Event related potentials (ERPs) and behavioral responses: comparison of tonal stimuli to speech stimuli in phonological and semantic tasks.

Event related potentials (ERPs) were recorded from 20 young subjects to auditory target stimuli while they were performing three different tasks, using an oddball paradigm: 1. Tones: Subjects were instructed to respond to a 1 kHz tone, and ignore a 2 kHz tone; 2. Phonological: Subjects were instructed to respond only to pseudowords that had a specific ending ('f"); 3. Semantic: Subjects were instructed to respond to words that belonged to a specific category (animals). EEGs were recorded from 19 electrode sites. Peak amplitude of the early component (N100) did not differ significantly across the three tasks, although N100 peak latency differed significantly across tasks. In contrast, the later endogenous component (P300) was stimulus- and task-dependent. P300 latency differed significantly across stimuli and tasks: 336 ms to target tones; 682 ms to the phonological targets; and 727 ms to target words in the semantic task. P300 amplitude was significantly larger to tones than to speech stimuli. P300 peak amplitude recorded from electrode sites over the left hemisphere to the tonal target stimuli did not differ significantly from that recorded over the right hemisphere. In contrast, P300 amplitude recorded to both the phonological and semantic targets was significantly larger over the left hemisphere than over the right hemisphere at the parietal electrodes. The present results can contribute to our understanding of how humans process linguistic stimuli. These findings emphasize the importance of using similar experimental protocols when conducting broad comparisons of ERPs to a variety of stimuli and tasks.