Gesture is the primary modality for language creation.

How language began is one of the oldest questions in science, but theories remain speculative due to a lack of direct evidence. Here, we report two experiments that generate empirical evidence to inform gesture-first and vocal-first theories of language origin; in each, we tested modern humans' ability to communicate a range of meanings (995 distinct words) using either gesture or non-linguistic vocalization. Experiment 1 is a cross-cultural study, with signal Producers sampled from Australia (n = 30, Mage = 32.63, s.d. = 12.42) and Vanuatu (n = 30, Mage = 32.40, s.d. = 11.76). Experiment 2 is a cross-experiential study in which Producers were either sighted (n = 10, Mage = 39.60, s.d. = 11.18) or severely vision-impaired (n = 10, Mage = 39.40, s.d. = 10.37). A group of undergraduate student Interpreters guessed the meaning of the signals created by the Producers (n = 140). Communication success was substantially higher in the gesture modality than the vocal modality (twice as high overall; 61.17% versus 29.04% success). This was true within cultures, across cultures and even for the signals produced by severely vision-impaired participants. The success of gesture is attributed in part to its greater universality (i.e. similarity in form across different Producers). Our results support the hypothesis that gesture is the primary modality for language creation.

Cultural selection drives the evolution of human communication systems.

Human communication systems evolve culturally, but the evolutionary mechanisms that drive this evolution are not well understood. Against a baseline that communication variants spread in a population following neutral evolutionary dynamics (also known as drift models), we tested the role of two cultural selection models: coordination- and content-biased. We constructed a parametrized mixed probabilistic model of the spread of communicative variants in four 8-person laboratory micro-societies engaged in a simple communication game. We found that selectionist models, working in combination, explain the majority of the empirical data. The best-fitting parameter setting includes an egocentric bias and a content bias, suggesting that participants retained their own previously used communicative variants unless they encountered a superior (content-biased) variant, in which case it was adopted. This novel pattern of results suggests that (i) a theory of the cultural evolution of human communication systems must integrate selectionist models and (ii) human communication systems are functionally adaptive complex systems.

Creating a communication system from scratch: gesture beats vocalization hands down.

How does modality affect people's ability to create a communication system from scratch? The present study experimentally tests this question by having pairs of participants communicate a range of pre-specified items (emotions, actions, objects) over a series of trials to a partner using either non-linguistic vocalization, gesture or a combination of the two. Gesture-alone outperformed vocalization-alone, both in terms of successful communication and in terms of the creation of an inventory of sign-meaning mappings shared within a dyad (i.e., sign alignment). Combining vocalization with gesture did not improve performance beyond gesture-alone. In fact, for action items, gesture-alone was a more successful means of communication than the combined modalities. When people do not share a system for communication they can quickly create one, and gesture is the best means of doing so.

Probing the implicit suicidal mind: does the Death/Suicide Implicit Association Test reveal a desire to die, or a diminished desire to live?

Assessment of implicit self-associations with death relative to life, measured by a death/suicide implicit association test (d/s-IAT), has shown promise in the prediction of suicide risk. The current study examined whether the d/s-IAT reflects an individual's desire to die or a diminished desire to live and whether the predictive utility of implicit cognition is mediated by life-oriented beliefs. Four hundred eight undergraduate students (285 female; Mage = 20.36 years, SD = 4.72) participated. Participants completed the d/s-IAT and self-report measures assessing 6 indicators of suicide risk (suicide ideation frequency and intensity, depression, nonsuicidal self-harm thoughts frequency and intensity, and nonsuicidal self-harm attempts), as well as survival and coping beliefs and history of prior suicide attempts. The d/s-IAT significantly predicted 5 out of the 6 indicators of suicide risk above and beyond the strongest traditional indicator of risk, history of prior suicide attempts. However, the effect of the d/s-IAT on each of the risk indicators was mediated by individuals' survival and coping beliefs. Moreover, the distribution of d/s-IAT scores primarily reflected variability in self-associations with life. Implicit suicide-related cognition appears to reflect a gradual diminishing of the desire to live, rather than a desire to die. Contemporary theories of suicide and risk assessment protocols need to account for the dynamic relationship between both risk and life-oriented resilience factors, and intervention strategies aimed at enhancing engagement with life should be a routine part of suicide risk management.

The cultural evolution of human communication systems in different sized populations: usability trumps learnability.

This study examines the intergenerational transfer of human communication systems. It tests if human communication systems evolve to be easy to learn or easy to use (or both), and how population size affects learnability and usability. Using an experimental-semiotic task, we find that human communication systems evolve to be easier to use (production efficiency and reproduction fidelity), but harder to learn (identification accuracy) for a second generation of naïve participants. Thus, usability trumps learnability. In addition, the communication systems that evolve in larger populations exhibit distinct advantages over those that evolve in smaller populations: the learnability loss (from the Initial signs) is more muted and the usability benefits are more pronounced. The usability benefits for human communication systems that evolve in a small and large population is explained through guided variation reducing sign complexity. The enhanced performance of the communication systems that evolve in larger populations is explained by the operation of a content bias acting on the larger pool of competing signs. The content bias selects for information-efficient iconic signs that aid learnability and enhance usability.