Biology subjects

Schnupp, J. W.

Publications and source records attributed to Schnupp, J. W..

6 recordsLinked to original sources

bioRxiv2025

Interactions of Interaural Time and Level Differences in Spatial Hearing with Cochlear Implants

Normally hearing humans can localize sound sources quite accurately, with minimum audible angles as small as 1{degrees}. To achieve this, our auditory pathways combine information from multiple acoustic cues, including interaural time and interaural level differences (ITDs and ILDs). Patients relying on cochlear implants (CIs) to hear the world cannot match normal performance. These deficits are most pronounced in patients with little or no hearing experience early in life, and they appear to result from an impaired sensitivity to ITDs, but not to ILDs. However, little is known about how ITD and ILD sensitivities develop and interact in an early deafened auditory system shortly after CI implantation. We fitted neonatally deafened rats with bilateral CIs, and, providing informative ITDs and ILDs from stimulation onset, trained them to lateralize CI stimuli. These animals were exquisitely sensitive to both ILDs and ITDs of CI stimulus pulses, and combined information from both cues in a weighted sum. Importantly, ITDs are weighted heavily in our CI rats, such that only very modest ITDs pointing in one direction can confound quite large ILDs pointing in the opposite direction. This underlines the importance of informative ITDs for maximizing the potential for spatial hearing with CI devices. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=181 SRC="FIGDIR/small/635454v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@15ee6e2org.highwire.dtl.DTLVardef@1881bd4org.highwire.dtl.DTLVardef@db17c7org.highwire.dtl.DTLVardef@1f62f2f_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2024

Interaural level difference sensitivity in neonatally deafened rats fitted with bilateral cochlear implants

Bilateral cochlear implant (CI) patients exhibit significant limitations in spatial hearing. Their ability to process interaural time differences (ITDs) is often impaired, while their ability to process interaural level differences (ILDs) remains comparatively good. Clinical studies aiming to identify the causes of these limitations are often plagued by confounds and ethical limitations. Recent behavioral work suggests that rats may be a good animal model for studying binaural hearing under neuroprosthetic stimulation, as rats develop excellent ITD sensitivity when provided with suitable CI stimulation. However, their ability to use ILDs has not yet been characterized. Objective of this study is to address this knowledge gap. Neontally deafened rats were bilaterally fitted with CIs, and trained to lateralize binaural stimuli according to ILD. Their behavioral ILD thresholds were measured at pulse rates from 50 to 2400 pps. CI rats exhibited high sensitivity to ILDs with thresholds of a few dB at all tested pulse rates. We conclude that early deafened rats develop good sensitivity, not only to ITDs but also to ILDs, if provided with appropriate CI stimulation. Their generally good performance, in line with expectations from other mammalian species, validates rats as an excellent model for research on binaural auditory prostheses.

neuroscience↗

bioRxiv2023

Is Inappropriate Pulse Timing Responsible for Poor Binaural Hearing with Cochlear Implants?

Cochlear implants (CIs) have restored enough of a sense of hearing to around one million severely hearing impaired patients to enable speech understanding in quiet. However, several aspects of hearing with CIs remain very poor. This includes a severely limited ability of CI patients to make use of interaural time difference (ITD) cues for spatial hearing and noise reduction. A major cause for this poor ITD sensitivity could be that current clinical devices fail to deliver ITD information in a manner that is accessible to the auditory pathway. CI processors measure the envelopes of incoming sounds and then stimulate the auditory nerve with electrical pulse trains which are amplitude modulated to reflect incoming sound envelopes. The timing of the pulses generated by the devices is largely or entirely independent of the incoming sounds. Consequently, bilateral CIs (biCIs) provide veridical envelope (ENV) ITDs but largely or entirely replace the "fine structure" ITDs that naturally occur in sounds with completely arbitrary electrical pulse timing (PT) ITDs. To assess the extent to which this matters, we devised experiments that measured the sensitivity of deafened rats to precisely and independently controlled PT and ENV ITDs for a variety of different CI pulse rates and envelope shapes. We observed that PT ITDs completely dominate ITD perception, while the sensitivity to ENV ITDs was almost negligible in comparison. This strongly suggests that the confusing yet powerful PT ITDs that contemporary clinical devices deliver to biCI patients may be a major cause of poor binaural hearing outcomes with biCIs. Significance StatementCIs deliver spectro-temporal envelopes, including speech formants, to severely deaf patients, but they do little to cater to the brains ability to process temporal sound features with sub-millisecond precision. CIs "sample" sound envelope signals rapidly and accurately, and thus provide information which should make it possible in principle for CI listeners to detect envelope ITDs in a similar way to normal listeners. However, here we demonstrate through behavioral experiments on CI implanted rats trained to detect sub-millisecond ITDs that pulse timing ITDs completely dominate binaural hearing. This provides the strongest confirmation to date that the arbitrary pulse timing widely used in current clinical CIs is a critical obstacle to good binaural hearing through prosthetic devices.

neuroscience↗

bioRxiv2022

Interaural time difference sensitivity under binaural cochlear implant stimulation even at high pulse rates up to 900 pps

BackgroundSpatial hearing remains one of the major challenges for bilateral cochlear implant (biCI) users, and early deaf patients in particular are often completely insensitive to interaural time differences (ITDs) delivered through biCIs. One popular hypothesis is that this may be due to a lack of early binaural experience. However, we have recently shown that neonatally deafened rats fitted with biCIs in adulthood quickly learn to discriminate ITDs as well as their normal hearing litter mates, and perform an order of magnitude better than human biCI users. MethodsOur unique behaving biCI rat model allows us to investigate other possible limiting factors of prosthetic binaural hearing, such as the effect of stimulus pulse rate and envelope shape. Previous work has indicated that ITD sensitivity may decline substantially at the high pulse rates often used in clinical practice. We therefore measured behavioral ITD thresholds in neonatally deafened, adult implanted biCI rats to pulse trains of 50, 300, 900 and 1800 pulses per second (pps), with either rectangular or Hanning window envelopes. ResultsOur rats exhibited very high sensitivity to ITDs at pulse rates up to 900 pps for both envelope shapes, similar to those in common clinical use. However, ITD sensitivity declined to near zero at 1800 pps, for both Hanning and rectangular windowed pulse trains. ConclusionsCurrent clinical cochlear implant (CI) processors are often set to pulse rates [≥]900 pps, but ITD sensitivity in human CI listeners has been reported to decline sharply above [~]300 pps. Our results suggest that the relatively poor ITD sensitivity seen at >300 pps in human CI users may not reflect the hard upper limit of biCI ITD performance in the mammalian auditory pathway. Perhaps with training or better CI strategies good binaural hearing may be achievable at pulse rates high enough to allow good sampling of speech envelopes while delivering usable ITDs.

neuroscience↗

bioRxiv2018

Microsecond Interaural Time Difference Discrimination Restored by Cochlear Implants After Neonatal Deafness

Cochlear implants (CIs) can restore a high degree of functional hearing in deaf patients however spatial hearing remains poor, with many early deaf CI users reported to have no measurable sensitivity to interaural time differences (ITDs) at all. Deprivation of binaural experience during an early critical period is often blamed for this shortcoming. However, we show that neonatally deafened rats provided with precisely synchronized CI stimulation in adulthood can be trained to localize ITDs with essentially normal behavioral thresholds near 50 s. Furthermore, neonatally deaf rats show high physiological sensitivity to ITDs immediately after binaural implantation in adulthood. The fact that our neonatally deaf CI rats achieved very good behavioral ITD thresholds while prelingually deaf human CI patients usually fail to develop a useful sensitivity to ITD raises urgent questions about whether shortcomings in technology or treatment may be behind the usually poor binaural outcomes for current binaural CI patients.

neuroscience↗

bioRxiv2017

Pitch discrimination performance of ferrets and humans on a go/no-go task.

Animal models are widely used to examine the neurophysiological basis of human pitch perception, and it is therefore important to understand the similarities and differences in pitch processing across species. Pitch discrimination performance is usually measured using two-alternative forced choice (2AFC) procedures in humans and go/no-go tasks in animals, potentially confounding human-to-animal comparisons. We have previously shown that pitch discrimination thresholds of ferrets on a 2AFC task are markedly poorer than those reported for go/no-go tasks in other non-human species (Walker et al., 2009). To better compare the pitch discrimination performance of ferret with other species, here we measure pitch change detection thresholds of ferrets and humans on a common, appetitive go/no-go task design. We found that ferrets pitch thresholds were ~10 times larger than that of humans on the go/no-go task, and were within the range of thresholds reported in other non-human species. Interestingly, ferrets thresholds were 100 times larger than human thresholds on a 2AFC pitch discrimination task using the same stimuli. These results emphasize that sensory discrimination thresholds can differ across tasks, particularly for non-human animals. Performance on our go/no-go task is likely to reflect different neurobiological processes than that on our 2AFC task, as the former required the subjects only to detect a pitch change while the latter required them to label the direction of the pitch change.\n\nABBREVIATIONS\n\nHIGHLIGHTSO_LIPitch discrimination thresholds of ferrets were 10 times larger than those of humans on a go/no-go task\nC_LIO_LIFerrets pitch thresholds are similar to those reported for a range of other mammals\nC_LIO_LIPitch thresholds of ferrets, but not humans, were drastically better on the go/no-go task than a 2AFC task using the same stimuli\nC_LI

animal behavior and cognition↗