Neural Representation of Loudness: Cortical Evoked Potentials in an Induced Loudness Reduction Experiment

Loudness context effects comprise differences in judgments of the loudness of a target stimulus depending on the presence of a preceding inducer tone. Interstimulus intervals (ISIs) between inducer tone and target tone of about 200 ms and above cause an induced loudness reduction (ILR) of the target tone. As the ILR increases, respectively, the perceived loudness of the target stimuli decreases with increasing ISI. This in turn means that identical stimuli in a different context have a differently perceived loudness. A correlation between specific characteristics in the electroencephalography responses and perceived loudness in an ILR experiment would therefore provide a neurophysiological indication of loudness processing beyond a neural representation of stimulus intensity only. To examine if such a correlation exists, we investigated cortical electroencephalography responses in a latency range from 75 to 510 ms during a psychoacoustical ILR experiment with different ISIs. With increasing ISI, the strength of the N1-P2 deflection of the respective electroencephalography response decreases similarly to the loudness perception of the target tone pulse. This indicates a representation based on loudness rather than on intensity at the corresponding processing stage.