Electromyographic (EMG) activity of the dominant forearm was recorded during lexical retrieval tasks involving abstract and concrete words. Using a within-subjects design, participants first tried to identify target words from their definitions; then, they generated sentences employing the same words. On both tasks, EMG amplitudes were significantly greater for concrete than for abstract words. The relationship between EMG amplitude and conceptual attributes of the target words also was examined. EMG was positively related to a word's judged spatiality, concreteness, drawability, and manipulability. The findings are consistent with the view that lexical gestures serve a facilitative role in lexical retrieval, and shed light on the ways word-concepts are represented in the mental lexicon.

 

The hand and arm gestures that people make while speaking vary in form and function. Some, like the "A-okay" sign made by bringing the thumb and index finger together, are symbolic behaviors that serve as the nonverbal surrogates of words. They are called symbolic gestures or emblems, and are clearly communicative both in function and intent. Another common type of speech-accompanying gesture consists of simple repetitive, rhythmic movements coordinated to speech prosody. These have been called motor gestures or beats, and they seem unrelated to the semantic content of the accompanying speech.

In this paper we are concerned with the properties and functions of lexical gestures, another class of gestures that, on a continuum of semanticity, lie somewhere between symbolic gestures and motor gestures. Lexical gestures are complex, nonrepetitive hand/arm movements that appear related to the ideational content of the accompanying speech. For example, a speaker describing a drawing, saying "It's supposed to be the earth" might make a symmetrical two-handed movement, as though encircling a sphere. Mounting evidence has undermined the traditional view that the primary role of these gestures is communicative (Krauss, Chen, & Chawla, 1996; Rimé, 1983), leading investigators to speculate about possible noncommunicative functions such movements might serve (Feyereisen & deLannoy, 1991; Krauss, Morrel-Samuels, & Colasante, 1991; Morrel-Samuels & Krauss, 1992; Rimé & Schiaratura, 1991).

Several observers have hypothesized that lexical gestures play a role in speech production by facilitating the retrieval of words from the mental lexicon, and there are some data consistent with this idea. Compared to those who can gesture, speakers prevented from gesturing have more retrieval failures in the Tip-of-the-Tongue paradigm (Frick-Horbury & Guttentag, 1998), employ less vivid imagery in their speech (Rimé, Schiaratura, Hupet, & Ghysselinckx, 1984), speak less rapidly, and make more speech errors associated with difficulty in lexical retrieval (Rauscher, Krauss, & Chen, 1996). Gestures tend to occur disproportionately during hesitations in speech (Butterworth & Beattie, 1978), and aphasics with speech problems primarily involving word retrieval tend to gesture more than both normal controls and other aphasics whose problems are primarily conceptual (Hadar, Wenkert-Olenik, Krauss, & Soroker, 1998).

The rate at which a speaker gestures will vary considerably with topic. Speech whose conceptual content is spatial is more likely to be accompanied by gesturing than speech with other kinds of content. Speakers gesture more when describing abstract graphic designs than they do when describing exotic synthesized sounds (Krauss, Dushay, Chen, & Rausher, 1995). When describing the plots of animated action cartoons, they gesture about four times as frequently during phrases that contain spatial prepositions than they do elsewhere, and preventing them from gesturing has a particularly deleterious effect on speech with spatial content (Rauscher et al., 1996). Verbal mental imagery tasks involving concrete words elicit more depictive or representational gestures than those involving abstract words (Souza-Poze & Rohrberg, 1977; Souza-Poze, Rohrberg, & Mercure, 1979).

The liaison of gesturing and lexical retrieval, we believe, reflects an underlying functional relationship in which lexical gestures facilitate access to words in the mental lexicon. Of course, the details of the speech production process are far from settled, and a number of models that differ in significant ways have been proposed. For our purposes their differences are less important than their similarities. This discussion will follow Levelt--(1989) description of the process, although accounts based on other models would not differ substantially.

According to Levelt, lexical entries are selected during a process called Formulating, in which target words are chosen based on semantic features furnished by the earlier process of Conceptualizing. We hypothesize that lexical gestures: (1) reflect embodied meanings (Glenberg 1997a, 1997b), in which mental representations are grounded in bodily processes that reflect patterns of interaction with the world, and (2) that they facilitate retrieval by sustaining the activation of semantic features of words in working memory long enough for formulation to take place (Krauss & Hadar, 2000). In our process model, these semantically-laden gestures continually furnish inputs to formulation through feedback from effectors or motor commands, in much the same way as vocal (or subvocal) rehearsal keeps active echoic representations in the phonological loop (Baddeley, 1986; Burgess & Hitch, 1999). This roundabout method of keeping things in mind may be necessary because purposefully-activated mental representations are transient and the process of activating them is effortful (Farah, 1995); hence, they are difficult to hold for the lengthy intervals that often occur in a tip-of-the-tongue state.

The kinds of mental representations involved in such a process are more likely to be analogical than propositional (Barsalou, 1999), and to reflect spatial or functional attributes of the target word-concept, than less tangible properties. For example, search for the word "level" might be accompanied by a horizontal hand motion with fingers extended and palm facing downward, and "corkscrew" by a twisting hand motion. We would expect words like "democracy" or "insipid" that lack tangible properties to be accompanied by such movements less often. Hence, in a TOT paradigm, we would expect to find more hand/arm movement during the retrieval of concrete words than abstract words. In the present experiment, we test this hypothesis and examine the conceptual properties of target words whose retrieval elicit gesturing.

To study the relationship between gesture and lexical retrieval, we monitored the electro-muscular activity of subjects' dominant forearms as they performed tasks that involved lexical retrieval. In most gestural research, speakers are videotaped and the properties of their gestures are determined by observation and coding of the videotaped record. Although some gestural properties (e.g., duration) can be determined this way with quite good accuracy, others such as gestural magnitude are difficult to measure objectively. Moreover, observation only can take into account muscular activation that results in visible movement. The electromyograph can detect muscular activity that does not result in overt movement (cf., Cacioppo, Tassinary, & Fridlund, 1990).

In our study, subjects performed two tasks: (1) word retrieval: identifying a target word from its definition, and 2) sentence generation, in which a target word was incorporated into a sentence.

Participants

Thirty Columbia University students (14 male and 16 female) received $8 for their participation. All were native English speakers. An additional 42 undergraduates (20 males and 22 females) received course credit for participating in a word rating study.

Test Materials

A total of 36 low frequency nouns and their definitions (Appendix I) gleaned from previous studies (Burke, MacKay, Worthley, & Wade, 1991; Brown & Nix, 1996; Frick-Horbury et al., 1998; Jones, 1989; Meyer & Bock, 1992; Perfect & Hanley, 1992) were used as stimuli. The nouns were classified as abstract or concrete a priori, according to the criterion of Gorman (1961), and this categorization was corroborated by ratings obtained from an independent sample of subjects (see below). Nineteen nouns were classified as concrete, and 17 as abstract.

Apparatus

The experimental set-up utilized two rooms. One (the experimental room) housed the participant and an experimenter (E1); in the other (the observation room) a second experimenter (E2) monitored and recorded the events occurring in the experimental room. The experimental room contained two chairs, a video camera, an intercom speaker, and a computer monitor. The chair used by the participant was fitted with special arm extensions that allowed nine electrode leads to be attached with enough slack to permit some arm movement. The input cable of the electrode leads ran through a port in the wall to a polygraph (Grass Instrument Wide-Band A.C. Pre-Amplifier and Integrator, Model 7P3B, DC Driver Amplifier, Model 7DAG, and Chart Drive, Model 7H 25-60) in the observation room. A video camera in the experimental room was trained on the subject, and a second camera in the observation room monitored the EMG chart. Their signals were inputted to a Panasonic 3500 System Switcher (WJ-3500), producing a split screen image showing both the subject and EMG output that was displayed on a video monitor and recorded on a VCR in the observation room.

Procedure

To minimize the likelihood of participants attending to their hand movements, the experiment was described as a study of the relationship between memory and stress--the latter purportedly indexed by the Galvanic Skin Response (GSR) measured by the attached electrodes. Following standard EMG preparations, two active electrodes (Grass Silver/Silver Chloride bipolar electrodes, 5mm) were placed on the participant's forearm (2 cm apart), on the region of the m. brachioradialis, one-third of the arm's distance from the lateral epicondyle of the humerus. A ground electrode was attached to the participant's left ear lobe. Dummy electrodes were attached to the same region of the non-dominant arm and to the right leg.

For Task 1, participants were told they would see the definition of an English word on a computer monitor, and that their task would be to identify the word. They were given up to 60 sec to identify the word, and were told the word if they could not identify it. E1 controlled the presentation of definitions and recorded the accuracy of the response. After completion of Task 1 participants performed a distractor task (counting backwards from 100 by threes), following which instructions for Task 2 were given. Participants were told that each of the 36 words would be displayed one at a time on the monitor, and that their task would be to generate a meaningful sentence using that word. In both Tasks 1 and 2, the 36 words were presented in random order.

After they completed Task 2, participants were debriefed and the true purpose of the research was revealed. None expressed suspicion that their gestural behavior was being studied.

Quantification of Data

To quantify the raw EMG signals, we first divided the response period into 5 s segments, and then took the amplitude (in µV) of the two largest pen deflections in each 5 s interval. We will refer to the mean of these measures across all response periods within each trial as EMG Amplitude. EMG Amplitudes were quantified blind with respect to the stimulus word. Signals resulting from activity unrelated to the tasks (e.g., scratching the nose, adjusting clothing, or fiddling with the electrodes) were noted on the EMG chart and excluded from the data analysis.

Each trial was coded as correct or incorrect. In Task 1, "correct" trials were ones on which the participant produced the target word; "incorrect" trials were those on which the participant indicated that he or she didn't know the word, produced a word other than the target word, or on which 60 s passed without a word being produced. On Task 2, "correct" trials were those on which the participant produced a well-formed sentence containing the target word; "incorrect" trials were ones on which the participant could not recall the word's meaning or used it in a sentence inappropriately.

EMG Amplitude

We calculated the mean EMG Amplitudes for concrete and for abstract words for each participant, and performed a paired t-test on them. Reliably greater EMG Amplitudes were elicited during retrieval of concrete words than abstract words (M = 9.87 vs. 8.06 µV; t (29) = 2.76, p < 0.01). For 22 of the 30 subjects, EMG Amplitude was greater for concrete words. The mean EMG Amplitudes for the 36 target words are shown in Figure 1. The effect of word type varied marginally among participants; the subject x condition interaction F(1,29) = 1.38; p - .09. Descriptive statistics for these and other findings can be found in Table 1.

We also examined EMG activation as a function of whether the participant was able to retrieve the target word. As is shown in Table 1, we found slightly greater EMG Amplitudes on incorrect trials for both abstract and concrete words, but the difference was not statistically reliable. On average, participants were able to identify correctly about 55 percent of the target words from their definitions. As expected, abstract words were more difficult to identify than concrete words (63 vs. 46 percent, respectively; t(29 ) = 4.93, p < .0001).

Trial Duration

The duration of individual trials in Task 1 varied considerably, due primarily to differences in response latency. As expected, abstract words took longer than concrete words to identify (Means = 23.6 vs. 15.5 s, respectively; t (29)= 7.91, p < .0001). Trials on which the target word was not correctly identified were about four times longer that those on which the participant produced the target word, for both abstract and concrete words.

Correlations among Dependent Measures

EMG Amplitudes were not correlated with Trial Duration and Identification Accuracy (r (35)= -0.041 and r(35)= -0.027, respectively), although Duration and Accuracy were highly correlated with each other (r(35) = -0.90).

Results on Task 2 replicate those on Task 1 for virtually all measures based on both a by-subject and by-item analysis. The main substantive performance difference between the two tasks was a somewhat larger correlation between EMG Amplitude and Trial Duration (r(35) = -0.34, p < .05). To ascertain that it was word type and not Duration that accounted for the EMG amplitude effect, partial correlation analyses were carried out. Duration accounts for less than 1% of the variance in EMG amplitude (pr² = 0.011), when other explanatory variables are taken into account (see below). We also found a larger correlation between EMG Amplitude and correct/incorrect than we had on Task 1 (r(35) = 0.32; p < .10); however, given the small number of incorrect trials on Task 2 (less than 4%) the implications of this difference are unclear. Descriptive statistics for Task 2 are shown in Table 1.

To gain some insight into the conceptual properties of words whose retrieval elicited muscular activity, EMG Amplitude was correlated with several word-concept attributes. The values for these attributes were obtained by having another group of participants rate the target words on 8 dimensions. Using a 7-point bipolar scale ranging from "not at all" to "very," they indicated how spatial, concrete, active, pantomimable, familiar, drawable, manipulable, and valuable each of the 36 word-concepts were. We then correlated the mean rating on the 8 dimensions for each word with the mean EMG Amplitude it elicited.

The four attributes most highly correlated (rs > 0.30) with EMG Amplitude on Task 1 were concrete, drawable, spatial, and manipulable. A multiple regression model with the four scales as independent variables accounted for 29% of the variance in EMG Amplitude (R = 0.53). However, most of that was due to the concrete and spatial scales. Removing drawable and manipulable affected R² negligibly, reducing it from 0.29 to 0.27. The same pattern of results was obtained for Task 2, though this time, interestingly, the variable manipulable accounted for 35% of the variance in EMG amplitude (pr² = 0.350), when all the other variables, including Duration (pr² = 0.011) and correct/incorrect (pr² = 0.025), were taken into account.

On both a word retrieval task (in which the word is identified from its definition) and a sentence generation task (in which the word is used in a sentence), concrete words elicited more electromyographic activity in speakers' dominant arms than did abstract words,. The concrete and abstract words differed conceptually on several dimensions, but it was primarily their spatiality and concreteness (and manipulability in Task 2) that accounted for the amount of muscular activity they elicited. These findings are consistent with the view that one function of lexical gestures is to facilitate the retrieval of lexical entries with concrete content (Krauss & Hadar, 1999), and that such gestures reflect embodied representations of meaning.

It seems unlikely that the lexical gestures observed in our experiment were intended to convey semantic information in visual form. In Task 1, subjects were presented with word definitions and tried to retrieve the phonological forms for the defined words. Their task was not to convey information, but to articulate the word form, and gesturally conveyed information was irrelevant to this task. In Task 2, subjects attempted to formulate grammatical sentences containing a target word. Again, the focus was on vocal production, and gesturally conveyed information was irrelevant. Nevertheless, both tasks elicited muscular activity, especially when the conceptual content of the verbal task was concrete.

Although EMG was recorded only from the dominant arm, we also observed muscular activity in other theoretically-important but unrecorded regions (e.g., hands and nondominant arm). Typically these movements were not general and diffuse; rather, they seemed related to the semantic attributes of the target words, regardless of whether these attributes were spatial (e.g., diamond-shaped movements for trellis and horizontal movements for bleachers) or functional (e.g., rotational movements of the hand for skewer).

What initiates gestural activity? In our model, the early conceptual processes that generate input to the speech production process routinely implicate non-propositional mental representations, and whenever such representations are activated, the kinds of movements we call lexical gestures are likely to be initiated (Krauss et al., 1999; Krauss, et al., 2000). Such movements serve to sustain the activation of the mental representations until the next stage of the speech production process (formulation) takes place. Again, a parallel can be drawn between the way these movements circuitously maintain non-propositional representations and the way vocal (or subvocal) rehearsal keeps active echoic representations in the phonological loop.

According to our process model, gestures facilitate retrieval by maintaining the activation of semantic features until lexical retrieval takes place. From a physiological standpoint, the claim that movements can maintain the activation of semantic features, and that these features can participate in the retrieval process, may strike the reader as far-fetched. How can the motor and sensory processes involved with these movements interact with representations belonging to a linguistic system? Such an interaction may seem less implausible in light of evidence showing that semantic knowledge is distributed throughout different regions of the brain (Tranel, Damasio, & Damasio 1997; Tranel, Logan, Randall, & Damasio, 1997), including ones subserving motor and perceptual functions (for a review see Gainotti, Silveri, Daniele, & Giustolsi, 1995; Martin, Wiggs, Ungerleider, & Haxby, 1996).

The specific area of the brain in which a particular bit of semantic knowledge is stored seems related to the brain regions involved in its acquisition. Reviewing the brain lesion literature, Giannotti et al. (1995) found support for the hypothesis that action words are localized in motor areas of the brain, and object names in areas of sensory integration. Martin et al. (1996) found that naming pictures of tools activates the same premotor area that is activated by imagined hand movements. Presumably such movements are important in acquiring functional knowledge about the objects. As evident in the Martin et al. (1996) study, it appears that sensory-motor semantic areas of the brain can be activated in diverse ways. Although at this point we can do little more than speculate about underlying neural mechanisms, we believe that gesturing is one way of activating these embodied representations in sensory-motor regions of the brain--;areas that are involved in the execution and propioception of these movements.

The research reported here was done by the first author in partial completion of the MA degree at Columbia University under the supervision of the second author. We gratefully acknowledge the advice and comments of Lois Putnam, Robert Remez, Michele Miozzo, and Robert B. Tallarico, and the assistance of Stephen Krieger, Lauren Walsh, Jennifer Kim, and Jillian White.

Task 1. Word Retrieval
				EMG Amplitude		Trial Duration			Percent Correct
Word Type				Mean	SD	Mean		SD	Mean		SD
Concrete (n = 19)				9.87	8.25	15.05		15.48	63		18
		Correct		9.25	8.57	7.77		3.03
		Incorrect		10.68	9.78	29.05		12.66
Abstract (n = 17)				8.06	8.22	23. 61		9.04	46		21
		Correct		7.81	7.97	9.26		3.82
		Incorrect		8.22	8.74	37.72		16.07
Task 2. Sentence Generation
				EMG Amplitude		Trial Duration			Percent Correct
Word Type				Mean	SD	Mean		SD	Mean		SD
Concrete (n = 19)				17.75	15.52	9.08		4.06	96		6
	Correct			18.04	15.55	9.10		4.06
	Incorrect			7.66	10.61	7.77		7.26
Abstract (n = 17)				15.05	13.32	13.44		5.38	86		12
	Correct			16.21	14.09	16.58		5.67
	Incorrect			6.55	6.55	14.04		13.83

Table 1, EMG Amplitude (µV), Trial Duration (sec), and Percent Correct on Tasks 1 and 2 for abstract and concrete target words.

Figure 1. EMG Amplitude (in µV) on Task 1 for the 36 target words (filled bars are concrete words, unfilled bars are abstract words).

ACCLIMATE: To get used to new weather.

AGNOSTICISM: The view that whether or not God exists is unknown.

APOSTASY: Renunciation of one's religion, principles, political party, etc.

AXIOM: An accepted truth (such as those in geometry).

BLEACHERS: Uncovered stand of progressively higher rows of wooden planks for spectators.

BUOY: A floating object moored to the bottom of a body of water.

CASTANETS: A small rhythm instrument used especially by dancers, consisting of two small shells that are clicked together by the fingers.

CELIBATE: Remaining unmarried, especially for religious reasons.

CHANDELIER: A large ornate lighting fixture hanging from the ceiling.

DETERMINISM: The view that human action is caused, not by the will, but by external factors.

ENIGMA: Something mysterious and difficult to understand.

FILAMENT: A flexible, threadlike incandescent object inside a light bulb.

GUILLOTINE: A machine used for beheading by means of a heavy blade.

GYROSCOPE: A toy or instrument used to illustrate the earth's rotation by balancing and spinning rapidly about an axis.

HARPOON: A large barbed spear used for hunting whales and large fish.

HIEROGLYPHICS: The ancient Egyptian script found on the walls of tombs.

HOSPICE: A house of rest for travelers or the terminally ill, often kept by a religious order..

HYPOCHONDRIA: Mental condition in which a person constantly shows unnecessary anxiety about his health.

INCOGNITO: With one's identity concealed; disguised.

INKLING: A hint, slight knowledge or suspicion.

JAVELIN: A slender shaft of wood tipped with iron and thrown for distance at an athletic event.

KALEIDOSCOPE: An instrument containing loose bits of colored glass that produce an ever changing pattern when revolved.

LABYRINTH: A large maze usually defined by tall shrubbery.

LASSO: A long rope with a running noose that is used for roping cows and horses.

MASOCHISM: The tendency to derive pleasure from pain.

MORALE: The state of a person's or group's spirits.

NEPOTISM: The use of undue favor in appointing one's relatives to office.

NOSTALGIA: An excessively sentimental condition in which one yearns for the past.

PARADOX: A true statement that appears contradictory (a puzzling contradiction).

RHEOSTAT: A type of light switch that dims or brightens a lighting fixture.

SENESCENCE: The state or process of growing old.

SKEWER: A piece of thin metal used to pierce and cook a beef kabob over a fire.

SUFFRAGE: The right to vote in political elections.

TRELLIS: A frame or latticework for climbing plants in a garden.

URN: A type of vase used to contain the cremated remains of a person.

WASHBOARD: A corrugated rectangular surface used for scrubbing clothes.

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