THÈSE DE DOCTORAT DE L’UNIVERSITÉ PARIS DESCARTES présentée par Claire CHAMBERS Sujet: Context effects in ambiguous frequency shifts: A new paradigm to study adaptive audition preparée à L’ÉQUIPE AUDITION LABORATOIRE DE PSYCHOLOGIE DE LA PERCEPTION ÉCOLE NORMALE SUPÉRIEURE – UNIVERSITÉ PARIS DESCARTES Soutenue le Mercredi 20 Novembre 2013 devant le jury composé de Rhodri Cusack Professeur, University of Western Ontario Rapporteur Andrew Oxenham Professeur, University of Minneapolis Rapporteur Israel Nelken Professeur, Hebrew University Jerusalem Examinateur John Rinzel Professeur, New York University Examinateur Daniel Pressnitzer Directeur de recherche, École Normale Supérieure Directeur de thèse i – – Abstract In this thesis, we developed a new experimental paradigm for studying how recent sensory history (the context) affects a basic aspect of auditory perception, the comparison of successive frequency components. Stimuli were devised to include ambiguous transitions between frequency components, as it was hypothesized that such an ambiguity would make the task especially prone to reveal context effects. Six psychophysical experiments are reported. Using pairs of Shepard tones (Shepard, J. Acoust. Soc. Am., 1964), we first demonstrate a strong hysteresis effect when successive pairs are judged, whereby past trials affect current judgments. We then isolate the cause of this context effect, by contrasting perceptual reports for a same ambiguous test pair when preceded by different contexts. We show that frequency shifts are preferentially reported when they encompass a frequency regions that was stimulated during the context. This context effect is rapidly introduced, as a single tone as short as 20ms can produce a reliable bias. Yet it also has an enduring effect on perception, persisting over more than 30s. Using random chords pairs designed to include ambiguous frequency shifts, it then shown that the context effect is not specific to Shepard tones but rather reflects a generic process acting on the tonotopic representation of sounds. Finally, the context effect is modulated by both low-level (ear-of-entry) and high-level (selective attention) manipulations, suggesting an interplay between several processing stages for the underlying neural mechanism. Our findings show that one of the most ubiquitous and basic tasks of the auditory system, comparing successive frequency components, is not a fixed function of the physical stimulus. Rather, it is highly malleable and depends on the ongoing context. ii – – Contents Chapter 1 Introduction _______________________________________________ 9 1.1 Should context matter? _____________________________________________ 9 1.2 Perception as an ill-posed problem ___________________________________ 10 1.3 Perceptual inference ______________________________________________ 11 1.4 Prior knowledge __________________________________________________ 12 1.5 Context _________________________________________________________ 13 1.6 Structure of thesis ________________________________________________ 13 Chapter 2 Neural evidence for auditory context effects ____________________ 15 2.1 Tonotopy _______________________________________________________ 15 2.2 Tones and tone sequences __________________________________________ 16 2.2.1 Adaptation in the auditory nerve ___________________________________________ 16 2.2.2 Sub-cortical adaptive coding ______________________________________________ 18 2.2.3 Enhancement __________________________________________________________ 19 2.2.4 Stimulus-specific adaptation ______________________________________________ 20 2.2.5 Time-to-space mapping __________________________________________________ 22 2.3 Plasticity and memory _____________________________________________ 23 2.3.1 Rapid plasticity _________________________________________________________ 23 2.3.2 Tonotopic activity during maintenance of tones in memory _____________________ 24 2.4 Conclusion: Pervasive neural context effects in the auditory system ________ 26 Chapter 3 Behavioral evidence for auditory context effects _________________ 27 3.1 Loudness recalibration _____________________________________________ 28 3.2 Spectral enhancement _____________________________________________ 30 3.3 Adaptation and enhancement of frequency shifts _______________________ 31 iii – – 3.3.1 Frequency-shift detectors ________________________________________________ 31 3.3.2 Adaptation of frequency shifts _____________________________________________ 34 3.3.3 Enhancement of frequency shifts __________________________________________ 35 3.4 Regression to the mean in frequency judgments ________________________ 37 3.5 Conclusion ______________________________________________________ 40 Chapter 4 Ambiguous stimuli as a tool to study context effects ______________ 41 4.1 Multistable perception ____________________________________________ 42 4.2 Hysteresis in visually ambiguous stimuli _______________________________ 43 4.2.1 Ambiguous images ______________________________________________________ 43 4.2.2 Motion quartet _________________________________________________________ 44 4.2.2.1 Short- and long-range interactions with the motion quartet __________________ 46 4.3 Perceptual memory in interrupted ambiguous stimuli ___________________ 47 4.4 Temporal dynamics of visual motion priming ___________________________ 49 4.5 Context effects in ambiguous auditory stimuli __________________________ 51 4.5.1 Auditory streaming ______________________________________________________ 51 4.5.2 Contrast enhancement in the categorization of ambiguous speech sounds _________ 53 4.6 Conclusion: perceptual stabilization and novelty detection _______________ 56 Chapter 5 Shepard tones: Ambiguous auditory stimuli to study context effects? 59 5.1 Shepard tones ____________________________________________________ 60 5.1.1 Definition _____________________________________________________________ 60 5.1.2 Circularity in pitch judgment ______________________________________________ 61 5.1.3 Ambiguity in pitch judgment ______________________________________________ 61 5.1.4 Is the circularity of Shepard tones related to pitch chroma? _____________________ 65 5.2 Biases in the perception of pitch class ________________________________ 65 5.3 Context effects in the perception of Shepard tones ______________________ 67 iv – – 5.3.1 Context-dependence of the pitch class bias __________________________________ 67 5.3.2 Context-invariance of the pitch class bias ____________________________________ 68 5.3.3 Spectral motion adaptation _______________________________________________ 70 5.3.4 Hysteresis in Shepard tone perception ______________________________________ 71 5.4 Conclusion ______________________________________________________ 73 Chapter 6 Experimental plan __________________________________________ 75 Chapter 7 Experiment 1: Hysteresis in the perception of Shepard tones _______ 77 7.1 Introduction _____________________________________________________ 77 7.2 Screening test ____________________________________________________ 79 7.2.1 Method _______________________________________________________________ 81 7.2.1.1 Stimuli _____________________________________________________________ 81 7.2.1.2 Procedure __________________________________________________________ 82 7.3 Experiment 1: Hysteresis in Shepard tones _____________________________ 83 7.3.1 Method _______________________________________________________________ 83 7.3.1.1 Participants _________________________________________________________ 83 7.3.1.2 Stimuli _____________________________________________________________ 83 7.3.1.3 Procedure __________________________________________________________ 83 7.3.1.3.1 6 st condition ___________________________________________________ 84 7.3.1.3.2 Random condition _______________________________________________ 84 7.3.1.3.3 Increasing condition ______________________________________________ 85 7.3.1.3.4 Decreasing condition _____________________________________________ 85 7.3.1.3.5 Omissions ______________________________________________________ 85 7.3.1.3.6 Repeats and number of trials _______________________________________ 85 7.3.1.3.7 Apparatus ______________________________________________________ 85 7.3.1.4 Data analysis ________________________________________________________ 86 v – – 7.3.2 Results ________________________________________________________________ 87 7.3.2.1 6 st condition _______________________________________________________ 87 7.3.2.2 Random condition ___________________________________________________ 90 7.3.2.3 Increasing and decreasing conditions ____________________________________ 91 7.3.2.4 Omissions __________________________________________________________ 92 7.3.2.5 Molecular analysis of the random condition _______________________________ 93 7.4 Discussion _______________________________________________________ 94 Chapter 8 Experiment 2: Tone sequences as context _______________________ 99 8.1 Introduction _____________________________________________________ 99 8.2 Method ________________________________________________________ 100 8.2.1 Participants ___________________________________________________________ 100 8.2.2 Stimuli _______________________________________________________________ 101 8.2.3 Procedure and apparatus ________________________________________________ 103 8.2.4 Data analysis __________________________________________________________ 103 8.3 Results_________________________________________________________