive evidence for the interactive theory of word recognition.