The basal ganglia contribute to acquisition, planning, initiation, and execution of vocal and gestural communication skills in primates, birds, and other animals. Consistent with dual-pathway models of language evolution, Ackermann et al. in the target article now speculate the basal ganglia also integrate and modulate (continuous or analog) affective prosody of vocalizations and gesticulations with little to no influence over (discrete or digital) propositional linguistic content of human phonetic and, presumably, signed speech. The authors cite comparative clinical and basic research findings to support their claim that high-level linguistic processing only occurs in phylogenetically newer brain systems, while omitting the recent small, but credible, neuroimaging literature which contradicts this assertion and implicates human cortico-striatal-thalamic circuitry in disambiguating lexical (Chenery et al. Reference Chenery, Angwin and Copeland2008; Copeland Reference Copeland2003), grammatical (Mestres-Missé et al. Reference Mestres-Missé, Turner and Friederici2012), and semantic (Ketteler et al. Reference Ketteler, Kastrau, Vohn and Huber2008; Marques et al. Reference Marques, Canessa and Cappa2009; Wittforth et al. Reference Wittforth, Schröder, Schardt, Dengler, Heinze and Kotz2010) uncertainties in perceived language. Failure to assimilate roles of the basal ganglia in both language production and comprehension seriously weakens the conceptual validity and power of Ackermann et al.'s treatise on selective fitness of advancing animal taxa to evolve increasingly sophisticated dual-pathway communication systems for affective and propositional information exchange.

Evolutionarily older functions of cortico-striatal-thalamic loops to generate and filter variances in affective prosody of non- and/or protolinguistic species-typical/atypical communications, as advocated by Ackermann et al., seem to have eventually and adaptively converged to help perform similar operations on propositional linguistic content, as evidenced in later human language use. Such (lateralized) developments in cortico-striatal-thalamic processing necessarily first enabled language-deficient nonhuman animals to better articulate innate and/or learned primitive communications (e.g., recombinant hierarchical call or song sequences with precise, intricate spectral patterns) and, therefore, to more successfully transmit meanings or labels of both continuously and discretely structured information for receiver understanding (Arnold & Zuberbühler Reference Arnold and Zuberbühler2006; Berwick et al. Reference Berwick, Okanoya, Beckers and Bolhuis2011; Bolhuis et al. Reference Bolhuis, Okanoya and Skarff2010; Doupe et al. Reference Doupe, Perkel, Reiner and Stern2005; Ouattara et al. Reference Ouattara, Lemasson and Zuberbühler2009; Zuberbühler Reference Zuberbühler2000a; Zuberbühler et al. Reference Zuberbühler, Cheney and Seyfarth1999). Despite lack of direct empirical proof, one can further safely reason that homologous or analogous neuromechanisms for disambiguating communication content arose from ecological forces that continue to drive changes in production, comprehension, and privatization of public vocal and gestural communications ancestral to and descendent from early hominin language innovations.

Capacities of cortico-striatal-thalamic pathways to regulate variability in communication production and comprehension likely coevolved with animal abilities to encrypt and decrypt sensitive public information at risk of corruption or interception from social eavesdroppers. Evolution conserved social eavesdropping across phylogeny, whereby unintended observers breach information security of communicating parties in attempts to gain survival and/or reproductive advantages (Clark Reference Clark2010; Reference Clark2013a; Reference Clark and Clark2013b; in press; Dabelsteen Reference Dabelsteen2004; Dall Reference Dall2005; Danchin et al. Reference Danchin, Giraldeau, Valone and Wagner2004; Joint Reference Joint2006; Peake & McGregor Reference Peake and McGregor2004; Seyfarth & Cheney Reference Seyfarth and Cheney2010; Stowe et al. Reference Stowe, Turlings, Loughrin, Lewis and Tumlinson1995). Cortico-striatal-thalamic circuitry, via involvement in automatic and/or volitional processing of affective and propositional content variability, predictably sets limits on useful complexity of naturally communicated information. These constraints determine probabilities that public exchanges may be discriminated by intended observers and safeguarded against social eavesdroppers. When communication complexity processed by phylogenetically or culturally distant unintended observers far subtends upper complexity limits for information processed over superior disambiguation neuromechanisms of intended observers, information content of public messages and replies will remain protected from eavesdropping. Complexity scaling of communication production and comprehension extends along the continuum of signals to protolanguage to language and figures to be an essential evolutionary strategy to secure communications within and across taxonomic boundaries.

One may begin to appreciate evolved neurobiological barriers to social eavesdropping by enlisting examples of dual-pathway systems for birdsong and human speech given by Ackermann et al. The cortico-striatal-thalamic circuitry of birds and humans effect complexity scaling through two broad, related domains of complexity – combinatorial and computational complexity – each having particular significance for communication production and comprehension as well as for other aspects of cognition (Clark Reference Clark and Floares2012). Classical combinatorial complexity differentiates levels of comparative language hierarchies and communication repertoires (Changizi Reference Changizi2001; Chomsky Reference Chomsky1956; Reference Chomsky1966; McNaughton & Papert Reference McNaughton and Papert1971), where complexity is proportional to number of discrete information elements, length of composite information sequences, and structure of recursive information patterns. Useful complexity under these conditions is defined by strictly ordered inclusive sets of information capable of being both generated and recognized with certain classical computational models, machines, or grammar rules emulating properties of cortico-striatal-thalamic loops. Three fundamental features of all computational complexity classes may be varied – computational resources (e.g., time, space), problem type to be solved (e.g., optimization or decision problem, language production and comprehension), and computational model to be employed (e.g., deterministic Turing Machine, probabilistic Turing Machine, quantum computer) (Clark Reference Clark and Floares2012). Disparities in classical communication complexities between birds and humans reveal dissociations for each computational feature and, consequently, for communication disambiguation involving affective prosodic or propositional information content (Berwick et al. Reference Berwick, Okanoya, Beckers and Bolhuis2011). As disparities narrow and computational features progressively overlap, threats of eavesdropping on public information should escalate for superior communicants, in this case humans.

More instructive scenarios, and ones that help identify flaws in purely classical complexity approaches toward language evolution, concern competing, closely related animals, such as bird or primate subspecies, with very similar communication complexities. Pressures of social eavesdropping rise when quality and/or quantity of niche resources dwindle and acquired public information facilitates selection and acquisition of preferred life necessities shared by conspecifics. Subspecies communication adaptations, including genetically and/or culturally acquired vocal dialects and behavioral modifications (Dabelsteen Reference Dabelsteen2004; Danchin et al. Reference Danchin, Giraldeau, Valone and Wagner2004) processed via cortico-striatal-thalamic pathways, increase degrees of freedom for classical information computation, further privatizing public information readily comprehended by conspecifics. However, when disambiguation demands for processing linguistic variations superposed (or nearing maximal entanglement) with affective prosodic variations grow exponentially with information input size, privatization becomes governed by quantum computational models involving the entropic uncertainty principle for indistinguishable communications content (Clark Reference Clark and Floares2012; in press; Nielsen & Chuang Reference Nielsen and Chuang2000). This principle imposes thresholds above which eavesdroppers with inferior, missing, or over-allocated communication disambiguation neuromechanisms cannot definitely and simultaneously decrypt partite affective and linguistic content of public information. However, intended communicants may violate the principle by enhancing public information security through privy subspecies-specific communication and memory specializations (cf. Bennett et al. Reference Bennett, Brassard, Crépeau, Jozsa, Peres and Wootters1993; Berta et al. Reference Berta, Christandl, Colbeck, Renes and Renner2010).