Tuning of Human Modulation Filters Is Carrier-Frequency Dependent

Abstract

Recent studies employing speech stimuli to investigate ‘cocktail-party’ listening have focused on entrainment of cortical activity to modulations at syllabic (5 Hz) and phonemic (20 Hz) rates. The data suggest that cortical modulation filters (CMFs) are dependent on the sound-frequency channel in which modulations are conveyed, potentially underpinning a strategy for separating speech from background noise. Here, we characterize modulation filters in human listeners using a novel behavioral method. Within an ‘inverted’ adaptive forced-choice increment detection task, listening level was varied whilst contrast was held constant for ramped increments with effective modulation rates between 0.5 and 33 Hz. Our data suggest that modulation filters are tonotopically organized (i.e., vary along the primary, frequency-organized, dimension). This suggests that the human auditory system is optimized to track rapid (phonemic) modulations at high sound-frequencies and slow (prosodic/syllabic) modulations at low frequencies.

Selective Adaptation to “Oddball” Sounds by the Human Auditory System

“…Our data are consistent with experimental recordings from small mammals in which firing rates of auditory neurons adapt to the unfolding distributions of sound intensity (Ulanovsky et al, 2003(Ulanovsky et al, , 2004Nelken, 2004;Dean et al, 2005Dean et al, , 2008Peréz-González et al, 2005;Sadagopan and Wang, 2008;Watkins and Barbour, 2008;Malmierca et al, 2009;Wen et al, 2009;Barbour, 2011;Jaramillo and Zador, 2011;Rabinowitz et al, 2011;Walker and King, 2011;Yaron et al, 2012). This feature of neural coding, which emerges at the level of the primary auditory nerve, improves coding (discrimination) of the most-likely occurring intensities in a distribution of sounds (Dean et al, 2008).…”

“…These two demands appear in conflict in terms of their call on neural resources. Adaptation to "enhance" representation of both common (Dean et al, 2005(Dean et al, , 2008Sadagopan and Wang, 2008;Watkins and Barbour, 2008;Wen et al, 2009;Barbour, 2011;Jaramillo and Zador, 2011;Rabinowitz et al, 2011;Walker and King, 2011) and rare (Ulanovsky et al, 2003(Ulanovsky et al, , 2004Nelken, 2004;Peréz-González et al, 2005;Malmierca et al, 2009;Yaron et al, 2012) sounds has been reported in neurophysiological studies, seemingly in the same brain centers and using similar probabilistic stimulus paradigms. How then does sensitivity to the statistical distribution of sounds manifest in sensitivity to both high-probability and low-probability events?…”

“…A phenomenological model of selective adaptation Selective adaptation to oddball sounds probably involves some form of interaction between adaptive effects (Ulanovsky et al, 2004;Dean et al, 2008;Yaron et al, 2012) and neural tuning widths on sensory continua (O'Connell et al, 2011). However, building a detailed biophysical model of this phenomenon is challenging given the paucity of relevant physiological data and the vast range of possible circuits.…”

“…Attention has featured prominently in investigations of "cocktail party listening." Cortical entrainment (synchronization of neuronal duty-cycle with the envelope of the stimulus) has been suggested as one low-level substrate (Ding and Simon, 2013;Lakatos et al, 2013;Zion Golumbic et al, 2013), and even if entrainment is not a substrate, it is associated with, and mediated by, attention. Auditory neurons appear to exist in a state of perpetual oscillation, between excitatory and refractory states, known as the duty cycle .…”

“…For many species, survival depends on the ability to encode the current sensory scene with a high degree of accuracy, while remaining alert to novel events in the environment (Bregman, 1990;McDermott, 2009). These two demands appear in conflict in terms of their call on neural resources.…”