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- 1. Exploratory Studies on Measuring Attentional Load Using a Dual-Task Paradigm: An Alternative Way to Evaluate Effects of Amplitude Compression University of Nebraska-Lincoln Sangsook Choi
- 2. 2 Overview n Background and interests n Motivation n Hearing aids not perfect n A lot more to be discovered to improve hearing and communication for individuals with hearing loss
- 3. 3 Rationale for Amplitude Compression n Discomfort and distortion avoidance n Compression limiting n Loudness normalization n WDRC, multiple bands n Phoneme recognition n Syllabic compression
- 4. 4 Acoustic consequences of compression n Temporal changes n Reduced envelope modulation n Distortion in amplitude envelopes n Alteration in average spectrum level n Other kinds of potential distortion
- 5. 5 Compression & Intelligibility n Conflicting results n Compression enhances and degrades the signal n Different theoretical perspectives (temporal approach) n Still in search for optimal compression to provide comfort and to improve speech intelligibility
- 6. 6 Traditional Intelligibility Measures n Recognition of phonemes, words, & sentences tested at threshold or suprathreshold levels n Tradition of engineers to measure speech intelligibility to evaluate communication systems based upon articulation index theory
- 7. 7 Limitations of intelligibility measures § Validity, reliability, & sensitivity of speech recognition tests § Low predictability of real life performance § Poor replicability § High performance in word recognition often possible with poorly specified speech (e.g., cochlear implant processed signals)
- 8. 8 Limitation of intelligibility measures (cont’) § Recognition based tests over simplifies the listening process § Understanding speech involves more than recognizing a sequence of phonemes n The listener integrates the acoustic signal with other information to comprehend the meaning of an utterance n Auditory disability is a complex problem n Recognition ability just one measure of the speech intelligibility.
- 9. 9 Traditional Approach to Intelligibility n Accuracy measures based on percent correct n Overall success rate in speech tests is result of true detectibility plus subject’s internal state n Attention and arousal n Biases and Expectations n High intelligibility scores due to perceptual effort is often not considered
- 10. 10 Alternative Approaches: n Influence of cognitive psychology n Attention and immediate memory in study of hearing and behavior (Broadbent, 1958; Rabbit, 1966) n Listeners as a cognitive interface (Pisoni, 1981) n Index of processing difficulty (listening effort) n Reaction time measures (Pratt, 1981) n STM & Free, Serial recall(Luce et al, 1982) n Dual task performance (Downs & Crum, 1978, Gordon et al, 1992)
- 11. 11 A Dual-Task Performance & Listening Effort n Attention is a limited resource (Broadbent, 1958) n For multiple tasks, attention must be shared n Kahneman’s channel capacity model (1973) n Processing capacity is overloaded, dual task performance decreases n In creased listening effort as decreased performance in the dual task.
- 12. 12 Overall Purpose n Due to the limitations of traditional intelligibility measures, an alternative method was sought to add to the traditional perspective. n To evaluate the acoustic change in speech, listening effort was considered as an additional measure of speech n The capacity demands was measured as an index of listening effort using a dual-task.
- 13. 13 Hypotheses n Increased processing demands due to distortion in speech material may not be well reflected in performance in speech recognition tests due to cognitive intervention (i.e, active top-down processes). n Increase in processing demands may be reflected as decreased performance in a dual-task as an indication of increased attentional load.
- 14. 14 Experiment 1 n The effect of amplitude compression on speech intelligibility and attention allocation was investigated. n The attentional load required for processing compressed speech was measured using a dual task dual-task to quantify listening effort. n A visual motor tracking was used to increase task demands.
- 15. 15 Experiment Design Within Groups Between Groups Cond1 Pursuit Rotor Cond2 Word repetition Cond3 Pursuit & Word repetition N Group1 Compression 32 32 32 32 Group2 Linear 32 32 32 32 N 64 64 64 64
- 16. 16 Experimental measures § Measure 1 § Word recognition ability by percent correct words: Primary task § Measure 2 § Visual-motor Tracking ability by percent of time on target: Secondary task
- 17. 17 Participants § N=64 (n1, n2=32) § Normal hearing § native English speakers § Ages 19 to 55 (mean=27) § 60 females and 4 males § Primarily students
- 18. 18 Material for Word Recognition § Monosyllabic words § Digitally recorded by a male talker with mid-western dialect § Digitally mixed with speech shaped noise at a 6 dB SNR § Two types of stimuli § Compressed: WDRC § Un-Compressed: Linear
- 20. 20 Procedures for Word recognition task n Random presentation by IDRT (Tice & Carrell, 1998) and TDT. n Binaural presentation n Approximately 72 dB SPL at circumaural headphones n Word repetition performed alone and along with tracking task
- 21. 21 Visual Motor Task § Pursuit Rotor: § Visual motor learning § Computerized by Dlhopolsky, 2000 § Tracking a dot using a mouse § Percent time on target
- 23. 23 Procedure § Hearing screening § Demographic information § Written instructions § Familiarization with Pursuit Rotor § Experiment trials § Post-experiment questionnaire § Subject’s impression, techniques, and comments
- 24. 24 The subject is performing listening and tracking simultaneously Pursuit Rotor Tracking “Cub”
- 25. 25 81.81 79.31 82.72 78.50 70 72 74 76 78 80 82 84 86 88 90 Linear Compressed PercentCorrectWords No Tracking Tracking Word Recognition Results
- 26. 26 Tracking Results 68.74 68.869.63 66.18 56 58 60 62 64 66 68 70 72 Linear Compression PercentTimeonTarget Single Dual
- 27. 27 Linear Compressed Word Recognition Pursuit Rotor -1.1439 2.68 -0.91 0.81 -2 -1 0 1 2 3 Differencein %Accuracy Inferential Statistics F(1, 56)= 6.517, P<.02 F(1, 56)= 2.48, P<.13 N=64
- 28. 28 Conclusion and Discussion n The effect of compression was to reduce performance on a simultaneous pursuit rotor tracking task. The simultaneous tracking task did not cause reduced performance on the word-repetition-task. n The Pursuit Rotor performance decrement was interpreted as due to increased capacity demands for processing compressed speech.
- 29. 29 Limitations n Fatigue, learning effect, n Small effect size and weak statistical power n This version of Pursuit Rotor is not customizable n Calibrating level of vigilance (right amount of attention, it doesn’t distract but helps concentration)
- 30. 30 Experiment 2 n A more sensitive measure of listener attention and effort was sought. A linguistic (lexical decision) task was investigated as a simultaneous task. n Linguistic distraction was explored to improve the level of interference based upon the modal model of attention theory.
- 31. 31 Modality of Interference n Modular theories n The degree of similarity between 2 tasks n Similar task compete for the same processing modules
- 32. 32 Hypotheses n It was assumed that the lexical decision task would use the same resource for word repetition to access lexicon. It was, therefore, expected that lexical decision task would result in a higher level of distraction than the visual motor tracking task so that it will differentiate better compressed speech from uncompressed speech. n It was hypothesized that simultaneous lexical decision performance would be better for uncompressed than compressed speech. This hypothesis was based on presumed reduction of cues available in compressed words.
- 33. 33 Experimental Measures § Measure 1:Primary § Word recognition § Percent correct words § Open-set format: verbal repetition § Measure 2: Secondary § Lexicality § P(c)max: unbiased measure, SDT § Forced choice: word vs. nonword
- 34. 34 Participants § N=40 (n1, n2=20) § Normal hearing § native English speakers § Ages 19 to 41 (mean=24) § 37 females and 3 males § Primarily students
- 35. 35 Visual Stimuli for Lexical Decision n Lexical lists consist of 50 % words (Balota & Spieler, 1998) and 50 % nonwords (Washington University Lexicon Project Website). n Subjective familiarity, length of words, reaction time, frequency of orthographs are matched for two lexical lists. n 48 points tall with an Arial typeface. n 15 inch monitor n Each word placed in a Gaussian noise background n Corel Photopaint 11.
- 36. 36 Examples of Visual Stimuli Left panel shows word “THAW” and right panel shows nonword “ACAS” that were used in the lexical decision task.
- 37. 37 Apparatus & Procedure for Lexical Decision n Random presentation of visual stimuli controlled using Presentation .7 (Neurobehavioral system, 2003) n Displayed on a 15 inch monitor n Resolution: n The distance between a subject and a computer screen approximately 63 cm. n Visual stimuli displayed on a center of the screen for 500 ms. n Subjects asked to push a button labeled either word or nonword corresponding to their lexical decisions
- 38. 38 The participant is pushing lexicality button in response to a visual stimulus The word “SCHEME” is displayed for the lexical decision task
- 39. 39 Lexical Decision Task Demo
- 40. 40 Results Word Repetition 50 60 70 80 90 Compressed Uncompressed PercentCorrect Distraction No-distraction P(c) max-Lexical Decision 0.7 0.75 0.8 0.85 0.9 0.95 Compressed Uncompressed P(c)max Distraction No_distraction Means and 95 % confidence intervals shown as error bars are displayed in the charts. No significance is found using a simultaneous lexical decision task.
- 41. 41 Conclusions and Discussion n The dual task using the lexical decision task failed to measure increased listening effort due to compression. n Linguistic distraction was no better than visual motor distraction. n Inconsistent findings using a dual-task might have resulted from an insufficient level of distraction (Task difficulty).
- 42. 42 Conclusion and Discussion (cont’) n Use of sensory memory (echoic vs. iconic). n Multiple resource theory seems to apply to the findings: Stage of processing, and code of processing, modalities of input and output. n 2/3 of Participants reported more difficulty performing a dual task than a single task. There might be relation between task difficulty and level of attention.
- 44. 44 Comparing Word Recognition 81 .81 79.31 83.20 79.35 82.72 78.50 83.05 79.1 5 70 75 80 85 90 95 100 Linear Compressed Linear Compressed Pursuit-R Lex-Dec PercentCorrect Alone Distract
- 45. 45 Comparing Distractor Performance 60 65 70 75 80 85 90 95 100 Linear Compression Linear Compression Pursuit Rotor Lexical Decision No_distraction Distraction
- 46. 46 Overall Conclusion and Discussion n Compression yielded lower word intelligibility compared to linear processing. n Compression decreased tracking ability but not lexicality. n Task difficulty seems more important factor than task similarity.
- 47. 47 Future Research n Additional levels of distraction should be investigated to find performance functions for simultaneous tasks. n Accurate measures of listener effort n Similar levels of distraction to be developed across different tasks n Additional dependent measures might be examined n Non-word vocalization, slurred articulation, and vocal loudness.
- 48. 48 Q & A
- 49. 49 Q & A
- 50. 50 Q & A
- 51. 51 81.81 79.31 82.72 78.50 70 72 74 76 78 80 82 84 86 88 90 Linear Compressed PercentCorrectWords No Tracking Tracking Word Recognition Results
- 53. 53 Descriptive Results Word Repetition 50 60 70 80 90 Compressed Uncompressed PercentCorrect Distraction No-distraction d'-Lexical Decision 0 0.5 1 1.5 2 2.5 3 3.5 Compressed Uncompressed d' Distraction No_distraction P(c) max-Lexical Decision 0.7 0.75 0.8 0.85 0.9 0.95 Compressed Uncompressed P(c)max Distraction No_distraction Decision Criteria (Log of Beta) Lexical Decision -0.5 -0.3 -0.1 0.1 0.3 0.5 Compresssed Uncompressedlogβ Distraction No_distraction Means and 95 % confidence intervals shown as error bars are displayed in the charts. No significance is found using a simultaneous lexical decision task.
- 55. 55 Compression Characteristics n A single-band WDRC n 4:1 compression ratio n 40 dB knee point n 5 ms attack /15 ms release time. Input Output
- 56. 56 Trial Sequence Graphic word + noise Repeat word Press button Delay Trial begins Spoken word Graphic noise alone Trial begins Time
- 57. 57 .122 3.816 2.000 55.000 .028 .878 3.816 2.000 55.000 .028 .139 3.816 2.000 55.000 .028 .139 3.816 2.000 55.000 .028 .566 35.815 2.000 55.000 .000 .434 35.815 2.000 55.000 .000 1.302 35.815 2.000 55.000 .000 1.302 35.815 2.000 55.000 .000 .481 25.503 2.000 55.000 .000 .519 25.503 2.000 55.000 .000 .927 25.503 2.000 55.000 .000 .927 25.503 2.000 55.000 .000 .080 2.388 2.000 55.000 .101 .920 2.388 2.000 55.000 .101 .087 2.388 2.000 55.000 .101 .087 2.388 2.000 55.000 .101 .018 .510 2.000 55.000 .603 .982 .510 2.000 55.000 .603 .019 .510 2.000 55.000 .603 .019 .510 2.000 55.000 .603 .029 .826 2.000 55.000 .443 .971 .826 2.000 55.000 .443 .030 .826 2.000 55.000 .443 .030 .826 2.000 55.000 .443 .013 .370 2.000 55.000 .693 .987 .370 2.000 55.000 .693 .013 .370 2.000 55.000 .693 .013 .370 2.000 55.000 .693 Pillai's Trace Wilks' Lambda Hotelling's Trace Roy's Largest Root Pillai's Trace Wilks' Lambda Hotelling's Trace Roy's Largest Root Pillai's Trace Wilks' Lambda Hotelling's Trace Roy's Largest Root Pillai's Trace Wilks' Lambda Hotelling's Trace Roy's Largest Root Pillai's Trace Wilks' Lambda Hotelling's Trace Roy's Largest Root Pillai's Trace Wilks' Lambda Hotelling's Trace Roy's Largest Root Pillai's Trace Wilks' Lambda Hotelling's Trace Roy's Largest Root Effect GROUP LIST ORDERDIS GROUP * LIST GROUP * ORDERDIS LIST * ORDERDIS GROUP * LIST * ORDERDIS Value F Hypothesi s df Error df Sig.
- 58. 58 2079.625 8 259.953 13.638 .000 1481.840 8 185.230 5.160 .000 47.266 1 47.266 2.480 .121 233.960 1 233.960 6.517 .013 1359.766 1 1359.766 71.340 .000 3.933 1 3.933 .110 .742 618.766 1 618.766 32.464 .000 1045.019 1 1045.019 29.110 .000 50.766 1 50.766 2.663 .108 47.793 1 47.793 1.331 .253 1.266 1 1.266 .066 .798 37.128 1 37.128 1.034 .314 .391 1 .391 .020 .887 55.194 1 55.194 1.537 .220 1.266 1 1.266 .066 .798 21.061 1 21.061 .587 .447 1067.375 56 19.060 2010.374 56 35.900 3147.000 64 3492.213 64 Dependent Variable WORDDIFF PRDIFF WORDDIFF PRDIFF WORDDIFF PRDIFF WORDDIFF PRDIFF WORDDIFF PRDIFF WORDDIFF PRDIFF WORDDIFF PRDIFF WORDDIFF PRDIFF WORDDIFF PRDIFF WORDDIFF PRDIFF Source Model GROUP LIST ORDERDIS GROUP * LIST GROUP * ORDERDIS LIST * ORDERDIS GROUP * LIST * ORDERDIS Error Total Type III Sum of Squares df Mean Square F Sig.