Examining the sentence superiority effect for sentences presented and reported in forwards or backwards order

Sentence superiority in the reading brain

When a sequence of written words is briefly presented and participants are asked to identify just one word at a post-cued location, then word identification accuracy is higher when the word is presented in a grammatically correct sequence compared with an ungrammatical sequence. This sentence superiority effect has been reported in several behavioral studies and two EEG investigations. Taken together, the results of these studies support the hypothesis that the sentence superiority effect is primarily driven by rapid access to a sentence-level representation via partial word identification processes that operate in parallel over several words. Here we used MEG to examine the neural structures involved in this early stage of written sentence processing, and to further specify the timing of the different processes involved. Source activities over time showed grammatical vs. ungrammatical differences first in the left inferior frontal gyrus (IFG: 321-406 ms), then the left anterior temporal lobe (ATL: 466-531 ms), and finally in both left IFG (549-602 ms) and left posterior superior temporal gyrus (pSTG: 553-622 ms). We interpret the early IFG activity as reflecting the rapid bottom-up activation of sentence-level representations, including syntax, enabled by partly parallel word processing. Subsequent activity in ATL and pSTG is thought to reflect the constraints imposed by such sentence-level representations on on-going word-based semantic activation (ATL), and the subsequent development of a more detailed sentence-level representation (pSTG). These results provide further support for a cascaded interactive-activation account of sentence reading.

Strength of target source segregation cues affects the outcome of speech-on-speech masking experiments

In speech-on-speech listening experiments, some means for designating which talker is the "target" must be provided for the listener to perform better than chance. However, the relative strength of the segregation variables designating the target could affect the results of the experiment. Here, we examine the interaction of two source segregation variables-spatial separation and talker gender differences-and demonstrate that the relative strengths of these cues may affect the interpretation of the results. Participants listened to sentence pairs spoken by different-gender target and masker talkers, presented naturally or vocoded (degrading gender cues), either colocated or spatially separated. Target and masker words were temporally interleaved to eliminate energetic masking in either an every-other-word or randomized order of presentation. Results showed that the order of interleaving had no effect on recall performance. For natural speech with strong talker gender cues, spatial separation of sources yielded no improvement in performance. For vocoded speech with degraded talker gender cues, performance improved significantly with spatial separation of sources. These findings reveal that listeners may shift among target source segregation cues contingent on cue viability. Finally, performance was poor when the target was designated after stimulus presentation, indicating strong reliance on the cues.