ERP Evidence for Ultra-Fast Semantic Processing in the Picture-Word Interference Paradigm

Abstract

We used the event-related potential (ERP) approach combined with a subtraction technique to explore the timecourse of activation of semantic and phonological representations in the picture-word interference paradigm. Subjects were exposed to to-be-named pictures superimposed on to-be-ignored semantically related, phonologically related, or unrelated words, and distinct ERP waveforms were generated time-locked to these different classes of stimuli. Difference ERP waveforms were generated in the semantic condition and in the phonological condition by subtracting ERP activity associated with unrelated picture-word stimuli from ERP activity associated with related picture-word stimuli. We measured both latency and amplitude of these difference ERP waveforms in a pre-articulatory time-window. The behavioral results showed standard interference effects in the semantic condition, and facilitatory effects in the phonological condition. The ERP results indicated a bimodal distribution of semantic effects, characterized by the extremely rapid onset (at about 100 ms) of a primary component followed by a later, distinct, component. Phonological effects in ERPs were characterized by components with later onsets and distinct scalp topography of ERP sources relative to semantic ERP components. Regression analyses revealed a covariation between semantic and phonological behavioral effect sizes and ERP component amplitudes, and no covariation between the behavioral effects and ERP component latency. The early effect of semantic distractors is thought to reflect very fast access to semantic representations from picture stimuli modulating on-going orthographic processing of distractor words.

Keywords: event-related potentials; phonological processing; semantic processing.

Figure 1

Examples of the stimuli used in the experiment. Semantics, from left to right (Italian phonology in parentheses): the picture of a banana (/ba'nana/) and a spoon (/kuk'kjajo/) paired with the distractor words orange (/a'ran?a/), fork (/for'ketta/), sword (/’spada/), and mushroom (/ ‘fu?go/). Phonology, from left to right: the same pictures paired with the distractor words banknote (/ba?ko'nta/), curve (/ ‘kurva/), ambulance (/ambu'lantsa/), and installation (/im'pjanto/). Picture and words in the figure are approximately to scale with those displayed on the monitor during the experiment. Words are reported in the figure in Roman font (rather than Romantri font used in the experiment, not available for our graphical software), which is just slightly less serifed than Romantri.

Figure 2

Unsubtracted ERPs at the nine regions of interest (ROIs) in the semantic condition. The gray bars along the x-axis of the graph-scale (bottom left of panel) correspond to the time-windows explored in the ERP analyses.

Figure 3

Unsubtracted ERPs at the nine regions of interest (ROIs) in the phonological condition. The gray bars along the x-axis of the graph-scale (bottom left of panel) correspond to the time-windows explored in the ERP analyses.

Figure 4

Black functions: difference ERPs at the nine regions of interest (ROIs). Red function: difference ERP generated by subtracting the semantic unrelated ERP from the phonological unrelated ERP. Red dots: semantic condition, jackknife latency of the difference ERP in the 50–200 ms time-window. Blue dots: semantic condition, jackknife latency of the difference ERP in the 250–450 ms time-window. Green dots: phonological condition, jackknife latency of the difference ERP in the 250–450 ms time-window. The gray bars along the x-axis of the graph-scale (bottom left of panel) correspond to the time-windows explored in ERP the analyses.

Figure 5

(A) Functional architecture subtending picture and word naming proposed by Chauncey et al. (; Figure 4). Blue numbers in the panel refer to the distinct interpretative Scenarios examined in Section “Discussion” (see text for details). (B) The same functional architecture reported in (A) modified with the addition of the red bidirectional arrow connecting semantics and whole-word orthographic processing (Scenario 4) providing the best conceptual fit with the present set of ERP results. The blue number in the panel refers to one of the Scenarios examined in Section “Discussion” (see text for details).