Biology subjects

Overath, T.

Publications and source records attributed to Overath, T..

3 recordsLinked to original sources

bioRxiv2025

Exploring Auditory Category Distinctions in Perception and Imagery

Imagery, the ability to generate perceptual experiences in the absence of external stimuli, is used every day when remembering a past event or imagining a novel situation. While most previous research on imagery has focused on the visual domain, the present study presents an investigation of auditory imagery. The perception of different categories of sound has been shown to evoke different neural responses. Further, the neural processes underlying auditory imagery and perception have been shown to be similar. Therefore, we hypothesized that auditory imagery would rely on similar categorical processing. Participants learned shape-sound associations and were then asked to imagine the matching sound when presented with the associated shape. We chose two example stimuli from two maximally different sound categories -- human speech sounds and nonhuman environmental sounds -- to investigate our hypothesis. Electroencephalography (EEG) data were recorded while participants listened to and imagined the sounds. The mean voltage in the P2 event-related potential time window (180-280 ms) was significantly larger for perception of the speech sounds than the environmental sounds, and the late positive event-related potential complex (LPC, 350-500 ms) associated with imagery was significantly smaller for imagery of the speech sounds than the environmental sounds. This suggests that, as in perception, the neural processing of imagined sounds is categorical.

neuroscience↗

bioRxiv2021

Linguistic modulation of the neural encoding of phonemes

Speech comprehension entails the neural mapping of the acoustic speech signal onto learned linguistic units. This acousto-linguistic transformation is bi-directional, whereby higher-level linguistic processes (e.g., semantics) modulate the acoustic analysis of individual linguistic units. Here, we investigated the cortical topography and linguistic modulation of the most fundamental linguistic unit, the phoneme. We presented natural speech and phoneme quilts (pseudo-randomly shuffled phonemes) in either a familiar (English) or unfamiliar (Korean) language to native English speakers while recording fMRI. This allowed us to dissociate the contribution of acoustic vs. linguistic processes towards phoneme analysis. We show that (1) the acoustic analysis of phonemes is modulated by linguistic analysis and (2) that for this modulation both of acoustic and phonetic information need to be incorporated. These results suggest that the linguistic modulation of cortical sensitivity to phoneme classes minimizes prediction error during natural speech perception, thereby aiding speech comprehension in challenging listening situations.

neuroscience↗

bioRxiv2019

From acoustic to linguistic analysis of temporal speech structure: acousto-linguistic transformation during speech perception using speech quilts.

Speech perception entails the mapping of the acoustic waveform to linguistic representations. For this mapping to succeed, the speech signal needs to be tracked over various temporal windows at high temporal precision in order to decode linguistic units ranging from phonemes (tens of milliseconds) to sentences (seconds). Here, we tested the hypothesis that cortical processing of speech-specific temporal structure is modulated by higher-level linguistic analysis. Using fMRI, we measured BOLD signal changes to 4-s long speech quilts with variable temporal structure (30, 120, 480, 960 ms segment lengths), as well as natural speech, created from a familiar (English) or foreign (Korean) language. We found evidence for the acoustic analysis of temporal speech properties in superior temporal sulcus (STS): the BOLD signal increased as a function of temporal speech structure in both familiar and foreign languages. However, activity in left inferior gyrus (IFG) revealed evidence for linguistic processing of temporal speech properties: the BOLD signal increased as a function of temporal speech structure only in familiar, but not in foreign speech. Network analyses suggested that left IFG modulates processing of speech-specific temporal structure in primary auditory cortex, which in turn sensitizes processing of speech-specific temporal structure in STS. The results thus reveal a network for acousto-linguistic transformation consisting of primary and non-primary auditory cortex, STS, and left IFG.\n\nSignificance StatementWhere and how the acoustic information contained in complex speech signals is mapped to linguistic information is still not fully explained by current speech/language models. We dissociate acoustic from linguistic analyses of speech by comparing the same acoustic manipulation (varying the extent of temporal speech structure) in two languages (native, foreign). We show that acoustic temporal speech structure is analyzed in superior temporal sulcus (STS), while linguistic information is extracted in left inferior frontal gyrus (IFG). Furthermore, modulation from left IFG enhances sensitivity to temporal speech structure in STS. We propose a model for acousto-linguistic transformation of speech-specific temporal structure in the human brain that can account for these results.

neuroscience↗