Dissociating Perceptual Quality Dimensions of Transmitted Speech Using Electroencephalography

The present study utilized electroencephalography (EEG) to explore the neuro-electrical correlates of perceptual dimensions underlying speech quality. Specific focus lay on the P300 event-related brain potential (ERP) component to provide indication for internal processes related to attention and stimulus categorization. A high-quality (HQ) recording of a spoken word was impaired on each of three perceptual dimensions at a time, “discontinuity” (F), “noisiness” (N) and “coloration” (C), with F being realized through random erasure of distinct frames in the speech signal parts of the audio file. In an active three-stimulus oddball task, repeated presentations of the HQ stimulus led to the formation of a sensory/perceptual HQ reference, which was interrupted by infrequent occurrences of degraded “oddball” stimuli (F, N, C). Initial analysis of the obtained subjective and electrophysiological data suggested the following conclusions: 1) Participants perceived the three degraded stimuli as clearly impaired, but equal in terms of degradation intensity. Thus, variations in neural responses were assumed to reflect changes in the perceptual dimension along which the speech degradation had been induced. 2) Timing of the evoked P300 corresponded with temporal differences in the impairments, implying a later onset for “discretely” (F) compared to “continuously” (N, C) degraded stimuli after being categorized as task-irrelevant. Hence, P300 peak latency might prove useful to dissociate both classes of speech quality impairments on a neural level of analysis.