Master 2014 2015
Stages de la spécialité SAR
Pitch sensitivity and context


Site :Laboratoire des systèmes perceptifs
Lieu :Ecole normale supérieure, 29 rue d'Ulm
Encadrant : Alain de Cheveigné
Dates :2015
Rémunération :standard
Mots-clés : Parcours ATIAM : Informatique musicale, Parcours ATIAM : Traitement du signal


Description

The aim is to explore issues related to context and sensory memory in pitch perception using an new efficient task. In classic pitch tasks, the listener is presented with a set of two (or more) tones and must judge which is higher. In the new task, the subject is presented with an ongoing sequence of tones, and must respond after each tone whether it is higher vs lower than the previous tone.

Because a response is gathered from each tone, and the tones can be presented at a relatively high rate, the yield is high (number of pitch judgments per unit time), so the task should be useful in studies of pitch sensitivity. It is also a good task to study context effects (effects of prior stimulus history), because tones preceding the last pair are equidistant, and all have the same status. Finally, the task should be useful in EEG / MEG studies, because there is no distinct trial-onset response.

(1) Validate the paradigm. To be useful as a tool to measure of sensory limits, the task should be validated by comparison with a standard task. We measure thresholds of a set of subjects (e.g. 8) using both a standard 2-interval task and the new task. For comparison we will measure thresholds for frequency (pitch) and another dimension such as intensity (loudness).

(2) Bias vs sensory noise. Pitch discrimination is usually analyzed as if performance were limited by the magnitude of sensory or memory noise relative to the size of the frequency step (as quantified by d’). This noise is supposed to arise within the process of encoding and/or retention of the pitch of the tones being compared, and should normally depend only on their parameters. However there is evidence that the judgment may also be biased by the history of prior stimulation. For example pitch thresholds in two-interval tasks are higher if the overall frequency is roved between each trial, as if the large inter-trial frequency step were interfering with the measurement of the smaller intra-trial step. If the bias is systematic it is misleading to analyze it as if it were due to sensory noise. We will use our new task to (a) determine the magnitude and nature of the bias, and (b) factor it out so that the "pure" sensory performance can be measured.

(3) Further explore the nature of context effects. The context effects themselves are of interest. By manipulating the tone frequency schedule, it is possible to explore issues such as the roles of temporally local (recent) vs global (longer term) statistics, sensory integration vs bayesian integration models, etc. For example one can contrast a random walk process (in which there is no long term constraint on the distribution of values, and thus no benefit for accumulating sensory evidence or a prior over successive stimuli) with a random process that instead draws from a small range of values (in which the global constraint is strong). One can explore the profile of sensitivity across frequency (are small/medium frequency differences more or less influential than large ?) or the relative role of absolute frequency vs frequency change in the context effects.

(4) Connection with other studies. The paradigm should be useful to better understand the effect of roving on pitch acuity, subject-specific-differences in sensitivity to direction vs sensitivity to change (Ofri et al 2012, Mathias et al 2010, Semal & Demany 2006, etc.), as well as other reported effects of frequency context (e.g. Shepard tones, Demany’s change detectors, Demany’s peak/trough asymetry, Deutch’s sensory memory interference effects).

Bibliographie

Mathias, S. R., Bailey, P. J., Semal, C., & Demany, L. (2011). A note about insensitivity to pitch-change direction. The Journal of the Acoustical Society of America, 130(4), EL129. doi:10.1121/1.3629139

Mathias, S. R., Micheyl, C., & Bailey, P. J. (2010). Stimulus uncertainty and insensitivity to pitch-change direction. The Journal of the Acoustical Society of America, 127(5), 3026. doi:10.1121/1.3365252

Mathias, S.R. (2010) Individual differences in pitch perception, thesis.

Nahum, M., Daikhin, L., Lubin, Y., Cohen, Y., & Ahissar, M. (2010). From Comparison to Classification : A Cortical Tool for Boosting Perception. Journal of Neuroscience, 30(3), 1128–1136. doi:10.1523/JNEUROSCI.1781-09.2010

Demany, L., & Ramos, C. (2005). On the binding of successive sounds : Perceiving shifts in nonperceived pitches. The Journal of the Acoustical Society of America, 117(2), 833. doi:10.1121/1.1850209

Raviv, O., Ahissar, M., & Loewenstein, Y. (2012). How Recent History Affects Perception : The Normative Approach and Its Heuristic Approximation. PLoS Computational Biology, 8(10), e1002731. doi:10.1371/journal.pcbi.1002731.s005

BULL, A. R., & CUDDY, L. L. (1972). Recognition Memory for Pitch of Fixed and Roving Stimulus Tones. Perception & Psychophysics, 11(1B), 105–&.

Chambers, C. & Pressnitzer, D. (2014). Perceptual hysteresis in the judgment of auditory pitch shift. Attention, Perception, & Psychophysics, 76 : 1271-1279.