Linguistic law-like compression strategies emerge to maximize coding efficiency in marmoset vocal communication.

Human language follows statistical regularities or linguistic laws. For instance, Zipf's law of brevity states that the more frequently a word is used, the shorter it tends to be. All human languages adhere to this word structure. However, it is unclear whether Zipf's law emerged de novo in humans or whether it also exists in the non-linguistic vocal systems of our primate ancestors. Using a vocal conditioning paradigm, we examined the capacity of marmoset monkeys to efficiently encode vocalizations. We observed that marmosets adopted vocal compression strategies at three levels: (i) increasing call rate, (ii) decreasing call duration and (iii) increasing the proportion of short calls. Our results demonstrate that marmosets, when able to freely choose what to vocalize, exhibit vocal statistical regularities consistent with Zipf's law of brevity that go beyond their context-specific natural vocal behaviour. This suggests that linguistic laws emerged in non-linguistic vocal systems in the primate lineage.

Author Correction: Cognitive control of complex motor behavior in marmoset monkeys.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Cognitive control of complex motor behavior in marmoset monkeys.

Marmosets have attracted significant interest in the life sciences. Similarities with human brain anatomy and physiology, such as the granular frontal cortex, as well as the development of transgenic lines and potential for transferring rodent neuroscientific techniques to small primates make them a promising neurodegenerative and neuropsychiatric model system. However, whether marmosets can exhibit complex motor tasks in highly controlled experimental designs-one of the prerequisites for investigating higher-order control mechanisms underlying cognitive motor behavior-has not been demonstrated. We show that marmosets can be trained to perform vocal behavior in response to arbitrary visual cues in controlled operant conditioning tasks. Our results emphasize the marmoset as a suitable model to study complex motor behavior and the evolution of cognitive control underlying speech.

Limited capabilities for condition-dependent modulation of vocal turn-taking behavior in marmoset monkeys.

Taking turns plays an important role in primate communication and involves individuals producing species-specific calls in response to conspecific vocalizations. Recent studies have revealed that marmoset monkeys are an ideal primate model system to investigate vocal turn-taking behavior and the corresponding sensory-motor interactions. However, it is largely unknown how external factors such as conspecific call latency influence this vocal behavior. Using interactive playback, we systematically answered vocalizations of monkeys with either short- or long-call response latencies. By placing marmosets in these different behavioral conditions, we demonstrate that vocal turn taking is a robust behavior with only minor condition-dependent changes that is exhibited not only in the range of species-specific call latencies of vocal partners but also in conditions well outside natural behavioral boundaries. We find that specific features of vocal performance such as call response rates and call sequences remain surprisingly stable, whereas others such as turn-taking rates and response latencies exhibit condition-dependent differences during this behavior. These condition-dependent modulations suggest that a combination of flexible and more rigid mechanisms control marmoset vocal turn-taking behavior. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

When is inhibition of return input- or output-based? It depends on how you look at it.

Two important diagnostics have been used to infer whether the effect of inhibition of return, when preceded by a saccade, is primarily upon input (i.e., attentional/perceptual level) or output (i.e., response/decision level) processes. Data from antisaccade paradigms involving luminance targets in peripheral vision suggest input effects whereas data from spatially compatible manual responses to centrally presented arrow targets suggest output effects. Here, we combine these diagnostics to resolve the discrepancy. In separate conditions participants made a pro- or antisaccade to a peripheral stimulus. Upon returning gaze to the original fixation, left and right manual responses were made to left- and right-pointing arrows at fixation, respectively. The primary objective of the prosaccade condition was to determine whether an eye movement toward a visual stimulus that was not associated with a manual localization response would bias spatially compatible manual responses against the prior saccade vector. Manual responses were slowest in the direction of the prior saccade, consistent with an output-based attribution (e.g., Posner, Rafal, Choate, & Vaughan, 1985). The primary objective of the antisaccade condition was to determine whether an eye movement away from a visual stimulus would also bias subsequent manual responses. No apparent response bias was detected, consistent with an input-based attribution (e.g., Fecteau, Au, Armstrong, & Munoz, 2004). Collectively, the findings indicate that there are 2, dissociable forms of inhibition depending on saccadic response demands. Converging evidence from other paradigms is discussed. (PsycINFO Database Record