Auditory stream segregation in cochlear implant listeners: Measures based on temporal discrimination and interleaved melody recognition

Abstract

The evidence that cochlear implant listeners routinely experience stream segregation is limited and equivocal. Streaming in these listeners was explored using tone sequences matched to the center frequencies of the implant's 22 electrodes. Experiment 1 measured temporal discrimination for short (ABA triplet) and longer (12 AB cycles) sequences (tone/silence durations = 60/40 ms). Tone A stimulated electrode 11; tone B stimulated one of 14 electrodes. On each trial, one sequence remained isochronous, and tone B was delayed in the other; listeners had to identify the anisochronous interval. The delay was introduced in the second half of the longer sequences. Prior build-up of streaming should cause thresholds to rise more steeply with increasing electrode separation, but no interaction with sequence length was found. Experiment 2 required listeners to identify which of two target sequences was present when interleaved with distractors (tone/silence durations = 120/80 ms). Accuracy was high for isolated targets, but most listeners performed near chance when loudness-matched distractors were added, even when remote from the target. Only a substantial reduction in distractor level improved performance, and this effect did not interact with target-distractor separation. These results indicate that implantees often do not achieve stream segregation, even in relatively unchallenging tasks.

Stream segregation on a single electrode as a function of pulse rate in cochlear implant listeners

“…Although both sequences resulted in increasing thresholds for increased electrode separation, build up is unlikely to occur for the shorter sequences (e.g. Bregman, 1978;Anstis and Saida, 1985), Cooper and Roberts (2009) argue that parallel performance for both sequences suggests that buildup is unlikely to be occurring for the longer sequences either, and therefore, the differences in rhythm detection thresholds were not likely due to stream segregation. Hong and Turner (2006) conducted a similar rhythm discrimination task using a short, three-tone sequence.…”

“…This type of perceptual instability is a common characteristic of stream segregation in normal hearing listeners (Anstis and Saida, 1985). Cooper and Roberts (2009) used a rhythm discrimination task to objectively investigate stream segregation. They found that increasing electrode separation led to rising rhythm detection thresholds.…”

Influence of pitch, timbre and timing cues on melodic contour identification with a competing masker (L)

“…Because of relatively poor pitch and timbre perception, CI users have difficulty in forming auditory streams. While some studies have shown that CI users can stream and segregate simple sequences using place and rate pitch cues (Chatterjee et al, 2006;Turner, 2006, 2009), others have shown that CI users cannot segregate auditory streams (Cooper and Roberts, 2009).…”

Rate and onset cues can improve cochlear implant synthetic vowel recognition in noise

“…Data from NH listeners show that a sound's harmonic structure (both resolved and unresolved), defined by its F0, can be a good segregation cue in acoustic hearing (Assmann and Summerfield, 1990;Culling and Darwin, 1993). The brain can group together energy from resolved harmonics, which create a predictable pattern of excitation on the cochlea, to form one auditory object (a speakers voice for example) while ignoring energy from other frequency regions (e.g., background noise).…”

“…They found that CI users could stream amplitude modulated noise at relatively low frequencies and that the ability to stream pure tones was significantly correlated with speech perception in noise. Cooper and Roberts (2009) also investigate stream segregation in CI users and found that it was poor, even with a comparatively simple task. In NH subjects using CI simulation, Gaudrain et al (2008) showed that when F0 spectral cues were severely reduced, listeners may still make use of a weak F0 spectral cue to facilitate streaming.…”