What's what in auditory cortices?

Abstract

Distinct anatomical and functional pathways are postulated for analysing a sound's object-related ('what') and space-related ('where') information. It remains unresolved to which extent distinct or overlapping neural resources subserve specific object-related dimensions (i.e. who is speaking and what is being said can both be derived from the same acoustic input). To address this issue, we recorded high-density auditory evoked potentials (AEPs) while participants selectively attended and discriminated sounds according to their pitch, speaker identity, uttered syllable ('what' dimensions) or their location ('where'). Sound acoustics were held constant across blocks; the only manipulation involved the sound dimension that participants had to attend to. The task-relevant dimension was varied across blocks. AEPs from healthy participants were analysed within an electrical neuroimaging framework to differentiate modulations in response strength from modulations in response topography; the latter of which forcibly follow from changes in the configuration of underlying sources. There were no behavioural differences in discrimination of sounds across the 4 feature dimensions. As early as 90ms post-stimulus onset, AEP topographies differed across 'what' conditions, supporting a functional sub-segregation within the auditory 'what' pathway. This study characterises the spatio-temporal dynamics of segregated, yet parallel, processing of multiple sound object-related feature dimensions when selective attention is directed to them.

Selective attention to sound features mediates cross-modal activation of visual cortices

“…Behavioural results on this task appear in Retsa et al (2018). Briefly, subjects performed at near-ceiling levels (i.e.…”

“…All participants reported normal hearing and had normal or corrected-to-normal vision. Aspects of this dataset were previously published in a study focusing on parallel processing of object-related feature dimensions in the auditory system (Retsa et al, 2018). However, in that work no analyses based on the lateralisation of the stimuli were performed.…”

“…We chose an absorption coefficient of 0.6 for the virtual walls of this simple room model, an appropriate value to approximate the quite highly absorbent walls of the actual recording room. For a more detailed description of the present stimuli generation, see Retsa et al, (2018). E-prime software controlled stimulus delivery and recorded the subjects’ behavioural performance (www.pstnet.com/eprime).…”

“…As such, it is possible that the ACOP is elicited only when spatial location is relevant to the currently performed task. In order to verify this hypothesis, we instructed participants to complete a series of two-alternative-forced-choice tasks involving sounds varying across four perceptual dimensions: location (left/right), pitch (high/low), syllable type (“ti”/”ta”) or speaker identity (man/boy) (Retsa et al, 2018). Across blocks of trials, we explicitly asked participants’ to attend to and discriminate one of these specific features of the sounds.…”

Do auditory mismatch responses differ between acoustic features?

“…In this experiment, we manipulated two consonant-vowel (CV) syllable stimuli, /ta/ and /ti/ (Retsa et al, 2018), along four independent acoustic features: duration, pitch, interaural level difference (ILD) or vowel (An et al, 2020). Prior to the EEG recording, per participant, we estimated the feature interval yielding ~80% behavioral performance by employing a 1-up-3-down staircase procedure.…”