Natural variability in species-specific vocalizations constrains behavior and neural activity

Abstract

A listener’s capacity to discriminate between sounds is related to the amount of acoustic variability that exists between these sounds. However, a full understanding of how this natural variability impacts neural activity and behavior is lacking. Here, we tested monkeys’ ability to discriminate between different utterances of vocalizations from the same acoustic class (i.e., coos and grunts), while neural activity was simultaneously recorded in the anterolateral belt region (AL) of the auditory cortex, a brain region that is a part of a pathway that mediates auditory perception. Monkeys could discriminate between coos better than they could discriminate between grunts. We also found AL activity was more informative about different coos than different grunts. This difference could be attributed, in part, to our finding that coos had more acoustic variability than grunts. Thus, intrinsic acoustic variability constrained the discriminability of AL spike trains and the ability of rhesus monkeys to discriminate between vocalizations.

Functional Organization of the Ventral Auditory Pathway

“…For example, AL neurons respond categorically, and in a manner consistent with listeners' behavioral reports, to morphed versions of two speech sounds (“bad” and “dad”). AL neurons also respond categorically to species-specific vocalizations; however, the degree to which AL (and listen-ers) can categorize these vocalizations is constrained by the vocalizations' acoustic variability ( Christison-Lagay et al 2014 ). In humans, the superior temporal gyrus is categorically and hierarchically organized by speech sounds ( Binder et al 2000 ; Chang et al 2010 ; Leaver and Rauschecker 2010 ): phoneme categories are found in the middle aspect; word categories in the anterior-superior aspect; and phrases in the most anterior aspect ( DeWitt and Rauschecker 2012 ; Rauschecker 2012 ).…”

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

“…For example, AL neurons respond categorically, and in a manner consistent with listeners' behavioral reports, to morphed versions of two speech sounds ("bad" and "dad"). AL neurons also respond categorically to species-specific vocalizations; however, the degree to which AL (and listeners) can categorize these vocalizations is constrained by the vocalizations' acoustic variability (Christison-Lagay et al 2014). In humans, the superior temporal gyrus is categorically and hierarchically organized by speech sounds (Binder et al 2000;Leaver and Rauschecker 2010): phoneme categories are found in the middle aspect; word categories in the anterior-superior aspect; and phrases in the most anterior aspect Rauschecker 2012).…”

Time as a supervisor: temporal regularity and auditory object learning

“…The effect will depend on the particular temporal statistics of each vocalization class. Indeed, previous work has report higher variability between coos as compared to other vocalization classes [20], perhaps explaining the higher discrimination performance for the coo class. It is possible that the discriminatory differences that are absent the five slowest features that we used may be present in the next fastest features of SFA.…”

“…We chose these classes because they had the most unique exemplars, and thus we could generate the most training data for them. This library encompasses a substantial fraction of the natural variability inherent in rhesus vocalizations [20], although it is not a complete sampling. Vocalizations were recorded at 50 kHz.…”