We agree with Goldin-Meadow & Brentari (G-M&B) that researchers must differentiate between sign/speech and gesture and believe that this distinction may be useful if situated in the context of theory of mind (ToM) use. Gesture is an important component that individuals must consider when predicting others’ mental states. We agree with G-M&B that gesture is imagistic, not linguistic. In addition, there seems to be a preferred method of using gesture to communicate, as in the silent gesturers described by G-M&B. While we concur that those individuals were replacing language, not supplementing it, the degree of similarity in direction and space without any American Sign Language (ASL) practice in attempts to communicate a thought to another person suggests the use of an automatic ToM system. Apperly and Butterfill (Reference Apperly and Butterfill2009) proposed that two systems of ToM use exist in typically functioning people. The first system is fast and efficient, developed early in life, but relatively inflexible and is used in tasks not requiring language. This system explains the success of infants and some primates on simple ToM tasks, some of which include the use of eye gaze. The second, a more effortful system, is cognitively demanding, yet more flexible and is used for linguistic tasks demanding inference, memory recall, and executive function. Complex tasks may require elaboration on an infinite number of possible explanations for someone's behavior, suggesting that this is a central process (Fodor Reference Fodor1983).

Research on sequential bilingualism has provided strong evidence for linguistic (first-language-based) transfer effects. The evidence from the few studies on first-language (L1) gestural transfer (in descriptions of motion events) suggests that L1 transfer also impacts gesture, even in contexts of long-term immersion in the L2 speech-community (Brown & Gullberg Reference Brown and Gullberg2008; Choi & Lantolf Reference Choi and Lantolf2008; Gullberg Reference Gullberg2006; Negueruela et al. Reference Negueruela, Lantolf, Jordan and Gelabert2004). Analyses of L1 gestural transfer effects in differing conditions of L2 linguistic convergence can help tease apart the connections between gesture and language (speech/sign). If gesture primarily derives from an automatic system, L1 gestural transfer may persist even when L2 learners have converged upon the target linguistic patterns. Interestingly, Casey et al. (Reference Casey, Emmorey and Larrabee2013) compared the effects of learning ASL versus a Romance language on co-speech gesture in L1 (English) story narrations. They found an increased gesture rate, iconic gestures, and a number of handshape types employed only in the case of the ASL learners, suggesting that learning ASL may lower the neural threshold for co-speech gesture production in the L1. Casey et al. (Reference Casey and Emmorey2008) compared bimodal bilinguals (native users of ASL and English) and nonsigning native-English speakers, and found that bimodal bilinguals produced more iconic gestures, fewer beat gestures, more gestures from a character's viewpoint and a greater variety of handshapes when narrating stories (in English) to a nonsigner. We suggest that it would be fruitful to compare simultaneous unimodal and bimodal bilinguals, in a monolingual versus bilingual communication mode, to shed light on the interaction between language (sign/speech) and gesture (see Emmorey et al. Reference Emmorey, Borinstein, Thompson, Cohen, McAlister, Rolstad and MacSwan2005 for evidence of code-blending rather than code-switching in bimodal bilinguals).

The theater community is a unique context to examine the role of gesture in ToM performance. Recent work has been investigating factors that impact ToM skills. Actors must imagine a character's enduring dispositions, life purpose, and overall objectives, and then use this understanding about what motivates the character throughout the play and in each moment (Noice & Noice Reference Noice and Noice2006). Early in their career, many actors are told by directors that they perform some gesture repetitiously. Oftentimes these gestures are not repeated on purpose, and therefore, to correct this, actors must practice awareness, inhibition, and substitution of the old gesture with a more appropriate action. Actors and directors appreciate the whole body and gesture as a tool to help tell a story, and to help the audience better understand the characters in a production. Gestures (and facial expressions), potentially aided by a mirror neuron system (Montgomery et al. Reference Montgomery, Isenberg and Haxby2007), may emphasize or aid in the understanding of language and the beliefs/intentions of others.

In our own research comparing actors and nonactors (Pilot Reference Pilot2015; Pilot & Lakshmanan Reference Pilot and Lakshmanan2015), differences were observed on a ToM task requiring the use of nonverbal facial cues, the Reading the Mind in the Eyes (RME) task (for similar findings, see Goldstein & Winner Reference Goldstein and Winner2012). However, when asked to judge the emotions of a woman shown from the waist up, in short muted video clips, actors and nonactors did not differ. Goldstein et al. (Reference Goldstein, Wu and Winner2009) used a similar video task, but with audible speech, and found a difference between actors and nonactors, revealing the use of a more effortful ToM system. When there is reliance on an automatic system, with interpretations informed only by facial expression and gesture, it may be more difficult to detect differences compared to effortful tasks, due to a common system that may be less subject to influences such as acting experience.

G-M&B propose studying how gestural frequency is impacted when a passage becomes rote. The rote context is similar to the form of acting most are familiar with and contrasts with improvisational theater. It would be interesting to teach one group gestures that help convey the passage and teach another group gestures that do not fit with the overall narrative. Examining gestural omissions in these contexts will provide insight into the use of gesture in communicating a salient message. Innovative research involving theater games based on improvisational performances may provide additional insights into gesture and its role where it doesn't merely replace language or supplement it. Incorporating improvisational elements into research can enable us to observe how gestures are employed to convey the use of objects that aren't physically present (e.g., gripping an imaginary steering wheel and performing a turning motion to convey that the performer is driving) while simultaneously gesturing and speaking to convey a narrative.

Gesture and facial expression pervade many forms of communication: that is, sign, speech, and text (emojis). Parsing out the gestural component from sign/spoken language may provide insight into ToM development and use and may open the door to new behavioral treatment options for addressing difficulties in social functioning, including autism spectrum disorder (ASD).