Spatiotemporal dynamics of orthographic and lexical processing in the ventral visual pathway

From letters to composed concepts: A magnetoencephalography study of reading

“…These initially discriminated between high and low visual noise properties of the stimuli, in the lateral occipital and posterior fusiform, and then differentiated letter- and symbol-string stimuli in the middle to anterior fusiform gyrus, with words exclusively diverging from length-matched symbol strings (while single letters did not) in the most anterior sections of the left fusiform. This sequence of responses thus replicates previous evidence (e.g., Gwilliams et al, 2016; Vinckier et al, 2007; Woolnough et al, 2020) for a transition along the ventral surfaces of left occipital and temporal cortex from visual and orthographic to lexical processing.…”

“…In the most anterior fusiform ROI, the waveforms suggested a divergence of at least 200 ms between words and symbols. In an examination of mid-fusiform responses to words and word-like stimuli, Woolnough et al, (2020) found that, in sentence reading, responses to high frequency words diverged from pseudowords by approximately 180 ms after onset, for a duration of upwards of 300 ms, congruent with the present findings. Low frequency words, on the other hand, did not diverge from pseudowords until later in the epoch, which the authors interpreted as evidence that the mid-fusiform maps visually presented word inputs to entries in the mental lexicon.…”

“…This was exclusively in its responses to adjective-noun stimuli and manifested as relatively early (150-300 ms) dissociations of two-word phrases from two-word lists, and one-word items (see Figure 2). We highlight this as a tentative site for the culmination of a visual-to-conceptual transformation in the anterior fusiform (similar to the proposal of Woolnough et al, 2020), which enables the meaning of a visually presented phrasal head (e.g., boat) to quickly feed into coarse conceptual combination operations (e.g., red + boat). The parallel timing of adjective-noun effects in the posterior and lateral anterior temporal lobe (also appearing between 150 and 300 ms) suggests that related information may be relayed to these perisylvian areas, either from the anterior terminus of this stream or earlier points along it.…”

“…Another issue relevant to neuroanatomical accounts of semantic knowledge, and the way this knowledge is used in language comprehension, concerns how neural responses related to the sensory processing of a word feed into hub regions that are proposed underpin conceptual knowledge of that word’s meaning. This is a particularly pertinent question in visual reading, as the proposed ventral location of the ATL hub (Chen et al, 2016) lays in the vicinity of occipital and temporal lobe areas known to support visual word recognition (Cohen et al, 2002; Dehaene et al, 2010; Tarkiainen et al, 1999; Taylor et al, 2019; Woolnough et al, 2020). Previous MEG studies of reading, which provide the temporal resolution to tease apart distinct processing stages in word recognition (Pylkkänen, Stringfellow, & Marantz, 2002; Tarkiainen et al, 1999), have identified a consistent sequence of responses along the left ventral occipital and temporal lobes, progressing from sensitivities to low-level visual properties to the discrimination of word vs. symbol-string stimuli in the middle and anterior fusiform and inferior temporal gyri (Gwilliams, Lewis, & Marantz, 2016; Neophytou et al, 2018; Tarkiainen et al, 1999).…”

“…Chan et al (2011) demonstrated that a first pass of activity to the ventral anterior temporal lobe, in response to visually presented words, enabled the discrimination of semantic classes (objects vs. animals) by as early as 130 ms after onset. While this was posited to be a posterior-to-anterior flow of information, Woolnough et al, (2020) recently highlighted the possibility of the reverse, finding that after left middle fusiform discriminated between words and non-words, there was a presumptive backward (anterior to posterior) pass of lexical processing. Woolnough et al, also found that the onset latency of the middle fusiform discrimination between words and non-words was sensitive to word frequency, such that lower frequency words led to later discrimination; a pattern they proposed indexed a search in one’s mental lexicon to match visual letter-strings to a meaning.…”