2/25/2013. Context Effect on Suprasegmental Cues. Supresegmental Cues. Pitch Contour Identification (PCI) Context Effect with Cochlear Implants

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1 Context Effect on Segmental and Supresegmental Cues Preceding context has been found to affect phoneme recognition Stop consonant recognition (Mann, 1980) A continuum from /da/ to /ga/ was preceded by /al/ or /ar/. The same target was more /da/-like following /al/ and more /ga/-like after /ar/. A perceptual process to compensate for co-articulation. Context Effects on Pitch Contour Identification in Normal-hearing Listeners and Cochlear-implant Users Krista Ashmore and Xin Luo Department of Speech, Language, and Hearing Sciences, Purdue University Vowel recognition (Ladefoged and Broadbent, 1957) A continuum from /bit/ to /bet/ was preceded by a precursor sentence. The same target was more often identified as /bet/ when the precursor sentence had lower F1 (i.e., a contrastive effect). A perceptual process to normalize talker variability in vocal tract size. Context Effect on Suprasegmental Cues Preceding context has been found to affect tone recognition Cantonese level tone recognition (Wang and Diehl, 2003; Francis et al., 2006) A continuum from low- to high-level tone was presented in a sentence context. The same target was more often identified as high-level tone in a low-f0 context (i.e., a contrastive effect). Mandarin contour tone recognition (e.g., Huang and Holt, 2009) A continuum from tone 1 (high-level tone) to tone 2 (mid-rising tone) was preceded by a precursor sentence. The same target was more often identified as tone 1 when the precursor sentence had lower F0 (again, a contrastive effect). A perceptual process to normalize talker variability in voice pitch. Nature of Context Processing Not linguistic or talker-based processing Similar effect was observed for non-speech context (e.g., Lotto and Kluender, 1998; Huang and Holt, 2009) Pure tones or harmonic complex tones were used to simulate the formant distributions or mean F0s of speech context. There were no phonetic or articulatory cues in the non-speech context. Not peripheral auditory processing The effect remained when the context was presented to the other ear or when the interval between target and context was increased to hundreds of milliseconds (Holt and Lotto, 2002) Context Effect with Cochlear Implants Cochlear implants (CIs) provide profoundly deaf people with good sentence and phoneme recognition in quiet. However, CI users have great difficulty in recognizing lexical tones, speech intonations, music melodies, and speech in noise, due to the lack of robust pitch and fine structure cues. Studies have focused on isolated tone recognition with CI. It s unclear if CI users would have similar context effect on tone recognition as normal-hearing (NH) listeners. Pitch Contour Identification (PCI) It would have been ideal to test Chinese-speaking CI users with Mandarin lexical tones, but such patients are only available in China. Instead, English-speaking NH listeners and CI users were tested with pitch contour identification (PCI) using non-speech stimuli that simulated the lexical tones in Mandarin. This allows us to further test the claim that pitch context effect is due to general auditory processing and requires no tonal language experience, linguistic, or talker information. 1

2 Exp. 1: NH Listeners 13 native English speakers with normal hearing in both ears Stimuli: complex tones with four equal-amplitude harmonics Testing Procedure Stimuli presented via a loudspeaker at 70 db SPL in a booth Two conditions: first without context, then with context Target Onset F0: Target Offset F0: Preceding Context F0: Hz in 5-Hz steps 200 Hz 160 or 200 Hz Two-alternative, forced-choice (2AFC) task: is it flat or rising? Recorded the percentage of rising responses in 20 repeats Response Boxes on the Screen Context: 500 ms Target: 500 ms F0: Gap: 50ms NH Results: PCI without Context NH Results: PCI with Context Target F0: F 8, 96 = , P < Target F0: Context F0: Interaction: F 8, 96 = 79.70, P < F 1, 96 = 4.70, P < 0.05 F 8, 96 = 0.96, P = 0.47 Significant contrastive effects of pitch context were found on PCI for English-speaking NH listeners. A general auditory processing that applies to non-speech stimuli and works even without tonal language experience. Compared with Mandarin tone recognition (Huang and Holt, 2009) Rising responses in English listeners > Tone 2 responses in Chinese listeners Relatively weaker context effects in English listeners than in Chinese listeners Exp. 2: CI Users 9 CI users were tested with their clinical speech processors Subject Age Gender Implant Strategy Years with CI C1 29 M Nucleus 5 ACE 0.7 C2 68 M Nucleus 5 ACE 2 C3 61 F Freedom ACE 4 C4 54 F Freedom ACE 4 C5 66 M Freedom ACE 5 C6 43 F HiRes90K HiRes C7 83 F HiRes90K HiRes C8 63 F HiRes90K HiRes 6 C9 47 M Clarion CI CIS 16 2

3 Stimuli and Procedure Complex tones with four equal-amplitude harmonics CI Results: PCI without Context Target Onset F0: Target Offset F0: Preceding Context F0: Hz in 20 Hz steps 300 Hz 100 or 300 Hz Context: 500 ms Target: 500 ms F0: Gap: 50ms Testing procedure was the same as in Experiment 1 Target F0: F 10, 80 = 41.43, P < CI Results: PCI with Context Significant contrastive effects of pitch context were found on PCI for English-speaking CI users. A central auditory processing that works even with the greatly degraded peripheral inputs from CI. CI users may be able to use context pitch cues to handle talker variability in voice pitch, similar to NH listeners. Target F0: Context F0: Interaction: F 10, 80 = 63.82, P < F 1, 80 = 1.53, P = 0.25 F 10, 80 = 2.33, P = 0.02 Pitch Cues Available in CI Exp. 3: Place Coding Basal Advanced Bionics CI users were tested with BEDCS on EL 2 & 3 Input: Harmonic complex tones F0 increases from 100 to 300 Hz Processor: ACE strategy in Nucleus CI Stimulation rate: 900 PPS Channel selection: 8 out of Center Frequency (khz) Current steering was applied to 1000-pps pulse trains at MCL Steering coefficient α was the proportion of current on EL3 α linearly increased to create rising pitch contours EL2 α = 0 α = Apical EL3 3

4 PCI with Place Coding Context Effect with Place Coding Target α: F 10, 20 = 31.99, P < Target α: Context α: Interaction: F 10, 20 = 28.59, P < F 1, 20 = 0.26, P = 0.66 F 10, 20 = 2.07, P = 0.08 Exp. 4: Temporal Coding Nucleus CI users were tested with HEINRI on EL 20 Advanced Bionics CI users were tested with BEDCS on EL 2 30% Sinusoidal AM was applied to 1000-pps pulse trains at MCL AM frequency linearly increased to create rising pitch contours PCI with Temporal Coding EL 2 Target AM Frequency: F 10, 70 = 18.83, P < Context Effect with Temporal Coding PCI was much poorer with temporal cues alone on a single electrode than with clinical speech processors. 30% AM may not be enough to support robust pitch perception In clinical speech processors, larger AM was available on multiple electrodes and the upper limit of stimulation pattern shifted over several electrodes Weak temporal pitch cues on a single electrode even resulted in assimilatory context effect on PCI TargetAM Frequency: Context AM Frequency: Interaction: F 10, 70 = 30.41, P < F 1, 70 = 7.89, P = 0.03 F 10, 70 = 1.75, P =

5 An Alternative Listening Strategy With weak temporal cues and confused pitch contours, CI users reported using discrimination between context and target to identify the target pitch contour. Context was perceived to be flat by subjects Target was identified as rising when it was different from context More similar Less similar less rising responses more rising responses Future Studies To test if Chinese-speaking CI users listening to Mandarin tones would experience stronger contrastive effect of pitch context. To better design the test with temporal coding Use AM depth greater than 30% Introduce small random frequency changes to context To test context effect on phoneme recognition with CI In Exp. 2, CI users with poorer PCI performance also reported using this strategy and obtained assimilatory context effect. Acknowledgements We are grateful to subjects for participating in this study We thank the CI team at IUSM for recruiting CI subjects We appreciate the comments and help from lab mates Research supported by NIH/NIDCD R21-DC and Purdue University Questions? 5