When Proactivity Fails: An Electrophysiological Study of Establishing Reference in Schizophrenia

Abstract

Background: Schizophrenia is characterized by abnormalities in referential communication, which may be linked to more general deficits in proactive cognitive control. We used event-related potentials to probe the timing and nature of the neural mechanisms engaged as people with schizophrenia linked pronouns to their preceding referents during word-by-word sentence comprehension.

Methods: We measured event-related potentials to pronouns in two-clause sentences in 16 people with schizophrenia and 20 demographically matched control participants. Our design crossed the number of potential referents (1-referent, 2-referent) with whether the pronoun matched the gender of its preceding referent(s) (matching, mismatching). This gave rise to four conditions: 1) 1-referent matching ("Edward took courses in accounting but he . . ."); 2) 2-referent matching ("Edward and Phillip took courses but he . . . "); 3) 1-referent mismatching ("Edward took courses in accounting but she . . ."); and 4) 2-referent mismatching ("Edward and Phillip took courses but she . . .").

Results: Consistent with previous findings, healthy control participants produced a larger left anteriorly distributed negativity between 400 and 600 ms to 2-referent matching than to 1-referent matching pronouns (the "Nref effect"). In contrast, people with schizophrenia produced a larger centroposterior positivity effect between 600 and 800 ms. Both patient and control groups produced a larger positivity between 400 and 800 ms to mismatching than to matching pronouns.

Conclusions: These findings suggest that proactive mechanisms of referential processing, reflected by the Nref effect, are impaired in schizophrenia, while reactive mechanisms, reflected by the positivity effects, are relatively spared. Indeed, patients may compensate for proactive deficits by retroactively engaging with context to influence the processing of inputs at a later stage of analysis.

Keywords: Comprehension; Discourse; ERPs; Language; Pronouns; Reference.

Figure 1. Trial presentation

The words were presented in white Arial font on a black background, with a viewing distance of 125cm and a visual angle of 2 degrees. Each trial began with a fixation cross followed by the sentence, presented word by word. The fixation cross and each word was presented for 400ms with an interstimulus interval of 150ms. The sentence-final word appeared with a period and was also presented for 400ms but was followed by a 700ms interstimulus interval, and then by a “?” which appeared in green font. This “?” cued participants to press either a “Yes” or “No” button, depending on whether they judged the sentence that they had just read was acceptable. After participants made their response, the word, “READY” in green font appeared on the screen. Participants then pressed a button to move them on to the next trial.

Figure 2. Electrode montage with regions used for analysis

For the purposes of statistical analyses, the scalp was divided into three-electrode regions. Regions in dark gray were part of the mid-regions omnibus ANOVA and regions in light gray were part of the peripheral regions omnibus ANOVA.

Figure 3. Contrast between 1-referent matching and 2-referent matching pronouns

Top: Grand-averaged waveforms evoked by pronouns in the control and schizophrenia groups at a left frontal site (F7) and a right parietal site (P4). Solid black lines indicate ERPs to the 1-referent matching pronouns; dotted blue lines indicate ERPs to the 2-referent matching pronouns. Negative voltage is plotted upwards for all ERP plots. Bottom: Voltage maps show differences between ERPs evoked by the pronouns in these two conditions between 400-600ms and between 600-800ms. In the 400-600ms time window, an Nref effect was seen in the control group but not in the schizophrenia group. In the 600-800ms time window, a late positivity effect was seen in the schizophrenia group but not in the control group.

Figure 4. Contrasts between 1-referent matching and the two types of mismatching pronouns

A. 1-referent mismatching vs. 1-referent matching. Grand-averaged waveforms evoked by pronouns in the control and schizophrenia groups at Cz and Pz. Solid black lines indicate ERPs to the 1-referent matching pronouns; dotted red lines indicate ERPs to the 1-referent mismatching pronouns. Negative voltage is plotted upwards for all ERP plots. Voltage maps show differences between ERPs evoked by the 1-referent mismatching and 1-referent matching pronouns between 400-600ms and 600-800mec. B. 2-referent mismatching vs. 1-referent matching. Grand-averaged waveforms evoked by pronouns in the control and schizophrenia groups at Cz and Pz. Solid black lines indicate ERPs to the 1-referent matching pronouns; dashed green lines indicate ERPs to the 2-referent mismatching pronouns. Negative voltage is plotted upwards for all ERP plots. Voltage maps show differences between ERPs evoked by the 2-referent mismatching and 1-referent matching pronouns between 400-600ms and 600-800ms.