When speakers name a picture (e.g., “duck”), a distractor word phonologically related to an alternative name (e.g., “birch” related to “bird”) slows down naming responses compared with an unrelated distractor word. This interference effect obtained with the picture–word interference task is assumed to reflect the phonological coactivation of close semantic competitors and is critical for evaluating contemporary models of word production. In this study, we determined the ERP signature of this effect in immediate and delayed versions of the picture–word interference task. ERPs revealed a differential processing of related and unrelated distractors: an early (305–436 msec) and a late (537–713 msec) negativity for related as compared with unrelated distractors. In the behavioral data, the interference effect was only found in immediate naming, whereas its ERP signature was also present in delayed naming. The time window of the earlier ERP effect suggests that the behavioral interference effect indeed emerges at a phonological processing level, whereas the functional significance of the later ERP effect is as yet not clear. The finding of a robust ERP correlate of phonological coactivation might facilitate future research on lexical processing in word production.

The aim of the current study was to shed further light on control processes that shape semantic access and selection during speech production. These processes have been linked to differential cortical activation in the left inferior frontal gyrus (IFG) and the left middle temporal gyrus (MTG); however, the particular function of these regions is not yet completely elucidated. We applied transcranial direct current stimulation to the left IFG and the left MTG (or sham stimulation) while participants named pictures in the presence of associatively related, categorically related, or unrelated distractor words. This direct modulation of target regions can help to better delineate the functional role of these regions in lexico-semantic selection. Independent of stimulation, the data show interference (i.e., longer naming latencies) with categorically related distractors and facilitation (i.e., shorter naming latencies) with associatively related distractors. Importantly, stimulation location interacted with the associative effect. Whereas the semantic interference effect did not differ between IFG, MTG, and sham stimulations, the associative facilitation effect was diminished under MTG stimulation. Analyses of latency distributions suggest this pattern to result from a response reversal. Associative facilitation occurred for faster responses, whereas associative interference resulted in slower responses under MTG stimulation. This reduction of the associative facilitation effect under transcranial direct current stimulation may be caused by an unspecific overactivation in the lexicon or by promoting competition among associatively related representations. Taken together, the results suggest that the MTG is especially involved in the processes underlying associative facilitation and that semantic interference and associative facilitation are linked to differential activation in the brain.

The human cognitive system is highly efficient in extracting information from our visual environment. This efficiency is based on acquired knowledge that guides our attention toward relevant events and promotes the recognition of individual objects as they appear in visual scenes. The experience-based representation of such knowledge contains not only information about the individual objects but also about relations between them, such as the typical context in which individual objects co-occur. The present EEG study aimed at exploring the availability of such relational knowledge in the time course of visual scene processing, using oscillatory evoked gamma-band responses as a neural correlate for a currently activated cortical stimulus representation. Participants decided whether two simultaneously presented objects were conceptually coherent (e.g., mouse–cheese) or not (e.g., crown–mushroom). We obtained increased evoked gamma-band responses for coherent scenes compared with incoherent scenes beginning as early as 70 msec after stimulus onset within a distributed cortical network, including the right temporal, the right frontal, and the bilateral occipital cortex. This finding provides empirical evidence for the functional importance of evoked oscillatory activity in high-level vision beyond the visual cortex and, thus, gives new insights into the functional relevance of neuronal interactions. It also indicates the very early availability of experience-based knowledge that might be regarded as a fundamental mechanism for the rapid extraction of the gist of a scene.

We present a new technique for studying the activation of semantic and phonological codes in speech planning using event-related brain potentials (ERPs) that extend a well-established behavioral procedure from speech production research. It combines a delayed picture-naming task with a priming procedure. While participants prepared the production of a depicted object's name, they heard an auditory target word. If the prepared picture name and the target word were semantically or phonologically related, the ERP waveform to the target word tended less towards the negative when compared to an unrelated control. These effects were widely distributed. By contrast, if participants performed a nonlinguistic task on the depicted object (natural size judgment), the semantic effect was still obtained while the phonological effect disappeared. This suggests that the former effect indexes semantic activation involved in object processing while the latter effect indexes word-form activation specific to lexical processing. The data are discussed in the context of models of lexical access in speech production.