Eyes on words: A fixation-related fMRI study of the left occipito-temporal cortex during self-paced silent reading of words and pseudowords

Abstract

The predominant finding of studies assessing the response of the left ventral occipito-temporal cortex (vOT) to familiar words and to unfamiliar, but pronounceable letter strings (pseudowords) is higher activation for pseudowords. One explanation for this finding is that readers automatically generate predictions about a letter string's identity - pseudowords mismatch these predictions and the higher vOT activation is interpreted as reflecting the resultant prediction errors. The majority of studies, however, administered tasks which imposed demands above and beyond the intrinsic requirements of visual word recognition. The present study assessed the response of the left vOT to words and pseudowords by using the onset of the first fixation on a stimulus as time point for modeling the BOLD signal (fixation-related fMRI). This method allowed us to assess the neural correlates of self-paced silent reading with minimal task demands and natural exposure durations. In contrast to the predominantly reported higher vOT activation for pseudowords, we found higher activation for words. This finding is at odds with the expectation of higher vOT activation for pseudowords due to automatically generated predictions and the accompanying elevation of prediction errors. Our finding conforms to an alternative explanation which considers such top-down processing to be non-automatic and task-dependent.

Figure 1. Experimental setup.

After fixating the fixation cross at the left side of the screen, participants silently read the words and pseudowords or scanned the slash-strings. Fixating the cross at the right side of the screen terminated the trial. The red fixation cross of a catch trial required a button press within 2 sec. For the purpose of illustration, prototypical fixation locations are depicted in the experimental trial. The word (w) and pseudoword (pw) sequence in the example is w, pw, pw, w, w.

Figure 2. The surface rendering of the lateral and ventral (z = −14) views depicts the activation of words (red) and pseudowords (blue) contrasted against slash-string scanning.

The overlap in the activation of words and pseudowords appears in cyan.

Figure 3. ROI analyses in left ventral visual stream.

The left panel illustrates the location of the posterior-to-anterior ROIs. The middle column provides the xyz-coordinates of the ROIs and illustrates the event-related time course of the signal change for words, pseudowords and slash-strings. The polygons denote 1 standard error of the mean (SEM). The right column depicts the mean percent signal change (error bar = 1 SEM) with indications about significant differences between the words, pseudowords and the slash-strings: ***p < .001; **p < .01 and *p < .05.