Monita Chatterjee | Boys Town National Research Hospital (original) (raw)
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Papers by Monita Chatterjee
Jaro-journal of The Association for Research in Otolaryngology, 2006
In multi-channel cochlear implants, electrical current is delivered to appropriate electrodes in ... more In multi-channel cochlear implants, electrical current is delivered to appropriate electrodes in the cochlea to approximate the spatial representation of speech. Theoretically, electrode configurations that restrict the current spread within the cochlea (e.g., bi- or tri-polar stimulation) may provide better spatial selectivity, and in turn, better speech recognition than configurations that produce a broader current spread (e.g., monopolar stimulation). However, the effects of electrode configuration on supra-threshold excitation patterns have not been systematically studied in cochlear implant patients. In the present study, forward-masked excitation patterns were measured in cochlear implant patients as functions of stimulation mode, level and location within the cochlea. All stimuli were 500 pulses-per-second biphasic pulse trains (200 μs/phase, 20 μs inter-phase gap). Masker stimuli were 200 ms in duration; the bi-polar configuration was varied from narrow (BP + 1) to wide (BP + 17), depending on the test condition. Probe stimuli were 20 ms in duration and the masker-probe delay was 5 ms; the probe configuration was fixed at BP + 1. The results indicated that as the distance between the active and return electrodes in a bi-polar pair was increased, the excitation pattern broadened within the cochlea. When the distance between active and return electrodes was sufficiently wide, two peaks were often observed in the excitation pattern, comparable to non-overlapping electric fields produced by widely separated dipoles. Analyses of the normalized data showed little effect of stimulation level on the shape of the excitation pattern.
Journal of The Acoustical Society of America, 1998
Temporal gap detection thresholds were measured between perceptually dissimilar electrical marker... more Temporal gap detection thresholds were measured between perceptually dissimilar electrical markers in cochlear implant listeners. Both markers were presented to the same electrode pair. The amplitude and pulse rate of the first marker were fixed, and gap thresholds were measured as a function of either the pulse rate or the amplitude of the second marker. In either case, U-shaped functions were obtained, with lowest gap thresholds occurring when the two markers were similar in both amplitude and pulse rate. Because the two markers were presented to the same electrode pair, the data cannot be accounted for on the basis of across-channel interactions. It is hypothesized that when different markers are used, the perceptual discontinuity from the first marker to the second is similar to the sensation of a brief gap, and dominates the gap detection process. Thus, gap threshold functions with electrically dissimilar markers serve more as indicators of perceptual distance between the markers and less as measures of temporal resolution.
Journal of The Acoustical Society of America, 1998
Across-channel interactions in multi-electrode cochlear implant patients may be critical to their... more Across-channel interactions in multi-electrode cochlear implant patients may be critical to their performance in the natural auditory environment. One measure of channel interaction can be obtained using forward masking. The patterns of threshold shift were obtained as a function of the separation between masker and probe electrode pairs in four Nucleus-implanted patients with varying levels of speech recognition. In the three subjects with better speech recognition ͑N4, N7, and N13͒, the masking patterns showed the least parameter dependence. In the subject with the lowest speech scores ͑N3͒, the masking patterns showed the greatest dependence on masker level and on probe delay. Masking as a function of masker level also reflected these differences: N3's functions showed the greatest changes for different probe delays. Similar rates of recovery were observed in the three good performers ͑time constant approximately 70 ms͒. In contrast, subject N3's recovery function shows a more rapid recovery. These data indicate that channel interaction is individually variable and parameter dependent, both of which may play a role in the perception of dynamic stimuli in the natural auditory environment.
Journal of The Acoustical Society of America, 2003
It is hypothesized that channel-interaction in cochlear implant listeners as measured in a modula... more It is hypothesized that channel-interaction in cochlear implant listeners as measured in a modulation-masking experiment would be influenced by both the tonotopic overlap between masker and signal as well as an interaction between their envelopes. Two experiments were conducted to measure the effects of maskers with noisy and steady-state envelopes on modulation detection by four adult Nucleus-22 cochlear implant listeners, as a function of tonotopic distance between the masker and the signal. In the first experiment, we measured detection thresholds for a 50-Hz modulation in the envelope of a 500-Hz carrier pulse train, in the presence of a masker stimulating regions basal and apical to, as well as overlapping with, the signal. The maskers had two kinds of envelopes: ͑i͒ amplitude-modulated by flat-spectrum noise ͑NAM͒ and (ii) steady-state (SS peak ) at a level corresponding to the maximum of the noise fluctuation range. In general, modulation thresholds obtained in the presence of the NAM maskers significantly exceeded thresholds obtained with the corresponding SS peak maskers. The ratio of the threshold modulation depth m obtained with the NAM masker to that obtained with the SS peak masker was defined as a conservative index of ''envelope masking.'' In the second experiment, was determined for two different tasks: the detection of modulation at 20 Hz and steady-state intensity increment detection. Compared to the 50-Hz modulation detection results, the ratio was reduced for the 20-Hz modulation detection task and even more so for the steady-state increment detection task. It is concluded that channel-interaction can be significantly increased in cochlear implant listeners when dynamic stimuli are used in place of steady-state stimuli.
Journal of The Acoustical Society of America, 2000
Journal of The Acoustical Society of America, 1999
The effect of increasing the separation between the two members of a stimulating electrode pair w... more The effect of increasing the separation between the two members of a stimulating electrode pair was studied in four users of the Nucleus-22 cochlear implant. Two experiments were performed. In experiment 1, detection threshold for a 200-ms, 500-pulses/s biphasic pulse train was measured as the spatial separation between the active and return electrodes was increased. In experiment 2, loudness-growth functions were measured as the electrode separation was increased. The results of experiment 1 indicate that ͑a͒ threshold decreases monotonically toward an asymptote ͑monopolar threshold͒ as the electrode separation is increased and ͑b͒ the threshold versus electrode separation function is similar across subjects and electrode location. The results of experiment 2 indicate that loudness L is related to the current amplitude I by a simple exponential function: Lϭe I , where , the exponent of the loudness function, is, to a first approximation, linearly related to the separation between the electrodes of the stimulating pair. Thus, dynamic range and the shape of loudness growth can be directly linked to the spatial separation between active and return electrodes.
IEEE Transactions on Rehabilitation Engineering, 1998
This study is part of a program to develop an auditory prosthesis for the profoundly deaf, based ... more This study is part of a program to develop an auditory prosthesis for the profoundly deaf, based on multichannel microstimulation in the cochlear nucleus. The functionality of such a device is dependent on its ability to access the tonotopic axis of the human ventral cochlear nucleus in an orderly fashion. In these studies, we utilized the homologies between the human and feline ventral cochlear nuclei and the known tonotopic organization of the central nucleus of the inferior colliculus (IC). In anesthetized cats, stimuli were delivered to three or four locations along the dorsal-to-ventral axis of the posteroventral cochlear nucleus (PVCN), and for each stimulus location, we recorded the multiunit neuronal activity and the field potentials at 20 or more locations along the dorsolateral-ventromedial (tonotopic) axis of the IC. The current source-sink density (CSD), which delimits regions of neuronal activity, was computed from the sequence of field potentials recorded along this axis. The multiunit activity and the CSD analysis both showed that the tonotopic organization of the PVCN can be accessed in an orderly manner by intranuclear microstimulation in several regions of the PVCN, using the range of stimulus pulse amplitudes that have been shown in previous studies to be noninjurious during prolonged intranuclear microstimulation via chronically implanted microelectrodes. We discuss the applicability of these findings to the design of clinical auditory prostheses for implantation into the human cochlear nucleus.
Jaro-journal of The Association for Research in Otolaryngology, 2006
In multi-channel cochlear implants, electrical current is delivered to appropriate electrodes in ... more In multi-channel cochlear implants, electrical current is delivered to appropriate electrodes in the cochlea to approximate the spatial representation of speech. Theoretically, electrode configurations that restrict the current spread within the cochlea (e.g., bi- or tri-polar stimulation) may provide better spatial selectivity, and in turn, better speech recognition than configurations that produce a broader current spread (e.g., monopolar stimulation). However, the effects of electrode configuration on supra-threshold excitation patterns have not been systematically studied in cochlear implant patients. In the present study, forward-masked excitation patterns were measured in cochlear implant patients as functions of stimulation mode, level and location within the cochlea. All stimuli were 500 pulses-per-second biphasic pulse trains (200 μs/phase, 20 μs inter-phase gap). Masker stimuli were 200 ms in duration; the bi-polar configuration was varied from narrow (BP + 1) to wide (BP + 17), depending on the test condition. Probe stimuli were 20 ms in duration and the masker-probe delay was 5 ms; the probe configuration was fixed at BP + 1. The results indicated that as the distance between the active and return electrodes in a bi-polar pair was increased, the excitation pattern broadened within the cochlea. When the distance between active and return electrodes was sufficiently wide, two peaks were often observed in the excitation pattern, comparable to non-overlapping electric fields produced by widely separated dipoles. Analyses of the normalized data showed little effect of stimulation level on the shape of the excitation pattern.
Journal of The Acoustical Society of America, 1998
Temporal gap detection thresholds were measured between perceptually dissimilar electrical marker... more Temporal gap detection thresholds were measured between perceptually dissimilar electrical markers in cochlear implant listeners. Both markers were presented to the same electrode pair. The amplitude and pulse rate of the first marker were fixed, and gap thresholds were measured as a function of either the pulse rate or the amplitude of the second marker. In either case, U-shaped functions were obtained, with lowest gap thresholds occurring when the two markers were similar in both amplitude and pulse rate. Because the two markers were presented to the same electrode pair, the data cannot be accounted for on the basis of across-channel interactions. It is hypothesized that when different markers are used, the perceptual discontinuity from the first marker to the second is similar to the sensation of a brief gap, and dominates the gap detection process. Thus, gap threshold functions with electrically dissimilar markers serve more as indicators of perceptual distance between the markers and less as measures of temporal resolution.
Journal of The Acoustical Society of America, 1998
Across-channel interactions in multi-electrode cochlear implant patients may be critical to their... more Across-channel interactions in multi-electrode cochlear implant patients may be critical to their performance in the natural auditory environment. One measure of channel interaction can be obtained using forward masking. The patterns of threshold shift were obtained as a function of the separation between masker and probe electrode pairs in four Nucleus-implanted patients with varying levels of speech recognition. In the three subjects with better speech recognition ͑N4, N7, and N13͒, the masking patterns showed the least parameter dependence. In the subject with the lowest speech scores ͑N3͒, the masking patterns showed the greatest dependence on masker level and on probe delay. Masking as a function of masker level also reflected these differences: N3's functions showed the greatest changes for different probe delays. Similar rates of recovery were observed in the three good performers ͑time constant approximately 70 ms͒. In contrast, subject N3's recovery function shows a more rapid recovery. These data indicate that channel interaction is individually variable and parameter dependent, both of which may play a role in the perception of dynamic stimuli in the natural auditory environment.
Journal of The Acoustical Society of America, 2003
It is hypothesized that channel-interaction in cochlear implant listeners as measured in a modula... more It is hypothesized that channel-interaction in cochlear implant listeners as measured in a modulation-masking experiment would be influenced by both the tonotopic overlap between masker and signal as well as an interaction between their envelopes. Two experiments were conducted to measure the effects of maskers with noisy and steady-state envelopes on modulation detection by four adult Nucleus-22 cochlear implant listeners, as a function of tonotopic distance between the masker and the signal. In the first experiment, we measured detection thresholds for a 50-Hz modulation in the envelope of a 500-Hz carrier pulse train, in the presence of a masker stimulating regions basal and apical to, as well as overlapping with, the signal. The maskers had two kinds of envelopes: ͑i͒ amplitude-modulated by flat-spectrum noise ͑NAM͒ and (ii) steady-state (SS peak ) at a level corresponding to the maximum of the noise fluctuation range. In general, modulation thresholds obtained in the presence of the NAM maskers significantly exceeded thresholds obtained with the corresponding SS peak maskers. The ratio of the threshold modulation depth m obtained with the NAM masker to that obtained with the SS peak masker was defined as a conservative index of ''envelope masking.'' In the second experiment, was determined for two different tasks: the detection of modulation at 20 Hz and steady-state intensity increment detection. Compared to the 50-Hz modulation detection results, the ratio was reduced for the 20-Hz modulation detection task and even more so for the steady-state increment detection task. It is concluded that channel-interaction can be significantly increased in cochlear implant listeners when dynamic stimuli are used in place of steady-state stimuli.
Journal of The Acoustical Society of America, 2000
Journal of The Acoustical Society of America, 1999
The effect of increasing the separation between the two members of a stimulating electrode pair w... more The effect of increasing the separation between the two members of a stimulating electrode pair was studied in four users of the Nucleus-22 cochlear implant. Two experiments were performed. In experiment 1, detection threshold for a 200-ms, 500-pulses/s biphasic pulse train was measured as the spatial separation between the active and return electrodes was increased. In experiment 2, loudness-growth functions were measured as the electrode separation was increased. The results of experiment 1 indicate that ͑a͒ threshold decreases monotonically toward an asymptote ͑monopolar threshold͒ as the electrode separation is increased and ͑b͒ the threshold versus electrode separation function is similar across subjects and electrode location. The results of experiment 2 indicate that loudness L is related to the current amplitude I by a simple exponential function: Lϭe I , where , the exponent of the loudness function, is, to a first approximation, linearly related to the separation between the electrodes of the stimulating pair. Thus, dynamic range and the shape of loudness growth can be directly linked to the spatial separation between active and return electrodes.
IEEE Transactions on Rehabilitation Engineering, 1998
This study is part of a program to develop an auditory prosthesis for the profoundly deaf, based ... more This study is part of a program to develop an auditory prosthesis for the profoundly deaf, based on multichannel microstimulation in the cochlear nucleus. The functionality of such a device is dependent on its ability to access the tonotopic axis of the human ventral cochlear nucleus in an orderly fashion. In these studies, we utilized the homologies between the human and feline ventral cochlear nuclei and the known tonotopic organization of the central nucleus of the inferior colliculus (IC). In anesthetized cats, stimuli were delivered to three or four locations along the dorsal-to-ventral axis of the posteroventral cochlear nucleus (PVCN), and for each stimulus location, we recorded the multiunit neuronal activity and the field potentials at 20 or more locations along the dorsolateral-ventromedial (tonotopic) axis of the IC. The current source-sink density (CSD), which delimits regions of neuronal activity, was computed from the sequence of field potentials recorded along this axis. The multiunit activity and the CSD analysis both showed that the tonotopic organization of the PVCN can be accessed in an orderly manner by intranuclear microstimulation in several regions of the PVCN, using the range of stimulus pulse amplitudes that have been shown in previous studies to be noninjurious during prolonged intranuclear microstimulation via chronically implanted microelectrodes. We discuss the applicability of these findings to the design of clinical auditory prostheses for implantation into the human cochlear nucleus.